shear wave velocity structure of the izmit bay area turkey estimated from active passive array surface wave and single station microtremor methods summary to provide quantitative information on the shear wave velocity structure of the izmit bay area we conduct active passive array surface wave and single station microtremor measurements at 60 sites we process these array measurements to produce combined rayleigh wave dispersion curves that span a broad frequency range 0 5 20 hz we also make use of horizontal to vertical spectral ratio hvsr curves obtained from the single station microtremor measurements to benefit from their close relation to the ellipticity of rayleigh waves using the dispersion curve sensitivity to the absolute velocities and the shape of the hvsr curve sensitivity to the velocity contrasts of the velocity depth model we have applied a combined inversion technique to derive better constrained shear velocity models at each site the derived shear velocity models are used to provide a vs30 site classification map and information on the sediment bedrock structure for the izmit bay area the vs30 map shows that the entire shoreline regions including artificial infill areas of the izmit bay have vs30 values less than 200 m s 1 locally as low as 80 m s 1 the older sediment areas of the izmit basin have vs30 values ranging between 250 and 350 m s 1 the highest vs30 values are associated with rock sites reaching about 950 1300 m s 1 we also present a high correlation between the vs30 values and the phase velocity of rayleigh wave corresponding to the 40 m wavelength c40 the important implication of this correlation is that vs30 may be estimated from c40 without inverting the dispersion curve the inferred sediment bedrock interface along a cross section shows an antisymmetric v shaped basin with a sedimentary cover thickness reaching about 1200 m at the deepest part of the izmit basin this deepest part coincides in the map view where the north anatolian fault zone crosses the basin in the east west direction the sedimentary cover thickness is found to be 750 m in the golcuk derince basin

elastic finite difference modeling of the 1971 san fernando california earthquake finite difference seismograms calculated for the 1971 san fernando earthquake show strong effects due to lateral variation in sediment thickness in the san fernando valley and the los angeles basin using basin structure derived mostly from well logs and teleseismically determined source parameters two dimensional sh and p sv finite difference calculations reproduce the amplitude and duration of the strong motion velocities recorded across the los angeles and san fernando basins for the period range of 2 to 10 sec the edges of basins nearest the seismic source show ground motion amplification up to a factor of 3 over the case without the basin and tend to convert direct shear waves into love and rayleigh waves that travel within the basins

simulation of long period ground motion in the osaka sedimentary basin performance estimation and the basin structure effects summary we assessed the applicability of the 3 d subsurface velocity structure model of the osaka sedimentary basin in western japan for simulations of long period ground motion 3 20 s based on two types of long period ground motion characteristics 1 strong ground motion from a specific earthquake and 2 site specific event independent horizontal to vertical spectral ratio hv characteristics obtained from earthquakes with various azimuths for the first type we compared the observed and synthetic ground motions in terms of velocity waveforms and pseudo velocity response spectra we then proposed an objective index to evaluate the goodness of fit from one site to the next the simulation satisfactorily reproduced the observed ground motion at many stations however the model needs improvement for reproducing the ground motion at some stations for the second type we first demonstrated that site specific hv characteristics can be obtained from the coda portion of strong motion observation records for earthquakes with various azimuths we then demonstrated that the hvs obtained from 3 d ground motion simulations for earthquakes with various azimuths 3dhv also have sitespecific stable values the synthetic 3dhv was compared with the observed hv and the 3 d basin velocity structure model was demonstrated as able to reproduce the hv peak periods within 1 s at many stations however at some stations the peak periods of the 3dhv were systematically longer than those of the observed hv by more than 1 5 s which corresponded to the stations of poor goodness of fit scores in the ground motion simulation 3dhv was also compared with the theoretical ellipticity of the fundamental rayleigh wave 1dhv the peak periods of 3dhv and 1dhv were inconsistent with each other at some sites which implies that 3dhv is affected by the lateral heterogeneity of the structure around the site we found the systematically biased characteristics of the discrepancy in 3dhv and 1dhv peaks in specific regions the spatial extent of the area that affects 3dhv is related to the complexity in the bedrock structure and the dominant period of 3dhv

finite difference modelling of s wave splitting in anisotropic media we have implemented a 3d finite difference scheme to simulate wave propagation in arbitrary anisotropic media the anisotropic media up to orthorhombic symmetry were modelled using a standard staggered grid scheme and beyond monoclinic and triclinic using a rotated staggered grid scheme the rationale of not using rotated staggered grid for all types of anisotropic media is that the rotated staggered grid schemes are more expensive than standard staggered grid schemes for a 1d azimuthally anistropic medium we show a comparison between the seismic data generated by our finite difference code and by the reflectivity algorithm they are in excellent agreement we conducted a study on zero offset shear wave splitting using the finite difference modelling algorithm using the rotated staggered grid scheme our s wave splitting study is mainly focused on fractured media on the scale of seismic wavelenghts small aligned fractures behave as an equivalent anisotropic medium we computed the equivalent elastic properties of the fractures and the background in which the fractures were embedded using low frequency equivalent media theories wave propagation was simulated for both rotationally invariant and corrugated fractures embedded in an isotropic background for one or more than one set of fluid filled and dry fractures s wave splitting was studied for dipping fractures two vertical non orthogonal fractures and corrugated fractures our modelling results confirm that s wave splitting can reveal the fracture infill in the case of dipping fractures s wave splitting has the potential to reveal the angle between the two vertical fractures we also notice that in the case of vertical corrugated fractures s wave splitting is sensitive to the fracture infill

three dimensional simulations of ground motions in the san bernardino valley california for hypothetical earthquakes on the san andreas fault three dimensional finite difference simulations of elastic waves in the san bernardino valley were performed for two hypothetical earthquakes on the san andreas fault a point source with moment magnitude m5 and an extended rupture with m6 5 a method is presented for incorporating a source with arbitrary focal mechanism in the grid synthetics from the 3 d simulations are compared with those derived from 2 d vertical cross section and 1 d flat layered models the synthetic seismograms from the 3 d and 2 d simulations exhibit large surface waves produced by conversion of incident s waves at the edge of the basin seismograms from the flat layered model do not contain these converted surface waves and underestimate the duration of shaking the seismograms from the 3 d simulations have larger amplitude coda than do the seismograms from the 2 d case because of the presence of off azimuth surface wave arrivals in the 3 d simulations that are not included in the 2 d simulations snapshots of the wavefield of the 3 d simulation show that these off azimuth arrivals represent surface waves reflected from the edges of the basin the anelastic attenuation of the sediments is a key parameter controlling the overall duration of motion some of the coda energy at rock sites near the basin edges represents leakage of surface wave energy out of the basin for the m6 5 earthquake simulation the largest ground velocities occur where surface waves reflected from the edge of the basin interfere constructively with the trapped waves that follow the direct s wave maps of maximum ground velocity are produced for two directions of rupture propagation the largest velocities occur in localized portions of the basin the location of the largest velocities changes with the rupture propagation direction contours of maximum shaking are also dependent on asperity positions and radiation pattern

site amplification in the los angeles basin from three dimensional modeling of ground motion it is well established that sedimentary basins can significantly amplify earthquake ground motion however the amplification at any given site can vary with earthquake location to account for basin response in probabilistic seismic hazard analysis therefore we need to know the average amplification and intrinsic variability standard deviation at each site given all earthquakes of concern in the region due to a dearth of empirical ground motion observations theoretical simu lations constitute our best hope of addressing this issue here 0 0 5 hz finite difference finite fault simulations are used to estimate the three dimensional 3d response of the los angeles basin to nine different earthquake scenarios amplifi cation is quantified as the peak velocity obtained from the 3d simulation divided by that predicted using a regional one dimensional 1d crustal model average ampli fication factors are up to a factor of 4 with the values from individual scenarios typically differing by as much as a factor of 2 5 the average amplification correlates with basin depth with values near unity at sites above sediments with thickness less than 2 km and up to factors near 6 above the deepest 9 km and steepest dipping parts of the basin there is also some indication that amplification factors are greater for events located farther from the basin edge if the 3d amplification factors are divided by the 1d vertical sh wave amplification below each site they are lowered by up to a factor of 1 7 the duration of shaking in the 3d model is found to be longer by up to more than 60 seconds relative to the 1d basin response the simu lation of the 1994 northridge earthquake reproduces recorded 0 0 5 hz particle velocities relatively well in particular at near source stations the synthetic and observed peak velocities agree within a factor of two and the log standard deviation of the residuals is 0 36 this is a reduction of 54 and 51 compared to the values obtained for the regional 1d model and a 1d model defined by the velocity and density profile below a site in the middle of the basin dow respectively this result suggests that long period ground motion estimation can be improved consid erably by including the 3d basin structure however there are uncertainties con cerning accuracy of the basin model model resolution the omission of material with shear velocities lower than 1 km s and the fact that only nine scenarios have been considered therefore the amplification factors reported here should be used with caution until they can be further tested against observations however the results do serve as a guide to what should be expected particularly with respect to increased amplification factors at sites located above the deeper parts of the basin

modeling of ground motion from a 1994 northridge aftershock using a tomographic velocity model of the los angeles basin the 1994 northridge mainshock and its aftershocks show a complex pattern of peak accelerations at stations located in the los angeles basin the waveforms contain multiples of body wave phases and extensive surface waves at frequencies mostly below 1 hz in particular for stations at distances greater than 18 km secondary arrivals show larger accelerations than the direct s wave arrivals the mainshock waveforms are further complicated by irregularities of the source rupture we use 2d finite difference to evaluate the effect of lateral variations in seismic velocity on the amplitude of shear wave energy and to distinguish the effects of source and propagation path we model waveforms from one aftershock recorded at nine stations deployed along a 60 km long profile extending into the los angeles basin we use a two dimensional slice through the 3d tomography model of the los angeles basin in the 2d finite difference calculations these synthetic waveforms fit the aftershock waveforms significantly better than corresponding waveforms determined from simple 1d velocity models with the addition of a thin low velocity surface layer above the tomography model the finite difference synthetics reproduce most of the important features of the recorded data in particular the large amplitude arrivals 7 to 10 sec following the direct s arrival these arrivals correspond to the ss arrival which is sharply refracted at the basin edge and the s wave with multiple legs trapped by the dipping near surface gradient for large earthquakes located either inside or outside the basin these phases can be the cause of the largest and hence potentially most hazardous shaking in the los angeles basin

