the attenuation of seismic shear waves in quaternary alluvium in santa clara valley california we used shear waves generated by an air powered source at the ground surface and recorded in a borehole to estimate the shear wave quality factor at strong motion station gilroy no 2 we find similar values of q using both the decay of the spectra with depth and the slope of the spectral ratio at two depths we find no evidence of a frequency dependence of q the mean value of q over the depth range 10 to 115 m is close to 10 the use of this value over the depth of the borehole and the observed travel time of 0 358 sec gives a cumulative attenuation factor t of 0 036 sec for the upper 180 m of the quaternary alluvium this is comparable to the differential decay between gilroy no 2 and a rock site 1 9 km away gilroy no 1 as measured from the decay of the high frequency spectra of accelerograms from large earthquakes plotted on a log linear scale t 0 05 0 04 and 0 03 sec for the 1979 coyote lake 1984 morgan hill and 1989 loma prieta earthquakes respectively the similarity between the attenuations measured from the low strain surface source and those from the larger amplitude earthquake sources suggests that increases of damping due to nonlinear wave propagation effects are limited

estimating severity of seismically induced landslides and lateral spreads using threshold water levels abstract the potential for an earthquake induced landslide increases when the shear strength of a slope decreases and the hydrostatic pressure increases from the dynamic stresses induced by seismic shaking and or heavy rainfalls this paper presents an assessment of seismically induced slope failure in the st louis mo usa area it emphasizes water elevations as the controlling factor realizing that such levels vary over space and time we estimated the threshold water table depths to initiate seismically induced landslides in the uplands and liquefaction induced lateral spreads in the alluvial floodplains under an m7 5 earthquake with a peak ground acceleration of 0 20 to 0 40 g these threshold water table depths were computed as a function of ground steepness using the newmark model for rigid block landslides and an empirical regression for lateral spreads the seismic microzonation was prepared by comparing the map of threshold water table depths and maps of average water levels the resultant hazard maps suggest that the river bluffs are prone to seismically induced landslides only when the water reaches its highest recorded levels while much of the floodplains are prone to lateral spreads lateral spreads occur more extensively when the water exceeds its normal level

three dimensional finite difference simulation of long period ground motions for the 2003 tokachi oki japan earthquake 1 to explore the generation and propagation mechanisms of long period ground motions we used a 3 d finite difference method to simulate wave propagation during the 2003 mw 8 3 tokachi oki japan earthquake a large scale computation with an inverted slip model and a geological and geophysical based velocity structure model successfully reproduced the overall characteristics of substantial observed velocity seismograms for a period range of 3 3 to 25 s significant long period ground motions of extended duration were observed in the yufutsu basin where oil tanks were damaged at tomakomai because of sloshing associated with the ground motions our simulation revealed that the combination of the large and shallow earthquake and the deep extent of the sedimentary basin generated long period ground motions with a duration of several hundred seconds the yufutsu basin contains an internal subbasin that deepens from east to west in contrast with the geometry of the overall basin that deepens from west to east the long period ground motions were amplified in both the eastern and western parts of the basin with the durations being greatly extended in the western part a series of computations with and without each of the velocity layers within the basin demonstrated that the basin response amplifies long period ground motions as expected and that the subbasin response is effective in amplifying and extending long period ground motions our quantitative 3 d finite difference simulations clarify the generation of disastrous long period ground motions that occurred in the yufutsu basin during the 2003 tokachi oki earthquake

strong shaking in los angeles expected from southern san andreas earthquake 1 the southernmost san andreas fault has a high probability of rupturing in a large greater than magnitude 7 5 earthquake sometime during the next few decades new simulations show that the chain of sedimentary basins between san bernardino and downtown los angeles form an effective waveguide that channels love waves along the southern edge of the san bernardino and san gabriel mountains earthquake scenarios with northward rupture in which the guided wave is efficiently excited produce unusually high long period ground motions over much of the greater los angeles region including intense localized amplitude modulations arising from variations in waveguide cross section

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

simplified method for spatial evaluation of liquefaction potential in the st louis area as a part of an earthquake hazard mapping program being undertaken by the u s geological survey in the st louis metropolitan area surficial geologic mapping and subsurface geotechnical data have been compiled into a three dimensional geographic information system gis the potential for soil liquefaction was then spatially evaluated by using subsurface information from 562 boreholes for an assumed m7 5 earthquake emanating from the new madrid seismic zone geotechnical data standard penetration test n values overburden pressure and depth to groundwater and the scenario peak ground accelerations pga 0 1 0 20 and 0 30 g were applied to evaluate the factor of safety fs against earthquake induced liquefaction the liquefaction potential index lpi method was used in these evaluations because it allows for calculations of fs with depth for 10 25 discrete stratigraphic horizons overlying the bedrock across the st louis metropolitan area lpi values were derived from the correlation between calc

seismic site classifications for the st louis urban area abstract regional national earthquake hazards reduction program nehrp soil class maps have become important input parameters for seismic site characterization and hazard studies the broad range of shallow shear wave velocity v s 30 the average shear wave velocity in the upper 30 m measurements in the st louis area results in significant uncertainties between the actual spot values and the averaged values used to assign nehrp soil classes for regional seismic hazard studies in the preparation of an nehrp site classification map of the st louis urban area we analyzed 92 shear wave velocity v s measurements supplemented by 1400 standard penetration test spt profiles in areas bereft of v s measurements spt blow counts correlated to v s values based on the published correlations the data were then compiled for respective surficial geologic units and bedrock type these data suggest that the reciprocal of v s 30 exhibits a fairly linear relationship with depth to bedrock likely because v s 30 is a function of the thickness of surficial materials exhibiting relatively low v s values the v s 30 values were interpolated by summing the regressed v s 30 on the depth to bedrock and kriged values of the regression residuals the resulting nehrp site classification maps predict that upland areas of the st louis area are spatially classified as soil site classes s b to s d while the low lying floodplains are consistently classified as s d to s f

single hole imaging using borehole gravity gradiometry abstractwe study the feasibility of imaging density variations away from boreholes using gravity gradient measurements in a single borehole the objective is to develop numerical interpretation tools and to understand the utility and limitations of borehole gravity gradiometry in anticipation of the development of such instruments for the exploration and production of minerals oil and gas we develop an analytic solution for directly locating discrete off hole mass anomalies and apply a generalized inverse approach to image anomalous density distribution in the analytic approach we solve for the distance and direction angles to a point source using the multiple components of the gravity gradient tensor from a set of observations in a single borehole and then apply this approach to the scenarios of prismatic sources in the generalized inverse approach we invert multiple gradient tensor components to construct 3d density contrast distributions around the borehole as few as two independent gravity gr

