microtremor measurement to evaluate site characteristics by horizontal to vertical spectral ratio technique in sikkim northeast himalayas india abstract the measurement of site amplification of microtremors is an important tool for evaluating seismic hazard at local and regional level the h v spectral ratio hvsr method is applied to estimate the amplification of ground motion at resonance frequency the fundamental resonance frequency is estimated at 8 different sites in study region and shows the maximum vulnerability of the site to the earthquakes this frequency ranges between a minimum of 2 8 hz to a maximum of 9 3 hz the thickness of the sediments below the surface of recording sites is calculated using the empirical relationship that comes out to be in a particular range of 9 5 m 33 1 m above the bed rock the sedimentary thickness and the resonance frequency clearly matched with geological setting of the study area the observation shows a slow reduction in the thickness of the sediments and increase in the resonance frequency from south western part to north eastern part of the study region the results show that most of the sites are highly vulnerable to seismic risks with high amplification of seismic waves in the area thus current study provides a deep insight in to the seismic hazard of the sikkim region with a clear emphasis on the site amplification and the sedimentary cover for the region

new relationships between vs thickness of sediments and resonance frequency calculated by the h v ratio of seismic noise for the cologne area germany noise measurements were carried out in the cologne area germany and the resonance frequency of each site was estimated from the main peak in the spectral ratio between the horizontal and vertical component for 32 of these sites the thickness of the sedimentary cover was known from boreholes and a clear correlation between resonance frequency and sediment thickness was observed a formula that correlates cover thickness with frequency of the main peak in the horizontal to vertical spectral ratio was derived in addition a best fitting shear wave velocity distribution with depth vs z as well as a relationship between average shear wave velocity vs and thickness of the sedimentary cover was calculated by using all of the noise measurements and applying the derived relationships we obtained a subsoil classification for the cologne area

stability assessment and quantitative evaluation of h v spectral ratios for site response studies in kumaon himalaya india using ambient noise recorded by a broadband seismograph network the kumaon himalaya region in india has accumulated considerable seismic risk potential from moderate to high seismicity due to ongoing tectonic evolutionary processes to assess conditions of high seismic risk arising from local site effects at populated locations we applied the empirical horizontal to vertical h v spectral amplitude ratio method nakamura in quarterly reports of the railway technical research institute tokyo 30 25 33 1989 using ambient seismic noise recorded by a network of 32 digital broadband seismographs from june 2005 to june 2008 the data and the estimated parameters were subjected to stability tests to assess the effect of seasonal variations seasonal variations in the ambient noise data seemed to show a lesser effect on fundamental frequency estimates and a slightly greater effect on the peak h v amplitudes validation of the ambient noise results was done by complementary tests using h v ratios of local and regional earthquakes the peak corresponding to the fundamental resonance frequency is prominently present in both the ambient noise and the earthquake datasets the study locations showed distinct h v curve topologies corresponding to the effects of both velocity contrast at well defined frequencies and characteristic topographic effect around a certain frequency range the clearly indicated peaks in the h v curves possibly correspond to velocity contrasts created by weathered sediments overlying hard rock basements in rocky hills our study indicates high site responses at many populated locations near the surface trace of the seismically active main central thrust mct and other fault boundaries the fundamental resonance frequencies estimated from the site response studies at the 32 locations could be useful in preliminary site characterization ground motion prediction and seismic hazard analysis

comparison of different site response estimation techniques using aftershocks of the 1999 izmit earthquake on 17 august 1999 the m w 7 4 izmit earthquake occurred in northwestern turkey a temporary seismic network was installed to improve the geometry of a previously installed network in this study 262 aftershocks of the izmit earthquake with magnitude m l ranging between 0 4 and 4 5 were analyzed using digital recordings from 17 stations of these networks s wave and p wave spectral records corrected for path attenuation function were inverted by means of the generalized inversion technique git the git site responses were compared with those calculated by horizontal to vertical h v ratios applied to both earthquake data and to pre event noise in most cases the h v of the earthquake data provided site responses with shapes consistent with those obtained using git however the level of amplification was occasionally found to be different in general these discrepancies can be explained either by the amplification affecting the vertical component of the ground motion that we detected by git or by the waves having a propagation in almost the vertical direction using the h v ratio applied to noise for most cases we obtained not only the peaks for the fundamental resonance frequencies but site responses with shapes similar to those obtained by git the detected level of amplifications using the h v ratio showed a tendency not to exceed those calculated by the inversion finally amplifications up to a factor 5 are found for stations placed over complex topography for these sites amplifications are not always correctly identified by the h v technique using either earthquakes or noise

microtremors as a geophysical exploration tool applications and limitations the usefulness of microtremors as a geophysical exploration tool has been analyzed this application is possible due to the relationship between the main resonance frequency of a given soil obtained from the h v spectral ratios of microtremors its thickness and average shear velocity we first measured the ambient noise at 33 sites and determined their main resonance frequency detailed geotechnical information was available for 23 of the sites thereby allowing us to establish a quantitative relationship between the resonance frequency and the thickness of the soil and indirectly between either of them and the shear velocity of the soil the practical application of this relationship has revealed its usefulness in determining the surface structure of a valley with excellent accuracy with an error of only 15 in the depths calculated these errors are due to the simplification of the problem that this method implies it requires that the shear velocity vary constantly with depth throughout the study region which is evidently not always so and that the input data themselves intrinsically have a certain degree of uncertainty this method is therefore not valid when there is no mechanical contrast between the study soil and the underlying layer or when the shear velocity varies irregularly with depth in the study area

