seismic structure of the crust and uppermost mantle of north america and adjacent oceanic basins a synthesis we present a new set of contour maps of the seismic structure of north america and the surrounding ocean basins these maps include the crustal thickness whole crustal average p wave and s wave velocity and seismic velocity of the up permost mantle that is pn and sn we found the following 1 the average thickness of the crust under north america is 36 7 km standard deviation s d 8 4 km which is 2 5 km thinner than the world average of 39 2 km s d 8 5 for continental crust 2 histograms of whole crustal p and s wave velocities for the north amer ican crust are bimodal with the lower peak occurring for crust without a high velocity 6 9 7 3 km sec lower crustal layer 3 regions with anomalously high average crustal p wave velocities correlate with precambrian and paleozoic orogens low average crustal velocities are correlated with modern extensional regimes 4 the average pn velocity beneath north america is 8 03 km sec s d 0 19 km sec 5 the well known thin crust beneath the western united states extends into north west canada 6 the average p wave velocity of layer 3 of oceanic crust is 6 61 km sec s d 0 47 km sec however the average crustal p wave velocity under the eastern pacific seafloor is higher than the western atlantic seafloor due to the thicker sediment layer on the older atlantic seafloor

equivalent point source modeling of moderate to large magnitude earthquakes and associated ground motion saturation effects we modeled the source and attenuation attributes of well recorded m6 earthquakes based on the equivalent point source approach with the goal of determin ing how to treat ground motion saturation effects within this context we consider ground motions as originating from an equivalent point source and mimic finite fault effects by treating the motion as emanating from a virtual point not a real point on the fault rupture such that ground motions are correctly predicted at close distances this is achieved by using an effective distance metric r d 2 h 2 0 5 in which drup is the closest distance to the rupture and h is a pseudodepth term that accounts for sat uration effects we found that the distance saturation effect is magnitude dependent extending to further distances with increasing magnitude for earthquakes of m 6 we model the saturation term as logh 1 72 0 43 m with a standard deviation of 0 19 in log10 units based on the values obtained from the study earthquakes the apparent source spectra of most m6 earthquakes can be modeled using a simple brune point source model for a few of the m6 earthquakes notably those in california we observed a spectral sag at intermediate frequencies for such earth quakes a two corner point source model provides a better match than the brune model we conclude that an equivalent point source model based on the effective distance concept can successfully predict the average ground motions from m6 earthquakes over a wide distance range including close distances 20 km

a model for lg propagation in the gulf coastal plain of the southern united states the southern united states experienced extensional tectonics during the early mesozoic development of the gulf of mexico and subsequent accumulation of up to 12 km of marine sediment few seismic stations have operated in the gulf coastal plain for extended periods of time and data for constraining ground motion prediction models are sparse previous studies found that the region differs from other parts of eastern north america in terms of lg attenuation the earthscope transportable array was in the south central united states in 2010 2012 during a time of increased seismicity that circumstance provided data for investigating lg propagation sixteen earthquakes with magnitudes in the 3 2 5 6 range occurred in oklahoma arkansas and texas and were recorded to distances of 1000 km stations in the coastal plain of texas arkansas louisiana and mississippi exhibit strong attenuation of the lg phase compared with stations located to the north in the ouachita orogenic belt and cratonic platform q associated with the crustal waveguide underlying the gulf coastal plain was estimated as q 365 f 0 62 however lg blockage due to crustal thinning and anelastic attenuation due to the presence of several kilometers of sedimentary deposits occurs near the gulf coast the average value south of latitude 33 n is 96 10 ms a remarkable linear correlation exists between the attenuation parameter and the thickness of post jurassic sediments in the study region such that stations near the coast of texas louisiana and mississippi which overlie 12 km of sediments exhibit values of 160 ms this strong spatial dependence of attenuation has important implications and should be incorporated in the development of ground motion prediction models using the approach suggested here online material figures showing maps of regression residuals and receiver terms for 12 frequency bands