hybrid broadband seismograms for seismic shaking scenarios an application to the po plain sedimentary basin northern italy the densely populated po plain a very deep sedimentary basin in northern italy is prone to heavy shaking during earthquakes seismic hazard assessment must account for local variation in wave amplification standard ground motion prediction equations may fail to picture the complexity of strong lateral gradients in seismic response due to sharp structural heterogeneity for this reason there is an increasing demand for full waveform predictions for engineering applications here we present an implementation of a hybrid broadband simulation based on the method of mai et al bull seismol soc am 100 6 3338 3339 2010 to obtain complete broadband seismograms of 0 1 10 hz with this method low frequency 1 hz and high frequency 1 10 hz seismograms are simulated separately using a deterministic and a stochastic method respectively we apply the method to four events recorded within the po basin with magnitude ranging from mw 4 4 to mw 5 6 the low frequency lf simulation is performed using specfem3d on a few test subsurface velocity models the three dimensional velocity model mambo molinari et al in bull seismol soc am 105 2a 753 764 2015 consisting of a detailed structural description of the basin based on extensive active source data embedded within a regional 3d crustal model provided the best results for broadband simulations that most closely corresponded with the observations it performed better than an ambient noise tomography model with more accurate s wave velocities but less well defined layer topographies emphasizing the importance of first order velocity discontinuities the high frequency hf seismograms are simulated using the multiple scattering approach of zeng et al j geophys res solid earth 96 b1 607 619 1991 the scattering coefficients are obtained by performing a non linear inversion for each station to find best fitting synthetic envelopes hf energy is then combined at sim 1 hz to match the amplitude and phase spectra of the lf signal we are able to simulate full waveforms throughout the po plain of which shaking duration matches observed data for stations located in the basin shaking amplitudes are generally overestimated in the low frequency simulation by the mambo velocity model updating the mambo velocity model with more accurate s wave velocity information of the ambient noise tomography model should improve the fit in future simulations

lithology and shear wave velocity in memphis tennessee we have derived a new three dimensional model of the lithologic struc ture beneath the city of memphis tennessee and examined its correlation with measured shear wave velocity profiles the correlation is sufficiently high that the better constrained lithologic model may be used as a proxy for shear wave velocities which are required to calculate site amplification for new seismic hazard maps for memphis the lithologic model and its uncertainties are derived from over 1200 newly compiled well and boring logs some sampling to 500 m depth and a moving least squares algorithm seventy six new shear wave velocity profiles have been measured and used for this study most sampling to 30 m depth or less all log and velocity observations are publicly available via new web sites

crustal structure and seismicity distribution adjacent to the pacific and north america plate boundary in southern california new three dimensional 3 d v p and v p v s models are determined for southern california using p and s p travel times from local earthquakes and controlled sources these models confirm existing tectonic interpretations and provide new insights into the configuration of geological structures at the pacific north america plate boundary the models extend from the u s mexico border in the south to the southernmost coast ranges and sierra nevada in the north and have a 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth the heterogeneity of the crustal structure as imaged by v p and v p v s models is larger within the pacific plate than the north american plate similarly the relocated seismicity deepens and shows more complex 3 d distribution in areas of the pacific plate exhibiting compressional tectonics the models reflect mapped changes in the lithology across major geological terranes such as the mojave desert the peninsular ranges and the transverse ranges the interface between the shallow mono of the continental borderland and the deep moho of onshore california forms a broad zone to the north beneath the western transverse ranges ventura basin and the los angeles basin and a narrow zone to the south along the peninsular ranges the near surface increase in velocity from the surface to up to 8 km depth is rapid and has a logarithmic shape for stable blocks and mountain ranges but is slow with a linear shape for sedimentary basins at midcrustal depths a rapid increase in v p is imaged beneath the sediments of the large sedimentary basins while beneath the adjacent mountain ranges the increase is small or absent

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

near surface attenuation and site effects from comparison of surface and deep borehole recordings abstract near surface attenuation and site effects are investigated using the seismograms of 17 local earthquakes recorded at depths of 0 0 3 1 5 2 5 and 2 9 km in the cajon pass borehole southern california the borehole penetrates 500 m of miocene sandstone and then crystalline granitic basement rock previous estimates of site response have been limited to shallower holes where the surface reflection interferes with the upgoing direct wave and the deepest sensor is not below the severe near surface effects in bedrock spectral ratios of the direct p and s waves for each earthquake between the different recording levels are well modeled with frequency independent q and amplification at the borehole q p 27 8 and q s 21 7 in the upper 2 9 km increasing from q p 26 and q s 15 in the upper 300 m to q p 133 and q s 47 between 1 5 and 3 km one event was also recorded at a surface granite site less than 1 5 km from the wellhead comparison of the 2 9 km recording with that at this granite site gives q p 50 and q s 23 the similarity of these values with those of previous studies at a wide range of sites suggests that q is very low in the near surface independent of rock type near surface amplification appears considerably more site dependent at the wellhead the amplifications at 1 hz of the direct p and s waves are 12 7 and 13 7 respectively these values include the free surface effect and are in reasonable agreement with the impedance contrast from the borehole logs at the granite site amplification of both p and s waves is less than four direct wave amplification at the wellhead is therefore at least three times that of the granite site the spectra of the direct and coda waves of the one earthquake recorded at both the wellhead and granite sites are compared with the corresponding 2 9 km recording coda wave amplification is in good agreement with the direct wave at the rock site but at the borehole the coda wave amplification factor overestimates the direct wave amplification by a factor of 3

estimation of q for long period 2 sec waves in the los angeles basin we simulate 0 to 0 5 hz 3d wave propagation through the southern california earthquake center seismic velocity reference model version 2 for the 1994 northridge earthquake in order to examine the effects of anelastic attenuation and amplification within the near surface sediments we use a fourth order finite difference staggered grid method with the coarse grained frequency independent anelastic scheme of day and bradley 2001 and a variable slip distribution from kinematic inversion for the northridge earthquake we find that the near surface material with s wave velocity v s as low as 500 m sec significantly affects the long period peak ground velocities compared with simulations in which the s wave velocity is constrained to 1 km sec and greater anelastic attenuation also has a strong effect on ground motion amplitudes reducing the predicted peak velocity by a factor of up to 2 5 relative to lossless simulations our preferred q model is q s v s 0 02 v s in meters per second for v s less than 1 2 km sec and much larger q s v s 0 1 v s in meters per second for layers with higher velocities the simple model reduces the standard deviation of the residuals between synthetic and observed natural log of peak velocity from 1 13 to 0 26 relative to simulations for the lossless case the anelastic losses have their largest effect on short period surface waves propagating in the los angeles basin which are principally sensitive to q s in the low velocity near surface sediments of the basin the low frequency ground motion simulated here is relatively insensitive to q p as well as to the values of q s at depths greater than roughly that of the 2 km sec s wave velocity isosurface

