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

europa s dynamic icy crust abstract europa s icy crust records active resurfacing by tectonic and thermal processes over tens of millions of years as rapidity demonstrated by a paucity of craters tidal working causes rotational torque surface stress internal heating and orbital evolution which can explain the formation of observed tectonic crack patterns ridges crustal displacement and chaotic terrain by processes involving connections between the surface and the underlying ocean through cracks melt sites and occasional impacts these processes were recent and thus most likely continue today the permeability of the crust allows exchange of materials including oxidants and exogenic organics from the surface and endogenic substances from the ocean such that a habitable biosphere might extend to within a few centimeters of the surface continual changes in environmental conditions in the ice crust such as deactivation of individual cracks after thousands of years due to non synchronous rotation and crustal thawing releasing any trapped organisms could provide drivers for biological adaptation as well as opportunity for evolution

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

average qlg qsn and observation of lg blockage in the continental margin of nova scotia the term lg blockage refers to the sudden disappearance of the lg phase along a particular propagation path which is commonly seen at continental oceanic transition zones in this paper we present observational evidence of lg blockage across the continental margin of nova scotia in eastern canada regional lg and sn spectra from 91 events with epicentral distances between 100 and 1200 km and magnitudes between 2 5 and 4 7 are inverted simultaneously for the source spectrum site amplification and average attenuation the vertical displacement spectra were estimated between 0 9 and 10 75 hz the assumptions include a fixed frequency independent geometric spreading rate for lg and a frequency dependent spreading model for the sn estimates for the apparent regional attenuations are qlg f 615 25 f0 35 0 04 and qsn f 404 23 f0 45 0 03 results from this study provide an accurate parameterization of observed amplitude spectra and are valuable for representing wave propagation in the region based on the observation of a strong trade off between sn and lg amplitudes which have different attenuation characteristics we conclude any attenuation study based on measuring amplitude of a package of several different phases without taking into consideration the propagation characteristics of individual waveforms at the region of study may bias the estimation of average regional q

topographic slope as a proxy for seismic site conditions and amplification we describe a technique to derive first order site condition maps directly from topographic data for calibration we use global 30 arc sec topographic data and v s 30 measurements here v s 30 refers to the average shear velocity down to 30 m aggregated from several studies in the u s as well as in taiwan italy and australia v s 30 values are correlated against topographic slope to develop two sets of parameters for deriving v s 30 one for active tectonic regions where topographic relief is high and one for stable shields where topography is more subdued by taking the gradient of the topography and choosing ranges of slope that maximize the correlation with shallow shear velocity observations we can recover to first order many of the spatially varying features of sitecondition maps developed for california our site condition map for the low relief mississippi embayment also predicts the bulk of the v s 30 observations in that region despite rather low slope ranges we find that maps derived from the slope of the topography is often well correlated with other independently derived regional scale site condition maps but the latter maps vary in quality and continuity and subsequently also in their ability to match observed v s 30 measurements contained therein alternatively the slope based method provides a simple approach to uniform site condition mapping

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

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

site response in victoria british columbia from spectral ratios and 1d modeling this article examines site response in victoria british columbia using weak ground motion recordings 3 5 g of the 2001 m w 6 8 nisqually earthquake in washington state 150 km distant significant variations are observed in acceleration spectra across the city that can be largely attributed to local site conditions thin soil sites 3 m generally have flat amplitude spectra at frequencies less than 10 hz whereas thicker soil sites 5 11 m show peak amplitudes at 2 5 hz standard spectral ratios bedrock reference and horizontal to vertical spectral ratios are computed for sites with varying geology thin soil sites show flat site response like bedrock at frequencies 10 hz whereas the thicker soil sites show peak amplification of up to six times that of bedrock at frequencies of 2 5 hz there is good agreement between these standard spectral ratio site response estimates with the horizontal to vertical spectral ratios at each site and spectral ratios from four other earthquakes between 1996 and 2002 ground motion spectra obtained from numerical 1d modeling indicate that 3 m of soft soil national earthquake hazard reduction program nehrp class e generates a flat response at 10 hz whereas thick layers of either grey victoria clay nehrp class e or pleistocene till nehrp class c produce peak amplitudes at 2 5 hz the correlation of near surface soft soil conditions on crystalline bedrock with observed weak ground motions provides an important baseline toward future seismic hazard studies in the victoria area

