nonlinear soil response of a borehole station based on one dimensional inversion during the 2005 fukuoka prefecture western offshore earthquake the objective of this article is to present the nonlinear response of a soft sedimentary site based on a one dimensional inversion by a genetic algorithm of the shear wave velocity structure and damping factors of a borehole soil column during the 2005 fukuoka prefecture western offshore earthquake first we confirm that according to the source rupture mechanism the major and minor axes in the horizontal plane at the borehole station are the transverse and radial directions respectively then in order to corroborate in the linear domain the s wave transfer function of the borehole s logging we perform time dependent spectral ratios analyses on small aftershocks finally we show qualitative evidence of nonlinearity during the main shock associated with a significant shift toward low frequencies of several resonant modes and we evaluate the degree of nonlinearity by inverting the shear wave veloc ity structure and damping factors because of a directional effect present only in the major axis around 8 hz which prevents the use of the conventional objective function that minimizes the integrated residuals between observed and theoretical ratios we introduce a simple objective function that depends only on peaks frequency and amplitude the efficiency of the objective function and the robustness of the inversion are shown by performing eight independent inversions converging to very similar minima

temporal changes of shallow seismic velocity around the karadere duzce branch of the north anatolian fault and strong ground motion we analyze temporal variations of seismic velocity along the karadere duzce branch of the north anatolian fault using seismograms generated by repeating earthquake clusters in the aftershock zones of the 1999 mw7 4 izmit and mw7 1 duzce earthquakes the analysis employs 36 sets of highly repeating earthquakes each containing 4 18 events the events in each cluster are relocated by detailed multi step analysis and are likely to rupture approximately the same fault patch at different times the decay rates of the repeating events in individual clusters are compatible with the omori s law for the decay rate of regional aftershocks a sliding window waveform cross correlation technique is used to measure travel time differences and evolving decorrelation in waveforms generated by each set of the repeating events we find clear step like delays in the direct s and early s coda waves sharp seismic velocity reduction immediately after the duzce main shock followed by gradual logarithmic type recoveries a gradual increase of seismic velocities is also observed before the duzce main shock probably reflecting post seismic recovery from the earlier izmit main shock the temporal behavior is similar at each station for clusters at various source locations indicating that the temporal changes of material properties occur in the top most portion of the crust the effects are most prominent at stations situated in the immediate vicinity of the recently ruptured fault zones and generally decrease with normal distance from the fault a strong correlation between the co seismic delays and intensities of the strong ground motion generated by the duzce main shock implies that the radiated seismic waves produced the velocity reductions in the shallow material

interferometric daylight seismic imaging summary claerbout s daylight imaging concept is generalized to a theory of interferometric seismic imaging ii interferometric seismic imaging is defined to be any algorithm that inverts correlated seismic data for the reflectivity or source distribution as examples we show that ii can image reflectivity distributions by migrating ghost reflections in passive seismic data and generalizes the receiver function imaging method used by seismologists interferometric seismic imaging can also migrate free surface multiples in common depth point cdp data and image source distributions from passive seismic data both synthetic and field data examples are used to illustrate the different possibilities of ii the key advantage of ii is that it can image source locations or reflectivity distributions from passive seismic data where the source position or wavelet is unknown in some cases it can mitigate defocusing errors as a result of statics or an incorrect migration velocity the main drawback with ii is that severe migration artefacts can be created by partial focusing of virtual multiples

observed evolution of linear and nonlinear effects at the dahan downhole array taiwan analysis of the september 21 1999 m 7 3 chi chi earthquake sequence in this paper the site characteristics of the dahan downhole array are studied by analyzing the september 21 1999 m 7 3 chi chi earthquake sequence including the main shock and some aftershocks the four level array 0 m 50 m 100 m and 200 m is located to the north of hualien city in eastern taiwan polarization analysis is used to check the orientation errors of the seismometers at different levels of depth if the surface instrument is chosen as reference the angle between the major polarization axes of the surface and any downhole records is the orientation error that must be corrected for the downhole accelerographs the orientation errors at depths of 50 m 100 m and 200 m are 32 120 and 84 after the corrections the coherency between the surface and downhole records is substantially improved spectral ratio analysis shows that the predominant frequency of the chi chi main shock shifts to a lower frequency we also simulate ground motions at different depths by using the haskell method with a linear velocity structure model the record at surface is chosen as the input motion compared with the observed data ground acceleration can be well reproduced for the aftershocks weak motion events of the september 21 1999 m 7 3 chi chi earthquake however for the chi chi main shock the synthetic waveform cannot match well with the observation neither in amplitude nor in phase this indicates that large ground shaking probably induced the nonlinear site effect at that time and the model used cannot support it

the physical effects of an intra aggregate structure on soil shrinkage clay and soil containing it have shrinkage curves that are qualitatively different in shape the objective of this work is to qualitatively show with maximum simplicity how a clay shrinkage curve turns into a soil shrinkage curve because of the crack volume the measured shrinkage curve is not the single valued feature of a soil we use a concept of the reference shrinkage curve that is only stipulated by soil shrinkage without cracking single valued and qualitatively similar to an observed shrinkage curve we also use new concepts of an intra aggregate soil structure i a rigid superficial layer of aggregates that loses water during shrinkage and ii lacunar pores micro cracks inside an intra aggregate clay that change in volume during shrinkage then through a series of consecutive steps illustrating each step by a separate graphic presentation we move from a clay shrinkage curve to a soil shrinkage curve with predicted qualitative features that coincide with those experimentally observed in numerous soil shrinkage publications we thereby demonstrate the qualitative physical impact of the intra aggregate structure on soil shrinkage

a comparison and test of various site response estimation techniques including three that are not reference site dependent abstract we compare various site response estimation techniques using after shock data of the 1989 loma prieta earthquake collected in oakland california because of recent interest in comparing results from weak and strong motion to infer any nonlinearity and between direct s and coda waves we pay particular attention to the uncertainties first sediment to bedrock spectral ratio estimates between pairs of sites are compared with those obtained from various generalized inversion approaches where the source and site effects of multiply recorded events are solved for simultaneously we find that the site amplification factors are very similar among these approaches but that the uncertainties can be significantly different depending on how the data are weighted we also examine and test three site response estimation techniques that do not rely on a reference site to estimate source and path effects the first involves a parameterized source and path effects inversion even when the bedrock data are excluded from consideration this approach is found to reveal the frequency dependence of site response at each of the sediment sites the second technique involves taking horizontal to vertical component spectral ratios receiver function type estimates of shear wave aftershock data these are also found to reveal the frequency dependence of site response at the sediment sites and the results for the bedrock site are relatively flat and near unity the third estimate is formed by taking horizontal to vertical component ratios of ambient seismic noise and these are shown to reveal the fundamental resonant frequency of the sediment sites unfortunately discrepancies exist among all of the site response estimates and with one dimensional predictions with respect to a frequency independent scaling factor nevertheless the highly frequency dependent character of site response is well constrained and the fact that non reference site dependent methods are capable of revealing this is promising for site specific hazard assessments in regions that lack adequate reference sites

scenario shakemaps for ottawa canada ottawa ranks third among canadian urban areas in terms of seismic risk scenario shakemaps are generated for the ottawa region to study the expected ground shaking intensity distribution patterns for input to damage and risk studies variability in near surface geology plays an important role in earthquake ground shaking in the region the quarter wavelength method is used to generate frequency dependent amplification functions for typical generic soil profiles across the city using shear wave velocity and depth to bedrock data from 17 250 compiled soil profiles the methodology is validated using the ground motion and did you feel it records from the 2010 m 5 val des bois earthquake which occurred 60 km from ottawa it is noted that the calculated amplifications for typical ottawa soil profiles are often greater than generic national earthquake hazards reduction program factors as applied in building code applications for a scenario earthquake corresponding to the national building code of canada probability level of graphic 1 expected modified mercalli intensity values in soft soil areas of ottawa would be near 7 on average the impact of event location on expected ground motions and intensities was tested by considering the occurrence of a scenario earthquake a given magnitude event at various locations in the region the results of this study may be used as input to seismic risk studies for ottawa 1 embed inline graphic 1 gif

