coseismic and postseismic deformation associated with the 2018 mw 7 9 kodiak alaska earthquake from low rate and high rate gps observationscoseismic and postseismic deformation associated with the 2018 mw 7 9 kodiak alaska earthquake

direct evidence of active deformation in the eastern indian oceanic plate conventional plate tectonics theory postulates that plates only deform on their boundaries to the contrary there is ample evidence of intraplate deformation in the equatorial indian ocean west of the ninetyeast aseismic ridge prior to this study no direct evidence of deforma tion east of the ninetyeast ridge was available we present the results of a multipurpose geo physical cruise showing that intraplate deformation also occurs in this area long at least 1000 km left lateral north south strike slip faults are active and reactivate fossil fracture zones this style of deformation is strikingly different from the east west folds and reverse faults that affect the region west of the ninetyeast ridge contrasting processes of convergence at the northern plate boundaries can account for the two styles of deformation west of the ninetyeast ridge there is a continent continent collision and east of the ridge oceanic lithosphere subducts along the sumatra trench the ninetyeast aseismic ridge therefore appears to be a mechanical border separating two distinct deformed areas

mw 8 6 sumatran earthquake of 11 april 2012 rare seaward expression of oblique subduction the magnitude 8 6 and 8 2 earthquakes off northwestern sumatra on 11 april 2012 generated small tsunami waves that were recorded by stations around the indian ocean combining differential travel time modeling of tsunami waves with results from back projection of seismic data reveals a complex source with a significant trench parallel component the oblique plate convergence indicates that 20 50 m of trench parallel displacement could have accumulated since the last megathrust earthquake only part of which has been taken up by the great sumatran fault this suggests that the remaining trench parallel motion was released during the magnitude 8 6 earthquake on 11 april 2012 within the subducting plate the magnitude 8 6 earthquake is interpreted to be a result of oblique subduction as well as a reduction in normal stress due to the occurrence of the sumatra andaman earthquake in 2004

deep seismic reflection images of the wharton basin oceanic crust and uppermost mantle offshore northern sumatra relation with active and past deformation 1 we present deep seismic reflection images along two profiles collected in 2006 in the wharton basin offshore northern sumatra the main profile is located subparallel to the sumatran trench at a distance of 32 66 km faulting of the entire sedimentary section strike slip deformation sometimes accompanied by a dip slip component is imaged over two fracture zones of the extinct wharton spreading center that prior studies have shown to be reactivated as left lateral faults the western fracture zone is associated with a wide region of strong basement topography a difference in crustal thickness of 1 5 km and an age offset of 9 ma the epicenters of the 11 april 2012 mw 8 6 great strike slip earthquake its mw 7 2 foreshock and mw 8 2 aftershock align along this major structure 100 km south of the profile intersection our high quality long offset seismic reflection data also reveal bright dipping reflections extending down to a maximum of 24 km into the oceanic mantle 37 km below sea level apparent dips are mostly 25 35 corresponding to 30 55 along either n s to nne ssw or e w to wnw ese directions which encompass the directions of plate fabric and nodal planes of the mw 8 6 event we suggest that these enigmatic reflections arise from presently inactive dip slip fault planes reaching for the deepest ones to the base of the brittle layer possible origins include extension related to plate bending or an episode of now inactive thrust type deformation reactivating paleonormal faults similar to that taking place in the central indian basin

rupture kinematics of the 2005 mw 8 6 nias simeulue earthquake from the joint inversion of seismic and geodetic data the 2005 mw 8 6 nias simeulue earthquake was caused by rupture of a portion of the sunda megathrust offshore northern sumatra this event occurred within an array of continuous global positioning system gps stations and produced measurable vertical displacement of the fringing coral reefs above the fault rupture thus this earthquake provides a unique opportunity to assess the source character istics of a megathrust event from the joint analysis of seismic data and near field static co seismic displacements based on the excitation of the normal mode data and geodetic data we put relatively tight constraints on the seismic moment and the fault dip where the dip is determined to be 8 to 10 with corresponding moments of 1 24 10 22 to 1 00 10 22 n m respectively the geodetic constraints on slip distribution help to eliminate the trade off between rupture velocity and slip kine matics source models obtained from the inversion of various combinations of the teleseismic body waves and geodetic data are evaluated by comparing predicted and observed long period seismic waveforms 100 500 sec our results indicate a rela tively slow average rupture velocity of 1 5 to 2 5 km sec and long average rise time of up to 20 sec the earthquake nucleated between two separate slip patches one beneath nias and the other beneath simeulue island the gap between the two patches and the hypocentral location appears to be coincident with a local geological disrup tion of the forearc coseismic slip clearly tapers to zero before it reaches the trench probably because the rupture propagation was inhibited when it reached the accre tionary prism using the models from joint inversions we estimate the peak ground velocity on nias island to be about 30 cm sec an order of magnitude slower than for thrust events in continental areas this study emphasizes the importance of util izing multiple datasets in imaging seismic ruptures

