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

theoretical study of the excitation spectral characteristics and geometrical attenuation of regional seismic phases abstract we present a theoretical study of the generation and geometrical attenuation of regional crustal phases we do this through the computation of seismograms in the epicentral distance range from 60 to 500 km the geometrical attenuation of lg waves with epicentral distance is of the form r 0 83 pg wave amplitudes display a much stronger decay of the form r 1 5 the spectral density of the crustal transfer function for pg waves is relatively flat for frequencies between 0 1 and 5 hz while lg wave spectra strongly fall off beyond 2 to 3 hz the excitation of pg wave is insensitive to the depth of the source within the crust while the lg amplitude is about 50 per cent higher for a source in the upper and middle crust than in the lower crust the amplitudes of these two phases drastically decrease when the source is below the moho these results illustrate the important role of wave guide played by the crust for the propagation of lg and pg we find that the geometrical attenuation of pg and lg waves is independent of source mechanisms in the case of an explosion the excitation of pg is insensitive to the source depth the lg wave amplitude is small in comparison to pg and rayleigh waves and depends on the closeness of the source to an interface or to the free surface

geometrical spreading and attenuation of lg waves a comparison between western anatolia turkey and southern spain abstract we compared the attenuation and geometrical spreading coefficient of lg waves for crustal paths in western anatolia and southern spain at source receiver distances between 80 and 400 km we used the coda normalization method which is based on the elimination of the source and site effects from observed spectra of lg waves q for lg waves in the crust was determined as a function of frequency in the range 1 5 10 0 hz for western anatolia and in the range 1 5 12 hz for southern spain we found that qlg shows a strong frequency dependence in both regions in western anatolia the frequency dependence of qlg is qlg f 82 f1 0 and the geometrical spreading coefficient ranges from 0 6 to 0 9 we found qlg 83 f0 88 and a geometrical spreading coefficient close to 0 5 in southern spain comparing our results with coda q values obtained in both regions qlg qc are similar qlg is close to qi in all frequency bands we interpret the geometrical spreading coefficient higher than 0 5 for western anatolia as due to a strong layered and heterogeneous crustal structure

the acquisition of source path and site effects from microearthquake recordings using q tomography application to the united kingdom source site and propagation parameters are inverted from a u k database of weak motion events 2 0 m l 4 7 this results in the complete spectral parameterization of over 3200 velocimetric records of 273 events from the year 1992 to 2006 the s wave is extracted from the vertical records and is processed using a multitaper fourier transform we initially use a nonlinear least squares log space optimization to obtain estimates of the attenuation parameter for each spectrum the estimates of t are then used to geometrically constrain a depth dependent q model using a technique adapted from velocity tomography we then invert for the remaining frequency dependent parameters and a collective amplitude parameter from the velocity spectra while fixing the newly computed attenuation parameters based on raytracing through our q model the resultant amplitude parameters are then split into source moments apparent geometrical spreading and site correction factors we find a frequency independent depth dependent q structure a linear relationship proportional to 0 7 m l between moment magnitude m w and local magnitude m l is found in the range of 2 4 7 m l the majority of stress drops are found to range on the order of 0 1 10 mpa a multiple segment apparent geometrical spreading model is found to best describe the amplitude decay with distance accounting for factors such as geometrical spreading and scattering along with multiple phase interference in the analysis window site response functions are found to broadly correlate with regional geology mean amplification occurring in the cenozoic sedimentary rock sites to the southeast of england relative to the harder palaeozoic rock sites of wales and scotland we use a bootstrap analysis technique to analyze the dependence of our results on the data in order to estimate the variance of the results and check the robustness of different inversions synthetic spectra are also computed in order to obtain minimum variance and bias of model parameters associated with the method in applying a geometrical q constraint through the use of q tomography we find that the robustness of the results is significantly increased a thorough analysis of the trade offs involved in the inversion is performed using synthetic datasets we find strong trade offs between the parameters but we are able to show that this covariance is reduced when adopting the q tomography approach

the complete synthesis of seismic crustal phases at regional distances using a new method to evaluate green s functions for elastic layered media we compute complete synthetic seismograms at regional distances for an earthquake in the earth crust we choose as source parameters the ones inferred for an earthquake in central france and compare the computed seismograms to the ones recorded at several short period stations of the french seismic network the major features of the records including complexity and duration are well reproduced by the synthetics lg waves which are the prominant phase are shown to be guided waves made up of sh and sv waves incident on the moho at angles of incidence more grazing than the critical angle and multiply reflected within the crust the length of the computed lg wave coda extends between group velocities of 3 5 and 2 8 km s and is in good agreement with the data

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

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

modelling of strong ground motions from 1991 uttarkashi india earthquake using a hybrid technique we present a simple and efficient hybrid technique for simulating earthquake strong ground motion this procedure is the combination of the techniques of envelope function midorikawaet al tectonophysics 218 287 295 1993 and composite source model zenget al geophys res lett 21 725 728 1994 the first step of the technique is based on the construction of the envelope function of the large earthquake by superposition of envelope functions for smaller earthquakes the smaller earthquakes sub events of varying sizes are distributed randomly instead of uniform distribution of same size sub events on the fault plane the accelerogram of large event is then obtained by combining the envelope function with a band limited white noise the low cut frequency of the band limited white noise is chosen to correspond to the corner frequency for the target earthquake magnitude and the high cut to the boore s fmax or a desired frequency for the simulation below the low cut frequency the fall off slope is 2 in accordance with the 2 earthquake source model the technique requires the parameters such as fault area orientation of the fault hypocenter size of the sub events stress drop rupture velocity duration source site distance and attenuation parameter the fidelity of the technique has been demonstrated by successful modeling of the 1991 uttarkashi himalaya earthquake ms 7 the acceptable locations of the sub events on the fault plane have been determined using a genetic algorithm the main characteristics of the simulated accelerograms comprised of the duration of strong ground shaking peak ground acceleration and fourier and response spectra are in general in good agreement with those observed at most of the sites at some of the sites the simulated accelerograms differ from observed ones by a factor of 2 3 the local site geology and topography may cause such a difference as these effects have not been considered in the present technique the advantage of the technique lies in the fact that detailed parameters such as velocity q structures and empirical green s functions are not required or the records of the actual time history from the past earthquakes are not available this method may find its application in preparing a wide range of scenarios based on simulation this provides information that is complementary to the information available in probabilistic hazard maps

