radiated energy from the mid niigata japan earthquake of october 23 2004 and its aftershocks 1 the mid niigata earthquake of october 23 2004 is a shallow reverse faulting event with mw 6 6 we analyze transverse component accelerograms of the main shock and four aftershocks mw 4 0 5 5 recorded at 29 strong motion observation stations the epicenters of the four aftershocks are located within 5 km from that of the main shock the stations are well distributed around the epicenters and their epicentral distances are between 15 and 60 km we calculate spectral ratio between records of the main shock and each of the aftershocks in order to obtain source spectral ratio by empirically removing the effects of wave propagation path and surface layers at the stations thus obtained source spectral ratio is inconsistent with that expected from the self similar omega square model fitting omega square source spectral ratio with variable corner frequency to the observed spectral ratio radiated energy and corner frequency are estimated radiated energy from the main shock is 3 2 1014 j although energy to moment ratios for the main shock and the aftershocks are all distributed within a narrow range from 8 10 6 to 4 10 5 they definitely increase with the event size this scale dependence is quite similar to that obtained previously for strike slip events in japan the relationship between the seismic moment m0 and the corner frequency f0 is m0 f0 3 3 0 2 these results suggest a break in self similarity

scale dependence of seismic energy to moment ratio for strike slip earthquakes in japan we analyzed four pairs of a large m w 6 and a small m w 3 5 to 4 shallow strike slip earthquakes to investigate the scale dependence of the seismic energy to moment ratio an important macroscopic parameter which reflects the basic physical process of seismic slip these earthquakes occurred in the south western part of japan and high quality close in records epicentral distance 50 km are available for both the small and large earthquakes the paired events have almost the same focal mechanism and hypocenter location we used the spectral ratio of the paired events in order to remove the effects of attenuation along the wave propagation path and the station site response we then estimated the seismic energy from the source spectra estimated from the spectral ratio the energy to moment ratio increases with the earthquake size this scale dependence is very similar to that found earlier for earthquakes in southern california

the critical slip distance for seismic faulting experimentally based friction laws1 2 have been found to predict virtually the entire range of observed behaviour of natural faults3 4 these laws contain a critical slip distance l which plays a key role in determining the degree of fault instability the size of the zone of earthquake nucleation the frictional breakdown width and the proportion of pre and post seismic slip to co seismic slip in laboratory measurements l is found to be about 10 5m but modelling results show that it must be about 10 2m if natural earthquake behaviour is to be simulated the discovery that fault surfaces are fractal over the scale range 10 5 105 refs 5 6 even for faults with large net slip has confused the problem of scaling this parameter from laboratory experiments to natural faults because fractal surfaces have no characteristic length here i show that geometrically unmated fractal surfaces when in contact under a normal load develop a characteristic length in their contact because long wavelength apertures close under load whereas short wavelength apertures may remain open this critical distance may be identified with l and calculations based on fault topography data show that at seismogenic depths it will be in the range anticipated from the earthquake modelling studies

the mw 5 8 mineral virginia earthquake of august 2011 and aftershock sequence constraints on earthquake source parameters and fault geometry the mw 5 8 earthquake of 23 august 2011 17 51 04 utc moment m0 5 7 10 17 n m occurred near mineral virginia within the central virginia seis mic zone and was felt by more people than any other earthquake in united states history the u s geological survey usgs received 148 638 felt reports from 31 states and 4 canadian provinces the usgs pager system estimates as many as 120 000 people were exposed to shaking intensity levels of iv and greater with approximately 10 000 exposed to shaking as high as intensity viii both regional and teleseismic moment tensor solutions characterize the earthquake as a northeast striking reverse fault that nucleated at a depth of approximately 7 2 km the distri bution of reported macroseismic intensities is roughly ten times the area of a similarly sized earthquake in the western united states horton and williams 2012 near source and far field damage reports which extend as far away as washington d c 135 km away and baltimore maryland 200 km away are consistent with an earthquake of this size and depth in the eastern united states eus within the first few days following the earthquake several government and aca demic institutions installed 36 portable seismograph stations in the epicentral region making this among the best recorded aftershock sequences in the eus based on modeling of these data we provide a detailed description of the source parameters of the mainshock and analysis of the subsequent aftershock sequence for defining the fault geometry area of rupture and observations of the aftershock sequence mag nitude frequency and temporal distribution the observed slope of the magnitude frequency curve or b value for the aftershock sequence is consistent with previous eus studies b 0 75 suggesting that most of the accumulated strain was released by the mainshock the aftershocks define a rupture that extends between approxi mately 2 8 km in depth and 8 10 km along the strike of the fault plane best fit modeling of the geometry of the aftershock sequence defines a rupture plane that strikes n36 e and dips to the east southeast at 49 5 moment tensor solutions of the mainshock and larger aftershocks are consistent with the distribution of aftershock locations both indicating reverse slip along a northeast southwest striking southeast dipping fault plane

