amplitude and decay of long period coda of great earthquakes abstract the earthquake coda is the residual vibration energy long after the main arrivals of an earthquake previous studies of coda waves have focused on high frequencies and small earthquakes which are generally attributed to the scattering from the earth s internal heterogeneities here we examined the early coda of great earthquakes at long periods 50 to 300 s at time window of 10 000 to 50 000 s after the origin time we used 10 major earthquakes magnitude 8 0 in recent decades that were recorded at global seismic networks we found that the coda energy can be well represented by a simple exponential decay model for the early coda the variation of the initial coda energy with distance is dominated by the effect of geometric spreading suggesting that the scattering of the earth s internal heterogeneities contributes little to the long period early coda the energy decay rate is largely insensitive to earthquake source location magnitude focal mechanism or rupture process station location or 3d variation of the earth s internal structure making it ideal to constrain the average global attenuation structure a small modification of the quality factor based on a global reference model can fit the coda energy decay well the long period coda energy may potentially provide a new way to determine the seismic moment of a major earthquake

estimation of radiated energy using the kik net downhole records old method for modern data we use kik net nied down hole records to estimate the radiated energy er of 29 japanese inland earthquakes with a magnitude range from mw 5 6 to 7 0 the method is based on the work of gutenberg and richter in which the time integral of s wave ground motion velocity squared is measured as a basic metric of the radiated energy only stations within a distance of 100 km are used to minimize complex path and attenuation effects unlike the teleseismic method that uses mainly p waves the use of s waves which carry more than 95 per cent of the radiated energy allows us to obtain robust results we calibrate the method using synthetic seismograms to modernize and improve the gutenberg richter method we compute synthetic seismograms for a source model of each event with a given source function i e known er the actual mechanism and the source station geometry then we compare the given er with the computed energy metric to correct for the unknown effect of wave propagation and the mechanism the use of down hole records minimizes the uncertainty resulting from the site response our results suggest that the currently available estimates of er from teleseismic data are probably within a factor of 3 on average of the absolute value the scaled energy er er m0 is nearly constant at about 3 10 5 over a magnitude range from mw 5 6 to 7 0 with a slight increasing trend with mw we found no significant difference in er between dip slip and strike slip events

evidence for non constant energy moment scaling from coda derived source spectra 1 we present two lines of evidence showing the ratio of seismically radiated energy er to seismic moment mo increases with increasing moment for crustal events spanning 5 orders in seismic moment this ratio often referred to as the scaled energy er m0 has been elusive and the subject of recent debate within the seismological community because significant frequency dependent corrections must be made to account for source and path heterogeneity it is not uncommon that energy estimates of the same event by different researchers have significantly different values to minimize some of the potential problems we used the regional coda methodology outlined by mayeda et al 2003 on 4 large earthquake sequences mw 7 4 and 7 2 izmit duzce mw 7 2 gulf of aqaba mw 7 3 landers and mw 7 2 hector mine this methodology has been shown to provide the lowest variance estimate of the source spectrum when compared against traditional direct wave estimates in our first approach we made energy estimates from coda derived spectra and observed that increases with increasing moment for 3 7 mw 7 4 in our second approach we used the simple idea outlined by prieto et al 2004 to directly test for self similarity under self similarity earthquake source spectra scaled by 3 should have the same shape to test this one needs very stable spectra either through spectral stacking of direct wave spectra or by the use of stable coda derived spectra for all sequences we found that the mainshocks and larger aftershocks had significantly different spectral shapes than the smaller events the scaled 3 spectra of the larger events represented an upper bound having larger amplitudes near the corner frequency in fact an 3 5 scaling moved the larger events closer to the mean of the spectral population though the spectral shape differences persisted these results strongly suggest that earthquakes are not scaling self similarly and that complexities in the rupture process such as variable slip velocity exist between small and large events

temporal correlation between seismic moment and injection volume for an induced earthquake sequence in central oklahoma the rapidly increased earthquake rate in the central united states has been linked with wastewater injection while the overall understanding appears clear at large scales the interaction between injection and faulting at smaller scales within individual sequences is still not clear for an earthquake sequence in central oklahoma we conduct finer scale analysis of the spatiotemporal evolution of seismicity and pore pressure modeling the pore pressure modeling suggests that nearby wells show much stronger correlation with earthquake sequence evolution detailed temporal analysis found correlation between earthquake rate seismic moment and injection rates from wells in close proximity however the observed maximum magnitude mmax is about one order of magnitude smaller than expected based on a theoretical relationship between mmax and cumulative volume this discrepancy may point toward additional parameters such as fault size and stress which influence mmax the lower mmax is consistent with the truncated gutenberg richter distribution observed from matched filter detected catalog overall the detailed observations suggest that it is possible to resolve relationships between individual disposal wells and induced earthquake sequences

a comparison of spectral parameter kappa from small and moderate earthquakes using southern california anza seismic network data kappa is a one parameter estimator of the spectral amplitude decay with frequency of a seismogram low values 5 ms indicate limited attenuation of high frequency energy whereas higher values 40 ms indicate high frequency energy has been removed kappa is often assumed to be a site term and used in seismic designs we address two key questions about kappa 1 how to identify source path and site contributions to kappa and 2 can kappa estimates from smaller earthquakes and more readily accessible weak motion recordings be reasonably extrapolated to esti mate kappa of larger earthquakes the use of small earthquakes ml 3 5 earthquakes inside the network we find kappa from small earthquakes predicts the relative values of kappa for larger earthquakes e g measurements at stations pfo and knw are small compared with those at stations tro and snd for the snd and tro data however kappa values from small earth quakes overpredict those from moderate and large earthquakes site effects are the most important contributor to kappa estimates but the scatter within kappa measure ments at a given station is likely caused by a significant contribution from near the source perhaps related to near source scattering because of this source side varia bility care is recommended in using individual small events as green s functions to study source time effects of moderate and large events