regional primitive equation studies of the gulf stream meander and ring formation region abstract primitive equation and quasi geostrophic eddy resolving open ocean models are used for hindcast studies in the gulf stream meander and ring formation region a feature model approach is used to initialize the models based on one month of observations during november to december 1984 flat bottom and topographic calculations are carried out using an initial gulf stream velocity profile based on the pegasus dataset all of the major events observed in the upper thermocline are reproduced by both numerical models the addition of bottom topography is shown to significantly alter the character of the deep velocity fields large basin scale circulations found near the bottom in both flat bottom calculations were replaced by energetic jets and eddies associated with the dominant spatial scales of the bottom topography use of the quasi geostrophic model to dynamically adjust the initial conditions for the primitive equation model is shown to reduce the growth of large scale meanders on time scales o

estimation of moment magnitude from ground motions at regional distances abstract we present a simple and robust approach to estimate moment magnitude m for events of m m can be estimated from 1 hz response spectral amplitudes for events in north america with an uncertainty standard deviation of residuals of m across regions and that it provides relationships that are consistent with the predictions of a stochastic point source model for typical regional attenuation models online material table of events for which the moment magnitude was estimated

calibration of time history simulation methods abstract ground motion time histories for use in engineering analyses of structures in eastern north america are often simulated from seismological models owing to the paucity of real recordings in the magnitude and distance ranges of interest two simulation methods have been widely used in recent years the stochastic method and the ray theory method in the stochastic method as im plemented in this study ground motion is treated as filtered gaussian noise whose underlying spectrum is determined from an empirical region specific seismological model of the source and propagation processes in the ray theory method as implemented in this study the ground motions are simulated by convolving an empirical source function with theoretical green s functions for a specified crustal structure model this article compares results of the two simulation methods for four well recorded calibration events and assesses the applicability of the methods the assessment is based on comparisons of ground motion parameters from the simulated data with those of the actual recordings ground motion parameters in the frequency range from 1 to 10 hz are sat isfactorily predicted by both methods averaged over the four events studied the stochastic method underpredicts 1 hz response spectra by 20 to 40 but accurately predicts response spectra for frequencies of greater than 2 hz it also accurately predicts peak ground acceleration and velocity the wave propaga tion method underpredicts 1 hz response spectra by 10 to 40 but accurately predicts response spectra for higher frequencies it overpredicts peak ground acceleration and velocity by 10 to 40 both methods are imprecise the stan dard error of an estimate is a factor of about 2 2 the bias and standard error of an estimate for the wave propagation method are generally slightly lower than for the stochastic method if the focal depth of the event can be specified i e as for a past earthquake if the focal depth of the event is not known i e as for a future earthquake then the accuracy and precision of thetwo methods are about the same the chief advantage of the wave propagation method is its predictive power since its attenuation func tion is derived from the focal depth and crustal structure it does not require knowledge of the empirical attenuation function the chief advantage of the stochastic model is its economy and simplicity introduction seismic hazard studies are often used to identify design earthquakes in terms of magnitude and dis tance from a site of interest ground motion time his tories for the desired magnitude s and distance s are then sought to be used as input for engineering analyses of a proposed structure for regions such as california where strong ground motion records are relatively abun dant a suite of recordings from past earthquakes is usu ally available in eastern north america by contrast relevant records for the desired magnitudes and distances are seldom available it is therefore necessary to simu late the required records based on seismological models of earthquake ground motion generation processes two simulation methods have been widely used in recent years the stochastic method and the ray theory method in the stochastic method ground motion is treated as bandlimited finite duration gaussian noise whose underlying spectrum is determined from a seismological model of source and propagation processes in the ray theory method the ground motions are simulated by convolving an empirical source function usually derived from a past event with theoretical green s functions for 400

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

new insights into path attenuation of ground motions in northeast india and northwest himalayas abstract we compile a data set of 585 weak broadband and strong ground motion recordings from 184 earthquakes covering hypocentral distances ranging from 9 to 436 km in northeast india and the northwest himalayas source normalized vertical component fourier amplitude s wave spectra are used to study path attenuation characteristics namely geometrical spreading and quality factor in the two regions a trilinear model of geometrical spreading of r 1 0 for hypocentral distance r r 0 0 for r between 125 km and 140 km and r 1 0 for r 140 km approximates the decay of low frequency 1 0 hz amplitudes in northeastern india better than the conventional theoretical bilinear geometrical spreading of r 1 0 for r r 0 5 otherwise in the northwestern himalayas the geometrical spreading is found to be r 1 0 which is the same as that of a bilinear model at hypocentral distances r f given by in the frequency range of 0 9 20 hz

the 1997 1998 umbria marche sequence central italy source path and site effects estimated from strong motion data recorded in the epicentral area 1 we apply a nonparametric spectral inversion scheme to calculate source spectra s wave attenuation and site transfer functions from strong motion records in the epicentral region of the 1997 1998 umbria marche seismic sequence central italy we use records from moderate size earthquakes 4 6 ml 5 9 to parameterize the spectral amplitude decay in the distance range from 5 to 40 km we find that the average quality factor q can be approximated by q f 49 f0 9 between 0 5 and 8 hz and the geometrical spreading by r 0 9 at high frequencies f 8 hz the dependence of q on frequency weakens and it takes an approximate constant value of 318 we fit the source spectra to the square model and calculate an average stress drop of 2 1 mpa the average value is consistent with the previous estimates from the weak events 1 4 ml 4 5 of the umbria marche seismic sequence the most remarkable site effects are found in correspondence of large sedimentary basins filled by alternation of sandy clayey deposits the estimated spectral parameters are used to simulate acceleration spectra recorded during several earthquakes of the umbria marche sequence both point source and finite fault effects are considered furthermore attenuation relationships for peak ground velocity and ground acceleration are estimated using synthetic data and compared to existing relationships

attenuation of strong ground motion in canada from a random vibrations approach abstract theoretical relations are developed for the attenuation of horizontal peak ground acceleration pga and velocity pgv in canada with emphasis on eastern canada the theoretical basis is a composite of several approaches at intermediate epicentral distances results from random vibration theory hanks and mcguire 1981 boore 1983 which can be used to describe pga and pgv in terms of shear radiation implied by brune9s 1970 source model are applied to canadian earthquakes motions are extended into the near source region using arguments concerning magnitude scaling joyner and boore 1981 at distances greater than two crustal thicknesses ground motions are attributed largely to the lg phase and are attenuated accordingly nuttli 1982 the resulting attenuation relations for pga and pgv in eastern canada are in excellent agreement with strong motion data from moderate eastern canadian and central united states earthquakes compared to empirical attenuation relationships based on modified mercalli intensity the theoretical model predicts a stronger dependence of peak ground motions on magnitude in other respects amplitude levels and distance decay empirical and theoretical predictions are similar the model predicts that eastern events will have higher peak accelerations but similar peak velocities in comparison to their western counterparts of the same moment magnitude this arises from the relative enrichment of eastern earthquakes in higher frequencies