stratigraphy and geochemistry of the balwan limestone vindhyan supergroup india evidence for the bitter springs δ13c anomaly abstract the vindhyan supergroup of india deposited in an intracratonic basin is one of the important proterozoic marine successions of the world that contains some of the most controversial precambrian fossil discoveries despite their importance the chronology of the host strata and global correlation of the events that occurred within the basin remain equivocal here we present results of a detailed geological geochemical and isotopic sr c o study of the balwan limestone the youngest carbonate formation of the supergroup exposed only in the western sector of the basin our results suggest that the vindhyan basin had become a structurally controlled marginal sea towards the end of its existence and that the limestone was deposited in a subtidal environment that had strong depositional currents we find evidence for a strong storm event or a tsunami during its deposition near primary 87sr 86sr of 0 70676 at the top and 207pb 206pb age of 866 90 ma gopalan et al 2013 of this 120 m thick formation suggest its deposition during late tonian 13c stratigraphy reveals the presence of the globally synchronous bitter springs anomaly 12 shift in the formation the first such report from india

a new spectral ratio method using narrow band coda envelopes evidence for non self similarity in the hector mine sequence 1 the use of local and regional s wave coda is shown to provide stable amplitude ratios that better constrains source differences between event pairs we first compared amplitude ratio performance between local and near regional s and coda waves in the san francisco bay region for moderate sized events then applied the coda spectral ratio method to the 1999 hector mine mainshock and its larger aftershocks we find 1 average amplitude ratio standard deviations using coda are 0 05 to 0 12 roughly a factor of 3 smaller than direct s waves for 0 2 f 15 0 hz 2 coda spectral ratios for the mw 7 0 hector mine earthquake and its aftershocks show a clear departure from self similarity consistent with other studies using the same datasets and 3 event pairs green s function and target events can be separated by 25 km for coda amplitudes without any appreciable degradation in sharp contrast to direct waves

the 2002 m5 au sable forks ny earthquake sequence source scaling relationships and energy budget 1 we find invariant high stress drops and radiated energies for a sequence of intraplate earthquakes we estimate source parameters of the au sable forks ny earthquake m5 2002 and aftershocks this intraplate earthquake was the largest to occur in eastern north america since 1988 and the largest to be recorded by regional broadband networks we use the empirical green s function egf method and define a set of qualitative and quantitative rules for the selection of egf earthquake pairs and for the quality verification of the obtained egf spectral ratio we use a multitaper code that performs the complex spectral division with minimum frequency leakage and allows transformation back to the time domain to check the validity of the egf event we estimate source parameters for 22 earthquakes m1 m5 in the sequence the median stress drop of 104 mpa using madariaga source model and 19 mpa for a brune model is significantly larger than estimates for interplate earthquakes the lower crustal strain rates and longer fault healing times in intraplate environments may be responsible for this high average value we find constant stress drop between m2 and m5 up to the bandwidth resolution limit 80 hz of the study and no evidence of stress drop breakdown for m2 to m1 earthquakes we find consistently high radiated seismic energy and apparent stress and a median radiated energy to seismic moment ratio of 9 10 5 this is significantly larger than estimates for interplate earthquakes 2 10 5 and consistent with higher stress drops and stronger faults

variability in earthquake stress drop and apparent stress 1 we apply empirical green s function coda based analysis to four earthquake sequences in japan that span a magnitude range of 1 8 to 6 9 to measure radiated energy corner frequency and stress drop we find no systematic dependence of apparent stress or stress drop on seismic moment for these sequences and find they both are log normally distributed however we identify several anomalous events both energetic and enervated that show sharply different spectral signatures from the rest of the population these events indicate that much of the variation in apparent stress and stress drop is statistically significant which may have important implications for seismic hazard analysis