the deep bedrock in rome italy a new constraint based on passive seismic data analysis seismic resonance inside sedimentary basins severely influences ground shaking at the free surface in case of earthquakes starting from few observations of a low frequency resonance in the historical center of rome italy we performed several single station ambient vibration measures to verify and estimate the resonance frequency in a wide area of the city by horizontal to vertical spectral ratio method we verified a stable low frequency peak in the range 0 3 0 4 hz recordings of august 24th 2016 mw 6 0 amatrice earthquake available both inside and outside the basin of rome confirm the presence of high energy components at frequencies of 0 2 0 4 hz within the basin these observations support the hypothesis of a deep seismic impedance contrast responsible for the low frequency resonance to infer the depth range of subsoil deposits related to this impedance contrast we analyzed ambient vibration data recorded by 2 d seismic arrays aiming at retrieving the shear wave velocity structure up to relevant depths to increase the investigation depth up to 2000 m we jointly inverted for rayleigh waves dispersion and ellipticity curves and resonance frequency the shear wave velocity profile shows two main discontinuities at depths of about 500 m and 1800 m that can be related to the bottom of the plio pleistocene filling of the rome basin and to the top of the basal limestone formation respectively these results fill a gap of knowledge about the deep velocity structure in the city that may be helpful for ground motion scenario studies

mapping the palaeo piniada valley central greece based on systematic microtremor analyses the application of seismic noise based techniques has become particularly popular in the last decades as they are not invasive and do not require large teams or expensive equipments the horizontal to vertical spectral ratio hvsr is commonly used not only in seismic microzoning studies as far as from noise recording constraining the fundamental resonant frequency but it is also possible to infer the depth of the bedrock knowing the average shear wave velocity of the overlying sedimentary cover or viceversa i e resonance equation for the purposes of the present research more than 300 single station noise measurements were carried out across the piniada valley central greece along and between several transects planned roughly perpendicular to the mean valley trend to understand the palaeogeographic and tectonic evolution of this area we needed an estimation of the geometry at depth of the bedrock underlying the fluvial deposits of the present day pinios river as a result for each measured site we calculated the depth of the bedrock and afterwards such values were opportunely interpolated for obtaining a 3d model of the palaeo piniada valley documenting for the first time the recent late quaternary inversion of the topographic gradient

linkages between geochemistry and microbiology in a proglacial terrain in the high arctic abstract proglacial environments are ideal for studying the development of soils through the changes of rocks exposed by glacier retreat to weathering and microbial processes carbon c and nitrogen n contents as well as soil ph and soil elemental compositions are thought to be dominant factors structuring the bacterial archaeal and fungal communities in the early stages of soil ecosystem formation however the functional linkages between c and n contents soil composition and microbial community structures remain poorly understood here we describe a multivariate analysis of geochemical properties and associated microbial community structures between a moraine and a glaciofluvial outwash in the proglacial area of a high arctic glacier longyearbreen svalbard our results reveal distinct differences in developmental stages and heterogeneity between the moraine and the glaciofluvial outwash we observed significant relationships between c and n contents 13 c org and 15 n isotopic ratios weathering and microbial abundance and community structures we suggest that the observed differences in microbial and geochemical parameters between the moraine and the glaciofluvial outwash are primarily a result of geomorphological variations of the proglacial terrain

diel behavior of rare earth elements in a mountain stream with acidic to neutral ph abstract diel 24 h changes in concentrations of rare earth elements ree were investigated in fisher creek a mountain stream in montana that receives acid mine drainage in its headwaters three simultaneous 24 h samplings were conducted at an upstream station ph 3 3 an intermediate station ph 5 5 and a downstream station ph 6 8 the ree were found to behave conservatively at the two upstream stations at the downstream station ree partitioned into suspended particles to a degree that varied with the time of day and concentrations of dissolved ree were 2 9 to 9 4 fold 190 to 830 higher in the early morning vs the late afternoon the decrease in dissolved ree concentrations during the day coincided with a corresponding increase in the concentration of ree in suspended particles such that diel changes in the total ree concentrations were relatively minor 27 to 55 increase at night across the lanthanide series the heavy ree partitioned into the suspended solid phase to a greater extent than the light ree filtered samples from the downstream station showed a decrease in shale normalized ree concentration across the lanthanide series with positive anomalies at la and gd and a negative eu anomaly as the temperature of the creek increased in the afternoon the slope of the ree profile steepened and the magnitude of the anomalies increased the above observations are explained by cyclic adsorption of ree onto suspended particles of hydrous ferric and aluminum oxides hfo hao conditional partition coefficients for each ree between the suspended solids and the aqueous phase reached a maximum at 1700 hours and a minimum at 0700 hours this pattern is attributed to diel variations in stream temperature possibly reinforced by kinetic factors i e slower rates of reaction at night than during the day estimates of the enthalpy of adsorption of each ree onto suspended particles based on the field results averaged 82 kj mol and are similar in magnitude to estimates in the literature for adsorption of divalent metal cations onto clays and hydrous metal oxides the results of this study have important implications to the use of ree as hydrogeochemical tracers in streams

the application of hvsr method in detecting sediment thickness in karst collapse area of pearl river delta china the microtremor horizontal to vertical spectral ratio hvsr or h v spectral ratio method is an effective tool for detecting sediment thickness firstly single station microtremor measurements were taken beside 52 boreholes located in pearl river delta china sediment thicknesses revealed by those boreholes range from 7 9 to 39 6 m then those microtremor data were analyzed using hvsr method and peak frequency of each site was extracted according to those peak frequencies of hvsr and corresponding sediment thicknesses the frequency to thickness fitting f z equation which is suitable for pearl river delta area was established and this equation was compared with several fitting equations derived from different regions by other researchers finally this fitting equation was applied in a collapse area in guangzhou city to estimate site sediment thickness compared with data from five boreholes in this collapse area the consistency between estimated sediment thickness and real value was relatively good karst sinkholes are generally located in regions where thickness of sediments is shallow therefore the method described in this paper can provide support for delineating potential collapse areas

