simultaneous rupture along two conjugate planes of the wharton basin earthquake analysis of broadband teleseismic data shows that the 18 june 2000 wharton basin earthquake a moment magnitude 7 8 intraplate event in the region of diffuse deformation separating the indian and australian plates consisted of two subevents that simultaneously ruptured two near conjugate planes this mode of rupture accommodates shortening by a mechanism different from that previously known elsewhere in the region the larger subevent occurred on a fossil fracture zone with a relatively high stress drop of about 20 megapascals showing that large stresses can accumulate in regions of distributed deformation

selection of earthquake scaling relationships for seismic hazard analysis a fundamentally important but typically abbreviated component of seismic hazard analysis is the selection of earthquake scaling relationships these are typically regressions of historical earthquake datasets in which magnitude is estimated from parameters such as fault rupture length and area the mix of historical data from different tectonic environments and the different forms of the regression equations can result in large differences in magnitude estimates for a given fault rupture length or area we compile a worldwide set of regressions and make a first order shortlisting of regressions according to their relevance to a range of tectonic regimes plate tectonic setting and fault slip type in existence around the world regression relevance is based largely on the geographical distribution age and quantity quality of earthquake data used to develop them our compilation is limited to regressions of magnitude or seismic moment on fault rupture area or length and our shortlisted regressions show a large magnitude range up to a full magnitude unit for a given rupture length or area across the various tectonic regimes these large differences in magnitude estimates underline the importance of choosing regressions carefully for seismic hazard application in different tectonic environments

long period seismic radiation from the may 23 1989 macquarie ridge earthquake evidence for coseismic slip in the mantle long period seismic source parameters of the may 23 1989 macquarie ridge earthquake are determined using a surface wave inversion procedure that incorporates detailed source time functions obtained from shorter period body waves the seismic source model obtained using this method is consistent with observations of both body waves and long period rayleigh waves from the earthquake the macquarie ridge earthquake rupture has a centroid time 28 s and a right lateral strike slip fault mechanism with a rake of 175 on a vertical fault plane striking n38 e this mechanism is consistent with p wave first motions of the event inversions performed for various earth models demonstrate that the choice of surface wave attenuation model in particular affects the estimates of centroid depth and seismic moment significantly allowing for uncertainty in attenuation the long period rayleigh waves periods from 150 to 300 s indicate that the macquarie ridge earthquake had a seismic moment of 1 9 0 2 1021 n m and a corresponding centroid depth of 21 6 km the static stress drop calculated using the depth and seismic moment is 0 7 0 5 107 pa 70 50 bars the centroid depth combined with the lack of resolvable directivity of the earthquake rupture suggests that significant slip occurred beneath the moho which has a maximum depth of about 16 km in the epicentral region the mantle slip component may have preferentially radiated long period seismic energy given the shallow centroid depths and low moments determined for the event from the shorter period body wave observations

distance and azimuthal dependence of ground motion variability for unilateral strike slip ruptures abstract we investigate near field ground motion variability by computing the seismic wavefield for five kinematic unilateral rupture models of the 1992 m w 7 3 landers earthquake eight simplified unilateral rupture models based on the landers event and a large m w 7 8 shakeout scenario we include the geometrical fault complexity and consider different 1d velocity density profiles for the landers simulations and a 3d heterogeneous earth structure for the shakeout scenario for the landers earthquake the computed waveforms are validated using strong motion recordings we analyze the simulated ground motion data set in terms of distance and azimuth dependence of peak ground velocity pgv our simulations reveal that intraevent ground motion variability is higher in close distances to the fault ln pgv is well described by a cauchy lorentz function that provides a novel empirical quantification to model the spatial dependency of ground motion online material figures of slip distributions residuals to ground motion prediction equations gmpes distance and azimuthal dependence and directivity predictor of ground motion variability for different source models

strike slip earthquakes on quasi vertical transcurrent faults inferences for general scaling relations the recent occurrence of several large strike slip earthquakes provides the opportunity to review and complement available data on the scaling of seismic moment mo with length of rupture l for large earthquakes depending on their tectonic setting and mechanism for strike slip earthquakes on quasi vertical transcurrent faults the mo versus l relation has a significant change of slope around mo 0 6 0 8 1020 n m and for larger earthquakes mo scales linearly with l this is compatible with models where slip is controlled by the width of the fault also it appears to be easier to categorize large earthquakes by their mechanism strike slip on vertical transcurrent fault versus pure thrust normal than their tectonic setting interplate intraplate

quantitative relations of seismic source parameters and a classification of earthquakes abstract relations between earthquake parameters moment m0 fault area s fault length l and width w stress drop time characteristics and magnitudes and faulting type dip slip ds and strike slip ss are quantitatively analyzed using a dataset of 240 events m 5 the analysis is carried further toward an earthquake systematization by introducing earthquake classes the results are 1 1 l w 2 1 for ds l w 2 30 for ss and l w 3 7 for giant m0 1029 dyne cm earthquakes respectively 2 2 log m0 1 5 log s 22 2 s in km2 and tentatively log m0 2 45 log s 17 49 for ds and ss and giant earthquakes respectively 3 3 the large scatter of data in m0 s dependences is the result of the combined effect of the variation in and l w 4 4 the concept of constant is replaced by variable to explain the large variations in relations between m0 s l and w for both ds and ss earthquakes and partly between body and surface wave magnitudes low intermediate and high stress drop gd 30 30 60 and 60 bar respectively earthquakes are defined 5 5 a relation of reciprocity exists between seismic slip fault length and width and stress drop 6 6 a saturation of s for some very large earthquakes is suggested from the interpretation of actual data on m0 s l w etc 7 7 the total source duration tsd increases with m0 in relation with earthquake type and tentatively log m0 2 16 log tsd 24 50 holds for ds earthquakes 8 8 log m0 1 5 mm 16 1 holds for mm brune engen mantle wave magnitude 8 5 8 75 9 9 more magnitudes of shorter or longer period on both body and surface wave basis are useful in constraining significant earthquake features 10 10 low and high frequency earthquakes can be distinguished using the gutenberg richter relation ms mb as a reference relation or a relation between ms and mmaxb 11 11 aki s similarity conditions are extended by adding two more conditions as to express more specifically four basic features geometry deformation frequency and time of the earthquake source 12 12 a reference earthquake is defined by criteria consistent with the similarity conditions 13 13 on this basis and in view of nonsimilarity of earthquakes in their totality a scheme for earthquake classification is proposed

updip and along strike aftershock migration model driven by afterslip application to the 2011 tohoku oki aftershock sequence

regional difference in scaling laws for large earthquakes and its tectonic implication we compiled 67 large earthquakes which occurred at and around plate boundaries for the last 140 yrs and classified them into four groups interplate strike slip events intraplate strike slip events underthrust events at island arc subduction zones and underthrust events at continental margin subduction zones for each group of earthquakes we examined relations between seismic moment m 0 fault length l fault width w and average fault slip d and found the following scaling laws in the case of interplate strike slip events the well known l cubed dependence of seismic moment breaks down when l exceeds 30 km because the extent of the seismogenic zone is limited in depth 12 km for large events l 30 km d and m 0 increase with l as d overline delta tau l mu left alpha l beta right and m 0 overline delta tau w l 2 left alpha l beta right respectively where the mean fault width bar w is 12 km and the mean stress drop overline delta tau is 1 8 mpa here and are structural parameters for intraplate strike slip events we obtained nearly the same relations except for significantly higher stress drop 3 1 mpa the difference in stress drop between interplate and intraplate events may be ascribed to the difference in stress accumulation rates and thus the recurrence time of earthquakes in the case of underthrust events at island arc subduction zones we also found the saturation of fault width bar w 120km and the breakaway from the l cubed dependence of m 0 for events larger than l 200 km if we consider the average dip angle of plate boundaries at island arc subduction zones to be 20 30 this indicates that the extent of the seismogenic zone in depth is limited to 40 60 km in the case of continental margin subduction zones on the other hand we could not find the saturation of fault width nor the breakaway from the l cubed dependence of m 0 from the analysis of the present data set w 200 km l 1000 km for sufficiently large earthquakes in general the downward rupture growth is limited to a certain depth due to the existence of a ductile unstressed region which extends under the brittle seismogenic zone since the brittle ductile transition occurs at 300 400 c the difference in the lower limit of the seismogenic zones between tectonically different regions may be attributed to the difference in thermal state there

