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Trishear 4.5 Users Manual

1. As you can see in the figure above the constant heave method commonly results in slip increasing up dip with synthetic shear and listric faults The constant heave construction shown below shows why this occurs slip shear shear planes constant heave slip shear constant heave Le LITT e Calculate strain ellipses This checkbox must be se lected before or during the setting up a new model Once a model has been set up by clicking Okay in a new model dialog clicking this option will have no effect until you next choose new model Checking Cal culate strain ellipses will automatically check Show Ellipses in the Plot Menu Calculate strain ellipses is selected by default unless you save preferences with this item turned off O Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 High resolution strain ellipses Normally ellipses are drawn as polygons with 15 vertices however if you want better quality with the overhead of more processing time you can click the High resolution strain ellipses check box and then ellipses will be drawn with 24 vertices Dense array of strain ellipses Normally ellipses are just drawn centered between bed tops At times you may want strain to be calculated on a denser gird for contouring of strain magnitude for example Clicking this box will draw ellipse along each bed top as well as
2. 2000 Trishear User s Manual 60 v 4 5 h polygon 1 vertex number 5 The first bed that you trace or the lowest polygon in your stack of objects will be labeled polygon number 1 when you open the DXF file in DigBeds the highest polygon 1 e the one that would cover all of the others if they overlapped will have the highest polygon number If you have beds offset across a fault it is best to trace them first or use Send to back in your graphics pro gram so that they are behind all the other beds This is because DigBedsresamples and renumbers offset poly gons first One of the main reasons to be concerned with bed numbering is because of the way that Trishear constructs it s strain ellipses the ellipses are drawn half way between consecutively numbered beds If the con secutively numbered beds aren t adjacent to each other the ellipses will still be drawn half way between probably overlapping other beds ellipses etc Remember how ever that you can renumber your beds within DigBeds 1 1 6 When you save your DXF file if your graphics program gives you the choice of saving polygons as lines or as polylines choose polylines References Cited Allmendinger R W 1998 Inverse and Forward numerical modeling of trishear fault propagation folds Tectonics v 17 no 4 p 640 656 Erslev E A 1991 Trishear fault propagation folding Geology v 19 no 6 p 617 620 Ersle
3. Here we provide a item by item description of each option available in each menu and in each dialog box in the Trishear program File Menu The File Menu handles most but not all see the section on the Restore Menu below input and output of data and graphics files as well as printing and quitting or exiting Note that you can set the default parameters for the program by choosing Save Prefer ences under the Edit Menu If no preferences have been saved you will have to choose New before you can plot anything New Commonly your first step once you have fired up the program will be to choose New particularly 1f you want to do a forward model The following dialog box will appear with the program s built in default values The dialog box is reasonably self explanatory except for the following e The Display Increment controls how frequently the screen updates during a model run If you set the value to 1 the screen will be updated at each step of the model producing essentially an animation of the model If your computer is fast this can be instructive Model runs however go faster if the program does not have to draw to the screen every step The default value is 5 meaning update the screen every five steps Note that this setting has no effect on the model run itself Richard W Allmendinger 1998 2000 23 IE Edit Model New SEN Save Mode
4. gt o T Sy S a Initial left X coord Initial left x coord 5 e If you want a normal fault you must enter a negative value as your initial Total Slip setting If you want the tipline to propagate upwards in the stratigraphic section during normal fault movement you must also enter a negative value for the Propagation Slip setting Other wise the tipline propagates in the same direction as the movement of the hanging wall e Strain ellipses can only be turned on at the beginning of a model run not in the middle This is accomplished by clicking Preferences and then checking the Strain ellipses check box When you show ellipses every fifth ellipse is plotted in a different color making it easier to track them through the deformation e Faults and beds are inclined down to the left if they have a positive dip and down to the right if they have a negative dip e You enter bed tops and their initial dips in the columns on the right A starting model can have a maximum of twelve 12 beds However a total of twenty beds can be analyzed using the Add Beds menu command under the Model Menu see below Thus you can have 12 pre growth beds and up to 8 growth beds or for example five pre growth beds and up to 15 growth beds Beds entered in this dialog box can have any initial dip but beds which you enter later are always flat unless entered with a mouse e The length of the beds is controlled in the Prefere
5. Change the P S to 1 0 and the Total Slip to 30 Choose Run from the Model Menu 5 You will see the fault bend fold grow When it stops choose Add Beds from the Model Menu and enter 170 for bed 7 Select Modify from the Model Menu and increase the total slip to 60 Choose Run from the Model Menu 6 Again add a bed this time at 190 Increase the total slip to 90 with Modify and choose Run Repeat this procedure as often as you like to build up the growth strata A few final words about fault bend folds in Trishear The program can only produce mode fault bend fold not mode 2 A perfect kink band fault bend fold is produced in this example because the tip line propagates so rapidly that there is essentially no time for any deformation to occur in the trishear zone before the tip line goes shooting past An interesting scientific question to pursue is just how low can P S be and still produce what would appear to be Lowering the P S to 1 is not really necessary this example would work fine if it were left at 150 However by lowering the P S we make it so that the fault tip doesn t continue to propagate huge distances This is a convenience if you want to save a graphics file and don t want to see a very long fault trajectory This step is necessary because the initial slip was 1 If we chose Continue the total slip would be changed to 30 1 We would have to choose
6. LI left edge at mouse click Fault Propagation75Slip 0 gt footwall fixed 0 gt hanging wall fixed Total slip Display increment ramp up from decollement O initial multi bend fault Pick New Model with Mouse x Bedding Number of beds El Initial left 5 coord 50 Faulk Propagation Slip i 5000 D if footwall fed 0 then hanging wall Total slip 100 00 Display increment 5 ramp up from decollement initial multi bend fault Preferences Cancel Trishear User s Manual v 4 5 choosing it from the Window Menu Save Model As text This command gives you a standard Macintosh save file dialog box which will allow you to save the exact configuration of the model currently on the screen in the Cross Section Window This model can be read back into the program using the Old menu command Save Model As PICT The current cross section in the Cross Section window can be saved as a Macintosh PICT file or a Windows BMP file for input into any graphics program The PICT file creator ID will be set to Canvas 5 but any graphics program can read this file The separate vector objects are all editable as such in the graphics program The BMP file is a generic Windows bitmap Save History As text At any time you can save up to the last 250 lines of the history of changes of your modeling session as a text file with this command This is particularly u
7. ec Tr z sz cml Cm o C Nes 2 ss C _ C c Cancel i Load Colors If you have saved a set of custom colors to disk with Save Colors below you can load them back in with Load Colors Richard W Allmendinger 1998 2000 Trishear User s Manual 49 v 4 5 Save Colors At any time you can save a set of custom colors to disk with Save Colors These colors can be read back into the program with Load Colors Set Line Weights This command will give you the fol lowing dialog box Just enter a number integers only next to the feature whose line weight you want to change As illustrated this can be particularly useful if you are trying to trace over a seismic line Single pixel width lines can be difficult to see when plotted on top of a seismic line but become much more visible when given a heavier line weight and changed to say yellow as shown below NAV SSE A 1 Il I dm mmm I S t r dar re a 0 Set Line Weights In the boxes below specify the line weight in pixels that you want for each graphic element in the program Integers only Beds pregrowth Kink axes Beds growth Ellipses Beds Digitized LHFE two way Taveltire 5 Fault active Principal axes Faults old Particle paths Trishear bndry Plot axes Cancel Scan Ligitize Windows H E Esa e ERE Show Digitized Beds Plot Menu Digitized Beds Plot Menu Scan Scan Digitize Menu eee Scale Digitized Beds
8. grid search should take no more than a few tens of minutes at most depending on the speed of your computer of course However if you search over even moderately broad ranges of all six parameters it can take many hours or even many days of computing time In general it is best to use relatively restricted searches with large step sizes first and then fine tune as you zero 1n on an answer Tests that we have run where we carried out inverse modeling on forward models generated with known trishear parameters shows that the grid search is very accurate at finding the correct answer Allmendinger et al in press However you may well be disap pointed with the results of the inversion when you apply it to your own real data Wasn t this supposed to make our lives easier by letting the computer do the work The answer lies in the probability that most real sections had variations in trishear parameters during their formation while the inverse method assumes no variation during deformation Ramp angles may change P S may vary as the tipline encounters different lithologies and so on Thus I use the grid search to get an general idea of the basic range of appropriate Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 parameters and then fine tune my fit to the real structure by forward modeling Needless to say this fine tuning generally takes con siderably longer than the grid searching Menu Reference
9. retrodeformed again with the new parameters Unrestore Beds If you overshoot your desired restoration you can back up the model by choosing Unrestore This behaves exactly like Restore but in reverse Automate You can perform a full inverse model by searching over the six parameter grid of values which define any simple trishear restoration This grid search is initiated by calling up the Automate Restoration dialog box The grid search is performed Richard W Allmendinger 1998 2000 Trishear User s Manual 43 v 4 5 just on one key bed which is specified in the upper left corner of the dialog box it can be any bed that you choose but normally would be the bed for which you have the best constraints When you choose Automate the program automatically displays the num bers of each bed on the screen for reference The inversion attempts to find the best combination of parameters with returns the key bed to a straight but not necessarily flat line We do this by calculating a least squares best fit and minimizing c chi squared as described in Numerical Recipes whose algorithm we have used We also calculate the correlation coefficient R Pearson s R which is 1n versely related to chi squared Note that the best fit for the key bed probably will not be the best fit for all of the other beds Automate Restoration Automate restoration min max step Enter the number of the key bed wich you penis Hep
10. then only the min will be used O Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 Automate Restoration Enter the number ofthe key bed min max step hich tto restore usi i wncnyenwanresore sne ranpanate 36 KeyBed 3 MATANA 1 between 1 amp 6 Trishear angle 1 Save Statistics O always search to max displacement O 2 D slices of 3 D matrix kb imbi i 421 C Column text of 3 D matrix kb TPINe X O LJ use mouse to select tip region in a region on a line P Fault type to restore ox e Reverse 3 Normal O best model applied to all beds 7 When you click Okay Trishear goes to work A dialog box or text on the screen will indicate the number of models being tested the current best model and an esti mate of the amount of time remaining which is wildly inaccurate at the beginning of a grid search run With the above settings it will say that 55 models are being tested yet each one of those models will have 500 dis placement steps Thus in the span of a minute or less your computer will have tested 27 500 unique combina tions of the six trishear parameters 8 When Trishear is finished it will show you the restoration of all the beds see following diagram based on the best fit parameters for the key bed Open the History window from the Windows Menu and you will see the grid of tested values as well as the statistics for the key bed If you want to see the
11. Continue thirty times to get to a total slip of 60 Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 a nearly perfect kink fold In our experimentation a value of P S as low as 15 produces a very respectable kink fault bend fold Fault bend fold the easy way The previous example shows you how one had to do a fault bend fold in version 3 0 of Trishear In version 4 and above there is a much easier way l Choose New from the File Menu Set the bed tops to 0 30 60 90 120 and 150 set the Slip to 30 Check the two check boxes ramp up from decollement and initial multi bend fault You can leave everything else at the default values When you click Okay in the New Model dialog another dialog will appear telling you to draw the fault beginning with the down dip most point and clicking and dragging to set each vertex the vertex is set when the mouse button is released The mouse coordinates and the ramp angle are shown For this example click the mouse at 300 0 and drag a ramp upward at 30 or less until you reach a point midway between beds 3 and 4 Click to set the vertex at the upper corner of the footwall ramp and then drag out a horizontal flat until you reach the edge of the beds Double click at the end of the flat to set the tip line Choose Run from the model menu and a small fault bend fold will appear Select Add Beds from the Model Menu and add a bed about 5 u
12. Principal Axes are available only if you have selected Calculate strain ellipses in the Preferences Dialog Likewise Show Windows Help Show Beds e Show Trishear zone 3el Show Kinks 36 Show Ellipses 0 Show LNFEs EL Show Principal Axes Show Particle Paths Shade Ellipses by Strain 9 Shade LNFE by Strain Digitized Beds can set Colors Load Colors save Colors set Line Weights Particle Paths is available only after you ve turned on the calculation of particle paths in Preferences In all cases a check mark appears in the menu if the program is set to plot the particular element Shade Ellipses by Strain In addition to showing the outlines of the ellipses you can color or shade them according to their strain magnitude The darker and more intense the color the larger the magnitude of the maximum principal stretch This option allows you to see very quickly where the zones of high strain are in your model You can shade ellipses without showing the ellipses then you will see the color fill but not the red or blue outline Also ellipse outlines are drawn everywhere even if they are undeformed 2OOOOOg circles whereas shading is only used where there is a stretch greater than 1 Shade LNFEs by Strain The same range of colors can be used to shade the LNFEs giving an immediate impression of where the strain is high even if ellipses are not shown If you choose Shade LNF
