Home

guidelines for the implementation of the h/v spectral ratio

1. gt 2 iii gt 2 Stability conditions iv the peak should appear at the same frequency within a percentage 5 on the H V curves corresponding to mean and one standard deviation V o lower than a frequency dependent threshold e f detailed in Table vi Ga fo lower than a frequency dependent threshold 0 f also detailed in Table 3 Table 3 gives the frequency dependent threshold values for the above given stability conditions v o lt e f and vi fo lt log O f or fo lt O f Table 3 Threshold values for stability conditions Frequency range Hz 0 2 0 2 0 5 0 5 1 0 1 0 2 0 gt 2 0 e fo Hz 0 25 fo 0 20 fo 0 15 fo 0 10 fy 0 05 fy 0 fo for OA fo log 0 fo for OlogH V fo For the property single we propose that none of the other local maxima of the H V curve fulfil all the above quantitative criteria for the clarity If the H V curves for a given site fulfil at least 5 out of these 6 criteria then the fy value can be considered as a very reliable estimate of the fundamental frequency If in addition the peak amplitude Ao is larger than 4 to 5 one may be almost sure that there exists a sharp discontinuity with a large velocity contrast at some depth However one has in any case to perform the two following checks 31 SESAME H V User Guidelines 17 03 05 e frequency fy is consistent with the sensor cut off f
2. eene 26 3 INTERPRETATION OF RESULTS eere ee ees roo eaa n e erro o ea eran ae aoa ee ape o 28 3d UNDERLYING ASSUMPTIONS Retard eene eiie een EM EQ ER TIE 28 3 2 CONDITIONS FOR RELIABILITY eese 30 3 3 IDENTIFICATION OF Fos dinne ANER 31 X3 Clearpedk aussehen HR I RD RED PER REESE indes 31 3 3 2 Unclear 6case suisz t aceti ee tee ruten 32 3 4 INTERPRETATION OF Fo IN TERMS OF SITE CHARACTERISTICS eee n n nen n nennen nnn nnn nnne nun 35 ACKNOWLEDGEMEBNTUS ree egi Vua od Easa ese o voe cree Fe Pn ives essesuussessovetcddsaete cstuseseosess 36 ee ceve es esee noob eo cocscoenasscssccnstenssesseauescgsuebeeies onseeecsuuasossasescautavesesuessessoutasoevensacedsdbecsseseuessoasece 37 APPENDIX A H V DATA EXAMPLES o Vo de eV pon eov aeo e Va aao edd 40 A 1 ILLUSTRATION OF THE MAIN PEAK TYPES ss00seseseseeesesesecesevevececesesesesesesesesesesesesesesesesesesecesesesesesesens 40 A 2 COMPARISON WITH STANDARD SPECTRAL RATIOS ssssseseeeseseseseseseseseseceseseseseseseseseseseseseseseseseeeeeeens 48 APPENDIX B PHYSICAL EXPLANATIONS e eene ee eren ee ee enne ense etta esee een 54 B 1 NATURE OF AMBIENT VIBRATION WAVEFIELD ecce h
3. 27 SESAME H V User Guidelines 17 03 05 3 INTERPRETATION OF RESULTS Table 2 Definitions of the parameters used in this section e window length e ny number of windows selected for the average H V curve e nE lw ny fo number of significant cycles e f current frequency fsensor Sensor cut off frequency e fo HIV peak frequency standard deviation of H V peak frequency fo Gr fo threshold value for the stability condition o lt e fo e Ao H V peak amplitude at frequency fo Au f H V curve amplitude at frequency f e f frequency between f 4 and fy for which Au r f lt Ao 2 e frequency between fo and 4fy for which lt Ao 2 og f standard deviation of f oa f is factor by which the mean Au f curve should be multiplied or divided Soga f standard deviation of the logAu f curve f is an absolute value which should be added or subtracted to the mean logAun f curve e 0 f threshold value for the stability condition lt 0 Vsa average S wave velocity of the total deposits Vssur S wave velocity of the surface layer e h depth to bedrock hmin lower bound estimate of h 3 1 Underlying assumptions As detailed in Appendix B the main information looked for within the H V ratio is the fundamental natural frequency of the deposits corresponding to the peak of the H V curve While the reliabi
4. Even a slight wind approx gt 5 m s may strongly influence the H V results by introducing large perturbations at low frequencies below 1 Hz that are not related to site effects A consequence is that wind only perturbs low frequency sites Measurements during heavy rain should be avoided while slight rain has no noticeable influence on H V results Extreme temperatures should be treated with care following the manufacturer s recommendations for the sensor and recorder tests should be made by comparing night day or sun shadow measurements Low pressure meteorological events generally raise the low frequency content and may alter the H V curve If the measurements cannot be delayed until quieter weather conditions the occurrence of such events should be noted on the measurement field sheet Disturbances gt gt gt gt No influence from high voltage cables has been noted All kinds of short duration local sources footsteps car train can disturb the results The distance of influence depends on the energy of the source on the soil conditions etc therefore it is not possible to give general minimum distance values However it has generally been observed for example that ambient vibration sources with short periods of high amplitude e g fast highway traffic influence H V ratios if they are within 15 20 metres but that more continuous sources e g slow inner city traffic only influence H V ratios when th
5. Figure 2 Comparison of the H V curves obtained at the same site on grass with and without wind top and in a hole on asphalt bottom and again on grass with wind This comparison shows the strong effect of the wind combined with grass whereas on asphalt or in a hole the wind has no significant effect if far away from any structure H V TEST H V REFERENCE s e epnirdury 10 10 Frequency Hz Frequency Hz 20 SESAME H V User Guidelines 17 03 05 Figure 3 Comparison of the H V curves obtained with and without a Styrofoam plate under the sensor at the same site showing a strong effect of the Styrofoam Nearby structures gt gt Users are advised that recording near structures such as buildings trees etc may influence the results there is clear evidence that movements of the structures due to the wind may introduce strong low frequency perturbations in the ground Unfortunately it is not possible to quantify the minimum distance from the structure where the influence is negligible as this distance depends on too many external factors structure type wind strength soil type etc Avoid measuring above underground structures such as car parks pipes sewer lids etc these structures may significantly alter the amplitude of the vertical motion Weather conditions gt Wind probably has the most frequent influence and we suggest avoiding measurements during windy days
6. H V curve exhibits amplitude values very different from 1 i e up to 10 or as low as 0 1 over a large frequency range it is very likely that the measurements are bad malfunction in the sensor or the recording system very strong and close artificial ambient vibration sources and should be redone e Finally if the H V curve is flat i e has values lying between around 0 5 and 2 0 without any clear peak it is very likely that the local underground structure does not exhibit any sharp impedance contrast at least approx 4 at any depth It does not necessarily mean however that there is no site amplification there are several examples of sites with low frequency amplification and flat H V curve see the example of Tehran ABM site in Appendix A 2 One should not be too hasty therefore in interpreting flat H V curve in terms of a no amplification site this can be done only for rock sites However such situations of a flat curve on non rock sites correspond to less that 596 of the total number of sites studied as can be seen on Figure 8 section 3 1 ACKNOWLEDGEMENTS The SESAME project has been supported by the European Commission Research General Directorate Project No EVG1 CT 2000 00026 and by the Swiss Federal Office for Education and Science OFES No 00 0085 1 We would like to kindly thank Benoit Le Brun Hanan Nimry Michael Schmitz and Bill Stephenson for their constructive review of the guidelines text 36 SES
7. working days week end to check whether these peaks also exist during non working hours There are however many plants that work 24h a day 7 days a week the test will not be conclusive in such a case but it should be possible to identify such a plant with a minimum knowledge of the local industrial activity If any of the proposed checks does suggest an industrial origin then the identified frequency should be completely discarded it has no link with the subsurface structure Note It may happen that the spurious frequency of industrial origin coincides with or is not far from a real site frequency The existence of such artefacts may then alter the estimation of the actual site frequency fo as much as possible it is then preferable to perform measurements outside working hours to avoid this spurious peak or to apply severe band reject filters to the microtremor recordings in order to totally eliminate the artefact and its effects 3 3 2 b Unclear low frequency peaks criterion i and possibly ii not fulfilled There exist a number of conditions where the H V curve exhibits a fuzzy unclear low frequency peak i e at frequencies lower than 1 Hz or a broad peak that does not satisfy all the criteria above especially the amplitude criteria It may have several origins nonexclusive of one another e alow frequency site with either moderate impedance contrast lower than approx 4 at depth or a velocity gradient or a low le
8. Interpretation of fo in terms of site characteristics After having analysed and checked the H V curves as indicated in the previous section the next step is to interpret the H V curve and in particular the peak frequency ies fo and f1 in terms of site characteristics When fy is clear case 3 3 1 and does not have an industrial origin then there is a quasi certitude that the site under study presents a large impedance contrast at least approx 4 at some depth and is very likely to amplify the ground motion fo is the fundamental frequency of the site there is around 80 chance that the actual site amplification for the Fourier spectra around the fundamental frequency fo is larger than the H V amplitude Ao amplification starts at fo but may occur at higher frequencies even though the H V amplitude remains small If the local thickness is known the average S wave velocity of the surface layer may be estimated with the formula Vsa fo 4h if a reliable estimate of the S wave velocity Vs sur is available close to the surface then a lower bound estimate of the thickness may be obtained with the formula hmin Vs sur I 4 fo This conclusion holds obviously even in the case of a rock site in that case the existence of a clear H V peak generally at high frequencies is proof of the existence of significant weathering at rock surface When there exist two clear frequencies f and f satisfying the criteria described in 3 3 2d it
9. a large impedance contrast 1D structure may thus be a good indicator of the composition of the wavefield One should remain very cautious however in interpreting H V ratios derived from earthquake recordings beyond the fundamental S frequency since this ratio is highly influenced by the amplification of the vertical component which cannot be neglected especially in sites with pronounced subsurface topography B 2 3 H V and complex wavefields results from numerical simulation Since the actual composition of the seismic noise wavefield is mostly unknown a series of numerical simulations have been performed to investigate the origin of an H V peak A wide variety of subsurface structures have been studied 1D 2D and 3D but only local sources have been considered i e less than about 10 km away from the receiver the microseism case has not yet been investigated incoming crustal surface waves generated by oceanic waves These comprehensive analyses are presented and discussed in various reports SESAME deliverables D12 09 and D17 10 Bonnefoy Claudet 2004 and only the main conclusions are summarised below e for 1D structures a single H V peak is obtained only when the predominant noise sources are located within the surface layer and within limited distances from the site less than around 20 30 times the layer thickness the wavefield then consists of a mixture of Rayleigh Love and body waves For more distant dominant nois
10. component while Love or body wave interpretations should be associated with a local peak in the Fourier spectra of the horizontal component This has the following direct practical consequences for H V investigations e One should always gather the available geological and geotechnical information looking in particular for a priori rough estimations of impedance contrasts keeping in mind that large impedance contrasts are generally associated with either very young unconsolidated deposits or very hard bedrock and indications as to the lateral variability of underground structures 59 SESAME H V User Guidelines 17 03 05 e Low frequency peaks i e 1 Hz are often less easy a to detect and b to interpret than high frequency peaks Additional measurements in the vicinity of the site of interest often help to find a consistent H V peak e One should never forget to have a look at the original Fourier spectra of the horizontal and vertical components especially when the H V maximum is not very clear One must also bear in mind that real ambient vibration recordings also include a number of spurious sources such as wind or industrial harmonic machinery which may affect the estimation of the H V curve and downgrade the possibility of interpretations while clear and sharp natural peaks generally remain visible fuzzy maxima may completely disappear B 3 1 1D media When the available geological information allows the deposit
11. ellipticity of Rayliegh waves Wave motion 40 1 57 67 Nakamura Y 1989 A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface Quaterly Report Railway Tech Res Inst 30 1 25 30 Nogoshi M and T Igarashi 1971 On the amplitude characteristics of microtremor part 2 in japanese with english abstract Jour Seism Soc Japan 24 26 40 Panou A A N P Theodulidis P M Hatzidimitriou A S Savvaidis and C B Papazachos Reliability of ambient noise horizontal to vertical spectral ratio in urban environment The case of Thessaloniki city Northern Greece PAGEOPH 2005 in press Panou A A N Theodulidis P Hatzidimitriou K Stylianidis and Papazachos Ambient noise horizontal to vertical spectral ratio in site effects estimation and correlation with seismic damage distribution in urban environment The case of the city of Thessaloniki Northern Greece Soil Dyn amp Earthq Engin 2004 accepted for publication SESAME European project 2002 Controlled instrumentation specification Deliverable D01 02 SESAME European project 2003 Nature of noise wavefield Deliverable D13 08 SESAME European project 2003 H V technique experimental conditions Deliverable D08 02 SESAME European project 2003 Multi platform H V processing software J SESAME Deliverable D09 03 SESAME European project 2004 J SESAME User Manual Version 1 08 SESAME Eur