reproduction of microseism h v spectral features using a three dimensional complex topographical model of the sediment bedrock interface in the osaka sedimentary basin summary estimating the velocity structure of microseisms based on the horizontal to vertical spectral ratio hvsr is an extremely practical means of modelling the subsurface structure necessary for strong ground motion predictions thus beyond the traditional framework of the 1 d velocity structure the hvsr derived from observation records of microseisms microtremors with a frequency of about 1 hz or lower originating from ocean waves in areas where the sediment bedrock interface has irregular topographies was reproduced by finite differential method fdm based simulation this study was conducted for the osaka sedimentary basin the sediment bedrock interface of which is three dimensionally complicated and contains grabens steps and ramps because high precision models for this basin have been constructed based on a wide range of existing exploration information the hvsrs of two components the east west direction and the north south direction to the vertical direction derived from the fdm simulations were both well reproduced in terms of not only the peak frequency hvfp but also the spectral curves for a number of observation sites above the sediment bedrock interface with complex geological features these results suggest that with a sufficient number of observation sites for microtremors and highly accurate a priori information on geophysical constants in the sedimentary layer that spatially serves as the reference the irregular shaped sediment bedrock interface may be estimated based on how well the hvsr curves and the hvfp agree between the observations and simulations furthermore the fdm simulations confirmed observed phenomena such as the polarization of the amplitude of horizontal motions and broad or plateau like hvsr peaks of microseisms in grabens and step structures it was determined that the hvfps in areas with these strong irregularities are higher than the peak frequency of rayleigh wave ellipticity for the fundamental mode rhvfp based on the 1 d velocity structure in addition there was a difference of about 20 per cent at most between the hvfp derived from fdm simulations and the rhvfp in areas where the depth of the sediment bedrock interface varies only slightly

velocity models and site effects at kawah ijen volcano and ijen caldera indonesia determined from ambient noise cross correlations and directional energy density spectral ratios abstract two different ambient seismic noise techniques allow the determination of velocity models at ijen caldera and kawah ijen volcano at ijen caldera two average velocity models are constrained down to a depth of 3 km by inverting the stacked dispersion curve obtained by ambient noise cross correlation in addition four local velocity models were obtained by inverting the horizontal to vertical spectral ratio of the directional energy densities of ambient noise dedhvr i e computed through auto correlation of ambient noise this set of velocity models is then compared to the geology of the caldera and the local discontinuities are evidenced at kawah ijen volcano a map of local dominant frequencies is provided by the dedhvr measurements recorded at 87 sites around kawah ijen volcano the horizontality of the shallow layers and the great outcrop of the crater rim facilitate the interpretation of the dedhvrs furthermore the inversion of several juxtaposed dedhvrs provided a complete 2 d velocity model of the flank of the crater unlike other stratovolcanoes the kawah ijen appears to have a remarkably homogeneous structure the dedhvr technique is used for the first time in a volcanic environment and shows a great potential for an accurate and fast computation of the velocity model on volcanoes

the buried shape of an alpine valley from gravity surveys seismic and ambient noise analysis summary it has long been observed that damage due to earthquakes depends greatly on local geological conditions alpine valleys represent a typical populated environment where large amplifications can take place owing to the presence of surface soils with poor mechanical properties combined to complex topography of the rock basin in the framework of the eu interreg iiib sismovalp project seismic hazard and alpine valley response analysis a stretch of the tagliamento river valley trv located in the north western part of the friuli region italy and close to the epicentre of the 1976 mw 6 4 earthquake has been investigated with the aim to define the buried shape of the valley itself two non invasive low cost independent geophysical methods were used i detailed gravity survey and ii h v spectral ratio hvsr of microtremors because of structural geological complexity and active tectonics of the friuli region an irregular valley shape was expected in this area the independent analysis performed by gravity and passive noise and complemented with refraction seismic velocity profiles confirms this hypothesis and leads to two models that were consistent but for some small scale details the maximum depth estimated is about 400 450 m in the southern part of the valley while a mean value of 150 180 m is estimated in the northern part the sediment thickness obtained for this stretch of the trv is quite large if compared to eastern alps plio quaternary rates therefore the valley shape imaged by this study better corresponds to the top of carbonate rocks finally on the basis of the obtained morphology and some direct measurements we conclude that the trv features an overall 1 d seismic response i e the resonance is related only to the sediment thickness rather than to the cross section shape but in its deepest part some limited 2 d effects could take place

experimental and numerical evidence of the clustering effect of structures on their response during an earthquake a case study of three identical towers in the city of grenoble france in this article interpretation of an equivalent to a macroseismic intensity survey performed in three identical stand alone buildings located in grenoble france after an m l 4 1 earthquake reveals a clustering effect resulting in different levels of perception of seismic loading by inhabitants the clustering effect is confirmed using numerical simulation the variation of the seismic response of the building in the middle of the cluster depends on the azimuth of the seismic source relative to the building cluster the major effect is the splitting of its resonance frequency accompanied by a decrease in vibration amplitude we conclude that clustering has an impact on urban effects calling into question the validity of seismic design which considers buildings in urban areas as stand alone constructions and the interpretation of macroseismic intensity surveys conducted in dense urban areas

a study of the seismic response of the city of benevento southern italy through a combined analysis of seismological and geological data abstract a previous analysis improta l g di giulio and a rovelli 2005 variations of local seismic response in benevento southern italy using earthquakes and ambient noise recordings j seism 9 191 210 of small magnitude earthquakes recorded at 12 sites within the city of benevento has stressed the significant role played by near surface geology in causing variability of the ground motion in this paper we extend the study of the seismic response from 12 sites to the entire urban area based on inferences from the comparison at the 12 sites between earthquake and ambient vibration results we have collected ambient noise at about 100 sites within the city intensifying measurements across the main shallow geological variations we use borehole data to interpret ambient noise h v spectral ratios in terms of near surface geology comparing h v curves to theoretical transfer functions of 1d models along five well constrained profiles on the basis of geological geotechnical and seismic data we identify three main typologies of seismic response in the city each type of response is associated to zones sharing common soil conditions and similar soil classes according to building codes for seismic design moreover we find that the spatial variation of the seismic response in the ancient town area is consistent with the damage pattern produced by a very destructive well documented historical earthquake that struck the city in 1688 causing mcs intensity of ix x in benevento finally we use ground motions recorded during the experiment by improta et al improta l g di giulio and a rovelli 2005 variations of local seismic response in benevento southern italy using earthquakes and ambient noise recordings j seism 9 191 210 to generate synthetic seismograms of moderate to strong mw 5 7 molise 2002 and ms 6 9 1980 irpinia earthquakes we calibrate the random summation technique by ordaz et al ordaz m j arboleda and s k singh 1995 a scheme of random summation of an empirical green s function to estimate ground motions for future large earthquakes bull seism soc am 85 1635 1647 using recordings of these earthquakes available in benevento after a satisfactory fit between observed and synthetic seismograms we compute response spectra at different sites and speculate on effects of the geology class at large level of shaking including soil nonlinearity we find that large discrepancies from design spectra prescribed by seismic codes can occur for a wide sector of benevento especially for periods