the 2012 sumatra great earthquake sequence the equatorial indian ocean is a well known place of active intraplate deformation defying the conventional view of rigid plates separated by narrow boundaries where deformation is confined on 11 april 2012 this region was hit in a couple of hours by two of the largest strike slip earthquakes ever recorded moment magnitudes mw 8 6 and 8 2 broadband seismological observations of the mw 8 6 mainshock indicate a large centroid depth 30 km and remarkable rupture complexity detailed study of the surface wave directivity and moment rate functions clearly indicates the partition of the rupture into at least two distinct subevents to account for these observations we developed a procedure to invert for multiple point source parameters the optimum source model at long period consists of two point sources separated by about 209 km with magnitudes mw 8 5 and 8 3 to explain the remaining discrepancies between predicted and observed surface waves we can refine this model by adding directivity along the wnw ese axis however we do not exclude more complicated models to analyze the mw 8 2 aftershock we removed the perturbation due to large surface wave arrivals of the mw 8 6 mainshock by subtracting the corresponding synthetics computed for the two subevent model analysis of the surface wave amplitudes suggests that the mw 8 2 aftershock had a large centroid depth between 30 km and 40 km this major earthquake sequence brings a new perspective to the seismotectonics of the equatorial indian ocean and reveals active deep lithospheric deformation

near real time simulations of global cmt earthquakes summary we have developed a near real time system for the simulation of global earthquakes prompted by a trigger from the global centroid moment tensor cmt project the system automatically calculates normal mode synthetic seismograms for the preliminary reference earth model and spectral element synthetic seismograms for 3 d mantle model s362ani in combination with crustal model crust2 0 the 1 d and 3 d synthetics for more than 1800 seismographic stations operated by members of the international federation of digital seismograph networks are made available via the internet global shakemovie princeton edu and the incorporated research institutions for seismology data management center iris iris edu the record length of the synthetics is 100 min for cmt events with magnitudes less than 7 5 capturing r1 and g1 at all epicentral distances and 200 min for cmt events with magnitudes equal to or greater than 7 5 capturing r2 and g2 the mode simulations are accurate at periods of 8 s and longer whereas the spectral element simulations are accurate between periods from 17 to 500 s the spectral element software incorporates a number of recent improvements for example the mesh honours the moho as a first order discontinuity underneath the oceans and continents and the performance of the solver is enhanced by reducing processor cache misses and optimizing matrix matrix multiplication in addition to synthetic seismograms the system produces a number of earthquake animations as well as various record sections comparing simulated and observed seismograms

strike slip earthquakes can also be detected in the ionosphere it is generally assumed that co seismic ionospheric disturbances are generated by large vertical static displacements of the ground during an earthquake consequently it is expected that co seismic ionospheric disturbances are only observable after earthquakes with a significant dip slip component therefore earthquakes dominated by strike slip motion i e with very little vertical co seismic component are not expected to generate ionospheric perturbations in this work we use total electron content tec measurements from ground based gnss receivers to study ionospheric response to six recent largest strike slip earthquakes the mw7 8 kunlun earthquake of 14 november 2001 the mw8 1 macquarie earthquake of 23 december 2004 the sumatra earthquake doublet mw8 6 and mw8 2 of 11 april 2012 the mw7 7 balochistan earthquake of 24 september 2013 and the mw 7 7 scotia sea earthquake of 17 november 2013 we show that large strike slip earthquakes generate large ionospheric perturbations of amplitude comparable with those induced by dip slip earthquakes of equivalent magnitude we consider that in the absence of significant vertical static co seismic displacements of the ground other seismological parameters primarily the magnitude of co seismic horizontal displacements seismic fault dimensions seismic slip may contribute in generation of large amplitude ionospheric perturbations