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

ground motion attenuation at short hypocentral distances 30 km near sudbury ontario abstract we use seismographic data from 12 local shallow earthquakes of magnitude m n 1 0 3 1 that occurred near sudbury ontario recorded at three stations within 30 km of the source to examine ground motion attenuation at close distances this is an important issue for development of ground motion prediction equations in eastern north america and for the inference of earthquake source parameters from regional earthquake observations we show that high frequency 3 10 hz horizontal component ground motions decay at a geometric spreading rate of approximately r 1 3 in the first 25 30 km from the earthquake source where r is the hypocentral distance this is in agreement with the geometric spreading rate determined by atkinson 2004 and used in the ground motion prediction equations of atkinson and boore 2006 vertical component ground motions in this distance range appear to decay at a slightly slower rate of r 1 1

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

estimating the diminution of shear wave amplitude with distance application to the los angeles california urban area the rate of decay with distance of shear wave amplitude computed from 20 sec s wave spectra is determined from terrascope records of small earthquakes in the greater los angeles area piecewise log linear interpolation functions and traditional diminution functions are used to fit spectral decay to a maximum distance of 150 km simultaneously isotropic source and receiver terms are determined separate branches of the spectral decay function are found for two categories of source depth greater than 10 km and less than 10 km in the hypocentral distance range of 20 to 150 km and in the frequency range of 0 5 to 8 0 hz an important result of the investigation is that the horizontal component decay rate associated with deeper crustal sources is generally greater than that associated with shallower sources and is greater than that which is estimated using more traditional models of spectral decay with distance the same behavior generally holds for vertical component spectra the variation in apparent attenuation rate with source depth should affect seismic hazard estimates associated with the rupture of blind thrust faults in the los angeles basin and vicinity the results of the inversions suggest that interpolation function representations of spectral decay are sensitive to perturbations of s wave amplitude due to crustal reflectors such as post critical s wave arrivals from mid crustal to deep crustal velocity interfaces

source spectra for the 1988 saguenay quebec earthquakes abstract source spectra are obtained for the 1988 saguenay quebec earthquake m n 6 5 its foreshock m n 4 8 and largest aftershock m n 4 1 using recordings from analog and digital seismographs on rock sites at epicentral distances from 40 to 700 km the source spectra of the foreshock and the aftershock are well matched by a single corner frequency 2 model with seismic moments of 2 2 10 22 and 2 2 10 21 dyne cm respectively and a stress parameter of 65 bars for both events by contrast the spectrum of the mainshock differs dramatically from this simple shape a stress parameter of 500 bars is required to match the observed high frequency amplitudes using the seismic moment determined from teleseismic observations as a constraint this single corner frequency model however overestimates amplitudes at frequencies near 1 hz by a factor of about 2 the relative radiation of short and long period energy for the mainshock is inconsistent with that from other intraplate earthquakes the fore and aftershocks appear typical in this regard the extraction of source spectra from the regional data required a careful examination of attenuation azimuthal variations were observed with the attenuation being most severe to the southeast normal to the st lawrence valley and the dominant structural grain of the region the st lawrence river coincides in part with the boundary between the grenville and appalachian tectonic provinces and the difference in attenuation may be related to the difference in tectonic province the distribution of data however makes it difficult to obtain good estimates of the attenuation in each province lumping the data from both provinces and the three earthquakes together results in an anelastic attenuation factor given by q 755 f 0 5 for frequencies f from 0 6 to 18 hz using data at distances r beyond 100 km from the sources and assuming 1 r geometrical spreading this attenuation is similar to that obtained in a number of other studies in the general area three component recordings were available at a few stations and from these the following frequency dependent ratio of horizontal to vertical motion was obtained hiv 1 14 0 118 f 0 00638 f 2 for frequencies from 0 2 to 15 hz different methods of correcting observations for attenuation in order to derive source spectra were examined source spectra derived by simple regression analyses of observed data assuming a uniform medium are very similar to those based on a more complicated synthetic seismogram correction which accounts for wave propagation in a layered earth

a review of the discrete wavenumber method we present a review of the discrete wavenumber dwn method the method introduced by bouchon and art 1977 allows the simple and accurate calculation of the complete green s functions for many problems in elastodynamics

local and regional p wave spectral attenuation model for iran a robust frequency dependent local and regional p wave attenuation model is estimated for continental paths in the iranian plateau in order to calculate the average attenuation parameters 46 337 vertical component waveforms related to 9267 earthquakes which are recorded at the iranian seismological center irsc stations have been selected in the distance range 10 1000 km the majority of the event s magnitudes are less than 4 5 this collection of records provides high spatial ray path coverage results indicate that the shape of attenuation p wave curve versus distance is not uniform and has three distinct sections with hinges at 90 and 175 km a trilinear model for attenuation of p wave amplitude in the frequency range 1 10 hz is proposed in this study fourier spectral amplitudes are found to decay as r 1 2 where r is hypocentral distance corresponding to geometric spreading within 90 km from the source there is a section from 90 to 175 km where the attenuation is described as r 0 8 and the attenuation is described well beyond 175 km by r 1 3 moreover the average quality factor for pg and pn waves qpg and qpn related to anelastic attenuation is obtained as qpg 54 2 2 6 f 1 0096 0 07 and qpn 306 8 7 4 f 0 51 0 05 there is a good agreement between the results of the model and observations also the attenuation model shows compatibility with the recent regional studies from the results it turns out that the amplitude of p waves attenuates more rapidly in comparison with the global models in local distances

ground motion attenuation and source spectral shape for earthquakes in eastern iran abstract we study source path and site effects for eastern iran earthquake based on regression analysis of 243 three component fourier acceleration spectra from 32 eastern iran earthquakes with moment magnitude m 4 4 7 4 recorded at hypocentral distances from 5 to 250 km the geometric spreading follows a trilinear behavior the first and second hinges of the trilinear behavior are at 87 and 119 km respectively the associated quality factor q based on the horizontal components is q f 166 f 1 13 the site dependent parameters 0 for vertical and horizontal components are 0 035 and 0 048 respectively because of lack of station specific site information the horizontal to vertical ratio is considered to be a rough estimation of generic site amplification the mean value of brune stress drops estimated for the events is 81 bars to construct an empirical model for source spectra horizontal component of the shear wave spectrum for m 4 4 7 4 we tested several functional forms including those suggested for california and eastern north america to search for the best combination of the coefficients that minimizes the average residual errors the model we attained is a function of two multiplicative corner frequencies of f a and f b and a parameter in which log f a 2 69 0 56 m log f b 3 40 0 53 m and