far source long period displacement response spectra in the po and venetian plains italy from 3d wavefield simulations abstract design elastic displacement spectra for seismic codes and zoning studies of seismic hazard for long period structures are becoming of utmost importance in modern earthquake engineering the increase of displacement based design approaches together with the availability of good quality digital strong motion data allow the creation of reliable spectral shapes for seismic design of up to 10 s nevertheless to characterize the site amplification effects during large levels of shaking additional studies are needed especially in deep sedimentary basins and plains that can be strongly excited by large amplitude long period waves data within deep basins is rare because accelerometric seismic networks are normally deployed on rock or stiff soil and modeling of waveforms is hence necessary for bridging this gap focusing on the numerical modeling of the 3d wavefield in 1d flat layered and 3d structures in the po and venetian plains northern italy and on earthquakes with magnitudes m 6 6 and hypocentral distances greater than 50 km in this study we 1 estimate the displacement response spectra drs from 1 to 10 s in the po and venetian plains 2 compare the drs from numerical simulations using flat layered and heterogeneous 3d models against the currently available uniform hazard drs for italy and 3 evaluate the influence of deep sediments on drs shape and thus on seismic codes finally 1d and 3d simulated drs are compared with drs obtained from recordings in the kanto basin where similar long period displacement is observed

resolving fault plane ambiguity for small earthquakes summary we have developed an automated procedure to resolve fault plane ambiguity for small to medium sized earthquakes 2 5 ml 5 using synthetic green s tensors computed in a 3 d earth structure model and applied this procedure to 35 earthquakes in the los angeles area for 69 per cent of the events we resolved fault plane ambiguity of our cmt solutions at 70 per cent or higher probability for some earthquakes the fault planes selected by our automated procedure were confirmed by the distributions of relocated aftershock hypocentres in regions where there are no precisely relocated aftershocks or for earthquakes with few aftershocks we expect our method to provide the most convenient means for resolving fault plane ambiguity our procedure does not rely on detecting directivity effects therefore it is applicable to any types of earthquakes

nonlinear sediment response during the 1994 northridge earthquake observations and finite source simulations we have addressed the long standing question regarding nonlinear sediment response in the los angeles region by testing whether sediment amplification was similar between the northridge earthquake and its aftershocks comparing the weak and strong motion site response at 15 sediment sites we find that amplification factors were significantly less for the main shock implying systematic nonlinearity the difference is largest between 2 and 4 hz a factor of 2 and is significant at the 99 confidence level between 0 8 and 5 5 hz the inference of nonlinearity is robust with respect to the removal of possibly anomalous sediment sites and how the reference site motion is defined furthermore theoretical ground motion simulations show no evidence of any bias from finite source effects during the main shock nonlinearity is also suggested by the fact that the four sediment sites that contain a clear fundamental resonance for the weak motion exhibit a conspicuous absence of the peak in the strong motion although we have taken the first step of establishing the presence of nonlinearity it remains to define the physics of nonlinear response and to test the methodologies presently applied routinely in engineering practice the inference of nonlinearity implies that care must be exercised in using sediment site data to study large earthquakes or predict strong ground motion

liquefaction potential map of charleston south carolina based on the 1886 earthquake a liquefaction potential map of the peninsula of charleston s c is presented in this paper liquefaction potential is expressed in terms of the liquefaction potential index developed by iwasaki et al and calculated using 44 cone penetration test profiles the cone profiles are supplemented with information from the 1 24 000 scale geologic map by weems and lemon several first hand accounts of liquefaction and ground deformation that occurred during the 1886 charleston earthquake and liquefaction probabilities determined by elton and hadj hamou based on standard penetration tests nearly all of the cases of liquefaction and ground deformation occurred in the holocene to late pleistocene beach deposits that flank the higher ground sediments of the wando formation to match the observed field behavior a deposit resistance correction factor of 1 8 is applied to cyclic resistance ratios calculated for the 100 000 year old wando formation no corrections are needed for the younger deposits in additional to 1886 field behavior the deposit resistance corrections are supported by ratios of measured to predicted shear wave velocity

terashake2 spontaneous rupture simulations of mw 7 7 earthquakes on the southern san andreas fault abstract previous numerical simulations terashake1 of large m w 7 7 southern san andreas fault earthquakes predicted localized areas of strong amplification in the los angeles area associated with directivity and wave guide effects from northwestward propagating rupture scenarios the terashake1 source was derived from inversions of the 2002 m w 7 9 denali alaska earthquake that source was relatively smooth in its slip distribution and rupture characteristics owing both to resolution limits of the inversions and simplifications imposed by the kinematic parameterization new simulations terashake2 with a more complex source derived from spontaneous rupture modeling with small scale stress drop heterogeneity predict a similar spatial pattern of peak ground velocity pgv but with the pgv extremes decreased by factors of 2 3 relative to terashake1 the terashake2 source excites a less coherent wave field with reduced along strike directivity accompanied by streaks of elevated ground motion extending away from the fault trace the source complexity entails abrupt changes in the direction and speed of rupture correlated to changes in slip velocity amplitude and waveform features that might prove challenging to capture in a purely kinematic parameterization despite the reduced pgv extremes northwest rupturing terashake2 simulations still predict entrainment by basin structure of a strong directivity pulse with pgvs in los angeles and san gabriel basins that are much higher than predicted by empirical methods significant areas of those basins have predicted pgv above the 2 probability of exceedance poe level relative to current attenuation relationships even when the latter includes a site term to account for local sediment depth and wave guide focusing produces localized areas with pgv at roughly 0 1 0 2 poe about a factor of 4 5 above the median in contrast at rock sites in the 0 100 km distance range the median terashake2 pgvs are in very close agreement with the median empirical prediction and extremes nowhere reach the 2 poe level the rock site agreement lends credibility to some of our source modeling assumptions including overall stress drop level and the manner in which we assigned dynamic parameters to represent the mechanical weakness of near surface material future efforts should focus on validating and refining these findings assessing their probabilities of occurrence relative to alternative rupture scenarios for the southern san andreas fault and incorporating them into seismic hazard estimation for southern california

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

sedimentary basin effects in seattle washington ground motion observations and 3d simulations seismograms of local earthquakes recorded in seattle exhibit surface waves in the seattle basin and basin edge focusing of s waves spectral ratios of s waves and later arrivals at 1 hz for stiff soil sites in the seattle basin show a dependence on the direction to the earthquake with earthquakes to the south and southwest producing higher average amplification earthquakes to the southwest typically produce larger basin surface waves relative to s waves than earthquakes to the north and northwest probably because of the velocity contrast across the seattle fault along the southern margin of the seattle basin s to p conversions are observed for some events and are likely converted at the bottom of the seattle basin we model five earthquakes including the m 6 8 nisqually earthquake using 3d finite difference simulations accurate up to 1 hz the simulations reproduce the observed dependence of amplification on the direction to the earthquake the simulations generally match the timing and character of basin surface waves observed for many events the 3d simulation for the nisqually earthquake produces focusing of s waves along the southern margin of the seattle basin near the area in west seattle that experienced increased chimney damage from the earthquake similar to the results of the higher frequency 2d simulation reported by stephenson et al 2006 waveforms from the 3d simulations show reasonable agreement with the data at low frequencies 0 2 0 4 hz for the nisqually earthquake and an m 4 8 deep earthquake west of seattle