13. The most basic trishear structure is a simple monocline with no changes in ramp angle etc This example will be a bit more complicated in order to show off some of the inherent flexibility of the program 1 Choose New from the File Menu Click on the Preferences button and you will get the Preferences Dialog superim posed on top of the New Dialog Check the box labeled Pick beds and fault with mouse and make sure that O Richard W Allmendinger 1998 2000 Types of Cursors k arrow gy hand cross watch Trishear User s Manual 8 v 4 5 Calculate strain is checked it should be by default Click Okay 2 In the Macintosh version a new dialog will automatically The New Model with Mouse appear in the Windows version you will have to click dialog box the Okay button in the New dialog first The new dialog is called Pick new model with mouse Make sure that Pick a New Model with Mouse E 5 beds are specified to be entered Check ramp up Bedding from decollement and click the Okay button Number ofbeds 5 Initial left X coord Fault Propagation Slip 3 Follow the on screen instructions for entering the beds and the fault Space the beds tops about 30 units apart starting at about O and ending about 120 You can enter Eu footwall fixed a flat bed by just clicking the left mouse button or a gt 0 gt hanging wall fixed dipping bed can be entered by clicking and dragging
14. Total slip The fault is specified by clicking on the initial tipline Display increment position say about 300 0 for this example and drag ramp up from decollement ging up to the right to define a positive ramp angle Drag a ramp angle of about 30 and a trishear angle of about 50 The Macintosh version shows the coordinates okay of the mouse at the cursor the Windows version shows the coordinates at the bottom of the screen Note that Trishear s screen coordinate system is positive up and positive to the right A positive dip is inclined down to the left After you are finished the initial section with circles along the beds will be drawn to the screen You can turn off the drawing of the circles ellipses using the Show Ellipses command under the Plot Menu The green line shows the position of the trailing active kink axis related to the footwall fault bend Note that hanging wall fixed kink axes are not drawn 4 Choose Run from the Model Menu The section pro ceeds to deform itself in increments as you watch If you wish to stop a model before it reaches the specified amount of displacement just click the left mouse button Depending on the speed of your computer you may have to hold the button down for a few moments Let the model run to its final slip 5 Now choose Modify from the Model Menu Enter a ramp angle of about 55 and click the Okay button 6 Choose Run again from t
15. Windows version of the Cross Section Window has scroll bars to allow you to see all parts of your cross section In the Macintosh version you give a menu command and click and drag the contents around to see the part that you want Both versions of the program show the same information The History Window maintains a text record of all of the changes that you make to a model Information from this window can be copied to the operating system clipboard or saved as a text file Both versions of the program use a large number of dialog boxes to get input from you The Macintosh version of the program has four types of cursors which clue you into the type of interaction that the program expects The arrow cursor is the standard A cross cursor appears when you are to click or click and drag in the window to measure or draw something A hand cursor appears when you are to drag the contents of the Cross Section Window or drag the digitized beds around in the window Finally a watch cursor tells you that a time consuming operation is occurring The Windows version of Trishear 4 5 uses only an arrow cursor A Quick Tutorial The bulk of this manual consists of a reference section organized by menu command To give you a quick overview of the capabilities of the program we provide some brief examples to follow here Each example assumes that you are starting the program from scratch and have dismissed the About dialogs Simple forward model
16. With this option in the Preferences dialog you can specify how much of the trishear zone is in the hanging wall and how much is in the footwall symmetric trishear where the trishear zone is 25 in the hanging wall left 50 in the hanging wall middle symmetric trishear and 75 in the hanging wall right In all three the dashed line shows the pro ection of the fault plane into the trishear zone e Pick beds and fault with mouse if checked this box allows you to draw the beds and fault s on the screen The following menu commands behave differently if Pick with Mouse is turned on File New Model Add Beds Model Start New Fault Although you can set the tops and dips of beds and the tipline position ramp angle and trishear angle of faults with the mouse you will still need to enter the number of beds left coordinate P S ratio displacement etc in a dialog box However in the case of Add Beds if Pick with mouse is turned on you will not see a dialog at all the cursor will simply change to a cross to allow you to click and drag to add a new bed Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 e Clip growth strata at surface By default growth strata layers that are added after the start of a model run are truncated where they run into any older strata which are higher than them This option can be toggled on and off with this check box in
17. an ellipse The results will be displayed on the screen or in a dialog box Select the History Window from the Windows Menu to see the changes that you made Then bring the Cross section Window to the front again Save this model to disk by choosing Save As from the File Menu Complex forward model The possibilities for making complex forward models are limitless In this example we will assume that you have completed the above example of a simple forward model and will add to it If the section is still on the screen you don t need to do anything otherwise start up the program 1f necessary and choose Open from the File Menu and select the file that you saved in step 8 above l Choose New Fault from the Model Menu Unless you have turned off pick beds and fault with mouse in the Preferences dialog box you will get the Pick New Fault with Mouse Dialog Leave all the parameters as they are but be sure that ramp up from decollement is checked Click on the new tipline position of about 600 0 and drag up to the left to define a fault with a negative dip Make the ramp angle about 35 and the trishear angle about 60 Choose Run from the Model Menu The old fault trajectory simply becomes a digitized surface and is de formed in the trishear field along with the beds The resulting geometry is complex but the section is com pletely area balanced Richard
18. and uncheck Pick beds and fault with mouse When you get the New Model dialog enter the following values ramp angle 70 trishear angle 70 Propagation slip 0 5 Total slip 30 initial coordinates of the tipline X 400 Y 0 and bed tops at 0 30 60 90 120 Click Okay 2 Lets move the model up so we can see it when the hanging wall moves downward From the Windows Menu select Shift in Window Leave delta X 0 and set delta Y 200 When you click Okay the cross section will shift upwards on the screen 3 Choose Run from the Model Menu The hanging wall will move downwards 30 units and a fold will form over the upwardly propagating tipline 4 Now select Add Beds from the Model Menu The dialog box that appears will show you the highest points the existing beds and will allow you to add a number of new beds In the blank space for Bed 6 enter 325 and Richard W Allmendinger 1998 2000 10 Trishear User s Manual 11 v 4 5 click the Okay button A new horizontal bed appears plotted in a different color light blue or cyan by default 5 Select Continue from the Model Menu The hanging wall moves downward another 30 units and the new bed top 1s folded 6 Select Add Beds again enter 330 for Bed top 7 Click Okay and choose Continue again from the Model Menu The hanging wall moves down another 30 units and the tipline be
19. fault can subse quently be modified with the Modify command under the Model Menu Note that the deformation in the hanging wall of the new fault is with vectors parallel to the new fault trace If you fold an older ramp over a new ramp everything will be sheared parallel to the new fault producing bedding thickness changes in the beds above the old ramp Any section can have a maximum of five inactive and one active fault Rotate Model With this command you can produce a global rotation of the model including the beds fault s trishear zone ellipses etc but not the axes themselves You can specify the axis of rotation either at the tip line or by clicking the mouse on the screen Using this command one could for example simulate a rotating domino fault etc Restore Menu You use the Restore Menu when you want to analyze de formed strata which you have digitized using some other program Once you have read in the beds using the Import Beds command you can then set the parameters for your restoration The whole reason for this restoration module is that when you are trying to model real structures it is often easier to evaluate the goodness of fit of a particular set of parameters by seeing how well they unfold the beds to an initial more or less planar state Forward modeling is much more time consuming even though both are by trial and error Import Beds With Import Beds you will be presented with a sta
20. ideal geometric ellipse you will get the message that you see to the right Such ellipses will not have LNFE plotted in them nor shading by strain magnitude Get Particle Path Info If you have turned on particle paths in the Preferences dialog then this menu option becomes available After selecting this you can click on any particle path in your plot and the length and average orientation of the particle path are displayed for you Show Bed Numbers This will temporarily label each bed on the screen according to the bed number that Trishear uses to identify it These numbers are not saved with the plot EEE HEN Uber on Belete eds This dialog allows you to change bed numbers or delete a bed entirely This will cause other beds to be renumbered as well Renumber or Delete Beds At any point in a model run Old bed number O Delete you can tell the program to change the numbering order of the beds o or even delete a bed entirely To change the number of a bed enter New bed number max 5 its current number in the Old bed number box and type the new ox number that you want the bed to have in the New bed number box Both number have to be less than or equal to the total number Renumber or Delete Beds E This dialog allows you to renumber beds or delete a bed entirely Eith il Il bed b of beds in a model To delete a bed enter its number in the Old e SYRE bed number box and check the Del
21. looks for this information in a file called TrishearPPC Prefs or Trishear_Prefs txt If this file is found the program uses these settings rather than its own built in defaults Note that the current state of bedding too is saved in this file If you choose Save Prefs with a deformed section on the screen you will get the same deformed section every time you start up the program The only way to go back to the built in defaults is to delete the prefs file manually The Macintosh version will save another prefs file at the same time called TrishearPPC colors This file contains any colors that you have set with the Set Colors submenu under the Plot Menu Reset to Default Choosing this menu item will erase what ever model you on the screen and will reset the program to its default values as defined either by a preferences file or if a prefs file cannot be found by internal defaults Model Menu Much of the manipulation of your model takes place with the commands in the Model menu Here is where you actually start the model run but also where you can change horses in mid stream so to speak by changing parameters in the middle of a model run Run After you have entered a model with New or Old you actually start the model run using the Run menu command Richard W Allmendinger 1998 2000 34 pla Restore Plot Wind Run R Continue SK Mo dif EM Add Beds HA Get Ellipse Info E Get Pa
22. of Program Geologic Elements Before going into the organization of program features such as menus and windows a few words about the types of objects to be manipulated are in order Trishear 4 5 draws two dimensional geologic cross sections of beds that are cut or folded by faults The Fundamental parameters needed to define a fault are its tip line position which changes with time ramp angles slip propagation to slip ratio P S and trishear angle Bed tops are defined graph ically as a polygons which have up to 1000 vertices There are two distinct types of beds O Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 1 Forward model beds these are defined completely with in the program and are the only ones which are changed 1 e folded or truncated by the faulting process You can add more beds to a forward model after the initial model has been set up these are referred to as growth strata but could equally well be dikes or sills intruded during deformation Forward models always have at least one fault associated with them 2 Digitized beds these are polygons which are imported into the program from a specially formatted file that you have generated elsewhere for example in your graph ics program and or with my utility program DigBeds Digitized beds can be moved around the screen and re scaled but they are not otherwise deformed by the program Digitized beds do not have to have a fault assoc
23. program to study individual structures Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 or small groups of structures Although it can help you to balance cross sections it is not a general cross section balancing program For that you need one of the readily available if expensive com mercial packages from different vendors Further reading The purpose of this manual is to instruct the user in the use of this program not to explain the trishear method fault bend folding etc The original concept of trishear was published by Erslev 1991 The algorithms used in Trishear 4 5 are described in Allmendinger 1998 and Zehnder amp Allmendinger 2000 earlier versions of the program used the velocity description of Hardy amp Ford 1997 The basic fault bend fold theory follows Suppe 1983 and the arbitrarily inclined simple shear folding uses the constant heave method which has been described by a variety of authors Some additional references of pertinence to the topic of fault related folding are Suppe amp Medwedeff 1990 Suppe et al 1992 Hardy amp Poblet 1995 Waltham amp Hardy 1995 and Medwedeff amp Suppe 1997 Many other references are also available on this topic Conventions in This Manual Information in this manual which is specific to the Macintosh version of the program is shown in red that which applies to the Windows version of trishear is shown in blue General Layout