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

regional differences in ground motion amplitudes of small to moderate earthquakes across north america abstract we studied the response spectral amplitudes and peak ground acceleration pga of earthquakes with moment magnitude m from 3 0 to 6 0 to investigate regional differences in ground motion amplitudes across north america on a nonparametric basis for a common national earthquake hazards reduction program b c site condition e g shear wave velocity of 760 m s in the top 30 m of the soil column we use southern california as the reference region because it has the most plentiful data against which to compare other regions amplitudes of response spectra in eastern canada northeastern united states become increasingly larger than those in southern california as distance frequency and magnitude increases in the central united states ground motion amplitudes are larger than those in southern california at distances more than 100 km and lower at distances less than 100 km over all frequency and magnitude ranges studied amplitudes for crustal events in the pacific northwest british columbia are lower than those in southern california at frequencies 1 hz over all magnitude and distance ranges but have similar amplitudes below 1 hz amplitudes in northern california are similar to those in southern california at low frequencies below 3 3 hz but have lower amplitudes at high frequencies pga over all distances and magnitudes we conclude that regional amplitude differences are largely attributable to complex frequency dependent differences in regional attenuation for example the slope of apparent geometric spreading at distances less than 100 km is significantly steeper more negative in eastern canada northeastern united states than other regions and may be frequency dependent the regional attributes of the attenuation comparisons appear to be the same for both vertical and horizontal components at least for b c site conditions online material figures of region dependent ground motion amplitudes apparent geometric spreading statistical tests of the ground motions and figures and table of ratios of ground motions relative to those from southern california

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

ground motions for induced earthquakes in oklahoma we examine ground motions for a sequence of earthquakes in oklahoma where assessment of hazard contributions from induced seismicity is of particular interest we aim to empirically calibrate a model driven equation that was derived for central and eastern north america cena so that it will match the observed ground motions of the 2011 prague oklahoma sequence we first show that ground motions in oklahoma decay at a rate similar to the average attenuation observed in the stable continental region of cena we then search for any needed adjustments to the cena source model to match ground motions from the induced seismicity sequence that occurred near prague in 2011 an interesting feature noted in the ground motion analysis is that the stress parameters for the prague mainshock events m 5 are notably higher than those for aftershocks moreover the stress parameter that characterizes the high frequency ground motion decays in both time and space relative to the three largest events the largest events in the prague sequence have similar source parameters to natural cena events of the same magnitude and focal depth but their aftershocks have weaker motions

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

cascadia onshore offshore site response submarine sediment mobilization and earthquake recurrence local geologic structure and topography may modify arriving seismic waves this inherent variation in shaking or site response may affect the distribution of slope failures and redistribution of submarine sediments i used seafloor seismic data from the 2011 to 2015 cascadia initiative and permanent onshore seismic networks to derive estimates of site response denoted sn in low and high frequency 0 02 1 and 1 10 hz passbands for three shaking metrics peak velocity and acceleration and energy density sn varies similarly throughout cascadia and changes primarily in the direction of convergence roughly east west in the two passbands sn patterns offshore are nearly opposite and range over an order of magnitude or more across cascadia sn patterns broadly may be attributed to sediment resonance and attenuation this and an abrupt step in the east west trend of sn suggest that changes in topography and structure at the edge of the continental margin significantly impact shaking these patterns also correlate with gravity lows diagnostic of marginal basins and methane plumes channeled within shelf bounding faults offshore sn exceeds that onshore in both passbands and the steepest slopes and shelf coincide with the relatively greatest and smallest sn estimates at low and high frequencies respectively these results should be considered in submarine shaking triggered slope stability failure studies significant north south sn variations are not apparent but sparse sampling does not permit rejection of the hypothesis that the southerly decrease in intervals between shaking triggered turbidites and great earthquakes inferred by goldfinger et al 2012 2013 2016 and priest et al 2017 is due to inherently stronger shaking southward