characteristics of radiation and propagation of seismic waves in northern finland estimated based on records of local earthquakes the characteristics of radiation and propagation of seismic waves required in various seismological applications especially in seismic hazard assessment are estimated in northern finland based on records of local earthquakes 80 records from four stations mw 1 5 to 4 1 h 3 to 25 km northern finland possesses relatively low seismic activity however rather strong earthquakes occurred there in the past we applied coda normalization method to estimate the quality factor q f q0fn and then verified and corrected the q f estimates at low frequencies by stochastic simulations we obtained q0 80 to 100 n 1 1 to 1 2 for hypocentral distances of 20 to 150 km and q0 180 to 350 n 0 7 to 0 9 for hypocentral distances of 150 to 320 km other parameters were estimated by the empirical methods and stochastic simulation of local earthquakes ml 2 0 we estimated the stress drop 200 bars geometrical spreading as a two segment function 1 r for r 0 to 80 km and 1 80 for r 80 to 300 km the duration of seismic motion depending on the hypocentral distance kappa value 0 001 to 0 03 s and some other parameters the obtained high estimates of the stress drop along with rather high q values may result in noticeably increased compared to those that could be expected on average pga estimates in seismic hazard assessment in northern finland

coda q in the southern appalachians the attenuation of seismic coda waves in the southern appalachian region was studied signal sources were five local and regional earthquakes and one explosion located in ohio virginia and south carolina the data were recorded digitally by a network of seven stations in western virginia joint least squares estimates of the quality factor q relative recording site responses and coda source amplitudes were obtained in five frequency bands using the single scattering model and assuming body wave geometrical spreading the results indicate a frequency dependent coda q represented by q 811 f0 42 1 5 f 12 hz for lapse times in the range 15 to 250 seconds site responses determined relative to the average network response differ by less than a factor of 2 in the range 3 to 12 hz at five of the seven stations however the differences in the response of the other two sites increase with frequency amounting to a factor of 5 at 12 hz estimated relative coda source amplitude spectra exhibit similar shapes consistent with the assumption that the scattering process is independent of path in the study region

regionally adjustable generic ground motion prediction equation based on equivalent point source simulations application to central and eastern north america abstract we develop a generic ground motion prediction equation gmpe that can be adjusted for use in any region by modifying a few key model parameters the basis of the gmpe is an equivalent point source simulation model whose parameters have been calibrated to empirical data in california in such a way as to determine the decoupled effects of basic source and attenuation parameters on ground motion amplitudes we formulate the generic gmpe as a function of magnitude distance stress parameter geometrical spreading rate and anelastic attenuation this provides a fully adjustable predictive model allowing users to calibrate its parameters using observed motions in the target region we also include an empirical calibration factor to account for residual effects that are different from and or missing in simulations compared to observed motions in the target region as an example we show how the generic gmpe can be adjusted for use in central and eastern north america cena and calibrated with the next generation attenuation east database we provide median predictions of ground motions in cena for average horizontal component peak ground motions and 5 damped pseudospectral acceleration periods up to t 10 s for magnitudes m 3 8 and distances up to 600 km

electrical resistivity of cajon pass cores at elevated pressures the electrical resistivity of rock cores recovered from the cajon pass hole ranged from 5 to 46 k m as determined at pressures to 200 mpa and frequencies of 10 30 000 hz the resistivities of cores recovered from depths less than 1 6 km are about one order of magnitude greater than the in situ resistivity as measured by the deep laterolog however at greater depths the laboratory resistivities and those from the deep laterolog are in fairly good agreement the results suggest that at these depths the fractures whether mineralized or fluid filled are no longer well interconnected

the attenuation of fourier amplitudes for rock sites in eastern north america we develop an empirical model of the decay of fourier amplitudes for earthquakes of m 3 6 recorded on rock sites in eastern north america and discuss its implications for source parameters attenuation at distances from 10 to 500 km may be adequately described using a bilinear model with a geometric spreading of 1 r 1 3 to a transition distance of 50 km with a geometric spreading of 1 r 0 5 at greater distances for low frequencies and distances less than 50 km the effective geometric spreading given by the model is perturbed using a frequency and hypocentral depth dependent factor defined in such a way as to increase amplitudes at lower frequencies near the epicenter but leave the 1 km source amplitudes unchanged the associated anelastic attenuation is determined for each event with an average value being given by a regional quality factor of q 525f 0 45 this model provides a match on aver age between the known seismic moment of events and the inferred low frequency spectral amplitudes at r 1 km obtained by correcting for the attenuation model the inferred brune stress parameters from the high frequency source terms are about 600 bars 60 mpa on average for events of m 4 5