24. read it Additional Options in DigBeds DigBeds can do several additional tasks for you by choosing one or more of the options under the Operations Menu Renumber Beds The order in which beds are saved in the DXF file is exactly as you drew them to begin with in your graphics program which may not be in stratigraphic order Although Trishear 4 5 can handle beds in any order it is most convenient if they are in stratigraphic order particularly for the drawing of strain ellipses This option in DigBeds 1 1 allows you to change the order of the beds in the graphics file O Richard W Allmendinger 1998 2000 Wiser Help 58 Trishear User s Manual 59 v 4 5 Renumber Beds Type the new bed number nex to the old in the boses below Old Number New Number fe ao E 3 3 f z E gt E gt 7 5 if you need more just choose Renumber again 3 1 x 5 Ei Cancel 7 1 i 6 Shift Beds When DigBeds imports your DXF file it a A Enler the values to shift the position of the automatically positions it in the upper left hand corner of the computer beds in the window Positive is down and to e right screen Use Shift Beds to change the position of the cross section RE eee on the screen Positive numbers move the section down and to the A a s Cancel OF right H stands for horizontal and V for vertical EZE Scale Beds The DXF format is quite high precision Set the position on the scre
25. set the bed length but it is more flexible and efficient Slip Increment This item controls the increments of the amount of slip on the fault that occur between pro cessing steps As set in the above picture the computer will recalculate the trishear displacement field every two pixels of slip Because trishear is a continuous deforma tion the smaller the slip increment the more accurate the resulting section but the long the processing time needed to accrue any particular amount of slip For for ward models 2 pixels is a reasonable value for inverse modeling of forward models however we found it nec essary to use slip increments as low as 0 25 Note that the smallest total slip that can be used is equal to the slip increment Thus in the fault bend fold example in the tutorial page 11 the slip increment had to be set a 1 to get the tipline to propagate 150 pixels at a P S ratio of 150 had we left the slip increment at 2 the tipline would have propagated 300 pixels e Center concentration factor Zehnder amp Allmend inger 2000 showed that a large number of potential velocity fields satisfy the trishear boundary conditions The value entered here determines how strongly the de formation is concentrated towards the center of the tris hear zone A value of 1 yields the linear trishear of all Richard W Allmendinger 1998 2000 29 Preferences Length of beds 75 pixels Spacing btwn points on bed 2
26. statistics for all beds choose Show Statistics from the Restore Menu 9 To watch a real time restoration of all the beds using the best fit parameters for the key bed select Set Pa rameters from the Restore Menu You will see the best fit values filled into the text boxes Make sure that none of the check boxes are checked Click the Okay button You will see the initial deformed cross section Choose Restore Beds from the Restore Menu and the section will be progressively retrodeformed before your very eyes stopping at the best fit slip If you want to back up to check out something choose Unrestore Beds from the Restore Menu to deform the section again Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 Forward Modeling of Restored section There are several reasons why you would want to forward model your best fit restoration One reason would simply be to see how well the idealized geometry matches the real deformed geome try Also strain and particle paths can be calculated only from a forward model As the final step in our example of the grid search 10 Choose New from the File Menu A dialog box appears asking if you want to model the deformed beds Click Yes 11 Do not change anything in the New Model dialog box which then appears You may wish to click the Prefer ences button to make sure that calculation of strain ellipses is turned on Close the New
27. these parameters over a pre specified range testing all unique combinations of these parameters The criteria for good ness of fit is simply how well any particular combination of values returns a key bed to an original linear orientation using a least squares linear regression and c as a Statistic the specific algorithm used is from Press et al 1986 The combination with the lowest c is the winner Trishear can save up to a four dimensional matrix of statistical values as a text file that can be read into various plotting programs for visualization This is important because the program will report to you only the very best model for the key bed but there may be many other combinations that are nearly as good for the key bed and produce a better overall fit to all of the beds in the structure Okay end of overview let s see how it works on the Catskill file the numbering below follows from the previous section 5 Once Trishear is running select Import from the Re store Menu or Open from the File Menu Select the file that you saved in step 4 Catskill dig from the standard File Open dialog box You are given the choice of scaling the deformed cross section so that it fits the screen or maintaining the original dimensions as scaled by DigBeds if you used that program Click on Original Richard W Allmendinger 1998 2000 18 Trishear User s Manual 19 v 4 5 Dimensions Once yo
28. 0000 pixels Slip increment 0000 pixels Center concentration factor 1 0000 O Asymmetric Trishear in HW 50 000 bd Pick beds and fault with mouse bd Clip growth strata at surface Backlimb Fold Kinematics Parallel O Similar Shear angle 0 00000 k Calculate Strain O High resolution strain ellipses LJ Dense array of strain ellipses L Particle paths Inversion O Allow background processing Robust linear fit O Save animation frames Preferences Bed Length JB Bed pt spacing 20000 Slip Increment 2 0000 Il Clip growth strata at surface T Pick beds and fault with mouse Trishear Parameters Center concentration factor 1 000000 FT Asurmetric trishear 2 in Hs 50 00000 Backlimb Fold Kinematics Parallel Similar Shear angle 0 000000 Strain I Calculate strain ellipses T High resolution strain ellipses FP Dense array of strain ellipses TT Calculate particle paths Inversion T Robust linear fit Cancel Trishear User s Manual 30 v 4 5 previous authors Increasing the value produces a nar rower and narrower shear zone in the center of the trian 66 99 gular zone as shown below where c is the center concentration factor e Asymmetric Trishear Zehnder amp Allmendinger 2000 also showed that trishear zones do not have to be symmetric with respect to the fault to preserve area
29. 00000 Average Dip of Bed 0 00000 Area calculation does not take into account the bends on okay a fault See manual for details gt Get Bed Info E Bed Number 3 Number of vertices 50D First vertex EJ Eg Last Vertex 576 22 126 82 Length of bed 656 8098 Area beneath bed 28320 28 chrsquared 0 000000 Average dip of bed 0000000 Area Between Two Beds Enter the numbers for the two beds that you want to measure the area between Area rea calculation does not take into account the bends on a fault See manual for details Cow Area Between Beds x Enter the numbers for the two beds that you want to know the area between 3 and 4 rea 41883 91 Calculate Trishear User s Manual v 4 5 program Click on successive points until you have defined the area that you want then double click to finish Note a double click in this case is defined by whether or not the mouse has moved more than one pixel from its previous position it is not defined by the speed with which you click The traced area is shown with a red line Your polygon should have less than 500 vertices Once traced a dialog box like that shown above will appear with information about the area traced and the cumulative length of the sides of the polygon Trishear will always close the polygon for you even if you do not return to the first vertex to double click thus showing you the area measured The length
30. 2 you can search on a line 1 e O Richard W Allmendinger 1998 2000 44 Trishear User s Manual v 4 5 the projection of the fault This second option is particularly useful of course 1f you know where the fault is but don t know exactly where 1t terminates within a bed It allows you to limit the number of tipline positions quite markedly with respect to the In a region option After the dialog box 1s dismissed 1f you have chosen in a region you drag the mouse on the screen to specify the rectangular region in which you want to search for the best tip line If you have chosen on a line you first drag the mouse to define the fault plane and then you drag the mouse again to indicate where along the trace of the fault you want to search for the tip line Even if you use the mouse you must enter a value for the tipline step in the appropriate place in the dialog one step value for both X and Y Note that searching for the best position of the tipline can easily be the most time consuming part of the modeling process 1f you drag the mouse across a 200 by 200 pixel area and indicate a 1 pixel step size the program will search 200 i e 40 000 models and this assumes no variation in any of the other four parameters On my PowerBook 3400 searching 40 000 models takes five to ten hours Search large areas with a coarse tipline grid During an inversion 7rishear will keep you informed of the total number of m
31. A eee Show Digitized Beds This option allows you to turn on or Forward Digitized Draw Beds off the plotting of digitized beds see the discussion of difference Clear Digitized Beds between digitized beds and forward model beds starting on page M w Show Scan 4 Drag Scan Clear Scan Shade LNFE by Strain LTL rta Drag Digitized Beds Once you select this menu MC TY Show Digitized beds 1 Drag Digitized Beds 2 option you can drag the digitized beds around on the Scale Digitized Beds Set Colors screen relative to the forward model beds Only the dig ee omnes calada Save Colors Digitized gt Forward itized beds are moved This is convenient to see how se UNE gt FR SEE a Clear Digitized Beds well your forward model fits the original deformed geom SSS A ee eee etry Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 Scale Digitized Beds Use this selection to rescale the dig itized beds The following dialog box will appear Note that you enter the scale factor as a percent of original size with 100 equal to no size change Scale Deformed Beds Scale Digitized Beds Fa Enter the percent amount by which you want to scale the digitized beds use a Enter the amount in percent by which you want to scale the digitized beds 4 number greater than 100 will enlarge the beds less than 100 will shrink the beds value larger than 100 to enlarge and less than 100 to shr
32. Es then Show LNFEs will be turned off automatically and vice versa Set Colors You can assign whatever color your computer is capable of drawing to any of nine different types of features that Trishear draws When you chose any of the options under Set Colors you will see the standard Macintosh Color Picker dialog box as shown below Richard W Allmendinger 1998 2000 ee 00000000 y 709 Meri ks W400 00000000 47 Plot Scan Digtze Windows w Show Trishear Zone Show Kink Ases Show Elipses Show LFNE Show Principal Axes w Show Particle Paths Shade Ellipses by Strain Shade LHFE s by Strain Set Colors Save Colors Load Colors Beds Pregrowth Beds Growth Ellipses oth Ellipse Principal Axes Particle Paths Deformed Beds Fault Active Faults Old Trishear boundaries Kink Axis Plot Axes Trishear User s Manual v 4 5 Choose a new fault color np HEE Original 120 REN CMYK Picker Hue Angle o Saturation Yalue Caner a HS Picker In the Windows version you are presented with the following dialog box In it you select from the drop list at the top the graphic element whose color you want to change and then click on the radio button next to the new color that you want for that element When you click OK the screen will be redrawn with the new color Pick a Color x Pick a color for the Beds Pregrowth
33. Model dialog box by clicking the Okay button You will see an idealized starting bed geometry appear 12 Choose Run from the Model Menu The forward model will run until it reaches the best fit total slip You can click the left mouse button at any time to stop the run before 1t reaches the final slip Once stopped you can do anything else you want such as modify the parameters etc 13 To compare the forward model to the initial deformed section you will have to return to your graphics program and paste the forward model over the original section rescaling as necessary At the present time it is not possible to compare the two within Trishear Once a forward model is run the deformed section is no longer in memory If you want to try another restoration of the same section you will have to import it again O Richard W Allmendinger 1998 2000 21 Trishear User s Manual v 4 5 a mh 20099090000000 00000 90000000 NY VYA 20 W y i DUM gt y WG0000000 ts VEGIDO0DOLGO0O UNponnogOOeODOIOYY 22 Forward model of Catskill structure overlaid on original tracing in green in a graphics program A few final words about inverse modeling The amount of time that the grid search can take depends on the number of parameters and the ranges that you search over If you can constrain three of the see parameters as in the Catskill example where the ramp angle and tipline position is known the
34. Start New Fault Rotate Model Modify Model Parameters E Hew Ramp Angle 30 000 Trishear Angle 60 000 centering factor 1 0000 Propagation Slip Total Slip Display Increment S O Similar Folding Modify Parameters xl New Ramp Angle Trishear Zone ngle Center Concentration Propagation Slip Total Slip Display Increment Similar folding Cancel Trishear User s Manual v 4 5 does not attempt to follow in detail the kinematics described by Medwedeff amp Suppe 1995 First any part of a section that lies above the intersection of two kink axes will not be area balanced In the example to the right below the two top beds are not balanced in the triangular region above the intersection of the two green kink axes Second because of the simple velocity description that we use for movement over ramps the program does not generate all of the subsidiary axial surfaces described by Medwedeff amp Suppe 1995 Where there are more than two ramps the section below the intersection of the kink axes will be area balanced but may locally have zones of similar folding rather than parallel folding You can identify these zones of similar folding by choosing to show lines of no finite elongation LNFE Parallel folding occurs where one of the two sets of LNFE is parallel to bedding similar folding is the implicit kinematics wherever neither of the two sets of LNFEs parallel the b
35. Trishear User s Manual v 4 5 Trishear 4 5 User s Manual for Macintosh M and Windows by Richard W Allmendinger O 1997 2000 Trishear by Richard W Allmendinger O 1997 2000 portions of this program include material copyrighted by Absott Corporation 1991 1998 By selecting Okay you agree explicitly to okay abide by the terms and conditions in the Okay software License Agreement included in the Trishear distribution DRAeeade About Trishear v 4 0 Trishear BY RICHARD W ALLMENDINGER J 1998 2000 Windows Version SPECIAL THANKS TO ERNESTO CRISTALLINI FOR WINDOWS PROGRAN HING HELP DYNAMIC LINK LIBR ARIES DIGITAL YISUAL FORTRAN By selecting Ukay you agree explicitly to abide by all the terme and conditions SS expressed in the Software Licensing Agreement which le included in the PA E Trishear distribution package even if that agreement is currently unavailable to vou additional copies are available from the Author Cancel IF You do not agree to those conditions click Cancel to exit now i O Richard W Allmendinger 1998 2000 Trishear User s Manual 2 v 4 5 Table of Contents 5 ligar Flo HOR AAA A O OOO O 3 What TA TS ea f re FAM UU Sra 3 REA 3 a NE Er SER SEN RSS NEN 4 OAV FITS IM Tot Sree IML ll nce cee ti evasive PLA reen enn 4 General Layout of Progra Msi ri aan 4 OOH IE NER BEES EEN ENE E aA 4 Grape FICS ha CS EJE MENES rare rad 6 A Quick Tutoria