observational constraints on earthquake source scaling understanding the limits in resolution abstract i examine the resolution of the type of stress drop estimates that have been used to place observational constraints on the scaling of earthquake source processes i first show that apparent stress and brune stress drop are equivalent to within a constant given any source spectral decay between 1 5 and 3 i e any plausible value and so consistent scaling is expected for the two estimates i then discuss the resolution and scaling of brune stress drop estimates in the context of empirical green s function results from recent earthquake sequences including the 1992 joshua tree california mainshock and its aftershocks i show that no definitive scaling of stress drop with moment is revealed over the moment range 1019 1025 within this sequence however there is a tendency for moderate sized m 4 5 events to be characterized by high stress drops however well resolved results for recent m 6 events are inconsistent with any extrapolated stress increase with moment for the aftershocks focusing on corner frequency estimates for smaller m

apparent break in earthquake scaling due to path and site effects on deep borehole recordings 1 we reexamine the scaling of stress drop and apparent stress rigidity times the ratio between seismically radiated energy to seismic moment with earthquake size for a set of microearthquakes recorded in a deep borehole in long valley california in the first set of calculations we assume a constant q and solve for the corner frequency and seismic moment in the second set of calculations we model the spectral ratio of nearby events to determine the same quantities we find that the spectral ratio technique which can account for path and site effects or nonconstant q yields higher stress drops particularly for the smaller events in the data set the measurements determined from spectral ratios indicate no departure from constant stress drop scaling down to the smallest events in our data set mw 0 8 our results indicate that propagation effects can contaminate measurements of source parameters even in the relatively clean recording environment of a deep borehole just as they do at the earth s surface the scaling of source properties of microearthquakes made from deep borehole recordings may need to be reevaluated

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

evidence for non self similarity and transitional increment of scaled energy in the 2005 west off fukuoka seismic sequence 1 we investigated seismic scaling relations of the 2005 west off fukuoka seismic sequence in japan using a coda based methodology two independent methods such as coda source spectrum method and coda spectral ratio method were applied to seismic waveform data recorded at four broadband seismic stations located around the epicenter of the mainshock the corner frequencies determined from both methods are consistent with each other and the scaling relations between the corner frequencies and the corresponding seismic moments are clearly non self similar in both cases moreover the scaled energy obtained from the coda source spectrum method shows that there is a transitional change in the scaled energy with seismic moment the scaled energy is larger for events with mw 5 0 than for events with mw 4 0 for events larger than mw 5 0 the scaled energy is almost constant and it means that they obey self similar scaling for events smaller than about mw 4 0 the scaled energy is more or less constant but it is difficult to decide whether it follows self similar or non self similar scaling because of scatter and the limitation of the minimum moment magnitude mw 3 4 the most important observation is a linear increment of the scaled energy between about mw 4 0 and 5 0 these observations imply that the rupture dynamics for larger and smaller earthquakes are different and that the change in dynamics may occur continuously between about mw 4 0 and 5 0 in this seismic sequence

selecting empirical green s functions in regions of fault complexity a study of data from the san jacinto fault zone southern california abstract to constrain an earthquake s source properties the path and site effect contributions to the seismic waveform can be approximated using another earthquake as an empirical green s function egf an ideal egf earthquake is smaller in magnitude than the mainshock and shares a similar focal mechanism and hypocenter here we quantify how to optimally select egf events using data from the spatially complex san jacinto fault zone sjfz in southern california the sjfz s high seismicity rate allows us to test the egf method for 51 target 3 m w 200 for each mainshock we purposefully select a large population of inappropriate egfs in order to identify thresholds and restrictions that optimize egf selection criteria for each mainshock egf pair we compute the spectral ratio fit the mainshock corner frequency and measure the variability of these corner frequencies across the network we assume a suitable egf event will produce similar corner frequency estimates at every station we discover that limiting hypocentral separation distances between mainshock and egf events to online material map of earthquake locations within our study region color coded to indicate the mapped spatial differential between the original catalog location in the anza catalog and the location in the lin et al 2007 relocated catalog