12. is likely that a the surface velocity is low b the deep bedrock is very hard and C there exist two large impedance contrasts at least approx 4 at two different scales so that the amplification should be significant over a broad frequency range starting at fo and extending beyond fi If the local total thickness is known the average S wave velocity of the surface layers may be estimated with the formula Vsav fo 4h if a reliable estimate of the S wave velocity Vs sur is available close to the surface then a lower bound estimate of the thickness of the topmost layer may be obtained with the formula Ay min R Vs surf 14 2 Frequencies of industrial origin associated with sharp peaks must be completely discarded for an interpretation in terms of site characteristics In the case of an unclear low frequency peak fy 1 Hz the safest attitude is to refrain from deriving quantitative interpretations from the H V curve If the same observation is consistent over several measurement sites in the same area and if stiff sediments are present at this site then we recommend going back in the field and to perform additional measurements if possible during night time and or under quiet weather conditions with a low frequency velocity sensor and over long periods of time The low frequency might 35 SESAME H V User Guidelines 17 03 05 then be extracted in a clearer manner In any case one must then keep in mind the possibility at su
13. numerical computations In addition this technique is also useful in calibrating site response studies at specific locations These practical guidelines recommend procedures for field experiment design data processing and interpretation of the results for the implementation of the H V spectral ratio technique using ambient vibrations The recommendations given here are the result of a consensus reached by the participants of the European research project SESAME Contract No EVG1 CT 2000 00026 and are based on comprehensive and detailed research work conducted during three years It is highly recommended that prior to planning a measurement campaign on ambient vibrations a local geological survey especially on Quaternary deposits should be performed Interpretation of the H V results will be greatly enhanced when combined with geological geophysical and geotechnical information In spite of its limitations the H V technique is a very useful tool for microzonation and site response studies This technique is most effective in estimating the natural frequency of soft soil sites when there is a large impedance contrast with the underlying bedrock The method is especially recommended in areas of low and moderate seismicity due to the lack of significant earthquake recordings as compared to high seismicity areas SESAME H V User Guidelines 17 03 05 TABLE OF CONTENTS INTRODUCTION rc A 5 PART I QUICK FIELD REFERENCE AND INTERPRETATI
14. of large impedance contrasts at least approx 4 while unclear H V peaks at low frequency are more likely for thick stiff sedimentary deposits e Check the weather bulletins corresponding to the recording period and the measurement field sheets e Check the low frequency asymptote limit value of H V ratio when frequency is close to zero if the asymptotic value is significantly larger than 2 some low frequency artefacts due to wind or traffic or bad sensor are likely e Check the cut off frequency fsensor of the sensor used e Check whether or not a peak around fy also appears on the mean one standard deviation curves item iv in 3 3 1 If not reprocess the data with longer windows and or more stringent window selection criteria in this case the standard deviation oa f is probably too large and has to be reduced e Check the smoothing parameters and reprocess the data with i proportional bandwidth and ii less smoothing if this improves the clarity and stability of the low frequency peak it is a hint that there are high chances it is due to site conditions however if even with this reprocessing the criteria of 3 3 1 are not fulfilled it is recommended that the site be re measured with longer recordings e Have a look at H V curves from individual windows at the corresponding H and V Fourier spectra and at the corresponding time histories Some of them may be eliminated some other windows may be added document the reaso
15. prograde to retrograde A few studies have been performed to investigate the variability of the ratio while Konno and Ohmachi 1998 report a value around 2 for a limited set of velocity profiles Stephenson 2003 concludes that peak trough structures with a frequency ratio around 2 witness both a high Poisson ratio in the surface soil and a high impedance contrast to the substrate Some other studies for more complex velocity profiles report a dependence of the ratio on the velocity gradient in the soft sediments iv Higher modes exhibit also H V peaks at higher frequencies corresponding to a vanishing V component some of these peaks especially for high contrast structures coincide with 56 SESAME H V User Guidelines 17 03 05 the higher harmonics of S wave resonance However for single layer structures no case is known for which all existing Rayleigh wave modes exhibit simultaneously a peak at the same frequency In other words for all frequencies for which several modes exist simultaneously i e generally beyond the S wave fundamental frequency there always exist one Rayleigh wave mode often the fundamental one which may carry some energy on the vertical component v These results may generally be extrapolated to more complex horizontally layered structures involving several layers or velocity gradients one major difference however concerns item iv and the number of ellipticity peaks Some sites may present a large veloc
16. so that the H V ratio should reflect at least partly the differential amplification between H and V components and be a more reliable indicator of the site frequency than for high frequency local surface sources This interpretation is not consensual and should be taken with caution B 3 2 2 Deeply embanked valleys and basins The presence of such deep structures should be at least guessed from the geological map and a minimum knowledge of the geological history of the area ancient glacier valleys filled with lacustrine deposits are a typical example of such structures However this kind of structure may also be met in the case of buried canyons which may remain unknown in the absence of detailed geophysical surveys When associated with large impedance contrasts the seismic response of these structures to incoming body waves exhibits a global 2D or 3D resonance pattern characterised by similar resonance frequencies at all sites whatever the local thickness and mode shapes with both a strong spatial dependence and a strong polarisation As a consequence a resonance frequencies may be different on the two horizontal components for instance in a valley the components parallel and perpendicular 1 to the valley axis and b the amplitude of the corresponding H V peak may undergo significant variations from site to site due to variations in both H and V components for instance a given mode may include a node in the component
17. the ambient vibration average HIV ratio thick red line multiplied divided by 109 thin red line When users of the H V spectral ratio method face one of the unclear examples presented below it is recommended that they refer to the reprocessing suggestions and guidelines for interpretation that are given for the corresponding situation either in Part I section 2 or in Part Il section 3 3 40 SESAME H V User Guidelines 17 03 05 1 Clear peak Volvi1997 LTST Amplification 1 Frequency Hz Basin geometry Elongated alluvial valley width 5km length 40km Depth 200m Site Information LTST site depth to bedrock 196m Type of bedrock Gneiss Average shear wave velocity of deposits 570m s Comments Criteria for a reliable H V curve are fulfilled that is fo gt 10 ly fo gt 200 calf lt 10910 2 Criteria for an ideal peak are also fulfilled Ao 76 gt 2 f e fo 4 fo Auv f lt Ao 2 4fo Auv f lt Ao 2 t 14 lt fo 71596 Oa fo 71 6 lt 0 fo 72 a Interpretation All criteria are fulfilled the fundamental frequency of the site may be reliably estimated at 0 7 Hz 41 SESAME H V User Guidelines 17 03 05 2 Unclear Low Frequency Peak Citta di Castello CD16 Amplification 1 10 Frequency Hz Basin geometry Elliptical alluvium valley width 10km length 25km depth 0 1km Site Information CD16 site is situated on soft all
18. times at low frequencies i e up to 400 and up to 4 to 5 times at high frequencies where transients are much more frequent i e up to 1000 iii An acceptably low level of scattering between all windows is needed Large standard deviation values often mean that ambient vibrations are strongly non stationary and undergo some kind of perturbations which may significantly affect the physical meaning of the H V peak frequency Therefore it is recommended that be lower than a factor of 2 for gt 0 5 Hz or a factor of 3 for fo 0 5 Hz over a frequency range at least equal to 0 5 2fo Therefore in case one particular set of processing parameters does not lead to satisfactory results in terms of stability we recommend reprocessing the recordings with some other processing parameters As conditions for fulfilling items i ii and iii above often lead to opposite tuning for some parameters see section 2 it may be impossible in some cases the safest decision is then to go back to the site and perform new measurements of longer duration and or with more strictly controlled experimental conditions In addition one must be very cautious if the H V curve exhibits amplitude values very different from 1 i e larger than 10 or lower than 0 1 over a large frequency range i e over two octaves in such a case it is very likely that the measurements are bad malfunction in the sensor or the recording system very strong and
19. 500 m grid and in case of lateral variation of the results densify the grid point spacing down to 250 m for example gt Single site response never use a single measurement point to derive an fo value make at least three measurement points Recording parameters gt level the sensor as recommended by the manufacturer gt fix the gain level at the maximum possible without signal saturation In situ soil sensor coupling set the sensor down directly on the ground whenever possible gt avoid setting the sensor on soft grounds mud ploughed Soil tall grass etc or soil saturated after rain Artificial soil sensor coupling gt avoid plates from soft materials such as foam rubber cardboard etc on steep slopes that do not allow correct sensor levelling install the sensor in a sand pile or in a container filled with sand gt on snow or ice install a metallic or wooden plate or a container filled with sand to avoid sensor tilting due to local melting Nearby structures Avoid recording near structures such as buildings trees etc in case of wind blowing faster than approx 5 m s It may strongly influence H V results by introducing some low frequencies in the curves gt Avoid measuring above underground structures such as car parks pipes sewer lids etc Weather conditions Wind Protect the sensor from the wind faster than approx 5 m s This only helps if there are no nearby str
20. AME H V User Guidelines 17 03 05 FOREWORD Site effects associated with local geological conditions constitute an important part of any seismic hazard assessment Many examples of catastrophic consequences of earthquakes have demonstrated the importance of reliable analyses procedures and techniques in earthquake hazard assessment and in earthquake risk mitigation strategies Ambient vibration recordings combined with the H V spectral ratio technique have been proposed to help in characterising local site effects This document presents practical user guidelines and software for the implementation of the H V spectral ratio technique on ambient vibrations The H V spectral ratio method is an experimental technique to evaluate some characteristics of soft sedimentary soil deposits Due to its low cost both for the survey and analysis the H V technique has been frequently adopted in seismic microzonation investigations However it should be pointed out that the H V technique alone is not sufficient to characterise the complexity of site effects and in particular the absolute values of seismic amplification The method has proven to be useful to estimate the fundamental period of soil deposits However measurements and the analysis should be performed with caution The main recommended application of the H V technique in microzonation studies is to map the fundamental period of the site and help constrain the geological and geotechnical models used for
21. AME H V User Guidelines 17 03 05 REFERENCES All deliverables and scientific papers stemming from the SESAME project are available on the project web site at http sesame fp5 obs ujf qrenoble fr index htm Atakan K A M Duval N Theodulidis P Y Bard and the SESAME Team 2004 On the reliability of tne H V Spectral Ratio Technique ICSDEE amp ICEGE Berkeley CA USA Atakan K A M Duval N Theodulidis B Guillier J L Chatelain P Y Bard and SESAME Team 2004 The HIV spectral ratio technique experimental conditions data processing and empirical reliability assessment 13th world conference in Earthquake Engineering Vancouver Paper 2268 Bard P Y and SESAME participants 2004 The SESAME project an overview and main results Proceedings of the 13th World Conference in Earthquake Engineering Vancouver August 2004 Paper f 2207 Bard P Y 1998 Microtremor measurements A tool for site effect estimation Proceeding of the Second International Symposium on the Effects of Surface Geology on Seismic Motion Yokohama Japan 3 pp 1251 1279 Bonnefoy Claudet S C Cornou J Kristek M Ohrnberger M Wathelet P Y Bard D F h P Moczo F Cotton 2004 Simulation of seismic ambient vibrations H V and array techniques on canonical models 13th world conference in Earthquake Engineering Vancouver Paper 1120 Cornou C G Di Giulio M Ohrnberger J Kristek M Wathelet 2004 Simulated Vs Observed s
22. BRIANO GRENOBLE GUADELOUPE A LOURDES NICE PREDAPPIO ROVETTA m TEHRAN VERCHIANO VOLVI94 VOLVI97 A0 H V Ambient vibrations vs A0 SPR earthquakes o 9 5 2 gt c 2 a E 2 T e 0 1 2 3 4 5 6 7 8 A0 SPR earthquakes ANNECY E BENEVENTO A CATANIA BRCITTAdiCASTELLO x COLFIORITO CORINTH X EBRON EUROSEISTEST FABRIANO X GRENOBLE GUADELOUPE A LOURDES NICE PREDAPPIO ROVETTA m TEHRAN A VERCHIANO VOLVI94 X VOLVI97 Figure 8 Comparison between H V ratio of ambient vibrations and standard spectral ratio of earthquakes Top comparison of the frequencies fo bottom comparison of the amplitudes Ao 29 SESAME H V User Guidelines 17 03 05 The following interpretation guidelines are mainly linked with the clarity and stability of the H V peak frequency value The clarity however is related at least partly to the H V peak amplitude see below While there are very clear situations where the risk of mistake is close to zero one may also face cases more than 50 in total where the interpretation is uneasy and must call to some extent on expert judgement the following guidelines propose a framework for such an expert judgement trying to minimise the subjectivity which however can never be completely avoided 3 2 Conditions for reliability The first requirement before any extraction of information and any interpretation co