time domain observations of a slow precursor to the 1994 romanche transform earthquake low frequency spectral anomalies have indicated that some large earthquakes are preceded by extended episodes of smooth moment release but the reality of these slow precursors has been debated because they have not been directly observed in the time domain high gain seismograms from the 14 march 1994 romanche transform event moment magnitude m w 7 0 show a precursory ramp with a moment of 7 1018 newton meters beginning about 100 seconds before the arrival of the high frequency p waves this precursor was the initial phase of a slow component of slip that released nearly half of the total moment of the earthquake such behavior may be typical for large earthquakes on the oceanic ridge transform system

a method for quantitatively analysing dynamic recrystallization in deformed quartzitic rocks abstract quantification of the microstructural changes brought about by dynamic recrystallization is essential for the interpretation of deformation mechanism histories and for the understanding of recrystallization as a syn kinematic process a method is presented for analysing the degree of dynamic recrystallization and for reconstructing the original grain size distribution from that measured in the deformed specimen this is based on size distribution measurements and comparative volume calculations between subsets of grains which contain rutile inclusions and subsets which do not application of the method to some quartzites from the kilmory bay syncline s w highlands scotland demonstrates that up to 25 of the apparent matrix grains are new grains produced by the dynamic recrystallization of porphyroclasts and that the new grains alone compose more than 12 of the total rock volume these figures are 2 3 times larger than estimates made by normal petrographic inspection it is also shown that grain size distributions alone convey little information about the microstructural changes and that grain size vs volume fraction graphs are more meaningful

aftershocks of the 2012 off coast of sumatra earthquake sequence abstract aftershocks of the 2012 off coast of sumatra earthquake sequence exhibit a complex and diffuse spatial distribution the first order complexity in aftershock distribution is clear and well beyond the influence of typical earthquake location uncertainty the sequence included rupture of multiple fault segments spatially separated we use surface wave based relative centroid locations to examine whether at the small scale the distribution of the aftershocks was influenced by location errors surface wave based relative location has delineated precise oceanic transform fault earthquake locations in multiple regions however the relocated aftershocks off the coast of sumatra seldom align along simple linear trends that are compatible with the corresponding fault strikes as estimated for the gcmt catalog the relocation of roughly 60 moderate earthquake epicentroids suggests that the faulting involved in the 2012 earthquake aftershock sequence included strain release along many short fault segments statistical analysis and temporal variations of aftershocks show a typical decay of the aftershocks but a relatively low number of aftershocks as is common for intraplate oceanic earthquakes coulomb stress calculations indicate that most of the moderate magnitude aftershocks are compatible with stress changes predicted by the large event slip models the patterns in the aftershocks suggest that the formation of the boundary and eventual localization of deformation between the indian and australian plate is a complicated process