source parameters of the 23 april 1992 m 6 1 joshua tree california earthquake and its aftershocks empirical green s function analysis of geos and terrascope data source parameters of the m 6 1 23 april 1992 joshua tree mainshock and 86 m 1 8 to 4 9 aftershocks are determined using an empirical green s function methodology for the aftershocks deconvolved p and s wave spectra are calculated for 126 pairs of closely spaced events recorded on portable geos stations s wave spectra from the two horizontal components are averaged the deconvolved spectra are fit by a ratio of omega square source models yielding an optimal least squares corner frequency for both the large and the small event in each pair we find no resolved difference between the inferred p and s wave corner frequencies using the standard brune model for stress drop we also find no resolved nonconstant scaling of stress drop with moment although we also conclude that detailed scaling systematics would be difficult to resolve in particular a weak increase of stress drop with moment over a limited moment magnitude cannot be ruled out for magnitudes smaller than m 3 to 3 5 the inferred stress drop values will be limited by the maximum observable corner frequency value of 60 hz for the mainshock source time functions are obtained from mainshock recordings at three terrascope stations pfo pas and gsc using an m 4 3 foreshock as an empirical green s function the results indicate a fairly simple single pulse source time function with clear south to north directivity and an inferred rupture radius of 5 to 6 km the deconvolved source time functions are inverted to obtain a finite rupture model that gives a robust estimate of rupture dimension early aftershocks are found to lie along the perimeters of regions with high mainshock slip the inferred mainshock stress drop value 56 bars is within the range determined for the aftershocks our derived mainshock source spectra do not show resolvable deviation from the omega square model

source parameters and rupture velocities of microearthquakes in western nagano japan determined using stopping phases we use an inversion method based on stopping phases imanishi and takeo 2002 to estimate the source dimension ellipticity and rupture velocity of microearthquakes and investigate the scaling relationships between source parameters we studied 25 earthquakes ranging in size from m 1 3 to m 2 7 that occurred between may and august 1999 at the western nagano prefecture japan which is characterized by a high rate of shallow earthquakes the data consist of seismograms recorded in an 800 m borehole and at 46 surface and 2 shallow borehole seismic stations whose spacing is a few kilometers these data were recorded with a sampling frequency of 10 khz in particular the 800 m borehole data provide a wide frequency bandwidth with greatly reduced ground noise and coda wave amplitudes compared with surface recordings high frequency stopping phases appear in the body waves in hilbert transform pairs and are readily detected on seismograms recorded in the 800 m borehole after correcting both borehole and surface data for attenuation we also measure the rise time which is defined as the interval from the arrival time of the direct wave to the timing of the maximum amplitude in the displacement pulse the differential time of the stopping phases and the rise times were used to obtain source parameters we found that several microearthquakes propagated unilaterally suggesting that all microearthquakes cannot be modeled as a simple circular crack model static stress drops range from approximately 0 1 to 2 mpa and do not vary with seismic moment it seems that the breakdown in stress drop scaling seen in previous studies using surface data is simply an artifact of attenuation in the crust the average value of rupture velocity does not depend on earthquake size and is similar to those reported for moderate and large earthquakes it is likely that earthquakes are self similar over a wide range of earthquake size and that the dynamics of small and large earthquakes are similar

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

radiated seismic energy from coda measurements and no scaling in apparent stress with seismic moment 1 the seismic coda consists of scattered waves that leave the earthquake source in a variety of directions the averaging of source radiation that results leads to stable ground motion spectra that we use as the basis for a robust measurement of radiated wave energy we apply an empirical green s function egf method to the seismic coda in order to investigate scaling of the radiated seismic energy we correct for path effects in the spectra of earthquakes by using a stack of closely located small earthquakes as an egf we apply this approach to four earthquake sequences in western north america that span a magnitude range from mw 3 0 mw 7 1 our estimates of scaled energy are consistent with independent measurements where available we find no dependence in individual seismic energy estimates on source station distance which validates the egf approximation we find that a constant scaled energy of 3 5 10 5 provides a reasonable fit to the data with no dependence of the scaled energy on seismic moment

investigating uncertainties in empirical green s function analysis of earthquake source parameters i use a well recorded earthquake sequence to investigate the uncertainties of earthquake stress drops calculated using an empirical green s function egf approach the earthquakes in the largest m 2 1 repeating sequence targeted by the san andreas observatory at depth safod parkfield california are recorded by multiple borehole stations and have simple sources well constrained stress drops and abundant smaller earthquakes to use as egfs i perform three tests to estimate quantitatively the likely uncertainties to arise in less optimal settings i use egf earthquakes with a range of cross correlation values and separation distances from the main earthquakes the stress drop measurements decrease by a factor of 3 as the quality of the egf assumption decreases a good egf must be located within approximately one source dimension of the large earthquake with high cross correlation i subsample the large number of measurements for the main earthquakes to investigate the expected stress drop uncertainties in studies where fewer stations or egfs are available if only one measurement is available the uncertainties are likely to be at least 50 the uncertainties decrease to 20 with five or more measurements using multiple egfs is a good alternative to multiple stations to investigate the effects of limited frequency bandwidth i recalculate the corner frequencies after progressively decimating the sample rate decreasing the high frequency limit of the bandwidth decreases the estimate of the corner frequency and stress drop the corner frequency may be underestimated if it is within a factor of 3 of the maximum frequency of the signal