23. GUIDELINES FOR THE IMPLEMENTATION OF THE H V SPECTRAL RATIO TECHNIQUE ON AMBIENT VIBRATIONS MEASUREMENTS PROCESSING AND INTERPRETATION SESAME European research project WP12 Deliverable D23 12 European Commission Research General Directorate Project No EVG1 CT 2000 00026 SESAME December 2004 SESAME H V User Guidelines 17 03 05 SESAME Site EffectS assessment using AMbient Excitations European Commission contract n EVG1 CT 2000 00026 Co ordinator Pierre Yves BARD Administrative Accounting assistance Laurence BOURJOT Project duration 1 May 2001 to 31 October 2004 Project Web site http sesame fp5 obs ujf qrenoble fr index htm Participating organisations Central Laboratory for Bridges and Roads Paris France Centre of Technical Studies Nice France Geophysical Institute Slovak Academy of Sciences Bratislava Slovakia Institute of Earth and Space Sciences Lisbon Portugal Institute of Engineering Seismology and Earthquake Engineering Thessaloniki Greece National Centre for Scientific Research Grenoble France National Institute of Geophysics and Volcanology Roma Italy National Research Council Milano Italy Polytechnic School of Z rich Switzerland R sonance Ing nieurs Conseils SA Geneva Switzerland University Joseph Fourier Grenoble France University of Bergen Norway University of Li ge Belgium University of Potsdam Germany List of particip
24. ON GUIDELINES eeeeee neenon 7 1 EXPERIMENTAL CONDITIONS MEASUREMENT FIELD SHEET ee eeee eee en eee oon 8 2 DIAGRAMS FOR INTERPRETATION OF H V RESULT ccccccccsssssscssssccsssssscssccccscsssscssecesssssees 10 2 1 CRITERIA FOR RELIABILITY OF RESULTS ccceeeeeeeeee eene hehehe nnne hehe rennen nenne nene enne eren eren eren enn 10 2 2 MAIN PEAK ne eie TE 10 PART II DETAILED TECHNICAL GUIDELINESI TECHNICAL REQUIREMENTS 15 1 TECHNICATL REOQUIREMBEN IS poe deseos ve icta nero sean pna 16 ll INSTRUMENTATION eene eee nU CUM eU IM Mm 16 12 EXPERIMENTAL CONDITIONS ete t E beta ideene et deep uelut 17 2 DATA PROCESSING STANDARD J SESAME SOFTWARE ee ee eee eee ee eee 22 2 1 GENERAL DESIGN OF THE SOFTWARE ceeeeertnne hehe nene ene n e ene nene nene nene eene nennen 22 2 2 WINDOW SELECTION eene enne nene nene enne ene ene nene ene EEOSE SEEEN nene nene nene nene 22 2 3 COMPUTING H V SPECTRAL RATIO ccscccssesesesesesesevecececeseseseseveseceseveseseseseseseseseceseseseseseseseseseseseseeeeens 25 2 4 SHOWING OUTPUT RESULTS ccccccccesesesesesesevevevesevevevesevesesesevevevevevevesevesereveseseseseseseseseseseseseseseresesesesens 25 2 5 SETTING GRAPH PROPERTIES AND CREATING IMAGES OF THE OUTPUT RESULTS
25. PENDIX B Physical explanations The interpretation of the H V spectral ratio is intimately related to the composition of the seismic wave field responsible for the ambient vibrations which in turn is dependent both on the sources of these vibrations and on the underground structure It is also related to the effects of the different kinds of seismic waves on the H V ratio The present section will briefly summarise for each of these issues the status of knowledge and consensus reached by the SESAME participants at the end of three years of intensive work and exchanges also benefiting from an abundant scientific literature see Bonnefoy Claudet et al 2004 SESAME deliverable D13 08 for a comprehensive review It will conclude with a presentation of our resulting preferred interpretations of the H V peak which form the basis of the interpretation guidelines presented in section 3 of Part II One must however admit that our knowledge is still very incomplete and partial we by no means claim everything is known and clear and much remains to be learnt The reader is thus strongly invited to consider this section simply as a snapshot of the views of the SESAME participants which though based on three years of in depth investigations will certainly evolve throughout the next decade B 1 Nature of ambient vibration wavefield Understanding the physical nature and composition of the ambient seismic noise wavefield especially in urban areas r
26. The recommendations given apply basically for the case where the method is used alone in assessing the natural frequency of sites of interest and are therefore based on a rather strict set of criteria The recommended use of the H V method is however to combine several other geophysical and geotechnical approaches with sufficient understanding of the local geological conditions In such a case the interpretation of the H V results can be improved significantly in the light of the complementary data The guidelines are organised in two separate parts the quick field reference and interpretation guidelines Part 1 and detailed technical guidelines Part Il Part aims to summarise the most critical factors that influence the data collection analysis and interpretation and provides schematic recommendations on the interpretation of results Part II includes a detailed description of the technical requirements standard data processing and the interpretation of results Several examples of the criteria described in Part I and II are given in Appendix A In addition some physical explanations of the results based on theoretical considerations are given in Appendix B In Part Il section 1 the results of the SESAME H V User Guidelines 17 03 05 experiments performed within the framework of the SESAME project are given in smaller fonts to separate these from the recommendations and the explanations given in the guidelines The word soil should be co
27. ance that this is anthropic forced ambient vibration and it should not be considered in the interpretation 32 SESAME H V User Guidelines 17 03 05 e Another check consists of reprocessing with less and less smoothing in the case of industrial origin the H V peak should become sharper and sharper while this is not the case for a site effect peak linked with the soil characteristics In particular checks with linear box smoothing with smaller and smaller bandwidth should result in box like peaks having exactly the same bandwidth as the smoothing e f other measurements have been performed in the same area determine whether a peak exists at the same frequencies with comparable sharpness the amplitude of the associated peak even for a fixed smoothing parameter may vary significantly from site to site being transformed sometimes into a trough e Another very effective check is to apply the random decrement technique Dunand et al 2002 to the ambient vibration recordings in order to derive the impulse response around the frequency of interest if the corresponding damping is very low say below 596 an anthropic origin may be assumed almost certainly and the frequency should not be considered in the interpretation e Whenever it is hard to reach a conclusion from the previous tests and this information is important it is often very instructive to perform continuous measurements over 24 h day night or over one week
28. ants Catello Acerra Gerardo Aguacil Anastasios Anastasiadis Kuvvet Atakan Riccardo Azzara Pierre Yves Bard Roberto Basili Etienne Bertrand Bruno Bettig Fabien Blarel Sylvette Bonnefoy Claudet Paola Bordoni Antonio Borges Mathilde B ttger S rensen Laurence Bourjot H loise Cadet Fabrizio Cara Arrigo Caserta Jean Luc Chatelain C cile Cornou Fabrice Cotton Giovanna Cultrera Rosastella Daminelli Petros Dimitriu Frangois Dunand Anne Marie Duval Donat F h Lucia Fojtikova Roberto de Franco Giuseppe di Giulio Margaret Grandison Philippe Gu guen Bertrand Guillier Ebrahim Haghshenas Hans Havenith Jens Havskov Denis Jongmans Fortunat Kind J rg Kirsch Andreas Koehler Martin Koller Josef Kristek Miriam Kristekova Corinne Lacave Alberto Marcellini Rosalba Maresca Bassilios Margaris Fabrizio Marra Peter Moczo Bladimir Moreno Antonio Morrone J r me Noir Matthias Ohrnberger Jose Asheim Ojeda Ivo Oprsal Marco Pagani Areti Panou Catarina Paz Etor Querendez Sandro Rao Julien Rey Gudrun Richter Johannes Rippberger Mario la Rocca Pedro Roquette Daniel Roten Antonio Rovelli Gilberto Saccoroti Alekos Savvaidis Frank Scherbaum Estelle Schissele Eva Sp hler Lanz Alberto Tento Paula Teves Costa Nikos Theodulidis Eirik Tvedt Terje Utheim Jean Frangois Vassiliades Sylvain Vidal Gisela Viegas Daniel Vollmer Marc Wathelet Jochen Woessner Katharina Wolff Stratos Zacharopoulos SES
29. at one site and a node on the V component at another site Considering the importance of diffraction phenomena of steep interfaces and the fact that these resonance modes are the eigen solutions of the wave equation in such structures it is logical to conclude that such modes will exist whatever the excitation wavefield provided there is enough energy in the corresponding frequency range This theoretical consideration is supported by the few numerical simulations performed on such structures Cornou et al 2004 SESAME deliverables D12 09 and D17 10 B 3 2 3 Common recommendations for 2D 3D structures In any case when other information sources geology geophysics suggest a 2D or 3D structure three kinds of actions processing are strongly recommended to check these possibilities e One should never limit one s investigations to one single measurement but should have a wide and dense spatial coverage starting with a mesh size comparable with 61 SESAME H V User Guidelines 17 03 05 the expected thickness of the softer cover The mesh size may be reduced in a second step in case of strong lateral discontinuities indicating either faults or very steep underground slopes e One should also investigate the differences between differently polarised horizontal components i e applying different rotation angles for instance along valley edges clear differences may appear between the 1 and components 62
30. bump peak is stable and Aun f is rather low SESAME H V User Guidelines 17 03 05 Multiple peaks multiplicity of maxima see 3 3 2 c and Appendix A Check no industrial origin of one of the peaks Increase the smoothing bandwidth If reprocessed H V curve fulfils the clarity criteria fo reliable If reprocessed H V curve does not fulfil the clarity NT Redo measurements over a longer time and or criteria during night l 2 peaks cases gt fo see 3 3 2 d and appendix A If industrial origin of fo fo not reliable and f reliable AND No industrial origin for f Likely sharp contrast at shallow depth fi fundamental frequency is known then Vs av 4h f If Vs sur is known then hmin Vs sur 4f1 If industrial origin of f fo reliable and f not reliable AND No industrial origin for fo Likely sharp contrast at rather large depth fo fundamental frequency If h is known then av 4h fo If Vs sur is known then hmin Vs sur 4fo fo and f reliable If the geology of the site shows possibility of having two large velocity contrasts at two Likely two large contrasts at shallow and different scales large depth at two different scales AND fo fundamental frequency The clarity criteria are fulfilled for both fO f1 other natural frequency and f1 If Vs sur is known then hi min 4 13 SESAME H V User Guidelines 17 03 05 Flat H V curve meeting the reliability conditions see 3 4 and appendi
31. ch a site of low frequency amplifications the safest way to investigate the reality of such low frequency amplification is to install temporary stations equipped with broad band velocity sensors in continuous recording mode including one on a nearby reference rock site and to evaluate the classical site to reference spectral ratios from earthquake recordings regional or teleseismic events are perfectly suited for showing low frequency amplification H V curve exhibits a broad maximum whatever the processing see 3 3 2 c then it is not easy to extract any information for the maximum frequency of this broad peak since this estimate may significantly vary with different processing parameters smoothing type bandwidth etc However it may be that such a broad peak is due to the presence of an underground sloping interface between softer and harder layers if other recordings are available in the same area one is then invited to check whether clearer peaks are observed in the vicinity and whether the associated frequencies a exhibit significant variations from site to site and b lie within the frequency range of the broad peak If all these conditions are fulfilled then there are large chances that the underground structure of the site under study exhibits significant lateral variations which lead to significant 2D or 3D effects Such broad peak or plateau like H V curves are indeed observed on many valley edges
32. close artificial ambient vibration sources for instance and should be redone It is mandatory to check the original time domain recordings first 30 SESAME H V User Guidelines 17 03 05 In the following interpretation guidelines we assume that these reliability conditions are met if not some reprocessing with other computational parameters should be attempted to try to meet them or some additional measurements made If none of these two options leads to satisfactory results then the results should be considered with caution and some reliability warning should be issued in the final interpretation 3 3 Identification of fo 3 3 4 Clear peak The clear peak case is met when the H V curve exhibits a clear single H V peak e clarity concept may be related to several characteristics the amplitude of the H V peak and its relative value with respect to the H V value in other frequency bands the relative value of the standard deviation oa f and the standard deviation o of fo estimates from individual windows e property single is related to the fact that in no other frequency band does the H V amplitude exhibit another clear peak satisfying the same criteria We propose the following quantitative criteria for the clarity Amplitude conditions i there exists one frequency f lying between 4 and fo such that Ao Anw f gt 2 ii there exists another frequency lying between fo and 4 f9 such that Ao
33. ction and H V process are standalone applications developed in Fortran J SESAME is mainly a tool for organising the input data executing window selection and processing and displaying the processing results The software operates in Unix Linux Macintosh and Windows environments Details concerning system requirements and installation procedure are given in the J SESAME user manual delivered with the software 2 1 General design of the software The general design of J SESAME is based on a modular architecture There are basically four main modules browsing module window selection module processing module display module The main functionalities are integrated through a graphical user interface which is part of the browsing module The display module is also tightly connected to the browsing module as there is close interaction between the two modules due to the integrated code development in Java Only two waveform data formats are accepted GSE and SAF SESAME ASCII Format see J SESAME user manual for more details 2 2 Window Selection Module Windows can be selected automatically or manually The manual window selection mode can be used if the check box labelled as Manual window selection Figure 4 is active Besides manual selection directly from the screen which is often the most reliable but also the most time consuming method an automatic window selection module has been introduced to enable the p