estimation and applicability of attenuation characteristics for source parameters and scaling relations in the garhwal kumaun himalaya region india abstract source parameters of the small to moderate earthquakes are significant for understanding the dynamic rupture process the scaling relations of the earthquakes and for assessment of seismic hazard potential of a region in this study the source parameters were determined for 58 small to moderate size earthquakes 3 0 m w 5 0 occurred during 2007 2015 in the garhwal kumaun region the estimated shear wave quality factor q f values for each station at different frequencies have been applied to eliminate any bias in the determination of source parameters the q f values have been estimated by using coda wave normalization method in the frequency range 1 5 16 hz a frequency dependent s wave quality factor relation is obtained as q f 152 9 7 f 0 82 0 005 by fitting a power law frequency dependence model for the estimated values over the whole study region the spectral low frequency spectral level and corner frequency and source static stress drop seismic moment apparent stress and radiated energy parameters are obtained assuming 2 source model the displacement spectra are corrected for estimated frequency dependent attenuation site effect using spectral decay parameter kappa the frequency resolution limit was resolved by quantifying the bias in corner frequencies stress drop and radiated energy estimates due to finite bandwidth effect the data of the region shows shallow focused earthquakes with low stress drop the estimation of zuniga parameter e suggests the partial stress drop mechanism in the region the observed low stress drop and apparent stress can be explained by partial stress drop and low effective stress model presence of subsurface fluid at seismogenic depth certainly manipulates the dynamics of the region however the limited event selection may strongly bias the scaling relation even after taking as much as possible precaution in considering effects of finite bandwidth attenuation and site corrections although the scaling can be improved further with the integration of large dataset of microearthquakes and use of a stable and robust approach

validation of non self similar source scaling using ground motions from the 2008 wells nevada earthquake sequence abstract the behavior of earthquake source scaling has been the topic of significant debate in the earthquake source community over the past two decades and validating recent results has been difficult in this study we focus on high quality records from the 21 february 2008 m w 5 9 wells nevada earthquake and its aftershocks which provide an unprecedented opportunity to take an in depth look at the source scaling and ground motions for this earthquake sequence conflicting scaling relations were reported in two previous studies baltay et al 2010 mayeda and malagnini 2010 in addition recent comparisons of the ground motion prediction equations gmpes with this data set have shown significant overestimation of ground motions for the aftershocks while being in rough agreement with the mainshock ground motions petersen et al 2011 in order to evaluate the reported scaling relationships and better understand the observed discrepancy in the gmpe s we chose to revisit the wells nevada earthquake sequence we investigate the source parameters of the earthquakes using the s wave and coda spectral ratio methods mayeda et al 2007 and find that the stress drops of the aftershocks are 2 5 times lower than that of the mainshock we compute pseudospectral acceleration psa ratios using direct s waves from broadband records and compare with theoretical source ratios assuming the self similar and non self similar source scaling assumptions as well as ratios derived from state of the art gmpe estimates we find that we can only simultaneously match source ratios between the mainshock and selected aftershocks if we use non self similar scaling accounting for the significant differences in the stress drop between small and large earthquakes will help to enhance the prediction capability of ground motions for this region by validating the source scaling with psa ratios these results can be used as constraints in stress parameterization used in the gmpe s

dynamic modeling of the 2004 mw 6 0 parkfield california earthquake 1 we present two spontaneous rupture models of the 2004 mw 6 0 parkfield earthquake constrained by near source ground motions we start with a stress drop distribution calculated from a kinematic slip distribution using a linear slip weakening friction law we utilize trial and error to obtain both the stress conditions and frictional parameters on the fault that produce synthetics consistent with records the material contrast across the san andreas fault is incorporated using different one dimensional velocity structures on each side of the fault an approximately constant s parameter of 0 3 and a uniform slip weakening distance of 0 15 m are used in the dynamic models in our preferred dynamic model consistent with the ground motion and gps the slip is bounded by seismicity streaks at 5 and 10 km depths confirming a locked zone at depth the stress drop is approximately 10 mpa in the hypocentral region and about 2 mpa elsewhere the material contrast across the fault causes significant normal stress variations 1 mpa leading to a larger strength drop to the southeast than to the northwest the main rupture front propagates at nearly a constant subshear rupture velocity 3 km s in both directions the total radiated energy determined from the preferred dynamic model is 1 1 1013 j seismic moment is 1 0 1018 nm and fracture energy is 3 0 1013 j the limited number of aftershocks in the slipped area suggests the important role of stress on the distribution of seismicity in the locked zone

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

a robust calibration technique for acoustic emission systems based on momentum transfer from a ball drop we describe a technique to estimate the seismic moment of acoustic emissions and other extremely small seismic events unlike previous calibration tech niques it does not require modeling of the wave propagation sensor response or signal conditioning rather this technique calibrates the recording system as a whole and uses a ball impact as a reference source or empirical green s function to correctly apply this technique we develop mathematical expressions that link the seismic mo ment m0 of internal seismic sources i e earthquakes and acoustic emissions to the impulse or change in momentum p of externally applied seismic sources i e me teor impacts or in this case ball impact we find that at low frequencies moment and impulse are linked by a constant which we call the force moment rate scale factor c f mm0 p this constant is equal to twice the speed of sound in the material from which the seismic sources were generated next we demonstrate the calibration technique on two different experimental rock mechanics facilities the first example is a saw cut cylindrical granite sample that is loaded in a triaxial apparatus at 40 mpa confining pressure the second example is a 2 m long fault cut in a granite sample and deformed in a large biaxial apparatus at lower stress levels using the empirical cali bration technique we are able to determine absolute source parameters including the seismic moment corner frequency stress drop and radiated energy of these magnitude 2 5 to 7 seismic events

the seismic magnitude of the 1989 loma prieta mainshock determined from strong motion records the work investigates the usefulness of regional broadband recordings to estimate rapidly the size of large earthquakes strong motion records of the loma prieta earthquake from 20 free field stations at distances 15 105 km from the source are used to compute the local magnitude of the mainshock frequency domain convolution and integration are used to obtain appropriate synthesized signals an azimuthal average of ml 6 7 0 09 was estimated from the maximum trace amplitudes measured on synthesized wood anderson torsion records the low gain wood anderson torsion seismograph 100 magnification at the university of california seismographic station gave ml 7 0 comparison between published local and teleseismic estimates indicates that the usual strong motion accelerometers in the near field of large earthquakes yield acceptable values of magnitude efforts to obtain estimates of the overall average radiated seismic energy from the integrated ground velocity squared records demonstrated the need for special site calibration

