source finiteness of large earthquakes measured from long period rayleigh waves the source finiteness parameters of 11 large shallow earthquakes were determined from long period rayleigh waves recorded by the global digital seismograph network and international deployment of accelerometers networks the basic data sets are the seismic spectra of periods from 150 to 300 s in the determination of source process times we used furumoto s phase method and a linear inversion method in which we simultaneously inverted the spectra and determined the source process time that minimizes the error in the inversion these two methods yielded consistent results the source process times of the sumbawa indonesia colombia ecuador valparaiso chile and michoacan mexico earthquakes were estimated to be 79 118 69 and 77 s respectively from the linear inversion method the source process times determined from long period surface waves were in general longer than those obtained from body waves source finiteness of large shallow earthquakes with rupture on a fault plane with a large aspect ratio was modeled with the source finiteness function introduced by ben menahem the spectra were inverted to find the extent and direction of the rupture of the earthquake that minimize the error in the inversion for a rupture velocity of 2 5 km s 1 the estimated rupture was unilateral 100 km long and along the strike n26 w for the may 26 1983 akita oki japan earthquake 165 km and s57 e for the september 19 1985 michoacan mexico earthquake 256 km and n31 e for the december 12 1979 colombia ecuador earthquake and 149 km and s15 w for the march 3 1985 valparaiso chile earthquake the results for the august 19 1977 sumbawa indonesia earthquake showed that the rupture was bilateral and in the direction n60 e these results are in general consistent with the rupture extent inferred from the aftershock area of these earthquakes

metastable olivine wedge and deep dry cold slab beneath southwest japan abstract oceanic plates subducted at trenches penetrate into the deep mantle and encounter a structural boundary at a depth of 410 km where olivine the dominant element of mantle rocks transforms into a higher density form wadsleyite this transformation may be delayed within the coldest core of subducting plates slabs due to kinetic effects and it has been suggested that metastable olivine may persist deeper than 410 km using high density seismic array data in japan we show the direct image of the structure corresponding to this metastable olivine wedge mow beneath southwest japan numerical simulation of a subducting slab including the kinetic effect of water h 2 o on the olivine wadsleyite transformation indicates that the presence of the imaged mow requires an insignificant amount of water less than 100 wt ppm be present in the slab mantle thus a deep dry cold slab we infer that the transportation of water into the deep mantle occurs along the top surface of the subducting slab but no significant amount within the slab itself we also demonstrate that a numerical simulation including the kinetics of 660 km phase transformation can reconcile the observed deep depression of the 660 km discontinuity with a gentle clapeyron slope

extrusion tectonics of the okhotsk plate northeast asia based on focal mechanism geologic and lineament data faulting in the chersky range northeast asia changes from right lateral transpression between north america and eurasia to left lateral strike slip between north america and the okhotsk plate the location of the okhotsk eurasia boundary is poorly constrained available data suggest this boundary is right lateral the okhotsk plate is being compressed and extruded from between north america and eurasia resulting in high levels of microseismic activity along the southern flanks of the chersky range

inversion of complex body waves we have developed a method that inverts seismic body waves to determine the mechanism and rupture pattern of earthquakes the rupture pattern is represented as a sequence of subevents distributed on the fault plane this method is an extension of our earlier method in which the subevent mechanisms were fixed in the new method the subevent mechanisms are determined from the data and are allowed to vary during the sequence when subevent mechanisms are allowed to vary however the inversion often becomes unstable because of the complex trade offs between the mechanism the timing and the location of the subevents many different subevent sequences can explain the same data equally well and it is important to determine the range of allowable solutions some constraints must be imposed on the solution to stabilize the inversion we have developed a procedure to explore the range of allowable solutions and appropriate constraints in this procedure a network of grid points is constructed on the i plane where and i are respectively the onset time and the distance from the epicenter of a subevent the best fit subevent is determined at all grid points then the correlation is computed between the synthetic waveform for each subevent and the observed waveform the correlation as a function of and i and the best fit mechanisms computed at each i grid point depict the character of allowable solutions and facilitate a decision on the appropriate constraints to be imposed on the solution the method is illustrated using the data for the 1976 guatemala earthquake

mechanisms for precipitation variability of the eastern brazil sacz convective margin the present study examines the mechanisms for the connection between the precipitation variability in eastern brazil and the south atlantic convergence zone sacz convective margin eastern brazil sacz convective margin and the variability of low level inflow on interannual time scales during austral summer theauthors methodologyisbasedontheanalysisofobservationaldatasetsandsimulationsby theuniversity of california los angeles ucla atmospheric general circulation model agcm coupled to the simplified simple biosphere model it is demonstrated that the inflow variability is associated with the leading mode of wind variability over subtropicalsouth america andtheconnection isestablishedthroughthemechanismofananalyticprototype for convective margin shifts proposed in previous studies over the eastern brazil sacz convective margin the weaker stronger convection tends to occur together with stronger weaker low level inflows in reference to the mean easterly trades by changing the ventilation effect stronger weaker inflows with low moist static energy from the atlantic ocean suppress promote convection the causal relationship is verified by agcm mechanism testing experiments performed in perpetual february mode in which low level nondivergent wind perturbations are imposed in a region overlapping eastern brazil and the western atlantic ocean with solely the imposed wind perturbations acting on the moisture advection in the model equation the agcm can reproduce the precipitation variability in the eastern brazil sacz convective margin the capability of the agcm in capturing such precipitation sensitivity to the low level inflow variability also suggests that the mechanism can be applied to other regions of convective margins or to other time scales