qp qs relations in the sedimentary basin of the upper mississippi embayment using converted phases abstract three component digital seismograms recorded by the 40 panda portable array for numerical data acquisition stations in the new madrid seismic zone were analyzed to study seismic wave attenuation in the sedimentary basin using the spectral ratio method a prominent s to p s p converted phase was generated at the boundary between the uppermost sedimentary basin and the underlying paleozoic rocks the direct s wave on the horizontal component is characterized by a lower frequency content than that of the converted s p wave on the vertical component the differences in frequency content between the direct s and the s p converted waves can be attributed to the different attenuation effects between p and s waves in the unconsolidated sediments the spectral ratio between the low frequency s wave and the high frequency converted s p wave from the bottom of the sediments can be used to yield a relationship between q p and q s in the sediments results from panda stations with well constrained spectral ratios in the frequency range from 2 to 25 hz give the q p value ranging from 25 to 60 and q s from 25 to 30 for the sedimentary basin in the upper mississippi embayment

ground motion and macroseismic intensities of a seismic event related to geothermal reservoir stimulation below the city of basel observations and modelling summary to stimulate a geothermal reservoir below the city of basel switzerland fluid was injected in december 2006 at high pressure into a 5 km deep borehole this stimulation led to an increase in local seismicity with the largest seismic event ml 3 4 occurring on 2006 december 8 the event was widely felt by the local population slight non structural damage to buildings was reported and ultimately this event was the cause to put the geothermal project on hold in this study we present recorded ground motion and determinations of macroseismic intensity of the ml 3 4 event as well as simulations of seismic wave propagation and a model to predict macroseismic intensities as the two models are based on different simplifying assumptions and different underlying physical processes the predicted intensity distributions exhibit differences in their details however the first order characteristics of the observed macroseismic intensity distribution are well matched based on this result we compute intensities also for hypothetical scenarios of earthquakes with larger magnitudes

a kriging method of interpolation used to map liquefaction potential over alluvial ground abstract soil liquefaction is a devastating geotechnical phenomenon associated with earthquakes that causes failure of foundations soil embankments and dams especially in cities built on young alluvial deposits therefore the ability to predict liquefaction potential is important and valuable for seismic hazard assessment the conventional approach to evaluating liquefaction potential at any given point is through the use of borehole data the liquefaction potentials within sedimentary basins vary over short distances with local soil properties the purpose of this paper is to evaluate liquefaction potentials at unsampled locations where borehole data are not available based on the measured liquefaction potentials at selected borehole locations the application and the importance of the geostatistical analytical technique kriging method for the estimation of liquefaction potential at unsampled locations are shown the data set consists of liquefaction potential values measured at 86 randomly distributed boreholes in saitama city japan with the use of calculated liquefaction potentials at sampled locations the experimental semivariograms were constructed the experimental variogram characterizes the spatial variability of the calculated liquefaction potential to interpolate the liquefaction potential over the entire area the ordinary kriging spherical model was applied in applying the kriging method both isotropic and anisotropic models were used however the anisotropic model exhibited a better fit for interpolating sedimentary deposits the interpolated liquefaction potentials are validated with the measured liquefaction potentials of an independently collected second set of 41 boreholes the interpolated liquefaction potentials show strong concurrence with the measured values

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

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

a site conditions map for california based on geology and shear wave velocity one simple way of accounting for site conditions in calculating seismic hazards is to use the shear wave velocity in the shallow subsurface to classify materials the average shear wave velocity to 30 m v 30s has been used to develop site categories that can be used for modifying a calculated ground motion to account for site conditions we have prepared a site category map of california by first classifying the geologic units shown on 1 250 000 scale geologic maps our classification of geologic units is based on v 30s measured in 556 profiles and geological similarities between units for which we have v s data and the vast majority of units for which we have no data we then digitized the geologic boundaries from those maps that separated units with different site classifications v s data for california shows that several widespread geologic units have ranges of v 30s values that cross the boundaries between nehrp ubc site categories the franciscan complex has v 30s values across ubc categories b and c with a mean value near the boundary between those two categories older alluvium and late tertiary bedrock have v 30s values that range from about 300 to about 450 m sec across the boundary between categories c and d to accommodate these units we have created intermediate categories which we informally call bc and cd geologic units that have or are interpreted to have v 30s values near the boundary of the ubc categories are placed in these intermediate units in testing our map against the available v 30s measurements we have found that 74 of the measured v 30s values fall within the range assigned to the v s category where they fall on the map this ratio is quite good considering the inherent problems in plotting site specific data on a regional map and the variability of physical properties in geologic units we have also calculated the mean and distribution of v 30s for each of our map units and prepared composite profiles showing the variation of v s in the upper 100 m from the available v s data these data show that the map categories that we have defined based on geologic units have different v s properties that can be taken into account in calculating seismic hazards

cokriging model for estimation of water table elevation in geological settings where the water table is a subdued replica of the ground surface cokriging can be used to estimate the water table elevation at unsampled locations on the basis of values of water table elevation and ground surface elevation measured at wells and at points along flowing streams the ground surface elevation at the estimation point must also be determined in the proposed method separate models are generated for the spatial variability of the water table and ground surface elevation and for the dependence between these variables after the models have been validated cokriging or minimum variance unbiased estimation is used to obtain the estimated water table elevations and their estimation variances for the pits and trenches area near oak ridge national laboratory water table estimations along a linear section both with and without the inclusion of ground surface elevation as a statistical predictor illustrate the advantages of the cokriging model

site response and attenuation in the puget lowland washington state simple spectral ratio ssr and horizontal to vertical h v site response estimates at 47 sites in the puget lowland of washington state document significant attenuation of 1 5 to 20 hz shear waves within sedimentary basins there amplitudes of the horizontal components of shear wave arrivals from three local earthquakes were used to compute ssrs with respect to the average of two bedrock sites and h v spectral ratios with respect to the vertical component of the shear wave arrivals at each site ssr site response curves at thick basin sites show peak amplifications of 2 to 6 at frequencies of 3 to 6 hz and decreasing spectral amplification with increasing frequency above 6 hz ssrs at nonbasin sites show a variety of shapes and larger resonance peaks we attribute the spectral decay at frequencies above the amplification peak at basin sites to attenuation within the basin strata computing the frequency independent depth dependent attenuation factor q s int from the ssr spectral decay between 2 and 20 hz gives values of 5 to 40 for shallow sedimentary deposits and about 250 for the deepest sedimentary strata 7 km depth h v site responses show less spectral decay than the ssr responses but contain many of the same resonance peaks we hypothesize that the h v method yields a flatter response across the frequency spectrum than ssrs because the h v reference signal vertical component of the shear wave arrivals has undergone a degree of attenuation similar to the horizontal component recordings correcting the ssr site responses for attenuation within the basins by removing the spectral decay improves agreement between ssr and h v estimates