sh propagator matrix and qs estimates from borehole and surface recorded earthquake data summary a new method is proposed for the solving of elastic and anelastic parameters of a medium between two seismometers one in a borehole and one at the surface this allows us to retrieve equivalent quality factors of the materials and at the same time gives wave velocities as well as reflection and transmission coefficients in a layered structure the study of local site effects shows that the quality factor of shallow materials can be completely masked by resonance effects and near surface amplification our method is based on the sh propagator matrix in the time domain this separates the effects of resonance and amplification in the elastic structure from those of attenuation due either to scattering or physical attenuation and we find that the elastic problem is decoupled from the anelastic one after a synthetic test we applied the method to seismic records made with a borehole surface instrument operated in the southern rhine graben valley on the french german border due to high seismic noise at the surface we were only able to resolve a one layered mean 500 m deep structure between the borehole and surface instrument an apparent qs of 40 is found between 1 and 5 hz a frequency band where classical methods failed this is in close agreement with qs at frequencies larger than 15 hz obtained from the classical method based on the slope of spectral ratios

ambient noise and weak motion excitation of sediment resonances results from the tiber valley italy abstract we recorded ambient noise and weak earthquake ground motion on holocene sediments in the tiber valey north of rome in order to help predict the response of these sediments to strong ground motion ambient noise within the valley is high and sharply peaked near 2 5 hz similar peaks are observed along the tiber valley towards the south in and south of rome a small local earthquake simultaneously recorded within the valley and at a reference hard rock site is dominated by energy at 4 to 20 hz at the reference site but appears to excite low frequency resonances at the sediment site we also recorded noise at a small array of four stations within the valley and apply the spatial auto correlation method of aki 1957 1965 to obtain rayleigh wave dispersion between 1 and 5 hz the observed resonance and dispersion can be used to determine velocity structure in the near surface sediments between 1 and 5 hz we obtain phase velocities of approximately 400 to 500 m sec implying a shear wave velocity of 440 to 530 m sec the holocene sediment layer is constrained from geotechnical data to have a thickness of 40 m our velocity results thus predict a quarter wavelength resonance of 2 8 to 3 3 hz close to that observed in the ambient noise and weak motion data

nonlinear ground motion amplification by sediments during the 1994 northridge earthquake it has been known since at least 1898 ref 1 that sediments can amplify earthquake ground motion relative to bedrock for the weak ground motion accompanying small earthquakes the amplification due to sediments is well understood in terms of linear elasticity hooke s law 2 but there has been a long standing debate regarding the amplification associated with the strong ground motion produced by large earthquakes the view of geotechnical engineers based largely on laboratory studies is that hooke s law breaks down at larger strains causing a reduced nonlinear amplification seismologists on the other hand have tended to remain sceptical of this nonlinear effect mainly because the relatively few strong motion observations seemed to be consistent with linear elasticity although some recent earthquake studies have demonstrated nonlinear behaviour under certain circumstances3 4 the significance of nonlinearity for the type of stiff soil sites found in the greater los angeles region remains unresolved5 here we report that ground motion amplification due to sediments for the main shock of the 1994 northridge earthquake was up to a factor of two less than the amplification observed for its aftershocks these observations imply significant nonlinearity in such amplification and bring into question the use of measurements of weak ground motion to predict the strong ground motion at sedimentary sites

on the effect of steep slope orientation on the intensity of daytime upslope flow abstract steep north and south facing slopes may differ significantly in the amount of solar radiation received on their surfaces and consequently also in the related daytime induced thermal flows this note provides a comparative analysis of the midday surface flows which developed on both slopes as a function of the slope steepness and the geographical latitude the most significant differences between the two slopes were found on steep slopes in high latitudes during the winter during the summer the differences due to slope steepness and geographical latitude are relatively small numerical model simulations support the analysis results

modelling the shrinkage curve of soil clay pastes the shrinkage properties of soil require an understanding of the volumetric changes to swelling clays the presence of non swelling minerals like silt and sand and the soil volume occupied by cracks and other voids it is natural to consider first the matrix of clay particles only the objective of this work is the further development of a basic model of the shrinkage curve of a soil clay based on its microstructure the specific goals include developments of a relation between the saturation degree and pore size distribution a physical condition determining the shrinkage limit of a soil clay paste the points of the basic model the major concepts definitions assumptions simple formulas and results that are relevant to these goals are preliminarily briefly summarized application of the points supplemented by the above developments allows one to reduce the number of independent macroparameters of clay paste that were introduced in the basic model to express the residual water content shrinkage limit and shrinkage curve of clay paste through the reduced number of its macroparameters to show additional interconnection between micro and macroparameters of the clay paste microstructure besides those indicated in the basic model comparison between model estimates and relevant available data on characteristic points of the shrinkage curve of soil clay pastes gives arguments in favour of the basic model supplemented here that enables one to predict the total shrinkage curve of a clay paste including the residual water content shrinkage and liquid limits

hysteretic and dilatant behavior of cohesionless soils and their effects on nonlinear site response field data observations and modeling in this study we present evidence that nonlinearity can be directly observed in acceleration time histories such as those recorded at the wildlife refuge and kushiro port downhole arrays from the 1987 superstition hills california and the 1993 kushiro oki japan earthquakes respectively these accelerograms and others compiled in this study present a characteristic waveform composed of intermittent high frequency peaks riding on a low frequency carrier in addition soil amplification of the surface records is strongly observed compared to their downhole counterpart this is contrary to the expected amplification reduction produced by the nonlinear soil behavior laboratory studies show that the physical mechanism that produces such phenomena is the dilatant nature of cohesionless soils which introduces the partial recovery of the shear strength under cyclic loads this recovery translates into the ability to produce large deformations followed by large and spiky shear stresses the spikes observed in the acceleration records are directly related to these periods of dilatancy and generation of pore pressure these results are significant in strong motion seismology because these spikes produce large if not the largest acceleration they are site related not source related using the in situ observations from the kushiro port downhole array we have modeled the 1993 kushiro oki earthquake the synthetic accelerograms show the development of intermittent behavior high frequency peaks as observed in the recorded acceleration time histories shear modulus degradation due to pore pressure produces large strains in the soil with large amplification in the low frequency band of the ground motion we also modeled data from the 1987 superstition hills earthquake recorded at the wildlife refuge station the results show the importance of better soil characterization when pore pressure may develop and the effects of dilatancy in the understanding of nonlinear site response

inversion of borehole weak motion records observed in istanbul turkey summary the estimation of shear wave velocity and attenuation in near surface geology is of primary importance in engineering seismology in fact such knowledge is essential for site response studies when preparing improved seismic hazard scenarios in this study we propose a linear inversion of the spectra of a deconvolved wavefield collected by a borehole array in istanbul turkey the spectra are calculated using as a reference the recordings collected by a sensor at the surface this allows us to minimize the effect of the deconvolution filter on the peaks amplitudes the feasibility of the proposed inversion scheme and the parametrization of the velocity and attenuation models were tested and assessed using synthetic data the real data inversion is carried out using observation from three weak motion events several starting models are used for each event changing the values of the quality factor qs whereas the starting vs profiles are fixed to what was obtained by the analysis of the deconvolved wavefield in the time domain our results showed that fairly well constrained vs models can be obtained while the variability of the qs profile both between different inversions of the same data set and between the inversions of different data sets might be large this indicates that qs variations observed in models derived by strong motion data inversions should be considered with care however the high agreement of the estimated soil profiles in the uppermost layer both when using different events and different starting models suggests that any variation in the s wave velocity that might be estimated when using strong motion data should be reliable

in situ assessment of the g γ curve for characterizing the nonlinear response of soil application to the garner valley downhole array and the wildlife liquefaction array abstract we analyze the nonlinear and near surface geological effects of two network for earthquake engineering simulation at university of california santa barbara nees ucsb instrumented sites the garner valley downhole array gvda and the wildlife liquefaction array wla the seismic interferometry by deconvolution method is applied to earthquake data recorded by the multisensor vertical array between january 2005 and september 2013 along the cross section local shear wave velocity is extracted by estimating travel time between sensors the s wave velocity profiles are constructed and compared with classical in situ geophysical surveys we show that velocity values change according to the amplitude of the ground motion and we find anisotropy between east west and north south directions at the gvda site the ratio between average peak particle velocity v and local s wave velocity between two boreholes is tested as a deformation proxy using average peak particle acceleration a the a versus curve is used to represent the stress strain curve for observing the site s nonlinear responses under different levels of excitation nonlinearity is observed from quite low shear strain levels 1 10 5 and a classic hyperbolic model is derived proves to be a good deformation proxy finally the shear modulus degradation curves are constructed for each depth and test site and they are similar to previous laboratory measurements or in situ geophysical surveys a simple comparison regarding nonlinear behavior between gvda and wla is performed