the effect of crustal structure on strong ground motion attenuation relations in eastern north america strong ground motion attenuation relations are usually described by smoothly decreasing functions of distance however consideration of wave propagation in the crust suggests that attenuation relations should be more complex such complexity may be present in strong ground motion data for eastern north american earthquakes which show amplitudes in the distance range of 60 to 150 km that lie above the trends at smaller and greater distances using a wavenumber integration method to compute green s functions and close in recordings of several earthquakes as empirical source functions we have generated synthetic seismograms that are in good agreement with regional and strong motion recordings of eastern north american earthquakes from these synthetic seismograms we have shown that the observed interval of relatively high amplitudes may be attributable to postcritically reflected s waves from the moho the presence and location of the interval of relatively high amplitudes is highly dependent on the crustal velocity structure and may therefore be expected to show regional variation however for any realistic structure model there will be a transition in the attenuation relation from an interval at shorter distances less than about 100 km that is dominated by direct waves to an interval at greater distances that is dominated by postcritically reflected waves the synthetic seismograms have response spectral velocities that match those of the recorded data and their m blg values are in good agreement with observed values

a study of ground motion excitation based on the earthquake of september 8 2017 evidence that normal faults influence the stress parameter we performed a study of ground motion modeling based on multiple linear regression and random vibration theory using the earthquake sequence of september 8 2017 mw 8 2 our results show that there is high attenuation in the region of oaxaca chiapas and central mexico however the peak amplitude excitations of normal fault earthquakes are higher than those of thrust fault earthquakes the earthquake sequence involved a large number of events but not all the seismic events were aftershocks because many earthquakes had different rupture styles the thrust events follow a simple scaling relation with a constant stress parameter but the normal fault events are difficult to represent with a constant self similar model our best result consists of a q 0 240 pm 032 with a frequency dependent factor of 0 63 pm 0 05 the excitation term is well determined with a stress parameter of 80 bars for the thrust faults but for the normal faults the stress parameter is at least 180 bars with a non self similar model our results show that it is necessary to include new ground motion prediction equations in seismic hazard analysis for meganormal faults which have not previously been considered in subduction zones

empirical attenuation of ground motion spectral amplitudes in southeastern canada and the northeastern united states a database of 1700 digital seismograms from 186 earthquakes of mag nitude mn 2 5 5 6 that occurred in southeastern canada and the northeastern united states from 1990 to 2003 was compiled maximum likelihood regression analysis of the database was performed to determine a model for the attenuation of fourier spectral amplitudes for the shear window for the vertical and horizontal component of motion for frequencies from 0 2 to 20 hz fourier amplitudes follow a hinged trilinear attenuation model fourier spectral amplitudes decay as r 1 3 where r is hypocentral distance within 70 km of the source there is a transition zone from 70 to 140 km as the direct waves are joined by strong postcritical reflections where the attenuation is described as r 0 2 spectral amplitudes actually increase with distance in this range for low frequencies beyond 140 km the attenuation is well described by r 0 5 corresponding to geometric spreading in two dimensions the associated model for the regional quality factor for frequencies greater than 1 hz can be ex pressed as q 893f 032 q can be better modeled over a wider frequency range 0 2 20 hz by a polynomial expression log q 3 052 0 393 log f 0 945 log f 2 0 327 log f 3 the polynomial expression accommodates the observation that q values are at a minimum about 1000 near 1 hz and rise at both lower and higher frequencies correction factors for the spectral amplitude model that describe the effects of focal depth on the amplitudes and their attenuation are developed using the subset of events with known focal depth the attenuation model is similar to that determined from an earlier study with more limited data atkinson and mereu 1992 but the enlarged database indicates more rapid near source amplitude decay and higher q the attenuation model is used to play back attenuation effects to determine the apparent source spectrum for each earthquake in the database and hence determine moment magnitude m and brune stress drop the events have moment magnitude in the range from 2 5 to 5 stress drop increases with moment magnitude for events of m 4 3 then appears to attain a relatively constant level in the range from 100 to 200 bars for the larger events as previously noted in atkinson 1993b the results of this study provide a useful framework for improving regional ground motion relations in eastern north america they further our understanding of attenuation in the region through analysis of an enlarged ground motion database in particular the inclusion of the three component broadband data gathered over the last decade allows extension of attenuation models to both horizontal and vertical components over a broad frequency range 0 2 20 hz