identifying 2d resonance in microtremor wave fields to predict local site effects during earthquakes we must know the geometrical and mechanical properties of local sedimentary structures and their resonance behavior we present a concept to identify resonance modes for 2d structures this is done for synthetic as well as measured microtremor wave fields the microtremor data were investigated by using the reference station and horizontal to vertical h v methods analyzing the synthetic microtremor data in profiles across 2d structures the reference station method rsm turned out to be much more suitable for the detection of 2d resonances than the h v method we therefore focused on rsm when analyzing the measurement data from two test sites in switzerland the st jakob tullingen trough near basel in the north and a site in the rhone valley near the village vetroz in the south the results of these two test sites led to different conclusions whereas the spectral peaks in data of the st jakob tullingen trough were not well developed and could only tentatively be interpreted those from the rhone valley clearly exhibited 2d resonance effects the sh 00 and the sv fundamental mode could be successfully identified at 0 32 0 03 and 0 35 0 03 hz respectively

site effect evaluation in the basin of santiago de chile using ambient noise measurements summary we performed extensive ambient vibration measurements in the basin of santiago de chile chile and we look for testing the reliability of the horizontal to vertical amplitude spectra ratio method h v as a tool to provide qualitative and quantitative information of site effects in complex geological media the interpretation of the h v data was carried out conformably to the sesame project consensus criteria and outlines three major patterns 1 clear peaked h v curves related to sharp underground velocity contrast 2 h v peak of low amplitude and flat curve related to weak contrast and 3 broad h v peak indicating the presence of strong lateral variations of underground structure h v measurements however reveal a discrepancy between the computed soil resonance frequencies and the expected building resonance therefore not leading to a straight interpretation of the intensity distribution derived from observed damage to one storey houses in santiago after the 1985 valparaiso earthquake indeed the h v technique mostly maps the first fundamental frequency however it fails to show higher resonance modes in the case of the city of santiago this method works well for assessing the seismic hazard for high rise buildings but is questionable for smaller structures as is the case of a great percentage of constructions in the city

paleotopographic control of landslides in lacustrine deposits trieves plateau french western alps paleotopography in quaternary sedimentary environments can be an important factor that controls landslide movement this study investigates the relation between paleotopography and landslide activity in two adjacent landslides in glaciolacustrine sediments located in the trieves area french western alps although both are in slopes underlain by the same lacustrine deposits the avignonet and harmaliere landslides exhibit major differences in morphology and displacement rates through a combination of geological mapping airborne light detection and ranging lidar data aerial photographs global positioning system gps and seismic noise measurements a three dimensional impression was made of both landslides the analysis reveals that the difference in kinematics between the two mass movements can be traced back to at least 50 years ago the results show that the harmaliere slide which failed catastrophically in 1981 is still much more active than the avignonet landslide the fear was that the avignonet landslide might develop in a similar catastrophic manner threatening a number of houses constructed on the landslide a geophysical survey based on ambient noise measurements allowed us to map the base of the lacustrine clays and the results indicate the presence of a n s ridge of hard sediments jurassic bedrock and or compact alluvial layers on the eastern side of the avignonet landslide this ridge disappears when approaching the harmaliere landslide and makes a place to what can be interpreted as a nw se oriented paleovalley of the river drac we proposed that the ridge acts as a buttress that could mechanically prevent the avignonet landslide from evolving as fast as the harmaliere furthermore the nw se paleovalley located under the harmaliere landslide corresponds to the motion direction of the slide therefore the different behaviour of the two landslides is partly controlled by the paleotopographic setting of lake trieves during the last glacial maximum extension these results suggest a major influence of the bedrock paleotopography on the kinematics of the landslides

the effect of lateral heterogeneity on horizontal to vertical spectral ratio of microtremors inferred from observation and synthetics abstract horizontal to vertical h v spectral ratios of microtremors hvrm have been traditionally interpreted as representing either the s wave amplification directly or the rayleigh wave ellipticity for a horizontally layered structure however based on the diffuse field theory we have derived an alternative theoretical basis that hvrm corresponds to the square root of the ratio between the imaginary part of the horizontal green s function and that of the vertical one under that condition the 1d horizontal layering assumption is not needed to interpret hvrm as observational evidence of such non 1d hvrm we discovered significant directional dependency at a site on the uji campus kyoto university japan the observed microtremor north south vertical spectral ratios are quite stable and have only one peak around 0 5 hz on the other hand the east west vertical spectral ratios are smaller in amplitude and have higher peak frequencies and sometimes two separated peaks the directional dependency of observed hvrm is aligned to the axis of the 2d basin structure we performed numerical analyses by spectral element method using a unit load on the surface to examine the effect of the 2d basin structure on the imaginary parts of the green s functions we found that the 2d basin structure clearly changes the characteristics of the h v spectral ratios in both perpendicular and parallel directions relative to the basin axis thus we succeeded in theoretically simulating the qualitative difference between the h v spectral ratios for two orthogonal horizontal components of the hvrm observed on the uji campus online material snapshots and animations of wave propagation