seismic source parameters of normal faulting inslab earthquakes in central mexico we studied 62 normal faulting inslab earthquakes in the mexican subduction zone with magnitudes in the range of 3 6 mw 7 3 and hypocentral depths of 30 z 108 km we used different methods to estimate source parameters to observe differences in stress drop corner frequencies source dimensions source duration energy to moment ratio radiated efficiency and radiated seismic energy the behavior of these parameters is derived we found that normal faulting inslab events have higher radiated seismic energy energy to moment ratio and stress drop than interplate earthquakes as expected this may be explained by the mechanism dependence of radiated seismic energy and apparent stress reported in previous source parameter studies the energy to moment ratio data showed large scatter and no trend with seismic moment the stress drop showed no trend with seismic moment but an increment with depth the radiated seismic efficiencies showed similar values to those obtained from interplate events but higher than near trench events we found that the source duration is independent of the depth we also derived source scaling relationships for the mentioned parameters the low level of uncertainties for the seismic source parameters and scaling relationships showed that the obtained parameters are robust therefore reliable source parameter estimation can be carried out using the obtained scaling relationships we also studied regional stress field of normal faulting inslab events heterogeneity exists in the regional stress field as indicated by individual stress tensor inversions conducted for two different depth intervals z 40 km respectively while the maximum stress axis 1 appears to be consistent and stable the orientations of the intermediate and minimum stresses 2 and 3 vary over the depth intervals the stress inversion results showed that the tensional axes are parallel to the dip direction of the subducted plate at depths greater than 40 km the maximum horizontal stresses are oblique to the dip direction following the general trend of the slab geometry

apparent stress variations near the osa peninsula costa rica influenced by subducted bathymetric features 1 we compute apparent stress for 114 aftershocks 0 9 ml 3 7 of the 1999 mw 6 9 quepos costa rica thrust faulting earthquake to examine the influence of subducting plate topographic complexity near the osa peninsula on earthquake rupture using seismic coda techniques we find a heterogeneous distribution in apparent stress of 0 1 2 5 mpa mean 0 6 mpa for these aftershocks mean aftershock apparent stress is more than twice the global mean for thrust faulting earthquakes at oceanic subduction zones and 1 5 times the mean for events just northward along the margin near the nicoya peninsula where the subducting plate has lower relief we also find constant source scaling for the osa aftershocks the variation in apparent stress found near the osa peninsula and high mean as compared to global and regional values suggest areas of stress concentration in the region of bathymetric complexity in the subduction zone

the rupture extent of low frequency earthquakes near parkfield ca the low frequency earthquakes lfes that constitute tectonic tremor are often inferred to be slow to have durations of 0 2 to 0 5 s a factor of 10 to 100 longer than those of typical m w 1 2 earthquakes here we examine lfes near parkfield ca in order to assess several proposed explanations for lfes long durations we determine lfe rupture areas and location distributions using a new approach similar to directivity analysis where we examine how signals coming from various locations within lfes finite rupture extents create differences in the apparent source time functions recorded at various stations we use synthetic ruptures to determine how much the lfe signals recorded at each station would be modified by spatial variations of the source station travel time within the rupture area given various possible rupture diameters and then compare those synthetics with the data our synthetics show that the methodology can identify inter station variations created by heterogeneous slip distributions or complex rupture edges and thus lets us estimate lfe rupture extents for unilateral or bilateral ruptures to obtain robust estimates of the sources similarity across stations we stack signals from thousands of lfes using an empirical green s function approach to isolate the lfes apparent source time functions from the path effects our analysis of lfes in parkfield implies that lfes apparent source time functions are similar across stations at frequencies up to 8 to 16 hz depending on the family the inter station coherence observed at these relatively high frequencies or short wave lengths down to 0 2 to 0 5 km suggest that lfes in each of the 7 families examined occur on asperities they are clustered in patches with sub 1 km diameters the individual lfes rupture diameters are estimated to be smaller than 1 1 km for all families and smaller than 0 5 km and 1 km for the two shallowest families which were previously found to have 0 2 s durations coupling the diameters with the durations suggests that it is possible to model these m w 1 2 lfes with earthquake like rupture speeds around 70 of the shear wave speed however that rupture speed matches the data only at the edge of our uncertainty estimates for the family with highest coherence the data for that family are better matched if lfes have rupture velocities smaller than 40 of the shear wave speed or if lfes have different rupture dynamics they could have long rise times contain composite sub ruptures or have slip distributions that persist from event to event

shallow dynamic overshoot and energetic deep rupture in the 2011 mw 9 0 tohoku oki earthquake strong spatial variation of rupture characteristics in the moment magnitude mw 9 0 tohoku oki megathrust earthquake controlled both the strength of shaking and the size of the tsunami that followed finite source imaging reveals that the rupture consisted of a small initial phase deep rupture for up to 40 seconds extensive shallow rupture at 60 to 70 seconds and continuing deep rupture lasting more than 100 seconds a combination of a shallow dipping fault and a compliant hanging wall may have enabled large shallow slip near the trench normal faulting aftershocks in the area of high slip suggest dynamic overshoot on the fault despite prodigious total slip shallower parts of the rupture weakly radiated at high frequencies whereas deeper parts of the rupture radiated strongly at high frequencies

magma reservoir conditions beneath tsurumi volcano sw japan evidence from amphibole thermobarometry and seismicity abstract calcic amphibole phenocrysts in the tsurumidake summit ts lava which was produced during the most recent eruption at tsurumi volcano sw japan at around 7 5 10 5 ka have been analyzed to determine the pre eruptive conditions such as temperature t pressure p oxygen fugacity fo2 sio2 content sio2melt and feo mgo ratio feo mgomelt of coexisting silicate melts in the magma reservoir beneath the volcano although most of the amphibole phenocrysts have been completely decomposed to a fine grained opaque symplectite 6 of the grains remain intact the degree of amphibole breakdown dab defined as the ratio of the area of symplectite to the area of symplectite plus relict amphibole in each phenocryst varies from 20 to 100 compositional zoning was not observed in the amphibole grains however two distinct groups of amphibole phenocrysts have been identified based on their chemical compositions group i amphiboles which are relatively si poor and 6 al rich and have a relatively high mg 100mg mg fe2 and group ii amphiboles which are si rich and 6 al poor and have a relatively low mg empirical equations for geothermobarometry oxygen barometry and chemometry that exclusively rely on the amphibole composition were applied to estimate the t p fo2 sio2melt feo mgomelt conditions of the silicate melts with which the amphibole crystals equilibrated the results show that group i and group ii amphiboles equilibrated with andesitic melts group i melts and dacitic rhyolitic melts group ii melts respectively the t p fo2 conditions of group i melts were estimated as 374 483 mpa 13 9 17 9 km depth 950 c and nno 1 3 respectively and those of group ii melts were 93 242 mpa 3 4 9 0 km depth 824 913 c and nno 0 6 1 7 respectively the estimated t p fo2 sio2melt feo mgomelt conditions were almost constant for group i melts whereas the t nno and feo mgomelt values of group ii melts decreased with increasing sio2melt the dab decreased as the temperature increased low dab grains are absent in group ii amphiboles our results suggest that 1 a deeper reservoir at a depth of 16 km stored an andesitic melt coexisting with group i amphiboles at 950 c 2 a chemically zoned reservoir at shallower depth 6 4 km was filled with dacitic rhyolitic melts that coexisted with group ii amphiboles at 824 913 c 3 the ts lava was the product of magma mixing of at least three components including the andesitic melt derived from the deeper reservoir the dacitic and rhyolitic melts from the shallower reservoir and a mafic magma derived from the lower crust and or upper mantle and 4 the ts lava eruption occurred within a month or less of the magma mixing