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

hvsr deep mapping tested down to 1 8 km in po plane valley italy abstract the horizontal to vertical spectral ratio hvsr of seismic noise is extensively used in seismic microzonation for its capability to provide a good approximation to the subsoil main resonance frequencies of geotechnical and seismic engineering interest this implies in turn that it has also an approximate passive subsoil mapping capability independent of the level of noise illumination albeit limited to relatively shallow depths since tilt sensitivity makes hvsr unreliable below 0 1 hz however we have experimentally verified that hvsr subsoil mapping capability extends to depths in the kilometer range by applying it to the largest sedimentary basin of italy the po plain valley there we were able to resolve the major stratigraphic discontinuities down to the sediment bedrock interface for which we estimated a depth of 1 6 km with a 25 uncertainty while the surface mapped from oil exploration indicates a depth of 1 8 km quarter of an hour recordings gave always stable signals that fitted to synthetic curves using as a constraint the parameters of the shallow subsoil provided a stratigraphic map consistent with the independent survey this candidates hvsr as a fast and inexpensive first order subsoil mapping tool down to depths of geological and exploration interest

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

3d ground motion estimation in rome italy paleoseismic evidence and seismic hazard analysis suggest that the city of rome italy has experienced considerable earthquake ground motion since its establishment more than 2000 years ago seismic hazards in rome are mainly associated with two active seismogenic areas the alban hills and the central apennines regions located about 20 km southeast and 80 100 km east of central rome within the twentieth century m 6 8 and m 5 3 earthquakes in the apennines and the alban hills respectively have generated intensities up to mercalli cancani sieberg scale mcs vii in the city with a lack of strong motion records we have generated a 3d velocity model for rome embedded in a 1d regional model and estimated long period 1 hz ground motions for such scenarios from finite difference simulations of viscoelastic wave propagation we find 1 hz peak ground velocities pgvs and peak ground accelerations pgas of up to 14 cm sec and 44 cm sec2 respectively for a m 5 3 alban hills scenario largest near the northwestern edge of the tiber river our six simulations of a m 7 0 central apennine scenario generate 0 5 hz pgvs in rome of up to 9 cm sec as well as extended duration up to 60 sec the peak motions are similar to but the durations much longer than those from previous studies that omitted important wave guide effects between the source and the city the results from the two scenarios show that the strongest ground motion amplification in rome occurs in the holocene alluvial areas with strong basin edge effects in the tiber river valley our results are in agreement with earlier 2d sh wave results showing amplification of peak velocities by up to a factor of 2 in the alluvial sediments largest near the contact to the surrounding plio pleistocene formations our results suggest that both earthquakes from the alban hills and the central apennines regions contribute to the seismic hazards in rome although earthquakes from the former area may generate the larger peak motions seismic waves from the latter region may generate ground motions with extended durations capable of causing significant damage on the built environment

evaluation of the liquefaction potential index for assessing liquefaction hazard in christchurch new zealand abstractwhile the liquefaction potential index lpi has been used to characterize liquefaction hazards worldwide calibration of lpi to observed liquefaction severity is limited and the efficacy of the lpi framework and accuracy of derivative liquefaction hazard maps are thus uncertain herein utilizing cone penetration test soundings from nearly 1 200 sites in conjunction with field observations following the darfield and christchurch new zealand earthquakes this study evaluates the performance of lpi in predicting the occurrence and severity of surficial liquefaction manifestations it was found that lpi is generally effective in predicting moderate to severe liquefaction manifestations but its utility diminishes for predicting less severe manifestations additionally it was found that lpi should be used with caution in locations susceptible to lateral spreading because lpi may inconsistently predict its occurrence a relationship between overpredictions of liquefaction severity and profiles h

attenuation of body waves in the central new madrid seismic zone abstract data from the portable array for numerical data acquisition panda deployment in the central part of the new madrid seismic zone have been used to study the attenuation of body waves the spectral decay technique is used to analyze acceleration amplitude spectra of both p and s waves in a frequency range of 5 to 25 hz in order to obtain the high frequency attenuation parameter a multiple weighted least squares method is applied to obtain the site attenuation factor 0 at each station and to get d dr which were interpreted in terms of a two layer q structure consisting of a sedimentary layer overlying the upper crust the 0 values for s waves are stable and show a positive correlation with sediment thickness the 0 values for p waves in the sediments show significant scatter which may be due to greater sensitivity of p wave attenuation to water content of the soils than that of s waves which gave more stable 0 values consistency checks on the assumptions made in obtaining the p and s values are made by studying the source spectrum of several events and the differential sp s from the spectral ratio of the converted sp to s phases the three sets of values are found to be internally consistent but our results are limited to deep sediment sites since the complete vertical distribution of q with sediment depth is not known

spectral element simulations of seismic waves generated by the 2009 l aquila earthquake abstract we adopt a spectral element method sem to perform numerical simulations of the complex wavefield generated by the 6 april 2009 m w 6 3 l aquila earthquake in central italy the mainshock is represented by a finite fault solution obtained by inverting strong motion and global positioning system data testing both 1d and 3d wavespeed models for central italy surface topography attenuation and the moho discontinuity are also accommodated including these complexities is essential to accurately simulate seismic wave propagation three component synthetic waveforms are compared to corresponding velocimeter and strong motion recordings the results show a favorable match between data and synthetics up to 0 5 hz in a 200 km 200 km 60 km model volume capturing features mainly related to topography or low wavespeed basins we construct synthetic peak ground velocity maps that for the 3d model are in good agreement with observations thus providing valuable information for seismic hazard assessment exploiting the sem in combination with an adjoint method we calculate finite frequency kernels for specific seismic arrivals these kernels capture the volumetric sensitivity associated with the selected waveform and highlight prominent effects of topography on seismic wave propagation in central italy online material movie of wave propagation waveform fits and stable of station parameters

long period amplification in deep alluvial basins and consequences for site specific probabilistic seismic hazard analysis an example from the po plain northern italy this study deals with the impact of deep soil discontinuities on ground motion amplification in the po alluvial basin northern italy and consequently on long period probabilistic seismic hazard analysis estimates the focus is on castelleone where a seismic station of the italian national seismic network has been deployed since 2009 to define a detailed shear wave velocity v s profile extensive active and passive geophysical surveys were carried out the active measurements included seismic profiles examined through standard refraction techniques and multichannel analysis of surface waves the passive methods included ambient vibration measurements in both single and array configurations in particular three microtremor arrays with increasing apertures were performed to capture the experimental dispersion curve down to 0 2 hz the horizontal to vertical spectral ratio hvsr showed two main peaks at 0 17 and 0 70 hz a joint inversion of the experimental phase velocity dispersion and hvsr curves was performed to obtain the v s profile the data show two main discontinuities at 160 and 1350 m in depth according to the italian and european seismic codes the shallow v s discontinuity can be ascribed to the seismic bedrock i e v s 800 m s whereas the deeper one is observed at the transition between pliocene quaternary deposits and miocene marls preliminary site specific seismic hazard analysis in terms of displacement response spectra for periods up to 10 s shows that neglecting the effects of the deeper discontinuity implies underestimation in hazard estimates of up to about 49 for mean return period mrp of 475 years and about 57 for mrp of 2475 years with possible consequences regarding the design of very tall buildings and large bridges