36. W Allmendinger 1998 2000 Trishear User s Manual v 4 5 4 If you want you can experiment with additional ramps in this new fault by choosing Modify from the Model Menu or you can add more new faults Normal fault with reverse reactivation Erslev 1991 showed that trishear could equally well be applied to normal faults Such structures were called extensional forced folds by Withjack et al 1990 To understand how exten sional trishear works one must have a clear understanding of the propagation to slip ratio P S P S governs how quickly the tipline propagates relative to the slip on the fault In a thrust fault the tipline propagates towards the surface in the same direction as the movement of the hanging wall In the case of a normal fault the tipline propagates up towards the surface as the hanging wall moves downward in the opposite direction from the tipline In Trishear 4 5 the sign of P S is defined relative to the hanging wall thus for reverse faults P S is positive but for normal faults it 1s negative Likewise the slip is defined as positive if the hanging wall moves up but negative if it moves down as in the case of normal faults In this exercise we will produce a simple trishear normal fault with grown strata 1 Choose New from the File Menu For this exercise we will not enter the data with the mouse so if you get the New Model with Mouse dialog click the Prefer ences button
37. ackage called DigBeds short for Digitize Beds clever huh DigBeds will read the DXF file extract the polygons automatically resample them so they have 500 points evenly spaced along the length of the bed and finally save the file in the format that Trishear needs for importing l Start up DigBeds Close the About dialog box Choose Open DXF file from the File Menu In the standard file open save dialog box select the DXF file from which you want to extract the polygons For this exercise we are using the file Catskill dxf which is included in the Trishear package 2 After you select the file a dialog box will appear asking if you want to shift the section on the screen Enter H orizontal 150 and V ertical 50 to shift the section down and to the left After you click Okay you will see the repositioned section with the beds numbered 3 Next you will see a dialog box asking you if there are any pairs of polygons which represent the same bed on either side of a fault In this example there are two such pairs Polygons 1 and 2 are the same bed and polygons 3 and 4 are a different bed Enter 1 and 2 in the two text boxes located on the first line and enter 3 and 4 in the two text boxes located on the first line When you click Okay DigBeds will resample the beds renumber 17 There are a few simple but important guidelines for tracing the polygons in your graphi
38. anual v 4 5 allowing you to get rid of the jaggies in your graphics Thanks go to Stuart Hardy for convincing me to implement this EPS export is available only on the Macintosh Export as DXF DXF files are a text file format developed by the makers of AutoCad Like EPS files they enable high resolution printing when imported into a graphics program As implemented in Trishear they are more flexible than EPS files because they include text whereas Trishear EPS files do not I recommend using DXF export over EPS export in general DXF export is available on both Windows and Macintosh versions Print Standard dialogs to send the contents of the front most window to whatever printer you have selected Macintosh files are printed as PICTs Windows as bitmaps Quit or Exit Does what it says You are asked whether or not you want to save anything first Edit Menu Undo Y ou can undo the most recent operation by choosing undo This not only returns the graphic to the previous state but also resets the model parameters to the previous state Undo uses a temporary scratch file written to your hard disk during operation of the program this file will be deleted automatically If you switch out of the program while it is still running or if the program crashes you will see these temporary files on your disk These files are standard Trishear output files so in the event that you do suffer a crash heaven forbid you can rec
39. bed Bed 1 Bed 7 Bed 2 30 Bed 8 Bed 3 Bed 9 Bed 4 Bed 10 Bed 5 120 Bed 11 Bed 6 Bed 12 Cancel The current high points on existing beds are shown for your reference Editing these values will have no effect Okay ne Trishear User s Manual 37 v 4 5 beds entered after the initial ones 1 e all growth strata are plotted with the Cyan color so that you can distinguish them easily Bed 1 000000 Bed on the screen Like the New model dialog the add beds dialog Te Bed 2 30 00000 Bed E initially shows only 12 beds However once you enter the twelfth bed the next time you call up Add Beds you will get a slightly sea EE es AA modified dialog box that will allow you to add up to 20 beds total Beda 000000 Bedi All beds entered in this dialog box start out flat If you want to add i a l Beds 120 0000 Bed 11 new dipping beds first go to Preferences and choose Pick beds amp fault with mouse Bed 6 Bedia l r MER high paints r pd OK Get Ellipse Info If you have turned on Calculate Strain i Cancel in the Preferences dialog then this menu option becomes available After selecting this you can click on any ellipse in your plot and the ellipse parameters orientations and magnitudes of the principal axes orientations of the lines of no finite elongations LNFE are displayed for you If the array of points defining the ellipse cannot be satisfactorily fitted to an
40. canned geologic cross sections seismic data etc These scanned data act as a backdrop to the model in the program The scans can be moved and scaled but cannot be edited in any way Richard W Allmendinger 1998 2000 Strain Markers JO Be me Se 00 PPR e LNFE shaded by magnitude Particle Paths Trishear User s Manual v 4 5 The final geologic elements are strain markers and particle paths The strain markers are initially circular arrays of points which are deformed along with your beds during fault motion You can extract various types of information from the strain markers including principal axes and lines of no finite elongation LNFE which may be used as proxies for shear plane orientation When you ask Trishear 4 5 to plot principal axes lines of no finite elongation or to shade ellipses by strain magnitude the program does a least squares best fit of an ellipse to the array of points which initially defined a circle If the strain 1s too heterogeneous within the region defined by the ellipse or in the rare cases where Trishear 4 5 does not preserve area correctly the program will not plot the lines shade the polygon etc even though it will still plot the ellipse Particle paths are the traces of positions occupied by a single particle during the deformation Graphic Interface Elements Trishear 4 5 has six main menus which are organized ac cording to the types of tasks that you wa
41. cross sections of simple trishear structures using an inverse grid search procedure for extracting the best fit trishear parameters Both thrust and normal faults can be modeled The user has great flexibility in designing a model Some of the principal features of the program are l Beds and faults can be entered with the mouse or they can be specified precisely via dialog boxes A model can have up to 20 bed tops Beds can be added to a model at any time e g to simulate growth strata Individual beds can have up to 1000 vertices A single fault can have up to 100 vertices 1 e ramps and a single section can have up to six faults Back limb fold kinematics can be modeled either by parallel kink folds or by arbitrarily inclined simple shear The user can change the trishear parameters ramp angles or scale of the model at any time The program maintains a complete record of the changes that have been made to a model The strain can be calculated at any time and particle paths can be plotted Cross sectional area and line length can be measured at any time and the section can be rotated globally about any user defined axis A section can be transferred to other programs via the clipboard or saved to disk PICT format for Macintosh version BMP format for Windows version or it can be exported at higher resolution as a DXF file for import into graphics programs What it cannot do Trishear 4 5 is really a
42. cs program See the details starting on page 59 of this manual In Trishear 4 5 and above you can just scan the cross section to be modeled import the scan using Plot Menu Scan Import Scan or Scan Digitize Menu Import Scan and trace over the beds with the mouse in Trishear to produce the digitized beds Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 them 1f there were any broken polygons and trace over the original polygons in red to show you the res ampling and renumbering 4 Choose Save in Trishear Format from the File Menu and you will get a standard file save dialog box to use the name the file call it Catskill dig for this exercise and store 1t wherever you want on disk This 1s the file that you will read into Trishear Quit DigBeds Grid search to find the best model Now that we have digitized the beds of the structure and converted them to a readable format it is time to fire up Trishear if it isn t already running and import the model into the program To understand the grid search inversion fully it is best to read Allmendinger 1998 and Allmendinger et al in press An ex tremely brief overview is provided here Basically there are six parameters that define a simple trishear geometry 1 trishear angle 2 P S 3 fault displacement 4 fault ramp angle and 5 the X and 6 Y positions of the fault tipline The grid search systematically varies each of
43. ds You can have Trishear calculate the area between any two beds in your section Trishear will show label all of the beds on the screen and then ask you for the two numbers The area is displayed in the same dialog box The area calculated is of a polygon where in the ends of each of the beds is connected to the other bed Trishear will check to make sure that the polygon vertices are ordered in the same direction in the case of forward models the vertex number always increases from left to right For deformed sections vertices are numbered in whatever order they were traced in your graphics program This command works with both forward models and deformed sections The program measures area very accurately but Where a bed is offset by a fault the program simply assumes that a straight line connects the hanging wall and footwall cutoffs If there is a change in ramp angle between those two cutoffs then the area calculation will be incorrect In those cases you would be better off using Measure Area below Measure Area By selecting Measure Area you can use the mouse to trace out any area you want on the screen To trace the area you draw a polygon much like you would in any graphics O Richard W Allmendinger 1998 2000 38 Get Bed Info Bed Number Number of vertices 375 x First vertex 50 000 60 000 Last vertex 798 00 60 000 Length of Bed 748 00 Area beneath bed 2244 Chi squared 0
44. e ault dip ramp r 50 0000 y 0 00000 use mouse for tipline O use mouse for angle l Propagation slip Trishear angle LJ use mouse for tipline Tipline Coordinates Propagation 5lip 1 50000 Fault type to restore Total Slip 0 00000 Total Slip w Reverse 0 Normal leave blank to run until mouse click leave blank to run until mouse click Fault type to restore Reverse Normal Restore Beds Choose this to begin the restoration The program displays every single step of the restoration on the screen the Display Increment parameter has no effect The only way to stop a restoration is to click the mouse just let it go until the beds become planar or it becomes apparent that they are not going to become planar and then click If you then want to forward model the restored beds just choose New from the File Menu The tipline position bed tops actually the highest points on the restored beds and slip will be entered in the New dialog as the default values Don t say I never did anything for you If you don t like your restoration just choose Set Parame ters again You will see the above dialog box again and can change any or all of the values either with text entry or the mouse As soon as you dismiss the dialog your original starting digitized deformed beds will be displayed again in the same position unless you have re scaled or shifted the plot see below ready to be
45. e H Add to History SY i i Shift in Window windows in the program The Cross Section Window 1s where all Drag in Window 32D Resize to Fit Shift in window plotting and restoration occurs The History Window keeps a text Set Scale as Resize to fit Windows Help Cross section History Add to history Windows Menu The Windows Menu provides access to display of the two record of your model run Either window can be saved to disk or Set Scale amp Origin copied to the clipboard when it is in front and is the active window Cross Section Brings the Cross Section Window to the front and makes it active History Brings the History Window to the front and makes it active The contents of the History Window can be saved as a text file at any time by selecting the appropriate option under the Save Submenu of the File Menu The most recent model run is Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 always added at the end of the window In the Windows version the History Window is a fully editable scrollable text window so that you can select things and cut and paste The contents of the window in the Macintosh version is a PICT so it is editable only when you cut and paste it into a graphics program In the Mac version the History Window is not scrollable and only that last 45 or so lines of the model history are shown When you save the History to desk as a text f
46. e bed 3 units above the highest bed Then choose Modify from the Model Menu and increase the ramp dip by about 5 Repeat step 4 except choosing Continue rather than Run several more times A screen shot of the final model is shown below with lines of no finite elongation shaded by strain magnitude Except near the fault one O Richard W Allmendinger 1998 2000 Backlimb Fold Kinematics O Parallel Similar Shear angle 15 Trishear User s Manual 16 v 4 5 of the two lines of no finite elongation always parallels to oblique shear in the hanging wall Note that the model shows the well known roll over anticline but it also displays normal drag near the fault due to tip line propagation Once the fault breaks the depositional sur face no further drag folding really tip line folding occurs Inverse grid search As the final example in this tutorial we will explore the inverse gird search modeling capabilities This procedure takes place in three parts 1 Digitizing and resampling the deformed section to be modeled 2 a grid search to find the best fitting trishear parameters that restore a key bed to an initial planar really linear because we are operating in two dimensions orientation and 3 making a forward model based on the best fit parameters As a general rule the grid search can only be carried out on a simple trishear monocline either normal or reverse which ev