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

large paleoearthquake timing and displacement near damak in eastern nepal on the himalayan frontal thrust an excavation across the himalayan frontal thrust near damak in eastern nepal shows displacement on a fault plane dipping 22 has produced vertical separation across a scarp equal to 5 5 m stratigraphic structural geometrical and radiocarbon observations are interpreted to indicate the displacement is the result of a single earthquake of 11 3 3 5 m of dip slip displacement that occurred 1146 1256 ad empirical scaling laws indicate that thrust earthquakes characterized by average displacements of this size may produce rupture lengths of 450 800 km and moment magnitudes mw of 8 6 to 9 sufficient strain has accumulated along this portion of the himalayan arc during the roughly 800 years since the 1146 1256 ad earthquake to produce another earthquake displacement of similar size

low frequency source characteristics of the great 1960 chilean earthquake the low frequency nature of the great 1960 chilean earthquake the earth s largest recorded event is characterized and a source model composed of three events with a combined seismic moment of 5 5 1023 n m and a duration of 1500 s is presented the results show conclusively that large scale slip which is only observed at low frequencies preceded the main shock complex amplitude measurements of normal mode data in the band 1 0 5 0 mhz recorded at eight vertical component stations comprise the data set in this band the earthquake source is assumed to be described by a line source propagating at a constant rupture velocity the data set is the basis for a sequence of least squares inversions to determine the seismic moment rupture velocity spatial slip distribution and the temporal slip function the data are best explained by a source model that begins 1150 s before the main shock with an event of moment 1 9 1023 n m and rise time of 300 s a main shock with moment of 3 2 1023 n m and for which most of the low frequency energy was released beginning about 50 s after the short period origin time and an event 350 s later with moment of 0 4 1023 n m the uncertainty in the moment estimate of the great 1960 chilean earthquake is about 50 and is due primarily to the probable range of fault plane dip which is not well constrained at this time

complexity of seismicity due to highly rate dependent friction we study a simple antiplane fault of finite length embedded in a homogeneous isotropic elastic solid in order to understand the origin of seismic source heterogeneity in the presence of nonlinear rate dependent friction all the mechanical properties of the medium and friction are assumed to be homogeneous starting from a heterogeneous initial stress distribution we apply a slowly increasing uniform stress load far from the fault and we simulate the seismicity for more than 20 000 events in some cases the style of seismicity produced by this model is determined by a control parameter which measures the degree of rate dependence of friction for classical friction models with rate independent friction no complexity appears and seismicity is perfectly periodic for weakly rate dependent friction seismicity becomes slightly nonperiodic but most events are still characteristic earthquakes when friction is highly rate dependent seismicity is completely irregular and ruptures of all sizes occur inside the fault highly rate dependent friction destabilizes the healing process producing premature healing of slip and partial stress drop premature healing causes rupture to take the form of narrow propagating slip episodes the so called heaton s 1990 pulses partial stress drop produces large variations in the state of stress which in turn produce earthquakes of different sizes we make the conjecture that all models in which static stress drop is only a fraction of the dynamic stress drop produce stress heterogeneity

appropriate boundary conditions for modeling very long earthquakes and physical consequences we have studied two sets of models to find appropriate boundary conditions for the theoretical modeling of very long earthquakes i e those for which the length l is much larger than the width w of the rectangular aftershock area and the resulting physical consequences in the first set we study the conventional rectangular crack model for l w 2 and 4 i e the stress drop is confined to a rectangular region and there is no rupture outside this region w model in the second set of models which is suggested by geologic data we constrain the stress drop to a rectangular zone seismogenic layer but we do not have any constraint on the rupture above and below this layer the applied stress in this region above and below the seismogenic layer is taken to be exactly equal to the yield stress of the material so that no stress drop occurs when it yields this implies that the material on either side of the seismogenic layer is shearing aseismically just before the earthquake occurs and also implies that the material in these regions is purely plastic the major conclusion of our work is that the second set of models the rupture propagates dynamically for some distance into these nonbrittle zones above and below the seismogenic layer this result is supported by geological evidence and also by recent seismic evidence that moments of some large earthquakes increase with increasing wavelength at very long periods the slip in large parts of these zones is found to be nonnegligible the slip is still confined to a finite width which may be considered as an effective width but this width is larger than the width of the seismogenic brittle layer this effective width increases as the length of the region of stress drop increases and may be larger than this length for long faults thus for the second set of models the aftershock area would underestimate the actual rupture area the moment and the slip at the center for the second set of models are larger than for the first set for the same l w ratio of the stress drop region even if we assume that there is no radiated energy from the regions above and below the seismogenic zone for l w 2 the duration of slip at interior points on the fault for the two models are the same but for l w 4 the duration of slip at a given interior point is much larger for the second set of models however the particle velocity during this added time of slip for the second class of models is small and almost constant so that at least for l w up to 4 this difference may not be significant for strong ground motion near such a fault the rise times and slips at any interior point of the fault is mainly width controlled for the first set of models and mainly controlled by the length of the elastic region or the effective width for the latter set since longer faults are observed to have larger slips than shorter ones of the same width the first set of models would predict that stress drops increase with rupture length for the same fault width however this observation can be explained by the second set of models even for constant stress drops for the second set of models we find that a fault twice the length of another has much less than double the slip for the same average stress drop we suggest that both classes of models studied are realistic models of earthquake sources but for different cases

the 1996 peru tsunamigenic earthquake broadband source process we investigate the spatio temporal complexity of moment release of the february 21 1996 peru earthquake mw 7 5 we use a non linear source tomographic technique based on simulated annealing to invert surface wave source spectra for the slip distribution on a gently dipping fault plane the spectra 5 65 mhz are obtained using an empirical green s function egf method applied to first and second orbit fundamental mode rayleigh waves spectra are well fit by a 110 km bilateral rupture subparallel to the trench updip of the hypocenter with a total moment of 2 0 1020 nm the non linear inversion reveals a 30 30 km major slip patch south the onset where rupture velocities attain 1 5 2 0 km s inversions of teleseismic broadband p and sh waves 10 500 mhz indicate little or no directivity consistent with the surface wave data the average source time functions for both the surface and body wave data are similar in shape and in duration 50 s part of the slip during the 1996 peru event occurred in a region of reduced background seismicity as was the case for the 1992 nicaragua slow event suggesting that the seismogenic potential of low seismicity regions near the trench should be globally reassessed