attenuation of ground motion spectral amplitudes and its variations across the central alborz mountains we selected 136 earthquakes recorded at stations of the institute of geo physics of the university of tehran igut during 1996 2007 in order to estimate the average attenuation parameters and variations of station corrections across the central alborz mountains the northern extension of the alpine himalayan orogeny in wes tern asia the selected events provide 1260 high signal to noise ratio snr records with relatively good spatial coverage we graphically find the distances at which the nature of geometrical spreading attenuation r b changes significantly using a locally weighted scatterplot smoothing lowess local regression smoothing method called robust lowess a trilinear function with hinges at distances of about 80 and 160 km describes the geometric spreading attenuation with distance by regressing to the hinged trilinear function we found that b1 1 15 0 21 b2 0 09 0 31 and a fixed b3 0 5 minimize the average absolute value of the fourier spectrum amplitude residuals using an anelastic attenuation coefficient at different frequencies the direct quality factor q in the central alborz region is obtained as q 109 2f 0 64 0 04 the geographical distribution of station corrections at 1 hz can be clearly separated along a dividing line connecting the north tehran mosha and attari faults into two regions the northern low attenuating and the southern high attenuating regions the stations with strong positive station corrections clearly align along the dividing line this suggests the existence of a higher attenuation zone south of the dividing line the presence of thick tertiary quaternary sedimentary rocks with thick layers of salt in the southern region may explain the observed greater attenuation of seismic waves

stochastic prediction of ground motion and spectral response parameters at hard rock sites in eastern north america empirical predictions of ground motions from large eastern north american earthquakes are hampered by a lack of data for such events for this reason most prediction techniques have been based at least in part on data from the seismically active and well instrumented western north america concentrating on the prediction of response spectra on hard rock sites we have used a relatively new theoretical technique that does not require western data to make ground motion predictions for eastern north america this method often referred to as the stochastic model has its origins in the work of hanks and mcguire who treat high frequency motions as filtered random gaussian noise for which the filter parameters are determined by a seismological model of both the source and the wave propagation the model has been successfully applied to the predictions of ground motions in the western united states and to short period magnitudes from large to great earthquakes worldwide for our application the essential parameters of the model are estimated by using existing data from small to moderate eastern north american earthquakes a crucial part of the model is the relation between seismic moment and corner frequency the relation proposed in 1983 by nuttli for mid plate earthquakes leads to predictions of ground motions that are lower than available data by a factor of about 4 on the other hand a constant stress parameter of 100 bars gives model predictions in good accord with the data to aid in applications the ground motion predictions are given in the form of regression equations for earthquakes of magnitude 4 5 to 7 5 at distances within 100 km of the source the explanatory variables are hypocentral distance and moment magnitude m because predictions are often required in terms of m g rather than m we have used the theoretical model to establish a relation between the two magnitudes the predicted relation agrees with the sparse data available although the large uncertainties in the observed magnitudes for the larger events as well as the sensitivity of the theoretical magnitude to the attenuation model make it difficult to discriminate between various source scaling models

evaluation of models for earthquake source spectra in eastern north america there have been several relations proposed in the last few years to describe the amplitudes of ground motion in eastern north america ena these relations differ significantly in their assumptions concerning the amplitude and shape of the spectrum of energy radiated from the earthquake source in this article we compare ground motions predicted for these source models against the sparse ena ground motion database the source models evaluated include the two comer models of boatwright and choy 1992 atkinson 1993a haddon 1996 and joyner 1997a b and the one comer model of brune as independently implemented by frankel et al 1996 and by toro et al 1997 the database includes data from ena mainshocks of m 4 and historical ena earthquakes of m 5 5 for a total of 110 records from 11 events of 4 m 7 3 all recorded on rock we also include 24 available rock records from 4 large earthquakes in other intraplate regions con clusions are checked to determine whether they are sensitive to the addition of these non ena data the atkinson source model as implemented in the ground motion relations of atkinson and boore 1995 is the only model that provides unbiased ground motion predictions over the entire period band of interest from 0 1 to 10 sec the source models of frankel et al 1996 toro et al 1997 and joyner 1997a b all provide unbiased ground motion estimates in the period range from 0 1 to 0 5 sec but over estimate motions at periods of 1 to 10 sec the haddon 1996 source model over predicts motions at all periods by factors of 2 to 10 these conclusions do not change significantly if data from non ena intraplate regions are excluded although the ten dency of all models toward overprediction of long period amplitudes becomes more pronounced the tendency of most proposed ena source models to overestimate long period motions is further confirmed by an evaluation of the relationship between ms a measure of the spectrum at 20 sec period and moment magnitude a worldwide catalog of shallow continental earthquakes triep and sykes 1996 is compared to the ms m relations implied by each of the source models the atldnson source model is consistent with these data while other proposed ena models overpredict the average ms for a given m the implications of mmi data from historical earthquakes are also addressed by exploiting the correlation between felt area and high frequency source spectral level high frequency spectral amplitudes as specified by the atkinson and boore 1995 frankel et al 1996 toro et al 1997 and joyner 1997a b source models equal or exceed the levels inferred from the felt areas of most of the large ena events with the noteable exception of the saguenay earthquake by contrast high frequency spectral amplitudes specified by the haddon 1996 source model agree with the felt area of the saguenay earthquake but overpredict the felt areas of nearly all other large events in general models that fit the saguenay data be it intensity data strong ground motion data regional seismographic data or teleseismic data will not fit the data from the remaining earthquakes a source model derived from the california database suitably modified for re gional differences in crustal properties is also evaluated this model is not signifi

stochastic finite fault modeling of ground motions from the 1999 chi chi taiwan earthquake application to rock and soil sites with implications for nonlinear site response the stochastic method for simulating strong ground motions from finite faults is applied to the records of the 1999 chi chi taiwan earthquake the method involves discretization of the fault plane into smaller subfaults each of which is assigned an x 2 spectrum the contributions from all subfaults are empirically atten uated to the observation site and summed to produce the synthetic acceleration time history the method is initially calibrated against the data recorded at 24 rock sites located within 7 120 km from the mainshock hypocenter and providing a broad azimuthal coverage of the fault plane the accuracy of the simulations is quantified through the model bias defined as the logarithm of the ratio of the observed to simulated spectrum averaged over all stations the calibrated model for the chi chi event has a near zero average bias in reproducing the ground motions at rock sites in the frequency range from 0 1 to 20 hz an unusually low value is found for the radiation strength factor s controlling the high frequency radiation level and directly related to the maximum slip velocity on the fault compared with the mean value found for north american earthquakes this result reflects the observed low peak ground ac celerations of the chi chi mainshock and physically its lower than usual slip ve locities the calibrated model is then used to simulate soil site site class d records using the linear response assumption the simulated soil site input motions are amplified by the weak motion amplification functions estimated by the spectral ratio technique from available aftershock records this analysis reveals an average reduction in strong motion amplification to about 0 5 0 6 of that in weak motions with an ac celeration threshold for detectable nonlinearity near 200 300 cm sec 2 however the derivation of soil site specific weak motion amplification was limited by the amount of aftershock data available further improvement in the quantification of nonlinear soil response during the chi chi earthquake may be possible with the release of additional aftershock datasets