47. edding The following diagram illustrates just such a case Parallel folding and no thickness change one of the two sets of LNFE are parallel to bedding Add Beds This command will get you a dialog box in which you can enter new beds The highest points on the existing beds are shown in editable fields but this is a cruel hoax you can t The first blank box is conveniently selected for you to add the next bed Although normally you will want this bed to be higher up you can in fact enter a next bed within or below the existing section in case you want to model sills for example All Richard W Allmendinger 1998 2000 36 Warning Any beds that lie above the intersections of two kink axes will not plot correctly Also local zones of similar folding may result but the section will still be area balanced JT 200000 el gt 500004 al 900000 MY of OC soo000to9 Woes O DD DS ISLA PS P eS 6 a et OR T DOAN 50 Ae a Age Iban Example of a case where the kink axes do not function properly in Trishear 20 thickening due to similar folding note LNFEs oblique to bedding Section is still area balanced however If it weren t area balanced the program would not draw the LNFE in the ellipse LEDE pep Strain in footwall due to PLL PCPRPPAP PPE Trishear deformation Add New Bed Tops Cross sections can have up to 20 beds A new dialog box will appear after you have added the 12th
48. el run can have up to 100 different ramp angles A change in ramp angle produces a fault bend fold whose kinematics is determined by the setting in the Preferences dialog A second ramp which is steeper than the first will produce a trailing syncline whereas a gentler ramp will produce an anticline If Parallel is selected in Preferences Trishear attempts to follow Suppe s 1983 rules for fault bend folds so that bedding thickness remains constant across the kink plotted as a green line related to the change in dip This is always possible for fault bend fold synclines but not always so for anticlines Trishear will warn you if you specify an illegal ramp for the case of anticlinal bends but will let you go ahead and enter it If you have ellipses turned on you can see the non volume constant deformation that this produces Although you can enter a large number of ramps in Trishear there are some aspects which you should take into account Trishear tries to follow Suppe s 1983 fault bend fold rules but multiple ramps can get pretty tricky and the program will warn you below the first time you enter a third ramp below left The program Richard W Allmendinger 1998 2000 35 A Cross Section Window Model Restore Plat Windows Bun Continue Modify Add beds Get Ellipse Info Get Particle Path Info Show Bed Numbers Renumber or Delete Beds Get Bed Info Area btwn 2 Beds Measure rea
49. en of the upper left corner ofthe cross section much higher than possible on a computer screen Therefore you can change the scale of your section without significantly affecting Ha v the resolution of your section In the Scale Beds dialog enter the amount in percent by which you want to scale your section You may wish to shift the beds on the screen after scaling them Enter the percent amount by which you want to scale your beds A number greater than 100 wall enlarge the beds less than 100 will shrink the beds Guidelines for tracing sections in your favorite graphics program Scale Factor je 1 Use the polygon tool not the Bezier curve tool or the Cancel freehand curve tool 2 Use as few points as you need to represent accurately the structure DigBeds will fill in the rest and save you a lot of mouse clicks Each polygon should have no more than 500 vertices 3 Ifa bed is cut by a fault do not connect it with a line segment along the fault Trace it as two separate polygons 4 Digitize each bed in the same direction If you start the first bed on the left start all beds on the left This rule is particularly important for beds which are offset by the fault The last point of the first polygon must be the cutoff against the fault and the first point of the second polygon must be the cutoff of the same bed on the other side of the fault See the following diagram Richard W Allmendinger 1998
50. ete check box Any number Old bed number 4 I Delle ce y 3 change to entered in New bed number is ignored The program will not oon i warn you that you are about to remove a bed Note that deleting a Cancel bed does not remove any strain ellipses associated with that bed O Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 Either deleting or renumbering will cause other beds in the model to be renumbered also Get Bed Info This command brings up a dialog box con taining a variety of information about whatever bed number you type into the bed number text box The Area beneath bed is the area between the bed top that you enter in the dialog box and the next lowest bed number in the case of the dialog box to the right it would be the area between bed tops 3 and 2 If bed 1 is your lowest bed and you enter it in this dialog the area will be that between bed 1 and the next higher bed This command works with both forward models and deformed sections You can get confusing results 1f your beds are not labeled sequentially with depth e g bed top 3 lies between tops and 2 You can change the bed number while the box 1s open to get information about more than one bed In the Windows version of Trishear you must first enter the Bed Number and then click the Calculate button to see the information For information on another bed just click the ap propriate button Area btwn 2 Be
51. gins to cut into the growth strata Add a final horizontal bed to mark the base of the post rift strata 7 Select Show LNFEs from the Plot Menu Select Get Ellipse Info from the Model Menu and click on the ellipse at 379 231 Note that one of the two lines of no finite elongation in this ellipse has a negative dip This means that 1f the line parallels a shear plane then that shear plane is a reverse fault even though the major fault is a normal fault See Withjack et al 1990 and Allmendinger 1998 for a discussion of this important point 8 Finally let s reactivate the fault as a reverse fault Select Modify from the Model Menu and change the P S to 1 2 and the Slip to 0 When you choose Run this will return the base of the model to a horizontal plane by uplifting the hanging wall with respect to the footwall Note the folding in the upper layers even thought the net slip is zero Fault bend fold the hard way Although the program is called Trishear we can construct true fault bend folds The example following this one shows you the easy way to do this Here is a more complicated but probably more realistic way The trick 1s to think about how mother nature would make a fault bend fold first make the fault trajectory with very little slip and then slip over the pre existing fault plane The way to make the entire fault trajectory is to specify a large propagation to slip ratio P S We wil
52. he Model Menu Oops nothing happens That s because we ve already reached the total slip initially specified You now have two choic Technical note The coordinate system used by the computer and used internally by trishear has 0 0 in the upper left corner of the screen with positive down and to the right 1 e the way you read a book If you examine any of Trishear s data files which are plain ASCII text the numbers that you see are not those related to the axes drawn on the screen but are the computer s internal coordinates This makes computation and drawing to the screen faster Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 es a you can do Modify again and give it a larger slip or b you can choose Continue rather than Run Choosing Continue tells the computer to run again until it reaches twice the initial total slip For example if your initial slip was 75 units the first time you choose Continue after the first run the model will run out to 150 units The second time you choose Continue you will get 225 units three times the initial run and so on You ve completed your first trishear model with a fault bend fold backlimb If you turned off the display of strain ellipses you can turn them back on with Show Ellipses under the Plot Menu To find out the details of the strain Choose Get Ellipse Info from the Model Menu and click on
53. hout releasing the button drag the mouse to define the hanging wall boundary of the trishear zone Then click and drag the mouse again to define the footwall boundary the program will automatically connect your second line segment to the tipline you chose with the first click When you do this you also automatically define the ramp angle because it must be the bisector of the trishear zone you have just defined If you know the ramp angle already then you would type it in on the left and then use one or both of the check boxes in the middle part of the right side of the dialog box If both are checked then you first click and let go of the mouse at the position of the tipline A small black dot will be drawn where you clicked Then you click and drag the mouse to define a trishear zone which is symmetric about the ramp which you typed in at the left If you leave either of the boxes unchecked then the text value at the left Richard W Allmendinger 1998 2000 41 Trishear User s Manual 42 v 4 5 will be used for that parameter Note that checking the top box will automatically uncheck the two boxes in the middle and vice versa Finally tell the program whether you are restoring a reverse fault or a normal fault with the radio buttons in the lower right set Restoration Parameters Set Restoration Parameters E Fault dip ramp O set ramp 15 angle amp tipline with mouse Fault di l Tipline Coordinates Trishear angl
54. iated with them Why this distinction between the two bed types This question is best answered by looking briefly at the restoration process Trishear 4 5 allows you to retrodeform real geologic sections that you have digitized and the program can find the best fitting trishear parameters to do so Let s say where are talking about a thrust related fold as in the example starting on page 16 To do so one first imports a digitized bed While you set the parameters for the restoration Trishear 4 5 automatically converts the digitized beds to a forward model then the forward model is restored by producing normal 1 e extensional displacement on the thrust fault But the original digitized beds remain in the program s memory in their original state so that you can compare them to the restoration If you don t like the restoration you can redo it with new parameters without importing the data again You may also want to do a forward model from scratch to try to compare to a deformed section that you have digitized and imported Finally if you want to do a forward model with a bed geometry that is more complicated than can be produced with the New Model dialog boxes e g beds with initial curving geometry channels pinch outs or pre existing struc tures you can import these as digitized beds and then convert them to a forward model ready to be deformed Trishear 4 5 can also import Windows BMP files or Macin tosh PICT files to show s
55. ile under the File Menu you will get the entire history or at least the last 250 lines of it 53 Hew Model X 335 Y 49 Ramp angle 36 End of run slip Prop Trishear Angle 37 PS 1 5808 of beds 5 x 465 Y 83 slip 188 Prop 158 PS 1 5000 Kamp angle S Trishear Angle 37 of beds 5 Modify Model Y 465 Y 83 Slip 190 Prop 158 PAS 1 5000 Kamp angle 55 Trishear Angle 37 of beds 3 End of run Y 543 Y 194 Slip 198 Prop 285 Pcs 1 5000 Ramp angle 55 Trishear Angle 37 of beds 5 Add to History The Trishear program automatically records major changes to the model in the History Window e g a new model addition of a bed change in ramp angle etc But there may be other times when you want to record that state of a model Choosing Add to History writes out the current state of the model Se eee iets with the annotation User added to reposition the cross section in the window delta i ja delta v Jo Shift in Window brings up the dialog box above which allows you to type in precise X and Y values for moving a plot around on the screen This change is applied to all parameters in the program When you use Shift in Window the model is moved relative to the coordinate system Thus all of the coordinates of the individual points in the model will be changed Drag in Window If you prefer to re position your cross section visually use this menu op
56. in between each top effectively doubling the number of ellipses and increasing processing and screen redraw Calculate particle paths Particle paths do have to be turned on in this dialog box before they can be plotted Clicking Plot particle path will automatically check Show Particle paths in the Plot Menu However you can turn off the plotting of particle paths while still calculating them in the background Allow Background processing this allows you to do other things with your computer but not within the trishear program while you are running an inverse model This will cause your Macintosh to run more slowly be cause each time through an inner loop it will check the System to see if there are any events pending The Win dows version of Trishear does not have this option be cause the inversion and several other operations always run in a separate thread from the main program Robust linear fit enables the statistical calculation of the same name as described in the book Numerical Rec ipes It will markedly slow down your inversions and is not necessary in the vast majority of inverse models Save Animation Frames If you select Save Anima tion Frames checkbox every single step of the subse quent analysis will be saved to a folder as a series of numbered PICT files This option is not yet available in the Windows version of Trishear The program will keep saving animation frames until you turn it off b
57. ine positions are entered in the various dialog boxes in that scale On the screen the area slip and prop agation are reported at the scale and units that you specify Note that the program maintains everything internally in decimal pixel coordinates this option simply allows you to enter more realistic cross sections directly You can enter anything you want e g 57 3 pixels 1542 5 meters It used to be that every Macintosh monitor had 72 pixels inch and every PC 96 pixels inch but with multi scan monitors the size of a pixel can vary depending on the resolution specified in the monitors control panel The choice of meters or feet is largely cosmetic controlling only the labeling on the screen You can now also put the origin of the on screen axes at any point on the screen by selecting Set origin with mouse The axes now cover the entire screen and are always visible anywhere you drag to scroll an image by choosing Drag in Window under the Window Menu as long as you drag along an axis of course The color of the axes are now drawn by default in gray rather than black you can select any color you want for the axes by using the Set Colors submenu under the Plot Menu Thus you can define a more realistic coordinate system for cross sections of features below sealevel as in the graphic below Richard W Allmendinger 1998 2000 54 Set Scale amp Origin all coordinates are stored internally in pixels th
58. ink scale factor Scale factor LLL z a Draw Bed You can now draw new digitized beds within the Trishear program Combined with the various Scan features above this allows you to digitize a section completely within Tris hear without using the DigBeds utility program To start select Draw Bed from the Digitize Beds submenu The cursor will change to a cross with the current coordinates displayed next to it If you wait long enough about four seconds before starting the bed the dialog box to the right will appear with instructions The bed 1s drawn as a polygon clicking the mouse button to defined the vertices The points are set when you release the mouse button not when you press it down If you want your bed to have a gap in it press the Shift Key at any time between the two vertices on either side of the gap or use the right mouse button key on the first point on the other side of the gap When you are done double click the mouse 1 e click twice without moving the mouse The polygon that you have defined will be resampled to have 500 evenly spaced points in it You can draw up to 20 beds this way Use the mouse to define the bed polygon Polygons can have up to 500 vertices Press the Shift Key while drawing a segment across a gap Q A Draw a polygon Use the mouse to define the bed polygon Polygons can have up to 500 vertices Press the RIGHT mouse button while drawing a segment across a gap Doub