effects of seismicity models and new ground motion prediction equations on seismic hazard assessment for four canadian cities seismicityratesandground motionpredictionequations gmpes arethe key uncertainties in probabilistic seismic hazard analysis psha we explore the impact of new findings and knowledge from seismological and ground motion studies on seismic hazard assessment for eastern and western canada updated information includes the reevaluation of seismicity rates and their interpretation in terms of seismic source zones and the use of new gmpes we refer to our model as an interim updated seismic hazard model as it does not treat all uncertainties comprehensively rather we address the impact of key uncertainties based on our updated interim seismic hazard model uniform hazard spectra uhs at four major cities across canada are obtained and compared with uhs in the current seismic hazard maps of canada 2005 2010 whicharebasedona1995seismichazardmodeldevelopedbythegeologicalsurveyof canada sensitivity analysis highlights the significant impact of seismicity smoothing in low to moderate seismic regions eastern canada while gmpes are important for all regions moreover our interim updated seismic hazard model can readily produce seismic hazard curves as well as seismic hazard deaggregation results for various site conditionsandformultipleprobabilitylevels thiscapabilityisessentialforcarryingout advanced earthquake engineering analyses

attenuation of ground motion spectral amplitudes in southeastern australia a dataset comprising some 1200 weak and strong motion records from 84 earthquakes is compiled to develop a regional ground motion model for southeastern australia sea events were recorded from 1993 to 2004 and range in size from moment magnitude 2 0 m 4 7 the decay of vertical component fourier spectral amplitudes is modeled by trilinear geometrical spreading the decay of low frequency spectral amplitudes can be approximated by the coefficient of r 1 3 where r is hypocentral distance within 90 km of the seismic source from approximately 90 to 160 km we observe a transition zone in which the seismic coda are affected by postcritical reflections from midcrustal and moho discontinuities in this hypocentral distance range geometrical spreading is approximately r 0 1 beyond 160 km low frequency seismic energy attenuates rapidly with source receiver distance having a geometrical spreading coefficient of r 1 6 the associated regional seismic quality factor can be expressed by the polynomial log q f 3 66 1 44 log f 0 768 log f 2 0 058 log f 3 for frequencies 0 78 f 19 9 hz fourier spectral amplitudes corrected for geometrical spreading and anelastic attenuation are regressed with m to obtain quadratic source scaling coefficients modeled vertical component displacement spectra fit the observed data well amplitude residuals are on average relatively small and do not vary with hypocentral distance predicted source spectra i e at r 1 km are consistent with eastern north american ena models at low frequencies f less than approximately 2 hz indicating that moment magnitudes calculated for sea earthquakes are consistent with moment magnitude scales used in ena over the observed magnitude range the models presented represent the first spectral ground motion prediction equations developed for the southeastern australian region this work provides a useful framework for the development of regional ground motion relations for earthquake hazard and risk assessment in sea

regional spectral analysis of three moderate earthquakes in northeastern north america abstract we analyze fourier spectra obtained from the horizontal components of broadband and accelerogram data from the 1997 cap rouge the 2002 ausable forks and the 2005 riviere du loup earthquakes recorded by canadian and american stations sited on rock at hypocentral distances from 23 to 602 km we check the recorded spectra closely for anomalies that might result from site resonance or source effects we use beresnev and atkinson s 1997 near surface velocity structures and boore and joyner s 1997 quarter wave method to estimate site response at hard and soft rock sites we revise the street et al 1975 model for geometrical spreading adopting a crossover distance of r o 50 km instead of 100 km we obtain an average attenuation of q 410 25 f 0 50 0 03 for s l g surface waves with ray paths in the appalachian and southeastern grenville provinces we correct the recorded spectra for attenuation and site response to estimate source spectral shape and radiated energy for these three earthquakes and the 1988 m 5 8 saguenay earthquake the brune stress drops range from 130 to 419 bars and the apparent stresses range from 39 to 63 bars the corrected source spectral shapes of these earthquakes are somewhat variable for frequencies from 0 2 to 2 hz falling slightly below the fitted brune spectra

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

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