strike slip earthquakes in the oceanic lithosphere observations of exceptionally high apparent stress summary the radiated energies e s and seismic moments m0 for 942 globally distributed earthquakes that occurred between 1987 to 1998 are examined to find the earthquakes with the highest apparent stresses a e s m0 where is the modulus of rigidity the globally averaged a for shallow earthquakes in all tectonic environments and seismic regions is 0 3 mpa however the subset of 49 earthquakes with the highest apparent stresses a greater than about 5 0 mpa is dominated almost exclusively by strike slip earthquakes that occur in oceanic environments these earthquakes are all located in the depth range 7 29 km in the upper mantle of the young oceanic lithosphere many of these events occur near plate boundary triple junctions where there appear to be high rates of intraplate deformation indeed the small rapidly deforming gorda plate accounts for 10 of the 49 high a events the depth distribution of a which shows peak values somewhat greater than 25 mpa in the depth range 20 25 km suggests that upper bounds on this parameter are a result of the strength of the oceanic lithosphere a recently proposed envelope for apparent stress derived by taking 6 per cent of the strength inferred from laboratory experiments for young less than 30 ma deforming oceanic lithosphere agrees well with the upper bound envelope of apparent stresses over the depth range 5 30 km the corresponding depth dependent shear strength for young oceanic lithosphere attains a peak value of about 575 mpa at a depth of 21 km and then diminishes rapidly as the depth increases in addition to their high apparent stresses which suggest that the strength of the young oceanic lithosphere is highest in the depth range 10 30 km our set of high a earthquakes show other features that constrain the nature of the forces that cause interplate motion first our set of events is divided roughly equally between intraplate and transform faulting with similar depth distributions of a for the two types secondly many of the intraplate events have focal mechanisms with the t axes that are normal to the nearest ridge crest or subduction zone and p axes that are normal to the proximate transform fault these observations suggest that forces associated with the reorganization of plate boundaries play an important role in causing high a earthquakes inside oceanic plates extant transform boundaries may be misaligned with current plate motion to accommodate current plate motion the pre existing plate boundaries would have to be subjected to large horizontal transform push forces a notable example of this is the triple junction near which the second large aftershock of the 1992 april cape mendocino california sequence occurred alternatively subduction zone resistance may be enhanced by the collision of a buoyant lithosphere a process that also markedly increases the horizontal stress a notable example of this is the aleutian trench near which large events occurred in the gulf of alaska in late 1987 and the 1998 march balleny sea m 8 2 earthquake within the antarctic plate

initiation of the great mw 9 0 tohoku oki earthquake abstract we determined the location size mechanism and the frequency content of the first 4 0 s of the 2011 tohoku oki earthquake since the beginning of this earthquake is very small we develop a comparative approach against a near by reference earthquake the master event we first determined the water depth near the master event using the differential timing between the water phase pwp reflected from the air water interface and the depth phase pp reflected from the water crust interface then we located the master event using the well known ocean bathymetry in the area after calibrating teleseismic arrays 30 to 90 at short periods for timing and amplitude with respect to the master event we were able to determine the initiation of the main event it began as a small m w 4 9 thrust event located at 38 19 n 142 68 e at a depth of 21 km and a few seconds later evolved into a slower extremely large slip event up dip

asthenosphere rheology inferred from observations of the 2012 indian ocean earthquake the concept of a weak asthenospheric layer underlying earth s mobile tectonic plates is fundamental to our understanding of mantle convection and plate tectonics however little is known about the mechanical properties of the asthenosphere the part of the upper mantle below the lithosphere underlying the oceanic crust which covers about 60 per cent of earth s surface great earthquakes cause large coseismic crustal deformation in areas hundreds of kilometres away from and below the rupture area subsequent relaxation of the earthquake induced stresses in the viscoelastic upper mantle leads to prolonged postseismic crustal deformation that may last several decades and can be recorded with geodetic methods the observed postseismic deformation helps us to understand the rheological properties of the upper mantle but so far such measurements have been limited to continental plate boundary zones here we consider the postseismic deformation of the very large moment magnitude 8 6 2012 indian ocean earthquake to provide by far the most direct constraint on the structure of oceanic mantle rheology in the first three years after the indian ocean earthquake 37 continuous global navigation satellite systems stations in the region underwent horizontal northeastward displacements of up to 17 centimetres in a direction similar to that of the coseismic offsets however a few stations close to the rupture area that had experienced subsidence of up to about 4 centimetres during the earthquake rose by nearly 7 centimetres after the earthquake our three dimensional viscoelastic finite element models of the post earthquake deformation show that a thin 30 200 kilometres low viscosity having a steady state maxwell viscosity of 0 5 10 1018 pascal seconds asthenospheric layer beneath the elastic oceanic lithosphere is required to produce the observed postseismic uplift