59. is scale factor just applies to what you see onthe screen and enter in dialog boxes t en 100 pixels 100 00 ae ee O set origin with mouse J Rescale current model Set Scale and Origin Sets the screen coordinate system to your desired scale and units internal coordinate system remains unchanged unless you choose rescale meters 0 ul foo pixels 100 0000 e A Set origin with mouse 7 Rescale current model rea Trishear User s Manual v 4 5 Slip 540 00 Propagation 960 00 Ramp angle 25 236 tishearangle 33 231 PIS ratio 1 5000 a Richard W Allmendinger 1998 2000 55 Trishear User s Manual 56 v 4 5 Using DigBeds One of the most arduous tasks in this digital world is digitizing data in a particular format so that a computer program can read it In the case of Trishear one must digitize a deformed cross section in a certain way before the program will recognize it Fortunately this task is not too difficult thanks to a small utility program that I have written called DigBeds which is available for both Windows and Macintosh Note that much of the same functionality of DigBeds is now contained within Trishear 4 5 thanks to the latter s ability to import scanned graphics and draw new digitized beds over the top However there are still reasons why you might want to use DigBeds Modern graphics programs like CorelDraw or Canvas are much more flexible than Trishear in allowing y
60. l also add growth strata in this example to prove that the program produces fault bend fold kinematics as described by Suppe et al 1992 At any point when a menu command is not pending you can click the right mouse button on the screen and get the coordinates of the point under the mouse Click and drag to measure distances and angles Richard W Allmendinger 1998 2000 Trishear User s Manual 12 v 4 5 1 Choose New from the File Menu Set the ramp angle to 30 trishear angle to 60 P S 150 yes that s right one hundred and fifty and slip 1 0 Click on the Preferences button and change the slip increment to 1 0 by default it is set to 2 pixels With these settings the fault tipline will propagate 150 pixels for each pixel of slip Enter bed tops at 0 30 60 90 120 and 150 Make sure that ramp up from decollement is checked 2 Select Run from the Model Menu The fault plane will propagate 150 pixels with almost no slip 3 Chose Modify from the Model Menu Change the ramp angle to 0 Then select Continue from the Model Menu until the tipline disappears off of the right side of the screen You will see a very slight uplift of the anticlinal crest Note that the two kink axes shown are active kink axes related to the footwall ramp 4 Now that we have made the fracture plane of the fault we can increase the slip to make the fold Choose Modify from the Model Menu
61. l as text 365 open gt l Close 7 EW save History as text Save b Save Strain as text aL Page Setup AutoCAD DXF Print P Quit 9 TRISHEAR Cross 38 Fie Edit Model Res New Open Close Save az Save plot Save strain as Export DF Print Exit Trishear User s Manual v 4 5 New Model Fault Trishear Zone Ramp ngle 30 000 Trishear angle 60 000 Propagation Slip 0 gt footwall fixed 0 gt hanging wall fixed Total slip 100 00 Display increment Initial coordinates of tipline x 300 00 Y 0 00000 O ramp up from decollement O initial multi bend fault Beds Tops 0 00000 30 000 60 000 90 000 120 00 Fault Trishear one Ramp angle 60 00000 1 500000 Trishear angle Propagation Slip if footwall fied 0 then hanging wall Total slip 100 0000 Display increment 5 Initial coordinates of tipline w 350 00 ye 00000 I ramp up from decollement Initial multibend fault Hodel data Fa Beds Tops Dips Bed 1 0 00000 0 00000 Bed 2 0 00000 Bed 3 0 00000 0 00000 0 00000 Bed 4 Bed 5 Bed E Bed 7 Bed E Bed 3 Bed 10 Bed 11 24 TT ia OMA MANE Bed 12 0 00000 pooo 0 000_ s0 000_ 12000 LL e AT Ca Preferences Positive dips are down to left os a o m SE T a a i w T a E
62. l nacio 7 Simple forward MOE susana 1 Complex TO Ward Ml aaa 9 Normal fault with reverse reactivation aaa 10 AU a a a a A 11 AO Mecas A O 13 SEN asar 14 MA A E SEGS ERE ENES ERE DER 16 e e o EM POUR SEE O In 17 urea nie A Ea ETEEN EErEE SE EEE 18 Forward Modeling Of Restored seco das 21 A tew Mal OFA SAD DUE KNEE ES e modelin ada dal 22 Meni RE TENCO cioran a E A E A 23 e oat oe ea us ac E anede ne 23 ECVE VMI ky AN BESKR 21 MOS Ms Eero ER 34 ASIS MNU SEERE vencenan EA EEN EEA T EEN REESE EO 40 A na AAAA Eee TOE 47 Plot Menu Digitized Beds Plot Menu Scan Scan Digitize M NU ccccsssssssssssscssssssssssesssessssserssssrssssesesseseseteesersesesstseses 49 WV NINOS TS TI aar tet gai puaean ct vay er ek ptpyunt wah stank vay peop nat vasy nee neve eRe er erne 52 Usma H BJ To CUS iia 56 NA 56 ACAI Hall PUSIMOS 58 Guidelines for tracing sections in your favorite graphics PLOGKAM cccccscsesessescscssssescsssssesssssesesssssessssssesseseesseseeren 59 References Ciela A a 60 O Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 Introduction What this program does Trishear 4 518 a program designed for forward and inverse modeling of fault related folds using trishear kinematics for the deformation at the tipline and fault bend folding over trailing ramps In this program the user can produce complex forward models of composite trishear fault bend fold structures and can retrodeform real
63. le click to finish the polygon Double click to finish the polygon Once you have drawn the beds it is the same as if you imported digitized beds in the Restore Menu You can drag them around the screen rescale them convert them to a forward model etc If you have a complex initial stratigraphy e g with lots of internal unconformities etc that you want to forward model you can now draw those layers on the screen convert them to a forward Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 model with Digitized gt Forward and run the model Note however that forward model beds that are made this way will not have any strain ellipses associated with them Digitized gt Forward You can load the digitized bed infor mation into the forward model bed arrays by choosing this command You might want to do this if you have a starting bed geometry which is too complicated to enter using the standard new model dialogs After you select this option the digitized beds will be redrawn in the forward model bed colors and the New Fault dialog box page 39 will appear asking you to specify the fault parameters associated with this new forward model Forward gt Digitized This menu option will place a copy of the forward model beds into the digitized beds array replacing whatever was already there You might use this option 1f you wanted to compare two models with slightly different parameters or if yo
64. ly the file is very large generally more than 1 Mb in size However data in this format can be read into IDL or Noesys or other visualization programs for plotting in 3 D The Best model applied to all beds check box will save an ASCII text file of the 2 D matrix with displacement on the vertical axis bed number on the horizontal axis and contours of chi squared You can read this file into your favorite graphing program as space delimited text for plotting When an inversion begins the program will display a small dialog box Macintosh version or will write on the screen in the Windows version showing the progress including the estimated time remaining which will actually increase early on in the inver sion In the Mac version you can click on the Stop button to terminate the inversion The current best model will be displayed on the screen Alternatively if you click suspend and save you will be presented with a standard save file dialog with which you can name a file to contain the interim results In the Windows version of Trishear 1f you simply click anywhere in the screen area while the inversion is going along a dialog box will pop up asking if you want to Stop Suspend and Save or Continue You would press Continue if you clicked in the window by accident Like on the Mac in the Windows version if you click Suspend and Save you will see a save file box to specify the file to save the interim re
65. n a new model or start a new fault Model Menu you can specify with a check box in the New dialog box whether the starting tipline position of the fault represents an initial ramp up from decollement or whether the faults continues to project downward from the tip line with the same ramp angle specified in the New dialog box 1 e the normal behavior in ver sions prior to Trishear 2 5 Having a ramp up from a decollement produces a trailing fault bend fold syncline with the forelimb of the fold a trishear fault propagation fold The ramp up from the decollement is modeled as a kink style fault bend fold or a similar fault bend fold depending on which option is selected in the Preferences dialog box This option enables one to model trishear detachment folds Old You can read back into the program any model at any stage of development that you have saved using the Save As menu command A standard Macintosh or Windows Open File dialog box will appear allowing you to select the file that you want Note that any ASCII text file will appear in this dialog box but only flies which match the exact format of the file produced using Save As will be read in successfully Close The close command will hide the front most window but otherwise has no effect You can show the window again by Richard W Allmendinger 1998 2000 25 Pick a New Model with Mouse E Bedding Humber of Beds Initial left X coord
66. nces dialog box Each bed can have up to 1000 vertices and you can adjust the spacing between points on a bed e If you choose Pick beds fault with mouse in the Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 Preferences Dialog see the Edit Menu section below you will instead get the dialog box to the right called Pick a New Model with Mouse After you set these parameters you will see a series of short dialog messages on screen instruction you on how to select the beds Beds which are picked with the mouse can be flat or dipping You can also specify whether the left edge of a bed occurs at the given x coordinate or wherever you first click the mouse by selecting the check box You set the fault with the mouse by clicking and dragging The first mouse click sets the position of the tip line and then the drag sets the fault ramp angle You can drag in either direction to set the fault angle but it is the first click that sets the tip position A click without a drag will give spurious results After the ramp and tipline are set a final click and drag sets the trishear angle e Whichever way you enter a new model if you have checked initial multi bend fault you will have to draw the fault trajectory on the screen with the mouse Any given ramp dip is ignored When entering an initial multi bend fault the tip line is drawn last and is identified by a double mouse click e When you ru
67. ndard Macintosh or Windows open file dialog box to select the file containing the deformed beds that you have digitized The file 1s an ASCII text file but the format must be followed exactly Here is part of a typical file in Courier font with comments Note that the internal coordinate system of the program is the same as that of the Mac or Windows screen X positive to the right and Y positive downward with the local origin at the top left corner of the window This is the coordinate system that Trishear O Richard W Allmendinger 1998 2000 40 Start New Fault with Mouse E Propagation Slip 0 gt footwall fixed 0 gt hanging wall fixed Total slip Display increment O ramp up from decollement O initial multi bend fault Cancel Rotate Model Enter the amount that you want to rotate the model by clockwise positive Rotation angle about tipline O click mouse Enter the amount that you want to rotate the model by clockwise positive pa i click mouse Rotation angle about tipline Cancel a Plot Windows Import Beds 36 Set Parameters 3 Restore Beds B Unrestore L Import bedz Restore beds Unrestore Automate a Resume Inversion Show Statistics 3 Automate Show statistics ss Section Window Restore Plot Windows Set parameters Resume inversion Trishear User s Manual v 4 5 expects digitized bed
68. nger because 1t does not truly search the entire parameter space leaving open the possibility that some smaller value of c i e a better model has been missed You can override this behavior of the program and force it to always search out to the maximum displacement you have entered by checking the always search to max displacement check box A maximum displacement is necessary because some models never converge on a minimum c if you leave the max displacement blank the program will automatically truncate any run at 2000 displacement units Because all cross sections are scaled to the screen before beginning 2000 displacement units 1s far more than you should need Note that 1f you enter a displacement larger than 2000 e g 4000 the program will search out to that larger value The sign on the displacement is in fact meaningless because the direction of restoration is actually controlled by the Reverse and Normal radio buttons as the bottom right of the dialog these work identically to the buttons of the same name in the Set param eters dialog You can choose to type in values for the X and Y positions of the tipline but it is commonly easier to check the box below and use the mouse to identify the region in which you want to search for the best tip line positions You have two options for using the mouse 1 you can search for the tip within a rectangular region in a region radio button or
69. nits above the highest bed in the current model Choose Continue from the Model Menu to run the model forward another 30 units of slip Repeat step 3 several more times each time adding a new bed 5 units above the highest one in the model You will see a perfect set of fault bend fold growth triangles developing just as described in Suppe et al 1992 and shown below note that this graphic is a simple screen capture bitmap and not the vector output which one would use for a presentation or publication Richard W Allmendinger 1998 2000 13 ramp up from decollement EX initial multi bend fault Trishear User s Manual v 4 5 TT SE LEN Listric Normal Fault We can use the same initial multi bend fault feature of the last example to make a listric normal fault 1 Choose New from the File Menu and enter the values as shown in the screen shot below Note that to make a normal fault both the propagation to slip ratio and the slip must be negative numbers Note also that we have checked ramp up and initial multi bend fault New Model Beds Fault Trishear one Tops Dip Ramp Angle 30 000 0 00000 30 000 60 000 90 000 0 gt footwall fixed 20 gt hanging wall fixed 120 00 Trishear angle 4 Propagation Stlip Total slip Display increment Initial coordinates of tipline ba ramp up from decollement be initial multi bend fault Cancel Initial left X coo
70. nt the program to carry out Like most programs 1t has a File Menu on the left hand side of the menu bar which handles the saving and reading of the program output input as well as printing and quitting or exiting the program Also reasonably standard is the Edit Menu where you undo copy and set the preferences for the program The Model Menu will be one of your main work horses here you tell the program to run modify add faults or add beds to forward models Here too you get information about forward models such as length area etc The Restore Menu allows you to import digitized beds and to specify the parameters necessary for retrodeforming the beds In the Plot Menu you tell Trishear 4 5 what elements you want it to draw on the screen and with what colors Several functions related to digitized beds also reside in a submenu of the Plot Menu or in the Scan Digitize Menu Finally the Window Menu determines which of Trishear s two main windows is showing on top It also allows you to scale the graphics and drag them around on the screen Trishear 4 5 has two main windows All drawing occurs in the Cross Section Window In addition to showing the cross section Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 the user can interact with this window via the mouse You can click the right mouse button in the window to get the position of a point or click and drag to measure the length and angle of a line The