rupture process of the 1983 japan sea akita oki earthquake using a waveform inversion method the rupture process of the 1983 japan sea earthquake mjma 7 7 is determined by applying waveform inversion of displacement type strong motion records based on the bayesian method the synthesis of the seismic motions from the main shock is made using the records from the two aftershocks mjma 7 1 and mjma 6 1 as empirical green s functions the main shock fault consists of two subfaults the aftershock m 6 1 occurring south of the main shock fault is used for the southern subfault empirical green s function and the aftershock m 7 1 occurring north of the main shock fault is used for the northern subfault in this synthesis it is not necessary to calculate propagation path and local site effects therefore the information about the source process can be extracted from the comparison between observed seismic motions and the synthetic ones without detailed information on the velocity structure along the whole path from the source to each station the inversion for the rupture process is attempted for both a line source model and an area source model in both models the main shock fault surface is divided into several elements whose sizes are determined from the scaling relations between the main shock and its aftershocks the slip displacement and the rupture starting time on each element are estimated as model parameters in the inversion a good convergence is obtained after about 10 iteration steps for the line source case and after 5 iteration steps for the area source case the results are summarized 1 the average rupture velocity is approximately 2 5 km sec for the southern subfault and 2 0 km sec for the northern subfault and 2 there is a large slip displacement near the rupture initiation point and the north edge of the fault thus there is considerable heterogeneity in rupture propagation and slip distribution over the fault plane

nied seismic moment tensor catalogue for regional earthquakes around japan quality test and application abstract we have examined the quality of the national research institute for earth science and disaster prevention nied seismic moment tensor mt catalogue obtained using a regional broadband seismic network freesia first we examined using synthetic waveforms the robustness of the solutions with regard to data noise as well as to errors in the velocity structure and focal location then to estimate the reliability robustness and validity of the catalogue we compared it with the harvard centroid moment tensor cmt catalogue as well as the japan meteorological agency jma focal mechanism catalogue we found out that the nied catalogue is consistent with harvard and jma catalogues within the uncertainty of 0 1 in moment magnitude 10 km in depth and 15 in direction of the stress axes the nied mt catalogue succeeded in reducing to 3 5 the lower limit of moment magnitude above which the moment tensor could be reliably estimated finally we estimated the stress tensors in several different regions by using the nied mt catalogue this enables us to elucidate the stress deformation field in and around the japanese islands to understand the mode of deformation and applied stress moreover we identified a region of abnormal stress in a swarm area from stress tensor estimates

incipient subduction and deduction along the eastern margin of the japan sea the eastern margin of the japan sea has been under convergent tectonics since sometime after the pliocene the suture line is on the ocean continent boundary between the japan yamato basins and the tohoku northeast japan arc incipient subduction and obduction of the oceanic and sub oceanic crust are observed along the suture line with the occurrence of numerous n s trending fault bounded ridges and troughs focal mechanism solutions of several compressional type earthquakes with magnitudes of m 6 9 to 7 7 which have occurred along the zone are consistent with the observation of geological thrust faults the convergent stresses in the japan sea may be due to india eurasia collision and its associated intra plate or inter microplate movements in east asia the eastward movement of the amurian plate causes baikal extension along its western margin and the japan sea convergence along its eastern margin

centroid single force inversion of seismic waves generated by landslides the centroid moment tensor cmt waveform inversion method of dziewonski et al 1981 is modified to analyze long period seismic waves generated by single force events such as the gigantic landslides associated with the 1980 eruption of mount st helens we refer to the method as centroid single force csf inversion as the result of the inversion we obtain the spatio temporal centroid and three components of a vector we call the csf vector which is the seismic point source representation of a landslide and whose direction is the opposite of the direction of sliding the sealer magnitude of the csf vector measures the overall size of the landslide and is given by mcsf md where m is the mass of the sliding object and d is the sliding distance we apply csf inversion to the long period surface waves generated by the 1980 mount st helens event the 1975 kalapana earthquake and the 1974 mantaro landslide using seismograms from the gdsn ida and hglp networks the csf solution for the st helens event is remarkably consistent with the actual geological observations and proves the efficacy of csf inversion the csf solution for the kalapana event does not fit the overall waveforms better than the cmt solution does however because the cmt solution does not explain the observed love wave radiation pattern it may be necessary to invoke a combination of both types of mechanism for this event although the geometry of the csf solution the direction of the force for the mantaro event is consistent with the actual landslide mcsf is about 5 times smaller than that expected from the mass and travel distance of the landslide estimated by geological observations this discrepancy may suggest either the relatively aseismic nature of this landslide or that the total volume of the slide was overestimated by analogy to single station cmt inversion single station csf inversion also appears to be stable and useful