low radiation efficiency of the intermediate depth earthquakes in the japan subduction zone robust determination of earthquake source parameters over a continuous depth range is central to inferring rupture mechanisms dominant at different depths we employed a cluster event method to constrain the source parameters as well as along path attenuation for earthquakes over 0 150 km depths and 4 orders of seismic moments in the japan subduction zone we found that corner frequency and stress drop increase with depth whereas the radiated energy scaled by seismic moment declines with depth slightly as a result the radiation efficiency exhibits a notable deficit for events deeper than 60 km together these suggest an increased energy dissipation during faulting in ductile deformation regime consistent with shear heating instability as an important faulting mechanism for intermediate depth earthquakes

earthquake source scaling relationships from 1 to 5 ml using seismograms recorded at 2 5 km depth the scaling relationships of earthquake sources less than about magnitude 3 have been the subject of considerable controversy over the last two decades studies of such events have shown a tendency for the constant stress drop self similarity of larger earthquakes to breakdown at small magnitudes and an apparent minimum source dimension of about 100 m has been observed other studies showed that this apparent breakdown in scaling could be an artifact of severe near surface attenuation limiting the spatial resolution of surface data in this study source parameters are determined for over 100 nearby tectonic earthquakes from recordings at a depth of 2 5 km in granite in the cajon pass scientific drill hole southern california comparison of the seismograms recorded at this depth with those at the wellhead clearly demonstrates the effect of the severe attenuation in the upper kilometers of the earth s crust source parameters are calculated by spectral modeling of three component p and s waves assuming four source models based on the brune 2 n 2 model in model l n 2 is fixed and q of p and s waves is determined to be 912 581 1433 and 1078 879 1323 respectively the numbers in parentheses are 1 standard deviation in model 2 qp qs 1000 is assumed and n is allowed to vary the 2 model is a good average for the data set but there is some real scatter supported by the data in model 3 qp qs 1000 is also assumed and 2 is constrained and in model 4 attenuation is ignored and n is allowed to vary source dimensions of less than 10m are observed for all four models 10 times smaller than the proposed minimum no breakdown in constant stress drop scaling is seen in the downhole data approximately ml 1 to 5 5 m0 109 1016 nm the ratio between radiated seismic energy estimated by integrating the velocity squared spectra with adequate signal bandwidth and seismic moment appears to decrease gradually with decreasing moment in the magnitude range 1 to 7 this is not incompatible with a constant stress drop but could result from errors in calculating energy the ratio of the s wave energy to that radiated by the p waves is about 14 after correction for attenuation this low value is consistent with the corner frequency shift of about 1 3 this corner frequency shift is observed for all four source models and therefore is interpreted as being source controlled

scale dependence of apparent stress for earthquakes along the subducting pacific plate in northeastern honshu japan apparent stress which quantifies the ratio of high frequency spectral amplitude to the direct current level of source displacement spectra is known to reflect the source rupture process whether this parameter depends on the seismic moment has not yet been well established because of the difficulties in the reliable estimation of high frequency source spectra to overcome this problem we estimate s wave source spectra by using site amplification factors and attenuation factor graphic 1 which are systematically measured by the coda normalization method analyzing horizontal components of velocity seismograms recorded at 70 borehole seismic stations of hi net national research institute for earth science and disaster prevention in northeastern honshu japan we estimate site factors and graphic 2 in the 0 5 32 hz frequency band by using these factors we evaluate the source spectra of 225 small to moderate earthquakes that occurred in and around the subducting pacific plate site amplification factors we obtained strongly depend on frequency and the frequency dependence clearly changes with the lithology and geologic age of rock obtained graphic 3 values decrease with frequency in proportion to the reciprocal of frequency the apparent stresses estimated from s wave spectra clearly increase from 104 to 107 pa with the seismic moment increasing which cannot be attributed to the limited frequency band and other artificial causes the power of scale dependence is estimated as 0 39 0 44 for the seismic moment range from 1011 to 1017 n m some of the scale dependence of apparent stress is attributed to the scale dependence of brune s stress drop 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif

on the characteristics of earthquake stress release variations in japan abstract the amount of stress released during earthquakes is a fundamental characteristic of the earthquake rupture process as such it represents a key parameter for improving our understanding of earthquake source physics and for reliable ground motion prediction large earthquake populations usually show variations in stress release as large as three orders of magnitude but the underlying mechanisms have remained largely elusive and particularly the dependence of stress release on earthquake size is still a matter of debate here i use a unique dataset from japan encompassing earthquakes of a wide magnitude range and spatial coverage to show that stress release variations of crustal earthquakes are strongly correlated with heat flow variations indicating that they are thermally controlled in contrast subcrustal events depict highest stress release in regions of strong subduction interface coupling and overall less pronounced variability as compared with crustal earthquakes stress release is overall only weakly dependent on earthquake size but at local scales i e within individual earthquake sequences the dependence can be very strong and apparently varies with stress regime accounting for these systematic variations reduces the stress release variability on local scale by a factor of two to three as compared with the full earthquake population a finding that is of key significance in the endeavor to reduce the uncertainties in future ground motion predictions