explicit convection and scale aware cumulus parameterizations high resolution simulations over areas of different topography in germany abstractan increase in the spatial resolution of regional climate model simulations improves the representation of land surface characteristics and may allow the explicit calculation of important physical processes such as convection the present study investigates further potential benefits with respect to precipitation based on a small ensemble of high resolution simulations with wrf with grid spacings up to 1 km the skill of each experiment is evaluated regarding the temporal and spatial performance of the simulation of precipitation of one year over both a mountainous region in southwestern germany and a mainly flat region in northern germany this study allows us to differentiate between the impact of grid spacing topography and convection parameterization furthermore the performance of a state of the art convection parameterization scheme in the gray zone of convection is evaluated against an explicit calculation of convection only our evaluation demonstrates the following high resolution si

calculation of synthetic seismograms in a laterally varying medium by the boundary element discrete wavenumber method abstract we investigate the propagation of lg waves in laterally varying crustal structures by numerical simulation the method of calculation is formulated in terms of boundary integral equations where the green9s functions are evaluated by wavenumber summation the approach is well suited to study the propagation of seismic waves in a layered medium where the interfaces are flat in some regions and irregular in others we investigate the effect of a crustal fault with vertical offset and study the case of a lateral change in crustal thickness the results show that the lg wave amplitude is only slightly affected by the presence of these heterogeneities they confirm the robustness of lg wave propagation in presence of lateral heterogeneities observed in other numerical simulations they show that large scale geometric features of the crust cannot account alone for the strong attenuation of lg waves observed in many regions the results also suggest a possible relation between the level of lg wave coda and the degree of roughness of the moho they further indicate the importance of backscattering and suggest a possible use of the backscattered wave field to map strong crustal heterogeneities

resolution dependence of the simulated precipitation and diurnal cycle over the maritime continent the maritime continent is a region of intense rainfall characterised by a strong diurnal cycle this study investigates the sensitivity of rainfall characteristics to resolution in a coupled regional climate model configuration in particular focusing on processes that modulate the diurnal cycle model biases are resolution dependent increasing resolution from 3 4 to 1 4 improves the mean state sea surface temperature and precipitation biases however at higher resolutions 1 12 rainfall becomes too strong in most areas daily maximum rainfall is simulated about 2 4 h earlier than in observations over both the land and the ocean with only small improvements over high topography at higher resolution we develop a technique to examine cross coastal processes associated with the rainfall diurnal cycle along all coastlines this is used to investigate the sensitivity of the diurnal cycle to resolution and to the direction of the prevailing wind during offshore prevailing winds most land rainfall is confined near the coastline and associated with a shallow land sea breeze circulation at all resolution though rainfall partly develops directly inland at 1 12 during onshore prevailing winds rainfall propagates from the coastline to the island interior at 1 4 and 1 12 whereas it appears directly over the island interior at 3 4 and this is associated with a deep convective cell across the coastline for all resolutions oceanic rainfall propagates far offshore during offshore prevailing winds at all resolutions whereas it tends to remain confined near the coastline under onshore prevailing winds condition particularly at higher resolution

weak motion based attenuation relationships for israel summary we performed a regional study of earthquake ground motion scaling relations to provide the seismic hazard community of israel with a new attenuation relationship that could be used for the prediction of earthquake induced ground motion strong earthquakes are rather scarce in israel and the existing collection of records from strong earthquakes is not sufficient to allow the use of traditional regression methods to develop a regional attenuation relationship we used velocity seismograms from the israel seismic network to estimate the distance and frequency dependence of ground motion in the israel region from frequent smaller regional earthquakes our analyses included 4814 waveforms recorded by 30 stations of the israel seismic network from 2000 to 2005 we restricted our analysis to 330 events recorded at five or more stations with duration magnitudes ranging between 1 0 and 5 2 we derived empirical excitation site and regional attenuation terms by regressing the peak amplitudes of narrowband filtered seismograms around the shear wave arrivals and the rms fourier spectral amplitudes taken around the specific sampling frequency in order to optimize the attenuation parameters in our scaling model we used a simple grid search an optimal solution for minimal error between empirical and theoretical attenuation function was found for the quality parameter q f 298f0 67 and the geometrical spreading g r parametrized as a bilinear piecewise function r 0 74 for r 60 km and r 0 47 for r 60 km the spectral parameters of 0 015 s and stress drop increasing from 0 3 to 4 mpa were used to model the excitation spectra a theoretical modelling effort based on brune s source spectrum and random vibration theory rvt was performed on the attenuation and source parameters estimated in this study comparison of the attenuation relationship derived with locally measured ground motions shows excellent agreement with the data in the magnitude range for which we have observations and seems to be adequate for predictions of earthquake ground motion for the israel region comparison of peak ground acceleration pga predictions based on our scaling relationship with those that have been recently used for seismic hazard analysis in israel shows that our attenuation relationship predicts significantly lower ground motions than other relations

variability of ground motions in southern california data from the 1995 to 1996 ridgecrest sequence seismograms from the 1995 to 1996 ridgecrest california earthquake sequence recorded by the trinet digital seismic network provide high quality waveforms from sites throughout southern california including sites in markedly heterogeneous areas like the los angeles area sedimentary basins synthetic seismograms calculated by the reflectivity method with various 1d models are used as a baseline to measure the variability of amplitudes throughout southern california regardless of the model used there is greater variability in the amplitudes from basin site records than from rock site records rock soil and basin sites are all rather insensitive to radiation pattern nodes at the three frequency bands investigated 0 1 to 0 2 hz 0 2 to 0 4 hz and 0 4 to 0 8 hz this complicates the analysis because the nodes create singularity points in the distribution of ratios of observed and synthetic amplitudes when stations near nodal planes are removed the surface waves observed at most rock sites have peak amplitudes within a factor of 2 of synthetic waveform amplitudes peak amplitude of the surface waves observed at the soil and basin stations are more variable with the bulk of the distribution of data synthetic amplitude ratios less than 3 and a few outliers greater than 5 these outliers occur at the higher frequency bands soil and basin sites are also more often larger than the synthetics higher median values most outliers can be explained by applying a water level of 50 to the radiation pattern this reduces the scatter in the distributions to about the same extent as removing data within 10 of nodes thus most of the outliers are sites that are insensitive to the nodes not sites that are larger than the overall data distribution

site response shallow shear wave velocity and wave propagation at the san jose california dense seismic array ground motion records from a 52 element dense seismic array near san jose california are analyzed to obtain site response shallow shear wave velocity and plane wave propagation characteristics the array located on the eastern side of the santa clara valley south of the san francisco bay is sited over the evergreen basin a 7 km deep depression with miocene and younger deposits site response values below 4 hz are up to a factor of 2 greater when larger regional records are included in the analysis due to strong surface wave development within the santa clara valley the pattern of site amplification is the same however with local or regional events site amplification increases away from the eastern edge of the santa clara valley reaching a maximum over the western edge of the evergreen basin where the pre cenozoic basement shallows rapidly amplification then decreases further to the west this pattern may be caused by lower shallow shear wave velocities and thicker quaternary deposits further from the edge of the santa clara valley and generation trapping of surface waves above the shallowing basement of the western evergreen basin shear wave velocities from the inversion of site response spectra based on smaller local earthquakes compare well with those obtained independently from our seismic reflection refraction measurements velocities from the inversion of site spectra that include larger regional records do not compare well with these measurements a mix of local and regional events however is appropriate for determination of site response to be used in seismic hazard evaluation since large damaging events would excite both body and surface waves with a wide range in ray parameters frequency wavenumber plane wave analysis is used to determine the backazimuth and apparent velocity of coherent phases at the array conventional high resolution and multiple signal characterization f k power spectra and stacked slowness power spectra are compared these spectra show surface waves generated scattered at the edges of the santa clara valley and possibly within the valley at the western edge of the evergreen basin

the diurnal cycle of precipitation over the maritime continent in a high resolution atmospheric model climate models can exhibit systematic errors in their mean precipitation over the maritime continent of the indonesian archipelago at the heart of the tropical warm pool these can often be traced back to an erroneous simulation of the diurnal cycle and can lead to errors in global climate through planetary wave propagation here we examine the simulation of the diurnal cycle over the maritime continent in a series of high resolution integrations of the uk met office atmospheric model with horizontal resolutions of 40 and 12 km where the convection is parametrised and 4 km where the convection is explicitly resolved as part of the cascade project in these models the vertical heating profile over the islands changes from a convective profile with a mid tropospheric maximum in the early afternoon to a more stratiform profile with upper tropospheric heating and mid tropospheric cooling later the convective heating profile forces a first internal mode gravity wave that propagates rapidly offshore the deep warm anomalies behind its downwelling wavefront suppress convection offshore during early afternoon the stratiform heating profile forces a gravity wave with a higher order vertical mode that propagates slowly offshore later in the afternoon this mode has a negative destabilising temperature anomaly in the mid troposphere together with the convergence zone between the wave fronts of the two modes favourable conditions are created for offshore convection in the 4 km explicit convection model the offshore convection responds strongly to this gravity wave forcing in agreement with observations supporting a gravity wave convection paradigm for the diurnal cycle over the maritime continent however the convective response in the lower resolution models is much less coherent leading to errors in the diurnal cycle and mean precipitation hence to improve climate model simulations sensitivity to gravity wave forcing should be a factor in future convective parametrisation schemes copyright c 2011 royal meteorological society

strong sh to love wave scattering off the southern california continental borderland seismic scattering is commonly observed and results from wave propagation in heterogeneous medium yet deterministic characterization of scatterers associated with lateral heterogeneities remains challenging in this study we analyze broadband waveforms recorded by the southern california seismic network and observe strongly scattered love waves following the arrival of teleseismic sh wave these scattered love waves travel approximately in the same azimuthal direction as the incident sh wave at a dominant period of 10 s but at an apparent velocity of 3 6 km s as compared to the 11 km s for the sh wave back projection suggests that this strong scattering is associated with pronounced bathymetric relief in the southern california continental borderland in particular the patton escarpment finite difference simulations using a simplified 2 d bathymetric and crustal model are able to predict the arrival times and amplitudes of major scatterers the modeling suggests a relatively low shear wave velocity in the continental borderland