three dimensional nonlinear seismic ground motion modeling in basins abstract in this paper we report on the development and application of a parallel numerical methodology for simulating large scale earthquake induced ground motion in highly heterogeneous basins whose soil constituents can deform nonlinearly we target sedimentary basins with large contrasts in wavelengths for which regular grid methods become inefficient and overcome the problem of multiple physical scales by using unstructured finite element triangulations we illustrate the methodology with an example of an idealized basin which contains a deep and a shallow sub basin the simulations show significant amplitude reduction of the ground accelerations due to inelastic soil behavior at sites above the deepest portions of the sub basins yet little shift in frequency under the assumption of linear anelastic material behavior there is a rapid spatial distribution of the ground acceleration of the basin which differs markedly from that for a one dimensional 1d analysis this characteristic three dimensional nature of the ground motion is preserved for the elastoplastic model concerning the ground displacement the main qualitative difference between the elastic and inelastic models is the occurrence of significant permanent deformations in the inelastic case these residual displacements can have practical implications for the design of long structures such as bridges and structures with large plan dimensions

site amplification and attenuation of strong ground motion abstract at the mcgee creek california site three component strong motion accelerometers are located at depths of 166 m 35 m and 0 m the surface material is glacial moraine to a depth of 30 5 m overlying hornfels accelerations were recorded from two california earthquakes round valley m l 5 8 23 november 1984 18 08 utc and chalfant valley m l 6 4 21 july 1986 14 42 utc anti plane shear strains for the round valley and chalfant valley events are less than 1 8 10 5 and 1 2 10 5 respectively by separating out the sh components of acceleration we were able to determine the orientations of the downhole instruments peak sh accelerations at the surface were 5 7 times greater than those at 166 m in both earthquakes a constant phase velocity haskell thomson model was applied to generate synthetic sh seismograms at the surface using the accelerations recorded at 166 m in the frequency band 0 10 to 10 0 hz we compared the filtered synthetic records to the filtered surface data the onset of the sh pulse and the reflections from the interface at 30 5 m are clearly seen in both the synthetics and the recorded data the synthetic records closely match the data in both amplitude and phase the fit between the synthetic accelerograms and the data indicates that the seismic amplification at the surface is a result of the resonance of the surface layers and the contrast of the impedances shear stiffness of the near surface materials the impedance contrast of the materials does not account for all of the amplification of the peak accelerations at the surface the resonances of the layer system below 10 hz contribute the most to this amplification we find that a linear model predicts the soil response for frequencies up to 10 hz material damping is added to the soil layers of the model in the form of a quality factor q the damping moderates the strong resonance effects by allowing energy to radiate into the half space the quality factor q 10 is constant in this frequency range but does not accurately model the attenuation at frequencies above 10 hz

site amplification and attenuation via downhole array seismogram inversion a comparative study of the 2003 miyagi oki aftershock sequence weak motion geotechnical array recordings at 38 stations of the japanese strong motion network kik net from the 2003 m w 7 0 miyagi oki aftershock sequence are used here to quantify the amplification and attenuation effects of near surface formations to incident seismic motion initially a seismic waveform optimization algorithm is implemented for the evaluation of high resolution low strain velocity v s attenuation q s and density profiles at the sites of interest based on the inversion results v s versus q s correlations are developed and scattering versus intrinsic attenuation effects are accounted for in their physical interpretation surface to downhole traditional spectral ratios ssr cross spectral ratios c ssr and horizontal to vertical h v site response estimates are next evaluated and compared while their effectiveness is assessed as a function of the site conditions classified on the basis of the weighted average vs of the upper 30 m v s30 of the formations single and reference station site response estimates are successively compared to surface to rock outcrop amplification spectra and are evaluated by deconvolution of the downhole records based on the inversion results comparison of the observed ssr and estimated surface to rock outcrop amplification spectra illustrates the effects of destructive interference of downgoing waves at the downhole instrument level as a function of the site class site amplification factors are successively computed in reference to the national earthquake hazards reduction program nehrp b c boundary site conditions v s30 760 m sec and results are compared to published values developed on the basis of strong motion data and site response analyses finally weak motion ssr estimates are compared to the mainshock spectra and conclusions are drawn for the implications of soil nonlinearity in the near surface results presented in this article suggest that currently employed site classification criteria need to be reevaluated to ensure intraclass consistency in the assessment of amplification potentials and nonlinearity susceptibility of near surficial soil formations

the atakoy vertical array turkey insights into seismic wave propagation in the shallow most crustal layers by waveform deconvolution summary a vertical array of accelerometers was installed in atak oy western istanbul with the longterm aim of improving our understanding of in situ soil behaviour to assess the modelling and parametric uncertainties associated with the employed methodologies for strong motion site response analysis and for shallow geological investigations geotechnical and geophysical investigations were carried out to define the subsoil structure at the selected site data associated with 10 earthquakes 2 7 m 4 3 collected during the first months of operation of the array were used to image the upgoing and downgoing waves by deconvolution of waveforms recorded at different depths results have shown that the velocity of propagation of the imaged upgoing and downgoing waves in the borehole is consistent with that of s or p waves depending on the component of ground acceleration analysed but independent of the chosen signal window in particular an excellent agreement was found between the observed upgoing and downgoing wave traveltimes and the ones calculated using a model derived by seismic noise analysis of array data the presence of a smaller pulse on the waveforms obtained by deconvolution of the horizontal components suggests both internal s wave reflection and s to p mode conversion as well as a not normal incidence of the wavefield the presence of a pulse propagating with s wave velocity in the uppermost 25 m in the waveforms obtained by the deconvolution of the vertical components suggests p to s mode conversion these evidences imply that even when site amplification is mainly related to 1 d effects the standard practice in engineering seismology of deconvolving the surface recording down to the bedrock using an approximate s wave transfer function generally valid for vertical incidence of sh waves might lead to errors in the estimation of the input ground motion required in engineering calculations finally downgoing waves with significant amplitudes were found down to 70 m and even to 140 m depth this result provides a warning about the use of shallow borehole recordings as input for the numerical simulation of ground motion and for the derivation of ground motion prediction relationships

water tank studies of atmospheric boundary layer structure and air pollution transport in upslope flow systems 1 heated mountain slopes sometimes vent air pollutants out of the boundary layer over the slope top and at other times trap pollutants in closed circulations field numerical and water tank studies of fair weather atmospheric conditions over complex terrain have shown more complicated vertical distributions of temperature moisture and aerosols than over horizontal terrain to study these phenomena we analyze flow fields densities and dye distributions in a bottom heated salt stratified water tank over a 19 slope with adjacent plain and plateau and compare with field and numerical model data vertical layering of dye results from upslope and plain plateau circulations the thermal boundary layer tbl the bottom layer up to neutral buoyancy height coincides with the lower branches of these circulations the return flow branches form elevated layers el with properties intermediate between the tbl and environmental background as heating continues the tbl rapidly entrains the els leading to deeper circulations with new els at greater heights field data suggest that successive formation and entrainment of els occurs at multiple scales in the atmosphere if the aerosol loading of an el is too high to distinguish it from the underlying tbl on lidar backscatter scans then both layers and the associated closed circulation appear embedded in one deep backscatter boundary layer the findings suggest defining the atmospheric boundary layer in complex terrain on the diurnal heating timescale rather than the commonly used 1 hour timescale which is more appropriate for flat terrain we discuss conditions leading to venting versus trapping of air pollutants

site response estimation for the 2003 miyagi oki earthquake sequence considering nonlinear site response the m w 7 0 miyagi oki earthquake which occurred on 26 may 2003 was well recorded by the kik net and k net networks a large number of stations recorded very high peak ground accelerations above 0 5g and large peak ground velocities above 0 5 m sec these high ground motion values are thought to come from a combination of the effect of shallow sediment layers of the upper couple of meters and the enhanced high frequency ground motion content associated with this intraslab earthquake the objective of this study is to examine the effect of sediment amplification at network stations with peak ground acceleration 0 3g linear site response is first estimated from observed weak motion aftershock records in this case we use a spectral inversion method without reference stations to separate the source path and site response effects the resulting weak motion analysis for the source path and site response agree with other previous studies the mainshock site response is obtained separately using the same spectral inversion technique with the addition of a frequency dependent radiation pattern the comparison of the site am plification from aftershocks with the mainshock indicates the possibility of nonlinear site response at many stations during the mw 7 0 event the results also suggest a correlation between lownear surface materialvelocity and thedegreeofnonlinearity