34. ctive way i e with the use of a statistical method The Student t test was chosen as it is one of the most commonly used techniques for testing an hypothesis on the basis of a difference between sample means It determines a probability that two populations are the same with respect to the variable tested The t test can be performed knowing only the means standard deviation and number of data points For further details or for users who would like to perform some comparison on their own please refer to the SESAME WP02 Controlled instrumentation specification Final report Further investigations would be welcome in some cases using a common software process and processing parameters to compare records and quantify their similarity This chapter is based on the following SESAME internal reports WP02 Controlled instrumentation specification Final report Deliverable DO 1 02 WP02 HIV technique experimental conditions Final report Deliverable 008 02 1 4 Instrumentation An instrument workshop was held during the SESAME project to investigate the influence of different instruments in using the H V technique with ambient vibration data There were four major tasks performed which consisted of testing the digitisers and sensors and of making simultaneous recordings both outside in the free field and at the lab for comparisons Influence of the digitiser In order to investigate the possible influence of the digitisers several tests w
35. e optionally used for the window selection one may wish to avoid signal saturation as saturation does affect the Fourier spectrum As gain and maximum signal amplitudes are not mandatory in the header of SAF and GSE formats the program looks for the maximum amplitude over the whole ambient vibration recording and automatically excludes windows during which the peak amplitude exceeds 99 5 96 of this maximum amplitude By default this option is turned on in some cases there might exist long transients for instance related to heavy traffic trains machines during which the sta lta will actually remain within the set limits but during which the ground motion may not be representative of real seismic ambient vibrations Another option was therefore introduced to avoid noisy windows during which the Ita value exceeds 8096 of the peak Ita value over the whole recording By default this option is turned off 81 x Project Config Processing Help C Manual Window Selection Insert DataFile CaPaulaiTrabalhofProjectosiLagosiRU A E 2 Site Name file Insert Ko CaPaulaTrabalhotProjectos Output File Name 20041027 1220 safout D CiPaulalTrabalholPro
36. e sources a case not often met in urban sites but possible in the countryside and or deep sources i e located at depth below the interface associated with the main impedance contrast the wavefield includes a large proportion of body or head waves especially at high frequencies and H V curves exhibit several peaks associated with fundamental and harmonics of S wave resonance n all cases the frequency of the fundamental peak exhibits a very good agreement within 20 at most with the actual fundamental S wave frequency of the layered structure e For laterally varying structures the wavefield associated with local noise sources is more complex since it also includes additional waves diffracted from the lateral heterogeneities The composition of this diffracted wavefield depends on the location of the site of interest with respect to the lateral heterogeneities away from them for instance in the flat central parts of valleys and basins it mainly consists of surface waves fundamental or higher mode depending on the frequency close to them it also includes 58 SESAME H V User Guidelines 17 03 05 a significant portion of body waves For all the investigated simulation cases all with a large impedance contrast H V curves exhibit clear sharp peaks in the flat parts i e those with only gentle underground interface slopes and broader and generally lower maxima at sites with rapidly varying thickness for instance at va
37. e structures i For intermediate to high S wave velocity contrasts i e larger than about 3 the H V ellipticity ratios of Rayleigh waves exhibit infinite peaks and or zeros corresponding to the vanishing of the vertical respectively horizontal component and inversion of rotation sense from retrograde to prograde or inversely For low impedance contrasts because the rotation sense does not change with frequency the ellipticity ratio only exhibits maxima at some frequencies and minima at other frequencies with no zeroes or infinities ii Focusing first on the fundamental mode the vanishing of the vertical component occurs at a frequency fr which is very close i e less than 596 different to the fundamental resonance frequency for S waves only if the S wave velocity contrast exceeds a value of 4 For intermediate velocity contrasts 2 6 to 4 the ellipticity peak is still infinite and occurs at a frequency that may be up to 50 higher than the S wave fundamental resonance frequency For lower velocity contrasts the infinite peak is replaced by a broad maximum that has only low amplitude less than 2 3 and occurs at a frequency that may range between 0 5 to 1 5 times the S wave fundamental frequency iii The ellipticity ratio H V of the fundamental mode may also exhibit not only a peak at fr but also a minimum zero at a higher frequency f corresponding to the vanishing of the H component and a second rotation sense inversion from
38. eismic ambient noise in the Colfiorito basin site effect estimation and noise wavefield characteristics XXIXth European Seismological Commission Session F3 September 2004 Cornou C J Kristek S Bonnefoy Claudet D F h P Y Bard P Moczo M Ohrnberger M Wathelet 2004 Simulation of seismic ambient vibrations II H V and array techniques for real sites Proceedings of the 13th World Conference on Earthquake Engineering Vancouver Canada August 2004 Paper 1130 Cultrera G R Azzara F Cara R d Anna G Di Giulio M S Giammarinaro G Passafiume A Rovelli and P Vallone 2004 Microtremor Measurements in Palermo Italy a comparison with macroseismic intensity and earthquake ground motion Proceedings of the 13th World Conference on Earthquake Engineering Vancouver August 2004 Paper 915 Dubos N A Souriau C Ponsolles J F Fels and G S n chal 2003 Etude des effets de site dans la vile de Lourdes Pyr n es France par la m thode des rapports spectraux Bull Soc G ol Fr 174 1 33 44 Dubos N 2003 Contribution l valuation du risque sismique dans les Pyr n es Centrales Th se de l Universit Paul Sabatier Toulouse III 210 pages Dunand F P Y Bard J L Chatelin Ph Gu guen T Vassail M N Farsi 2002 Damping and frequency from randomec method applied to in situ measurements of ambient vibrations Evidence for effective soil structure interaction 12 European Conference o
39. ement technique indicates very low damping lt 5 peaks get sharper with decreasing smoothing fo reliable Likely sharp contrast at depth Ao gt 4 5 If fo gt fsensor and no industrial origin fo fundamental frequency If h is known then Vsa 4h fo If is known then hmin Vs sur 4fo 11 SESAME H V User Guidelines 17 03 05 Unclear low frequency peak see 3 3 2 b and appendix A no reliable fo If steady increase of H V ratio with decreasing frequency Check H V curves from individual windows and eliminate windows giving spurious H V curves Use longer time windows and or more stringent window selection criteria Use proportional bandwidth and less smoothing If reprocessed H V curve fulfils the clarity criteria fo reliable If reprocessed H V curve does not fulfil the clarity eplet c me weather conditions and or use earthquake recordings using also a nearby rock site Broad peak see 3 3 2 c and appendix A Decrease the smoothing bandwidth If bump peak is not stable no reliable fo and or is very large If clearer peaks are observed in the vicinity and if their related frequencies lie within the frequency range of the broad peak if their related frequencies exhibit significant variation from site to site Then examine the possibility of underground lateral variation especially slopes Otherwise not recommended to extract any information If
40. ene nene enne enne eene eren ener eren eren ener 54 B 2 LINKS BETWEEN WAVE TYPE AND H V 56 CONSEQUENCES FOR THE INTERPRETATION 59 SESAME H V User Guidelines 17 03 05 INTRODUCTION A significant part of damage observed in destructive earthquakes around the world is associated with seismic wave amplification due to local site effects Site response analysis is therefore a fundamental part of assessing seismic hazard in earthquake prone areas A number of experiments are required to evaluate local site effects Among the empirical methods the H V spectral ratios on ambient vibrations is probably one of the most common approaches The method also called the Nakamura technique Nakamura 1989 was first introduced by Nogoshi and lgarashi 1971 based on the initial studies of Kanai and Tanaka 1961 Since then many investigators in different parts of the world have conducted a large number of applications An important requirement for the implementation of the H V method is a good knowledge of engineering seismology combined with background information on local geological conditions supported by geophysical and geotechnical data The method is typically applied in microzonation studies and in the investigation of the local response of specific sites In the present document the application of t
41. ensor The influence of the type of sensor was tested by recording simultaneously with two sensors coupled to the same digitiser In total 17 sensors were tested In general signals are similar as expected However gt The accelerometers were not sensitive enough for frequencies lower than 1 Hz and give very unstable H V results It is not recommended that H V measurements be performed using seismology accelerometers as they are not sensitive enough for ambient vibration levels gt Stability is important It is not recommended that H V measurements be performed using broadband seismometers with natural period higher than 20 s as they require a long stabilisation time without providing any further advantage Users are encouraged to test sensor stability before use gt It is not recommended that sensors that have their natural frequency above the lowest frequency of interest be used If fo is lower than1 Hz while the sensor used is a high frequency velocimeter double check the results with the procedure indicated in 3 3 2 b 1 2 X Experimental conditions As a general recommendation it is suggested that before doing H V measurements on the field the team should have a look at the available geological information about the study area In particular the types of geological formations the possible depth to the bedrock and possible 2D or 3D structures should be looked at An evaluation of the influence of experimental conditions on t
42. equires answering two sets of questions which are not independent of each other What is the origin of the ambient vibrations where and what are the sources e What is the nature of the corresponding waves i e body or surface waves What is the ratio of body and surface waves in the seismic noise wavefield Within surface waves what is the ratio of Rayleigh and Love waves Again within surface waves what is the ratio of fundamental mode and higher modes While there is a relative consensus on the first question only few and partial answers were proposed for the second set of questions for which a lot of experimental and theoretical work still lies ahead As known and taught for a long time in Japan sources of ambient vibrations are usually separated in two main categories natural and human which very often and more particularly within urban areas correspond to different frequency bands e At low frequencies f lt fm 1Hz the origin is essentially natural with a particular emphasis on ocean waves which emit their maximal energy around 0 2 Hz These waves can be very easily seen on islands and or during oceanic storms Higher frequencies around 0 5 Hz are emitted along coastal areas due to the interaction between sea waves and coasts Some lower frequency waves f 0 1 Hz are also associated with atmospheric forcing but this frequency range has very little interest for engineering seismology Higher frequencies g
43. ere performed to quantify the experimental sensitivity internal noise stability with time and channel consistency The influence of various parameters was checked warm up time electronic noise synchronism between channels difference of gain between channels etc gt Most of the tested digitisers finally gave correct results gt In general it was found that all digitisers need some warm up time From 2 to 10 minutes is usually sufficient for most instruments to assure that the baseline is more or less stable Users are encouraged to test instrument stability before use gt For an optimal analysis of the H V curve it appears to be necessary to check the energy density along the studied frequency band to ensure that the energy is sufficient to allow the extraction of the signal from the instrumental noise Furthermore deviations must be the same on all components gt Users should check synchronisation between channels From numerical simulation it was demonstrated that no H V modification occurs below 15 Hz Over 15 Hz modifications in the H V results depend on the percentage of sample desynchronisation the minimum being obtained for a round number of desynchronised samples and the maximum up to 80 of H V amplitude change for 0 5 sample gt Users should choose the same gain for all three channels Small gain differences might cause slight changes to the results 16 SESAME H V User Guidelines 17 03 05 Influence of the s
44. ey are much closer Our experience is that it is the impulsiveness of the noise envelope that is crucial Therefore traffic is much less of a problem in a city than it is close to a highway for example Users are anyway encouraged to check recorded time series in the field when they perform measurements in a noisy environment Short duration disturbances of the signal can be avoided during the H V analysis by using an anti trigger window selection to remove the transients A consequence is that the time duration of the recordings should be increased in order to gather enough duration of quiet signal see sections 2 and 3 unless for example only one train has perturbed the recordings Avoid measurements near monochromatic sources such as construction machines industrial machines pumps etc The recording team should not keep its car engine running during recordings 21 SESAME H V User Guidelines 17 03 05 2 DATA PROCESSING STANDARD J SESAME SOFTWARE This chapter is based on the following SESAME internal reports Multi platform H V processing software J SESAME Deliverable D09 03 3 J SESAME User Manual Version 1 07 4 J SESAME is a JAVA application for providing a user friendly graphical interface for the H V spectral ratio technique which is used in local site effect studies The program uses the functions of automatic window selection and H V spectral ratio by executing external commands The automatic window sele