common features of the excitation and propagation of strong ground motion for north american earthquakes the central matter of this investigation is the commonly held belief that eastern north america ena earthquakes are felt to much greater distances at all levels of intensity than their western u s wus counterparts of the same source strength by comparing the areas enclosed by modified mercalli intensities i to iii felt iv v vi and vii for ena and wus earthquakes at the same source strength we find that this proposition is mostly false at damaging levels of ground motion intensities vi to vii and greater for m 7 neither should such differences exist if strong ground motion is confined to r 150 km and arrives principally as body waves and if ena and wus earthquakes share the same average stress drop in fact observable differences in the areas enclosed by intensity vi a vi for ena and wus earthquakes at the same m point to slight but significant differences in stress drop the ena earthquakes having stress drops a factor of about 2 higher only for the largest earthquakes m 7 as the 1811 to 1812 new madrid and 1886 charleston earthquakes seem to be can strong ground motion propagate to much greater distances as low loss higher mode surface waves in ena relative to wus the strong dependence of high frequency strong ground motion on stress drop and its weak dependence on m admit the possibility that the 1811 to 1812 events and the 1886 charleston earthquakes are no larger than m 6 to 7 provided that their stress drops are higher than average by a factor of 2 or so

global comparisons of earthquake source spectra a key question in earthquake seismology is whether earthquake sources in different tectonic regions are functionally equivalent in terms of radiated ground motion this article compares the apparent earthquake source radiation for six different regions japan mexico turkey california british columbia b c western canada and eastern north america ena the source path and site effects were consistently separated to the extent possible to allow interregional comparisons of apparent source radiation large fourier spectra databases were created for both horizontal and vertical components for earthquakes with magnitude between 2 5 and 7 5 regional parameters characterizing source path and site properties including crustal and near surface site amplifications were investigated to isolate apparent source spectra based on the vertical component spectra at a reference distance of 1 km a new magnitude scale m 1 was defined from the spectral level at 1 hz the magnitude scale m 1 is a natural complement to existing magnitude scales that measure the low frequency and high frequency spectral amplitudes moment magnitude m and high frequency m hf respectively in all regions the apparent source spectra for small to moderate earthquakes m 6 show good agreement with the single corner brune 1970 1971 point source model 2 spectrum suggesting a stress parameter of about 100 bars 10 mpa a two corner source model better matches the spectra for large magnitude earthquakes m 6 especially at intermediate frequencies for small to moderate events the two source models are nearly equal apparent source spectra from small to moderate earthquakes e g m 1 3 5 6 5 suggest a general similarity between the different tectonic regions studied although minor discrepancies appear in some cases there are no noticeable regional characteristics no evident depth effects were found on the apparent source spectra manuscript received 1 april 2001

frequency dependence of crustalqβ in stable and tectonically active regions fundamental mode rayleigh wave attenuation data for stable and tectonically active regions of north america south america and india are inverted to obtain several frequency independent and frequency dependentq models because of trade offs between the effect of depth distribution and frequency dependence ofq on surface wave attenuation there are many diverse models which will satisfy the fundamental mode data higher mode data such as 1 hz lg can however constrain the range of possible models at least in the upper crust by using synthetic lg seismograms to compute expected lg attenuation coefficients for various models we obtained frequency dependentq models for three stable and three tectonically active regions after making assumptions concerning the nature of the variation ofq with frequency

an ml scale in northeastern iran local magnitude scales are derived for northeastern iran khorasan province from waveform data recorded at six stations from 205 local earthquakes ranging in distance from 10 to 600 km by averaging the horizontal components in a single measure we used 1506 zero to peak amplitudes from synthetic wood anderson seismograms to determine in a least squares sense the appropriate loga0 attenuation functions the event local magnitude and the station corrections both a parametric and a nonparametric description of loga0 is considered while performing the inversions in both cases the constraint of 1 mm motion recorded at 100 km for m 3 0 earthquakes was used to evaluate the distance correction curves in determining the local magnitude ml in northeastern iran we applied both linear and trilinear inversions to our datasets the result of the linear inversion for dis tance correction is given by loga0 1 370 0 050logr 100 0 0020 0 0001r 100 3 for trilinear inversion we have applied the monte carlo technique the resulting coefficients evaluated for the area are r1 106 5 km r2 347 49 km n1 1 380 0 045 n2 0 597 0 132 n3 0 415 0 236 k 0 0033 0 0003 where n1 n2 and n3 are the coefficients of geometrical spreading for distances from the source to r1 r1 to r2 and beyond r2 k is the coef ficient of inelastic attenuation the remarkable agreement between the parametric and nonparametric results confirms that both linear and trilinear attenuation functions that we made for deriving the parametric distance correction are equally reasonable more over inversion of bootstrap replications of our dataset furnished stable solutions sta tion magnitude corrections range between 0 17 and 0 27 suggesting a variable and noticeable effect of station site properties on recorded amplitudes

aftershock sequences of the 1982 miramichi new brunswick earthquakes the mb 5 7 miramichi new brunswick earthquake of 9 january 1982 was located by comparison to the aftershock distribution in central new brunswick canada at 47 00 n 66 60 w with a focal depth of 7 km and an uncertainty of 3 km on each of the spatial coordinates the main shock was followed by a long and complex aftershock sequence with four events m 4 5 and more than 800 events m 1 0 until 30 june 1982 the aftershocks were studied by three temporary field networks set up in the epicentral areas from 10 to 20 january 2 to 7 april and 17 to 23 june 1982 and by the permanent canadian seismograph networks the aftershock activity was concentrated in a volume approximately 6 km ns 6 km ew 8 km deep and arranged in a north trending conjugate v pattern the miramichi earthquakes were predominatly thrust earthquakes occurring on north trending mid to high angle faults in the upper 8 km of the crust in the presence of an east west compressive horizontal regional stress field detailed field surveys have not yet been able to associate the earthquakes with any known preexisting faults the main shock had a moment of 2 2 0 7 1024 dyne cm and a stress drop of 35 to 70 bars the rupture started at 7 km depth on a plane striking 195 dipping 50 down to the west and propagated up to the east with a rake angle of 120 aftershocks deeper than 3 5 km had composite mechanisms very similar to the main shock s but shallower events took place on more steeply dipping planes up to 78 dip the rupture planes of the main shock and its principal aftershocks may have been similarly curved the magnitude frequency relationship b 0 8 of the aftershocks was comparable to the regional one the aftershock activity decayed as t 0 8 and had the highest rate of activity following the principal aftershock on 11 january that aftershock mb 5 4 appears to have ruptured the east dipping plane conjugate to the main shock s plane two other principal aftershocks mb 5 1 on 9 january and mb 5 0 on 31 march were associated with the main shock rupture plane while the fourth large event mb 4 7 on 16 june occurred 30 km west of the other activity and was seemingly unrelated however all the earthquakes were apparently associated with the same granitic terrain the miramichi earthquakes did not produce any significant surface faulting one small 25 mm surface displacement was found but it was identified as a secondary stress induced movement along a preexisting joint