the information content of high frequency seismograms and the near surface geologic structure of hard rock recording sites due to hardware developments in the last decade the high frequency end of the frequency band of seismic waves analyzed for source mechanisms has been extended into the audio frequency range 20 hz in principle the short wavelengths corresponding to these frequencies can provide information about the details of seismic sources but in fact much of the signal is the site response of the nearsurface several examples of waveform data recorded at hard rock sites which are generally assumed to have a flat transfer function are presented to demonstrate the severe signal distortions includingfmax produced by near surface structures analysis of the geology of a number of sites indicates that the overall attenuation of high frequency 1 hz seismic waves is controlled by the whole path q between source and receiver but the presence of distinctfmax site resonance peaks is controlled by the nature of the surface layer and the underlying near surface structure models of vertical decoupling of the surface and nearsurface and horizontal decoupling of adjacent sites on hard rock outcrops are proposed and their behaviour is compared to the observations of hard rock site response the upper bound to the frequency band of the seismic waves that contain significant source information which can be deconvolved from a site response or an array response is discussed in terms offmax and the correlation of waveform distortion with the outcrop scale geologic structure of hard rock sites it is concluded that although the velocity structures of hard rock sites unlike those of alluvium sites allow some audio frequency seismic energy to propagate to the surface the resulting signals are a highly distorted limited subset of the source spectra

hydraulic conductivity of bentonite sand mixtures the use of bentonite alone or amended with natural soils for construction of liners for water retention and waste containment facilities is very common the importance of bentonite content in reduc

coseismic and postseismic velocity changes measured by repeating earthquakes 1 repeating earthquakes that rupture approximately the same fault patch and have nearly identical waveforms are a useful tool for measuring temporal changes in wave propagation in the earth s crust since source and path effects are common to all earthquakes in a repeating earthquake sequence multiplet differences in their waveforms can be attributed to changes in the characteristics of the medium we have identified over 20 multiplets containing between 5 and 40 repeating events in the aftershock zones of the 1989 loma prieta and 1984 morgan hill california earthquakes postmain shock events reveal delays of phases in the early s wave coda of as much as 0 2 s relative to premain shock events the delay amounts to a path averaged coseismic velocity decrease of about 1 5 for p waves and 3 5 for s waves since most of the multiplets are aftershocks and follow omori s law we have excellent temporal sampling in the immediate postmain shock period we find that the amplitude of the velocity decrease decays logarithmically in time following the main shock in some cases it returns to the premain shock values while in others it does not similar results are obtained for the morgan hill main shock because the fractional change in s wave velocity is greater than the fractional change in p wave velocity it suggests that the opening or connection of fluid filled fractures is the underlying cause the magnitude of the velocity change implies that low effective pressures are present in the source region of the velocity change our results suggest that the changes are predominantly near the stations and shallow but we cannot exclude the possibility that changes occur at greater depth as well if the variations are shallow we may be detecting the lingering effects of nonlinearity during main shock strong ground motion if the variations are deep it suggests that pore pressures at seismogenic depths are high which would likely play a key role in the earthquake process

urban seismology northridge aftershocks recorded by multi scale arrays of portable digital seismographs we deployed portable digital seismographs in the san fernando valley sfv the los angeles basin lab and surrounding hills to record aftershocks of the 17 january 1994 northridge california earthquake the purpose of the deployment was to investigate factors relevant to seismic zonation in urban areas such as site amplification sedimentary basin effects and the variability of ground motion over short baselines we placed seismographs at 47 sites not all concurrently and recorded about 290 earthquakes with magnitudes up to 5 1 at five stations or more we deployed widely spaced stations for profiles across the san fernando valley as well as five dense arrays apertures of 200 to 500 m in areas of high damage such as the collapsed interstate 10 overpass sherman oaks and the collapsed parking garage at calstate northridge aftershock data analysis indicates a correlation of site amplification with mainshock damage we found several cases where the site amplification depended on the azimuth of the aftershock possibly indicating focusing from basin structures for the parking garage array we found large ground motion variabilities a factor of 2 over 200 m distances for sites on the same mapped soil unit array analysis of the aftershock seismograms demonstrates that sizable arrivals after the direct s waves consist of surface waves traveling from the same azimuth as that of the epicenter these surface waves increase the duration of motions and can have frequencies as high as about 4 hz for the events studied here we do not observe large arrivals reflected from the southern edge of the san fernando valley

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

modeling the pore structure and shrinkage curve of soil clay matrix abstract the clay matrix of a soil has a number of characteristics many of them are structural features and shrinkage swelling phenomena including cracking hydraulic properties are determined by the geometry of the crack network and pore structure of the clay matrix the objective of the work is to develop a simple quantitative model of the pore structure and the shrinkage curve of clay matrix through parameters of matrix microstructure we assume that clay particles or quasicrystals form a microstructural network comprising pores of different dimensions and propose a probabilistic description of such a structure the model predictions are in quite satisfactory agreement with published experimental data on the pore distribution microparameters and shrinkage curves of soil clay matrices

site response for urban los angeles using aftershocks of the northridge earthquake ground motion records from aftershocks of the 1994 northridge earthquake are used to estimate site response in the urban los angeles area over 1300 shear wave records from 61 sources and 90 sites are used in a linear inversion for source and site response spectra the methodology makes no assumptions about the shape of the source spectrum to obtain a stable unique inverse a q model and geometrical spreading factor are assumed in addition the site response at a hard rock site is constrained to be approximately 1 0 with a kappa of 0 02 the site response spectra compare favorably with the results of previous and on going investigations in los angeles a couple of first order effects are lower site response in the surrounding mountains dominated by mesozoic and tertiary rocks and higher values in the san fernando and los angeles basins containing surficial pleistocene and holocene alluvial deposits results show good correlation of high site response spectral values with localized areas of severe damage interstate 10 collapse sherman oaks northridge interstate 5 14 collapse however widespread trends in site response across the sedimentary basins are not obvious the data suggest that site responses are lower near the southern margin of the san fernando valley for sources to the north due to north dipping sedimentary structures but the general pattern of site response is characterized by high variability on length scales less than a kilometer variations of a factor of 2 in site response are observed over the length scale of 200 m and for the same surficial geologic unit for some of the alluvial basin sites surface wave generation is a significant contributor to elevated site response at lower frequencies below 2 hz the total damage pattern for the northridge earthquake is influenced by strong source directivity to the north and strong local site effects the correlation of weak motion site response estimates with areas of significant damage demonstrates the value of these field measurements in future urban planning and in the reduction of seismic risk in urban areas

the formation of spherical clay balls on the slopes of sandpit quarry the rudice sec czech republic clays on the steep slopes of a small artificial sedimentary basin sandpit quarry alternately desiccate crack and erode during hot dry and rainy seasons respectively small irregular blocks of clay ibc predefined by cracks are released by gully erosion the ibcs are quickly transported to the slope base and then rolled down the basin bottom by runoff due to rotation about a randomly changing axis and under an effect of deformation forces the ibcs are transformed into spherical clay balls scb the scbs are transported in general towards the depositional base where they are buried by assorted sandy clayey sediment as soon as the kinetic energy of the runoff has decreased the scbs remain spread along transport path from their distribution the shaping process was evaluated based on data processing the dependency psi 1 1 psi 0 x10 8 9e 5 lambda d ef relating the clay ball projection sphericity psi to the effective diameter d ef and to the distance from the steep slope base lambda was found based on this equation the length of clay ball transport can be estimated if the projection sphericity and effective diameter are known

expected seismic shaking in los angeles reduced by san andreas fault zone plasticity computer simulations of large m 7 8 earthquakes rupturing the southern san andreas fault from se to nw e g shakeout widely used for earthquake drills have predicted strong long period ground motions in the densely populated los angeles basin due to channeling of waves through a series of interconnected sedimentary basins recently the importance of this waveguide amplification effect for seismic shaking in the los angeles basin has also been confirmed from observations of the ambient seismic field by simulating the shakeout earthquake scenario based on a kinematic source description for a medium governed by drucker prager plasticity we show that nonlinear material behavior could reduce the earlier predictions of large long period ground motions in the los angeles basin by up to 70 as compared to viscoelastic solutions these reductions are primarily due to yielding near the fault although yielding may also occur in the shallow low velocity deposits of the los angeles basin if cohesions are close to zero fault zone plasticity remains important even for conservative values of cohesions suggesting that current simulations assuming a linear response of rocks are overpredicting ground motions during future large earthquakes on the southern san andreas fault