simulation of long period ground motion near a large earthquake we estimated the possible range of long period ground motion for sites located on a soft sedimentary basin in the immediate vicinity of a large earthquake since many large cities in the world e g los angeles san francisco and tokyo where many large structures have been recently constructed are located in this type of environment a better understanding of long period ground motion is becoming increasingly important our objective is to estimate the possible range of long period ground motion rather than ground motion for a specific fault model we computed ground motion time series and pseudo velocity response spectra pvs for more than 5 000 models for the 1923 kanto japan earthquake m w 7 9 using 180 slip distributions eight rupture geometry and rupture velocities ranging from 1 5 to 3 0 km sec two seismograms recorded in tokyo during the 1923 kanto earthquake are used for comparison the response spectra computed using seismologically reasonable sets of source parameters for the 1923 kanto earthquake vary by more than an order of magnitude at periods of 10 to 13 sec they range from 25 to 170 cm sec in tokyo for some combinations of model parameters the response spectra exhibit peaks in the range of 10 to 13 sec many of the computed response spectra have peaks at periods longer than 10 sec which is considerably longer than the dominant period 6 to 8 sec estimated from studies of small earthquakes and microtremor measurements thus the dominant period of the subsurface structure determined locally may not be representative of the dominant period of ground motion from a nearby large earthquake which is controlled by rupture directivity and source depth we performed a similar simulation for a hypothetical m w 7 5 earthquake located beneath the los angeles basin for a site just above the center of the fault the ground motion spectral amplitude at a period of 10 sec can vary from 50 to 350 cm sec this range though very large is what is expected for a seismologically plausible range of source parameters

3d seismic response of the deep basement structure of the granada basin southern spain the granada basin is located in the southeast of spain in the central sector of the betic cordilleras in an area of high seismic hazard in the iberian peninsula this hazard is due in part to local ground motion amplification effects that have been observed at various locations in this basin in this work we use the indirect boundary element method ibem to compute the three dimensional 3d seismic response of the deep structure of the granada basin for incident p and s plane waves coming from the south we have analyzed the results in both frequency and time domains and for the range of frequencies that we have been able to compute between 0 and 0 312 hz the most relevant site effects are the local amplifications produced inside the sediments generally speaking the observed amplification pat terns of the displacements for incident sh waves are the highest at those locations where the basin is deeper for p and sv waves the snapshots show the amplifi cation effects of both radial and vertical components when the direct waves cross the granada basin the amplification levels with respect to the amplitude of the incident wave are not so large because the impedance contrast between the sedi ments and the bedrock equal to 2 45 is relatively low moreover two perpendicular receiver profiles are used to analyze the wave propagation and we have observed the propagation of phases that can be identified as surface waves along the two profiles the rayleigh waves propagate with more energy on the forward direction from south to north of the incident body wave

the seismic coda site effects and scattering in alluvial basins studied using aftershocks of the 1986 north palm springs california earthquake as source arrays abstract we use single station recordings of widely distributed earthquake sources to identify heterogeneities in the earth9s crust that scatter energy into the early part of the observed s wave codas we assume that ray theory accurately describes the propagation of body waves from the earthquake sources to the scatterers but we assume no propagation mechanism between the scatterers and the seismic station a grid of hypothetical scatterers is assumed to cover the earth9s surface and the strength of each scatterer is determined by an iterative inversion method our data are recordings of aftershocks of the 1986 north palm springs earthquake recorded at a seismic station in the coachella valley smp and at a station in the morongo valley smc the technique is applied separately to each horizontal component of motion at each station we identify a particular spot at the northwest edge of the quaternary alluvium in the coachella valley that scatters waves into the s coda observed at smp 8 km distant in the valley the geologic structure that causes the strong scattering seems to be the basin edge structure rather than the mountainous terrain 3 km farther west the early coda at smc is dominated by scattering within a few kilometers of smc either in the basin itself or in the morongo valley fault zone this study shows that laterally propagating waves are sometimes observable in the early coda casting doubt on the use of 1 d techniques for estimating site responses the northwest edge of the coachella valley seems to be an especially strong scatterer of incident waves if other basins have similar loci of strong scattering perhaps these places can be identified using microearthquake seismograms and used to predict strong ground motions in the basins

simulations of ground motion in the los angeles basin based upon the spectral element method we use the spectral element method to simulate ground motion generated by two recent and well recorded small earthquakes in the los angeles basin simulations are performed using a new sedimentary basin model that is constrained by hundreds of petroleum industry well logs and more than 20 000 km of seismic reflection profiles the numerical simulations account for 3d variations of seismic wave speeds and density topography and bathymetry and attenuation simulations for the 9 september 2001 m w 4 2 hollywood earthquake and the 3 september 2002 m w 4 2 yorba linda earthquake demonstrate that the combination of a detailed sedimentary basin model and an accurate numerical technique facilitates the simulation of ground motion at periods of 2 sec and longer inside the basin model and 6 sec and longer in the regional model peak ground displacement velocity and acceleration maps illustrate that significant amplification occurs in the basin

estimation of strong ground motion from the great 1964 mw 9 2 prince william sound alaska earthquake we are generating physically plausible near field synthetic ground motions for the great 1964 prince william sound alaska earthquake compatible with available seismological data tectonic information and eyewitness accounts the first objective of this study is the simulation of the low frequency i e f 0 03 hz strong ground motions on selected locations and on a dense grid of observation points extending over the shallow dipping causative fault of the 1964 alaska earthquake in order to accomplish this task we are utilizing the slip model proposed by johnson et al 1996 based on a joint inversion of tsunami waveforms and geodetic data the calculations are carried out using the discrete wavenumber representation method bouchon and aki 1977 bouchon 1979 and the generalized transmission and reflection coefficient technique luco and apsel 1983 the second objective of this study is the reconstruction of the strong ground motion time histories and response spectra that the city of anchorage experienced during the 1964 alaska earthquake the low frequency i e f 0 03 hz ground motions are generated using the methodology described previously the intermediate frequency i e 0 03 f 0 50 hz ground motions are simulated by convolving green s functions generated by the discrete wavenumber representation method with far field radiation pulses of circular cracks sato and hirasawa 1973 dong and papageorgiou 2002a the high frequency i e 0 5 f 8 0 hz ground motions are simulated using the stochastic modeling approach the three independently derived ground motion components are then properly combined to generate synthetic broadband ground motion time histories and response spectra for the city of anchorage due to the 1964 prince william sound earthquake the third objective of this study is the validation of the synthetic strong ground motions for the 1964 alaska earthquake against observed tectonic deformation ground motion estimates inferred from descriptions of structural damage and eyewitness accounts in summary the analysis presented in this study contributes to a better understanding of the seismological aspects of the 1964 alaska earthquake and provides synthetic time histories and response spectra for engineering applications compatible with all available information i e seismological tectonic and eyewitness accounts it should be noted however that the generated strong ground motions are not necessarily unique nor do they reflect the entire uncertainty that characterizes the problem under investigation

dense array recordings in the san bernardino valley of landers big bear aftershocks basin surface waves moho reflections and three dimensional simulations abstract fourteen geos seismic recorders were deployed in the san bernardino valley to study the propagation of short period t 1 to 3 sec surface waves and moho reflections three dense arrays were used to determine the direction and speed of propagation of arrivals in the seismograms the seismograms for a shallow d 1 km m 4 9 aftershock of the big bear earthquake exhibit a very long duration 60 sec of sustained shaking at periods of about 2 sec array analysis indicates that these late arrivals are dominated by surface waves traveling in various directions across the valley some energy is arriving from a direction 180 from the epicenter and was apparently reflected from the edge of the valley opposite the source a close in aftershock 25 km depth 7 km displays substantial short period surface waves at deep soil sites a three dimensional 3d finite difference simulation produces synthetic seismograms with durations similar to those of the observed records for this event indicating the importance of s wave to surface wave conversion near the edge of the basin flat layered models severely underpredict the duration and spectral amplification of this deep soil site i show an example where the coda wave amplitude ratio at 1 to 2 hz between a deep soil and a rock site does not equal the s wave amplitude ratio because of the presence of surface waves in the coda of the deep soil site for one of the events studied 90 km there are sizable phases that are critically reflected from the moho pmp and sms at one of the rock sites the sms phase has a more peaked spectrum that the direct s wave

climatic changes along the northwestern african continental margin over the last 30 kyrs two sediment cores were investigated to study the regional climatic variability of the nw african upwelling over the late quaternary biomarker data and sea surface temperatures ssts predicted from alkenones at 25 n and 21 n exhibited distinct features the amplitude of the last deglaciation was estimated to 4 5 c at 25 n and 2 2 5 c at 21 n at 25 n terrestrial and marine glacial inputs were higher than holocene ones as a result of a strengthening of the trade winds and intensification of oceanic production in contrast at 21 n warmer ssts and lower organic carbon and alkenone productions during the last glacial suggest a regression of the upwelling and therefore a change of wind regime low glacial n alkanols are consistent with the migration of the vegetation belt during the maximum of african aridity while their decrease towards the core top may be indicative of anthropogenic disturbances

the san andreas fault system through the transverse ranges as illuminated by earthquakes the pattern of seismogenic faulting in the san gorgonio pass san bernardino basin area of the san andreas fault saf zone is mapped from about 7000 quality selected focal mechanisms 1981 nov 92 they are derived from phase data of the southern california network by a relocation procedure based on location dependent station corrections and by a grid search procedure about 3 4 of the mechanisms have been interpreted as planes of rupture or slip planes that delineate many distinct faults one of these faults is right lateral dips steeply northeast and is continuous trough the san gorgonio pass area we interpret it as the main branch of the saf a very large earthquake seems possible on this portion of the saf because of its continuity and because of the unusually deep reach of the seismicity 23 km southwest of this fault a volume of diffuse and persistent seismicity has a sharp downward cut off which may reflect a basal detachment dipping 20 northeast and intersecting the saf along the deepest seismicity northeast of the saf the floor of the seismicity is shallower by as much as 10 km stress characteristics are derived from slip planes in 10 selected subregions the regime is transpressional near the constricting bend of the saf at san gorgonio pass it is dominated by horizontal extension in the san bernardino basin area and it is again transpressional in the eastern san gorgonio mountains north of the cucamonga thrust the broad features of this zonation may be related to the intersection of the saf with the pinto mountain fault and with the san jacinto fault a change of fault kinematics in the yucaipa cluster coincides with the 1992 landers and big bear main shocks and may be a manifestation of static stress change