preliminary map of soil s predominant periods in barcelona using microtremors in order to evaluate soil effects in the urban area of barcelona the nakamura s technique has been used to estimate the predominant periods of soils noise measurements for 195 sites were performed using a strong motion accelerograph and a velocimeter in this work the resulting preliminary map of predominant periods is presented the obtained predominant periods are coherent with the geological and geotechnical features of the area the analysis of the information has allowed the distinctions among several types of soil and underlying materials a predominant period of about 0 06 s is evaluated for sites located over outcrop paleozoic rock in the tibidabo collserola mountains for sites consisting of material named tricycle that is the most extensive and also the most heterogeneous zone predominant period range from 0 10 s up to 2 0 s depending on the thickness of the surface materials and the kind and thickness of the underlying materials in the besos river two zones are observed the riverside with periods between 0 50 s and 0 83 s and a second area with periods between 1 0 and 2 1 s in the llobregat river delta the obtained periods are quite homogeneous with values around 0 72 s other predominant periods are found in some tertiary rock outcrop

geometry and evolution of a fault controlled quaternary basin by means of tdem and single station ambient vibration surveys the example of the 2009 l aquila earthquake area central italy we applied a joint survey approach integrating time domain electromagnetic soundings and single station ambient vibration surveys in the middle aterno valley mav an intermontane basin in central italy and the locus of the 2009 l aquila earthquake by imaging the buried interface between the infilling deposits and the top of the pre quaternary bedrock we reveal the 3 d basin geometry and gain insights into the long term basin evolution we reconstruct a complex subsurface architecture characterized by three main depocenters separated by thresholds basin infill thickness varies from 200 300 m in the north to more than 450 m to the southeast our subsurface model suggests a strong structural control on the architecture of the basin and highlights that the mav experienced considerable modifications in its architecture over time the buried shape of the mav suggests a recent and still ongoing predominant tectonic control by the nw se trending paganica san demetrio fault system psdfs which cross cuts older ca ene and nne trending extensional faults furthermore we postulate that the present day arrangement of the psdfs is the result of the linkage of two previously isolated fault segments we provide constraints on the location of the southeastern boundary of the psdfs defining an overall 19 km long fault system this allows for earthquakes larger than m6 5 this study emphasizes the benefit of combining two easily deployable geophysical methods for reconstructing the 3 d geometry of a tectonically controlled basin our joint approach provided us with a consistent match between these two independent estimations of the basin substratum depth within 15

assessment of site effects in alpine regions through systematic site characterization of seismic stations abstract in the framework of the renewal project of the swiss strong motion network ssmnet a procedure for site characterization has been established the aim of the procedure was to systematically derive realistic 1d velocity profiles at each station it is mainly based on the analysis of surface waves particularly from passive experiments and includes cross checks of the derived amplification functions with those obtained through spectral modeling of recorded earthquakes the systematic use of three component surface wave analysis allowing the derivation of both rayleigh and love dispersion curves also contributes to the improvement of the quality of the retrieved profiles the procedure is applied to the 30 ssmnet stations installed on various site types within the project covering different aspects of seismic risk the characterization of these 30 sites gives an overview of the variety of possible effects of surface geology on ground motion in the alpine area such effects ranged from deamplification at hard rock sites to amplification up to a factor of 15 in lacustrine sediments with respect to the swiss reference rock velocity model the derived velocity profiles are shown to reproduce observed amplification functions from empirical spectral modeling although many sites are found to exhibit 1d behavior the procedure allows the detection and qualification of 2d and 3d effects the sites are therefore classified with respect to the occurrence of 2d 3d resonance and edge generated surface waves in addition to the large and deeply incised alpine valleys of the rhone the rhine and the aar smaller structures such as local alpine valleys and alluvial fans are shown to exhibit 2d 3d behavior

on the limitation of the h v spectral ratio using seismic noise as an exploration tool application to the grenoble valley france a small apex ratio basin the h v spectral ratio method based on seismic noise hvsrn was used in the grenoble basin france an alpine valley characterized by a small apex ratio the resonance frequencies obtained in the experiments were compared to the thickness of the sediments deduced from a microgravimetric survey and to the 1 d theoretical assessment of site responses given the abundance of data on the sediments and depth of the basin the values of the theoretical resonance frequency fo can be determined quite accurately however it has been observed that the effects of basin geometry can disturb fo measurements using the hvsr method in particular for a case like the grenoble basin which has a small apex ratio w h and strong suspected 2 d and or 3 d effects interpretation of fo values in terms of bedrock depth gives rise to estimation errors of about 10 in certain cases with the most significant errors 50 occurring on the edges of the basin where subsurface layers are characterised by larger heterogeneities and where the basin topography is accentuated this study suggests that great care must be taken when using the hvsrn method as an exploration tool at least in valleys with a small apex ratio

site effect study in urban area experimental results in grenoble france three methods are used to determine the site effect in the town of grenoble located in the western alps first we use the classical spectral ratio method in 14 sites to calculate the transfer function of the basin we find an amplification of 10 in the frequency range of 0 25 to 10 hz second we compare these results with the h over v spectral ratio method and propose a map of resonance frequency of the basin we find a lower resonance frequency in the center of the basin than on the edge that is consistent with the structure deduced from a gravity bouguer anomaly map finally we use the empirical green s function method to simulate a m w 5 5 earthquake at a distance of 20 km from the town the simulated acceleration reaches the level of 2 m s2 in the center of the basin compared to 0 2 m s2 on the edges the simulated ground motion we compute is smaller than the french seismic codes on the edge of the valley but significantly larger in the center

geophysical and geomorphological investigations of a quaternary karstic paleolake and its underground marine connection in cassis bestouan cassis se france an original karstic system in a coastal alluvial plain located in a carbonate environment cassis provence se france was studied using a multi method approach electrical resistivity tomography gravimetric passive seismic survey combined with geomorphologic methods surface observations and drilling limestone dissolution and or cavity collapse led to the development of a polje which was filled rapidly by erosion of aptian marls the combination of several dating and paleoenvironmental proxies indicates that the polje was filled during a glacial period mis 6 8 or 10 i e in the 130 360 ka age range this discovery has implications for the understanding of karst processes the connection between the polje and the three km long bestouan underwater karstic conduit with submarine outlet is strongly suggested by sedimentological studies and geophysical prospections