the shape of ground motion attenuation curves in southeastern canada the shape of the attenuation curve of the fourier spectrum of acceleration is established for southeastern canada from empirical data the dataset is comprised of 1200 digital vertical component seismograms from 100 earthquakes recorded on 30 stations of the eastern canada telemetered network the distance range of the observations is 10 to 1700 km focal depths are from 5 to 30 km results indicate that the attenuation curve has three distinct sections at distances less than 70 km corresponding to attenuation of the direct wave amplitudes decay slightly more rapidly than 1 r r 1 1 between 70 and 130 km where the direct wave is joined by sms spectral amplitudes are approximately constant beyond 130 km corresponding to the lg phase amplitudes decay at a rate that is consistent with r 0 5 and q 670 f 0 33 the findings support the hypothesis of burger et al 1987 that postcritical reflections from the moho discontinuity play an important role in determining the shape of the attenuation curve however the influence of sms is subtle allowing the shape to be approximated by simple functional forms for example the commonly assumed bilinear form r 1 r 0 5 with frequency dependent q fits well if the transition from direct wave to lg spreading is placed at approximately 60 km a linear form r 1 over all distances with constant q 2000 also provides a satisfactory fit overall we find little evidence for the dependence of attenuation on focal depth or tectonic province

modeling some empirical vertical component lg relations abstract higher mode surface wave theory is used to model the vertical component lg wave observed in eastern north america at regional distances tests of the model are made to determine whether it is capable of describing empirical spectral scaling laws spatial attenuation and peak time domain lg amplitudes it is found that a simple crustal model and a rough estimate of crustal qb are all that are required to accomplish this good results are obtained if the average crustal qp is equated to the coda q of the same frequency introduction the lg wave is a wave observed on short period seismograms of local and regional seismic events which travels with a group velocity of approximately 3 5 km sec in the central united states it is usually the largest arrival on the seismogram which makes it suitable for defining a magnitude scale nuttli 1973 herrmann and nuttli 1982 as part of developing the magnitude scale there have been many studies on the spatial attenuation of the lg wave nuttli 1973 street 1976 bollinger 1979 singh and herrmann 1982 the lg wave is usually thought of as a superposition of higher mode surface waves propagating within the crustal wave guide herrmann and nuttli 1975a b attempted to deterministically model observed lg amplitudes in terms of focal mechanism focal depth and seismic moment using surface wave techniques they were limited by their inability to compute surface wave eigenfunctions at frequencies greater than 0 5 hz however their results were encouraging harkrider 1979 drawing upon the work of apsel 1979 discovered a way to compute surface wave energy integrals of the higher modes very precisely bache

a composite source model for computing realistic synthetic strong ground motions a composite source model is presented for convolution with synthetic green s functions in order to synthesize strong ground motions due to a complex rupture process of a large earthquake subevents with a power law distribution of sizes are located randomly on the fault each subevent radiates a displacement pulse with the shape of a brune s pulse in the far field at a time determined by a constant rupture velocity propagating from the hypocenter thus all the input parameters have a physical basis we simulate strong ground motions for event station pairs that correspond to records obtained in mexico by the guerrero accelerograph network the synthetic accelerations velocities and displacements have realistic amplitudes durations and fourier spectra

earthquake ground motion prediction equations for eastern north america new earthquake ground motion relations for hard rock and soil sites in eastern north america ena including estimates of their aleatory uncertainty vari ability have been developed based on a stochastic finite fault model the model incorporates new information obtained from ena seismographic data gathered over the past 10 years including three component broadband data that provide new in formation on ena source and path effects our new prediction equations are similar to the previous ground motion prediction equations of atkinson and boore 1995 which were based on a stochastic point source model the main difference is that high frequency amplitudes f 5 hz are less than previously predicted by about a factor of 1 6 within 100 km because of a slightly lower average stress parameter 140 bars versus 180 bars and a steeper near source attenuation at frequencies less than 5 hz the predicted ground motions from the new equations are generally within 25 of those predicted by atkinson and boore 1995 the prediction equations agree well with available ena ground motion data as evidenced by near zero average residuals within a factor of 1 2 for all frequencies and the lack of any significant residual trends with distance however there is a tendency to positive residuals for moderate events at high frequencies in the distance range from 30 to 100 km by as much as a factor of 2 this indicates epistemic uncertainty in the prediction model the positive residuals for moderate events at 100 km could be eliminated by an increased stress parameter at the cost of producing negative residuals in other magnitude distance ranges adjustment factors to the equations are provided that may be used to model this effect