dynamics of the 2015 m7 8 nepal earthquake the 2015 m7 8 nepal earthquake ruptured part of the main himalayan thrust beneath kathmandu to study the dynamics of this event we compute p wave spectra of the main shock and of two large aftershocks to estimate stress drop and radiated energy we find that surface reflections depth phases of these shallow earthquakes produce interference that severely biases spectral measurements unless corrections are applied measures of earthquake dynamics for the main shock are within the range of estimates from global and regional earthquakes we explore the azimuthal and temporal variations of radiated energy and highlight unique aspects of the m7 8 rupture the beginning of the earthquake likely experienced a dynamic weakening mechanism immediately followed by an abrupt change in fault geometry correlation of backprojection results with frequency dependent variations in the radiated energy rate and with the suggested geometry of the main himalayan thrust yields new constraints on dynamic ruptures through geometrical barriers

stress drop heterogeneity within tectonically complex regions a case study of san gorgonio pass southern california in general seismic slip along faults reduces the average shear stress within earthquake source regions but stress drops of specific earthquakes are observed to vary widely in size to advance our understanding of variations in stress drop we analysed source parameters of small magnitude events in the greater san gorgonio area southern california in san gorgonio the regional tectonics are controlled by a restraining bend of the san andreas fault system which results in distributed crustal deformation and heterogeneous slip along numerous strike slip and thrust faults stress drops were estimated by fitting a brune type spectral model to source spectra obtained by iteratively stacking the observed amplitude spectra the estimates have large scatter among individual events but the median of event populations shows systematic statistically significant variations we identified several crustal and faulting parameters that may contribute to local variations in stress drop including the style of faulting changes in average tectonic slip rates mineralogical composition of the host rocks as well as the hypocentral depths of seismic events we observed anomalously high stress drops 20 mpa in a small region between the traces of the san gorgonio and mission creek segments of the san andreas fault furthermore the estimated stress drops are higher below depths of 10 km and along the san gorgonio fault segment but are lower both to the north and south away from san gorgonio pass showing an approximate negative correlation with geologic slip rates documenting controlling parameters of stress drop heterogeneity is important to advance regional hazard assessment and our understanding of earthquake rupture processes

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

source pulse enhancement by deconvolution of an empirical green s function observations of the earthquake source time function are enhanced if path recording site and instrument complexities can be removed from seismograms assuming that a small earthquake has a simple source its seismogram can be treated as an empirical green s function and deconvolved from the seismogram of a larger and or more complex earthquake by spectral division when the deconvolution is well posed the quotient spectrum represents the apparent source time function of the larger event this study shows that with high quality locally recorded earthquake data it is feasible to fourier transform the quotient and obtain a useful result in the time domain in practice the deconvolution can be stabilized by one of several simple techniques in this paper the method is implemented and tested on high quality digital recordings of aftershocks of the jan 9 1982 miramichi new brunswick earthquake in particular seismograms from a jan 17 aftershock 017 13 33 gmt local mag 3 5 exhibit path or site effects which complicate the determination of source parameters after deconvolution the apparent far field source of this event is a simple pulse in displacement with duration 0 07 second for both p and s

determination of earthquake energy release and ml using terrascope we estimated the energy radiated by earthquakes in southern california using on scale very broadband recordings from terrascope the method we used involves time integration of the squared ground motion velocity and empirical determination of the distance attenuation function and the station corrections the time integral is typically taken over a duration of 2 min after the p wave arrival the attenuation curve for the energy integral we obtained is given by q r cr n exp kr r 2 2 h ref 2 with c 0 49710 n 1 0322 k 0 0035 km 1 and h ref 8 km where is the epicentral distance a similar method was used to determine m l using terrascope data the station corrections for m l are determined such that the m l values determined from terrascope agree with those from the traditional optical wood anderson seismographs for 1 5 6 5 m l saturates the ratio e s m 0 m 0 seismic moment a measure of the average stress drop for six earthquakes the 1989 montebello earthquake m l 4 6 the 1989 pasadena earthquake m l 4 9 the 1990 upland earthquake m l 5 2 the 1991 sierra madre earthquake m l 5 8 the 1992 joshua tree earthquake m l 6 1 and the 1992 landers earthquake m w 7 3 are about 10 times larger than those of the others that include the aftershocks of the 1987 whittier narrows earthquake the sierra madre earthquake the joshua tree earthquake and the two earthquakes on the san jacinto fault the difference in the stress drop between the mainshock and their large aftershocks may be similar to that between earthquakes on a fault with long and short repeat times the aftershocks which occurred on the fault plane where the mainshock slippage occurred had a very short time to heal hence a low stress drop the repeat time of the major earthquakes on the frontal fault systems in the transverse ranges in southern california is believed to be very long a few thousand years hence the events in the transverse ranges may have higher stress drops than those of the events occurring on faults with shorter repeat times such as the san andreas fault and the san jacinto fault the observation that very high stress drop events occur in the transverse ranges and the los angeles basin has important implications for the regional seismic potential the occurrence of these high stress drop events near the bottom of the seismogenic zone strongly suggests that these fault systems are capable of supporting high stress that will eventually be released in major seismic events characterization of earthquakes in terms of the e s m 0 ratio using broadband data will help delineate the spatial distribution of seismogenic stresses in the los angeles basin and the transverse ranges

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

stress release and source scaling of the 2010 2011 canterbury new zealand earthquake sequence from spectral inversion of ground motion data the canterbury earthquake sequence beginning with the 2010 m w 7 2 darfield earthquake is one of the most notable and well recorded crustal earthquake sequences in a low strain rate region worldwide and as such provides a unique opportunity to better understand earthquake source physics and ground motion generation in such a tectonic setting ground motions during this sequence ranged up to extreme values of 2 2 g recorded during the february 2011 m w 6 2 event beneath the city of christchurch a better understanding of the seismic source signature of this sequence in particular the stress release and its scaling with earthquake size is crucial for future ground motion prediction and hazard assessment in canterbury but also of high interest for other low to moderate seismicity regions where high quality records of large earthquakes are lacking here we present a source parameter study of more than 200 events of the canterbury sequence covering the magnitude range m w 3 7 2 source spectra were derived using a generalized spectral inversion technique and found to be well characterized by the 2 source model we find that stress drops range between 1 and 20 mpa with a median value of 5 mpa which is a factor of 5 larger than the median stress drop previously estimated with the same method for crustal earthquakes in much more seismically active japan stress drop scaling with earthquake size is nearly self similar and we identify lateral variations throughout canterbury in particular high stress drops at the fault edges of the two major events the m w 7 2 darfield and m w 6 2 christchurch earthquakes