assessment of liquefaction potential for two liquefaction prone areas considering the may 20 2012 emilia italy earthquake abstract on the 20th and 29th of may 2012 two earthquakes occurred in emilia romagna region northern italy triggering extensive liquefaction of the subsoil units the consequences of liquefaction have been observed and reported by several agencies in a widespread area the most impressive liquefaction manifestations were documented in a zone 3 4 km long and 1 km wide where the villages of sant agostino san carlo and mirabello are located the existing post earthquake reports and the availability of geotechnical data provided by in situ tests consist the basic ingredients for a computation of the liquefaction potential parameters within this zone in particular the liquefaction potential index lpi and liquefaction severity number lsn indexes were evaluated and then correlated by considering liquefaction phenomena either observed on site or not thus the existing classifications of the lpi and lsn were evaluated and compared with the observed liquefaction induced deformations the latter was applied and validated for the first time within a liquefiable area using post earthquake data after the development by tonkin and taylor 2013 the outcome of this study shows that a threshold value of lpi around 13 or 14 is better to be taken into account instead of 5 for discriminating sites where liquefaction surface evidences should be expected from the non liquefied ones moreover from the correlation of the lsn values with the cases of liquefaction induced ground disruption it is concluded that the proposed threshold value of 10 fits statistically well with our dataset in addition a preliminary correlation of lpi and lsn indicates a trend that could be useful in future studies for delineating sites likely to liquefaction

vertical seismic profiling of oroville microearthquakes velocity spectra and particle motion as a function of depth direct evidence of site distortion of p and s wave microearthquake source spectra at oroville california is presented the data were gathered by placing vertical and three component seismometers at 90 m intervals in a 500 m borehole through the cleveland hill normal fault on which the 1975 ml 5 7 oroville earthquake took place high pressure hydraulic locking mechanisms were used to firmly lock the seismometer packages against the borehole wall digital event triggering geos recorders were used to receive the data some 30 seismic events including 12 microearthquakes were recorded during the 4 months the seismometers were deployed by comparing the velocity spectra of microearthquake waves at the different depths it can be seen that scattering and attenuation in the shallow crust around the borehole dominantly affect high frequency s waves above 15 hz the value of the apparent s wave quality factor qas for the upper 500 m of crust at this site is 9 one feature of this low qas is a gross difference between s wave corner frequencies observed at ground level and 500 m downhole for example the uphole and downhole s wave corner frequencies for the mcoda 0 4 microearthquake of julian day 259 differ by a factor of 2 or more low quality factors and depth dependent corner frequencies were also observed for p waves but these data are less definitive due to lower signal to noise ratios based on their three component particle motions and polarizations the direct s waves of the microearthquakes appear to be composed of two phases which have similar amplitudes but different apparent velocities it is possible that the velocity differences are a result of anisotropy in the underlying rock

three dimensional compressional wave attenuation tomography for the crust and uppermost mantle of northern and central california i present a frequency independent three dimensional 3 d compressional wave attenuation model indicated by quality factor qp for the crust and uppermost mantle of northern and central california the tomographic inversion used t values measured from amplitude spectra of 80 988 p wave arrivals of 3247 events recorded by 463 network stations through a 3 d seismic velocity model the model has a uniform horizontal grid spacing of 15 km and the vertical node intervals range between 2 and 10 km down to 45 km depth in general the resulting qp values increase with depth and agree with the surface geology at shallow depth layers the most significant features observed in the qp model are the high qp values in the sierra nevada mountains and low qp anomalies in the western fault zones low qp values are also imaged in owens valley and long valley at shallow depths and the cape mendocino region in the lower crust 25 km depth an overall contrast of qp values across the fault is observed in the creeping parkfield and cholame carrizo sections of the san andreas fault the new 3 d qp model provides an important complement to the existing regional scale velocity models for interpreting structural heterogeneity and fluid saturation of rocks in the study area

influence of the vs profiles beyond 30 m depth on linear site effects assessment from the kik net data site effects may be assessed using a standard soil classification parameter vs30 the harmonic average shear wave velocity in the first 30 m however this index does not account for the complexity of the velocity profile especially its variability at depth in the present study in addition to vs30 we propose consideration of the gradient of the vs profile from 0 to 30 m depth denoted b30 a lower gradient value means low velocity increases with depth a higher gradient indicates a rapid velocity increase with depth in the shallow layers in addition we consider the fundamental resonance frequency of the soil f0 which has been shown to be a relevant parameter for site effect assessment and which is obtained from the empirical site response using the japanese kik net database we analyze the variability of the vs profiles and the empirical borehole site responses of selected sites through the vs30 the velocity gradient b30 and f0 we select 289 sites for which the 1d linear numerical modeling is close to the empirical site response and a vs at the downhole station is greater than 1000 m s for a given vs30 class b30 and f0 can be used to distinguish between two types of sites deep sedimentary sites and sites with high velocity contrast at shallow depths we find that even if the gradient is calculated using shallow information its use improves the site amplification characterization compared to using only vs30 by reducing the intersite site response variability as expected however this improvement is limited for deep sedimentary sites on the other hand f0 is able to reduce the intersite response variability for deep sedimentary sites even though it is limited to specific vs30 classes thus the combined use of vs30 b30 and f0 improves the assessment of linear site amplification

seismic shaking in the north china basin expected from ruptures of a possible seismic gap a 160 km long seismic gap which has not been ruptured over 8000 year was identified recently in north china in this study we use a dynamic source model and a newly available high resolution 3 d velocity structure to simulate long period ground motion up to 0 5 hz from possibly worst case rupture scenarios of the seismic gap we find that the characteristics of the earthquake source and the local geologic structure play a critical role in controlling the amplitude and distribution of the simulated strong ground shaking rupture directivity and slip asperities can result in large amplitude i e 1 m s ground shaking near the fault whereas long duration shaking may occur within sedimentary basins in particular a deep and closed quaternary basin between beijing and tianjin can lead to ground shaking of several tens of cm s for more than 1 minute these results may provide a sound basis for seismic mitigation in one of the most populated regions in the world