why large earthquakes do not nucleate at shallow depths although by definition tectonic earthquakes may nucleate anywhere within the seismogenic layer in almost all cases those earthquakes that become large nucleate near the base of the seismogenic layer because frictional strength and stress drop should increase with depth and in situ stress measurements suggest that the ambient stress increases with depth we have examined spontaneous rupture models with gradients of both average stress drop and average strength relative to ambient stress to determine whether this explains the observed phenomena we report here that ruptures that are nucleated with in the low stress drop shallow regions of the model are inhibited from propagating but those that are nucleated within the high stress drop regions can propagate over the entire fault plane

seismic cycles along the aleutian arc analysis of seismicity from 1957 through 1991 we catalog and relocate aleutian arc seismicity between 1957 and 1991 two great earthquakes ruptured the same 250 km long portion of the central aleutian arc the 1957 aleutian islands earthquake and the 1986 andreanof islands earthquake because accurate estimates of the moment distribution of the 1957 earthquake are not available the spatial distribution of aftershocks for each of these events is compared and tested against models describing the modes of occurrence of great subduction zone earthquakes earthquake relocations are based on p wave arrival times published in the international seismological summary the bureau central international seismologique and the international seismological centre bulletins and include corrections for the near source velocity structure associated with the down going slab magnitude estimates are extracted from bulletins and prior to 1964 are estimated by us from microfilmed records our catalog is complete above magnitude 5 5 aftershocks associated with the 1957 and 1986 earthquakes appear to occur in different areas east of the main shock epicenters aftershock locations are anticorrelated west of the main shock epicenter aftershocks of the 1986 earthquake tended to concentrate along the updip edge of aftershock clusters associated with the 1957 earthquake if we assume aftershocks rim the distribution of seismic moment release associated with each event these observations imply that the moment distribution of the 1986 earthquake was different from that of the 1957 earthquake this suggests that we should use caution in identifying mechanically strong portions of a fault asperities by simply mapping the moment distribution of a single great earthquake a fundamental tenet of the asperity model that rupture always occurs on the strongest portions of the fault with weaker portions rupturing either aseismically or dynamically as a result of rupture on a strong fault patch may in the case of the central aleutian arc not be correct thus observing the moment distribution from a single great earthquake may tell us little about what the distribution of moment release will look like during the next earthquake

source process of the great 1977 sumba earthquake in order to investigate the applicability of the asperity model to intraplate earthquakes we have studied the rupture process of the great 1977 sumba normal faulting earthquake mw 8 2 8 3 one of the largest earthquakes since 1963 this event has been variously interpreted as a plate detachment event i e rupture through the entire lithosphere or a shallow plate bending event we have analyzed long period body waves in order to determine the spatiotemporal rupture characteristics including the depth extent of the rupture area visible depth phases in the initial stage of weak radiation beginning about 15 s before the main pulse suggest that the earthquake nucleated near 29 km depth which corresponds to the maximum depth of the aftershock sequence the excitation of a strong tsunami implies that rupture extends to the surface while deconvolutions of long period p waves suggest a relatively shallow 50 km maximum depth extent however the existence of slip below this depth cannot be ruled out particularly if it preferentially radiates frequencies below the passband of the body waves used 0 02 hz for undiffracted phases the source time function of the principal rupture which initiated 30 km west of the epicenter of the precursor comprises a dominant initial short duration 24 s triangular pulse followed by several smaller pulses however slightly diffracted phases indicate a simple basic underlying character for the rupture consisting of the initial 24 s triangle superimposed on a longer duration 42 44 s trapezoid the absence of observable directivity in the deconvolved source time functions suggests a bilateral rupture mode although the body waves do not require a fault length greater than 80 km the aftershock area and surface wave results of zhang and kanamori 1988 imply a total length of at least 200 km the body wave source functions are well modeled by a 200 km long fault extending to 30 50 km depth on which slip nucleates at the center of the fault and has variable displacement along strike the peak moment release of the deconvolved source functions indicates higher displacement in the hypocentral area than in other areas of the fault the spatial relationship of the precursor and the main pulse is suggestive of rupture initiating at and propagating along the edge of an asperity prior to the rupture of the asperity itself the large size of the event may be due to an unusual stress environment arising from strong lateral gradients in seismic interplate coupling along the java timor arc

the 2017 july 20 mw 6 6 bodrum kos earthquake illuminates active faulting in the gulf of gokova sw turkey

variability of seismic source spectra estimated stress drop and radiated energy derived from cohesive zone models of symmetrical and asymmetrical circular and elliptical ruptures large variability of earthquake stress drops and scaled energy has been commonly reported in the literature but it is difficult to assess how much of this variability is caused by underlying physical source processes rather than simply observational uncertainties here we examine a variety of dynamically realistic rupture scenarios for circular and elliptical faults and investigate to what extent the variability in seismically estimated stress drops and scaled energy comes from differences in source geometry rupture directivity and rupture speeds we numerically simulate earthquake source scenarios using a cohesive zone model with the small scale yielding limit where the solution approaches a singular crack model with spontaneous healing of slip compared to symmetrical circular source models asymmetrical models result in larger variability of estimated corner frequencies and scaled energy over the focal sphere the general behavior of the spherical averages of corner frequencies and scaled energy in the subshear regime extends to the supershear regime although shear mach waves generated by the propagation of supershear rupture lead to much higher corner frequency and scaled energy estimates locally our results suggest that at least a factor of 2 difference in the spherical average of corner frequencies is expected in observational studies simply from variability in source characteristics almost independent of the actual stress drops translating into a factor of 8 difference in estimated stress drops furthermore radiation efficiency estimates derived from observed seismic spectra should not be directly interpreted as describing rupture properties unless there are independent constraints on rupture speed and geometry

the role of meteoritics in spaceflight missions and vice versa research on extraterrestrial materials plays a critical role in formulating the science rationale and design for spacecraft missions and conversely spaceflight holds great promise for solving perplexing problems in meteoritics the connections between meteoritics and sample return missions are obvious meteorite research can define sampling strategies the capabilities of sampling devices acceptable levels of chemical contamination and physical alteration of samples and the conditions under which samples are stored prior to and during recovery for their part sample return missions can provide geologic context for meteorites increased sampling diversity including materials not sampled as meteorites such as unconsolidated regolith ices and atmosphere calibration for crater counting chronology and ground truth for remote sensing measurements of meteorite parent bodies meteoritics also relates to spacecraft flyby rendezvous and lander missions that do not necessarily return samples specific illustrations of this mutual relationship based on a selection of recent or planned spacecraft missions include identifying source asteroid classes for ordinary and carbonaceous chondrites and reconstructing their thermal and collisional histories galileo near clementine ii and muses c determining the extent to which cometary dust and interstellar grains are found as interplanetary dust particles and assessing volatile abundances isotopic compositions and molecular species in cometary nuclei stardust and rosetta understanding the compositions of ancient martian crust and the mantle sources for snc meteorites as well as inventorying the planet s volatile reservoirs and interactions mars pathfinder mars global surveyor and mars volatiles and climate surveyor assessing whether lunar meteorites provide a more representative chemical sampling of the highlands crust and of mare volcanism than do apollo samples galileo clementine and lunar prospector spaceflight is the first priority of the space agencies that fund most research on extraterrestrial materials and the continued level of support for such research may be linked in part to its use in exploration by spacecraft