earthquake source properties from pseudotachylite abstract earthquake radiated motions contain information that can be interpreted as source displacement and therefore related to stress drop except in a few notable cases these displacements cannot be easily related to the absolute stress level or the fault strength or attributed to a particular physical mechanism in contrast paleoearthquakes recorded by exhumed pseudotachylite have a known dynamic mechanism whose properties constrain the coseismic fault strength pseudotachylite can be used to directly address a discrepancy between seismologically measured stress drops which are typically a few mpa and much larger dynamic stress drops expected from thermal weakening during slip at seismic speeds in crystalline rock mckenzie and brune 1972 sibson 1973 lachenbruch 1980 mase and smith 1987 rice 2006 and as have been observed in laboratory experiments at high slip rates di toro hirose nielsen pennacchioni et al 2006 this places pseudotachylite derived estimates of fault strength and inferred crustal stress within the context and bounds of naturally observed earthquake source parameters apparent stress stress drop and overshoot including consideration of fault surface roughness off fault damage fracture energy and the strength excess the analysis which assumes stress drop is related to corner frequency as in the madariaga 1976 source model is restricted to earthquakes of the gole larghe fault zone in the italian alps where the dynamic shear strength is well constrained by field and laboratory measurements we find that radiated energy is similar to or exceeds the shear generated heat and that the maximum strength excess is 16 mpa these events have inferred earthquake source parameters that are rare for instance a low percentage of the global earthquake population has stress drops as large unless fracture energy is routinely greater than in existing models pseudotachylite is not representative of the shear strength during the earthquake that generated it or the strength excess is larger than we have allowed

stress drops and radiated seismic energies of microearthquakes in a south african gold mine 1 we estimate stress drops and radiated seismic energies of 20 microearthquakes 0 0 mw 1 3 in a south african gold mine to investigate their rupture characteristics and scaling relationships to large earthquakes we analyze seismograms of borehole accelerometers recorded with high sampling rate 15 khz within 200 m of the hypocenters at the depth of 2650 m the waveform data have very high signal to noise ratio and no significant later phases are observed at all stations corner frequencies and quality factors of the anelastic attenuation q are estimated from spectra of velocity seismograms by assuming the omega squared model of boatwright 1978 we also investigate moment tensors for double couple solutions and volumetric components from the waveform inversion static stress drops of the 20 earthquakes calculated from the model of madariaga 1976 are from 3 2 to 88 mpa and scaled energies er mo the ratio of the radiated energy er to the seismic moment mo are from 4 2 10 6 to 1 1 10 4 we find that both the static stress drops and the scaled energies of the analyzed earthquakes are comparable to those values of larger earthquakes our results indicate that the dynamic rupture processes of these microearthquakes are similar to those of larger earthquakes

new perspectives on self similarity for shallow thrust earthquakes scaling of dynamic rupture processes from small to large earthquakes is critical to seismic hazard assessment large subduction earthquakes are typically remote and we mostly rely on teleseismic body waves to extract information on their slip rate functions we estimate the p wave source spectra of 942 thrust earthquakes of magnitude mw 5 5 and above by carefully removing wave propagation effects geometrical spreading attenuation and free surface effects the conventional spectral model of a single corner frequency and high frequency falloff rate does not explain our data and we instead introduce a double corner frequency model modified from the haskell propagating source model with an intermediate falloff of f 1 the first corner frequency f1 relates closely to the source duration t1 its scaling follows m0 t13 for mw 7 5 and changes to m0 t12 for larger earthquakes an elliptical rupture geometry better explains the observed scaling than circular crack models the second time scale t2 varies more weakly with moment m0 t25 varies weakly with depth and can be interpreted either as expressions of starting and stopping phases as a pulse like rupture or a dynamic weakening process estimated stress drops and scaled energy ratio of radiated energy over seismic moment are both invariant with seismic moment however the observed earthquakes are not self similar because their source geometry and spectral shapes vary with earthquake size we find and map global variations of these source parameters

an apparent mechanism dependence of radiated seismic energy we develop an extension to the method of boatwright and choy 1986 for determining the radiated seismic energy es that accounts for factors that bias the estimate we apply our technique to 204 events worldwide during the period 1992 1999 and find that the apparent stress is on average largest for strike slip events 0 70 mpa while for reverse and normal events it is significantly smaller 0 15 and 0 25 mpa respectively these results support the mechanism dependence of es reported by choy and boatwright 1995 although we find that once likely sources of bias are accounted for the mechanism dependence is not as strong as found previously the source of the mechanism dependence is unclear but one possibility is that it reflects a mechanism dependent difference in the stress drop this hypothesis is suggested by the scaling of slip with width in large strike slip earthquakes and makes two predictions which could be used to test it the first is that the discrepancy should disappear for the very largest dip slip earthquakes as the length of the fault greatly exceeds the downdip extent the second is that the discrepancy ought to disappear for smaller earthquakes the first can not yet be tested due to a lack of recent very large dip slip earthquakes the second is supported by the lack of mechanism dependence to es for smaller earthquakes an alternative hypothesis is that the apparent mechanism dependence could result if faults are opaque during rupture blocking seismic radiation across them brune 1996 this could cause radiated seismic energy to be trapped preferentially in the crust near the source volume for dipping faults there remains however a large discrepancy between estimates of es obtained from teleseismic versus regional data this discrepancy indicates a problem with teleseismic and or regional estimates of the seismic energy and must be resolved before a definite conclusion can be drawn

seismic energy release in mexican subduction zone earthquakes we estimated radiated seismic energy es from 18 shallow thrust mexican subduction zone earthquakes 4 1022 m 1 1 1028 dyne cm 11 h 37 km using digital accelerograms from the guerrero accelerograph array and neglecting stations with large site effects es is computed by integrating squared velocity spectra after applying geometrical spreading and q corrections we discarded epicentral recordings for the largest michoacan event we find that log es m 4 152 0 275 which gives a median value of es m and apparent stress a of 7 1 10 5 and 24 bars respectively the median es m value is in accordance with gutenberg and richter s g r 1956 formula for es in which es m 5 10 5 is implicit worldwide es m data where es is computed from local records mostly fall between 5 10 5 and 5 10 4 for events with m 1022 dyne cm on the other hand es m values generally lie between 5 10 6 and 5 10 5 if es is estimated from teleseismic records especially anomalous are the es m data from kikuchi and fukao 1988 for large and great earthquakes which fall near 5 10 6 thus while es from local data suggests that the g r relation seldom overestimates seismic energy release the teleseismic data point to the contrary the cause of this discrepancy may lie in the difficulty of resolving incoherent radiation from the fault and inappropriate choice of t in the analysis of teleseismic data