near source geometrical spreading in the central virginia seismic zone determined from the aftershocks of the 2011 mineral virginia earthquake we used aftershocks of the 2011 mineral virginia earthquake to study geometrical spreading at hypocentral distances less than 60 km in the central virginia seismic zone sixty nine aftershocks occurring from 25 august 2011 through 24 december 2011 provided the data we used the coda normalization method to estimate the attenuation coefficient associated with geometrical spreading we filtered the time domain signals in several octave wide frequency bands and examined attenuation of peak s wave amplitude in the 1 0 30 0 hz frequency range amplitude was assumed to decrease as a function of hypocenter distance r according to r the coefficient of attenuation was examined for the three component s wave amplitudes with corrections for sh and sv radiation patterns we observed no systematic frequency dependence of the coefficient of attenuation for the radial and transverse components assuming infinite quality factor q derived as a weighted mean over the entire range of frequencies 1 30 hz are both 1 51 0 05 the weighted mean value of the attenuation coefficient on the vertical component over the same range of frequencies is 1 45 0 05 slightly less than for the horizontal components we corrected the data assuming three q models the estimated geometrical spreading coefficients are in the 1 30 1 46 range depending on the assumed q model and component which is only slightly less than the estimates of determined assuming infinite q the estimated attenuation coefficients differ significantly from the value of 1 0 expected for a whole space the results for the horizontal components are in agreement with previous full wavefield modeling however the observed vertical component attenuation is substantially less than that predicted by the synthetics the depths of the earthquakes are less than 8 km so these results may not be representative of geometrical spreading in parts of eastern north america where earthquakes occur at greater depths online material table of earthquake hypocenters and focal mechanisms

observations on regional variability in ground motion amplitudes for small to moderate earthquakes in north america abstract the regional variability in earthquake ground motion amplitudes for a given magnitude and distance in western north american environments was examined using shakemap data from small to moderate events the abundance of data for small to moderate events in california allows average ground motion levels as a function of magnitude and distance to be resolved with a high level of confidence ground motion amplitudes in northern california are lower on average than those for southern california for events of the same magnitude at distances in the range from 120 to 250 km over all frequencies the observed regional variations could be indicative of regional differences in attenuation effects or site effects an unexpected result of the study is the finding that ground motions for events of m m m m

q for p waves in the sediments of the virginia coastal plain the seismic quality factor q for p waves in atlantic coastal plain sediments is estimated using data from the 2004 u s geological survey seismic survey in eastern virginia the estimates are based on spectral ratios derived from reflections and sediment guided p waves in late cretaceous and tertiary sediments within the annular trough of the late eocene chesapeake bay impact structure the estimates of q for the frequency range of 10 150 hz are from 75 to 100 with the best estimate of 80 based on multichannel stacking of spectral ratios from receivers in the offset range of 200 2000 m this result is approximately a factor of 2 larger than the results previously reported for the charleston south carolina area and it is approximately one half of that recently reported for the mississippi embayment

high frequency spectral falloff of earthquakes fractal dimension of complex rupture b value and the scaling of strength on faults the high frequency falloff omega sup minus gamma of earthquake displacement spectra and the b value of aftershock sequences are attributed to the character of spatially varying strength along fault zones the author assumes that the high frequency energy of a main shock is produced by a self similar distribution of subevents where the number of subevents with radii greated than r is proportional to r sup minus d d being the fractal dimension in this model an earthquake is composed of a hierarchical set of smaller earthquakes the static stress drop is parameterized to be proportional to r sup eta and strength is assumed to be proportional to static stress drop he finds that a distribution of subevents with d 2 and stress drop independent of seismic moment eta 0 produces a main shock with an omega sup minus 2 falloff if the subevent areas fill the rupture area of the main shock by equating subevents to islands of high stress of a random self similar stress field on a fault he relates d to the scaling of strength on a fault such that d 2 minus eta thus d 2 corresponds to constant stress drop scaling eta 0 and scale invariant fault strength amore self similar model of aftershock rupture zones on a fault is used to determine the relationship between the b value the size distribution of aftershock rupture zones and the scaling of strength on a fault the b value for aftershock sequences on a fault is found to equal 3 minus 1 5 eta 3 eta therefore this model indicates that the typically observed spectral falloffs of omega sup minus 2 and b values of 1 can be entirely caused by scale invariant strength eta 0 along fault zones less