predicting nonlinear site response using spectral acceleration vs pgv vs30 a case history using the volvi test site in this study we analyze the efficiency of the ratio between particle velocity and shear wave velocity as a strain proxy for evaluating the nonlinear seismic response of sediments the in situ stress strain relationships are derived from accelerometric vertical array recordings at the tst site in volvi thessaloniki greece first the shear wave velocity between two successive sensors was computed by seismic interferometry and strain was computed as the velocity ratio or the relative displacement between sensors the shear wave velocity profile and in situ shear modulus degradation curve with strain were compared with previous studies performed at the tst site finally the stress strain relationships were derived from data recorded at the surface by extending the strain proxy and stress values to the ratio between peak ground velocity and the vs30 parameter used for site classification i e without requiring the accelerometric vertical array our model captures the in situ nonlinear response of the site without consideration of azimuth or distance of the earthquakes in conclusion the acceleration stress values based on the accelerometric response spectra instead of peak ground acceleration compared with the deformation strain proxy provide an effective model of the in situ nonlinear response providing information that can be integrated into ground motion prediction equations

determination of geomechanical site effects in france from macroseismic intensities and reliability of macroseismic magnitude of historical events results from a detailed analysis of the french macroseismic database sirene96 show that geomechanical site effects i e site effects due to superficial geology can be statistically detected and quantified from macroseismic data our results are used to derive a predictive map of potential site effects in france and to check if site effects induce a significant overestimation of macroseismic magnitude of historical events the key hypothesis of our work is that geological formations of similar age produce similar site effects because one expects the younger sediments to be less compacted and therefore more prone to cause site effects a geological formation is associated with each intensity using a geographic information system gis and the digital geological map of france two approaches are developed in order to characterise the intensity increase associated with geological formations having the same age the first approach is based on the intensities that differ significantly from the average pattern intensities which are labelled as anomalies in the second approach a theoretical intensity attenuation law is computed for each selected event only from observations located on formations older than 2 my according to the results of the first approach these formations are unlikely to cause site effects and for the sake of simplicity they are labelled as rocks younger formations are defined as sediments the derived attenuation laws are then used to compute the residuals for each observation residuals are classified as a function of the age of the formations on which they are located the results of the two approaches are in good agreement no intensity amplification is detected for formations older than 1 my for younger formations the younger the formations the larger the average intensity increase the average intensity increase reaches 0 6 0 2 degree on the msk scale for 0 my sediments the results are better expressed in terms of probability for 0 my sediments there is an estimated 83 probability of observing an intensity increase for 0 01 my and 0 75 my sediments this probability is about 52 the magnitude of the intensity increase is variable but it is generally small it has a 26 probability to reach 1 degree or above on the msk scale for 0 my sediments and this probability falls to about 5 for 0 01 and 0 75 my formations a predictive map of geomechanical site effects is produced by extrapolating the characteristics of intensity increases to all geologic formations of similar age in france glacial and fluvial valleys already known as being subject to site effects clearly appear on this map as well as less expected areas such as the south atlantic coast lastly new estimations of macroseismic magnitude that exclude intensities potentially affected by geomechanical site effects are realised a magnitude overestimation due to site effects can possibly exist but it remains limited 0 2 this result tends to demonstrate that geomechanical site effects in france do not significantly distort our knowledge of historical seismicity

clay mineralogy as a crucial factor in badland hillslope processes abstract comprehensive and important work has been done in understanding badland processes on both the big scale and more recently on smaller scale in order to understand the subtle differences between sites however most studies lack important information regarding clay mineralogy and their importance for weathering processes type and rate of weathering depend on material physico chemical properties climatic regimes and slope characteristics as weathering progresses the surface conditions change influencing erosion processes usually badland lithologies are reported as sodium rich highly dispersive materials but that is not invariably true the primary objective of this study is to show that clay minerals have an important role in defining surface and subsurface processes on badland hillslopes field studies conducted in dinosaur park badlands alberta canada chinguacousy badlands ontario canada and sestino badlands tuscany italy have shown that there are two dominant clay rich lithologies smectite rich and smectite poor mudrocks different surface crust and weathering profiles were observed on smectite rich mudrocks during two field years with distinct precipitation inputs after a dry fall winter season the popcorn surface was very well developed 2 3 cm the subsurface layer 10 15 cm thick overlaid the layer of smaller shards followed by the unweathered material after a very wet fall winter season the surface layer was denser and thinner 0 5 cm with wider cracks and a thin subsurface layer attached to the crust weathering profiles on smectite poor lithologies did not show any differences with variable climatic conditions a thin surface layer was composed of soft thin and small 0 5 0 3 0 1 cm shards a layer of larger shards overlying unweathered material was beneath it in order to better understand the described occurrences badland materials were monitored in controlled laboratory conditions during an incremental weathering experiment six samples of each material were subjected to 10 cycles of simulated rainfall which duration ranged 10 60 min very short rainfalls 10 20 min can cause swelling of clay minerals in smectite rich materials and formation of popcorn surface during drying periods during subsequent wetting drying periods the crust becomes flatter and denser and desiccation cracks become wider and deeper samples subjected to 50 and 60 min of rainfall showed maximum swelling after only one cycle of rainfall after this swift swelling samples became unstable and dispersive during subsequent wetting dispersion became dominant resulting in flatter surfaces thinner crust and narrower desiccation cracks smectite poor mudrocks appeared to be resistant to variable wetting and drying large shards broke down into smaller due to differential swelling of illite and chlorite once they were reduced to tiny flaky shards the surface became compacted the surface cracks served as the initial pathways for sediment and water movement knowing if the material is smectite rich or smectite poor can help in prediction of processes and the erosion rates the amount intensity and duration of precipitation will determine not only the rate of weathering but also the type of the weathered surface on smectite rich surfaces smectite poor materials appear to be more resistant to change in precipitation

stochastic finite fault modeling of ground motions from the 1994 northridge california earthquake ii widespread nonlinear response at soil sites on average soil sites behaved nonlinearly during the m 6 7 1994 north ridge california earthquake this conclusion follows from an analysis that combines elements of two independent lines of investigation first we apply the stochastic finite fault simulation method calibrated with 28 rock site recordings of the north ridge mainshock to the simulation of the input motions to the soil sites that recorded this event the calibrated model has a near zero average bias in reproducing ground motions at rock sites in the frequency range from 0 1 to 12 5 hz the soil sites selected are those where there is colocation of strong motion acce lerographs and temporary instruments from the northridge aftershock observation network at these sites weak motion amplification functions based on numerous aftershock records have been empirically determined in three separate investigations reported in the literature these empirical weak motion amplification factors can be applied to the simulated input rock motions at each soil site to determine the ex pected motions during the mainshock i e neglecting nonlinearity these expected motions can then be compared to the actual recordings during the mainshock this analysis shows that the recorded strong motion spectra are significantly over estimated if weak motion amplifications are used the null hypothesis stating that the inferred differences between weak and strong motion amplifications are statis tically insignificant is rejected with 95 confidence in the frequency range from approximately 2 2 to 10 hz on average the difference between weak and strong motion amplifications is a factor of 2 nonlinear response at those soil stations for which the input peak acceleration exceeded 150 to 200 cm sec 2 contributes most to this observed average difference these findings suggest a significant nonlinear re sponse at soil stations in the los angeles urban area during the northridge main shock the effect is consistent with the increase in damping of shear waves at high levels of strain which is well known from geotechnical studies of soil properties

rupture processes of the 1999 august 17 izmit and november 12 duzce turkey earthquakes summary we derive the rupture history of the 1999 august 17 izmit mw 7 4 and 1999 november 12 duzce mw 7 1 earthquakes in turkey from teleseismic body waves using broad band data of the global seismograph network aftershock locations and mapped surface breaks the centroid solutions indicate strike slip mechanisms for both events the izmit earthquake was characterized by rupture propagating predominantly eastwards it consisted of a main rupture lasting about 25 s followed within 1 min by two more events of mw 6 9 and mw 7 0 with the teleseismic data we could not resolve the westward extent of rupture into the marmara sea however an upper bound of the seismic moment release west of the epicentre of the izmit event is estimated to be 1 9 1019 n m the duzce earthquake lasted about 14 s and was characterized by a bilateral mode of rupture in excellent agreement with mapped surface breaks and aftershock locations