subsurface profiling of granite pluton using microtremor method southern aravalli gujarat india we report using the microtremor method a subsurface granitic pluton underneath the narukot dome and in its western extension along a wnw profile in proximity of eastern fringe of cambay rift india the dome and its extension is a part of the champaner group of rocks belonging to the mesoproterozoic aravalli supergroup the present finding elucidates development of an asymmetric double plunge along narukot dome microtremor measurements at 32 sites were carried out along the axial trace n95 of the dome fourier amplitude spectral studies were applied to obtain the ratio between the horizontal and vertical components of persisting rayleigh waves as local ambient noise fundamental resonant frequencies with amplitude 1 sigma for each site are considered to distinguish rheological boundary two distinct rheological boundaries are identified based on frequency ranges determined in the terrain 1 0 2219 10 364 hz recorded at 31 stations identified as the champaner metasediment and granite boundary and 2 10 902 27 1119 hz recorded at 22 stations identified as the phyllite and quartzite boundary the proposed equation describing frequency depth relationship between granite and overlaying regolith matches with those already published in the literature the morphology of granite pluton highlights the rootless character of champaner group showing sharp discordance with granitic pluton the findings of manifestation of pluton at a shallower depth imply a steep easterly plunge within the champaner metasediments whereas signature of pluton at a deeper level implies a gentle westerly plunge the present method enables to assess how granite emplacement influences the surface structure

combining borehole log stratigraphies and ambient vibration data to build a 3d model of the lower var valley nice france abstract in seismic hazard studies site effects assessment is based on an accurate knowledge of mechanical properties and geometry of superficial geological formations the lower var valley nice southeastern france is a 2 km wide fluvial sedimentary basin where site effects have been observed on earthquake recordings in addition this area is a significant economically developing zone including the second largest airport of france therefore it is highly important to define a 3d sub surface model of the basin to understand the ground motion amplifications based on the compilation of several years of geotechnical and geophysical studies the quaternary alluvial deposits of the lower var valley were investigated using 331 borehole log stratigraphies and 439 ambient vibration measurements these data were combined in a commercial software that models and allows to visualize geoscientific data and geological models in 3d the borehole log stratigraphies helped to define a representative lithostratigraphic soil profile and the geometry of the different sedimentary layers only few boreholes are reaching the engineering bedrock pliocene conglomerates characterized by a s wave velocity larger than 800 m s 1 from the ambient vibration data the fundamental resonance frequency identified from h v curves indicates the bedrock depth using the well known f0 vs 4h relationship these h v curves were interpreted using geological knowledge of the studied zone our results show that the bedrock depth varies in the center of the valley between 50 m in the northern part of the studied zone and more than 100 m on the river estuary first the average s wave velocity in the alluvial deposits is estimated according to combined analysis of the borehole log stratigraphies and h v calculations on ambient vibration measurements the spatial variability of this velocity has been translated into a velocity zonation of the valley second this zonation allows us to extrapolate the quaternary pliocene limit in the whole valley the 3d model of the lower var valley will be useful in future numerical simulations of seismic ground motions in order to evaluate and mitigate seismic risk in the area

interaction between tectonic and erosion processes on the morphogenesis of an alpine valley geological and geophysical investigations in the lower romanche valley belledonne massif western alps in the belledonne massif the steep paleozoic belledonne middle fault bmf separates micaschists displaying numerous landslides from amphibolites the massif is incised by the lower romanche river valley when crossing the bmf the valley widens into a lozenge shaped basin recently interpreted as an active pull apart type structure associated with a major n110 striking quaternary fault multidisciplinary investigations were carried out in the basin to check if this model has implications on the seismic and landslide hazard assessment this study demonstrated the existence of a n80 sinistral strike slip sechilienne fault zone sfz this fault zone is suspected to offset the bmf by 375 m across the basin geophysical experiments revealed that the bedrock depth increases strongly in the basin up to 350 m our study invalidates the active pull apart origin of the basin and suggests it results from quaternary glacial and fluvial erosion processes magnified by the intersection of two inherited structures the bmf and the sfz

site effects and microzonation in the city of thessaloniki greece comparison of different approaches ten seismological stations were installed for 3 months in the city of thessaloniki greece to record earthquakes and ambient noise over areas of different geotechnical characteristics about 40 local earthquakes were recorded with a good signal to noise ratio in more than two stations we analyze the records with three different techniques a the classical spectral ratios to a reference station b the receiver functions and c the horizontal to vertical h v spectral ratios on noise recordings the results are compared in terms of predominant frequencies and amplification levels the three methods are found equally able to reveal the fundamental frequency regarding local site amplification they provide significantly different results with a general trend of the two h v ratio methods b and c to underestimate the amplification levels compared to that inferred from the classical spectral ratio technique a the results are then used in relation with the microzonation of the city of thessaloniki a good correlation is found between the local site amplification and the type and age of the local geological formation as well as with the depth of bedrock finally we compare our observations with the damage distribution in the city which was hit by a magnitude 6 5 earthquake in 1978 the amplification levels from spectral ratios obtained at each site exhibit a good agreement with the map of damage intensity

site effect evaluation using spectral ratios with only one station the spectral ratio technique is a common useful way to estimate empirical transfer function to evaluate site effects in regions of moderate to high seismicity the purpose of this paper is to show that it is possible to estimate empirical transfer function using spectral ratios between horizontal and vertical components of motion without a reference station the technique originally proposed by nakamura to analyze rayleigh waves in the microtremor records is presented briefly and it is discussed why it may be applicable to study the intense s wave part in earthquake records results are presented for three different cities in mexico oaxaca oax acapulco gro and mexico city these cities are very different by their geological and tectonic contexts and also by the very different epicentral distances to the main seismogenic zones affecting each city each time we compare the results of nakamura s technique with standard spectral ratios in all three cases the results are very encouraging we conclude that if site effects are caused by simple geology a first estimate of dominant period and local amplification level can be obtained using records of only one station

site response attenuation and source spectra of s waves along the guerrero mexico subduction zone acceleration spectra from nine earthquakes and up to 11 stations per earthquake are inverted to find the source spectra the site response and the quality factor q of s waves this method is applied to moderate earthquakes 4 0 0 8 hz does not follow a simple linear relation as observed in previous studies of attenuation in other regions when the source spectra are interpreted in terms of brune s model the stress drops obtained are less than 20 bars for the four larger events analyzed the site functions obtained indicate that although all the stations used are on rock the effect of the near surface geology caused important amplifications at some stations