source characterization of nevada test site explosions and western u s earthquakes using lg waves implications for regional source discrimination an investigation is made of the lg waves from 15 nuclear tests at the nevada test site nts and 25 shallow western united states earthquakes to obtain a scheme for discriminating between possible source mechanisms the data were recorded at four broadband stations operated by lawrence livermore national laboratory llnl which encircle the nts the lg wave spectra are modeled through a genetic algorithm search to find optimal values for 1 the seismic moment m o 2 the corner frequency of the amplitude spectrum f c 3 the 1 hz attenuation quality factors q o for all of the paths and 4 the frequency dependence of attenuation along the paths because the inversion solves for the path attenuation characteristics little a priori information is needed for the analysis the resulting m o and f c values are used in conjunction with the m b values as seismic discriminants the populations of earthquakes and explosions have nearly identical relationships between their moments and corner frequencies for earthquakes the relationship is log m o 16 07 2 93 log f c for the set of nts explosions using an earthquake source model the relationship is log m o 15 87 2 76 log f c a source discriminant is found however through a comparison of the moments and m b values this gives a line log m o 10 20 1 16 m b which cleanly separates the earthquake and explosion populations with earthquakes falling above and explosions below the line reliability tests examine the inverse trade off between moments and q o values noise in the lg spectra has a limited effect on the scaling relations

an improved approach for nonstationary strong ground motion simulation a new stochastic ground motion model for generating a suite of ground motion time history with both temporal and frequency nonstationarities for specified earthquake and site characteristics is proposed based on the wavelet method this new model is defined in terms of 6 key parameters that characterize the duration evolving intensity predominant frequency bandwidth and frequency variation of the ground acceleration process all parameters except for peak ground acceleration pga are identified manually from a database of 2444 recorded horizontal accelerations the two stage regression analysis method is used to investigate the inter and intra event residuals for any given earthquake and site characteristics in terms of the fault mechanism moment magnitude joyner and boore distance and site shear wave velocity sets of the model parameters are generated and used in turn by the stochastic model to generate strong ground motion accelerograms which can capture and properly embody the primary features of real strong ground motions including the duration evolving intensity spectral content frequency variation and peak values in addition it is shown that the characteristics of the simulated and observed response spectra are similar and the amplitude of the simulated response spectra are in line with the predicted values from the published seismic ground motion prediction equations sgmpe after a systematic comparison the proposed method can be used to estimate the strong ground motions as inputs for structural seismic dynamic analysis in engineering practice in conjunction with or instead of recorded ground motions

simulation of acceleration field of the lushan earthquake ms7 0 april 20 2013 china abstract the acceleration field of the lushan earthquake ms7 0 april 20 2013 china is simulated using a new modified version of the stochastic finite fault method exsim based on a dynamic corner frequency approach to incorporate the effect of heterogeneous slip distribution on the variation of source spectrum we adopt an empirical source spectral model and derive the corresponding dynamic parameters which vary with the cumulative seismic moment of the ruptured area the new modified method is validated by 1 comparison of the simulation results with those obtained from the exsim method using near fault ground motion data of the 1994 northridge earthquake 2 comparison of simulated pga contour map inferred from synthetic time histories at 315 grid locations with the observed pga shakemap for the 2013 lushan earthquake 3 comparison of simulated pga with those predicted by ground motion prediction equations gmpes and 4 comparison of simulated time histories with observed acceleration records at six strong motion stations during the mainshock of the lushan earthquake in which local site response is considered in the simulation these comparisons confirm the validity of the new simulation procedure for purposes of regional strong ground motion estimation limitations of the procedure in modeling the phasing of different arrivals in the seismic signal and near surface response of geologic deposits are discussed

attenuation of ground motion in the eastern united states abstract frequency dependent attenuation of ground motion in the eastern united states is investigated for both vertical and horizontal components of motion this is accomplished by digitizing and analyzing three component short period long range seismic measurements data from over 200 earthquake station pairs with epicentral distances less than about 1000 km pseudo relative velocity as well as velocity response spectra for 5 per cent damping are obtained for the frequency range of 0 5 to 7 hz a multi variate least squares inversion is used to derive the station and source terms as well as the mean q analysis of data for the entire eastern united states indicates q values for the vertical and horizontal components to be indistinguishable substantial increase in q with frequency a factor of about 2 from 1 to 7 hz large as much as a factor of 20 in amplitude site terms for both the vertical and horizontal components and the mean ratio of the peak horizontal to peak vertical component to be a stable characteristic of the site large regional variations in q are also indicated by subsets of data such as for the central united states and the appalachian mountains region

advancement in strong motion analysis by the use of evolutionary power spectra abstract illustrated by strong motion records from the michoacan earthquake 19 september 1985 and the loma prieta earthquake 17 october 1989 the application of the evolutionary power spectrum as a tool in strong motion analysis is demonstrated it is shown that a strong motion record is not a realisation of a simple stationary stochastic process it is a non stationary stochastic process which can be explained and modeled by some basic parameters and through the separation of the seismic process into stationary stochastic sub processes which are due to the dominant wave types

modeling short period crustal phases p lg for long range refraction profiles abstract the short period seismic phases known as p and lg are often recorded at distances of 200 1000 km on long range refraction profiles and are usually the largest amplitude features on record sections for this distance range p and lg propagate as multiply reflected compressional and shear waves in a crustal waveguide whose principal boundaries are the moho and the free surface equivalently they can be interpreted as the interference pattern produced by a superposition of higher mode p sv and sh waves propagating in a leaky waveguide for compressional waves the waveguide efficiency is a strong function of frequency and depends on the presence or absence of low velocity layers within a few kilometers of the surface such as deep sedimentary sections commonly found in active tectonic areas such low velocity surface layers create constructive interference effects for upcoming p waves incident at near grazing angles at the free surface and lead to efficient p propagation several good examples of strong p phases can be found on long range refraction profiles for the tectonically active western united states the 550 km profile eastward from shoal to delta ut is analyzed here we have used a modified reflectivity method computer program to model crustal phases for the shoal delta profile the reflectivity technique accounts for all body and surface waves contributing to the short period seismograms it is found that the synthetic waveforms realistically model the observed p characteristics in this case the decay of p amplitudes with distance appears to be dominated by surface reflection leakage from the waveguide rather than by anelastic attenuation due to q of crustal rocks