a method for calibration of the local magnitude scale based on relative spectral amplitudes and application to the san juan bautista california area we develop and use a spectral empirical green s function approach to estimate the relative source amplitudes of earthquakes near san juan bautista california we isolate the source amplitudes from path effects by comparing the recorded spectra of pairs of events with similar location and focal mechanism without computing the path effect with this method we estimate the relative moments of 1600 m 1 5 4 local earthquakes and we use these moments to recalibrate the duration magnitude scale in this region the estimated moments of these small earthquakes increase with catalog magnitude m d roughly proportionally to 101 1 m d slightly more slowly than a moment magnitude scaling of 101 5 m w this more accurate magnitude scaling can be used in analyses of the local earthquakes such as comparisons between the seismic moments and geodetic observations electronic supplement 1 additional description and figures showing estimated source amplitudes obtained with different parameters and observed amplitudes of some earthquakes with large misfits 1 http www bssaonline org lookup suppl doi 10 1785 0120160141 dc1

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

global and along strike variations of source duration and scaling for intermediate depth and deep focus earthquakes the systematic behavior of earthquake rupture as a function of earthquake magnitude and or tectonic setting is a key in our understanding of the physical mechanisms involved during earthquake rupture geophysical evidence suggests that although deep earthquakes including intermediate depth and deep are similar to shallow ones the mechanism involved during deep earthquakes is different from that of shallow ones in particular the magnitude and depth dependence of scaled duration a measure of earthquake rupture duration has led to controversy of what controls deep earthquake behavior here we estimate scaled source durations for 600 intermediate depth and deep focus earthquakes recorded at teleseismic distances and show deviation from self similar scaling no depth dependence is observed which we interpret as due to little differences between intermediate depth and deep focus earthquake mechanisms the data show no correlation between durations and plate age or thermal parameters suggesting that the thermal properties of the plate have little effect on source durations we nevertheless report differences in average source duration and scaling between subduction zones and along strike variations of source durations that more closely resemble the geometry of subduction flat or steep subduction rather than plate age

global patterns of radiated seismic energy and apparent stress radiated energies from shallow earthquakes with magnitudes 5 8 that occurred between 1986 and 1991 are used to examine global patterns of energy release and apparent stress in contrast to traditional methods which have relied upon empirical formulas these energies are computed through direct spectral analysis of broadband seismic waveforms velocity squared spectra of body waves are integrated after they have been corrected for effects arising from depth phases frequency dependent attenuation and focal mechanism the least squares regression fit of energy es to surface wave magnitude ms for a global set of 397 earthquakes yields log es 4 4 1 5ms which implies that the gutenberg richter relationship overestimates the energies of earthquakes the least squares fit between es and seismic moment m0 is given by the relationship es 1 6 10 5 m0 which yields 0 47 mpa as the average global value of apparent stress however the regression lines of both es ms and es m0 yield poor empirical predictors for the actual energy radiated by any given earthquake the scatter of data is more than an order of magnitude about each of the regression lines on the other hand global variations between es and mo while large are not random when subsets of es m0 are plotted as a function of seismic region and faulting type the scatter in data is substantially reduced the es m0 fits for many seismic regions and tectonic environments are very distinctive and a characteristic apparent stress c can be derived the lowest apparent stresses 3 0 mpa are associated with strike slip earthquakes that occur at oceanic ridge ridge transforms and in intraplate environments seaward of island arcs intermediate values of apparent stress 1 5 a 3 0 mpa are associated with strike slip earthquakes at incipient or transitional plate boundaries in general the dominant mode of failure for a tectonic environment is associated with the faulting type that has the lowest apparent stress an energy magnitude me can complement moment magnitude mw in describing the size of an earthquake me being derived from velocity power spectra is a measure of seismic potential for damage mw being derived from the low frequency asymptote of displacement spectra is more physically related to the final static displacement of an earthquake when earthquake size is ranked by moment a list of the largest events is dominated by earthquakes with thrust mechanisms when earthquake size is ranked by energy the list of the largest events is dominated by strike slip earthquakes

comprehensive analysis of earthquake source spectra in southern california we compute and analyze p wave spectra from earthquakes in southern california between 1989 and 2001 using a method that isolates source receiver and path dependent terms we correct observed source spectra for attenuation using both fixed and spatially varying empirical green s function methods estimated brune type stress drops for over 60 000 m l 1 5 to 3 1 earthquakes range from 0 2 to 20 mpa with no dependence on moment or local b value median computed stress drop increases with depth in the upper crust from about 0 6 mpa at the surface to about 2 2 mpa at 8 km where it levels off and remains nearly constant in the midcrust down to about 20 km however the results at shallow depths could also be explained as reduced rupture velocities near the surface rather than a change in stress drop spatially coherent variations in median stress drop are observed with generally low values for the imperial valley and northridge aftershocks and higher values for the eastern transverse ranges and the north end of the san jacinto fault we find no correlation between observed stress drop and distance from the san andreas and other major faults significant along strike variations in stress drop exist for aftershocks of the 1992 landers earthquake which may correlate with differences in main shock slip

temporal changes in stress drop frictional strength and earthquake size distribution in the 2011 yamagata fukushima ne japan earthquake swarm caused by fluid migration