gutenberg richter law for deep earthquakes revisited a dual mechanism hypothesis deep earthquake b values appear to vary with slab thermal state and earthquake magnitude the physical reason for the variations and the relation with deep rupture mechanisms are still unclear here i confirm the spatial variations of b value and the dependence on slab temperature using about 40 yr of data from the global centroid moment tensor catalog a new bimodal pattern is observed for the 500 700 km depth range b is close to 1 in the cold tonga slab while in warmer slabs e g south america japan kuril izu bonin mariana b is close to 0 5 for intermediate magnitudes m w 5 3 6 5 and increases to 1 for large magnitudes m w 6 5 to explain these observations i propose a dual mechanism hypothesis in which deep earthquakes nucleate only within the metastable olivine wedge mow but can rupture outside mow by a different mechanism the fractal dimension of earthquake size distribution changes from 2 to 1 as the thermally controlled mow thickness decreases and back to 2 as the mechanism outside mow dominates

global large deep focus earthquakes source process and cascading failure of shear instability as a unified physical mechanism abstract we apply a multiple source inversion method to systematically study the source processes of 25 large deep focus depth 400 km earthquakes with mw 7 0 from 1994 to 2012 based on waveform modeling of p pp sh and ssh wave data the earthquakes are classified into three categories based on spatial distributions and focal mechanisms of the inferred sub events 1 category one with non planar distribution and variable focal mechanisms of sub events represented by the 1994 mw 8 2 bolivia earthquake and the 2013 mw 8 3 okhotsk earthquake 2 category two with planar distribution but focal mechanisms inconsistent with the plane including eighteen earthquakes and 3 category three with planar distribution and focal mechanisms consistent with the plane including six earthquakes we discuss possible physical mechanisms for earthquakes in each category in the context of plane rupture transformational faulting and shear thermal instability we suggest that the inferred source processes of large deep focus earthquakes can be best interpreted by cascading failure of shear thermal instabilities in pre existing weak zones with the perturbation of stress generated by a shear instability triggering another and focal mechanisms of the sub events controlled by orientations of the pre existing weak zones the proposed mechanism can also explain the observed great variability of focal mechanisms the presence of large values of clvd compensated linear vector dipole and the super shear rupture of deep focus earthquakes in the previous studies in addition our studies suggest existence of relationships of seismic moment source duration 3 and moment source dimension 3 in large deep focus earthquakes

the amurian plate motion and current plate kinematics in eastern asia we use global positioning system gps velocity data to model eastern asian plate kinematics out of 15 stations in korea russia china and japan studied here three sites considered to be on the stable interior of the hypothetical amurian plate showed eastward velocities as fast as 9 10 mm yr with respect to the eurasian plate they were stationary relative to each other to within 1 mm yr and these velocity vectors together with those of a few additional sites were used to accurately determine the instantaneous angular velocity euler vector of the amurian plate the predicted movement between the amurian and the north american plates is consistent with slip vectors along the eastern margin of the japan sea and sakhalin which reduces the necessity to postulate the existence of the okhotsk plate the euler vector of the amurian plate predicts left lateral movement along its boundary with the south china block consistent with neotectonic estimates of the displacement at the qinling fault possibly the southern boundary of the amurian plate the amurian plate offers a platform for models of interseismic strain buildup in southwest japan by the philippine sea plate subduction at the nankai trough slip vectors along the baikal rift the boundary between the amurian and the eurasian plates are largely inconsistent with the gps based euler vector suggesting an intrinsic difficulty in using earthquake slip vectors in continental rift zones for such studies

the 2013 okhotsk deep focus earthquake rupture beyond the metastable olivine wedge and thermally controlled rise time near the edge of a slab the 2013 m8 3 okhotsk earthquake involves two primary mechanisms of deep focus earthquake rupture mineral phase transformation of olivine to spinel and thermal shear instability backprojection imaging of broadband seismograms recorded by the north american and european networks indicates bilateral rupture toward ne and sse the rupture paths of the ne segment and other regional m7 earthquakes are confined in narrow regions along the slab contours consistent with the phase transformation mechanism however the sse rupture propagates a long distance across the slab and aftershocks are distributed across a 60 km wide zone beyond the plausible thickness of the metastable olivine wedge favoring thermal shear weakening while the ne rupture is only visible at high frequencies the sse rupture is consistently observed across a broad frequency range this frequency dependent rupture mode can be explained by lateral variations of rise time controlled by thermal thinning of the slab near its northern end