71. odels being tested as well as how many have been tested so far The total time will be reported at the end of the run but is not saved as part of the cross section If you have selected allowing background processing in preferences or if you are using the Windows version you can switch out of Trishear start up other programs surf the web etc Trishear will continue testing models in the background albeit more slowly You can speed up a model run by turning off back ground processing but will only gain about 5 to 10 in execution time unless you are doing something really processor intensive like ray tracing and will not be able to use your Mac for anything else The statistics from a grid search can be saved in a variety of ASCII text formats The checkbox 3 D matrix for key bed will work only if the ramp angle and the tip line are constant and the only variation is in the trishear angle and in P S Then a suite of files will be saved one file for each P S step with each file containing trishear angle vs displacement with contours of c the Column text of 3 D matrix check will save a single large file of a 4 Richard W Allmendinger 1998 2000 45 Trishear User s Manual v 4 5 dimensional matrix the c values at every unique combination of ramp angle trishear angle P S and displacement This file consists of five columns one for each of the dimensions and the final one for c consequent
72. olved without variation in any of the key parameters Geophysicists use the terms inverse model and inversion specifically to refer to the inversion of a matrix Our grid search is thus not an inversion by that definition In the case of a thrust fault like the Catskill example what we really do is run a large number of forward models treating the thrust fault as if it were a normal fault unfolding a deformed section We use the term inverse model in a loose sense to refer to the fact that we are extracting the initial undeformed geometry from the deformed geometry Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 Digitizing and re sampling You can prepare a section for input to Trishear s grid search routine in a number of ways as long as it is digitized as a text file and follows a simple format see details elsewhere in this manual I have found that a particularly convenient way 1s to scan a section and read it into a graphics program In the graphics program you simply trace over the beds that you want to import into Trishear with the program s polygon tool not the Bezier curve tool Then save just your traced beds as a DXF AutoCad file The starting point for this tutorial example is a sample file called Catsk1l1 dxf which contains a tracing of the structure presented in Allmendinger 1998 We will first process this file with a small utility program that is included in the Trishear p
73. only enter a minimum value leaving max and step blank not zero the program will test models using a single value for that particular parameter This would be the case if for example you could measure the real ramp angle in an outcrop or on seismic Constraining a parameter to a single value vastly reduces the number of models your computer will test Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 For displacement you do not enter a step size because the that is built into the program it is fixed at the Slip Increment specified in the Preferences dialog Likewise all restorations actu ally start at zero displacement regardless of what you enter into the min box The number in the min displacement box just deter mines the displacement step at which the program starts to calculate the statistics for the bed If you know that all reasonable models will have well over 100 units of displacement you can save yourself some run time by skipping the statistical calculations for the first part of each model run As a default the program finds a minimum value for c in a least squares fit to a straight line through the key bed array Then to make sure that it is not a local minimum it searches another 100 displacement units beyond this best model If it doesn t find a smaller c then the program iterates to the next set of model parameters This can speed up your model run consid erably but 1t does have some da
74. or deformation of a layer above a buried fault of arbitrary dip and sense of slip Journal of Structural Geology v 17 no 10 p 1455 1472 Suppe J 1983 Geometry and kinematics of fault bend folding American Journal of Science v 283 no 7 p 684 721 Suppe J and Medwedeff D 1990 Geometry and kinematics of fault propagation folding Eclogae Geologicae Helvetiae v 83 no 3 p 409 454 Suppe J Chou G T and Hook S C 1992 Rates of folding and faulting determined from growth strata in McClay K R ed Thrust tectonics London Chapman 4 Hall p 105 121 Williams G and Chapman T 1983 Strains developed in the hangingwalls of thrusts due to their slip propagation rate a dislocation model Journal of Structural Geology v 5 no 6 p 563 571 Withjack M O Olson J and Peterson E 1990 Experimental models of extensional forced folds American Association of Petroleum Geologists Bulletin v 74 p 1038 1054 Zehnder A T and Allmendinger R W 2000 Velocity field for the trishear model Journal of Structural Geology v 22 p 1009 1014 Richard W Allmendinger 1998 2000
75. ore slowly if checked However the slowest part of the program exe Richard W Allmendinger 1998 2000 28 Trishear User s Manual v 4 5 cution 1s drawing the graphics to the screen If for example you want to calculate strain ellipses you can select them in Preferences they are turned on by default but turn off the plotting of strain ellipses in the Plot Menu and you will notice little slow down You will be able to turn on plotting of strain ellipses at any time using the Plot menu The following explains each of the items in the Preferences Dialog e Length of beds Spacing btwn points on bed Each bed in Trishear can have a maximum of 1000 vertices so the maximum length of the bed is a function of the spacing between the vertices If you use a two pixel spacing you can enter any length up to 2000 pixels If you enter a length of 1000 with a two pixel spacing then Trishear will have to process only 500 vertices per bed and the program will run more rapidly Note that the spacing between points on a bed does not have to be an integer you can enter for example 1 5 There is a trade off between spacing of points and resolution in general closer spacing will result in smoother curves but will take a longer time to calculate If you set a combination that would need more than 1000 vertices the program will automatically adjust the bed length to the nearest possible value This may be a somewhat confusing way to
76. ou to change magnification Because of this one can do a much more careful job of digitizing layers in those programs than in Trishear It is also much easier to erase edit and change the order of individual polygons in those programs Basic Steps The basic procedure for getting a section into a format that Trishear can read 1s the following 1 Read the section into your favorite graphics program The section could initially be a cross section on paper or a photograph that you have scanned or it could already be in digital format 2 Trace the beds that you want to model in Trishear with the polygon tool of the program see the Guidelines below If you need to know the precise position of the fault you can digitize that too Just don t base any grid search inversions on it 3 Export just the polygons that you traced as a DXF file a common ASCII text file format originally devel oped by the makers of AutoCad 4 Start up DigBeds and choose Open from the File Menu Select the DXF file that you just saved from your graphics program The polygons are drawn to the screen and numbered in the order in which they appear in the DXF file Richard W Allmendinger 1998 2000 Trishear User s Manual 57 v 4 5 Show here any polygon pairs that 1 G correspond to a single bed cut by 2 d 4 a fault A 2 2 z 2 2 6 A dialog box will appear asking you if any of the polygons Connect Bed Pairs
77. oup your section be reading the old scratch file back into Trishear the next time you start up On the Macintosh it is labeled FORO0000000 Particularly in the Windows version of the program you may notice a slight delay at the beginning of an operation while Trishear writes the scratch file to disk Redo You can redo the most recent operation by choosing this command Redo also writes a separate scratch file to your hard disk On the Macintosh it is labeled FOROOOOOOO1 Richard W Allmendinger 1998 2000 Sie Model Restore Redo Cut Copy 380 Paste ay Clear Preferences 3 Save Prefs Reset to Defaults 27 HEAR Cross Sectio Edit Model Restore Undo Reda Select Text Select Graphics Select All cp Preferences Save prets Trishear User s Manual v 4 5 Select Text Copying text 1s a two step process in the Win dows version of Trishear First you select the items to be copied then you choose copy Select Text works only in the History Window of the Windows version First bring the History Window to the front then choose this menu item then drag across the text that you want with the left mouse button down finally choose Copy from the Edit Menu Select Graphics Copying graphics is a two step process in the Windows version of Trishear First you select the items to be copied then you choose copy Select Graphics works only in the Cro
78. preferences growth strata clipped at pre growth surface y Y oN 31 e Backlimb fold kinematics With these two radio but tons you set the fold kinematic model that is used to construct folds over changes in fault dip If Parallel is selected then the program will attempt to use parallel kink folds over bends in the fault Note however that the program does not follow the Medwedeff amp Suppe 1997 multibend kink fold geometry Therefore parallel folding with multi bend faults can result in local zones of non parallel but still balanced folding and lack of balance can result if the kink axes cross within the strati graphic section Select the Similar radio button if you want arbitrarily inclined shear oblique to the layers as the kinematic model In this case the program will use the constant heave method to construct the folds while preserving cross sectional area With this option you must specify the shear angle which 1s defined as the deviation from vertical of the shear planes as shown in the figure below In the figure all initial fault trajectories were the same as was the slip in from the left The only thing that varies is the fold kinematic style Richard W Allmendinger 1998 2000 Trishear User s Manual 32 v 4 5 Parallel Vertical a 20 Antithetic 450 Synthetic gt L
79. rd UT i T a wy Tw EL TI Li EL Ly CL E a T Fr 1 Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 2 Click on the Preferences button We need to specify how the hanging wall is folded over the listric fault Most people assume shear oblique to bedding or similar folding so click on the appropriate radio button The number to the right of the similar fold button is where you specify the angle of simple shear as an angle mea sured from the vertical Leave this number set at 0 0 which will produce vertical shear planes or the Chevron method roll over of the hanging wall Close the Prefer ences Dialog by clicking Okay When you close the New Model Dialog you will be asked to draw the initial fault trace finishing with a double click on the tip line If you have Show Kink Axes turned on in the Plot Menu you will see a green line drawn parallel to the shear plane direction in this case vertical After drawing the fault and before pro ducing any slip choose Modify from the Model Menu and increase the ramp angle which initially shows the angle of the final fault segment by about 5 We do this so that the fault will not propagate at the same angle as the last segment drawn but at a steeper angle My initial fault trajectory looks like Choose Run from the Model Menu At the end of the run select Add Beds and add a singl
80. reported however is just that of the actual polygon that you traced out If your polygon was open you will get the length of just the sides drawn Area of the traced polygon 17208 Length of polygon 722 55 Start New Fault The menu selection under the Model Menu called Start New Fault allows you to stop movement on the existing fault and begin to deform the already deformed stratigraphic package as well as the old fault by movement on a new fault located wherever you specify The dialog box for starting a new fault depends on whether or not you have selected Pick with beds and fault with mouse in Preferences both are shown Even if you choose to pick the fault with the mouse you will still have to enter P S total slip and display increment by typing You can choose whether the fault ramps up from a decollement or not etc As with the initial fault your new fault can dip either to the left positive Richard W Allmendinger 1998 2000 39 Start New Fault A section can have up to 34 inactive faults and 1 active fault Ramp Angle Trishear angle Propagation Slip 0 footwall fixed 0 gt hanging wall fixed Total slip Display increment 30 000 60 000 Initial coordinates of tipline Y 0 00000 O ramp up from decollement O initial multi bend fault Preferences Coy Cancel Trishear User s Manual v 4 5 dip or down to the right negative dip The new
81. represent the same bed which has been offset by a fault Show here any polygon pairs that In this dialog you can enter up to five pairs of beds o enone This step is important because Trishear expects only NT a one polygon per bed and yet you don t want to digitize gt any points on the line segment of the polygon located FP between the hanging wall and footwall cutoffs In the 7 above section polygons 1 and 2 are the same bed and polygons 3 and 4 are the same bed Note that the order E in which you specify the polygons in this dialog box is ren ES important If you had written 4 and 3 then the left end of 3 would be connected to the right end of 4 E 7 DigBeds will then resample the polygons so that there are 500 equally spaced points for each bed In the process of connecting any beds across a fault the beds may be reordered so that what was the first bed in a section may become a later 1 e a higher number bed See the comments below for more details DigBeds will also re draw the beds on the screen in red so that you can see the new beds numbers and check to make sure that any offset beds were connected correctly In the example below note that polygons 1 and 2 are now bed 1 and 3 and 4 are now bed 2 Richard W Allmendinger 1998 2000 Trishear User s Manual v 4 5 8 Select Save in Trishear Format from the File Menu in order to save your section resampled and formatted so that Trishear can
82. rticle Path Info Show Bed Numbers Renumber Delete Beds Get Bed Info Area btwn 2 beds Measure rea Start New Fault Rotate Model EF Trishear User s Manual v 4 5 The model will run until it has reached the slip that you have specified either in the New Model or the Modify model dialog boxes If you want to stop the model before it has reached that amount of slip just click the left mouse button You can then resume the model run using either Run or Continue Continue This command works just like Run except for the following If your model has reached the amount of slip specified Run will have no effect you would have to open the Modify dialog box to increase the slip before Run would make the model keep going Continue however will automatically increase the total slip setting by an amount equal to the first slip entered Thus 1f you enter 30 as the slip in the New dialog when the model reaches 30 it will stop If you then choose Continue it will automatically resume until it reaches a slip of 60 when it will again stop Choosing Continue a third time will run the model out to a slip of 90 etc all without having to bring up a dialog box This 1s particularly useful for inputting growth strata as additional beds at regular intervals Modify This Dialog box left contains much of the power of Trishear You can change any of the parameters shown at the right Note that a single mod