salt redistribution during extension and inversion inferred from 3d backstripping abstract a 3d backstripping approach considering salt flow as a consequence of spatially changing overburden load distribution isostatic rebound and sedimentary compaction for each backstripping step is used to reconstruct the subsidence history in the northeast german basin the method allows to determine basin subsidence and the salt related deformation during late cretaceous early cenozoic inversion and during late triassic jurassic extension in the northeast german basin the deformation is thin skinned in the basinal part but thick skinned at the basin margins the salt cover is deformed due to late triassic jurassic extension and late cretaceous early cenozoic inversion whereas the salt basement remained largely stable in the basin area in contrast the basin margins suffered strong deformation especially during late cretaceous early cenozoic inversion as a main question we address the role of salt during the thin skinned extension and inversion of the basin in our modelling approach we assume that the salt behaves like a viscous fluid on the geological time scale that salt and overburden are in hydrostatical near equilibrium at all times and that the volume of salt is constant because the basement of the salt is not deformed due to decoupling in the basin area we consider the base of the salt as a reference surface where the load pressure must be equilibrated our results indicate that major salt movements took place during late triassic to jurassic e w directed extension and during late cretaceous early cenozoic nne ssw directed compression moreover the study outcome suggests that horizontal strain propagation in the salt cover could have triggered passive salt movements which balanced the cover deformation by viscous flow in the late triassic strain transfer from the large graben systems in west central europe to the east could have caused the subsidence of the rheinsberg trough above the salt layer in this context the effective regional stress did not exceed the yield strength of the basement below the rheinsberg trough but was high enough to provoke deformation of the viscous salt layer and its cover during the late cretaceous early cenozoic phase of inversion horizontal strain propagation from the southern basin margin into the basin can explain the intensive thin skinned compressive deformation of the salt cover in the basin the thick skinned compressive deformation along the southern basin margin may have propagated into the salt cover of the basin where the resulting folding again was balanced by viscous salt flow into the anticlines of folds the huge vertical offset of the pre zechstein basement along the southern basin margin and the amount of shortening in the folded salt cover of the basin indicate that the tectonic forces responsible for this inversion event have been of a considerable magnitude

evidence for shallow megathrust slip across the unalaska seismic gap during the great 1957 andreanof islands earthquake eastern aleutian islands alaska we reassess the slip distribution of the 1957 andreanof islands earthquake in the eastern part of the aftershock zone where published slip models infer little or no slip eyewitness reports tide gauge data and geological evidence for 9 23 m tsunami runups imply seafloor deformation offshore unalaska island in 1957 in contrast with previous studies that labeled the area a seismic gap here we simulate tsunami dynamics for a suite of deformation models that vary in depth and amount of megathrust slip tsunami simulations show that a shallow 5 15 km deep rupture with 20 m of slip most closely reproduces the 1957 dutch harbor marigram and nearby 18 m runup at sedanka island marked by stranded drift logs models that place slip 20 km predict waves that arrive too soon our results imply that shallow slip on the megathrust in 1957 extended east into an area that presently creeps

three dimensional spontaneous rupture propagation and implications for the earthquake source mechanism summary we consider spontaneous cracks spreading out areally over a fault plane in an infinite medium as a realistic earthquake source model the boundary integral equation technique described in das is used to determine the displacements and stresses everywhere on the crack plane for faults spreading out symmetrically in all four quadrants over infinite planes of constant yield strength we find that the terminal rupture velocity viiicr in the direction of purely anti plane rupture is given by viiicr in the purely in plane direction of rupture propagation we find the terminal rupture velocity viicr to be given by viicr or viicr 0 5 depending on the yield strength we also find that crack propagation in the purely antiplane direction does not influence crack propagation in the purely in plane direction and vice versa for infinitely long shear cracks of finite width the slip at a point is found to grow more slowly after the arrival of a shear wave diffracted from the nearer crack edge the slip virtually ceases after the shear arrival from the further crack edge this implies that for such faults the slip is controlled by the fault width for a rectangular fault in an infinite medium our final dynamic solution is in closer agreement with the static elliptical crack solution of eshelby than with the static rectangular dislocation model solution of chinnery we find the relationship between the average slip and average dynamic stress drop e on such a rectangular fault of half width w to be e c w where c 0 7 the slip at an interior point is again controlled by the fault width for faults that are much longer than wide so that the slip may stop in the region where the fault initiated before the completion of the rupture process this implies that two rectangular faults of varying lengths but of the same width have the same slip for the same average stress drop a fact clearly contradicted by observations that fault slip increases with earthquake size for great earthquakes occurring along the same fault this contradiction is resolved if stress drops are also bigger for bigger earthquakes

expansion of the aftershock zone following the vanuatu new hebrides earthquake on 15 july 1981 following a large ms 7 0 interplate earthquake on 15 july 1981 in the vanuatu new hebrides islands the area defined by the aftershocks dramatically increased over a two week period of time the aftershocks were located using the cornell orstom seismograph network that has been monitoring earthquakes with magnitudes larger than mb 2 9 in the region since mid 1978 in the first few hours following the mainshock the area defined by the aftershocks was consistent with the rupture zone of a typical interplate earthquake with the observed seismic moment of 5 8 1026 dyne cm however during the 16 days following the mainshock the area of the aftershock zone increased to approximately 10 times the area of expected coseismic rupture the final aftershock zone included earthquakes that were located within the overriding and descending plates as well as along the interplate fault zone the migration of aftershocks away from the rupture zone of the 1981 mainshock indicates that at least in some cases the aftershock zone can overestimate the extent of coseismic rupture

centroid moment tensor solutions for october december 1996 abstract centroid moment tensor solutions are presented for 237 earthquakes that occurred during the fourth quarter of 1996 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 in emert h harjes h p eds acoustical imaging plenum 19 pp 785 797 a new model of anelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 bull seism soc am 86 144 158 is used to predict the decay of the waveforms

seismicity gaps and the shape of the seismic zone in the banda sea region from relocated hypocenters 1 we relocate hypocenters for more than 800 earthquakes deeper than 50 km with mb 5 0 along the banda arc using several thousand handpicked direct depth and core reflected phases in addition to phases reported by the international seismological centre the seismicity distribution is found to be very nonuniform both along the arc and in depth gaps in the relocated hypocenters exist along depth in most places of the arc with the upper edge of the gaps varying from 100 to 450 km depth and the lower edge varying from 350 to 670 km in different portions of the arc the seismic zone between 129 and 131 e in the 100 200 km depth range is the widest along the arc both in strike and downdip this region near the highest arc curvature has the highest seismic activity and is the only part of the arc with earthquakes continuously occurring from the surface down to below 600 km the very deep earthquakes under sulawesi are shown to be part of the west southwest dipping seram slab in the westernmost part of the banda arc the slab is under downdip tension in the 50 250 km depth range while the deepest portion of the slab in this region is under compression from 128 to 131 e the slab between 100 and 200 km depth is under mainly horizontal compression our study supports the two slab model for the banda arc the depth of the wadati benioff zone below the volcanoes is 60 100 km for the five volcanoes between 128 and 130 e and 150 km for the 23 volcanoes between 118 and 124 e

on the scaling of slip with rupture length for shallow strike slip earthquakes quasi static models and dynamic rupture propagation we explore whether observations of average surface rupture properties among strike slip earthquakes reflect the underlying mechanics we compare the observed relationship between average slip and rupture length for 27 surface ruptures 18 plate boundary earthquakes and 9 away from transform plate boundaries with predictions from two families of uniform stress drop models purely elastic models with a rupture limiting locking depth predict a nonlinear relationship while a quasidynamic model with no locking depth predicts a linear relationship we explore whether observations of fault slip at the earth s surface distinguish which if either of these two families of models may be favored we find that the data provide insufficient constraints to rule out either a linear or a nonlinear relationship this might arise from uncertainties in the observations or from reasonable but unrecoverable variations in locking depths and uniform stress drops among earthquakes we advance an alternative interpretation that the complexity among the observations is consistent with dynamic rupture models featuring spatially varying stress drops