45. ferent cases For detailed explanations of each case see section 3 in Part Il of the guidelines See Appendix A for illustrations The definitions given in the table below are valid for all section 2 2 1 Criteria for reliability of results Criteria for a reliable H V curve 1 window length fo 10 1 ny number of windows selected for the average H V curve x en lw ny fo number of significant cycles and e f current frequency Nc fo gt 200 fsensor Sensor cut off frequency e fo HIV peak frequency and o standard deviation of H V peak frequency fo of iii cA f 2 for 0 5f lt f lt 2fp if f0 gt 0 5Hz fo threshold value for the stability condition o lt e fo or oa f lt 3 for 0 5fysf lt 2fo if f0 lt 0 5Hz o peak amplitude at frequency fo Aww f H V curve amplitude at frequency f rx e f frequency between 4 and fo for which lt Ao 2 Criteria for a clear H V peak e frequency between fo and 4f for which lt Ao 2 at least 5 out of 6 criteria fulfilled e f standard deviation of f oa f is the factor by 3f fo 4 fo lt Ao 2 which the mean curve should be multiplied or divided f standard deviation of the logAn f curve f If e fo 4fo Auv f lt 2 is an absolute value which should be added to or subtracted iii Ao 2 from the mean logAun f curve e 0 fo th
46. fi lt A1 2 I fo 4 lt A2 This second peak around 13 Hz is certainly associated with a very shallow structure 43 SESAME H V User Guidelines 17 03 05 4 Broad Peak or Multiple Peaks Volvi1997 LPAS Amplification Frequency Hz Basin geometry Elongated alluvial valley width 5km length 40km Depth 200m Site Information LTST site depth to bedrock 180m Type of bedrock Gneiss Average shear wave velocity of deposits 570m s Comments Criteria for a reliable H V curve are fulfilled that is fo gt 10 ly fo gt 200 calf lt 10910 2 Interpretation All three peaks fulfil the criterion for amplitude A gt 2 However only the peaks F and F fulfil all clarity criteria 3 3 1 The availability of other information geology deposit thickness geophysics in that area allows us to identify f as the fundamental frequency of the site The location of this site close to a valley edge may explain the presence of these two peaks with rather low amplitude while another nearby site LTST see above the clear peak example exhibits a clear peak with larger amplitude the latter is located in the central part of the graben 44 SESAME H V User Guidelines 17 03 05 5 Sharp Peaks and Industrial Origin Tehran TAR Amplification Tehran TAR 100 Smooth K O 8d 10 Spectral amplitude Amplification 01 04 1 10 100 micr
47. for non horizontal underground layering including both surface and body waves Even when considering surface weathering the impedance contrast between surface and depth usually remains limited there is therefore only a small probability that the H V peak comes from a vanishing of the V component and we consider more likely an explanation in terms of body waves involving both diffraction and focusing This is however only a suggestion and the topic would deserve thorough further investigations especially as the surface topography amplification effect itself is far from being properly understood B 3 Consequences for the interpretation of H V curves The above mentioned results exhibit a few consistent robust characteristics which have to be kept in mind when interpreting H V curves and peak s e The results are clear and simple in case of horizontally layered structures with large impedance contrasts 4 5 e The results become more and more fuzzy a for decreasing contrasts and b for increasing underground interface slopes e Theoretical and numerical results are by far more numerous and easier to interpret for local anthropic like sources i e essentially above 1 Hz e Clear urban situations with non stationary spatially distributed local sources are generally associated with one single H V peak e n the Rayleigh wave interpretation the H V peak should be associated with a local trough in the Fourier spectra of the vertical
48. he H V technique in assessing local site effects due to dynamic earthquake excitations is the main focus whereas other applications regarding the static aspects are not considered In the framework of the European research project SESAME Site Effects Assessment Using Ambient Excitations Contract No EVG1 CT 2000 00026 the use of ambient vibrations in understanding local site effects has been studied in detail The present guidelines on the H V spectral ratio technique are the result of comprehensive and detailed analyses performed by the SESAME participants during the last three years In this respect the guidelines represent the state of the art of the present knowledge of this method and its applications and are based on the consensus reached by a large group of participants It reflects the synthesis of a considerable amount of data collection and subsequent analysis and interpretations In general due to the experimental character of the H V method the absolute values obtained for a given site require careful examination In this respect visual inspection of the data both during data collection and processing is necessary Especially during the interpretation of the results there should be frequent interaction with regard to the choices of the parameters for processing The guidelines presented here outline the recommendations that should be taken into account in studies of local site effects using the H V technique on ambient vibrations
49. he stability and reproducibility of H V estimations from ambient vibrations was carried out during the SESAME project 2 The results obtained are based on 593 recordings used to test 60 experimental conditions that can be divided into categories as following recording parameters recording duration measurement spacing in situ soil sensor coupling artificial soil sensor coupling sensor setting nearby structures weather conditions disturbances Recording parameters gt As long as there is no signal saturation results are equivalent irrespective of the gain used However we suggest fixing the gain level at the maximum possible without signal saturation The only noticeable effect is a compression of the H V curve when too high a gain value is used implying too much saturation of the signal A sampling rate of 50 Hz is sufficient as the maximum frequency of engineering interest is not higher than 25 Hz although higher sampling rates do not influence H V results Length of cable to connect the sensor to the station does not influence H V results at least up to a length of 100 meters Recording duration gt n order for a measurement to be reliable we recommend the following condition to be fulfilled fo gt 10 Iw This condition is proposed so that at the frequency of interest there be at least 10 significant cycles in each window see Table 1 gt A large number of windows and
50. his result is valid when the impedance contrast is large both for S and P waves and comes from the conversion from P and SV 57 SESAME H V User Guidelines 17 03 05 waves at the bedrock layer interface and their relatively small incidence angles within the surface lower velocity layer This has very interesting consequences for the fundamental mode since the S wave fundamental frequency is always significantly smaller than the P wave fundamental frequency ratio equal to the S P velocity ratio within the surface layer e As the fundamental frequency is only weakly dependent on subsurface topography for usual configurations this explains why the H V ratio for a body wavefield should always exhibit a peak around the fundamental S wave frequency for high impedance contrast sites e In the case of horizontally stratified media the H V ratio should also exhibit peaks at the S wave harmonics at least for all peaks that do not coincide with a lower order harmonic of P wave resonance e Finally again for high impedance contrast horizontally stratified media the amplitude of the first H V peak is also expected to be somewhat correlated with the S wave amplification These latter two items constitute the main differences from the surface wave case where it is not generally expected to have either harmonics or any correlation between H V peak amplitude and actual amplification values The presence or absence of harmonics at least for
51. ht distance TRANSIENTS trees polls buildings bridges underground structures pedestrians other OBSERVATIONS FREQUENCY if computed in the field 17 03 05 MEASUREMENT FIELD SHEET DATE HOUR PLACE OPERATOR GPS TY PE and LATITUDE LONGITUDE ALTITUDE STATION TY PE SENSOR TY FE STATION SENSOR DISK FILE NAME POINT ite GAIN SAMPL FREQ REC DURATION sec wEATHER WIND none 7 weak Smis medium RAIN none weak medium CONDITIONS Temperature approx Remarks 9 sand O rock L asphalt Jeement L concrete paved L other dry soil wet soil ARTIFICIAL GROUND SENSOR COUPLING L strong Measurement if any strong Measurement if any O grass E Remarks lves type BUILDING DENSITY Jnone Scattered Jdense other type MONOCHROMATIC NOISE SOURCES factories works pumps rivers le type NEARBY STRUCTURES description height distance TRANSIENTS trees polls buildings bridges underground structures pedestrians other OBSERVATIONS FREQUENCY if computed in the field 1 SESAME HH V User G uidelines 17 03 05 2 DIAGRAMS FOR INTERPRETATION OF H V RESULTS This section presents diagrams with criteria and recommendations to help in the result interpretation for dif
52. ibiting a flat H V curve though also exhibiting a significant low frequency amplification less that 5 of the total number of sites studied as can be seen on Figure 8 section 3 1 Note the peak around 1 3 Hz was shown to have an industrial origin 46 SESAME H V User Guidelines 17 03 05 6b Flat H V Ratio Curves on rock Lourdes ROC Amplification Frequency Hz Basin geometry Confluence of two valleys Site Information ROC site is situated on rock outcrop at the confluence of two valleys reference site Dubos et al 2003 Dubos 2003 Comments Criteria for a reliable H V curve are fulfilled that is fo gt 10 ly fo gt 200 calf lt 10910 2 The HIV ratio is flat over the whole frequency range examined As the available geological information unambiguously indicates that it is a hard rock site this flat H V curve may be interpreted as indicative of a good non weathered reference site free of any amplification even at high frequencies 47 SESAME H V User Guidelines 17 03 05 A 2 Comparison with standard spectral ratios Following the Practical User Guidelines for the implementation of the H V ratio technique data examples relevant to physical explanation are presented Along with each figure some explanation comments with respect to the site information and its fundamental frequency are given Figures below represent the ambient vibration average H V ratio thick red line multiplied d
53. iles are selected 2 4 Showing output results By pressing the View Output button Figure 4 the user can navigate through three dialogue boxes The first dialogue box Figure 6 shows the H V spectral ratio of the merged horizontal components as well as the plus and minus one standard deviation curves The second dialogue box shows the H V spectral ratio for each one of the NS and EW components The third one Figure 7 shows the spectral ratio of the merged H NS and EW horizontal components and the spectra of V NS and EW for each individual window only if output single window information is selected in the configuration parameter of the processing module 25 SESAME H V User Guidelines 17 03 05 amp output 1 3 x Spectral ratio HIV 5 C Paula Trabalho Projectos Lagos Ruido_edifLagos HYViSd Main Processing Parameters freq_spacing fit offset_rem r_mean taper cos 5 instrument resp na smooth konno ohmachi 40 0 merge type geometric single componentno average type log single win outna Spectral ratio Frequency Hz Figure 6 H V ratio for the merged horizontal components mean in black mean multiplied and divided by 10994 in red and blue The pink strip shows the frequency range where the data has no significance due to the sampling rate and the window length The grey strip represents the mean fo plus and minus the standard deviation It is calculated from
54. ity contrast i e exceeding at least 2 5 at different depths 2 however given the minimum threshold of 2 5 the number of such depths rarely exceeds 2 In such cases the S wave response will exhibit major amplifications at frequencies fk corresponding to the fundamental frequencies of the layering located above these depths with major discontinuity In such cases the available results show that all Rayleigh wave modes existing at frequency f do exhibit a common ellipticity peak in other words the vertical component of all existing Rayleigh wave modes vanish at frequencies fi In such sites a H V curve with several sites is therefore consistent with the surface wave interpretation An example of this situation is a shallow very soft layer resting on a thick stiff unit underlain by very hard bedrock vi No relation could be established between the S wave amplification at the resonance frequency and the characteristics of the H V infinite peak for instance its width or maximum amplitude B 2 1 2 H V and Love waves Love waves carry energy only on the horizontal component Their influence on the frequency dependence of the H V ratio can therefore come only from the frequency dependence of the H component Different studies see for instance Konno amp Ohmachi 1998 have shown that at least for high impedance contrast cases Love waves do strengthen the H V peak all surface waves carry their maximum energy for frequencies correspondi
55. ivided by 109 thin red line and the earthquake recordings average standard spectral ratio SSR thick black line multiplied divided by 109 9557 thin black line 48 SESAME H V User Guidelines 17 03 05 Volvi1997 LTST Amplification 0 1 1 Frequency Hz Site LTST Mygdonian Basin Northern Greece Surface Geology Soft Basin Geometry Semi elliptical 3D basin Surface Topography Flat Site Description Agricultural area Comments A clear and unique H V spectral ratio peak is shown Both approaches SSR H V exhibit the same fundamental frequency f 0 7Hz The LTST site is very well documented with geotechnical geophysical data and the 2D theoretical transfer function is in good agreement with the experimental one 49 SESAME H V User Guidelines 17 03 05 Lourdes AUZ 20 Amplification 0 1 1 Frequency Hz Site Auzon Lourdes France Surface Geology Stiff and shallow sediments Dubos et al 2003 Dubos 2003 Basin Geometry 3D Basin Surface Topography Flat Site Description Urban Comments A clear and unique H V spectral ratio peak is shown Both approaches SSR H V exhibit almost the same fundamental frequency f 5 0 Hz 50 SESAME H V User Guidelines 17 03 05 Predappio SCA Amplification 0 1 1 Frequency Hz Site Predappio Italy Surface Geology Soft 8m overlying rock Basin Geometry Cylindrical Surface Topography Flat Site Desc