wave propagation in a three dimensional circular basin abstract wave propagation in a three dimensional circular basin model is studied by using a ray technique which employs the method of principal curvature for geometric spreading calculation three components of ground motion are calculated at surface stations assuming incident plane p and sh waves with various incidence angles computed results show that seismic energy is substantially enhanced in the central region of the basin while it diverges rapidly toward the edge of the basin compared to a two dimensional basin with the same cross section amplitudes are larger for stations in the central region and smaller for stations near the edge waveforms and amplitudes can change drastically between two nearby stations due to caustics and geometric focusing for different paths it is found for the particular basin geometry and velocity contrast used that the first multiple p wave and other particular phases experience two caustics near the basin center which are associated with the principal curvatures of the wave front this results in the reversal of the polarity of the waveform as incidence angle increases later arrivals at near edge stations and the stations in the diagonal direction are more strongly developed from the curved boundary of the basin but amplitudes of ground motions generally decrease as incidence angle increases in general wave responses strongly depend on the incidence angle and station location these results have important implications for site amplification of strong ground motions since wave behavior is so complex even for this simple idealized structure

modeling finite fault radiation from the ωn spectrum the high frequency seismic field near the epicenter of a large earth quake is modeled by subdividing the fault plane into subelements and summing their contributions at the observation point each element is treated as a point source with an o92 spectral shape where co is the angular frequency ground motion contributions from the subsources are calculated using a stochastic model attenuation is based on simple geometric spreading in a whole space coupled with regional anelastic atten uation q operator the form of the co n spectrum with natural n follows from point shear dislocation theory with an appropriately chosen slip time function the seismic moment and comer frequency are the two parameters defining the point source spectrum and must be linked to the subfanlt size to make the method complete two coefficients aa and k provide this link assigning a moment to a subfault of specified size introduces the stress parameter ao the relationship between comer frequency dislocation growth rate and fault size is established through the coefficient k which is inherently nonunique these two parameters control the number of subsources and the ampli tudes of high frequency radiation respectively derivation of the model from shear dislocation theory reveals the unavoidable uncertainty in assigning ogn spectrum to faults with finite size this uncertainty can only be reduced through empirical vali dation the method is verified by simulating data recorded on rock sites near epicenters of the m8 0 1985 michoacan mexico the m8 0 1985 valparaiso chile and the m5 8 1988 saguenay qurbec earthquakes each of these events is among the largest for which strong motion records are available in their respective tectonic environ ments the simulations for the first two earthquakes are compared to the more de tailed modeling of somerville et al 1991 which employs an empirical source function and represents the effects of crustal structure using the theoretical impulse response both methods predict the observations accurately on average the precision of the methods is also approximately equal the predicted acceleration amplitudes in our model are generally within 15 of observations an unexpected result of this study is that a single value of a parameter k provides a good fit to the data at high frequencies for all three earthquakes despite their different tectonic environments this suggests a simplicity in the modeling of source processes that was unanticipated

lg attenuation in the central and eastern united states as revealed by the earthscope transportable array abstract lg waveforms recorded by earthscope s transportable array ta are used to estimate lg q 0 in the central and eastern united states ceus attenuation is calculated based on lg spectral amplitudes filtered at a narrow band from 0 5 to 1 5 hz two station and reverse two station techniques are used to calculate q 0 values 39 events occurring from 2010 to 2012 and ranging from magnitude 3 to magnitude 6 are used in this study 39 258 and 4 627 interstation q 0 values are determined using the two station and reverse two station techniques respectively the results show northeast trending high q 0 regions low attenuation ranging from eastern new mexico to wisconsin regions of low q 0 high attenuation are seen along the minnesota wisconsin border the gulf coastal plain gcp along the south dakota nebraska border and along the oklahoma texas border a positive correlation between heat flow sediment thickness recent tectonic activity fluids and low q 0 was observed areas with low heat flow thin sediment cover no recent tectonic activity and a lack of fluids were observed to have consistently high q 0 these new models use a greater amount of data attain more coverage than previous studies and better constrain attenuation this increase in detail can improve high frequency ground motion predictions of future large earthquakes for more accurate far field hazard assessment and improve the overall understanding of the structure and assemblage of the ceus

the seismic radiation from composite models of faulting abstract the failure of an asperity i e the dynamic rupture of a small fault area with finite stress drop surrounded by a broken or weak fault area which has no stress drop but which slips after the asperity fails is proposed as a model for the rupture process of a subevent in a composite earthquake the rupture area of the composite earthquake surrounding the subevent is modeled by the weak fault area surrounding the asperity in the subevent model the resulting seismic moment of the subevent is proportional to the stress drop and the rupture area of the subevent as well as the radius of the composite earthaquake by setting the stress drops of the asperity models equal to the dynamic stress drops of the subevents the composite earthquake can be modeled as the sum of a set of subevents which cover the rupture area of the composite earthquake the scaling of the high and low frequency radiation from composite earthquakes composed of asperities is commensurate with generally observed spectral scaling laws in contrast to composite earthquakes composed of cracks or smaller earthquakes a simple filtering strategy is proposed for filtering the waveforms radiated by cracks to approximate the waveforms radiated by asperities the p and s waves radiated by an m l 5 2 earthquake which occurred on 9 may 1983 at coalinga california are simulated using the p and s waves radiated by an m l 3 6 aftershock the aftershock waveforms are first filtered to approximate the radiation from asperities with the appropriate rupture areas and then the waveforms of 12 asperity subevents are summed together to simulate the waveforms and spectra of the composite earthquake

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

prediction of strong ground motion in the puget sound region the 1965 seattle earthquake spatial variations in strong ground motion in the 1965 seattle washington earthquake ms 6 5 can be accurately reproduced using three dimensional ray tracing techniques synthetic accelerograms calculated at nearly 1600 receivers spread over the puget sound region indicate that peak ground accelerations are significantly affected by subsurface structure as well as by near receiver soil properties the large synthetic accelerations computed for the harbor island downtown seattle area appear to be due to subsurface focusing of rays within a deep sedimentary basin and are consistent with the observed isoseismal distribution in extreme circumstances such as a bedrock site adjacent to a site situated upon a soft sedimentary lens peak accelerations may vary by nearly an order of magnitude predicted values of peak ground acceleration as a function of distance reproduce both the trend and scatter in data from subduction zone earthquakes of comparable depth in japan