aftershock zone scaling we investigate the distribution of aftershock zones for large earthquakes scalar seismic moment m 10 19 5 n m moment magnitude m 7 mainshocks are selected from the harvard centroid moment tensor catalog and aftershocks are selected from the preliminary determination of epicenters neic catalog the aftershock epicenter maps are approximated by a two dimensional gaussian distribution the major ellipse axis is taken as a quantitative measure of the mainshock focal zone size the dependence of zone length l on earthquake size is studied for three representative focal mechanisms thrust normal and strike slip although the numbers of mainshocks available for analysis are limited maximum a few tens of events in each case all earthquakes show the same scaling m l 3 no observable scaling break or saturation occurs for the largest earthquakes m 10 21 n m m 8 therefore it seems that earthquake geometrical focal zone parameters are self similar

a reappraisal of large earthquake scaling abstract twelve years ago i pointed out that observations indicate that the slip in large earthquakes scales with their length rather than their width as expected from the canonical model romanowicz 1992 has recently argued that more recent data show that the opposite is true which has obliged me to re examine the question i point out here a defining flaw in her analysis in that she allowed mo the moment at the cross over from small to large earthquakes to be a free variable in her curve fitting whereas this parameter can be defined independently when this parameter is independently fixed i find that the up dated data set confirms my earlier conclusion that for large crustal earthquakes m0 scales with l 2 a little over a decade ago i pointed out that obser vations indicate that the slip in large earthquakes scales with their rupture length scholz 1982 several sub sequent papers provided additional data supportive of this view chen and molnar 1983 shimazaki 1986 scholz et al 1986 large earthquakes are defined in this con text as those that rupture the entire seismogenic thick ness w0 and are thus constrained to propagate farther in a horizontal direction only for crustal earthquakes w0 is nearly constant 15 km so this scaling conflicts with conventional models of earthquakes such as dislocation models because they predict that slip scales with width which is invariant for these earthquakes i offered two alternative ways to interpret these observations one is that such conventional w models are correct but that stress drop could no longer be regarded as scale invariant but must scale with fault length as an alternative i sug gested the possibility of what i termed an l model in which slip intrinsically scales with fault length this created a minor crisis in seismology which has yet to be resolved it is no exaggeration to say that my l model suggestion has not attracted a noticeable coterie of admirers nor has my other suggestion and there has been no other model proposed in the interim that ex plains the observed l scaling although heaton 1990 has suggested a way in which length may scale with stress drop a variation of my w model scaling alternative in the face of this an alternative is to question the obser vations which is what romanowicz 1992 has recently chosen to do in her interpretation of an updated data set she concluded that seismic moment m0 scales lin early with rupture length l for large earthquakes which is consistent with w models and implies that slip u is scale invariant for large crustal earthquakes this great discrepancy with the earlier result she implies is due to the presence of superior modern measurements in the updated data set this issue has major implications both practical and theoretical and merits some debate here i present my own reappraisal of the data in which the conclusions are very different reappraisal of the data romanowicz s conclusions were based on a log log plot of m0 versus l for a data set of strike slip earth quakes she showed that the data in this figure could be better fit by two straight lines one with slope 3 in the lower scale range and one with slope 1 in the upper scale range than with a single line of slope 2 for small earth quakes which grow in both dimensions with l w m0 should scale with l 3 for large earthquakes where w has saturated at w0 and growth only occurs in the l di rection m0 should scale with l according to conven tional models hence the problem produced by my ob servation that m0 scales with l 2 for those events superficially then it appears that she has resolved the issue the problem however is that she has allowed the cross over length l which separates small from large earthquakes to be a free variable in her curve fitting ex ercise she thus obtains a cross over moment of 0 6 to 0 8 x 1020 n m which is appropriate for a rupture length of 60 to 70 km by adding an additional free parameter to the curve fitting one would expect a much better fit to be achieved the question is whether such a step is justified if small earthquakes grow with l w then the transition to large earthquakes defined as an event that ruptures the entire seismogenic thickness would be l w0 10 to 20 km for the data being studied this may be checked observationally because large earth quakes almost invariably nucleate near the base of the seismogenic layer das and scholz 1983 it follows that the transition to large earthquakes is at the length at which one begins to consistently see surface ruptures inspec tion of the earthquakes in romanowicz s 1992 figure 215

expansion of aftershock areas caused by propagating post seismic sliding summary it is known that the aftershock areas of large earthquakes often expand over time this expansion indicates that the stress increase associated with a main shock gradually propagates outward from the main shock rupture area it is likely that this propagating stress increase is caused by the propagation of post seismic sliding which has been detected for many large earthquakes from geodetic observations mainly global positioning system gps in the present study i perform a numerical simulation of the expansion of the aftershock area caused by the propagation of post seismic sliding the model fault exists within an infinite elastic medium and is loaded at a constant displacement rate the frictional stress on the fault obeys a laboratory derived rate and state dependent friction law non uniformity of the frictional constitutive parameters is introduced to the model fault plane to represent a large asperity for a large earthquake main shock and many possible nucleus sites for aftershocks around the main shock asperity negative values of a b are assigned to areas of seismic slip for the main shock and aftershocks while positive values of a b are assigned to regions where aseismic sliding occurs here a b is defined by d ss d ln v that describes the velocity v dependence of steady state friction stress ss seismic slip may be nucleated for negative a b and aseismic slip occurs for positive a b slip histories on the model fault plane are simulated through numerical integration of the friction law under the condition of uniform shear loading of a constant velocity the simulation can reproduce aftershocks triggered by stress increases related to postseismic sliding and expansion of the aftershock area the rate of expansion of the aftershock area decreases with increasing distance from the main shock asperity or increasing value of a b in the velocity strengthening region this finding suggests that the a b value for a plate interface can be estimated from aftershock data the simulation indicates that the 7 day and 30 day aftershock areas are 14 22 and 24 39 per cent larger respectively than the 1 day aftershock area these numbers are approximately consistent with observations from large earthquakes at subduction zones

structural context of the 2015 pair of nepal earthquakes mw 7 8 and mw 7 3 an analysis based on slip distribution aftershock growth and static stress changes the great himalayan earthquakes are believed to originate on the main himalayan thrust and their ruptures lead to deformation along the main frontal thrust mft the rupture of the april 25 2015 mw 7 8 earthquake was east directed with no part relayed to the mft the aftershock distribution coseismic elevation change of 1 m inferred from the insar image and the spatial correspondence of the subtle surface deformations with pt2 a previously mapped out of sequence thrust lead us to explore the role of structural heterogeneities in constraining the rupture progression we used teleseismic moment inversion of p and sh waves and coulomb static stress changes to map the slip distribution and growth of aftershock area to understand their relation to the thrust systems most of the aftershocks were sourced outside the stress shadows slip 1 65 m of the april 25 earthquake the may 12 mw 7 3 earthquake that sourced on a contiguous patch coincides with regions of increased stress change and therefore is the first known post instrumentation example of a late distant and large triggered aftershock associated with any large earthquake in the nepal himalaya the present study relates the slip aftershock productivity and triggering of unbroken stress barriers to potential out of sequence thrusts and suggests the role of stress transfer in generating large great earthquakes