1 d and 2 d resonances in an alpine valley identified from ambient noise measurements and 3 d modelling summary h v spectral ratios are regularly used for estimating the bedrock depth in 1 d like basins exhibiting smooth lateral variations in the case of 2 d or 3 d pronounced geometries observational and numerical studies have shown that h v curves exhibit peculiar shapes and that the h v frequency generally overestimates 1 d theoretical resonance frequency to investigate the capabilities of the h v method in complex structures a detailed comparison between measured and 3 d simulated ambient vibrations was performed in the small size lower romanche valley french alps which shows significant variations in geometry downstream and upstream the sechilienne basin analysing the h v curve characteristics two different wave propagation modes were identified along the valley relying on previous geophysical investigation a power law relationship was derived between the bedrock depth and the h v peak frequency which was used for building a 3 d model of the valley geometry simulated and experimental h v curves were found to exhibit quite similar features in terms of curve shape and peak frequency values validating the 3 d structure this good agreement also evidenced two different propagation modes in the valley 2 d resonance in the sechilienne basin and 1 d resonance in the external parts this study underlines the interest of h v curves for investigating complex basin structures

contribution of dense array analysis to the identification and quantification of basin edge induced waves part ii application to grenoble basin french alps settled on a deep sediment filled valley the city of grenoble french alps faces important site effects large amplification and significant duration in crease of ground motion even for moderate size events in order to study multidi mensional site effects a very dense array composed of 29 three component seis mometers over a 1 km aperture was operated during spring 1999 in the center of the city a total of 18 events 6 local 4 regional and 8 teleseismic with an acceptable signal to noise ratio could be recorded over a 4 month period the complexity of the wave field and in situ seismic noise constraints led us to develop a procedure based on time frequency coherence and the multiple signal classification algorithm to iden tify and characterize wave arrivals cornou et al 2003 applying the procedure to the 18 records it is clearly indicated that ground motion inside the valley is domi nated by basin edge induced waves that carry 4 times more energy than the direct wave field regardless of the type of event considered in addition the basin induced wave field is composed of 60 rayleigh waves and 40 love waves when consid ering energy carried by the three components if one considers only the energy of horizontal components this proportion is 50 rayleigh waves and 50 love waves the diffraction phenomena are mostly constrained by the 3d structure of the basin regardless of the azimuth of the event a study of the relative contribution of 1d and 2d 3d effects on recorded ground motion suggests at least at frequencies below 1 hz that the difference between the standard spectral ratio and 1d transfer function or possibly the horizontal to vertical ratio receiver function and nakamura esti mates might be due mainly to laterally propagating waves

new approach for coupling k 2 and empirical green s functions application to the blind prediction of broad band ground motion in the grenoble basin summary we present a new approach for performing broad band ground motion time histories 0 1 30 hz of a future earthquake in a sedimentary basin synthetics are computed with an hybrid scheme combining reciprocity based 3 d spectral element method simulations at low frequencies and empirical green s functions egf at high frequencies the combination between both deterministic and empirical parts results in a set of hybrid green s functions summed according to a new k 2 kinematic model algorithm the summation technique enables to remove the high frequency artefacts that appear above the egf corner frequency the ground motion variability is assessed by generating a variety of source parameter sets selected from ap rioriprobability density functions this leads to a population of response spectra from which the median spectral acceleration and standard deviation values are derived the method is applied to simulate a m w 5 5 event in the deep grenoble basin french alps the comparison with ec8 regulations suggests the need of specific design spectra in the grenoble valley

multimethod characterization of the french pyrenean valley of bagneres de bigorre for seismic hazard evaluation observations and models a narrow rectilinear valley in the french pyrenees affected in the past by damaging earthquakes has been chosen as a test site for soil response characteriza tion the main purpose of this initiative was to compare experimental and numerical approaches a temporary network of 10 stations has been deployed along and across the valley during two years parallel various experiments have been conducted in particular ambient noise recording and seismic profiles with active sources for struc ture determination at the 10 sites classical observables have been measured for site amplification evaluation such as spectral ratios of horizontal or vertical motions between site and reference stations using direct s waves and s coda and spectral ratios between horizontal and vertical h v motions at single stations using noise and s coda records vertical shear velocity profiles at the stations have first been obtained from a joint inversion of rayleigh wave dispersion curves and ellipticity they have subsequently been used to model the h v spectral ratios of noise data from synthetic seismograms the h v ratio of s coda waves based on equipartition theory and the 3d seismic response of the basin using the spectral element method general good agreement is found between simulations and observations the 3d simulation reveals that topography has a much lower contribution to site effects than sedimentary filling except at the narrow ridge crests we find clear evidence of a basin edge effect with an increase of the amplitude of ground motion at some distance from the edge inside the basin and a decrease immediately at the slope foot