influence of asperities along subduction interfaces on the stressing and seismicity of adjacent areas abstract dmowska r and lovison l c 1992 influence of asperities along subduction interfaces on the stressing and seismicity of adjacent areas in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 23 43 we have investigated the influence of large scale fault inhomogeneities in large subduction earthquakes on the style of deformation and seismic behavior of the incoming oceanic plate and slab at intermediate depths during the earthquake cycle the zones of the large subduction events of rat islands 1965 alaska 1964 and valparaiso 1985 have been searched for earthquakes with m b 5 0 if available and for time periods as long as possible it has been found that in general the seismicity in the incoming oceanic plate clusters in front of asperities areas of highest seismic moment release and strongest locking and is positioned relative to them in the direction of plate motion it is usually lacking in areas adjacent to non asperities that is to zones that slip during the main event but with appreciably smaller seismic moment release and possibly slip seismically aseismically during the whole cycle similar behavior occurs in the downgoing slab at intermediate depths where seismicity during the cycle clusters but less strongly than in the oceanic crust next to asperities and down dip from them we infer that the locking of asperities causes higher stresses associated with the earthquake cycle itself to occur in areas adjacent to asperities both up dip and down dip from them along the direction of plate motion and that such stressing is much less pronounced in the areas adjacent to non asperities this opens the possibility of identifying the areas of highest seismic moment release in future subduction earthquakes and carries implications for where the highest deformation and possibly precursory phenomena and or nucleation of a future event might occur

s coda and rayleigh waves from a decade of repeating earthquakes reveal discordant temporal velocity changes since the 2004 sumatra earthquake temporal changes in the subsurface seismic velocity structure reflect the physical processes that modulate the properties of the media through which seismic waves propagate these processes such a

en echelon and orthogonal fault ruptures of the 11 april 2012 great intraplate earthquakes the magnitude 8 7 earthquake that occurred off the coast of the sumatra subduction zone on 11 april 2012 is shown to have had an extraordinarily complex four fault rupture these great ruptures represent large lithospheric deformation that may eventually lead to a localized boundary between the indian and australian plates on 11 april 2012 two of the largest strike slip earthquakes ever recorded at magnitudes of 8 7 and 8 2 occurred in the northeastern indian ocean a few hundred kilometres off the coast of sumatra three groups now report the analysis of seismic data from the days and months before and after these events as well as the events themselves matthias delescluse and co authors show that these earthquakes are part of the ongoing boost of intraplate deformation between india and australia that followed the aceh 2004 and nias 2005 megathrust earthquakes they conclude that the australian plate driven by slab pull forces at the sunda trench is gradually detaching from the indian plate han yue and colleagues show that the 11 april event involved a complex four fault rupture lasting several minutes followed two hours later by a magnitude 8 2 aftershock these great ruptures on a lattice of strike slip faults that extends through the crust and into the upper mantle represent large lithospheric deformation that may eventually create a localized boundary between the indian and australian plates fred pollitz and colleagues show that in the six days following 11 april the global rate of remote earthquakes with magnitudes greater than 5 5 increased nearly fivefold and events up to magnitude 7 seem to have been triggered the unprecedented delayed triggering power of this earthquake may arise from its strike slip source geometry or because it struck at a time of an unusually low global earthquake rate and increased the number of nucleation sites that were very close to failure the indo australian plate is undergoing distributed internal deformation caused by the lateral transition along its northern boundary from an environment of continental collision to an island arc subduction zone1 2 on 11 april 2012 one of the largest strike slip earthquakes ever recorded seismic moment magnitude mw 8 7 occurred about 100 200 kilometres southwest of the sumatra subduction zone occurrence of great intraplate strike slip faulting located seaward of a subduction zone is unusual it results from northwest southeast compression within the plate caused by the india eurasia continental collision to the northwest together with northeast southwest extension associated with slab pull stresses as the plate underthrusts sumatra to the northeast here we use seismic wave analyses to reveal that the 11 april 2012 event had an extraordinarily complex four fault rupture lasting about 160 seconds and was followed approximately two hours later by a great mw 8 2 aftershock the mainshock rupture initially expanded bilaterally with large slip 20 30 metres on a right lateral strike slip fault trending west northwest to east southeast wnw ese and then bilateral rupture was triggered on an orthogonal left lateral strike slip fault trending north northeast to south southwest nne ssw that crosses the first fault this was followed by westward rupture on a second wnw ese strike slip fault offset about 150 kilometres towards the southwest from the first fault finally rupture was triggered on another en echelon wnw ese fault about 330 kilometres west of the epicentre crossing the ninetyeast ridge the great aftershock with an epicentre located 185 kilometres to the ssw of the mainshock epicentre ruptured bilaterally on a nne ssw fault the complex faulting limits our resolution of the slip distribution these great ruptures on a lattice of strike slip faults that extend through the crust and a further 30 40 kilometres into the upper mantle represent large lithospheric deformation that may eventually lead to a localized boundary between the indian and australian plates