analysis of the relationship between seismic moment and fault length for large crustal strike slip earthquakes between 1977 92 we have used an uniform data set to determine the scaling relation between seismic moment m0 and fault length for 34 large crustal strike slip earthquakes in the period 1977 92 the seismic moments used were obtained by the centroid moment tensor analysis the aftershocks of each event were relocated in this study and the fault length estimated from their spatial extent for large events we find that in spite of some scatter in the data the trend of this uni form data set indicates that m0 c 2 our data set does not show any obvious change of slope around m0 6 8 x 102o n m as was seen in a previous non uniform data set in

tsunami threat in the indian ocean from a future megathrust earthquake west of sumatra abstract several independent indicators imply a high probability of a great m 8 earthquake rupture of the subduction megathrust under the mentawai islands of west sumatra the human consequences of such an event depend crucially on its tsunamigenic potential which in turn depends on unpredictable details of slip distribution on the megathrust and how resulting seafloor movements and the propagating tsunami waves interact with bathymetry here we address the forward problem by modelling about 1000 possible complex earthquake ruptures and calculating the seafloor displacements and tsunami wave height distributions that would result from the most likely 100 or so as judged by reference to paleogeodetic data additionally we carry out a systematic study of the importance of the location of maximum slip with respect to the morphology of the fore arc complex our results indicate a generally smaller regional tsunami hazard than was realised in aceh during the december 2004 event though more than 20 of simulations result in tsunami wave heights of more than 5 m for the southern sumatran cities of padang and bengkulu the extreme events in these simulations produce results which are consistent with recent deterministic studies the study confirms the sensitivity of predicted wave heights to the distribution of slip even for events with similar moment and reproduces plafker s rule of thumb additionally we show that the maximum wave height observed at a single location scales with the magnitude though data for all magnitudes exhibit extreme variability finally we show that for any coastal location in the near field of the earthquake despite the complexity of the earthquake rupture simulations and the large range of magnitudes modelled the timing of inundation is constant to first order and the maximum height of the modelled waves is directly proportional to the vertical coseismic displacement experienced at that point these results may assist in developing tsunami preparedness strategies around the indian ocean and in particular along the coasts of western sumatra

real time forecasting of the april 11 2012 sumatra tsunami the april 11 2012 magnitude 8 6 earthquake off the northern coast of sumatra generated a tsunami that was recorded at sea level stations as far as 4800 km from the epicenter and at four ocean bottom pressure sensors darts in the indian ocean the governments of india indonesia sri lanka thailand and maldives issued tsunami warnings for their coastlines the united states pacific tsunami warning center ptwc issued an indian ocean wide tsunami watch bulletin in its role as an interim service provider for the region using an experimental real time tsunami forecast model rift ptwc produced a series of tsunami forecasts during the event that were based on rapidly derived earthquake parameters including initial location and mwp magnitude estimates and the w phase centroid moment tensor solutions w phase cmts obtained at ptwc and at the u s geological survey usgs we discuss the real time forecast methodology and how successive real time tsunami forecasts using the latest w phase cmt solutions improved the accuracy of the forecast

the great march 25 1998 antarctic plate earthquake moment tensor and rupture history we use broadband body and mantle wave data to study the 1998 antarctic intraplate earthquake the centroid moment tensor cmt has a large non double couple component there exist two pure double couple constrained solutions that fit the data almost equally well the frequent practice of taking the best double couple gives a far from optimal solution we use p and sh body waves to determine the rupture parameters of the first and larger of the two observed subevents the best rupture plane with strike 96 dip 69 and rake 18 is compatible with only one of the two cmt solutions strike 96 dip 64 rake 23 centroid location 63 1 s 148 4 e 10 km depth centroid time 0313 02 ut and m0 1 3 1021 n m mw 8 0 the first subevent is a simple primarily westward propagating 140 km rupture of 45 s duration with average velocity 3 km s 1 it has a seismic moment of 1 2 1021 n m mw 8 0 with 75 of its moment released between 10 and 27 s and a stress drop of 240 bars the rupture is physically bounded by two fracture zones at 147 5 e and 150 e the second subevent lasted from 70 to 90 s on a fault extending from 210 to 270 km west of the epicenter with a moment of 0 3 0 6 1021 n m mw 7 6 7 8 this is a spectacular example of dynamic stress triggering over a 100 km separation distance with a time delay of 40 s the complex pattern of aftershocks is primarily controlled by preexisting fracture zones on the ocean floor

the macquarie ridge earthquake of 1989 summary a study of the seismicity on the central portion of the macquarie ridge before and after the 1989 may 23 macquarie ridge earthquake mw 8 2 and the solution of the inverse problem to obtain the moment release time history during the earthquake are presented the aftershock study shows that there were remarkably few and small aftershocks on the main fault the aftershocks were distributed along a 220 km portion of the india australia pacific plate boundary and indicate that the motion was bilateral on a vertical fault in addition the earthquake reactivated a 175 km section of a fault to its west which had been dormant since at least 1964 and 44 per cent of the aftershocks occurred on this feature moreover the largest aftershocks in the five month period following the event occurred not on the main fault plane but on the reactivated one based on available bathymetry gravity and magnetic anomaly data from the region this reactivated feature is interpreted as being an old oceanic fracture zone and hence a pre existing zone of weakness the aftershock distribution and their focal mechanisms are interpreted in terms of the tectonics of the region and suggest that a triangular piece of crust to the west of the macquarie ridge is being squeezed to the north and west the centroid moment tensor solution was obtained using both gdsn and geoscope data simultaneously it shows that the motion was primarily strike slip on a vertical fault with a moment of mo 1 5 x lo2 n m and a centroid depth of 19 5 km the moment release distribution and time history were obtained by inversion of broad band body waves recorded digitally by the gdsn and geoscope networks the rupture is found to be bilateral with the propagation first starting towards the north east and a few seconds later towards the south west the moment release was low in the hypocentral area with the higher areas of moment located towards the north east and south west of this the average rupture speed was approximately the shear wave speed no simple relation between the moment release pattern and the distribution of aftershocks on the fault plane was found instead the aftershock distribution is seen to be dominated by the intersection of the reactivated fault and the main fault plane with most aftershocks occurring to the north of this intersection

aftershock zones of large shallow earthquakes fault dimensions aftershock area expansion and scaling relations summary we determine the aftershock areas from relocated hypocentres for 64 dip slip and eight strike slip earthquakes in the period 1977 1996 together with those for three recent earthquakes the 1998 antarctic plate earthquake the 1999 izmit turkey earthquake and the 2000 wharton basin earthquake we also include the data for 27 strike slip earthquakes from pegler das 1996 we find that the location of the hypocentre is essentially random along strike for both strike slip and dip slip earthquakes subduction zone earthquakes appear to initiate more frequently towards the down dip edge of the fault whereas the non subduction zone dip slip earthquakes do not have any preferred depth of initiation the aftershock zones of subduction zone earthquakes often expand substantially along strike and up dip but far less in the down dip direction whereas those for non subduction zone earthquakes do not expand significantly in either the up or the down dip direction subduction zone thrust earthquakes have larger and more numerous aftershocks than earthquakes in all other tectonic settings for strikeslip earthquakes we find that slip increases at least linearly with length for dip slip earthquakes we find that the ratio of length to width increases systematically with length for lengths 40 km indicating that there is some restriction on fault width slip is found to be proportional to length over the moment range 10 17 nm m0 3r10 21 nm