aboriginal stone walled intertidal fishtrap morphology function and chronology investigated with high resolution close range unmanned aerial vehicle photogrammetry abstract stone walled intertidal fishtraps surround the australian coastline and are among the largest structures built by indigenous australians globally fishtraps are considered important elements in food production domestication territoriality and ceremonial landscapes yet the level of detail in documentation is highly varied and scholarly fishtrap knowledge sparse comparative analysis is currently restricted by a lack of detail and reproducibility in recording hindering analysis of morphology function and chronology in this study we employ high resolution close range unmanned aerial vehicle uav photogrammetry and a suite of spatial information analytical techniques to investigate the kaiadilt aboriginal stone walled intertidal fishtraps of sweers island southern gulf of carpentaria australia tidal inundation modelling is undertaken to assess 1 fishtrap working range 2 individual and simultaneous trap function 3 seasonal functionality and 4 chronology based on function relative to sea level history thirteen fishtraps were identified in the study area ranging from 38 m to 287 m in length flow accumulation indicates that shape and placement of fishtraps reflects underlying topography inundation modelling shows that all fishtraps operate most efficiently at present mean sea level pmsl indicating construction in the last 3500 years quantitative recording techniques analytical procedures and terminology developed in this study provide an opportunity to improve approaches to recording large scale stone features and standardise documentation of stone walled intertidal fishtrap sites

some aspects of source characteristics of the 19 september 1985 michoacan earthquake and ground motion amplification in and near mexico city from strong motion data abstract the fourier amplitude ratio of the 19 september m s 8 1 to the 21 september 1985 m s 7 6 michoacan earthquakes obtained from data in and near mexico city increases from about 3 5 at 0 5 hz to about 10 at 0 2 hz this increase is neither seen in the coastal data nor in the teleseismic broadband gdsn p wave spectra it is also not predicted by 2 or gusev9s scaling laws we tentatively attribute the increase at frequencies of less than 0 5 hz to a special path and or a depth of energy release effect for the 19 september earthquake the damage to mexico city is mostly related to 0 5 hz energy since at f 0 5 hz the fourier amplitude ratios in and near mexico city along the coast and at teleseismic distances are nearly equal we attribute this energy to the source characteristics of the 19 september earthquake the evidence suggests that the 19 september was about twice more energetic at f 0 5 hz than expected from scaling laws and from spectral regression of coastal earthquakes recorded in mexico city the analysis of strong motion data recorded in mexico city shows that the ground motions in the lake bed zone are amplified by 8 to 50 times with respect to a hill zone site in ciudad universitaria the frequency at which the maximum relative amplification occurs varies from site to site and lies between 0 2 and 0 7 hz the data suggest that f o 4 h where f o frequency at which maximum relative amplitude occurs and and h are the shear wave velocity and the thickness of the clay layer respectively relatively small if any nonlinear behavior of the clay is found at strains of about 0 2 per cent during the great 19 september earthquake for a given lake bed site maximum relative amplitude and f o are roughly constant independent of magnitude depth and azimuth of sources located more than about 200 km ground motion at lake bed sites in mexico city with f o 0 5 hz appear to be amplified 75 times with respect to hard rock coastal sites at equal distances from the source this is also confirmed by m l calculation of the 19 and 21 september earthquakes for the 19 and 21 september earthquakes the average values of m l at hard rock coastal sites 100 distance 250 km are 7 4 and 6 7 whereas they are 8 7 and 8 4 in the lake bed zone distance 300 km respectively

forearc versus backarc attenuation of earthquake ground motion understanding of the attenuation of seismic wave amplitudes with distance is a crucial issue for ground motion prediction equations and seismic hazard analysis in this study we empirically evaluate the influence of regional geologic structure in particular the attenuation effects of traveling through a volcanic arc region forearc versus backarc attenuation in northern japan we perform regression analysis of fourier amplitude spectra fas of five well recorded japanese events that occurred very close to the line formed in map view by the volcanic arc this provides an approximately symmetrical distribution of stations for each event relative to the volcanic front forearc stations lie to the east of the front while backarc stations lie to the west to compare the characteristics of shallow and deep events we have included both crustal and in slab events in our dataset based on inspection of the data we assume a hinged bilinear geometric spreading model with a fixed slope of 1 out to a distance of 50 km with slope of 0 5 thereafter for all events our results show with a very high level of confidence that high frequency attenuation is greater in the backarc direction the q values for forearc regions q 240 at 1 hz increasing to q 3890 at 10 hz are about a factor of 2 larger than those for backarc regions q 196 at 1 hz increasing to q 1669 at 10 hz at high frequencies implying much stronger attenuation as waves travel through the volcanic crustal structure to the backarc stations the separation of forearc and backarc travel paths results in a significant reduction in the standard deviation of ground motion predictions by as much as 0 05 log10 units which has important implications for hazard analyses in subduction zone regions

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

an investigation into earthquake ground motion characteristics in eastern north america abstract a random vibration model of the hanks mcguire type is used to predict peak ground motions at rock sites in eastern north america the assumed geometric decay and distance dependent duration approximate the propagation of direct body waves at short distances and lg waves at regional distances the model predicts peak acceleration and velocities as well as response spectra and magnitude for a given seismic moment and corner frequency to predict ground motions for a given lg magnitude m lg the model is first used to calculate the seismic moment corresponding to that magnitude assuming a source scaling law then knowing the moment and corner frequency the model is used to calculate peak ground motions available data from strong motion recordings and from the ectn and lrsm networks modified to estimate horizontal ground motions on rock where appropriate are used to verify the model9s assumption and predictions modified mercalli intensity data are also used ground motions predicted by the model with a stress drop of 50 to 200 bars agree with the ground motion data but the m lg values computed by the model for given seismic moments do not agree with nuttli9s 1983 moment versus m lg data for large earthquakes resolution of the latter disagreement awaits the collection of instrumental data from large events in eastern north america

evaluation of functional forms for the attenuation of small to moderate earthquake response spectral amplitudes in north america abstract we studied several attenuation forms to evaluate their ability to describe the decay of response spectral amplitudes in eastern canada northeastern united states central united states pacific northwest british columbia northern california and southern california linear bilinear and trilinear regression forms with different combinations of geometric spreading coefficients were tested to assess their ability to describe spectral amplitude decay from 0 33 to 10 hz in the distance range from 10 to 400 km the residual trends and the shapes of the attenuation forms do not show significant differences in goodness of fit between these trial forms making it difficult to see a meaningful distinction between them furthermore statistical measures such as the akaike information criterion are not particularly helpful in drawing such distinctions a simple linear model as well as more complex forms can fit the data in almost every region however this linear model has steeper slope in the west 1 3 than in the east 1 and may not extend well over large distances the linear model effectively smoothes through complications in functional form such as the moho bounce or the transition to surface wave spreading at regional distances a trilinear model has the best statistical fit in most cases but the added complications in shape and parameterization do not appear warranted by the marginal improvement in residuals the bilinear form offers a good compromise between simplicity and the ability to model amplitude decay appropriately at both near and regional distances