investigation of 3 d basin structures in the izmit bay area turkey by single station microtremor and gravimetric methods summary we investigate 3 d basin structures and site resonance frequencies in the izmit bay area of turkey by new geophysical surveys based on 239 single station microtremor and 405 point gravity measurements a fundamental resonance frequency map of the izmit bay was produced from the main peak in the horizontal to vertical component spectral ratio hvsr of microtremors the hvsr analysis of the microtremor data reveals single double broad peaked or no peak type hvsr curves varying in accordance with the surface geology and spatial extent of the three basins present in the izmit bay area in the deepest sections of the izmit golcuk and derince basins of the izmit bay the fundamental resonance frequencies are dominantly 0 24 0 30 hz these resonance frequencies should be taken into consideration along with higher mode frequencies to construct earthquake resistant structures in the izmit bay area the 3 d gravimetric bedrock depth map of the izmit basin shows that the basin has an asymmetric shape with its deepest section coinciding with the surface trace of the north anatolian fault the northern shoulder of the basin has a gentle dip on the kocaeli peneplain side and the southern shoulder is much steeper and it is bounded by the samanli mountains we derive a power law relationship that correlates the fundamental site resonance frequencies with the sedimentary cover thickness obtained from the gravity and shear wave velocity data in the izmit bay we use this relationship to estimate bedrock depths beneath golcuk and derince basins our estimation of maximum basin depths is 1400 m for the izmit and is 800 m for the golcuk and derince basins finally we have analysed a converted sp phase from a local earthquake recording made at site cmp to calculate and verify the sediment thickness estimations obtained from our gravimetric and microtremor analyses this calculation shows close agreement with that of the gravimetric and microtremor results our results show that the basins in the izmit bay area have a very thick sedimentary cover with very low shear velocities underlined by hard bedrock forming a sharp impedance contrast we anticipate that these results will be a key contribution to the quantitative assessment of seismic hazard for the izmit bay area before the occurrence of strong earthquakes in the marmara region

microtremor measurements used to map thickness of soft sediments the observations about the behavior of microtremor spectra presented here show that noise measurements can be used as a powerful tool to determine the thickness of soft cover layers the most suitable method for this determination is nakamura s technique which is the ratio of the horizontal component noise spectrum and that of the vertical component i i v spectrum the frequency of the main peak in these spectral ratios correlates well with the sediment thickness at the site using an extensive database of microtremor measurements carried out in the western lower rhine embayment germany it was possible to show that this correlation is clearly valid for a wide range of thickness namely from tens of meters to more than 1000 m a simple formula was derived that for the sediments to be found in the area investigated directly calculates the cover thickness from the frequency of the main peak in the h v spectrum a comparison with calculated resonant frequencies sug gests the relation derived from the noise measurements depending on the velocity depth function of the shear wave classical spectral ratios are shown to be strongly influenced by the noise level and are therefore less reliable in determining the res onant frequency of the subsoil the practical relevance of the investigation is illus trated by means of cross sections constructed from results of the microtremor anal yses which provide a convincing image of the surficial structure of the areas investigated

determination of shallow shear wave velocity profiles in the cologne germany area using ambient vibrations summary we have used both single station and array methods to determine shallow shear velocity site profiles in the vicinity of the city of cologne germany from ambient vibration records based on fk analysis we assume that fundamental mode rayleigh waves dominate the analysed wavefield in the frequency range of 0 7 2 2 hz according to this view a close relation exists between h v spectral ratios and the ellipticity of the contributing rayleigh waves the inversion of the shape of h v spectral ratios then provides quantitative information concerning the local shear wave velocity structure however based on tests with synthetic data believed to represent a typical situation in the lower rhine embayment dispersion curves were found to provide stronger constraints on the absolute values of the velocity depth model than the ellipticities the shape of the ellipticities was found to be subject to a strong trade off between the layer thickness and the average layer velocity we have made use of this observation by combining the inversion schemes for dispersion curves and ellipticities such that the velocity depth dependence is essentially constrained by the dispersion curves while the layer thickness is constrained by the ellipticities in order to test this method in practice we have used array recordings of ambient vibrations from three sites where the subsurface geology is fairly well known and geotechnical information is at least partially available in order to keep the parameter space as simple as possible we attempted to fit only a single layer over a half space model however owing to earlier studies from the region we assume a power law depth dependence for sediment velocities for all three sites investigated the inversion resulted in models for which the shear wave velocity within the sediment layer both in absolute value at the surface and in depth dependence are found to be remarkably similar to the results obtained by budny from downhole measurements this is strong support for the interpretation of h v spectral ratios as rayleigh wave ellipticities for all three sites the predicted sh wave site amplification factors at the fundamental frequency are of the order of 5 6 with a slightly smaller value south of cologne

the belledonne border fault identification of an active seismic strike slip fault in the western alps summary in the french western alps east of grenoble we identify the belledonne border fault as an active seismic fault this identification is based on the seismic monitoring of the grenoble area by the sismalp seismic network over the past 12 yr 1989 2000 we located a set of earthquakes with magnitudes ranging from 0 to 3 5 along a 50 km long alignment which runs in a n30 e direction on the western flank of the belledonne crystalline massif available focal solutions for these events are consistent with this direction n36 e strike slip fault with right lateral displacement these events along the belledonne border fault have a mean focal depth of 7 km in the crystalline basement with a probably very low slip rate the belledonne border fault has never been mapped at the surface where the otherwise heavily folded and faulted mesozoic cover makes this identification difficult historical seismicity also shows that over the past two and a half centuries a few events located mainly along the southern part of the belledonne border fault caused damage with the magnitude 4 9 1963 monteynard earthquake reaching intensity vii the most recent damaging event in the study area is the magnitude 3 5 1999 laffrey earthquake intensity v vi although its epicentre lies at the southern tip of the belledonne border fault there is clear evidence that aftershocks were activated by the left lateral slip of a n122 e striking fault the length of the belledonne border fault which could easily accommodate a magnitude 6 event as well as the proximity to the isere valley with its unlithified quaternary deposits up to 500 m thick known to generate marked site effects make the identification of the belledonne border fault an important step in the evaluation of seismic risk in the grenoble area besides the activity observed on the fault will now have to be taken into account in future geodynamic models of the western alps