data dependent non double couple components of shallow earthquake source mechanisms effects of waveform inversion instability seismic moment tensors are routinely determined for global earthquakes using waveform inversions and the resulting double couple and non double couple characteristics are extensively used in tectonic analyses for shallow events several moment tensor components are intrinsically poorly resolved especially for surface wave inversions which can lead to artificial non double couple components or can obscure actual non double couple components in the source representations the relatively greater instability of surface wave inversions can cause differences between inversions based on only body waves and joint inversions of body and surface waves the harvard cmt catalog exhibits systematic variations in non double couple components with seismic moment which can be attributed to use of only body waves in inversions for small events and combined body and surface waves for large events systematic behavior of non double couple components with regional strain environment is significantly less dependent on seismic moment when solutions influenced by less stable surface waves are omitted

inversion of surface wave spectra for source parameters of large earthquakes using aspherical earth models abstract amplitude and phase spectra of rayleigh and love waves of periods of 150 to 300 s from eight large earthquakes which occurred between 1990 and 1993 are corrected for wave propagation and then inverted for the source duration rupture directivity and moment tensor of the earthquake source for various propagation anomalies predicted by models of the earth s aspherical elastic and anelastic structure the application of corrections for the focusing and take off azimuth anomaly in addition to conventional corrections for the phase anomaly improves inversions of surface waves rayleigh waves provide better constraints than love waves in the determination of source parameters the data consist of either only rayleigh waves or both love and rayleigh waves whenever the full moment tensor is involved for several earthquakes there is clear discrepancy between source parameters determined from different data sets particularly from rayleigh or love waves the moment tensor solution tends to underpredict observed amplitude spectra for data sets with large amplitude anomalies especially for love waves this study shows that 1 the 1990 sudan earthquake is anomalous for its unusually large non double couple component of the moment tensor 2 the 1990 iran earthquake has a strike slip mechanism with a subvertical nw striking nodal plane which is the fault plane inferred from surface ruptures 3 the 1991 costa rica earthquake may have a seismic moment larger than previously determined from long period surface waves 4 the 1992 nicaragua earthquake involves a predominant rupture parallel to the trench and a large centroid offset up dip to the trench axis and the latter process may be responsible for large tsunami generation 5 the 1993 hokkaido earthquake has a shallow dipping and west plunging nodal plane which is consistent with the p wave first motions but differs from the centroid moment tensor solutions

duration and depth of faulting of the 22 june 1977 tonga earthquake the 22 june 1977 mw 8 2 tonga earthquake has the longest rupture duration ever reported for a normal fault event the 150 km depth range spanned by aftershocks of the earthquake is also unusually large there has been substantial controversy over both the depth and duration of faulting for this great event obscuring its tectonic significance we study the source process of the tonga event using long period rayleigh waves recorded by the global digital seismograph network gdsn and international deployment of accelerometers ida networks for a standard assumption of a haskell source a total duration of 84 4 sec is obtained using a least squares inversion method we introduce the use of the spectral amplitude as a weighting factor in measuring the misfit between the data and a given source finiteness model which reduces the scatter and improves the resolution of source duration determined from data ranging in period from 150 to 300 sec using a more realistic shape for the source time function in the inversion drawing upon results from body wave analysis reveals a much longer 165 sec process time component of the source process of the tonga earthquake the fundamental mode rayleigh waves do not resolve any horizontal source directivity however the centroid depth of the earthquake is well resolved as 96 km with 90 per cent confidence range 93 104 km the estimated error in the depth determination due to the uncertainties in the source finiteness and earth models is only a few kilometers the results indicate that the rupture of the earthquake excited long period seismic waves at depths somewhat greater than the 70 to 80 km depth range where the primary bodywave radiation occurred favoring rupture on the steeply dipping plane of the focal mechanism the fundamental mode rayleigh waves with periods longer than 150 sec cannot resolve vertical extent of the faulting however additional information from body wave and free oscillation analyses indicates a vertical fault extent of about 50 km with a frequency dependent variation in seismic radiation with depth

anisotropic models of the upper mantle long period rayleigh wave and love wave dispersion data particularly for oceanic areas have not been simultaneously satisfied by an isotropic structure in this paper available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy anelastic dispersion sphericity and gravity we assume that the surface wave data represents an azimuthal average of actual velocities thus we can treat the mantle as transversely isotropic the resulting models for average earth average ocean and oceanic regions divided according to the age of the ocean floor are quite different from previous results which ignore the above effects the models show a low velocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studies the correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggestive for most of the earth sh sv in the vicinity of the low velocity zone neat the east pacific rise however sv sh at depth consistent with ascending flow anisotropy is as important as temperature in causing radial and lateral variations in velocity the models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age this layer defines the lid or seismic lithosphere in the pacific the lid thickens with age to a maximum thickness of 50 km this thickness is comparable to the thickness of the elastic lithosphere the lid thickness is thinner than derived using isotropic or pseudo isotropic procedures a new model for average earth is obtained which includes a thin lid this model extends the fit of a prem type model to shorter period surface waves