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 regional view of urban sedimentary basins in northern california based on oil industry compressional wave velocity and density logs compressional wave sonic and density logs from 119 oil test wells provide knowledge of the physical properties and impedance contrasts within urban sedimentary basins in northern california which is needed to better understand basin amplification these wire line logs provide estimates of sonic velocities and densities for primarily upper cretaceous to pliocene clastic rocks between 0 1 and 5 6 km depth to an average depth of 1 8 km regional differences in the sonic velocities and densities in these basins largely 1reflect variations in the lithology depth of burial porosity and grain size of the strata but not necessarily formation age for example miocene basin filling strata west of the calaveras fault exhibit higher sonic velocities and densities than older but finer grained and or higher porosity rocks of the upper cretaceous great valley sequence as another example hard eocene sandstones west of the san andreas fault have much higher impedances than eocene strata mainly higher porosity sandstones and shales located to the east of this fault and approach those expected for franciscan complex basement rocks basement penetrations define large impedence contrasts at the sediment basement contact along the margins of several basins where quaternary pliocene and even miocene deposits directly overlie franciscan or salinian basement rocks at depths as much as 1 7 km in contrast in the deepest geographic centers of the basins such logs exhibit only a modest impedance contrast at the sediment basement contact at depths exceeding 2 km prominent up to 1 km sec and thick up to several hundred meters velocity and density reversals in the logs refute the common assumption that velocities and densities increase monotonically with depth online material borehole log regression parameters and metadata

stochastic strong ground motion simulation of the 12 november 1999 duzce turkey earthquake using a dynamic corner frequency approach on 12 november 1999 only three months after the 17 august 1999 kocaeli earthquake mw 7 4 an earthquake of mw 7 1 occurred immediately to the east of the kocaeli rupture in northwestern turkey resulting in extensive structural damage in the city of duzce and its surrounding area it was reported to be a right lateral strike slip event on the previously unbroken segment of the north anatolian fault zone with a north dipping fault plane this paper presents stochastic finite fault simulation of near field ground motions from this earthquake at selected near fault stations based on a dynamic corner frequency approach using the computer program exsim motazedian and atkinson 2005 the method requires region specific source path and site characterizations as input model parameters the source mech anism of the 1999 duzce event and regional path effects are well constrained from previous studies of the earthquake the local site effects at the selected stations are studied as a combination of the kappa operator and frequency dependent soil ampli fication the model parameters are validated against recordings and a stress drop value of 100 bars is estimated for the 1999 duzce earthquake the validated model is then used to compute synthetic records around the fault distribution of peak ground motion parameters is observed to be consistent with the building damage dis tribution in the near fault region most affected by the seismic shaking the attenuation of synthetic ground motion parameters is compared with recent ground motion pre diction equations proposed for the region by gulkan and kalkan 2002 ulusay et al 2004 and akkar and bommer 2007 as well as two next generation attenuation models by boore and atkinson 2007 and campbell and bozorgnia 2007 despite discrepancies at several stations stochastic finite fault modeling based on a dynamic corner frequency approach confirms to be a practical tool to reproduce the ground motions of large earthquakes

microearthquake s wave observations from 0 to 1 km in the varian well at parkfield california abstract high gain three component seismometers from 0 to 1 km deep along the varian a 1 well at parkfield california were used to record the waveforms of nearby microearthquakes despite being in the thick tertiary sediments of the parkfield syncline the s wave amplification at this site is only about a factor of 3 the spectral content and spectral ratios of s waves along the well show that the average qs in the top 1 km at this site is 37 with the qs in different subintervals varying between 8 and 65 based on initial s wave polarizations a complex s wave velocity structure must exist at and below the varian site this structure appears to include position dependent anisotropy as well as steep lateral velocity gradients at a depth of 1 km s wave splitting parallel and normal to the san andreas fault zone is consistently observed this splitting scales at roughly 0 01 sec km subsequent to the split s waves the particle motion seems to be controlled by event focal mechanism above 1 km the upgoing s waves attenuate and change directions of polarization with a new splitting rate of 0 1 sec km uniquely for some events on the san andreas fault immediately below the varian site large post s wave signals with normal dispersion are present we propose that these phases are fault zone guided waves channeled from the san andreas fault to the varian site along the gold hill fault

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

the seismic response of the los angeles basin california using strong motion data recorded in the los angeles region from the 1992 mw 7 3 landers earthquake we have tested the accuracy of existing three dimensional 3d velocity models on the simulation of long period 2 sec ground motions in the los angeles basin and surrounding san fernando and san gabriel valleys first the overall pattern and degree of long period excitation of the basins were identified in the observations within the los angeles basin the recorded amplitudes are about three to four times larger than at sites outside the basins amplitudes within the san fernando and san gabriel valleys are nearly a factor of 3 greater than surrounding bedrock sites then using a 3d finite difference numerical modeling approach we analyzed how variations in 3d earth structure affect simulated waveforms amplitudes and the fit to the observed patterns of amplification significant differences exist in the 3d velocity models of southern california that we tested magistrale et al 1996 graves 1996a hauksson and haase 1997 major differences in the models include the velocity of the assumed background models the depth of the los angeles basin and the depth location and geometry of smaller basins the largest disparities in the response of the models are seen for the san fernando valley and the deepest portion of the los angeles basin these arise in large part from variations in the structure of the basins particularly the effective depth extent which is mainly due to alternative assumptions about the nature of the basin sediment fill the general ground motion characteristics are matched by the 3d model simulations validating the use of 3d modeling with geologically based velocity structure models however significant shortcomings exist in the overall patterns of amplification and the duration of the long period response the successes and limitations of the models for reproducing the recorded ground motions as discussed provide the basis and direction for necessary improvements to earth structure models whether geologically or tomographically derived the differences in the response of the earth models tested also translate to variable success in the ability to successfully model the data and add uncertainty to estimates of the basin response given input scenario earthquake source models

garner valley downhole array of accelerometers instrumentation and preliminary data analysis the garner valley downhole array gvda in southern california 33 41 60 n 116 40 20 w is a five element array of three component dual gain force balance accelerometers that are capable of measuring accelerations from 3 10 6 to 2 0 g over a frequency range from 0 0 to 100 hz the accelerometers are placed at depths of 0 6 15 22 and 220 m the lithostratigraphy is 19 m of soil overlying a 24 m layer of weathered granite below which is granite tonalite the array only 7 km from the san jacinto fault is located at the northern end of the anza seismic gap on the san jacinto fault where an m 6 5 or greater earthquake can be expected it is only 35 km from the indio segment of the san andreas fault which last ruptured with an m 8 earthquake around 1700 a d from its installation in july 1989 through july 1991 gvda has recorded 280 earthquakes with magnitudes ranging from 1 2 to 4 7 and epicentral distances ranging from from 0 to 110 km the maximum acceleration recorded was 89 cm sec 2 from an m l 4 2 earthquake 15 8 km hypocentral distance from gvda the average amplification of the apparent seismic moment between 220 m depth and the surface is about 13 for over five orders of magnitude in the size of the recorded earthquakes the spectral ratio 0 220 of horizontal acceleration amplitude spectrum shows a mean amplification of about 10 for the frequency range of 2 0 to 30 hz for 17 events resonance peaks exist at about 1 7 3 0 and 12 0 hz where the spectral ratio 0 220 is nearly 40 analysis of the acceleration spectra of two specific earthquakes that have nearly the same hypocenter but with different magnitudes m 4 2 and 2 5 shows that the weathered granite zone beneath the soil strongly attenuates the spectral amplitudes for frequencies greater than 40 hz the impedance of the soil relative to the weathered granite amplifies all frequencies by about a factor of 3 leading to spectral levels that are greater at the surface than at 22 m depth near the top of the weathered granite the acceleration spectra at each depth show resonant peaks at the same frequencies the spectra at each depth are well correlated for both earthquakes the acceleration spectrum at 220 m is nearly constant for frequencies less than 60 hz which implies that there is little or no attenuation