sensitivity analysis for finite difference seismic basin modeling a case study for kinburn basin ottawa canada we used a finite difference modeling method to investigate the sensitivity of the ground motion simulation results to the main input parameters including the source model regional path properties and local site conditions we used a spectral frequency range of 0 1 1 hz for the kinburn bedrock topographic basin ottawa canada for the ladysmith earthquake mw 4 7 some findings are known facts however the unique geophysical conditions in the ottawa area such as the high contrast between the shear wave velocities of the bedrock and the shear wave velocity of the soil were the reason for a comprehensive sensitivity analysis using a gaussian source function with a short half duration increased the peak ground velocities pgvs and the amplitude of the velocity fourier spectrum relaxation times and relaxation coefficients for the viscoelastic simulation significantly increased the amplitude of later arrivals at the soil site which consequently led to an increase in pgv the amplitude of the pseudospectral acceleration psa ratio and the velocity fourier spectrum for a small earthquake employing a small soil q model damped a significant amount of energy of the waves in the basin thus pgv the psa of soil to rock ratios and the velocity fourier spectrum were dependent on the soil q model also using a high velocity contrast between soil and rock increased pgvs and the amplitude of the psa of the soil to rock ratios whereas the frequency content of the waves shifted toward lower frequencies using a finite fault source model for a scenario large earthquake mw 7 significantly reduced the pgv values relative to a point source model using nonlinear viscoelastic simulation for a large earthquake mw 7 reduced the amplitude of the later arrivals and the amplitude of the psa of the soil to rock ratios and shifted the frequency content of waves toward lower frequency

summary of the gk15 ground motion prediction equation for horizontal pga and 5 damped psa from shallow crustal continental earthquakes we present a revised ground motion prediction equation gmpe for computing medians and standard deviations of peak ground acceleration pga and 5 damped pseudospectral acceleration psa response ordinates of the horizontal component of randomly oriented ground motions to be used for seismic hazard analyses and engineering applications this gmpe is derived from the expanded next generation attenuation nga west 1 database see data and resources 1 chiou et al 2008 the revised model includes an anelastic attenuation term as a function of quality factor q to capture regional differences in far source beyond 150 km attenuation and a new frequency dependent sedimentary basin scaling term as a function of depth to the 1 5 km s shear wave velocity isosurface to improve ground motion predictions at sites located on deep sedimentary basins the new graizer kalkan 2015 gk15 model developed to be simple is applicable for the western united states and other similar shallow crustal continental regions in active tectonic environments for earthquakes with moment magnitudes m 5 0 8 0 distances 0 250 km average shear wave velocities in the upper 30 m v s 30 200 1300 m s and spectral periods t 0 01 5 s our aleatory variability model captures interevent between event variability which decreases with magnitude and increases with distance the mixed effect residuals analysis reveals that the gk15 has no trend with respect to the independent predictor parameters compared to our 2007 2009 gmpe the pga values are very similar whereas spectral ordinates predicted are larger at t 0 2 s and they are smaller at longer periods 1 sec 21

site response models for charleston south carolina and vicinity developed from shallow geotechnical investigations the study models the response of near surface materials in charleston south carolina and the adjacent area geotechnical investigations at 281 locations were made available by local engineering firms the data used for dynamic site response analysis were derived from shear wave velocity measurements at 52 loca tions site response was quantified as the ratio of surface motion to hypothetical hard rock basement outcrop motion scenario earthquake motions were developed with the stochastic model acceleration response ratios for 5 critical oscillator damping were computed for 12 frequencies ranging from 0 1 to 30 hz and for peak ground acceleration two features determine the general nature of site response in the study area the impedance contrast between mesozoic basement and cretaceous sediments and the shallow impedance contrast between quaternary and tertiary sediments average s wave velocities in the quaternary are relatively uniform and range from 150 to 250 m sec they are not strongly correlated with surface geology the velocities of the immediately underlying tertiary sediments range from 300 to 500 m sec because of the uniformity of velocity in the quaternary depth to the quaternary tertiary contact appears to be the most important variable leading to differences in calculated site response this surface is irregular and varies in depth from near surface at inland sites to approximately 30 m at sites near the coast as a consequence estimated site response in the frequency band 1 10 hz varies by as much as a factor of 3 site response at frequencies less than 1 hz is dominated by the first few resonant har monics of the entire sedimentary section with fundamental frequency near 0 2 hz