seismic wave propagation in shallow layers at the gonaf tuzla site istanbul turkey using the first dataset available from the downhole geophysical observatory of the north anatolian fault we investigated near surface seismic wave propagation on the tuzla peninsula istanbul turkey we selected a dataset of 26 seismograms recorded at tuzla at sensor depths of 0 71 144 215 and 288 m to determine near surface velocities and attenuation structures the waveforms from all sensors were pairwise deconvolved and stacked this produced low noise empirical green s functions for each borehole depth interval from the green s functions we identified reflections from the free surface and a low velocity layer between 90 and 140 m depth the presence of a low velocity zone was also confirmed by a sonic log run in the borehole this structure plus high near surface p and s wave velocities of 3600 4100 and 1800 m s lead to complex interference effects between upgoing and downgoing waves as a result the determination of quality factors q with standard spectral ratio techniques was not possible instead we forward modeled the green s functions in the time domain to determine effective q values and to refine our velocity estimates the effective q p values for the depth intervals of 0 71 0 144 0 215 and 0 288 m were found to be 19 35 39 and 42 respectively for the s waves we obtained an effective q s of 20 in the depth interval of 0 288 m considering the assumptions made in our modeling approach it is evident that these effective quality factors are biased by impedance contrasts between our observation points our results show that even after correcting for a free surface factor of 2 the motion at the surface was found to be 1 7 times greater than that at 71 m depth our efforts also illustrate some of the difficulties of dealing with site effects in a strongly heterogeneous subsurface online material plots of resistivity and caliper logs and the spectra of all 26 events

mechanisms of up valley winds abstract the basic physical mechanisms governing the daytime evolution of up valley winds in mountain valleys are investigated using a series of numerical simulations of thermally driven flow over idealized three dimensional topography the three dimensional topography used in this study is composed of two two dimensional topographies one a slope connecting a plain with a plateau and the other a valley with a horizontal floor the present two dimensional simulations of the valley flow agree with results of previous investigations in that the heated sidewalls produce upslope flows that require a compensating subsidence in the valley core bringing down potentially warmer air from the stable free atmosphere in the context of the three dimensional valley plain simulations the authors find that this subsidence heating in the valley core is the main contributor to the valley plain temperature contrast which under the hydrostatic approximation is the main contributor to the valley plain pressure differe

nonlinear soil response a reality geotechnical models consistently indicate that the stress strain relationship of soils is nonlinear and hysteretic especially at shear strains larger than 10 5 to 10 4 nonlinear effects such as an increase in damping and reduction in shear wave velocity as excitation strength increases are commonly recognized in the dynamic loading of soils on the other hand these effects are usually ignored in seismological models of ground motion prediction because of the lack of compelling corroborative evidence from strong motion observations the situation is being changed by recently obtained data explicit evidence of strong motion deamplification accompanied by changes in resonant frequencies are found in the data from the 1985 michoacan mexico and the 1989 loma prieta california earthquakes the events recorded by the vertical and surface accelerograph arrays in taiwan as well as a number of other events throughout the world evidence of nonlinear behavior becomes apparent beyond a threshold acceleration of 100 to 200 gal nonlinearity is considerable in cohesionless soil but may be negligible in stiff soils the findings of recent years indicate that nonlinear site effects are more common than previously recognized in strong motion seismology

ground deformation in an area later damaged by an earthquake monitoring the avcilar district of istanbul turkey by satellite radar interferometry 1992 1999 summary the avcilar district of istanbul was severely damaged by the m 7 4 izmit kocaeli earthquake of 1999 the same area underwent ground subsidence before the earthquake as revealed by geodetic monitoring analysis of 14 synthetic aperture radar images acquired by the ers 1 and ers 2 satellites between 1992 and 1999 by interferometry insar measures the rate of subsidence using the general inversion for phase technique gipht we analyse a set of 12 interferometric pairs the interferometric fringe patterns show a rounded triangular shape that we interpret as secular subsidence at a constant rate the maximum subsidence rate of 6 mm per year occurs at a point located at latitude 40 98 n and longitude 28 71 e a simple four parameter elastic mogi model consisting of three infinitesimal spherical sinks at a depth of 2 4 0 4 km deflating at 78 000 16 000 cubic metres per year describes subsidence signal to first order the model also accounts for tropospheric effects by estimating a vertical phase gradient and an additive offset for each image acquisition epoch the model fits the data with a cost of 0 18 cycles per datum for the 4644 phase measurements included in the inversion this fit is significantly better than either the null hypothesis or the initial model with 95 per cent confidence for 32 free parameters the association of ground deformation with earthquake damage may be interpreted in terms of weak compressible material in shallow subsurface layers

spectral analysis of k net and kik net data in japan part ii on attenuation characteristics source spectra and site response of borehole and surface stations abstract in this study we apply a nonparametric spectral inversion scheme to a data set of accelerograms recorded by the k net and kik net networks in japan in order to derive attenuation characteristics source spectra and site response for this purpose we use a total of more than 67 000 s wave records from 2178 earthquakes m jma 2 7 8 obtained at 1555 stations at the earth s surface and more than 29 000 records from 1826 events recorded at 637 borehole stations at depths of 100 to 3000 m attenuation characteristics are investigated in five separate regions showing that crustal q depicts lower values in central compared to southern japan and a significant frequency dependence is observed in every region the source spectra follow the 2 model with higher stress drops for subcrustal earthquakes as compared with crustal ones while strong amplification effects dominate the site contributions for the surface sensors those for the borehole sensors are characterized by smaller variability nevertheless consistent with observations from deconvolution of borehole surface recording pairs downgoing wave effects are visible in the site contributions for many borehole stations finally the site amplification functions obtained at the surface are compared with surface to borehole s b and horizontal to vertical h v spectral ratios showing that the s b ratios generally provide better estimates of the horizontal amplification than the h v ratios due to amplification of the vertical component of ground motion

assessing the applicability of deconvolution of borehole records for determining near surface shear wave attenuationassessing the applicability of deconvolution of borehole records

what is a reference site many methods for estimating site response compare ground motions at sites of interest to a nearby rock site that is considered a reference motion the critical assumption in these methods is that the surface rock site record reference is equivalent to the input motion at the base of the soil layers data collected in this study show that surface rock sites can have a site response of their own which could lead to an underestimation of the seismic hazard when these sites are used as reference sites data were collected from local and regional earthquakes on digital recorders both at the surface and in boreholes at two rock sites and one basin site in the san jacinto mountains southern california the two rock sites keenwild and pinon flat are located on granitic bedrock of the southern california peninsular ranges batholith the basin site garner valley is an ancestral lake bed with watersaturated sediments on top of a section of decomposed granite which overlies the competent bedrock ground motion is recorded simultaneously at the surface and in the bedrock at all three sites when the surface rock sites are used as the reference site i e the surface rock motion is used as the input to the basin the computed amplification underestimates the actual amplification at the basin site for frequencies above 2 to 5 hz this underestimation by a factor of 2 to 4 depending on frequency and site results from the rock sites having a site response of their own above the 2 to 5 hz frequencies the near surface weathering and cracking of the bedrock affects the recorded ground motions at frequencies of engineering interest even at sites that appear to be located on competent crystalline rock the bedrock borehole ground motion can be used as the reference motion but the effect of the downgoing wave field and the resulting destructive interference must be considered this destructive interference may produce pseudo resonances in the spectral amplification estimates if one is careful the bedrock borehole ground motion can be considered a good reference site for seismic hazard analysis even at distances as large as 20 km from the soil site

finite difference modeling of two aftershocks of the 1994 northridge california earthquake recent evidence for nonlinear behavior of strong motions generated by the northridge california earthquake relies explicitly on the analysis of aftershock data thus correcting these observations for propagational and source effects becomes a crucial step in these studies here we demonstrate that the dipping structure near the edges of the san fernando valley can strongly alter the local site responses especially for shallow events we model two aftershocks with similar epicenters but with shallow 4 km and deep 16 km hypocentral depths waveforms from 12 portable instruments deployed across the basin and recording these events were processed and studied in the 0 3 4 hz bandpass for the shallow event distinctive features are a broad direct s phase and large amplitude surface waves at the basin stations and high frequency s phases at stations in the santa monica mountains the deep event is less strongly affected by the basin but displays strong evidence of the source radiation pattern an array analysis indicates 2d propagation for most of the strong arrivals some of these features are explained by a simple 2d basin model containing a strong shallow contrast a factor of 2 jump in seismic velocity at a depth of 1 km within the basin and a moderate deeper gradient