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

a methodology for seismic loss estimation in urban regions based on ground motion simulations seismic vulnerability assessment of residential buildings in regions of high seismicity is an interdisciplinary problem requiring major inputs from fields of seismology and earthquake engineering the basic two components of loss estimation methods are information on regional seismicity and building stock this study presents a realistic loss estimation methodology where the first component input ground motions is obtained from regional ground motion simulations using the stochastic finite fault technique the second component building vulnerability information on the other hand is taken into account using fragility analyses introducing the ground motion intensity parameters obtained from simulations to the fragility curves we obtain seismic loss distribution in a region in this study we demonstrate the loss estimation methodology with an application to three northwestern cities in turkey duzce bolu and kaynasli that experienced two major earthquakes graphic 1 and graphic 2 in less than three months in 1999 we initially verify the methodology with comparisons of observed and estimated damage ratios for the 12 november 1999 graphic 3 duzce earthquake later we present the estimated damage ratios under scenario earthquakes in the region for a magnitude range of graphic 4 graphic 5 is predicted to be the threshold magnitude for the cities of duzce and kaynasli where more than 60 of the building stock experience moderate and heavy damage because bolu is at a farther distance from the fault plane less damage is estimated for graphic 6 than those in the other centers for graphic 7 all three cities are predicted to experience substantial rates of heavy damage and collapse 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif 4 embed inline graphic 4 gif 5 embed inline graphic 5 gif 6 embed inline graphic 6 gif 7 embed inline graphic 7 gif

liquefaction potential index field assessment cone penetration test cpt soundings at historic liquefaction sites in california were used to evaluate the predictive capability of the liquefaction potential index lpi which was defined by iwasaki et al in 1978 lpi combines depth thickness and factor of safety of liquefiable material inferred from a cpt sounding into a single parameter lpi data from the monterey bay region indicate that the probability of surface manifestations of liquefaction is 58 and 93 respectively when lpi equals or exceeds 5 and 15 lpi values also generally correlate with surface effects of liquefaction decreasing from a median of 12 for soundings in lateral spreads to 0 for soundings where no surface effects were reported the index is particularly promising for probabilistic liquefaction hazard mapping where it may be a useful parameter for characterizing the liquefaction potential of geologic units

mapping liquefiable layer thickness for seismic hazard assessment investigations of liquefaction sites combining subsurface mapping and evaluation of liquefaction damage are summarized for four areas in san francisco affected by 1906 and 1989 earthquakes where more than 950 borehole and sounding records were collected and analyzed the maps developed from this database provide a comprehensive picture of subsurface conditions with substantial practical value postliquefaction settlement horizontal displacement caused by lateral spread and earthquake damage to buried pipelines are shown to be related closely with the thickness of underlying liquefiable soil the influence of surface and liquefiable layer thicknesses on liquefaction damage is evaluated mapping liquefiable layer thickness is shown to be an excellent means of locating areas of potentially severe liquefaction which is adapted easily to geographic information systems gis for planning and design purposes

high frequency borehole seismograms recorded in the san jcinto fault zone southern california part 2 attenuation and site effects we examine surface and downhole p and s wave spectra from local earthquakes recorded at two borehole seismometer arrays knw bh and pfo bh installed in the southern california batholith region of the san jacinto fault zone by the u s geological survey to assess the influence of the weathered layer on the spectral content of high frequency 2 to 200 hz seismic signals earthquake signals recorded downhole at both sites show significantly improved seismic bandwidth due to both a reduction in ambient noise levels and especially to dramatically increased levels of high frequency signal significant seismic signal is observed up to approximately 190 hz for p waves at knw bh stacked spectral ratios from these signals indicate that the highly weathered near surface between 0 and 150 m at knw bh and pfo bh exerts a much larger influence on seismic signals than deeper between 150 and 300 m material modeling of uphole downhole spectral ratio data suggests q 6 5 and q 9 between 0 and 150 m increasing to q 27 and q 26 between 150 and 300 m an outcrop mounted anza network station deployed approximately 0 4 km from knw bh displays roughly similar high frequency content to the knw bh downhole sensors but it exhibits spectra that are significantly colored by directional resonances low q and low velocity near surface material forms a lossy boundary layer at these borehole sites that is advantageous to the high frequency downhole environment not only are noise levels reduced but reflections from the surface and near surface are greatly attenuated as a result high frequency recordings from below the weathered zone more nearly resemble those recorded in a whole space than would otherwise be expected

ground motion modeling of the 1906 san francisco earthquake part i validation using the 1989 loma prieta earthquake we compute ground motions for the beroza 1991 and wald et al 1991 source models of the 1989 magnitude 6 9 loma prieta earthquake using four different wave propagation codes and recently developed 3d geologic and seismic velocity models in preparation for modeling the 1906 san francisco earthquake we use this well recorded earthquake to characterize how well our ground motion simulations reproduce the observed shaking intensities and amplitude and durations of recorded motions throughout the san francisco bay area all of the simulations generate ground motions consistent with the large scale spatial variations in shaking associated with rupture directivity and the geologic structure we attribute the small variations among the synthetics to the minimum shear wave speed permitted in the simulations and how they accommodate topography our long period simulations on average under predict shaking intensities by about one half modified mercalli inten sity mmi units 25 35 in peak velocity while our broadband simulations on average under predict the shaking intensities by one fourth mmi units 16 in peak velocity discrepancies with observations arise due to errors in the source models and geologic structure the consistency in the synthetic waveforms across the wave propagation codes for a given source model suggests the uncertainty in the source parameters tends to exceed the uncertainty in the seismic velocity structure in agree ment with earlier studies we find that a source model with slip more evenly distributed northwest and southeast of the hypocenter would be preferable to both the beroza and wald source models although the new 3d seismic velocity model improves upon previous velocity models we identify two areas needing improvement nevertheless we find that the seismic velocity model and the wave propagation codes are suitable for modeling the 1906 earthquake and scenario events in the san francisco bay area online material modified mercalli intensities and velocity waveforms and a movie of simulated wave propagation