estimation of the coda wave attenuation and geometrical spreading in the new madrid seismic zone using the single backscattering method coda quality factor functions through coda window lengths of 20 30 40 50 and 60 s have been estimated for the new madrid seismic zone nmsz furthermore geometrical spreading functions for distances less than 60 km have been determined in this region at different center frequencies exploiting the coda normalization method a total of 284 triaxial seismograms with good signal to noise ratios snr 5 from broadband stations located in the nmsz were used the database consisted of records from 57 local earthquakes with moment magnitudes of 2 6 4 1 and hypocentral distances less than 200 km q factor values were evaluated at five frequency bands with central frequencies of 1 5 3 6 12 and 24 hz vertical components were utilized to estimate vertical coda q factor values horizontal coda q factor values were determined using the average amount of the q factor values estimated from two orthogonal horizontal components the coda q factor increases with increasing of the coda window length implying that with increasing the depth the coda q factor increases the intermediate values of the q factor and intermediate values of the frequency dependency indicate that the earth s crust and upper mantle beneath the entire nmsz is tectonically a moderate region with a moderate to relatively high degree of heterogeneities the geometrical spreading factors of s wave amplitudes are frequency dependent and determined to be 0 761 0 991 1 271 1 182 and 1 066 for center frequencies of 1 5 3 6 12 and 24 hz respectively at hypocentral distances of 10 60 km the geometrical spreading factors for lower frequencies are not recommended to be used due to the greater impact of the radiation pattern and directivity effect on low frequencies as well as the greater sensitivity of band pass filtered seismograms of small earthquakes to the noise in low frequencies

determination of stress parameters for eight well recorded earthquakes in eastern north america we determined the stress parameter for the eight earthquakes stud ied by atkinson and boore 2006 using an updated dataset and a revised point source stochastic model that captures the effect of a finite fault we consider four geometrical spreading functions ranging from 1 r at all distances to two or three part functions the values are sensitive to the rate of geometrical spreading at close distances with 1 r 1 3 spreading implying much higher than models with 1 r spreading the important difference in ground motions of most engineering con cern however arises not from whether the geometrical spreading is 1 r 1 3 or 1 r at close distances but from whether a region of flat or increasing geometrical spreading at intermediate distances is present as long as is constrained by data that are largely at distances of 100 km 800 km the simple 1 r model fits the sparse data for the eight events as well as do more complex models determined from larger datasets where the larger datasets were used in our previous ground motion predic tion equations this suggests that uncertainty in attenuation rates is an important com ponent of epistemic uncertainty in ground motion modeling for the attenuation model used by atkinson and boore 2006 the average value of from the point source model ranges from 180 bars to 250 bars depending on whether or not the stress parameter from the 1988 saguenay earthquake is included in the average we also find that for a given earthquake is sensitive to its moment magnitude m with a change of 0 1 magnitude units producing a factor of 1 3 change in the derived

modeling geometrical spreading and the relative amplitudes of vertical and horizontal high frequency ground motions in eastern north america abstract horizontally layered velocity models were used with point source and finite fault sources to investigate geometrical spreading and the relative amplitudes of vertical and horizontal ground acceleration within 120 km of the source full wave field simulations were done for a range of focal depths and for strike slip and reverse focal mechanisms the attenuation of the geometric mean of randomly oriented horizontal component maximum acceleration amplitudes averaged over all azimuths significantly exceeds the theoretical geometrical spreading for far field body waves in a homogeneous whole space for hypocentral distances less than approximately 60 km the behavior of the vertical component is different from the horizontal vertical attenuation near the epicenter is greater and is more dependent on source mechanism and depth because of the rapid near source decay of the direct s wave reflections from the mid lower crust and moho control the maximum amplitude of the vertical component acceleration in the 60 120 km hypocenter distance range resulting in a flattening of the vertical amplitude distance relation near source vertical maximum amplitudes averaged over all source receiver azimuths tend to be less than the geometric mean horizontal amplitude for strike slip focal mechanisms but near the source for reverse faults the azimuthally averaged vertical component amplitude exceeds that of the geometric mean horizontal the modeling indicates that similar vertical and horizontal component geometrical spreading and approximately constant horizontal vertical amplitude ratios observed in connection with the lg phase at distances greater than approximately 100 km in eastern north america may not hold at smaller distances ground motion prediction models for the vertical component near the source may need to incorporate strong geometrical spreading and dependence on radiation pattern