site amplification in the san fernando valley california variability of site effect estimation using the s wave coda and h v methods during the months that followed the 17 january 1994 m 6 7 northridge california earthquake portable digital seismic stations were deployed in the san fernando basin to record aftershock data and estimate site amplification factors this study analyzes data recorded on 31 three component stations from 38 aftershocks ranging from m 3 0 to m 5 1 and depths from 0 2 to 19 km site responses from the 31 stations are estimated from coda waves s waves and ratios of horizontal to vertical h v recordings for the coda and the s waves site response is estimated using both direct spectral ratios and a generalized inversion scheme results from the inversions indicate that the effect of qs can be significant especially at high frequencies site amplifications estimated from the coda of the vertical and horizontal components can be significantly different from each other depending on the choice of the reference site the difference is reduced when an average of six rock sites is used as a reference site in addition when using this multi reference site the coda amplification from rock sites is usually within a factor of 2 of the amplification determined from the direct spectral ratios and the inversion of the s waves however for nonrock sites the coda amplification can be larger by a factor of 2 or more when compared with the amplification estimated from the direct spectral ratios and the inversion of the s waves the h v method for estimating site response is found to extract the same predominant peaks as the direct spectral ratio and the inversion methods the amplifications determined from the hiv method are however different from the amplifications determined from the other methods finally the stations were grouped into classes based on two different classifications general geology and a more detailed classification using a quaternary geology map for the los angeles and san fernando areas average site response estimates using the site characterization based on the detailed geology show better correlation between amplification and surface geology than the general geology classification

seismic ground motion hazard mapping incorporating site effects for los angeles orange and ventura counties california a geographical information system application abstract the seismic ground motion hazard with site conditions incorporated is mapped for a 10 probability of exceedance in 50 years for the three counties affected by the 1994 northridge earthquake mw 6 7 the source model of petersen et al 1996 was used to calculate peak horizontal acceleration pga and 5 damped spectral acceleration sa levels at 0 3 and 1 sec periods for alluvium soft rock and hard rock site conditions a geologic map that differentiates the three site conditions was produced using shear wave velocity maps of tinsley and fumal 1985 and extended into other areas that were not mapped by tinsley and fumal using 1 250 000 scale geologic maps ground motion maps for each site condition were overlaid with the geologic map to produce the resulting hazard maps the effect of geology on the hazard is observed only slightly in the peak ground acceleration map more in the 0 3 sec sa map and significantly more in the 1 sec sa map the uncertainties for ground motions represented on these three maps ranges from 0 1 to 0 3 g for pga and 0 2 to 1 0 for sa in general 95 confidence limits are about 50 of the mean ground motion value

the slip history of the 1994 northridge california earthquake determined from strong motion teleseismic gps and leveling data we present a rupture model of the northridge earthquake determined from the joint inversion of near source strong ground motion recordings p and sh teleseismic body waves global positioning system gps displacement vectors and permanent uplift measured along leveling lines the fault is defined to strike 122 and dip 40 to the south southwest the average rake vector is determined to be 101 and average slip is 1 3 m the peak slip reaches about 3 m our estimate of the seismic moment is 1 3 0 2 10 26 dyne cm potency of 0 4 km3 the rupture area is small relative to the overall aftershock dimensions and is approximately 15 km along strike nearly 20 km in the dip direction and there is no indication of slip shallower than about 5 to 6 km the up dip strong motion velocity waveforms are dominated by large s wave pulses attributed to source directivity and are comprised of at least 2 to 3 distinct arrivals a few seconds apart stations at southern azimuths indicate two main s wave arrivals separated longer in time about 4 to 5 sec these observations are best modeled with a complex distribution of subevents the initial s wave arrival comes from an asperity that begins at the hypocenter and extends up dip and to the north where a second larger subevent is centered about 12 km away the secondary s arrivals at southern azimuths are best fit with additional energy radiation from another high slip region at a depth of 19 km 8 km west of the hypocenter the resolving power of the individual data sets is examined by predicting the geodetic gps and leveling displacements with the dislocation model determined from the waveform data and vice versa and also by analyzing how well the teleseismic solution predicts the recorded strong motions the general features of the geodetic displacements are not well predicted from the model determined independently from the strong motion data likewise the slip model determined from geodetic data does not adequately reproduce the strong motion characteristics whereas a particularly smooth slip pattern is sufficient to satisfy the geodetic data the strong motion and teleseismic data require a more heterogeneous slip distribution in order to reproduce the velocity amplitudes and frequency content although the teleseismic model can adequately reproduce the overall amplitude and frequency content of the strong motion velocity recordings it does a poor job of predicting the geodetic data consequently a robust representation of the slip history and heterogeneity requires a combined analysis of these data sets

evaluation and optimization of seismic networks and algorithms for earthquake early warning the case of istanbul turkey earthquake early warning eew systems should provide reliable warnings as quickly as possible with a minimum number of false and missed alarms using the example of the megacity istanbul and based on a set of simulated scenario earthquakes we present a novel approach for evaluating and optimizing seismic networks for eew in particular in regions with a scarce number of instrumentally recorded earthquakes we show that while the current station locations of the existing istanbul eew system are well chosen its performance can be enhanced by modifying the parameters governing the declaration of warnings furthermore unless using ocean bottom seismometers or modifying the current eew algorithm additional stations might not lead to any significant performance increase

combining genetic and linearized algorithms for a two step joint inversion of rayleigh wave dispersion and h v spectral ratio curves summary the joint inversion of rayleigh wave dispersion and h v curves from environmental noise measurements allows the retrieval of s wave velocity profiles for the shallow subsoil for this purpose genetic and linearized algorithm have been combined in a two step inversion procedure that allows the principal drawbacks typical of the application of each algorithm separately to be overcome in the first step a genetic algorithm procedure is used to constrain the subvolume of the parameter space where the absolute minimum of the misfit function is located in the second step a linearized inversion algorithm having as an initial guess the minimum misfit model deduced from the first step is applied to force the inversion towards the optimal solution to evaluate the feasibility and effectiveness of this approach seismic noise recordings at a test site in the po river valley north italy have been analysed here detailed geophysical and geological information is available along with earthquake recordings which allow a well constrained definition of both the local shear wave profile and transfer function comparisons between theoretical and experimental s wave velocity profiles and above all between the theoretical and experimental site response functions shows that this combination of inversion procedures can very efficiently to manage the extreme non linearity of the problem

a modeling study and scaling analysis of orographic effects on boundary layer shallow convection effects of orography on boundary layer shallow convection under various background winds are studied using a two dimensional model together with scaling analysis under a motionless background state the flow response over a heated hill is a vortex pair with one horizontal vortex over each slope additional lifting of the inversion by this vortex pair is estimated by wt n with wt being the intensity of the terrain induced thermal circulation and n the brunt vaisalafrequency for which a simple expression is given based on heat engine framework modification of the cbl top by terrain induced waves is quantified using linear gravity wave theory in a two layer atmosphere configuration these simple estimates of the cbl top perturbation are found to be consistent with the model results when waves and convection dominate the flow pattern a convective core is found to occur over high hills when the winds are light developing in the late afternoon when the cbl depth is high a scaling is proposed to determine the existence of the convective core in terms of hill slope background winds boundary layer depth and tropospheric stability the downstream modification of convection by terrain related processes is also examined under light wind conditions the reversed thermal circulation in the lee and corresponding downward motions may suppress thermal eddies in the vicinity of the lee of a hill