accounting for site effects in probabilistic seismic hazard analyses of southern california overview of the scec phase iii report this article presents an overview of the southern california earthquake center scec phase iii effort to determine the extent to which probabilistic seismic hazard analysis psha can be improved by accounting for site effects the contri butions made in this endeavor are represented in the various articles that compose this special issue of bssa given the somewhat arbitrary nature of the site effect distinction it must be care fully defined in any given context with respect to psha we define the site effect as the response relative to an attenuation relationship averaged over all damaging earthquakes in the region a diligent effort has been made to identify any attributes that predispose a site to greater or lower levels of shaking the most detailed maps of quaternary geology are not found to be helpful either they are overly detailed in terms of distinguishing different amplification factors or present southern california strong motion observations are inadequate to reveal their superiority a map based on the average shear wave velocity in the upper 30 m however is found to delineate significantly different amplification factors a correlation of amplification with basin depth is also found to be significant implying up to a factor of two difference between the shallowest and deepest parts of the los angeles basin in fact for peak accel eration the basin depth correction is more influential than the 30 m shear wave ve locity questions remain however as to whether basin depth is a proxy for some other site attribute in spite of these significant and important site effects the standard deviation of an attenuation relationship the prediction error is not significantly reduced by making such corrections that is given the influence of basin edge induced waves subsur face focusing and scattering in general any model that attempts to predict ground motion with only a few parameters will have a substantial intrinsic variability our best hope for reducing such uncertainties is via waveform modeling based on first principals of physics finally questions remain with respect to the overall reliability of attenuation re lationships at large magnitudes and short distances current discrepancies between viable models produce up to a factor of 3 difference among predicted 10 in 50 yr exceedance levels part of which results from the uncertain influence of sediment nonlinearity

precipitation features of the maritime continent in parameterized and explicit convection models abstractthe maritime continent is the largest archipelago in the world and a region of intense convective activity that influences earth s general circulation the region features one of the warmes

propagation of the madden julian oscillation through the maritime continent and scale interaction with the diurnal cycle of precipitation the convectively active part of the madden julian oscillation mjo propagates eastward through the warm pool from the indian ocean through the maritime continent the indonesian archipelago to the western pacific the maritime continent s complex topography means the exact nature of the mjo propagation through this region is unclear model simulations of the mjo are often poor over the region leading to local errors in latent heat release and global errors in medium range weather prediction and climate simulation using 14 northern winters of trmm satellite data it is shown that where the mean diurnal cycle of precipitation is strong 80 of the mjo precipitation signal in the maritime continent is accounted for by changes in the amplitude of the diurnal cycle additionally the relationship between outgoing long wave radiation olr and precipitation is weakened here such that olr is no longer a reliable proxy for precipitation the canonical view of the mjo as the smooth eastward propagation of a large scale precipitation envelope also breaks down over the islands of the maritime continent instead a vanguard of precipitation anomalies of 2 5 mm day 1 over 10 6 km 2 jumps ahead of the main body by approximately 6 days or 2000 km hence there can be enhanced precipitation over sumatra borneo or new guinea when the large scale mjo envelope over the surrounding ocean is one of suppressed precipitation this behaviour can be accommodated into existing mjo theories frictional and topographic moisture convergence and relatively clear skies ahead of the main convective envelope combine with the low thermal inertia of the islands to allow a rapid response in the diurnal cycle which rectifies onto the lower frequency mjo hence accurate representations of the diurnal cycle and its scale interaction appear to be necessary for models to simulate the mjo successfully

observations of loma prieta aftershocks from a dense array in sunnyvale california a small aperture 300 m four station array was deployed in sunnyvale california for 5 days to record aftershocks of the loma prieta earthquake of october 1989 the purpose of the array was to study the seismic response of the alluvium filled santa clara valley and the role of surface waves in the seismic shaking of sedimentary basins strong motion records of the loma prieta mainshock indicate that surface waves produced the peak velocities and displacements at some sites in the santa clara valley we use the recordings from the dense array to determine the apparent velocity and azimuth of propagation for various arrivals in the seismograms of four aftershocks with magnitudes between 3 6 and 4 4 apparent velocities are generally observed to decrease with increasing time after the s wave in the seismograms phases arriving less than about 8 sec after the s wave have apparent velocities comparable to the s wave and appear to be body waves multiply reflected under the receiver site or reflected by crustal interfaces for times 10 to 30 sec after the direct s wave we observe long period 1 to 6 sec arrivals with apparent velocities decreasing from 2 5 to 0 8 km sec we interpret these arrivals to be surface waves and conclude that these surface waves produce the long duration of shaking observed on the aftershock records much of the energy in the 40 sec after the s wave is coming approximately from the direction of the source although some arrivals have backazimuths as much as 60 different from the backazimuths to the epicenters two of the aftershocks show arrivals coming from 30 to 40 more easterly than the epicenters this energy may have been scattered from outcrops along the southeastern edge of the basin in contrast the deepest aftershock studied d 17 km displays later arrivals with backazimuths 30 to 40 more westerly than the epicenter a distinct arrival for one of the aftershocks propagates from the southwest possibly scattered from the western edge of the basin synthetic seismograms derived from a plane layered crustal model do not produce the long period love waves observed in the waveforms of the ml 4 4 aftershock these love waves may be generated by the conversion of incident s waves or rayleigh waves near the edge of the basin

three dimensional simulation of a magnitude 7 75 earthquake on the san andreas fault simulation of 2 minutes of long period ground motion in the los angeles area with the use of a three dimensional finite difference method on a parallel supercomputer provides an estimate of the seismic hazard from a magnitude 7 75 earthquake along the 170 kilometer section of the san andreas fault between tejon pass and san bernardino maximum ground velocities are predicted to occur near the fault 2 5 meters per second and in the los angeles basin 1 4 meters per second where large amplitude surface waves prolong shaking for more than 60 seconds simulated spectral amplitudes for some regions within the los angeles basin are up to 10 times larger than those at sites outside the basin at similar distances from the san andreas fault

broadband ground motion simulation within the city of duzce turkey and building response simulation in areas with significant seismic activity and insufficient seismic networks simulated ground motions are required for both seismic hazard and engineering analyses one important task is evaluating the efficiency of the simulated records in building response estimation in this study a hybrid ground motion simulation framework is presented to obtain broadband ground motion time histories of a past major earthquake in duzce turkey the hybrid ground motion simulation framework presented herein is a combination of a discrete wavenumber finite element method for simulating low frequencies and a stochastic finite fault method for the higher frequencies the proposed technique is first validated by the simulation of the 12 november 1999 duzce earthquake m text w 7 1 which occurred in the north anatolian fault zone turkey peak simulated ground motions at selected nodes are then compared against ground motion prediction equations derived with global and local data sets next the spatial distribution of simulated peak ground motion intensities are obtained in the region and compared with the observed damage distribution results demonstrate that the earthquake is simulated effectively despite the limitations in number of stations and velocity models finally to evaluate the simulated records in building response estimation nonlinear time history analyses of three reinforced concrete multi degree of freedom structures are performed with real and simulated records of the 1999 duzce earthquake in the opensees platform the results reveal that reasonable predictions can be made regarding the dynamic response of structures using the records simulated with the approach presented herein

role of topography on the mjo in the maritime continent a numerical case study the role of topography on a madden julian oscillation mjo event in the maritime continent mc is explored using a regional model four simulations are conducted lower resolution 12 km simulations using cumulus parameterization in the presence lr and absence lr flat of topography and higher resolution 4 km simulations without cumulus parameterization in the presence hr and absence hr flat of topography in the lr simulation the mjo remains unorganized with no clear eastward propagation while the lr flat simulation captures the mjo and its eastward propagation across the mc in the absence of cumulus parameterization both hr and hr flat capture the mjo and show several similarities and differences compared to the lr and lr flat simulations to better understand these differences a moisture budget analysis is conducted during the passage of the mjo in the lr flat simulation vertical advection of moisture is increased to the east of the islands leading to continuity in mjo associated convection continuity that was not present in the lr simulation the increase in vertical advection in the absence of topography is due to an increase in the mean moisture advection by the anomalous vertical winds in the middle of the mc horizontal advection seems to be the most important for an uninterrupted eastward propagation of the mjo the increase in the horizontal advection in the absence of topography is primarily due to an increase in the anomalous moisture advection by the mean zonal winds to what extent the mjo was influenced by the upstream effect from the new guinea topography was also explored these results indicate that the important physical processes for mjo associated convection may be different in different parts of the mc further implications of these results in the context of other recent studies on mjo propagation across the mc are discussed

wave propagation in 3d spherical sections effects of subduction zones abstract in order to understand details in the seismic wave field observed on regional and global scales on the earth s surface accurate modeling of 3d wave propagation is necessary while numerical techniques are now routinely applied to local seismic wave propagation only recently has the possibility of simulating wave propagation on larger scales in spherical geometry been investigated we apply a high order staggered grid finite difference scheme to the elastic wave equations in spherical coordinates r using regular grid spacing in a single domain the physical space is limited to spherical sections which do not include the axis 0 while the staggering of the space dependent fields improves the overall accuracy of the scheme some of the tensor elements have to be interpolated to the required grid locations by comparing with quasi analytical solutions for layered earth models we demonstrate the accuracy of the algorithm finally the technique is used to study the effects of a source located in a simplified slab structure the 3d technique will allow us to study the wave field due to laterally heterogeneous structures such as subduction zones plumes or oceanic ridges