cenozoic intracontinental dextral motion in the okhotsk japan sea region a right lateral shear zone trending northerly along more than 2000 km is recognized from central japan to northern sakhalin it was active mainly during the neogene and has accommodated several hundreds of kilometers of displacement the whole structure of sakhalin is built on this shear zone en echelon sigmoidal folds and thrusts en echelon narrow miocene basins and a major discontinuity which is observed along more than 600 km the tym poronaisk fault characterize the deformation there in hokkaido en echelon folds and thrusts and a ductile shear zone with high temperature metamorphism constitute the southern extension of this transpressional shear zone it continues to the south as a zone of transtensional deformation along the eastern margin of japan sea as en echelon basins and dextral transfer faults observed as far south as noto peninsula and yatsuo basin the style of the shear zone thus evolves from transpressional in the north far from the subduction zone to transtensional in the south in the back arc region strike slip motion along this shear zone was primarily responsible for the dextral pull apart opening of japan sea during the early and middle miocene dextral motion is still active in the north along the tym poronaisk fault in sakhalin as well as on the continental margin of japan sea korea and asia mainland active e w compression replaced the dextral motion along the eastern margin of japan sea in late miocene time and incipient subduction began in the early quaternary

the 12 july 1993 hokkaido nansei oki japan earthquake effects of source complexity on surface wave radiation abstract we present an analysis of the data dependency of surface wave inversions for source parameters of the 12 july 1993 hokkaido nansei oki japan earthquake this dependency is demonstrated by differences between source mechanisms obtained from different data sets particularly from rayleigh waves or love waves although inversions of various data sets yield unanimously thrust fault mechanisms for the inversion of rayleigh waves the mechanism is characterized by a shallow dipping west plunging nodal plane which is consistent with p wave first motion data and the distribution of aftershocks close to the hypocenter however for the inversion of both rayleigh and love waves the mechanism is characterized by a shallow dipping east plunging nodal plane several numerical experiments were carried out to test a hypothesis that the data dependency is attributed to the effects of source complexity on the surface wave radiation with the source complexity being characterized by tempo spatial changes in focal mechanism and moment release during the rupture process the experiments show that source parameters obtained from inversions of surface waves with periods as long as a few hundred seconds can be largely affected by using various models of source complexity proposed previously for the hokkaido earthquake and the effects on love waves tend to be systematically different from those on rayleigh waves our preferred source model is characterized by significant tempo spatial changes in focal mechanism the experiments based on this model provide a good explanation for the data dependency although our analysis cannot completely reject the alternative explanation that attributes the dependency to the manifestation of errors in modeling the surface wave propagation and or inversion instability the model is consistent with the data of body waves and long period surface waves for a very broad frequency band implying the existence of weak zones with various fault geometries along the eastern margin of the japan sea

the mechanism of the 1983 japan sea earthquake as inferred from long period surface waves and tsunamis abstract the source process of the japan sea earthquake of may 26 1983 is studied by using the long period surface waves and tsunamis the moment tensor inversion of rayleigh waves which consider the lateral heterogeneity of the earth is developed and applied to the ida records of this event the moment tensor solution and first motion data indicate that the mechanism is dip slip and the seismic moment is 7 6 1027 dyne cm the fault is estimated to be 120 km in length 40 km in width and dips eastward with a dip angle of 30 from the aftershock distribution tsunami simulation for an actual topography is made to restrain the slip on the fault the aftershock area and the tsunami records suggest that the fault is divided into two segments the northern part strikes nnw and slips 4 m while the southern part strikes nne and slips 5 m the fault geometry the aspect ratio and the stress drop of this event are similar to those of the 1964 niigata earthquake but differ from those of the earthquakes in the pacific coast of japan

examination of slow and late moment release of the 1988 spitak and 1991 racha caucasus earthquakes summary two large shallow earthquakes occurred in the caucasus part of the collisional belt caused by the northward movement of the arabian plate with respect to the eurasian plate the 1988 december 7 spitak armenian m 6 7 and 1991 april 29 racha m 6 9 earthquakes in the present study slow and late moment releases of the earthquakes which were previously proposed based on the body wave analyses are examined using long period surface waves results from spectral inversions using fundamental mode surface waves show that the source durations of both earthquakes are about 20 s although additional investigations utilizing the long period surface waves which are optimized to detect slow and late moment release were employed no evidence of slow and late moment release was found for either earthquake for the racha earthquake the obtained source duration is consistent with the result from body wave analyses within the resolution of the body wave data the simple p and sh waveforms are well modelled by a source time history model with a duration of 20 s however for the spitak earthquake the source duration obtained from the surface waves is about 30 s shorter than the source model suggested in the body wave analysis this discrepancy is attributed to a slow and late thrust fault slip in the body wave source model which was proposed in order to interpret the late arrivals of p waves as the result of source complexity numerical experiments predict that rayleigh wave radiation is sensitive to the radiation from the proposed slow and late slip a comparison between the observed and predicted rayleigh wave radiation patterns however provides no indication of the surface wave radiation from the slow and late slip it is unlikely that the discrepancy in the source model is only due to errors in modelling the propagation of long period surface waves because for the racha earthquake the source models obtained from body and surface waves are consistent the present results thus indicate that the late arrivals of p waves are probably caused by something other than source complexity for example complex local structure near the earthquake source in the continental collisional belt for the spitak earthquake a large non double couple component is observed in the moment tensor solution obtained at long periods if the non double couple component is due to source complexity it should be produced within the 20 s rupture process