56. jectos 1 Ben 3 C Paula Trabalho Projectos Number of Windows 18 CiPaulalTrabalholProjectosiL Plot Traces D E C1PaulalTrabalholProjectosi E SE View Output 4 72 Last Processing Time 2004 10 27 8 47 3 66 0 v 67 59 NS Ew 79 180 0 360 0 540 0 72C counts 1000 Time in seconds Figure 4 This figure shows the graphical user interface of J SESAME Selected windows are shown in green 23 SESAME H V User Guidelines 17 03 05 The program automatically looks for time windows satisfying the above criteria when one window is selected the program looks for the next window and allows two subsequent windows to overlap by a specified amount roverlap default value is 20 The window selection module has been written as an independent Fortran subroutine for which The input parameters are the selection parameters tsta STA window length tlta LTA window length smin smax lower and upper allowed bounds for the sta lta ratio tlong ambient vibration window length over which the sta lta should remain within the bounds yes no 1 0 parameters for turning on or off the saturation and noisy window options overlapping percentage allowed for two subsequent windows The output parameters are the name of the ambient vibration file the start and end times of each selected window the recording status of each component the
57. lity of its value will increase with the sharpness of the H V peak no straightforward information can be directly linked to the H V peak amplitude Ao This latter value may however be considered as indicative of the impedance contrasts at the site under study large H V peak values are generally associated with sharp velocity contrasts Figure 8 shows a comparison between the H V ratio of ambient vibrations and the standard spectral ratio of earthquakes using a reference site The comparison is performed using all the sites investigated in the framework of the SESAME project The top part of the figure compares the value of the fundamental natural frequency fo derived using both methods An overall good agreement can be observed for the frequency values The bottom part of Figure 8 compares the value of the peak amplitude Ao This comparison shows that it is not scientifically justified to use Ao as the actual site amplification However there is a general trend for the H V peak amplitude to underestimate the actual site amplification In other words the H V peak amplitude could generally be considered as a lower bound of the actual site amplification 28 SESAME H V User Guidelines 17 03 05 f0 H V Ambient vibrations vs f0 SPR earthquakes N E o c 9 5 a z 1 t o a E 4 gt 2 0 1 10 f0 SPR earthquakes Hz ANNECY m BENEVENTO A CATANIA BEICITTACASTELLO X COLFIORITO CORINTH X EBRON EUROSEISTEST FA
58. lley edges The frequency of the sharp peaks flat parts agrees within 20 with the resonance frequency of the structure possibly different from the 1D value for deeply embanked valleys while the bandwidth of the broad peaks sites with steep underground interfaces is generally indicative of the fundamental frequency variations between the shallowest and deepest sections however the amplitude of this broad maximum is often too small to allow a clear identification at least in the absence of any additional geological information and or dense geographic coverage of ambient vibration measurement points Additional comment H V and surface topography All the above discussion and results implicitly addressed mainly sedimentary alluvial sites within valleys or plains and are therefore valid only for horizontal free surfaces As frequency dependent site amplification has been repeatedly observed also on top of rocky hills several attempts have been performed to investigate whether H V ratios from ambient vibrations also exhibit a peak in the same frequency range These attempts have generally been successful but no theoretical interpretation and no numerical simulation have been proposed to explain this apparent success The surface topography issue was not addressed within the SESAME project and we will therefore only indicate here that surface waves are certainly affected by non flat free surfaces resulting in a diffracted wavefield as
59. m microseisms is thus easier on islands such as Japan than in the heart of continental areas such as Kazakhstan High frequency waves generally correspond to much closer sources which most of the time are located very close to the surface while the wavefield in the immediate vicinity less than a few hundred meters includes both body and surface waves at longer distances surface waves become predominant Besides this very qualitative information only very little information is available on the quantitative proportions between body and surface waves and within the different kinds of surface waves that may exist Rayleigh Love fundamental higher The few available results reviewed in Bonnefoy Claudet et al 2004 report that low frequency microseisms f lt fan predominantly consist of fundamental mode Rayleigh waves while there is no real consensus for higher frequencies gt 1 Hz Different approaches were followed to reach these results including analysis of seismic noise amplitude at depth and array analysis to measure the phase velocity The very few investigations on the relative proportion of Rayleigh and Love waves all agree on more or less comparable amplitudes with a slight trend towards a slightly higher energy carried by Love waves around 60 40 In addition there are a few reports about the presence of higher surface wave modes from several very different sites some very shallow other much thicker some
60. main processing module then reads the ambient vibration file and performs the H V computation over each selected window Figure 5 shows an example where the same signal has been processed with and without the automatic window selection that is the transient removal This example shows that the peak on the H V curve is much clearer when the transient removal is applied and also that standard deviation is lower especially at low frequencies SITE TST RR dry LO RR RE HU ET TRE TT ME AME PURA I PIU NG EL Nene TUR I E Eu ut I TESTES Time s Ist noseleclion hvO Ist noselection hvm 1811 noselection hvp Ist selection selection hvm HA ratio Frequency Hz Figure 5 Signal top processed with red curves bottom or without blue curves bottom the automatic window selection selected windows are indicated by the red segments on the top of the signal The peak on the H V curve is much clearer when the transient removal is applied and also the standard deviation is lower especially at low frequencies 24 SESAME H V User Guidelines 17 03 05 The choice of the window selection parameters should be carefully optimised before any automatic processing 2 3 Computing H V spectral ratio The main processing module is developed in FORTRAN90 It performs H V spectral ratio computations and the other associated processing such as DC offset removal filteri
61. n Earthquake Engineering London Paper 869 Duval A M J L Chatelain B Guillier and SESAME Project WP02 Team 2004 Influence of experimental conditions on H V determination using ambient vibrations noise Proceedings of the 13th World Conference on Earthquake Engineering Vancouver August 2004 Paper 306 Duval A M J L Chatelain B Guillier and the SESAME WP02 Team 2004 Influence of experimental conditions on H V determination using ambient vibrations noise ICSDEE amp ICEGE Berkeley CA USA 37 SESAME H V User Guidelines 17 03 05 Kanai K and T Tanaka 1961 On microtremors VIII Bulletin of the Earthquake Research Institute 39 97 114 Koller M G J L Chatelain B Guillier A M Duval K Atakan C Lacave P Y Bard and the SESAME participants 2004 Practical user guidelines and software for the implementation of the H V ratio technique measuring conditions processing method and results interpretation 13th World Conference on Earthquake Engineering Vancouver Paper 3132 Konno K and T Ohmachi 1998 Ground motion characteristics estimated from spectral ratio between horizontal and vertical components of microtremors Bull seism Soc Am 88 1 228 241 Kudo K 1995 Practical estimates of site response State of the art report Proceedings of the fifth Internationnal Conference on Seismic Zonation Nice France Malischewsky P and F Scherbaum 2004 Love s formula and H V ratio
62. ncerns the reliability of the H V curve Reliability implies stability i e the fact that actual H V curve obtained with the selected recordings be representative of H V curves that could be obtained with other ambient vibration recordings and or with other physically reasonable window selection Such a requirement has several consequences i In order for a peak to be significant we recommend checking that the following condition is fulfilled fp gt 10 ly This condition is proposed so that at the frequency of interest there be at least 10 significant cycles in each window see Table 1 If the data allow but this is not mandatory it is always fruitful to check whether a more stringent condition fo gt 20 lw can be fulfilled which allows at least ten significant cycles for frequencies half the peak frequency and thus enhances the reliability of the whole peak ii A large number of windows and of cycles is needed we recommend that when using the automatic window selection with default parameters the total number of significant cycles nc ly Ny fo be larger than 200 which means for instance for a peak at 1 Hz that there be at least 20 windows of 10 s each or for a peak at 0 5 Hz 10 windows of 40 s each see Table 1 for other frequencies of interest In case no window selection is considered all transients are taken into account we recommend for safety this minimum number of cycles be raised around 2
63. ng smoothing merging of horizontal components etc on the selected windows for individual files or alternatively on several files as a batch process The instrument response is assumed to be removed by the user in the case of identical components H V ratios should not be affected by the instrument response Main functionalities of the processing module are described below FFT including tapering e Smoothing with several options The Konno amp Ohmachi smoothing is recommended as it accounts for the different number of points at low frequencies Be careful with the use of constant bandwidth smoothing which is not suitable for low frequencies Merging two horizontal components with several options Geometric mean is recommended H V Spectral ratio for each individual window Average of HIV ratios Standard deviation estimates of spectral ratios Details of the different options are to be found in the Appendix of the J SESAME User Manual The parameter settings for the above options are controlled through an input file The processing module is applied according to the selected nodes in the tree If the selected node is a site then all the selected windows of the data files collected for this site will be used for computing the average H V spectral ratio Output for each window can be also obtained by setting up the configuration parameters of the processing module Batch processing will be performed when several sites or data f
64. ng to group velocity minima Airy phase for high impedance contrast layering the group velocity minimum of the fundamental Love mode occurs like for the vanishing of V component at a frequency fi which is very close to the fundamental S wave frequency Higher modes of Love waves may also have group velocity minima and associated Airy phases at higher frequencies this may result in other maxima if higher modes carry a significant amount of energy B 2 2 H V and body waves As site amplifications occurring during actual earthquakes essentially involve incoming body waves it is obvious that the horizontal and vertical components of body waves are both highly sensitive to site conditions The main question to address here is the relation of the H V ratio and site conditions for body waves a side question concerns the differences or similarities between H V ratios derived from earthquake recordings and H V ratios derived from ambient vibration recordings When considering once again a simple horizontally layered structure with one soft layer over a half space and its response to obliquely incident plane waves a striking result is the fact that whatever the incident wave type P or SV or SH the horizontal components systematically exhibit resonant peaks at the S wave resonance frequencies even for P wave incidence while the vertical component always exhibit resonant peaks at the P wave resonance frequencies even for S wave incidence T
65. ns for each window which may lead to a clearer low frequency peak satisfying all criteria of 3 3 1 3 3 2 c Broad peak case or multiple peak case In some cases the H V curve may exhibit a broad peak or a multiplicity of local maxima none of which fulfils the above criteria i ii and possibly v 3 3 1 In each of these cases the first check to perform is to change the smoothing parameters in case of a broad peak decrease the smoothing bandwidth in the multiple peak case increase the smoothing bandwidth In this latter case however another mandatory check consists of investigating the possible industrial origin of any one of these peaks see 3 3 2 8 It may sometimes happen that other acceptable processing parameters allow the broad or multiple peaks to be transformed into a clear H V curve according to the criteria of 3 3 1 This is however rather rare If broad nature seems stable with a rather small standard deviation then one may consider the possible link with a sloping underground interface see below 3 4 and appendix B e With large smoothing a multiple peak curve may always be transformed into a broad peak or plateau like curve Smoothing parameters that are too large are nevertheless not recommended Since our experience taught us the scarcity of such cases and their links very often to unsatisfactory recordings we recommend in such cases either that the H V results for the site be discarded or that
66. nsidered as a generic term used throughout the text to refer to all kinds of deposits overlying bedrock without taking into account their specific origin The processing software J SESAME developed specifically for using in H V technique is explained provided on a separate CD accompanying the guidelines in Part Il However the recommendations given in the guidelines are meant for general application of the method with any other similar software J SESAME is provided as a tool for the easy implementation of the recommendations outlined in this document Regarding the processing of the data several options can be chosen but the recommended processing options are provided as defaults by the J SESAME software SESAME H V User Guidelines 17 03 05 PART I QUICK FIELD REFERENCE AND INTERPRETATION GUIDELINES SESAME H V User Guidelines 17 03 05 1 EXPERIMENTAL CONDITIONS MEASUREMENT FIELD SHEET gt This sheet is only a quick field reference It is highly recommended that the complete guidelines be read before going out to perform the recordings A field sheet is also provided on the next page This page containing two identical sheets can be printed and be taken in the field Type of parameter Main recommendations Recording duration Minimum expected fo Hz diii recording 0 2 30 0 5 20 1 10 2 5 5 3 10 2 Measurement spacing gt Microzonation start with a large spacing for example a