experimental study of site effects in the fort de france area martinique island abstract we used weak motion recordings of regional events to quantify the site effects in the fort de france martinique area in the frequency band 1 to 25 hz the studied area extends over three distinct geological units the morne pitault volcanic massif 15 to 11 m a the carbet volcanic massif 4 to 2 m a and the lamentin alluvial plain quaternary age the topography being complex 31 sites were selected in order to get a representative sampling of the various topographical and geological configurations the large number of studied sites also allowed us to define a reference site whose selection was not obvious large broadband amplifications are observed in the lamentin plain instead of the expected peak resonances more surprising such resonance is observed around 2 to 3 hz on several sites of the volcanic vauclain pitault chain though no sedimentary layer is present on the other hand in the inner fort de france where significant effects were expected because of the very complex topography no large amplication is observed except for at one site clear three dimensional 3d effects are also observed at some stations though not very well documented the low frequency behavior deduced from teleseismic observations seems rather different illustrating the difficulty in finding a convenient reference site in such a volcanic area

rupture process of the ms 6 6 superstition hills california earthquake determined from strong motion recordings application of tomographic source inversion abstract we analyze strong motion recordings of the m s 6 6 superstition hills earthquake to determine the timing location spatial extent and rupture velocity of the subevents that produced the bulk of the high frequency 0 5 to 4 hz seismic energy radiated by this shock the earthquake can be characterized by three principal subevents the largest ones occurring about 3 and 10 sec after initiation of rupture timing relationships between pulses on the seismograms indicate that the three subevents are located within 8 km of each other along the northern portion of the superstition hills fault the two largest subevents display different directivity effects we apply a tomographic source inversion to the integrated accelerograms to determine the slip acceleration on the fault as a function of time and distance based on a one dimensional fault model the azimuthal distribution of amplitudes for the second subevent can be largely explained by a rupture that propagated about 2 km to the southeast along the superstition hills fault at a velocity about equal to the p wave velocity an alternative model with rupture propagating to the northeast along a conjugate fault plane can also account for the observed directivity of this subevent but it is not supported by the aftershock distribution the third subevent ruptured to the southeast along an 8 km long portion of the superstition hills fault at about the shear wave velocity this rupture propagation caused the relatively large accelerations and velocities observed in strong motion records for stations southeast of the hypocenter the long time intervals between the subevents and their relative proximity to each other indicate a very slow component to the rupture development the southern half of the superstition hills fault did not generate significant high frequency strong ground motion although it showed substantial co seismic surface displacement the subevents are situated along the same northern portion of the fault where most of the aftershocks are located the locations of the subevents appear to be controlled by bends in the fault mapped at the surface and by changes in basement structure at depth

3d viscoelastic wave propagation in the upper borrego valley california constrained by borehole and surface data we have simulated 2 hz wave propagation in a three dimensional model of the upper borrego valley southern california for a m 4 9 earthquake with epicenter 5 km north of the valley a 4th order staggered grid finite difference method was used to calculate viscoelastic ground motion in a basin model 9 km by 5 km by 0 4 km consisting of heterogeneous sediments surrounded by bedrock we simulated the earthquake as a double couple point source and computed the ground motions in the valley separately for the parts of the source incident from below and from the north the earthquake was recorded by a surface array as well as a deep downhole array 0 238 m depth in the center of the valley all equipped with digital three component seismic instruments the simulation reproduces the overall pattern of ground motions at basin and borehole sites and shows a good correlation of observed to synthetic waveforms in particular the 3d simulation reproduces the recorded peak motions cumulative kinetic energies and fourier spectral amplitudes within a factor of 2 for most components at the individual sites the correlation between data and simulation allows us to identify the secondary arrivals in the records as love and rayleigh waves generated at the edges of the valley and the troughs of the basin the peak velocities for the waves incident into the valley from below are generally more than an order of magnitude larger than those for the waves incident from the north the success of the prediction requires the inclusion of anelastic attenuation in the simulation with q values for p and s waves in the alluvium of about 30 we also used a profile of the 3d model and the soil parameters at the deep borehole to examine the ability of 2 5d and 1d model approximations to predict the data the maximum peak velocities and total cumulative kinetic energies are reproduced at the recording sites within a factor of 2 for both 2 5d and 1d model approximations but are underpredicted by up to an order of magnitude at some depths for individual components in particular the 2 5d and 1d simulations tend to underpredict the duration

why precipitation is mostly concentrated over islands in the maritime continent abstract high resolution observations and regional climate model simulations reveal that precipitation over the maritime continent is mostly concentrated over islands analysis of the diurnal cycles of precipitation and winds indicates that this is predominantly caused by sea breeze convergence over islands reinforced by mountain valley winds and further amplified by the cumulus merger processes comparison of a regional climate model control simulation to a flat island run and an all ocean run demonstrates that the underrepresentation of islands and terrain in the maritime continent weakens the atmospheric disturbance associated with the diurnal cycle and hence underestimates precipitation the implication of these regional modeling results is that systematic errors in coarse resolution global circulation models probably result from insufficient representation of land sea breezes associated with the complex topography in the maritime continent it is found that precipitation in the maritime continent

distribution of ground motion intensity inferred from questionnaire survey earthquake recordings and microtremor measurements a case study in christchurch new zealand during the 1994 arthurs pass earthquake the areal distribution of seismic ground motion intensity in the city of christchurch new zealand during the 1994 arthurs pass earthquake ml 6 6 was evaluated using an intensity questionnaire together with local site amplifications inferred from seismic recordings and microtremors in order to estimate the intensity in parts of the city where no intensity data were available intensity data were compared to relative levels of shaking determined from both weak motion and microtremor recordings weak ground motion amplification factors were determined using ratios of ground accelerations at five sediment sites with respect to a rock site microtremor amplification factors were determined from horizontal to vertical spectral ratios at a 1 km spacing throughout the city a positive correlation between weak motion and microtremor amplification factors allowed extrapolation of microtremor amplification to estimated mm intensity emmi emmi ranged from 3 to 6 and was consistent with the questionnaire intensity and geological conditions and showed detailed information on the areal distribution of ground motion intensity in the city

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

a finite difference approach for simulating ground responses in sedimentary basins quantitative modelling of the nile valley egypt summary on 1992 october 12 egypt was struck by an earthquake with m b 5 9 or equivalently m s 5 2 it occurred southwest of greater cairo cairo and giza and was widely felt from alexandria in the north to aswan in the south this earthquake also caused widespread destruction and damage mostly concentrated in greater cairo along the nile valley and in the nile delta area the extent of damage caused by this earthquake motivated this study we computed a 2 d finite difference fd synthetic wavefield for a prototype model of the nile valley with a maximum sedimentary basin thickness of 5 km and assumed uniform crustal thickness of 35 km a variant of the latter model tested is a thin crust moho bump beneath the basin we used a 2 5 hz ricker wavelet source that excites both p and or s waves initiated as point sources focal depths vary from 5 to 20 km to simulate different scenarios we investigated how various model features such as source location focal depth and epicentral distance deep sedimentary basin near surface attenuation and crustal thinning beneath the sedimentary basin may influence the wavefield across the nile valley the outstanding result of the wavefield simulations is that the nile valley sedimentary basin and the associated strong impedance contrast produce significant focusing and amplification effects it was found that the peak amplitudes might vary by one order of magnitude in the 3 8 hz frequency band across the nile valley the high vulnerability of the buildings in greater cairo in combination with focusing amplification in the nile valley explain qualitatively the extensive damage in the city itself even for moderate size earthquakes in fact the predicted area of high amplification coincides closely with that of greatest housing damage the effects of near surface attenuation in the uppermost 500 m within the basin and or crustal thinning beneath the basin is less significant these results are interesting on two accounts 1 the extent of variation in the synthetic wavefield will always be less than that observed but unfortunately there are no egyptian records to corroborate these results and 2 wavefield variations are significantly larger than those deduced from ranges of q variations and seismotectonic modelling as used in most seismic risk analysis these results imply that the wavefield simulations can be very informative and provide realistic results in particular when accurate structural model information is available and even more so if the synthetics can be corroborated with dense seismic network recordings

structural model of the san bernardino basin california from analysis of gravity aeromagnetic and seismicity data 1 the san bernardino basin is an area of quaternary extension between the san jacinto and san andreas fault zones in southern california new gravity data are combined with aeromagnetic data to produce two and three dimensional models of the basin floor these models are used to identify specific faults that have normal displacements in addition aeromagnetic maps of the basin constrain strike slip offset on many faults relocated seismicity focal mechanisms and a seismic reflection profile for the basin area support interpretations of the gravity and magnetic anomalies the shape of the basin revealed by our interpretations is different from past interpretations broadening its areal extent while confining the deepest parts to an area along the modern san jacinto fault west of the city of san bernardino through these geophysical observations and related geologic information we propose a model for the development of the basin the san jacinto fault related strike slip displacements started on fault strands in the basin having a stepping geometry thus forming a pull apart graben and finally cut through the graben in a simpler bending geometry in this model the san bernardino strand of the san andreas fault has little influence on the formation of the basin the deep central part of the basin resembles classic pull apart structures and our model describes a high level of detail for this structure that can be compared to other pull apart structures as well as analog and numerical models in order to better understand timing and kinematics of pull apart basin formation

earthquake ground motion and 3d georgia basin amplification in southwest british columbia shallow blind thrust scenario earthquakes abstract finite difference modeling of 3d long period 2 s ground motions for large m w 6 8 scenario earthquakes is conducted to investigate the effects of the georgia basin structure on ground shaking in greater vancouver british columbia canada scenario earthquakes include shallow blind thrust north america na plate earthquakes simulated in locations congruent with linear clusters of shallow seismicity that is potential active faults a slip distribution model of the m w 6 7 northridge california blind thrust earthquake with the hypocenter modified to 5 km depth is used to characterize the source rupture process two sets of simulations are performed for a given scenario earthquake using models with and without georgia basin sediments the ratio of predicted peak ground velocity pgv for the two simulations is applied here as a quantitative measure of amplification due to 3d basin structure a total of eight shallow blind thrust na plate scenario earthquakes are simulated within 100 km of greater vancouver overall predicted ground motions are higher in the down dip direction of each epicenter due to the source radiation pattern hence scenario earthquakes located south of vancouver produce the highest motions in the city the average maximum pgv at stiff soil sites across greater vancouver considering all eight scenario earthquakes is 17 8 cm s modified mercalli intensity vii the average increase in peak motion due to the presence of georgia basin sediments is a factor of 4 1 the effective duration of moderate level 3 4 cm s shaking within greater vancouver is an average of 22 s longer when georgia basin sediments are included in the 3d structure model online material snapshots and videos of wave propagation and peak ground velocity maps