crouching enemy hidden ally the decisive role of groundwater discharge features in two major british battles flodden 1513 and prestonpans 1745 geomorphological features associated with groundwater discharge zones can affect ground conditions so greatly that they determine the outcomes of battles two cases in point are found in scottish history i despite outnumbering their english foes the scots lost the battle of flodden field 9 september 1513 largely due to failing to identify the presence of marshy ground associated with an area of groundwater discharge ii on 21 september 1745 the jacobites defeated the hanoverian army at prestonpans by finding a way around marshland corresponding to a regional groundwater discharge zone upon which the hanoverian commander had been relying as a natural defensive feature analysis of both battlefields drawing upon present day understanding of local stratigraphy and hydrogeological conditions allows identification of the specific groundwater discharge patterns that largely determined the outcomes of these two emblematic battles at flodden the proximal source of groundwater discharge is quaternary outwash gravels distally fed from sedimentary strata cementstones of lowermost dinantian age in the case of prestonpans the groundwater emerges from particularly arenaceous coal bearing strata of namurian age both case studies suggest that military commanders selecting advantageous terrain could benefit from consulting hydrogeologists who are familiar with the intricacies of groundwater geomorphology

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

shaking from injection induced earthquakes in the central and eastern united states abstract in this study i consider the ground motions generated by 11 moderate m w 4 0 5 6 earthquakes in the central and eastern united states that are thought or suspected to be induced by fluid injection using spatially rich intensity data from the u s geological survey did you feel it system i show the distance decay of intensities for all events is consistent with that observed for tectonic earthquakes in the region but for all of the events intensities are lower than the values predicted from an intensity prediction equation that successfully characterizes intensities for regional tectonic events i introduce an effective intensity magnitude m ie defined as the magnitude that on average would generate a given intensity distribution for all 11 events m ie is lower than the event magnitude by 0 4 1 3 magnitude units with an average difference of 0 82 units this suggests stress drops of injection induced earthquakes are systematically lower than tectonic earthquakes by an estimated factor of 2 10 however relatively limited data suggest intensities for epicentral distances less than 10 km are more commensurate with expectations for the event magnitude which can be reasonably explained by the shallow focal depth of the events the results suggest damage from injection induced earthquakes will be especially concentrated in the immediate epicentral region

stress drops of repeating earthquakes on the san andreas fault at parkfield i calculate well resolved corner frequencies and stress drops for 25 earthquakes 1989 2006 in the three repeating sequences targeted by the san andreas fault observatory at depth using borehole data and multiple highly correlated empirical green s functions egfs the earthquakes in the largest magnitude m 2 1 cluster exhibit source spectra well fit by a circular source model the corner frequencies correlate with those from the regional study by allmann and shearer 2007 suggesting that the interevent variability is resolvable the earthquakes have stress drops between 25 and 65 mpa with a gradual increase before the 2004 m6 earthquake followed by an immediate decrease then a rapid return to previous levels the spectra of the cluster of m 1 9 earthquakes include high frequency energy not fit by simple source models and so stress drops are unreliable and probably underestimated 1 20 mpa there is no correlation with previous studies and interevent variation is not resolvable the earthquakes in the smallest magnitude cluster m 1 8 have the highest corner frequencies but similar stress drops 4 120 mpa the stress drops exhibit the same temporal variation as the first cluster but there is poor correlation with allmann and shearer 2007 probably because their frequency bandwidth is too limited

scaling differences between large interplate and intraplate earthquakes a study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes in which m 0 l 2 or u l where l is rupture length and u is slip in contrast to interplate earthquakes for which 1 10 5 for for the intraplate events 6 10 5 which implies that these earthquakes have stress drops about 6 times higher than interplate events this result is independent of focal mechanism type this implies that intraplate faults have a higher frictional strength than do plate boundaries and hence that faults are velocity or slip weakening in their behavior this factor may be important in producing the concentrated deformation that creates and maintains plate boundaries