67. nsor coupling should be handled with care Concrete and asphalt provide good results whereas measuring on soft irregular soils such as mud grass ploughed soil ice gravel uncompacted snow etc should be looked at with more attention gt To guarantee a good soil sensor coupling the sensor should be directly set up on the ground except in very special situations steep slope for example for which an interface might be necessary see next section gt Topping of asphalt or concrete does not affect H V results in the main frequency band of interest although slight perturbations can be observed in the 7 8 Hz range which do not change the shape of the H V curves In the 0 2 20 Hz range no artificial peaks are Observed Tests should be performed on higher frequency sites in order to check the influence of the asphalt thickness See Figure 1 for a comparison with and without asphalt at the same site gt Grass by itself does not affect H V results provided that the sensor is in good contact with the ground and not for example placed unstably on the grass as can be the case for tall grass folded under the sensor In such cases it is better to remove the high grass before installing the sensor or to dig a hole in order to install the sensor directly on soil Recording on grass when the wind is blowing can lead to completely perturbed results below 1 Hz as shown on Figure 2 gt Avoid setting the sensor on superficial layers of
68. of cycles is needed we recommend that the total number of significant cycles n ly ny fo be larger than 200 which means for 17 SESAME H V User Guidelines 17 03 05 instance that for a peak at 1 Hz there be at least 20 windows of 10 s each or for a peak at 0 5 Hz 10 windows of 40 s each or 20 windows of 20 s but not 40 windows of 10 s See Table 1 for other frequencies of interest As there might be some transients during the recording these should be removed from the signal for processing and the total recording duration should be increased in order to have the above mentioned conditions fulfilled for good quality signal windows Table 1 Recommended recording duration Minimum value significant number of Minimum useful minimum recor cycles n windows duration min 0 2 50 200 10 1000 30 0 5 20 200 10 400 20 10 200 10 200 10 2 5 200 10 100 5 5 5 200 10 40 3 10 5 200 10 20 2 Measurement spacing gt For a microzonation it is recommended that a large spacing be initially adopted for example a 500 m grid and in case of lateral variation of the results to densify the grid point spacing down to 250 m for example gt For a single site response study one should never use a single measurement point to derive an fy value It is recommended that at least three measurement points be used In situ soil sensor coupling In situ soil se
69. oise energy certainly undergo some conversion mode conversion Rayleigh Love fundamental higher and or type conversion surface to body waves along laterally varying substructures at some distance from the site For instance for a deep inland basin incoming low frequency crustal waves have a penetration depth of at least 1 km and will be diffracted along basin edges in such a case the sources of seismic noise may be seen as a collection of point sources located along the basin bedrock interface re emitting the same energy envelope spectrum as different waves local surface waves and body waves The associated H V ratio should then be somewhat similar to the H V ratio derived from earthquake recordings in the low frequency range only of course if available site to reference rock spectral ratios should then be also comparable for ambient vibration and earthquake recordings Low frequency H V peaks are associated either with extremely soft soil e g Mexico City clays with a thickness of several tens of meters or with normal soil deposits having a very large thickness several hundred meters at least the former case is obviously associated with a large impedance contrast while this can occur in the latter case only if the bedrock is very hard the confining pressure at large depth automatically induces a stiffness increase B 3 2 2D 3D structures We consider here sites under which at least one of the interfaces with significan
70. opean project 2004 Report on parameter studies Deliverable D12 09 SESAME European project 2004 Overall comparisons for test sites Deliverable D17 10 Stephenson W R 2003 Factors bounding prograde rayleigh wave particle motion in a soft soil layer Proceedings of the 2003 Pacific Conference on Earthquake Engineering 13 15 February 2003 Christchurch New Zealand Paper 56 8 pages Teves Costa P L Senos and C S Oliveira 2004 Correlation between damage distribution and soil behaviour estimated with ambient vibrations Proceedings of the 13th World Conference on Earthquake Engineering Vancouver August 2004 Paper 1004 Theodulidis N G Cultrera A Tento D Faeh K Atakan P Y Bard A Panou and the SESAME Team 2004 Empirical evaluation of the horizontal to vertical spectral ratio 38 SESAME H V User Guidelines 17 03 05 technique results from the SESAME project Proceedings of the 13th World Conference on Earthquake Engineering Vancouver August 2004 Paper 2323 39 SESAME H V User Guidelines 17 03 05 Appendix A H V Data Examples A 1 Illustration of the main peak types Following the practical user guidelines for the implementation of the H V ratio technique for the seven peak types presented in Part 1 section 2 respective data examples are given Each case is illustrated by a Figure along with some detailed explanation comments with respect to the proposed quality criteria Figures below represent
71. or and the ground does not modify the results In case of a steep slope that does not allow correct sensor levelling the best solution is to install the sensor on a pile of sand or in a plastic container filled with sand In general avoid soft non cohesive materials such as foam rubber cardboard gravel whether in a container or not etc to help setting up the sensor See Figure 3 for a comparison with the sensor directly on the natural soil or on a Styrofoam plate Sensor setting gt The sensor should be installed horizontally as recommended by the manufacturer gt There is no need to bury the sensor but it does not hurt if this is the case It can be useful however to set up the sensor in a hole no need to fill it about its own size in order to get rid for example of the effect of a weak wind on grass This would be effective only if there are no structures nearby such as buildings or trees that might also induce some strong low frequency perturbations in the ground due to the wind see below 19 17 03 05 SESAME H V User Guidelines gt Do not put any load on the sensor ui H z an H V TEST 10 e S 5 e Grass without wind opnurdury 10 10 ND T B a o 2 E m Frequency Hz H V REFERENCE 10 10 d E E e lt Not filled hole with wind A H 10 Frequency Hz 10 Frequency Hz
72. other with low velocity zone at depth The following Table summarises with some simplification however the above discussion Natural Human Name Microseism Microtremor Frequency 0 1 fin 0 5 Hz to 1 Hz fnn 0 5 Hz to 1 Hz gt 10 Hz Origin Ocean Traffic Industry Human activity Incident wavefield Surface waves Surface body Amplitude variability Related to oceanic storms Day Night Week week end Rayleigh Love issue Incident wavefield Comparable amplitude slight indication predominantly Rayleigh that Love waves carry a little more energy Fundamental Higher Mainly Fundamental Possibility of higher modes at high mode issue frequencies at least for 2 layer case Further Comments Local wavefield may be diffe Some monochromatic waves related to rent from incident wavefield machines and engines The proximity of sources as well as the short wavelength probably limits the quantitative importance of waves generated by diffraction at depth 55 SESAME H V User Guidelines 17 03 05 These results although partial do indicate that the seismic noise wavefield is indeed complex especially at high frequencies where the origin is human activity when interpreting the H V ratio one has therefore to consider the possible contributions to H V from both surface and body waves including also higher modes of surface waves B 2 Links between wave type and H V ratio The wavefield being a mi
73. ovolts 10000 0 Hz Frequency Hz 1 Frequency Hz Basin geometry Unknown Site Information TAR site is overlain with stiff soil coarse grained alluvium Comments Criteria for a reliable H V curve are fulfilled that is fo gt 10 ly fo gt 200 calf lt 10910 2 The local narrow peak has an industrial origin This H V spectral ratio peak is due to manmade noise machinery the reprocessing with different smoothing parameters bottom right shows it becomes narrower and narrower with a larger and larger amplitude when the b value Konno Ohmachi smoothing approach is increasing this behaviour is typical of industrial origin Another confirmation is obtained form the fact this narrow peak occurs at the same frequency in the Fourier spectra of all three components Figure on bottom left 45 SESAME H V User Guidelines 17 03 05 6a Flat H V Ratio Curves on sediments Tehran ABM Amplification Frequency Hz Basin geometry Unknown Site Information ABM site is characterised by stiff soil coarse grained alluvium overlying bedrock at an unknown depth Comments Criteria for a reliable H V curve are fulfilled that is fo gt 10 ly Ne fo gt 200 calf lt log10 2 Significant low frequency amplification F lt 1 0 Hz was found for the ABM sedimentary site using earthquake data which does not appear in the HIV ratio This site is one of the few examples of non rock sites exh
74. requency fsensor and sensitivity if fo is lower than1 Hz while the sensor used is a high frequency velocimeter check the results with the procedure indicated in 3 3 2 b e this sharp peak does not have an industrial origin cf 3 3 2 a 10 tat H V Amplitude Frequency Hz Window Number of Number of Frequency statistics from individual windows length lw s windows ny significant cycles 41 14 1561 Figure 9 Example of a clear H V curve that fulfils all the criteria for reliability and clarity given in sections 3 2 and 3 3 1 3 3 2 Unclear cases 3 3 2 a Sharp peaks and Industrial origin It often occurs in urban environments that H V curves exhibit local narrow peaks or troughs In most cases such peaks or troughs have an anthropic usually industrial origin related to some kind of machinery turbine generators Such perturbations are recognised by two general characteristics e They may exist over a significant area in other terms they can be seen up to distances of several kilometres from their source e As the source is more or less permanent at least within working hours the original non smoothed Fourier spectra should exhibit sharp peaks Several kinds of checks are therefore recommended e Have a look at the raw spectra from each individual window if they all exhibit a sharp peak often on the 3 components together at this particular frequency there is a 95 ch
75. reshold value for the stability condition oa f lt O fo iV fpeac Auv f oa f fo 576 Vs av average S wave velocity of the total deposits V o lt amp fo Vs surf S wave velocity of the surface layer e h depth to bedrock oa fo lt 9 fo e hmin lower bound estimate of h Threshold Values for c and oa fo Frequency range Hz 0 2 0 2 0 5 0 5 1 0 fo Hz 0 25 fo 0 20 fo 0 15 fy fo for c fo 3 0 2 5 2 0 log fo for GiogHy fo 0 48 0 40 0 30 2 2 Main peak types This section is not an exhaustive list of the different types of H V curves that might be obtained but it gives suggestions for the processing and interpretation of the most common situations 10 SESAME H V User Guidelines 17 03 05 Sharp peaks and industrial origin see 3 3 2 d and appendix A If industrial origin is proved i e if raw spectra exhibit sharp peaks on all components liable f random decrement technique indicates no reliable very low damping 5 peaks get sharper with decreasing smoothing Perform continuous recordings during i day and night If industrial origin is not obvious Check the existence of 24 h 7 day plant within the area ES E E E EE E E E Clear peak see 3 3 1 and appendix A If industrial origin 3 3 2 d i e the raw spectra exhibit sharp peaks on all three components no reliable fo the random decr
76. ription Urban Comments A clear and unique H V spectral ratio peak is shown in high frequencies Both approaches SSR H V exhibit the same fundamental frequency f 7 0 Hz 51 SESAME H V User Guidelines 17 03 05 Tehran ABM Amplification 0 1 1 Frequency Hz Site Tehran Iran Surface Geology Stiff ABM site is characterised by stiff soil coarse grain alluvium overlying bedrock at an unknown depth Basin Geometry Unknown Surface Topography Flat Site Description Urban Comments No clear H V spectral ratio peak appears in the low frequency band f 1 0Hz although it is clear in the SSR technique To the contrary a sharp peak with an amplitude of about 1 5 appears at about 1 3Hz This H V spectral ratio peak is due to manmade noise machinery since it appears in the Fourier spectra of all three components 52 SESAME H V User Guidelines 17 03 05 Katania GENI Amplification 0 1 1 Frequency Hz Site Catania Italy Surface Geology Soft Basin Geometry Unknown Surface Topography Flat Site Description Urban Comments No clear H V spectral ratio peak appears in the frequency band 1 0 Hz 4 0 Hz although it is clear in the standard spectral ratio technique The low frequency peak 0 25 Hz in the H V curve is not reliable since the associated standard deviation is large and the amplitude does not decrease enough at lower frequencies 53 SESAME H V User Guidelines 17 03 05 AP
77. rocessing of large amounts of data The objective is to keep the most stationary parts of ambient vibrations and to avoid the transients often associated with specific sources footsteps close traffic This objective is exactly the opposite of the usual goal of seismologists who want to detect signals and have developed specific trigger algorithm to track the unusual transients As a consequence we have used here an antitrigger algorithm which is exactly the opposite it detects transients but it tries to avoid them The procedure to detect transients is based on a classical comparison between the short term average STA i e the average level of signal amplitude over a short period of time denoted tsta typically around 0 5 to 2 0 s and the long term average LTA i e the average level of signal amplitude over a much longer period of time denoted tlta typically several tens of seconds 22 SESAME H V User Guidelines 17 03 05 In the present case we want to select windows without any energetic transients this means that we want the ratio sta Ita to remain below a small threshold value smax typically around 1 5 2 over a long enough duration Simultaneously we also want to avoid ambient vibration windows with abnormally low amplitudes we therefore also introduce a minimum threshold smin below which the signal should not fall during the selected ambient vibration window There are also two other criteria that may b