causes of low frequency ground motion amplification in the salt lake basin the case of the vertically incident p wave summary we use simulations of 1 d 2 d and 3 d wave propagation to identify the major causes of low frequency 0 2 1 2 hz seismic amplification in the salt lake basin for a simple two layer basin model and a vertically incident p wave we examine how amplification is influenced by mode conversion surface wave generation impedance effects at the sediment bedrock boundary resonance and 2 d and 3 d focusing and scattering results show the following 1 approximately 30 per cent of the total cumulative kinetic energy at the salt lake valley floor consists of shear wave energy generated by p to s converted waves and surface waves the surface waves appear to be generated primarily along the edges of the basin and the instantaneous sip energy ratio in the sedimentary layer is as large as 3 2 the largest peak particle velocity at the free surface is due to the direct p wave the value is roughly predicted by the transmission coefficient of 1 46 at the sediment bedrock interface i e a normally incident p wave in the stiff bedrock will be magnified in amplitude by 1 46 times as it enters the softer sediments 3 the low frequency elastic response of the two layer salt lake basin model is characterized by surface wave propagation and resonance from vertically interfering waves 4 the peak particle velocities cumulative kinetic energies and mean spectral magnitudes computed from the 2 d 1 d synthetics underestimate the values computed from the 3 d synthetics by up to 40 per cent 48 per cent along a profile above the deepest part of the basin model the 2 d and 1 d signal duration times underestimate the 3 d values by up to 59 and 94 per cent respectively our results suggest that 2 d basin modelling may yield good approximations to the 3 d ground motion amplification above the deepest part of the salt lake basin our results show that several mechanisms contribute significantly to lowfrequency seismic amplification in the semi consolidated sediments of the salt lake basin p to s wave conversion surface wave generation impedance effects at the sediment bedrock boundary and resonance future attempts to estimate ground motion amplification in the salt lake basin should therefore account for the amplification effects of all these mechanisms

basin induced love waves observed using the strong motion array at fuchu japan phases have been observed in the s wave coda of local earthquakes recorded at the fuchu strong motion array located in the kanto basin in the western suburbs of tokyo japan these phases are often larger than the direct s wave at a period of 1 sec because these phases are observed only on horizontal components at surface sites and are weakly observed at only the shallowest 150 m of a number of borehole sites they are interpreted as love waves particle motions indicate significantly off azimuth travel directions the fuchu array is too sparse to allow the application of standard array analysis to determine the origin of these phases instead we use a combination of three component polarization enveloping and slant stack techniques that allows propagation directions to be reasonably well determined 10 however group slownesses are more difficult to obtain precisely 1 to 2 sec km using these results and assuming that the love waves are generated by the scattering of s waves at the earth s surface we estimate locations of scattering points we find that the scattering occurs along a short segment of the kanto basin boundary for widely distributed earthquake source locations we believe that this segment is important because it is the closest part of the basin boundary to the observation sites the existence of these basin induced love waves violates backscattering models for the generation of the coda of local earthquakes this must be kept in mind when applying coda techniques to sediment basin sites at periods of 1 sec or more

a three dimensional semianalytic viscoelastic model for time dependent analyses of the earthquake cycle 1 exploring the earthquake cycle for large complex tectonic boundaries that deform over thousands of years requires the development of sophisticated and efficient models in this paper we introduce a semianalytic three dimensional 3 d linear viscoelastic maxwell model that is developed in the fourier domain to exploit the computational advantages of the convolution theorem a new aspect of this model is an analytic solution for the surface loading of an elastic plate overlying a viscoelastic half space when fully implemented the model simulates 1 interseismic stress accumulation on the upper locked portion of faults 2 repeated earthquakes on prescribed fault segments and 3 the viscoelastic response of the asthenosphere beneath the plate following episodic ruptures we verify both the analytic solution and computer code through a variety of 2 d and 3 d tests and examples on the basis of the methodology presented here it is now possible to explore thousands of years of the earthquake cycle along geometrically complex 3 d fault systems

how does the ground shake when earthquakes occur near man made structures such as buildings or dams not only the absolute magnitude but also the precise characteristics of ground motions of the main shock and the aftershock determine the damage that occurs unconsolidated materials such as soil amplify ground motions more than rocks do but at the high strains near major earthquakes the behavior of the soils may be modified by scattering or nonlinear effects frankel discusses recent insights gained by o9connell page 2045 that shed new light on these scattering effects and points out that closely spaced monitoring networks are imperative if we are to understand the time histories of earthquake ground motions

love wave propagation in a three dimensional sedimentary basin abstract a simplified three dimensional finite element method has been developed for simulation of love wave propagation in three dimensional sedimentary basins the eigenfunctions for the fundamental mode surface waves are employed as interpolation functions in the finite element scheme by reducing the number of degrees of freedom the method enables us to analyze wave propagation in an area of 2000 km 2 as large as the southern part of the kanto plain japan time histories of the near izu ohshima earthquake of 1990 are calculated and compared with observation calculated displacement snapshots show the effect of three dimensional topography on direction of love wave propagation the three dimensional simulation is also compared with a two dimensional one demonstrating amplitude increase and extended duration time histories and their spectra from the three dimensional model show better agreement with the observations than those from the two dimensional model

three dimensional simulation of earthquakes on the los angeles fault system we have used a 3d finite difference method to simulate ground motion from elastodynamic propagating ruptures with constant slip on faults in the metropolitan area of los angeles california simulations are carried out for hypothetical m 6 75 earthquakes on the palos verdes and elysian park faults and for comparison an approximation to the 17 january 1994 m 6 7 northridge earthquake the dominant subsurface features of this area are the deep sedimentary los angeles basin and the smaller and shallower san fernando basin simulated ground motions are restricted to the frequency range 0 0 to 0 4 hz ground motion time histories show that in general sites associated with the largest particle velocities and cumulative kinetic energies are located 1 in the epicentral area 2 above the deepest parts of the basins and 3 near the steepest edges of the los angeles basin we find maximum particle velocities for the palos verdes elysian park and northridge simulations of 0 44 0 67 and 0 58 m sec respectively in each case both the directivity of the rupture and the lower impedance of the basins significantly amplify the ground motion although the gross radiation pattern from these ruptures is observable the 3d basin structure distorts the wave field and becomes a source for edge generated waves signal durations at some basin sites last beyond 90 sec due to love waves and refracted s waves that propagate into the sediments from the basin edges compared with the palos verdes event the durations are generally smaller for the elysian park earthquake due to a smaller amount of love waves generated at the basin edges a simple approximation to the northridge earthquake reproduces the overall spatial pattern of the long period particle velocities successfully predicts the timing of late arriving waves and matches the peak velocities with discrepancies generally less than a factor of 2 however for localized areas immediately north and south of the santa monica mountains the computed ground motion underpredicts the observed horizontal peak velocities but matches the vertical ones the pattern of simulated total cumulative kinetic energies is similar to that for the damage intensities observed near the epicenter of the northridge event while the northridge earthquake caused damage in the los angeles area the 3d simulations show that earthquakes with the same magnitude on the palos verdes or elysian park faults produce more severe ground shaking in the los angeles basin

a three dimensional simulation of seismic waves in the santa clara valley california from a loma prieta aftershock abstract the finite difference method is used to propagate elastic waves through a 3 d model of the santa clara valley an alluvium filled basin that underlies the city of san jose california the model was based on depth to bedrock information from water wells in the area the simulation corresponded to a region 30 east west by 22 north south by 6 depth km and contained about 4 million grid points synthetic seismograms from the simulation are accurate at frequencies up to 1 hz motions from a magnitude 4 4 aftershock of the loma prieta earthquake were modeled snapshots of ground motion and synthetic seismograms from the simulation are presented the simulation illustrates s to surface wave conversion at the edges of the basin and the large amplitude and long duration of ground motion in the basin compared to the surrounding rock love waves produced at the edge of the basin are the largest arrivals in the transverse synthetics because of the slow group velocity of the love waves sites near the center of the basin have longer durations of significant motions than basin sites near the valley edges sites near the center of the basin also show larger peak amplitudes on the transverse component array analysis of the synthetic seismograms indicates that love waves tend to propagate parallel to the eastern and western edges of the valley rayleigh waves are produced along the southern margin of the basin from incident s waves large radial motions occur where a rayleigh wave impinges on the northeast margin of the valley some rayleigh waves travel westward across the basin after being scattered from the eastern edge of the valley synthetic seismograms from the simulation have similar peak amplitudes as seismograms recorded by the sunnyvale dense array for this aftershock although the duration of the tranverse component is not matched by the synthetic seismogram using this basin model the simulation indicates that the love waves observed on the actual seismograms were produced by conversion of incident s waves at the southern margin of the santa clara valley 2 d simulations show how the s to love wave conversion is affected by the angle of incidence of the s wave and the sharpness of the velocity transition between the alluvium and bedrock as more accurate basin models are developed 3 d simulations should become valuable for predicting ground motions in sedimentary basins for future large earthquakes