the 1977 sumba earthquake series evidence for slab pull force acting at a subduction zone the great 1977 sumba earthquake occurred at the eastern sunda trench just west of the collision of australian continental lithosphere with the island arc the length of the aftershock zone of this normal faulting earthquake is about 200 km aftershocks are concentrated 65 115 km east of the main shock epicenter with very few aftershocks in a 50 km long segment that spans the main shock epicenter relocated hypocenters and focal mechanism data are consistent with normal faulting throughout the upper 28 km of the oceanic lithosphere there is no evidence for thrust faulting of the deeper aftershocks these data imply that the neutral bending surface must be at least 35 40 km deep a second aftershock zone about 180 km northwest of the main shock became active immediately following the main shock but events were concentrated during days 50 52 this zone is a 70 km long lineation that trends toward the main shock epicenter and reflects right lateral strike slip faulting within the subducted oceanic plate seismicity exists to a depth of about 650 km in the very old plate beneath the sunda banda arc and that plate s negative buoyancy causes very large slab pull forces great interface thrust earthquakes are absent at the sumba region and slab pull forces are inferred to have partially decoupled the subducted plate from the overriding plate this decoupling permits slab pull stresses to be guided updip to the region of the sumba main shock such shallow acting slab pull provides a bending moment at the trench and explains the deformation and timing observed for the entire sumba earthquake series in this model slab pull forces stretch the subducted plate until the increasing stresses at the shallow subduction zone lead to a subduction zone earthquake postseismically the released oceanic plate undergoes a pulse of downdip strain returning the plate to a less extended state the moment of this downdip plate motion could exceed the seismic moment of the main shock

self consistent earthquake fault scaling relations update and extension to stable continental strike slip faults using seismic moment m length l data for stable continental region scr faults augmented by data not included in previous studies this article reassesses and confirms the bilinear scaling relation for the dip slip faults of leonard 2010 furthermore using the new data i propose a separate bilinear relation for estimating magnitude from surface rupture length there are now a small number of scr strike slip earthquakes for which the fault dimensions have been estimated i use these to constrain a trilinear scaling relation for this class of fault for the four fault types interplate dip slip interplate strike slip scr intraplate dip slip and scr intraplate strike slip the scaling relations for the 10 permutations of m d l w and a are given

the 1992 nicaragua earthquake a slow tsunami earthquake associated with subducted sediments the 1992 nicaragua earthquake was a tsunami earthquake that is it generated tsunamis disproportionately large for its surface wave magnitude m s the moment magnitude m w determined from long period 250 s surface waves was 7 6 significantly larger than the 20 s m s of 7 this m s m w disparity is also characteristic of tsunami earthquakes the nicaragua earthquake is the first tsunami earthquake to be captured by modern broadband seismic networks allowing us to present here seismograms of sufficiently high quality to make inferences about the rupture mechanisms we conclude that the nicaragua earthquake was a slow thrust earthquake which occurred on the subduction interface between the cocos and north american plates and because of the absence of sediments on the trench floor offshore of nicaragua the slip propagated up dip all the way to the ocean bottom exciting large tsunamis the occurrence of slip on a plate interface filled with soft subducted sediments caused the rupture process to be slower than in ordinary subduction zone thrust earthquakes our results reinforce the idea that tsunami warning systems using long period 100 s waves are necessary to reduce the hazard from this type of earthquake

a possible explanation for difference in stress drop between intraplate and interplate earthquakes 1 it is known from observations that stress drop of intraplate earthquakes is larger than that of interplate earthquakes on average i present a mechanical model for explaining the difference in stress drop where an intraplate fault is assumed to be loaded uniformly while a locked area an asperity on a plate boundary is nonuniformly loaded by surrounding aseismic sliding a numerical simulation is conducted to quantitatively evaluate the difference in stress drop for different loading processes because the model intraplate fault is uniformly loaded stress drop is uniform over the fault with a larger average value in contrast stress concentration is generated at a boundary region between locked area and aseismic sliding area for a model interplate earthquake this stress concentration hastens earthquake occurrence resulting in lower average stress drop the stress drop of simulated intraplate earthquakes is several tens percent larger than that of simulated interplate earthquakes

examination of scaling between earthquake magnitude and proposed early signals in p waveforms from very near source stations in a south african gold mine 1 we analyze near source seismograms recorded in a deep south african mine for scaling between signals early in p waveforms and the magnitude m of the events the data consist of recordings at 26 stations of 122 events with 1 5 0 implying that the final earthquake size is affected statistically by the initial rupture process if these correlations hold for larger earthquakes as suggested by other studies the early predominant period and peak displacement are useful for early warning systems

focal depths and moment tensor representations of shallow earthquakes associated with the great sumba earthquake focal depths in the range 8 to 24 km below the seafloor were determined for seven of the larger shocks associated with the great sumba earthquake of august 19 1977 depth control was achieved by modeling digitized long period p waves recorded by the world wide standard seismic network if the base of the rupture at the time of the mainshock were no greater than the depth of the deepest aftershock the stress drop would be nearly 500 bars amplitude and first motion data from the p waves were inverted for point source moment tensors the inversion of rayleigh and love wave spectra computed from digital seismograms recorded by the seismic research observatories sro and the abbreviated seismic research observatories asro broadened the source study to include earthquakes with moments as small as 1024 dyn cm too small for either traditional first motion solutions or p wave modeling the inversion procedure was applied to data in the passband from 30 to 120 s the propagation phase for the love and the rayleigh waves was calibrated with signals from two earthquakes for which the source phase was inferred from the p wave solutions agreement with the corresponding p wave solutions is nearly the same whether or not the smaller eigenvalues of the inner product matrix are retained in the inversions the double couple components generally account for more than two thirds of the total moment normal faulting along an east to northeasterly strike characterizes the mechanisms in the principal zone of aftershock activity strike slip mechanisms consistent with horizontal compression normal to the arc prevail in the delayed aftershock zone located 200 km northwest of the mainshock of the earthquakes subjected to this surface wave analysis the foreshock stood out as having felt a significantly higher apparent stress perhaps as much as one half an order of magnitude higher than the others these results suggest that accurate source parameters for moderate to small magnitude earthquakes can be determined from surface waves recorded by the sro and asro in particular the mechanisms of small magnitude foreshocks could be obtained in this way

the 1960 chilean earthquakes an unusual foreshock sequence that began with an earthquake of moment 2 0 1021 n m and rupture length of about 150 km preceded the great 1960 chilean earthquake earthquake relocations of the sequence show a progression of seismic activity toward the initiation of the main shock the rupture length of the great 1960 chilean earthquake is estimated from the distribution of aftershocks and crustal deformation to be 920 100 km the source mechanisms of a foreshock and two aftershocks are determined and used to constrain the source mechanism of the main shock the first event in the sequence ruptured the segment of the peru chile trench between 37 03 s and 38 74 s whereas the great 1960 chilean main shock ruptured the adjoining segment to the south the great 1960 chilean main shock initiated within the rupture area of the first event and terminated near the intersection of the chile ridge with the peru chile trench 46 5 s