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

moment energy stress drop and source spectra of western united states earthquakes from regional coda envelopes we present a new method to estimate stable seismic source parameters such as energy moment and orowan stress drop using regional coda envelopes from as few as one broadband station we use the method to compute path and site corrected seismic moment rate spectra for 117 recent western united states earthquakes empirical green s function corrections were applied to our surface and body wave coda envelope measurements to generate s wave source spectra these source spectra provide stable single station estimates of radiated seismic energy es and seismic moment mo that for common events are in excellent agreement with network averaged estimates obtained using local and regional data teleseismic moment estimates are compatible with our regional results but teleseismic energy estimates appear to be nearly an order of magnitude low we estimated the seismic moment of events ranging between mw 2 2 and 7 3 and energy estimates for which we had measured at least 70 of the total energy generally events above mw 3 3 we use these estimates to examine the behavior of derived parameters such as the orowan stress drop 2 es mo while the earthquakes we studied have a small range in orowan stress drop generally between 0 1 and 20 mpa they show a strong tendency for orowan stress drop to increase with moment approximately as mo0 25 we believe this is a source effect and is not due to inadequate bandwidth or attenuation correction and note that this trend appears to continue for microearthquakes as described in a recent deep borehole study in southern california many of the large high stress drop earthquakes show complexity in their moment rate spectra near the corner frequency and cannot be fit by a simple square model instead above the first corner frequency the spectral decay ranges between f 1 0 and f 1 5 this leads to larger estimates of radiated energy than predicted with a simple square model and has implications for seismic hazard estimation coda envelopes have three main advantages over direct arrivals for estimating seismic moment and energy 1 coda amplitudes vary little with geology and source radiation anisotropy and allow accurate single station applications 2 path corrected coda amplitude measurements can be applied to very large regions allowing a comparison of source parameters throughout the western united states using a common methodology and stations 3 because long period coda can last for hours for large local and regional events it allows the analysis of seismograms with clipped early arrivals

spectral analysis of dike induced earthquakes in afar ethiopia shallow dike intrusions may be accompanied by fault slip above the dikes a superposition which complicates seismic and geodetic data analyses the diverse volcano tectonic and low frequency local earthquakes accompanying the 2005 2010 large volume dike intrusions in the dabbahu manda hararo rift afar some with fault displacements of up to 3m at the surface provide an opportunity to examine the relations among the earthquakes dike intrusions and surface ruptures we apply the frequency index fi method to characterize the spectra of swarm earthquakes from six of the dikes these earthquakes often have broad spectra with multiple peaks making the usual peak frequency classification method unreliable our results show a general bimodal character with high fi earthquakes associated with deeper dikes top 3 km subsurface and low fi earthquakes associated with shallow dikes indicating that shallow dikes result in earthquakes with more low frequency content and larger amplitude surface waves low fi earthquakes are more common during dike emplacement suggesting that interactions between the dike and faults may lead to lower fi taken together likely source processes for low fi earthquakes are shallow hypocenters 3 km possibly with surface rupture slow rupture velocities and interactions with dike fluids strong site effects also heavily influence the earthquake spectral content additionally our results suggest a continuum of spectral responses implying either that impulsive volcano tectonic earthquakes and the unusual emergent earthquakes have similar source processes or that simple spectral analyses such as fi cannot distinguish different source processes

source parameters and radiation efficiency for intermediate depth earthquakes in northeast japan we estimated source parameters of 216 intermediate depth 65 150 km earthquakes mw 4 0 7 0 in the pacific slab beneath japan along using hi net data we made determinations of static stress drop radiated energy and radiation efficiency along with estimates of the whole path attenuation to study the source scaling as a function of earthquake size and depth our results show that there is a small increase in the values of the ratio of radiated energy to seismicmoment as a function of seismic moment which is due to an associated slight increase of static stress drop with earthquake size we also estimated the radiation efficiency for these events using the static stress drops and radiated energies the values of radiation efficiency are slightly lower compared to shallow crustal earthquakes these results indicate that dissipative energy processes may be relatively more important for intermediate depth earthquakes

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

time lapse change in anisotropy in japan s near surface after the 2011 tohoku oki earthquake 1 we apply seismic interferometry to strong motion records to detect the near surface i e an upper few hundred meters deep change in anisotropy caused by the mw9 0 tohoku oki earthquake on 11 march 2011 we show that the earthquake increased the difference between fast and slow shear wave velocities arising from shear wave splitting in most parts of northeastern japan but it did not significantly change fast shear wave polarization directions in the near surface through monitoring of anisotropy and shear wave velocity we find that the changes in anisotropy and velocity partially recover with time they are however still different from the pre event values after nine months the comparison of the spatial distribution between changes in anisotropy and velocity indicates the changes in anisotropy and velocity are generally correlated especially in the northeastern honshu the main island in japan the change in the largest principal stress direction weakly correlates with the change in anisotropy

low stress drop earthquakes in the rupture zone of the 1992 nicaragua tsunami earthquake tsunami earthquakes events that generate larger than expected tsunami and are deficient in high frequency seismic radiation are rare but hazardous to coastal populations one model for these events is shallow rupture through low strength materials we calculate seismic moment corner frequency and stress drop for 216 earthquakes 2 1 mw 4 7 november 2005 june 2006 within and external to the 1992 nicaragua tsunami earthquake rupture zone to test the hypothesis that differences in fault zone properties defined the limits of the 1992 tsunami rupture zone and continue to produce spatial variations in earthquake source properties mean stress drop of events within the rupture area is 1 2 mpa and 5 5 mpa for events just outside of the rupture zone with similar magnitude earthquakes in each group our results demonstrate different source parameter characteristics for microseismicity in the region of a past tsunami earthquake

stress drops and radiated energies of aftershocks of the 1994 northridge california earthquake we study stress levels and radiated energy to infer the rupture characteristics and scaling relationships of aftershocks and other southern california earthquakes we use empirical green functions to obtain source time functions for 47 of the larger m 4 0 aftershocks of the 1994 northridge california earthquake m6 7 we estimate static and dynamic stress drops from the source time functions and compare them to well calibrated estimates of the radiated energy our measurements of radiated energy are relatively low compared to the static stress drops indicating that the static and dynamic stress drops are of similar magnitude this is confirmed by our direct estimates of the dynamic stress drops combining our results for the northridge aftershocks with data from other southern california earthquakes appears to show an increase in the ratio of radiated energy to moment with increasing moment there is no corresponding increase in the static stress drop this systematic change in earthquake scaling from smaller to larger m3 to m7 earthquakes suggests differences in rupture properties that may be attributed to differences of dynamic friction or stress levels on the faults

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

investigating microearthquake finite source attributes with iris community wavefield demonstration experiment in oklahoma author posting the authors 2018 this article is posted here by permission of the royal astronomical society for personal use not for redistribution the definitive version was published in geophysical journal international 215 2018 1072 1087 doi 10 1093 gji ggy203