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

assessment of simulated ground motions in earthquake engineering practice a case study for duzce turkey simulated ground motions can be used in structural and earthquake engineering practice as an alternative to or to augment the real ground motion data sets common engineering applications of simulated motions are linear and nonlinear time history analyses of building structures where full acceleration records are necessary before using simulated ground motions in such applications it is important to assess those in terms of their frequency and amplitude content as well as their match with the corresponding real records in this study a framework is outlined for assessment of simulated ground motions in terms of their use in structural engineering misfit criteria are determined for both ground motion parameters and structural response by comparing the simulated values against the corresponding real values for this purpose as a case study the 12 november 1999 duzce earthquake is simulated using stochastic finite fault methodology simulated records are employed for time history analyses of frame models of typical residential buildings next the relationships between ground motion misfits and structural response misfits are studied results show that the seismological misfits around the fundamental period of selected buildings determine the accuracy of the simulated responses in terms of their agreement with the observed responses

explosion earthquake and ambient noise recordings in a pliocene sediment filled valley inferences on seismic response properties by reference and non reference site techniques abstract explosion earthquake and ambient noise recordings were collected at the eastern edge of a pliocene sediment filled valley nearby the town of san casciano dei bagni tuscany central italy the anomalous amplification of amplitudes as high as a factor of 20 between sediment and hard rock sites shown by classical spectral ratios were compared with results obtained by using non reference site techniques like that of nakamura 1989 and its receiver function like extension the explosion data were collected in june 1990 as part of a crustal refraction experiment carried out in the monti vulsini volcanic area a linear array of 13 digital stations was deployed orthogonally to the eastern border of the radicofani graben 2 stations were set up on a bedrock outcrop whereas the remaining 11 were deployed on soft sediments 100 m apart along a straight line toward the center of the valley during a second part of the study two stations were left in the field to record local and regional seismicity acquiring data from more than 150 events from a seismic swarm that occurred in the monti vulsini volcanic area in february 1992 with a maximum magnitude m d 3 8 spectral ratios were computed on the 41 strongest events showing a seismic response consistent with that computed using explosion data at least in the 0 5 to 4 hz frequency band non reference site techniques were employed to analyze earthquake and noise data although it is clear that the horizontal vertical h v spectral ratios describe some intrinsic properties of sites noise and earthquake data give equivalent results in our case they failed in recognizing both resonances and amplification levels large amplifications shown by classical spectral ratios were probably due to basin induced surface waves and 3d resonances seismic waves recorded by a small 50m radius 2d array deployed within the valley provided instrumental evidence for the existence of waves diffracted locally on lateral heterogeneities

simulation of 3d elastic wave propagation in the salt lake basin abstract we have used a 3d finite difference method to model 0 2 to 1 2 hz elastodynamic site amplification in the salt lake valley utah the valley is underlain by a sedimentary basin which in our model has dimensions of 48 by 25 by 1 3 km simulations are carried out for a p wave propagating vertically from below and for p waves propagating horizontally to the north south east and west in a two layer model consisting of semi consolidated sediments surrounded by bedrock results show that in general sites with the largest particle velocities cumulative kinetic energies duration times of motion and spectral magnitudes overlie the deepest parts of the basin the maximum values of these parameters are generally found above steeply dipping parts of the basin walls the largest vector particle velocities are associated with p or sv waves that come from within 10 of the source azimuth low energy s and surface waves follow the strongest arrivals the largest peak particle velocities cumulative kinetic energies signal durations and spectral magnitudes in the simulations are respectively 2 9 15 9 40 0 and 3 5 times greater than the values at a rock site measured on the component parallel to the propagation direction of the incident p wave scattering and or mode conversions at the basin boundaries contribute significantly to the signal duration times as a check on the validity of our simulations we compared our 3d synthetic seismograms for the vertically incident plane p wave to seismograms of nearly vertically incident teleseismic p waves recorded at an alluvium site in the valley and at a nearby rock site the 3d synthetics for the alluvium site overestimate the relatively small amplification of the initial p wave and underestimate the large amplification of the coda using 2d simulations we find that most of the discrepancies between the 3d synthetic and observed records can be explained by an apparently incorrect total sediment thickness omission from the model of the near surface low velocity unconsolidated sediments and of attenuation and the inexact modeling of the incidence angle of the teleseism the records from a 2d simulation in which these deficiencies are remedied with q 65 and which also includes topography and a near surface velocity gradient in the bedrock provide a better match to the teleseismic data than the records from the simple two layer 3d simulation our results suggest that for steeply incident p waves the impedance decrease and resonance effects associated with the deeper basin structure control the amplification of the initial p wave arrival whereas reverberations in the near surface unconsolidated sediments generate the large amplitude coda these reverberations are caused mainly by p to s converted waves and their strength is therefore highly sensitive to the incidence angle of the source

the scec southern california reference three dimensional seismic velocity model version 2 we describe version 2 of the three dimensional 3d seismic velocity model of southern california developed by the southern california earthquake center and designed to serve as a reference model for multidisciplinary research activities in the area the model consists of detailed rule based representations of the major southern california basins los angeles basin ventura basin san gabriel valley san fernando valley chino basin san bernardino valley and the salton trough embedded in a 3d crust over a variable depth moho outside of the basins the model crust is based on regional tomographic results the model moho is represented by a surface with the depths determined by the receiver function technique shallow basin sediment velocities are constrained by geotechnical data the model is implemented in a computer code that generates any specified 3d mesh of seismic velocity and density values this parameterization is convenient to store transfer and update as new information and verification results become available

seismic investigation of near surface geological structure in the paducah kentucky area application to earthquake hazard evaluation abstract seismics method were used to evaluate shallow geological conditions at 33 sites in the vicinity of paducah kentucky a combined set of p and s wave seismic refraction and reflection soundings were used in addition to local borehole information to produce structure maps of 1 a shallow 160 m deep shear wave velocity contrasts across the shallow unconformity were generally 2 to 1 while the contrast at the top of the paleozoic bedrock exceeds 5 to 1 these seismic boundaries have been determined to be very important in modelling and interpreting earthquake ground motion amplification in the paducah area the quality and accuracy of the data and the cost effective nature of the methods suggest that other communities in areas at risk to damage from seismic activity with foundation conditions comparable to paducah might benefit from similar characterization in order 1 to identify seismically hazardous near surface geological conditions and 2 to develop geological models that could be used in computer simulations of site response

3 d wave propagation in the los angeles basin for the whittier narrows earthquake abstract elastic wave propagation within and around the los angeles basin during the whittier narrows earthquake in 1988 is simulated with a 3 d finite difference method the model consists mainly of a sedimentary layer over the basement but lateral variations inside the sedimentary basin is also included to approximate observed variations in surface shear velocity the minimum shear velocity is 1 km sec on the surface and fairly reliable results are obtained up to 0 75 hz the total simulation lasts 26 sec our simulation can reproduce the general amplification pattern small east of the epicenter and large in the l a basin and the san fernando valley due to thick sediments of low velocity in these areas surface waves are generated by the primary s wave and trapped inside the basins in the southern part of the l a basin a distinct later phase delayed by 5 to 6 sec relative to the primary s wave is produced in our simulation which matches some strong motion records

earthquake ground motion and structural response in alluvial valleys this paper is concerned with the problem of soil amplification and structural damage due to local site conditions in sedimentary valleys during earthquakes it focuses on a small valley in kirovakan for which 1d wave propagation analyses have failed to provide adequate answers for the large extent and spatial distribution of damage during the 1988 armenia earthquake a more realistic 2d finite element analysis is performed herein in search of an explanation of the observed behavior using as input an inferred rock accelerogram the response of the valley is calculated for a vertically incident sh wave synthetic accelerograms of the surface ground motion are presented for different sites these accelerograms are then used to determine the amplification ratios of the surface response with respect to that of the free field motion of the rock outcrop for different frequencies and for a continuous set of sites in addition response spectra are evaluated for simple oscillators representing structures located at various sites results of the 2d simulations show striking differences with respect to those from 1d analyses in particular 1 while the resonant frequencies exhibited by a 1d model for a given site also appear in the 2d model the peak ground response and structural response are almost twice as large for the 2d as for the 1d model 2 the 2d model exhibits in addition a new set of resonant frequencies and concomitant mode shapes across the valley which are directly related to its finite width and 3 due to these additional resonances the ground amplification ratio tends to oscillate very rapidly both spatially and with frequency leading to the observation that two identical structures located in the same vicinity or two slightly different structures located essentially on the same site can be subjected to significantly different seismic forces even if the underlying soils have very similar characteristics these results provide a meaningful explanation for the observed damage and thus serve to exemplify a situation in which site effects caused by the finite lateral extent of a valley must be taken into consideration in order to model satisfactorily seismic behavior

roles of deep and shallow convection and microphysics in the mjo simulated by the model for prediction across scales the november event of the madden julian oscillation mjo during the dynamo field campaign was simulated using the global compressible nonhydrostatic model for prediction across scales mpas with global coarse 60 and 15 km and regional the indian ocean cloud permitting 3 km meshes the purpose of this study is to compare roles of parameterized deep and shallow cumulus and microphysics in mjo simulations two cumulus schemes were used tiedtke and grell freitas the deep and shallow components of tiedtke scheme can be turned on and off individually the results reveal that microphysics alone without cumulus parameterization is able to produce strong signals of the mjo in precipitation with 3 km mesh and weak mjo signals with 15 km mesh a shallow scheme tiedtke along with microphysics strengthens the mjo signals but makes them less well organized on large scales a deep cumulus scheme can either improve the large scale organization of mjo precipitation produced by microphysics and shallow convection tiedtke or impair them grell freitas the deep scheme of tiedtke cannot reproduce the mjo well without its shallow counterpart the main role of shallow convection in the model is to transport moisture upward to the lower mid troposphere by doing so it removes dry biases in the lower mid troposphere a distinct feature in simulations with weak or no mjo signals and enhances total precipitation and diabatic heating produced by microphysics and deep cumulus schemes changing model grid spacing from 60 to 15 km makes a little difference in the model fidelity of reproducing the mjo all roles of shallow convection in 15 km simulations with parameterized deep convection cannot be reproduced in 3 km simulations without parameterized deep convection results from this study suggest that we should pay more attention to the treatment of shallow convection and its connection to other parameterized processes for improving mjo simulations in other words a holistic approach should be taken that consider parameterization of shallow cumulus microphysics boundary layer as well as deep cumulus as a whole for model improvement