frequency moment distribution of deep earthquakes implications for the seismogenic zone at the bottom of slabs abstract we present a systematic investigation of the variation with depth of the frequency of earthquake occurrence vs seismic moment based on 16 years of harvard centroid moment tensor cmt solutions we analyze depth variations of earthquake size distribution in terms of variations in the absolute value of the slope of the regression of the logarithm of the population vs seismic moment a quantity known as the parameter the shallowest earthquakes 0 50 km depth exhibit a well defined and robust size distribution regime characterized by a discontinuous increase in with increasing moment others have shown that this increase probably represents the effects of a physical limit in the dimensions of the area of seismogenic slip of shallow earthquake sources the population of deep earthquakes in the depth interval 500 600 km shows two markedly different distributions the deep earthquakes in the tonga region feature an initially high value 0 92 at small moments and a lower value 0 41 at high moments in contrast the size distribution of non tonga deep events shows the reverse of those changes 0 41 at low moment and 1 17 at higher moment to help explain these observations we propose a model of deep seismogenesis that assumes three dimensional earthquake source regions that vary principally in their transverse dimensions the two segment behavior in the tonga region and other subduction zones is thought to represent in part constraints owing to the threshold of completeness of the cmt catalog and to its short time interval of sampling we interpret the differences between tonga and other deep wadati benioff zones as being a consequence of tonga s markedly higher subduction rate and hence its colder thermal structure and presumably thicker region of seismogenesis we interpret the critical moments at which values change in terms of variations in the transverse thickness of deep seismogenic zones and estimate that it is about 11 km for the tonga region and about 3 km for other zones at depths of 500 600 km these results are generally consistent with deep earthquakes being restricted to wedge shaped regions of peridotite persisting metastably to as deep as 700 km in old rapidly descending and hence cold slabs failure is thought to occur in metastable peridotite by transformational faulting great deep earthquakes present special challenges to any theory of deep earthquakes based on slab thermal structure for example a continuing question is how such large events can fit in a thermally controlled seismogenic zone that is diminishing in its transverse dimensions with increasing depth the very concept of a scale invariant earthquake size distribution may be inappropriate for these rare events and the unusual settings in which they are found

re examination of the 1940 shakotan oki earthquake and the fault parameters of the earthquakes along the eastern margin of the japan sea abstract the fault model of the 1940 shakotan oki japan earthquake of aug 1 1940 is re examined on the basis of magnitude aftershock distribution and tsunami data from a careful examination of the s p time distribution of aftershocks and comparison of the tide gauge records with numerical simulation of tsunami the fault area is estimated to be 100 km 35 km the slip 1 5 m and the seismic moment 2 4 1027 dyn cm the fault parameters estimated in this study are significantly different from those of fukao and furumoto and do not support their conclusion that this event has a very long duration and is a tsunami earthquake the source process time is estimated to be 30 s which is normal for an earthquake of this size fault parameters of six earthquakes along the eastern margin of the japan sea including the shakotan oki event are compiled and compared with those of inter plate earthquakes in the pacific ocean different relations from well known scaling laws of the inter plate shocks are found for the earthquakes in the japan sea dip angles aspect ratios of the fault and the average stress drop are larger in the japan sea than those of the pacific events although the seismic moment release per unit fault length is the same the differences can be interpreted in terms of a recent plate boundary model in which the young immature boundary between the north american and the eurasian plates lies at the eastern margin of the japan sea they also partially reflect the different excitation of the tsunami in the japan sea and the pacific ocean

evidence for transformational faulting from a deep double seismic zone in tonga double seismic zones planes or earthquakes parallel to the dip of a subducting slab and separated by 20 40 km provide important clues about the earthquake generating mechanisms and strain distribution inside subducting slabs double seismic zones have been found at intermediate depths 70 200 km in many subduction zones1 6 but have not been previously reported in deep slabs here by relocating earthquakes with a hypocentroidal decomposition technique7 and visualizing the earthquake positions and uncertainties in three dimensions we identify a double seismic zone at depths of 350 460 km in the tonga subduction zone source parameters of the earthquakes determined by waveform analysis suggest different stress orientations for the two zones with in plane compression in the lower zone and in plane tension in the upper zone the double zone may be due to transformational faulting as olivine along the edges of a metastable olivine wedge becomes warmer and transforms to spinel8 11