78. soft soils such as mud ploughed soil or artificial covers such as synthetic sport covering Avoid recording on water saturated soils for example after heavy rain 18 SESAME H V User Guidelines 17 03 05 gt Avoid recording on superficial cohesionless gravel as the sensor will not be correctly coupled to the ground and strongly perturbed curves will be obtained Try to find another type of soil a few meters away or remove the superficial gravel to find the firm ground below if possible Recording on snow or ice can affect the results In such cases it is recommended that the snow be compacted and the sensor installed on a metal or wood plate in order to avoid sensor tilting due to local melting under the sensor legs When recording in such conditions make sure that the temperature is within the equipment specifications given by the manufacturer H V REFERENCE 10 H V TEST 30 em filled hole H V Amplitude H V Amplitude Frequency Hz Frequency Hz Figure 1 Comparison of the H V curves obtained with and without asphalt at the same site showing no significant effect of the asphalt layer Artificial soil sensor coupling When an artificial interface is needed between the ground and the sensor it is highly recommended that some tests be performed before doing the recordings in order to examine a possible influence of the chosen interface gt gt gt The use of a metal plate in between the sens
79. t 1 Hz may also be associated with wind and water flows e At high frequencies f gt fm 1Hz the origin is predominantly related to human activity traffic machinery the sources are mostly located at the surface of the earth except some sources like metros and often exhibit a strong day night and week weekend variability The 1 Hz limit for fa is only indicative and may vary from one city to another Some specific civil engineering works highways dams involving very big engines and or trucks may also 54 SESAME H V User Guidelines 17 03 05 generate low frequency energy Locally this limit may be found by analysing the variations of seismic noise amplitude between day and night and between work and rest days as well Energetic low frequency sources are often distant being located at the closest oceans and the energy is carried from the source to the site by surface waves guided in the earth s crust However locally these waves may and actually often do interact with the local structure especially deep basins Their long wavelength induces a significant penetration depth so that the resulting local wavefield may be more complex subsurface inhomogeneities excited by the long period crustal surface waves may act as diffraction points and generate local surface waves and even possibly body waves The energy at frequencies between 0 1 and 1 0 Hz decreases with increasing distance from oceans extracting information fro
80. t impedance contrast exhibits steep slopes i e larger than around 10 this value being however only 60 SESAME H V User Guidelines 17 03 05 indicative Such sites are therefore either transition zones between areas with more or less horizontal layering or deeply embanked valleys and basins having a large thickness to width ratio typically larger than 0 2 B 3 2 1 Transition zones If such transition zones are expected from the available geological geotechnical geophysical information it is always recommended that measurements be made on each part of the transition zone and to have a rather dense measurement mesh the density being related to the predominant wavelength i e to the frequency the higher the frequency the smaller the mesh size High frequencies human origin f gt fan fnn 1 Hz possibly varying from site to site Numerical simulations have consistently shown that for local surface sources the H V curve at such transition sites exhibit broader and lower maxima which may be hard to identify surface waves cannot develop with one single pure mode nor can resonance of body Waves occur Low frequencies oceanic origin f fan fnn 1 Hz possibly varying from site to site No simulation is available for incoming crustal surface waves the local diffraction phenomena already mentioned for this case let us think that the wavefield should include a significant proportion of body waves generated at depth
81. the fo of each individual window 2 5 Setting graph properties and creating images of the output results For each graph shown for example as in Figure 6 and 7 there is a small red box in the upper right corner without any label By clicking there the properties and scale of the graph can be modified and images of the graph can be created The button Properties and series pops up a dialogue box where line type width and colour can be changed for each spectral curve The button Scales pops up a dialogue box where the minimum maximum and scale type for each one of the vertical and horizontal axes can be modified The button Save allows an image of the graph to be created 26 SESAME H V User Guidelines 17 03 05 xi D portable_paula Ruido_Portimao Fich_originais SAF PORT_20021112_0049 saf 8 c paulattempPORT 20021112 0049 saf out 86 0 68 89 0 NS 89 96 0 BN 105 120 0 240 0 360 0 480 0 counts 100 Time in seconds Horizontal vertical ratios im Spectra for the V NS and EW components m 3 5 Merged HV 10 000 Spec V Spec NS EWN 1 000 Spec EW a 2 100 z 2 E 4 E 10 H 1 1 0 0 1 D 1 1 10 100 0 1 1 10 100 Frequency Hz counts Hz Frequency Hz Figure 7 Result for individual windows H V ratios and spectra shown are derived from the signal displayed in the red window
82. the measurements be repeated 3 3 2 d Two peaks case In some cases the H V curve may exhibit two peaks satisfying the above criteria 3 3 1 this is however rather rare Theoretical and numerical investigations have shown that such a situation occurs for two large impedance contrasts say around 4 minimum for each at two different scales one for a thick structure and the other one for a shallow structure The two frequencies fo and f 34 SESAME H V User Guidelines 17 03 05 with fo lt fj may then be interpreted as characteristics at each scale f being the fundamental frequency In order to check whether this is actually the case the following checks are recommended 3 4 check the geology of the site and the possibility of a shallow soft deposits b thick rather stiff sediments or soft rock and c very hard underlying bedrock at depth Reprocess the data with other smoothing parameters the peaks should be stable and withstand broader and narrower smoothing around the recommended default values consider in particular the possibility that one of these peaks generally at the higher frequency may have an industrial origin cf 3 3 2 a The statistics on several hundred measured sites and a number of theoretical cases show that the two contrasts should be at very different scales which means that the two frequencies fi and fo should be sufficiently different so that both peaks fulfil the clarity criteria
83. to be considered as horizontally layered with a smooth and flat interface with the underlying bedrock at least locally then the wavefield composition and interpretation of H V ratio can be seen as follows B 3 1 1 High frequencies human origin f gt fan fnn 1 Hz e the site is located an urban environment the noise sources are essentially local and superficial the wavefield predominantly consists of surface waves Rayleigh and Love with however a slight proportion of body waves The H V curve should exhibit one single peak at a frequency that is within 20 of the S wave resonant frequency of the site The amplitude of that peak should not be interpreted in terms of amplification values e f the site is located in the countryside and the predominant sources are distant the wavefield also includes resonating head waves and the H V curve may exhibit several peaks corresponding to the various harmonics B 3 1 2 Low frequencies oceanic origin f lt fin fnn 1 Hz Unless there exist energetic low frequency sources big trucks or engines close to the site under consideration the seismic noise wavefield is most probably caused by oceanic activity This may be checked through continuous measurements and an analysis of the daily weekly amplitude variations The local geological structure certainly does not exist over the whole distance between the site and the ocean therefore the low frequency crustal surface waves carrying the n
84. uctures Rain avoid measurements under heavy rain Slight rain has no noticeable influence gt Temperature check sensor and recorder manufacturer s instructions Meteorological perturbations indicate on the field sheet whether the measurements are performed during a low pressure meteorological event Disturbances gt Monochromatic sources avoid measurements near construction machines industrial machines pumps generators etc gt Transients In case of transients steps cars increase the recording duration to allow for enough windows for the analysis after transient removal 1 SESAME HH V User G uideliines OPERATOR GPS TY PE and LATITUDE LONGITUDE ALTITUDE STATION TY PE SENSOR TY PE STATION SENSOR DISK FILE NAME POINT ite GAIN SAMPL FREQ REC DURATION n wEATHER WIND none wesk medium RAIN none weak medium CONDITIONS L1 Temperature approx Remarks soft J ravet O sand L rock Ll asphalt L eement L concrete L paved other O dry soil L wet soil ARTIFICIAL GROUND SENSOR COUPLING O no DATE HOUR PLACE L strong Measurement if any L strong Measurement if any Des Remarks yes type BUILDING DENSITY Jnone L Scattered Jdense _ other type MONOCHROMATIC NOISE SOURCES factories works pumps rivers o _ yes type NEARBY STRUCTURES description heig
85. uvium sediments and silty clay Type of bedrock Sandstone Middle Miocene Comments Criteria for a reliable H V curve are fulfilled that is fo gt 10 ly fo gt 200 calf lt 10910 2 In addition Although Ao 2 9 gt 2 the peak cannot be qualified clear since the amplitude is not decreasing rapidly on each side None f fo 4 fo lt Ad 2 None fo fo 4fo Aun f2 lt Ad 2 Interpretation further tests should be performed as listed in section II 3 3 2 b 42 SESAME H V User Guidelines 17 03 05 3 Two Peaks Cases fj gt fo Grenoble pt50 Amplification Frequency Hz Basin geometry Y shaped sedimentary valley Depth 800m Site Information PT50 site is situated on late quaternary post glacial deposits Type of bedrock Jurassic marls and marly limestone Comments Criteria for a reliable H V curve are fulfilled that is fo gt 10 1 fo gt 200 oa f lt log10 2 Interpretation For the low frequency peak Ao 4 0 gt 2 and 3 fo 4fo lt Ao 2 Although strictly speaking one cannot find fi fo 4 fo Auv fi lt Ao 2 the general trend of the curve together with the known geology of the site allow the meaning of the low frequency peak to be assigned with confidence another processing with more narrow band smoothing would satisfy the criteria For the second peak all the criteria are fulfilled A4 73 5 22 Ifi e f 4
86. vel of low frequency ambient vibrations for instance in continental areas e wind blowing during recording time especially in the case of non optimal recording conditions for instance proximity of trees or buildings e measurements performed during a meteorological perturbation that may significantly enhance the low frequency content and alter the H V ratio e soil sensor coupling for instance on very wet soils after rain or with grass with a non satisfactory plate in between the sensor and the soil low frequency artificial ambient vibration sources such as heavy trucks public works machines at close to intermediate distance within a few hundred meters e inadequate smoothing parameters smoothing with a constant bandwidth may completely or partially erase low frequency peaks e inadequate sensor with very low sensitivity at low frequency Distinguishing between these various possibilities is not easy The following tests checks may however help to decide whether the unclear low frequency peak is indeed a site characteristic 33 SESAME H V User Guidelines 17 03 05 e Consider the geology of the site if it is on rock it is likely that the low frequency fuzzy peak is an artefact if it is on sedimentary deposits there might exist low frequency effects due either to very soft surface layers or to stiff but thick deposits In general very soft layers such as in Mexico City result in clear peaks because
87. x A if soil deposits Likely absence of any sharp contrast at depth Does not necessarily mean no amplification Perform earthquake recordings on site and nearby rock site Use of other geophysical techniques likely unweathered or only lightly weathered rock may be considered as a good reference site 14 SESAME H V User Guidelines 17 03 05 PART Il DETAILED TECHNICAL GUIDELINES SESAME H V User Guidelines 17 03 05 1 TECHNICAL REQUIREMENTS It is important to understand which recording parameters influence data quality and reliability as this can help speed up the recording process H V measurements in cities are conducted within the following context Anthropic noise is very high It is quite rare to be able to get data on the soil per se Most data will be obtained on streets and sidewalks i e asphalt pavement cement or concrete and to a lesser extent in parks i e on grass or soil Measurements are performed in an environment dominated by buildings of various dimensions Recordings are not always performed at the same time and under the same weather conditions The presence of underground structures i e pipes is often unknown The influence of various types of experimental parameter had to be tested on the results of HIV curves both in frequency and amplitude For each tested parameter H V data were compared with a reference situation This comparison had to be made in an obje
88. xture of Love Rayleigh and body waves the origin of the H V peaks and troughs is multiple Rayleigh wave ellipticity Airy phase of Love wave modes resonance of S and or P body waves This section begins with a brief outline of the effect of each individual wave type on the H V ratio on the basis of simple wave propagation physics The issue of more complex wavefields is then addressed with a summary presentation of the main learnings obtained from numerical simulation in complex media B 2 1 H V and surface waves B 2 1 1 H V and Rayleigh waves Rayleigh waves are characterised by an elliptical particle motion in the radial plane and their phase velocity In horizontally stratified media where velocity varies with depth both characteristics exhibit frequency dependence Stratification also gives rise to the existence of distinct Rayleigh wave modes while the fundamental mode exists at all frequencies higher modes appear only beyond some cut off frequencies the values of which increases with the mode order The H V ratio of all modes of Rayleigh waves which is a measure of the ellipticity ratio exhibits therefore a frequency dependence in stratified media There exist a rich literature on that topic a list of which may be found in Kudo 1995 Bard 1998 Stephenson 2003 Malischewsky and Scherbaum 2004 and Bonnefoy Claudet 2004 The main relevant results may be summarised as follows considering first simple one layer over half spac

guidelines for the implementation of the h/v spectral ratio

Contents

Download Pdf Manuals

Related Search

Related Contents