three dimensional simulations of ground motions in the seattle region for earthquakes in the seattle fault zone we used the 3d finite difference method to model observed seismograms of two earthquakes m l 4 9 and 3 5 in the seattle region and to simulate ground motions for hypothetical m 6 5 and m 5 0 earthquakes on the seattle fault for periods greater than 2 sec a 3d velocity model of the seattle basin was constructed from studies that analyzed seismic reflection surveys borehole logs and gravity and aeromagnetic data the observations and the simulations highlight the importance of the seattle basin on long period ground motions for earthquakes occurring just south of the basin the edge of the basin and the variation of the thickness of the quaternary deposits in the basin produce much larger surface waves than expected from flat layered models the data consist of seismograms recorded by instruments deployed in seattle by the usgs and the university of washington uw the 3d simulation reproduces the peak amplitude and duration of most of the seismograms of the june 1997 bremerton event m l 4 9 recorded in seattle we found the focal mechanism for this event that best fits the observed seismograms in seattle by combining green9s functions determined from the 3d simulations for the six fundamental moment couples the february 1997 event m l 3 5 to the south of the seattle basin exhibits a large surface wave arrival at uw whose amplitude is matched by the synthetics in our 3d velocity model for a source depth of 9 km the m 6 5 simulations incorporated a fractal slip distribution on the fault plane these simulations produced the largest ground motions in an area that includes downtown seattle this is mainly caused by rupture directed up dip toward downtown radiation pattern of the source and the turning of s waves by the velocity gradient in the seattle basin another area of high ground motion is located about 13 km north of the fault and is caused by an increase in the amplitude of higher mode rayleigh waves caused by the thinning of the quaternary deposits

three dimensional simulation of the near fault ground motion for the 1995 hyogo ken nanbu kobe japan earthquake abstract the 17 january 1995 hyogo ken nanbu earthquake is a typical example showing that the ground motions along basin edge faults can be very destructive in this study we simulate the near fault ground motion from this earthquake based on a kinematic fault model and a simplified 3d velocity structure of the kobe area the kinematic earthquake rupture and the wave propagation are modeled using a 3d finite difference method fdm our simulation identifies the basin edge effect as an important factor that influenced the ground motion amplification pattern in the kobe area we found that the coupling of the source directivity and basin edge effects causes impulsive ground motions with extremely high amplitude at periods greater than 1 sec and in a narrow zone offset less than 1 km from the basin edge the combination of these effects acted to create a fairly continuous band of amplification that extends about 30 km in an elongated zone parallel to the basin edge boundary in some areas localized site effects might have been as important as the abovementioned effects but they cannot explain the continuity of the extended east west zone of damage

the effect of quaternary alluvium on strong ground motion in the coyote lake california earthquake of 1979 abstract the effect of alluvium on strong ground motion can be seen by comparing two strong motion records of the coyote lake california earthquake of 6 august 1979 m l 5 9 one record at a site on franciscan bedrock had a peak horizontal acceleration of 0 13 g and a peak horizontal velocity of 10 cm sec the other at a site 2 km distant on 180 meters of quaternary alluvium overlying franciscan had values of 0 26 g and 32 cm sec amplifications by factors of 2 and 3 horizontal motions computed at the alluvial site for a linear plane layered model based on measured p and s velocities show reasonably good agreement in shape with the observed motions but the observed peak amplitudes are greater by a factor of about 1 25 in acceleration and 1 8 in velocity about 15 per cent of the discrepancy in acceleration and 20 per cent in velocity can be attributed to the difference in source distance the remainder may represent focusing by refraction at a bedrock surface concave upward there is no clear evidence of nonlinear soil response fourier spectral ratios between motions observed on bedrock and alluvium show good agreement with ratios predicted from the linear model in particular the observed frequency of the fundamental peak in the amplification spectrum agrees with the computed value indicating that no significant nonlinearity occurs in the secant shear modulus computations show that nonlinear models are compatible with the data if values of the coefficient of dynamic shear strength in terms of vertical effective stress are in the range of 0 5 to 1 0 or greater the data illustrate that site amplification may be less a matter of resonance involving reinforcing multiple reflections and more the simple effect of the low near surface velocity application of traditional seismological theory leads to the conclusion that the site amplification for peak horizontal velocity is approximately proportional to the reciprocal of the square root of the product of density and shear wave velocity

surface motion over a sedimentary valley for incident plane p and sv waves abstract finite difference techniques are applied to study the response of a sedimentary basin in an isotropic elastic half space to vertically incident compressional and shear sources the sedimentary rock of the basin is modeled as a transversely isotropic material improved finite difference approximations to the boundary conditions are developed of primary interest is the formation of rayleigh waves over the flank of the basin displacement time series at points on the free surface and rayleigh orbits are plotted three dimensional spectral amplitude graphs of the entire time series up to a period of temporary quiescence are presented the rayleigh wave is the dominant scattered phase for the basin geometry considered having 20 to 30 per cent of the source displacement amplitude at the free surface in a basin with 26 flanks 0 7 km depth 6 km width over a half space whose acoustic impedance contrast with the basin was two the effect of varying the degree of compressional anisotropy in the basin on the amplitudes of refracted and scattered phases of engineering interest was minimal

modeling path effects in three dimensional basin structures path effects for seismic wave propagation within three dimensional 3 d basin structures are analyzed using a reciprocal source experiment in this experiment a numerical simulation is performed in which a point source is excited at a given location and then the wave field is propagated and recorded throughout a 3 d grid of points using the principle of reciprocity source and receiver locations are reversed this allows the modeling of path effects into a particular observation site for all possible source locations using only one simulation the numerical technique is based on the use of paraxial extrapolators and currently tracks only acoustic waves however the method is capable of handling arbitrary media variations thus effects due to focusing diffraction and the generation of multiple reflections and refractions are modeled quite well the application of this technique to model path effects for local earthquakes recorded at stations in the los angeles area of southern california indicates the strong influence of the 3 d crustal basins of this region on the propagation of seismic energy the modeling results show that the los angeles san fernando and san gabriel basins create strong patterns of focusing and defocusing for paths into these stations from various source locations these simulations correlate well with earthquake data recorded at both stations by comparing these calculations with earthquake data we can begin to evaluate the importance of these basin effects on observed patterns of strong ground motions

an analysis of simulated and observed blast records in the salt lake basin we have simulated 0 2 to 1 2 hz 3d elastic wave propagation in the salt lake basin from a blast at a nearby open pit mine a fourth order staggered grid finite difference method was used to simulate the blast in a two layer basin model 58 43 9 km consisting of semiconsolidated sediments up to 1 3 km thick surrounded by bedrock data from four blasts in the mine pit recorded by a network of 10 digital three component instruments were compared to the results of the simulation the simulation reproduces the overall pattern of ground motion amplification at basin sites relative to a rock site as measured by ratios of peak particle velocities cumulative kinetic energies and spectral magnitudes considering the simple two layer basin model used in the 3d simulation this finding suggests that the deep 3d basin structure significantly contributes to low frequency ground motion amplification in the salt lake basin 1 1 effects of a near surface layer of low velocity unconsolidated sediments p and s wave velocities of 1 65 and 0 41 km sec respectively that at soil sites along the profile increase the peak particle velocities by up to a factor of 3 and significantly increase the ground motion durations 2 2 attenuation in the sediments which greatly diminishes the ground motion durations on the synthetic seismograms when parameterized by realistic values of the quality factor q 20 for soil sites and 35 for bedrock sites 3 3 2d topographic scattering which increases the peak particle velocities by up to a factor of 2 and increases the signal durations for sites along the profile compared to the records from the simple two layer 3d simulation the records from a 2d p sv wave simulation that includes processes 1 through 3 provide a better match to the blast data especially the observed durations of shaking at five of the six stations along the profile the 2d simulation reproduces the normalized radial and vertical peak particle velocities to within a factor of 2 and the normalized cumulative kinetic energies and spectral amplitudes on these components to within generally a factor of 3 our results suggest that deep basin resonance reverberations in the near surface low velocity layer attenuation and topographic scattering significantly influence site amplification in the salt lake basin future studies of site amplification in the salt lake basin should include the effects of all of these mechanisms

replication of apparent nonlinear seismic response with linear wave propagation models it is necessary to understand ground motion amplification by sediment defined as the ratio of ground motions at sediment sites to those at rock sites to predict seismic loadings for earthquake engineering at sediment sites observed weak motion amplifications from magnitude 3 to 4 aftershocks of the 1994 northridge earthquake were twice as large as magnitude 6 7 mainshock amplifications amplitude dependent nonlinear amplification by sediment is one explanation however earthquake simulations with empirical impulse responses and elastic finite difference calculations with weakly heterogeneous random three dimensional 3d crustal velocity variations show that linear wave propagation can explain observed apparently nonlinear sediment responses random 3d velocity variations also reproduce the observed log normal dispersion of peak ground motions deterministic wave propagation models are not adequate to quantify the scaling and dispersion of near source ground motions

mesoscale variation in diabatic heating around sumatra and its modulation with the madden julian oscillation abstractdiabatic heating in the maritime continent region is controlled by a unique blend of mesoscale variability associated with steep topography and complex coastlines and intraseasonal variabil

delineation of faulting and basin geometry along a seismic reflection transect in urbanized san bernardino valley california fourteen kilometers of continuous shallow seismic reflection data acquired through the urbanized san bernardino valley california have revealed numerous faults between the san jacinto and san andreas faults as well as a complex pattern of downdropped and uplifted blocks these data also indicate that the loma linda fault continues northeastward at least 4 5 km beyond its last mapped location on the southern edge of the valley and to within at least 2 km of downtown san bernardino previously undetected faults within the valley northeast of the san jacinto fault are also imaged including the inferred western extension of the banning fault and several unnamed faults the rialto colton fault is interpreted southwest of the san jacinto fault the seismic data image the top of the crystalline basement complex across 70 of the profile length and show that the basement has an overall dip of roughly 10 southwest between perris hill and the san jacinto fault gravity and aeromagnetic data corroborate the interpreted location of the san jacinto fault and better constrain the basin depth along the seismic profile to be as deep as 1 7 km these data also corroborate other fault locations and the general dip of the basement surface at least 1 2 km of apparent vertical displacement on the basement is observed across the san jacinto fault at the profile location the basin geometry delineated by these data was used to generate modeled ground motions that show peak horizontal amplifications of 2 3 5 above bedrock response in the 0 05 to 1 0 hz frequency band which is consistent with recorded earthquake data in the valley