83. s to be in When you read in a deformed bed data file it will automatically be resized to fit to the screen I tend to digitize beds by scanning them tracing over them in a graphics program such as Canvas and then saving the resulting polygons not Bezier curves ina DXF file I have written a utility program DigBeds which massages and resamples DXF files for reading into Trishear See the end of this manual for brief instructions on the use of DigBeds You can do it however you want as long as it fits the above format When Trishear imports the beds it gives you two choices as shown in the dialog box at left You can either scale the beds to the screen or maintain the original dimensions the default Note that scaling to the screen will not increase the accuracy of the inversion and may result in longer inversion runs if the original graphic was smaller than the screen Set Parameters You choose restoration parameters with the dialog box below You can enter all of the necessary parameters by typing numbers into the left side of the dialog box However it is often easier to use the mouse to enter some or most of the parameters the P S ratio must be typed in of course To use the mouse you select from the check boxes at the right but there are several ways that you can do this The most general way is with the top check box After selecting this you first click the mouse that the position of the tipline and then wit
84. seful in the Macintosh version because the History Window of the Mac version 1s not scrollable and can only display the final 45 lines of the history of the model To see older steps you must save the History buffer to disk In Windows the History window 1s scrollable Save Strain As text To save a text file of the strain values of each of the ellipses in the current model select this command The data for a single ellipse occurs on a single line in the text file and is as follows X coordinate of the center of the ellipse Y coordinate of the center of the ellipse the maximum principal stretch the angle of the maximum principal stretch axis Each of these four values 1s separated by a space not a tab Note that the X and Y coordinates in the file correspond to the coordinate axes shown on the screen not the internal coordinate system This file can be read into a plotting program and contoured for striking graphical presentations Export as EPS EPS files are ASCII text files which can be used to send high resolution graphics data to Postscript printers or can be read by Postscript compatible graphics programs such as Illustrator Freehand and Canvas The advantage of an EPS file over a PICT file 1s that the former has much higher resolution O Richard W Allmendinger 1998 2000 26 Screen shots showing the differences among different graphics formats at 200 magnification in a graphics program Trishear User s M
85. ss Section Window of the Windows version First bring the Cross Section window to the front choose this menu item and then drag across the graphics that you want holding down the left mouse button Note that a selection rectangle will not appear Finally choose Copy from the Edit Menu Select All Use Select All in either window to select the entire contents of the window for copying Then choose Copy from the Edit Menu This command is available only in the Windows version of Trishear Copy In the Macintosh version Selecting Copy will auto matically copy the entire contents of the front most window to the operating system Clipboard for immediate importing into other applications The information is copied as a PICT file and retains its full vector and text editing capabilities in the receiving application Copy in the Windows version is enabled only after you have chosen Select Graphics Select Text or Select All Text copied this way is fully editable graphics are copied as bitmaps and can be modified as bitmaps in painting programs Graphics do not retain their vector information Clear This command will erase the contents of the front most window It only affects the currently displayed graphics or text It does not change the model in any way Preferences The Preferences dialog shown below al lows you to set many of the advanced features in Trishear Note that several of these options will cause the program to run m
86. sults in The current best model is written to the screen and you can then shut down your computer if you want Resume Inversion If you have previously saved interim results from an inversion you can resume that inversion at any time First though you must import the beds using the Import command under the Restore Menu Then you select Resume Inversion you will be presented with a second dialog box where you can select the file in which you saved the interim results in the first place Then the inversion will proceed as before Show statistics At any stage of an analysis you can write the linear least squares best fit statistics for each bed to the History Window with this command Richard W Allmendinger 1998 2000 46 Inversion Status Total models 656 Current Model number 50 Current best model 4592 7 Estimated time remaining 4 5113 mins Suspend and Save Trishear User s Manual v 4 5 Plot Menu The Plot Menu controls several aspects of drawing on the screen but none of its options influence the models themselves Basically you use the top part of the plot menu to turn on or off the plotting of various graphic ele ments For example forward models will run much faster if the program doesn t have to take time drawing strain ellipses to the screen at each step of a model run even if the strain at each step is being calculated in the background The choices Show Ellipses Show LNFEs and Show
87. t Line Weights Trishear User s Manual 52 v 4 5 If you import a very large scan Trishear may not have the memory available to display it in that case you should quit Trishear and increase the memory partition Trishear always plots the scan behind all other graphic elements in the program Show Scan You can show or hide the scan while leaving it in memory This can be useful if the scan obscures features in your model but you are not finished with it yet Drag Scan This allows you to grab and drag the imported PICT BMP around screen while keeping everything else in the program stationary This is useful for positioning the scan relative to your model Clear Scan You cannot import another scan into the pro gram until you clear the first one from memory with Clear Scan Scale Scan allows you to adjust the dimensions of your S Seale the Scan scan If you check keep current proportions the default behavior _ fnitr the horizontal and vertical scaling factors in percent below you need only enter a single number and the other box will be Horizontal 100_ vertical 1507 adjusted automatically Setting horizontal and vertical scales inde keep current proportions pendently allows you to correct for horizontal or vertical exaggeration in the original PICT file The Windows version does not yet allow scaling of the BMP file within the program Vo Help Cross Section dT l History d
88. tion Once selected the program will wait while you click and drag the mouse anywhere within the Cross Section window An outline of the deformed beds will follow the mouse around until you release the button Drag in Window move both the coordinate system and the model therefore O Richard W Allmendinger 1998 2000 la positive value will move the cross ection to the right a positive Y value will move it up Cancel OK Shift in Window Enter the X horizontal and Y vertical values to reposition the cross section in the window a positive X value will move the cross section to the right a positive Y value will move it up Trishear User s Manual v 4 5 the axes will move but the coordinates of the individual points will not change Drag in Window function like scrolling the window by dragging Drag in Window is not available in the Windows version because the Windows version has scroll bars Resize to Fit This option both re scales your model to fit and positions it in the center of the Cross Section Window As in Shift in Window all parameters are changed so that you can choose this in the middle of a model run that wanders off the page to move it back to the middle before continuing Set Scale You can change the scale and position of the axes on the screen with this option Selecting it brings up the dialog to the right Once you set a new scale all of the bed tops slip magnitudes and tip l
89. u want to carry out the grid search inversion on the current forward model Clear Digitized Beds Use this to erase the digitized beds from the program memory All menu options related to Digitized beds will be disabled until you read in new ones with Import under the Restore Menu of both Mac and Windows versions or Open in the Mac version Save Digitized Bed To save digitized beds as an ASCII text file on your hard disk select this option Import Scan will open a standard file open dialog box from which you can select any PICT or BMP file The file can contain vectors or scanned raster images at any resolution and can be color gray scale or black and white images Different graphics programs save bitmaps in PICT BMP files in different ways so you will have to experiment with the best settings If you want to import a high resolution scan the surest way is to expand it to 72 dpi in the graphics program and then use the scale scan feature in Trishear see below to reduce its dimensions and increase its dpi s In the Windows version you must scale the BMP in your graphics program before importing it into Trishear In general B amp W bitmaps take much less memory but do not render as nicely as gray scale scans Richard W Allmendinger 1998 2000 51 VIYILUZEU DEUS BAD Mop fo Import 5 can b Show Scan 4 Drag Scan 5 Scale 5can Clear Scan set Colors Load Colors save Colors se
90. u do this the deformed section is drawn to the screen as below and several additional menu items become available under the Restore Menu 6 Select Automate from the Restore Menu A large complicated and somewhat imposing dialog box appears Each of the options is explained more fully starting on page 42 of this manual For this example we will use bed top 3 as the key bed The ramp angle is know from field data so enter 36 in the box for minimum ramp angle and leave the other two boxes for ramp angle max and step blank For P S enter min 2 4 max 2 8 and step 0 1 indicating that we will test five values of P S 1 e 2 4 2 5 2 6 2 7 and 2 8 For trishear angle enter min 30 max 40 and step 1 Leave the displacement settings just as they are There are many options for searching for the tipline which can easily be the most time consuming part of a grid search At this point just enter Tipline X min 421 and Tipline Y min 146 with the step size blank indicating a single tipline position very close to faulted bed top 2 The fault 1s a reverse fault so make sure that the Reverse radio button is enabled When you are ready to click Okay the dialog box should look like the following screen shot This is the standard way of specifying a known value always enter it in the min field and leave the other two fields blank If you enter something in the max field but no step size
91. v E A and Mayborn K R 1997 Multiple geometries and modes of fault propagation folding in the Canadian thrust belt Journal of Structural Geology v 19 no 3 4 p 321 335 Erslev E A and Rogers J L 1993 Basement cover geometry of Laramide fault propagation folds in Schmidt C J Chase R B and Erslev E A eds Laramide basement deformation in the Rocky Mountain foreland of the Western United States Special Paper Boulder Colorado Geological Society of America p 125 146 Hardy S and McClay K 1999 Kinematic modelling of extensional fault propagation folding Journal of O Richard W Allmendinger 1998 2000 Trishear User s Manual 61 v 4 5 Structural Geology v 21 p 695 702 Hardy S and Ford M 1997 Numerical modelling of trishear fault propagation folding and associated growth strata Tectonics v 16 no 5 p 841 854 Medwedeff D A and Suppe J 1997 Multibend fault bend folding Journal of Structural Geology v 19 no 3 4 p 279 292 Mitra S and Mount V S 1998 Foreland basement involved structures American Association of Petroleum Geologists Bulletin v 82 no 1 p 70 109 Molinero J Colombo F and Hardy S 1996 Disposici n geom trica profunda de los materiales terciarios en el corte del r o Najerilla Sector Riojano de la cuenca del Ebro Geogaceta v 20 no 4 p 792 795 Patton T L and Fletcher R C 1995 Mathematical block motion model f
92. want to restore using a planar best fit Ramp angle P S ratio 3 Kep Bed tt E P75 ratio 1500000 E Key Bed 3 between 1 amp 6 E ho between 1 and E Trishear angle fao 70 E Displacement eee bp poo Save Statistics O always search to max displacement always search to max displacement Tipline Y Tipline 350 00 O best model applied to all beds fio Hd use mouse to select tip region Fault type to restore Tipline Y 0 00000 CD ina region on a line Reverse Normal i use mouse to select tip region Fault type to restore reen ale ox Reverse Normal Cancel Enter the number of the key bed which you want to restore using a planar best fit Save Statistics TM 2 D slices of 3 D matriz for key bed T Column text of 3 0 matrix best model applied to all beds O 2 D slices of 3 D matrix kb O Column text of 3 D matrix kb The grid of values to search is specified in the right hand side of the dialog there are six parameters which completely define any trishear model 1 the ramp angle 2 the P S ratio 3 the trishear apical angle 4 the displacement or slip and 5 amp 6 the X and Y positions of the tip line In general for each of these parameters you specify a minimum value a maximum value and the step size For example if for ramp angle you entered min 30 max 50 and a step of 5 the program would test values of 30 35 40 45 and 50 degrees If you
93. y un checking Save Animation Frames in Preferences if you forget you can fill up your hard disk rapidly This means though that you can add beds modify faults and start new faults all during a single animation You can only start to save animations at the start of a new model run You will be asked only once to provide a root name e g my animation and a folder to store the animations in and then the program will save all frames there prefaced by numbers so they sort correctly e g 001my animation OO2my animation etc Do Richard W Allmendinger 1998 2000 33 Trishear User s Manual v 4 5 not preface the root name with a number if you do you will get files named something like 00100Imy anima tion With the correct software you can turn these into an imated GIFs QuickTime movies etc for smoother an imation than is possible within the Trishear program itself Animated GIFs can for example be posted to Web pages for viewing without any additional software QuickTime movies can also be viewed within web pages using the QuickTime plug in I use Yves Piguet s freely available GifBuilder 0 5 to make animated GIFs which can then be viewed either in a web browser or in any of the available QuickTime movie players Save Prefs This command will automatically save the current state of the Trishear program to disk in the same fold directory as the program itself Every time Trishear starts up it

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