interseismic coupling stress evolution and earthquake slip on the sunda megathrust 1 the extent to which interseismic coupling controls the slip distribution of large megathrust earthquakes is unclear with some authors proposing that it is the primary control and others suggesting that stress changes from previous earthquakes are of first order importance here we develop a detailed stress history of the sunda megathrust modified by coupling and compare the correlation between slip and stress with that of slip versus coupling we find that the slip distributions of recent earthquakes are more consistent with the stress field than with the coupling distributions but observe that in places the stress pattern is strongly dependent on poorly constrained values of slip in historical earthquakes we also find that of the 13 earthquakes in our study for which we have hypocentral locations only two appear to have nucleated in areas of negative stress and these locations correspond to large uncertainties in the slip distribution of pre instrumental events citation nalbant s j mccloskey s steacy m nicbhloscaidh and s murphy 2013 interseismic coupling stress evolution and earthquake slip on the sunda megathrust geophys res lett 40 4204 4208

the 1957 great aleutian earthquake the 9 march 1957 aleutian earthquake has been estimated as the third largest earthquake this century and has the longest aftershock zone of any earthquake ever recorded 1200 km however due to a lack of high quality seismic data the actual source parameters for this earthquake have been poorly determined we have examined all the available waveform data to determine the seismic moment rupture area and slip distribution these data include body surface and tsunami waves using body waves we have estimated the duration of significant moment release as 4 min from surface wave analysis we have determined that significant moment release occurred only in the western half of the aftershock zone and that the best estimate for the seismic moment is 50 100 1020 nm using the tsunami waveforms we estimated the source area of the 1957 tsunami by backward propagation the tsunami source area is smaller than the aftershock zone and is about 850 km long this does not include the unalaska island area in the eastern end of the aftershock zone making this area a possible seismic gap and a possible site of a future large or great earthquake we also inverted the tsunami waveforms for the slip distribution slip on the 1957 rupture zone was highest in the western half near the epicenter little slip occurred in the eastern half the moment is estimated as 88 1020 nm or m w 8 6 making it the seventh largest earthquake during the period 1900 to 1993 we also compare the 1957 earthquake to the 1986 andreanof islands earthquake which occurred within a segment of the 1957 rupture area the 1986 earthquake represents a rerupturing of the major 1957 asperity

modeling of the february 1996 peruvian tsunami the february 1996 peruvian earthquake generated a larger tsunami than expected from its surface magnitude this discrepancy as well as the long rupture duration indicate that this event is a tsunami earthquake the associated tsunami was strong locally with runup heights of 1 to 5 meters along a coastline of 400 km it is shown that this tsunami can be modeled for a seismic moment of 2 1020 nm using a rigidity of 2 1010 n m the tsunami propagation is modeled solving long wave equations by a finite difference method the maximum run up heights in the region of chimbote can be simulated using a grid increment of 10 meters the propagation of this small tsunami across the pacific ocean is modeled taking into account frequency dispersion the only notable amplification occurred in the marquesas islands where wave heights of 2 meters were observed and are simulated

mechanism of the 1992 nicaragua tsunami earthquake the 1992 nicaragua earthquake generated larger tsunamis than expected from its surface wave magnitude ms 7 2 and is known as a tsunami earthquake seismological studies showed that the duration was very long for its size about 100 s other studies have shown that the seismic moment estimated from tsunamis is an order of magnitude larger than that from seismic waves even after the long duration is accounted for numerical computations of tsunamis from various fault models are made to reconcile this discrepancy comparison of calculated waveforms with tide gauge records shows that the fault width is 40 km much narrower than the aftershock area and extends only into the upper 10 km of the ocean bottom slip amount on the fault is estimated to be 3 m from amplitude comparisons the fault length is estimated to be 250 km slightly longer than the aftershock area from comparison of the tsunami height distribution the rigidity around the shallow fault may be smaller than that of a standard underthrust fault and the seismic moment is estimated as 3 1020 nm consistent with the seismic observations a slow rupture on the shallow fault presumably in the subducted sediments is responsible to the unusually large tsunami excitation

heightened odds of large earthquakes near istanbul an interaction based probability calculation we calculate the probability of strong shaking in istanbul an urban center of 10 million people from the description of earthquakes on the north anatolian fault system in the marmara sea during the past 500 years and test the resulting catalog against the frequency of damage in istanbul during the preceding millennium departing from current practice we include the time dependent effect of stress transferred by the 1999 moment magnitude m 7 4 izmit earthquake to faults nearer to istanbul we find a 62 15 probability one standard deviation of strong shaking during the next 30 years and 32 12 during the next decade

three dimensional finite difference simulation of fault dynamics rectangular faults with fixed rupture velocity we analyze three dimensional finite difference solutions for a simple shear crack model of faulting to determine the effects of fault length and width on the earthquake slip function the fault model is dynamic with only rupture velocity fault dimensions and dynamic stress drop prescribed the numerical solutions are accurate for frequencies up to 5 hz and are combined with asymptotic results for shear cracks in order to characterize the slip function at higher frequencies near the hypocenter the slip velocity exhibits a square root singularity whose intensity increases with hypocentral distance at distances greater than the fault width w growth of the velocity intensity ceases and the slip function becomes nearly invariant with distance along the fault length closed form expressions are developed for the dependence of static slip s slip rise time tr and slip velocity intensity v on fault geometry along the center line of a long narrow fault at hypocentral distances exceeding w these expressions reduce to s w tr 0 5 w vr and v w 2 vr where is the dynamic stress drop the shear modulus and vr the rupture velocity the numerical results imply that uniform dislocation kinematic earthquake models in which slip is represented by a ramp time function will underpredict high frequency ground motion relative to low frequency ground motion a further implication of the numerical solutions is that the nature of inelastic processes at the advancing edge of a long fault will depend on fault width but will be independent of rupture length

long term seismic behavior of the focal and adjacent regions of great earthquakes during the time between two successive shocks we analyze the spatial temporal energy distribution of shallow depth h 70 km seismicity surface wave magnitude ms 7 occurring in the focal and adjacent regions of very great shallow earthquakes rupture lengths of the order of hundreds of kilometers in the circum pacific seismic belt for as many decades as possible before and after the occurrence of the main shock for this purpose we have revised the catalog of data for the world instrumental seismicity 1900 1995 by removing a series of heterogeneities in the earthquake reporting and magnitude determination this revised catalog is fairly complete for earthquakes with m 7 since early in the century our findings indicate that once a main shock aftershock sequence occurs the focal region enters a period of relative quiescence for large ms 7 earthquakes significant seismic activity ms 7 occurs during many decades prior to the next main shock this activity is fairly continuous or random in time and lasts until the onset of the main event but clusters in space around the ends of the forthcoming rupture and or in the vicinity of the principal epicenter except in the case of rare bilateral breaks the main epicenter is located at one of these ends thus major portions of the rupture zone experience no events with ms 7 during the seismic cycle larger aftershocks also cluster near the edges of the rupture and near the principal epicenter preshock activity minutes to weeks before the main shock if any occurs in general near the main epicenter we also find that the nucleation and ends of the rupture often coincide in space with recognizable geometrical and or geological inhomogeneities barriers existing in the lithosphere it appears that while strain energy accumulates high stress concentrations often occur at the ends of the future rupture zone which results in the long term foreshock activity and in the subsequent initiation of the main rupture from within those regions we suggest a simple mechanical model that explains the observed pattern of earthquake occurrence for both unilateral and bilateral ruptures in all cases of great earthquakes that have occurred this century for which a long and complete to a level of 2 to 3 orders of magnitude smaller than the moment of the main shock catalog of prior seismicity exists we can not recognize any statistically significant quiescent or doughnut patterns in the preceding seismicity at the ms 7 level