collision rotation and back arc spreading in the region of the okhotsk and japan seas the india eurasia collision caused extensive deformation in the eurasia continent since late eocene time we propose that back arc spreading in the okhotsk and japan seas was related to the movement of microplates relevant to the india eurasia collision the kuril basin of the okhotsk sea and the basins of the japan sea were formed as back arc basins simultaneously their late oligocene to middle miocene age is constrained by sediment stratigraphy basement depth and heat flow data the movements of two microplates the okhotsk and amuria plates are significant for the tectonics of the okhotsk and japan seas simultaneous retreat of both microplates from trench hinge lines caused back arc spreading in the kuril basin and the japan sea the amuria plate moved north northeastward due to the india eurasia collision this caused pull apart opening of the baikal rift along a transform boundary between the siberia and amuria plates and a collision along the stanovoy range at its northern margin this movement triggered a clockwise rotation of the okhotsk plate with a component of dextral collision between the okhotsk and amuria plates which is well observed along the central zone of the sakhalin hokkaido islands between the two back arc plates the clockwise rotation of the okhotsk plate is suggested by the southwestward fan shaped opening of the kuril basin the kuril basin narrows to the northeast and terminates south of the kamchatka peninsula where a relative rotation pole between the okhotsk and kuril forearc plates is located the kamchatka peninsula was a zone of collision on the other side of the clockwise rotating okhotsk plate during the opening of the kuril basin the sredinny range in the kamchatka peninsula is one of the results of the collision between the okhotsk plate and the forearc plate of the kuril arc the bending of the japanese islands occurred in association with the back arc spreading of the yamato basin of the japan sea

a great earthquake doublet and seismic stress transfer cycle in the central kuril islands temporal variations of the frictional resistance on subduction zone plate boundary faults associated with the stick slip cycle of large interplate earthquakes are thought to modulate the stress regime and earthquake activity within the subducting oceanic plate here we report on two great earthquakes that occurred near the kuril islands which shed light on this process and demonstrate the enhanced seismic hazard accompanying triggered faulting on 15 november 2006 an event of moment magnitude 8 3 ruptured the shallow dipping plate boundary along which the pacific plate descends beneath the central kuril arc the thrust ruptured a seismic gap that previously had uncertain seismogenic potential although the earlier occurrence of outer rise compressional events had suggested the presence of frictional resistance within minutes of this large underthrusting event intraplate extensional earthquakes commenced in the outer rise region seaward of the kuril trench and on 13 january 2007 an event of moment magnitude 8 1 ruptured a normal fault extending through the upper portion of the pacific plate producing one of the largest recorded shallow extensional earthquakes this energetic earthquake sequence demonstrates the stress transfer process within the subducting lithosphere and the distinct rupture characteristics of these great earthquakes illuminate differences in seismogenic properties and seismic hazard of such interplate and intraplate faults

is northern honshu a microplate abstract seismic slip vectors along the japan trench the eastern margin of the japan sea and the sagami trough are compared with global relative plate motions rm2 minster and jordan 1978 to test a new hypothesis that northern honshu japan is part of the north american plate this hypothesis also claims that the eastern margin of the japan sea is a nascent convergent plate boundary kobayashi 1983 nakamura 1983 seismic slip vectors along the japan trench are more parallel to the direction of the pacific north american relative motion than that of the pacific eurasian relative motion however the difference in calculated relative motions is too small avoid to the possibility that a systematic bias in seismic slip vectors due to anomalous velocity structure beneath island arcs causes this apparent coincidence seismic slip vectors and rates of shortening along the eastern margin of the japan sea for the past 400 years are also consistent with the relative motion between the north american and eurasian plates calculated there seismic slip vectors and horizontal crustal strain patterns revealed by geodetic surveys in south kanto beneath which the philippine sea plate is subducting indicate two major directions one is the relative motion between the north american and philippine sea plates and the other that between the eurasian and philippine sea plates one possible interpretation of this is that the eastern margin of the japan sea may be in an embryonic stage of plate convergence and the jump of the north american eurasian plate boundary from sakhalin central hokkaido to the eastern margin of the japan sea has not yet been accomplished in this case northern honshu is a microplate which does not have a driving force itself and its motion is affected by the surrounding major plates behaving as part of either the eurasian or north american plate another possibility is that the seismic slip vectors and crustal deformations in south kanto do not correctly represent the relative motion between plates but represent the stresses due to non rigid behaviors of part of northern honshu

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

effect of slab temperature on deep earthquake aftershock productivity and magnitude frequency relations deep earthquakes generally show fewer aftershocks and a larger variability in magnitude frequency relations than shallow earthquakes1 5 these characteristics and the factors that control them may place constraints on the mechanism of deep earthquakes which is still uncertain6 8 here we show that systematic variations in aftershock productivity and magnitude frequency relations are related to the temperature of the downgoing slab as inferred from the vertical velocity and age of the subducting lithosphere deep earthquakes with substantial aftershock sequences are found only in colder slabs and earthquakes in warmer slabs consistently show few aftershocks magnitude frequency relations for deep earthquakes also show systematic variations as a function of slab thermal structure with warmer slabs showing fewer small earthquakes lower b values the statistical properties of deep earthquakes thus appear to be temperature sensitive to an extent not observed for shallow earthquakes and not adequately explained by simple geometrical limitations on fault width