rupture model of the 2011 mineral virginia earthquake from teleseismic and regional waveforms 1 we independently invert teleseismic p waveforms and regional crustal phases to examine the finite fault slip model for the 2011 mw 5 8 mineral virginia earthquake theoretical and empirical green s functions are used for the teleseismic and regional models respectively both solutions show two distinct sources each about 2 km across and separated by 2 5 km the source at the hypocenter is more localized in the regional model leading to a higher peak slip of 130 cm and higher average stress drop of 250 bars compared with 86 cm and 150 bars for the same source in the teleseismic model both sources are centered at approximately 8 km depth in the regional model largely below the aftershock distribution in the teleseismic model the sources extend updip to approximately 6 km depth into the depth range of the aftershocks the rupture velocity is not well resolved but appears to be near 2 7 km s

a review study of the source parameters of the 23 august 2011 mw 5 7 virginia earthquake abstract the source parameters of the 23 august 2011 m w 5 7 virginia earthquake have been further studied to perform our source parameter review study we first retrieved waveform records from incorporated research institutions for seismology we then carefully selected 17 stations that had good rayleigh wave records we used these 17 vertical records to retrieve a crustal shear wave velocity model surrounding the epicenter using the regional depth phase modeling method we retrieved focal depths for the mainshock and seven larger aftershocks which ranged from about 3 to 10 km with the retrieved focal depths the arrival times of the p and s phases at four close stations and a revised hypodd program package we relocated the mainshock and seven larger aftershocks on the vertical profile with an azimuth of 119 the hypocenter trend was at 52 down from horizontal the moment tensor of the mainshock was inverted by modeling long period rayleigh wave records at 11 stations selected with consideration of a balanced distribution around the epicenter combined with the hypocenter trend a plane solution with a strike of 29 a dip of 55 and a slip of 113 was identified to be close to the real rupture plane of the mainshock the rupture process of the mainshock was preliminarily analyzed using regional waveform records at least four subevent ruptures were found the initiate depth of the first subevent rupture was at about 7 8 km and the rupture speed was at about 1 3 km s the time gap between subevent ruptures 1 and 2 was about 0 34 s

comparison of direct and coda wave stress drop measurements for the wells nevada earthquake sequence 1 i calculate the corner frequencies and stress drops of the seven largest earthquakes m4 6 in the wells nevada sequence 2008 using both coda and direct waves i use spectral ratio empirical green s function egf and methods to investigate whether differences and uncertainties in the analyses could affect the calculated source parameters i find that the source spectral ratios from the coda and direct s waves are similar for the same pairs of earthquakes but that the source spectra and corresponding source parameters depend systematically on whether the earthquake of interest is the larger or smaller within the spectral ratio mayeda and malagnini 2009a calculated coda spectral ratios between the m6 main shock and six large aftershocks m 4 and performed a combined inversion to calculate source parameters they found that the main shock had a higher stress drop than the large aftershocks i model the identical spectral ratios individually in the manner that i use for direct waves i find that the choice of source model and fitting procedure produces significant random scatter but no systematic biases i calculate direct wave ratios for the same earthquake pairs and find higher variability but no systematic difference in the results lastly i use m2 8 3 2 aftershocks as egfs for the large aftershocks these spectral ratios yield significantly higher corner frequencies and stress drops for the large aftershocks than when the same earthquakes are the denominator in ratios with the main shock to improve the quality of egf analyses i propose strict objective criteria for acceptance of a spectral ratio fit 1 observable source pulse 2 the amplitude ratio of the low to high frequency limits of the fit is at least 5 and 3 the corner frequency only varies by 50 when the variance is within 5 of the minimum