subsonic near surface p velocity and low s velocity observations using propagator inversion detailed knowledge of near surface p and s wave velocities is important for processing and interpreting multicomponent land seismic data because 1 the entire wavefield passes through and is influenced by the near surface soil conditions 2 both source repeatability and receiver coupling also depend on these conditions and 3 nearsurface p and s wave velocities are required for wavefield decomposition and demultiple methods however it is often difficult to measure these velocities with conventional techniques because sensitivity to shallow wave velocities is low and because of the presence of sharp velocity contrasts or gradients close to the earth s free surface we demonstrate that these near surface p and s wave velocities can be obtained using a propagator inversion this approach requires data recorded by at least one multicomponent geophone at the surface and an additional multicomponent geophone at depth the propagator between them then contains all information on the medium parameters governing wave propagation between the geophones at the surface and at depth hence inverting the propagator gives local estimates for these parameters this technique has been applied to data acquired in zeist the netherlands the near surface sediments at this site are unconsolidated sands with a thin vegetation soil on top and the sediments considered are located above the groundwater table a buried geophone was positioned 1 05 m beneath receivers on the surface propagator inversion yielded low near surface velocities namely 270 15 m s for the compressional wave velocity which is well below the sound velocity in air and 150 9 m s for the shear velocity existing methods designed for imaging deeper structures cannot resolve these shallow material properties furthermore velocities usually increase rapidly with depth close to the earth s surface because of increasing confining pressure we suspect that for this reason subsonic near surface p wave velocities are not commonly observed

in situ measurements of nonlinear and nonequilibrium dynamics in shallow unconsolidated sediments abstract we present results and in situ measurements from a field experiment in which a large seismic shaker truck is used to induce nonlinear and nonequilibrium dynamics in shallow unconsolidated sediments an array of accelerometers was deployed adjacent to the shaker truck to record strong ground motions exceeding 1 g we determined high strain rayleigh wave dispersion across the array in the band from 5 to 60 hz rayleigh wave phase velocities at frequencies above 10 hz are wave amplitude dependent and a function of the driving force amplitude as driving force was increased phase velocity decreased consistent with nonlinear dynamics we demonstrate the existence of a temporary nonequilibrium state occurring in the near surface soils during and after the induced nonlinear behavior nonlinear conditioning is demonstrated by measuring changes in rayleigh wave phase velocity for input signals with the same applied driving force amplitude a logarithmic slow dynamic recovery process is observed by analyzing the temporal variation in velocity of the noise field produced by the shaker truck when sitting idle measurements from weak motion seismic surveys taken before and after shaking show compelling evidence that induced nonlinear behavior in the shallow sediments is reversible we demonstrate that an active source field based approach has the potential to expand our knowledge of how sediments respond to strong ground motions provide additional insight into the poorly understood slow dynamic recovery process and possibly even lead to a new site specific and noninvasive technique for characterizing the nonlinear properties of sedimentary deposits

joint inversion of h v ratios and dispersion curves from seismic noise estimating the s wave velocity of bedrock 1 a joint inversion of phase velocity and h v ratio curves both obtained from seismic noise recordings permits the retrieval of the shear wave velocity structure of local sedimentary cover our inversion scheme uses a genetic algorithm and considers the influence of higher modes on the data sets encouraged by the results published previously on joint inversion parolai et al 2005 we went one step further we found using a synthetic data set that the impedance contrast at the sediment bedrock interface has a strong influence on the shape of the h v ratio curve which therefore allows the bedrock s wave velocity to be well constrained in the joint inversion procedure our observations were further confirmed using a real data set

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

downhole receiver function a case study receiver function is defined as the spectral ratio of the radial component and the vertical component of the ground motion it is used to characterize converted waves we extend the use of the receiver function to downhole data using waves recorded in a borehole excited by an earthquake of magnitude 4 0 near san fran cisco california on 26 june 1994 the focal depth of the event was 6 6 km and the epicenter was located at a distance of 12 6 km from the borehole array six three component sensors were located at different depths in a borehole to extract a co herent response of the near surface from the incoherent earthquake waves we de convolve the waves recorded by the sensors at different depths with the waves recorded by the sensor on the surface deconvolution applied to the waves in the s time window recorded by the radial component result in an upgoing and adowngoing wave propagating with s wave velocity for the waves in the p time window re corded by the radial component deconvolution also gives an upgoing and a down going wave propagating with s wave velocity this interesting result suggests a p to s conversion at a depth below the deepest sensor to diagnose this we compute the receiverfunction forthe borehole recording of the earthquakewaves thereceiver function shows an upgoing wave with an arrival close to time t 0 for the deepest sensor the agreement of the upgoing wave in the receiver function with the travel time curve for the p to s converted wave calculated using the p and the s wave velocity profile supports the hypothesis of a pronounced p to s conversion we present a synthetic example to illustrate that the first arrival of the receiver function applied to borehole data gives the upward propagating p to s converted wave to corroborate the observation of the mode conversion we apply receiver function to a different earthquake data recorded by the same borehole array in 1998 the focal depth of the event was 6 9 km and the epicenter was located at a distance of 13 km from the borehole array the receiver function for these data also show an upgoing wave with a pulse close to time t 0 at the deepest sensor the moveout of the upgoing wave agrees with the travel time curve for the p to s converted wave hence supporting our observation of the mode conversion

determination of shallow s wave attenuation by down hole waveform deconvolution a case study in istanbul turkey summary the estimation of shear wave velocity and attenuation in near surface geology is of primary importance in engineering seismology in fact their knowledge is essential for site response studies when preparing improved seismic hazard scenarios in this study we propose two approaches for estimating the average shear wave quality factor qs by using recordings of a vertical array of accelerometers the methods are mainly based on the deconvolution of the wavefield recorded in a borehole with that recorded at the surface the first method requires the fourier transform of the deconvolved wavefield to be fitted with a theoretical transfer function valid for the vertical or nearly vertical in the case at hand up to 30 incidence angle propagation of s waves the second method is based on the spectral fitting of the fourier transform of only the acausal part of the deconvolved wavefield with a theoretical transfer function both methods can be applied without any prior knowledge of the subsoil structure since they are based on empirical data analysis and do not require a precise knowledge of the azimuthal orientation of the sensors in the boreholes which is seldom available first we describe the theoretical framework of the proposed methodologies for qs estimation which are based on the assumption that the structure in the borehole is weakly heterogeneous in the vertical direction i e no large impedance contrast exists between the borehole sensor and the surface second by using synthetic accelerograms we verify that in a realistic subsoil structure the assumption of vertical homogeneity can hold and we investigate the robustness and the suitability of the proposed methods finally only the method that was shown to provide the more stable results based on fitting the borehole to surface spectral ratio with a theoretical function is applied to earthquakes signals recorded by a vertical array of accelerometers installed in atak oy western istanbul results show that using borehole data provides a fair and robust estimate of an average qs of about 30 46 and 99 for the 0 50 0 70 0 140 m depth ranges respectively that can be used for numerical simulations of ground motion

properties of vertical ground motions a typical engineering approach to developing site specific design vertical ground motions starts with rock outcrop horizontal motions converts them into the vertical component using an empirical vertical to horizontal v h ratio for response spectra and propagates the resulting motion through the soil column as a vertically incident p wave in the absence of data on strain dependent soil properties in compressional deformation strain compatible shear wave properties from the horizontal component analyses are utilized this approach makes two assumptions 1 that the vertical motions are primarily composed of compressional waves and 2 that strain dependent material properties in shear deformation can be extrapolated to compressional deformation our study deals with the empirical validation of both assumptions first we investigated the ratio of sv to p wave spectra of the vertical component of ground motions from significant recent events in california to find which wave type predominantly contributed to vertical motions in the frequency range of 0 5 25 hz the results indicate that shear waves dominate the vertical motions at frequencies up to approximately 10 hz above which the contribution of compressional deformation is about as strong or greater this result holds for both soil and rock sites second using the data from the kik net borehole arrays in japan we estimated the nonlinearity in compressional deformation by studying p wave amplification at variable amplitude levels frequency shifts and in some instances reduced amplification compatible with the hysteretic softening type of nonlinearity known for shear waves is found as the amplitude of compressional strain increases a tentative curve of constrained modulus reduction is also similar to the existing shear modulus reduction curves the results of this study suggest that for most practical applications vertical motions can be modeled as nonvertically propagating sv waves this could be implemented through conventional one dimensional horizontal component modeling using shake and the application of empirical depth dependent v h correction factors to account for the inclined propagation path at high frequencies vertical motions may have to be modeled as near vertically propagating p waves with strain dependent properties specifically developed for compressional deformation however these frequencies may be of lesser importance for design applications manuscript received 11 january 2002

the importance of distinguishing pseudoresonances and outcrop resonances in downhole array datathe importance of distinguishing pseudoresonances and outcrop resonances in downhole array data