depths of large earthquakes determined from long period rayleigh waves the depths and source mechanisms of nine large shallow earthquakes were determined from long period 150 to 300 s rayleigh waves recorded by the global digital seismograph network gdsn and international deployment of accelerometers ida networks we inverted the data set of complex source spectra for a moment tensor linear or a double couple nonlinear by solving a least squares problem we obtained the centroid depth or the extent of the distributed source for each earthquake the depths and source mechanisms of large shallow earthquakes determined from long period rayleigh waves depend on the models of source finiteness wave propagation and excitation we tested various models of source finiteness q group velocity and excitation in the determination of earthquake depths in order to determine the depth of large earthquakes from long period surface waves source finiteness effects must be corrected using adequate models the depth estimates obtained using the q model of dziewonski and steim 1982 and the excitation functions computed for the average ocean model of regan and anderson 1984 are considered most reasonable dziewonski and steim s q model represents a good global average of q determined over a period range of the rayleigh waves used in this study since most of the earthquakes studied here occurred in subduction zones regan and anderson s average ocean model is considered most appropriate our depth estimates are in general consistent with the harvard centroid moment tensor cmt solutions the centroid depths and their 90 confidence intervals numbers in parentheses determined by the student s t test are colombia ecuador earthquake december 12 1979 d 11 km 9 24 km santa cruz island earthquake july 17 1980 d 36 km 18 46 km samoa earthquake september 1 1981 d 15 km 9 26 km playa azul mexico earthquake october 25 1981 d 41 km 28 49 km el salvador earthquake june 19 1982 d 49 km 41 55 km new ireland earthquake march 18 1983 d 75 km 72 79 km chagos bank earthquake november 30 1983 d 31 km 16 41 km valparaiso chile earthquake march 3 1985 d 44 km 15 54 km michoacan mexico earthquake september 19 1985 d 24 km 12 34 km

temporal variation in the magnitude frequency distribution during the guy greenbrier earthquake sequence the recent increase in earthquake activity in the central u s has led to concerns about the hazard posed by induced earthquakes understanding earthquake phenomena and monitoring in all settings can be improved by the detection of small events however the catalog of induced earthquakes is incomplete for small events due to the sparse instrumentation this is particularly true in settings of low background seismicity like the central u s we apply single station template matching to detect small earthquakes during the guy greenbrier sequence in central arkansas and find over 100 times more earthquakes than are registered in the advanced national seismic system catalog between july 2010 and october 2011 a complete catalog over nearly 4 units of magnitude enables us to analyze the magnitude frequency distribution of induced earthquakes we find that earthquakes deviated from the gutenberg richter statistics during the operation of nearby injection wells but returned to gutenberg richter statistics after the wells were shut in

a test of present day plate geometries for northeast asia and japan alternative geometries for the present day configuration of plate boundaries in northeast asia and japan are tested using nuvel 1 and 256 horizontal earthquake slip vectors from the japan and northern kuril trenches statistical analysis of the slip vectors is used to determine whether the north american eurasian or okhotsk plate overlies the trench along the northern kuril trench sup vectors are well fit by the nuvel 1 pacific north america euler pole but are poorly fit by the pacific eurasia euler pole results for the japan trench are less conclusive but suggest that much of honshu and hokkaido are also part of the north american plate the simplest geometry consistent with the trench slip vectors is a geometry in which the north american plate extends south to 41 n and possibly includes northern honshu and southern hokkaido although these results imply that the diffuse seismicity that connects the lena river delta to sakhalin island and the eastern sea of japan records motion between eurasia and north america onshore geologic and seismic data define an additional belt of seismicity in siberia that cannot be explained with this geometry assuming that these two seismic belts constitute evidence for an okhotsk block two published kinematic models for motion of the okhotsk block are tested the first model which predicts motion of up to 15 mm yr 1 relative to north america is rejected because kuril and japan trench slip vectors are fit more poorly than for the simpler geometry described above the second model gives a good fit to the trench slip vectors but only if okhotsk north america motion is slower than 5 mm yr 1

determination of earthquake source mechanisms using teleseismic 30 140 s waves the january 17 1994 northridge earthquake complete seismic waveforms with periods between 30 and 140 s recorded at teleseismic distances 10 are used to determine the source mechanism of the january 17 1994 northridge earthquake ms 6 8 an algorithm called the earth simplifying transformation est is applied to the mainshock primary event data to calibrate and remove propagation effects of earth s lateral and radial heterogeneities that are not predicted by a reference earth model the procedure involves frequency domain division of each pair of observed and synthetic waveforms for an auxiliary event with a well constrained source mechanism in proximity to the primary event with the synthetics being computed for a reference earth model if the auxiliary event source mechanism is correct the differences between the data and synthetics represent the residual effects of the earth s structure that are not predicted by the earth model the frequency dependent deconvolution filters are convolved with the corresponding observed signals for the primary event the resulting waveforms are then used to determine the source mechanism of the primary event by forward modeling and by centroid moment tensor inversion with excellent fits to the complete waveforms being achieved the resulting solution for the northridge event has a centroid depth of 12 1 km and a mechanism with strike 115 dip 40 and rake 95 with 5 uncertainty for each parameter the est procedure holds promise for reliable source inversion for small earthquakes in a region calibrated by large events with well determined source parameters