ground motion amplification at rock sites across canada as determined from the horizontal to vertical component ratio we determine the frequency dependent amplification inherent in hard rock sites across canada under the assumption that it can be estimated from the ratio of the horizontal to vertical h v components of ground motion the use of h v as an estimate of amplification was originally proposed by nakamura 1989 for microtremors and then generalized to earthquake ground motions by lermo and chavez garcia 1993 the h v method was applied to a fourier spectra database compiled from 424 earthquakes of magnitude greater than or equal to 2 recorded on 32 three component stations of the canadian national seismograph network cnsn all sited on rock shear wave velocity 1500 m sec in each case we analyzed the s wave portion of the seismograms including the direct s and other strong s phases such as lg the average amplification h v for rock sites does not vary significantly across the country it is weakly frequency dependent increasing from a factor near unity at 0 5 hz to a maximum in the range from 1 2 to 1 6 at 10 hz this amplification is consistent with what would be expected from a gradual decrease in shear wave velocity as the seismic waves approach the surface due to factors such as near surface weathering the interpretation of the h v ratio as a measure of site response is consistent with the general geological conditions of the recording sites in particular the 5 hz h v ratio can be correlated with local geological conditions the central canada sites have the lowest estimated site amplification this is consistent with competent hard rock site conditions with high near surface shear wave velocities there are two stations that show anomalous h v ratios that suggest significant local site effects these are edm near edmonton which may be influenced by topographic amplification and a61 a station in the charlevoix seismic zone

accurate estimation of seismic source parameters of induced seismicity by a combined approach of generalized inversion and genetic algorithm application to the geysers geothermal area california the accurate determination of stress drop seismic efficiency and how source parameters scale with earthquake size is an important issue for seismic hazard assessment of induced seismicity we propose an improved non parametric data driven strategy suitable for monitoring induced seismicity which combines the generalized inversion technique together with genetic algorithms in the first step of the analysis the generalized inversion technique allows for an effective correction of waveforms for attenuation and site contributions then the retrieved source spectra are inverted by a non linear sensitivity driven inversion scheme that allows accurate estimation of source parameters we therefore investigate the earthquake source characteristics of 633 induced earthquakes mw 2 3 8 recorded at the geysers geothermal field california by a dense seismic network i e 32 stations more than 17 000 velocity records we find a non self similar behavior empirical source spectra that require an source model with 2 to be well fit and small radiation efficiency sw all these findings suggest different dynamic rupture processes for smaller and larger earthquakes and that the proportion of high frequency energy radiation and the amount of energy required to overcome the friction or for the creation of new fractures surface changes with earthquake size furthermore we observe also two distinct families of events with peculiar source parameters that in one case suggests the reactivation of deep structures linked to the regional tectonics while in the other supports the idea of an important role of steeply dipping faults in the fluid pressure diffusion

a statistical model for ground motion produced by earthquakes at local and regional distances to adapt random process theory techniques for statistical estimation of peak ground motion to more realistic earth models we constrain the parameters of duration geometrical spreading and spectral shape by modeling the main ground motion as being the result of major contributions by the direct s wave and supercritically reflected s waves the results of our modeling are constrained to be consistent with values from full wave synthetics for the test models the combination of estimation theory and theoretical amplitude spectrum of the main ground motion within the ergodic window successfully predicts the mean peak vertical ground displacements velocities and accelerations of the 1982 miramichi earthquakes in new brunswick canada in addition upon considering the effects of source depth and crustal structure for the november 25 1988 saguenay earthquake m 5 8 in quebec canada the predicted mean peak horizontal ground accelerations match the observed data very well the effects of source depth and crustal structure on the peak ground motion are complicated for different source sizes and at different epicentral distance ranges