source scaling of inland crustal earthquake sequences in japan using the s wave coda spectral ratio method we estimate corner frequencies and stress drops for 298 events ranging from m w 3 2 7 0 in 17 inland crustal earthquake sequences in japan to investigate the source scaling and variation in stress drops we obtain the source spectral ratio from observed records by the s wave coda spectral ratio method the advantage of using the s wave coda is in obtaining much more stable source spectral ratios than using direct s waves we carefully examine the common shape of the decay of coda envelopes between event pair records the corner frequency and stress drop are estimated by modeling the observed source spectral ratio with the omega square source spectral model we investigate the dependences of stress drops on some tectonic effects such as regionality focal mechanism and source depth the principal findings are as follows 1 a break in self similar source scaling is found in our dataset events larger than m w 4 5 show larger stress drops than those of smaller events 2 stress drops of aftershocks are mostly smaller than those of mainshocks in each sequence 3 there are no systematic differences between stress drops of events occurring inside and outside the niigata kobe tectonic zone in japan 4 clear dependence of the faulting type on stress drops cannot be seen 5 stress drops of aftershocks depend on their source depth 6 the crack size obtained from the corner frequency corresponds to the total rupture area of heterogeneous slip models for large events

empirical green s function analysis taking the next step an extension of the empirical green s function egf method is presented that involves determination of source parameters using standard egf deconvolution followed by inversion for a common attenuation parameter for a set of colocated events recordings of three or more colocated events can thus be used to constrain a single path attenuation estimate i apply this method to recordings from the 1995 1996 ridgecrest california earthquake sequence i analyze four clusters consisting of 13 total events with magnitudes between 2 6 and 4 9 i first obtain corner frequencies which are used to infer brune stress drop estimates i obtain stress drop values of 0 3 53 mpa with all but one between 0 3 and 11 mpa with no resolved increase of stress drop with moment with the corner frequencies constrained the inferred attenuation parameters are very consistent they imply an average shear wave quality factor of approximately 20 25 for alluvial sediments within the indian wells valley although the resultant spectral fitting using corner frequency and is good the residuals are consistent among the clusters analyzed their spectral shape is similar to the the theoretical one dimensional response of a layered low velocity structure in the valley an absolute site response cannot be determined by this method because of an ambiguity between absolute response and source spectral amplitudes i show that even this subtle site response can significantly bias estimates of corner frequency and if it is ignored in an inversion for only source and path effects the multiple egf method presented in this paper is analogous to a joint inversion for source path and site effects the use of colocated sets of earthquakes appears to offer significant advantages in improving resolution of all three estimates especially if data are from a single site or sites with similar site response

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

earthquake scaling characteristics and the scale in dependence of seismic energy to moment ratio insights from kik net data in japan 1 we investigate earthquake source characteristics and scaling properties using the results of a spectral inversion of more than 29 000 accelerometric borehole recordings from 1 826 earthquakes mjma 2 7 8 throughout japan we find that the calculated source spectra can be well characterized by the omega square model and show on average self similar scaling over the entire magnitude range with median stress drops of 1 1 and 9 2 mpa for crustal and subcrustal events respectively the seismic energy to moment ratio as theoretically expected if the omega square model is valid shows a strong dependency on stress drop only which in conjunction with data selection practice in some studies to cope with limited recording bandwidth can explain the often observed apparent scale dependence our observations suggest that there is no significant deviation from similarity of the energy radiation in the investigated magnitude range and that the observed scatter is mainly related to the scatter in stress drop

bayesian inversion of seismic spectral ratio for source scaling application to a persistent multiplet in the western corinth rift we propose a method to precisely estimate earthquake source parameters as magnitude size of rupture stress drop and coseismic slip and their uncertainties this method that relies on a bayesian approach allows the determination of the scalar seismic moment corner frequency fc and their associated uncertainties by inverting ratios between seismic displacement spectra of nearby located earthquakes we apply this method to a large earthquake multiplet 56 events located under the northern coast of the corinth gulf at 8 km depth this multiplet is regularly active between 2001 and 2007 results show fcp fcs ratios globally between 1 0 and 1 5 which is compatible with the values predicted by madariagas circular rupture model in details 6 earthquakes however exhibit corner frequency variations as a function of the station azimuth compatible with linear rupture propagation magnitude ranges 1 08 and 2 80 with a b value of 1 04 source rupture length globally ranges between 40 and 170 m for stress drop between 1 and 100 mpa we show that the number of ruptures and the cumulated coseismic slip are maximal at the center of the multiplet this suggests that multiplet 866 could be seen as a weak seismogenic patch surrounded by a locked fault how ever the large value of the maximum coseismic slip cumulated over the period 2000 2008 10 cm rather suggests creep allowing rapid stress reloading and repeated earthquakes with short delays we therefore propose that multiplet 866 is surrounded by a heterogeneous fault surface with both locked and creeping areas