upper mantle water stratification inferred from observations of the 2012 indian ocean earthquake postseismic recordings of the moment magnitude 8 6 indian ocean earthquake of 2012 combined with the characteristics of olivine creep provide constraints on the water content of the asthenosphere sylvain barbot and colleagues infer that observed transient deformation in the aftermath of the 2012 indian ocean earthquake as recorded by continuous geodetic stations in the region requires a minimum olivine water content of about 0 01 per cent by weight in the oceanic asthenosphere the earthquake ruptured conjugate faults throughout the entire overlying oceanic lithosphere down to great depths compatible with dry olivine in the upper layer the authors explain the rheological contrast by dehydration across the lithosphere asthenosphere boundary presumably by buoyant melt migration that formed the oceanic crust elsewhere in this issue of nature yan hu et al use observations of postseismic deformation following this earthquake to constrain the structure of oceanic mantle rheology water the most abundant volatile in earth s interior preserves the young surface of our planet by catalysing mantle convection lubricating plate tectonics and feeding arc volcanism since planetary accretion water has been exchanged between the hydrosphere and the geosphere but its depth distribution in the mantle remains elusive water drastically reduces the strength of olivine1 and this effect can be exploited to estimate the water content of olivine from the mechanical response of the asthenosphere to stress perturbations such as the ones following large earthquakes here we exploit the sensitivity to water of the strength of olivine2 the weakest and most abundant mineral in the upper mantle and observations of the exceptionally large moment magnitude 8 6 2012 indian ocean earthquake3 to constrain the stratification of water content in the upper mantle taking into account a wide range of temperature conditions and the transient creep of olivine we explain the transient deformation in the aftermath of the earthquake that was recorded by continuous geodetic stations along sumatra as the result of water and stress activated creep of olivine this implies a minimum water content of about 0 01 per cent by weight or 1 600 h atoms per million si atoms in the asthenosphere the part of the upper mantle below the lithosphere the earthquake ruptured conjugate faults down to great depths4 compatible with dry olivine in the oceanic lithosphere we attribute the steep rheological contrast to dehydration across the lithosphere asthenosphere boundary presumably by buoyant melt migration to form the oceanic crust

anisotropic shear wave velocity structure of the earth s mantle a global model 1 we combine a new large data set of surface wave phase anomalies long period waveforms and body wave travel times to construct a three dimensional model of the anisotropic shear wave velocity in the earth s mantle our modeling approach is improved and more comprehensive compared to our earlier studies and involves the development and implementation of a new spherically symmetric reference model simultaneous inversion for velocity and anisotropy as well as discontinuity topographies and implementation of nonlinear crustal corrections for waveforms a comparison of our new three dimensional model s362ani with two other models derived from comparable data sets but using different techniques reveals persistent features 1 strong 200 km thick high velocity anomalies beneath cratons likely representing the continental lithosphere underlain by weaker fast anomalies extending below 250 km which may represent continental roots 2 weak velocity heterogeneity between 250 and 400 km depths 3 fast anomalies extending horizontally up to 2000 3000 km in the mantle transition zone beneath subduction zones 4 lack of strong long wavelength heterogeneity below 650 km suggesting inhibiting character of the upper mantle lower mantle boundary and 5 slow velocity superplumes beneath the pacific and africa the shear wave radial anisotropy is strongest at 120 km depth in particular beneath the central pacific lateral anisotropic variations appreciably improve the fit to data that are predominantly sensitive to the uppermost and lowermost mantle but not to the waveforms that control the transition zone and midmantle depths tradeoffs between lateral variations in velocity and anisotropy are negligible in the uppermost mantle but noticeable at the bottom of the mantle

tsunamis from strike slip earthquakes in the wharton basin northeast indian ocean march 2016 mw7 8 event and its relationship with the april 2012 mw 8 6 event

coseismic rupture process of the large 2019 ridgecrest earthquakes from joint inversion of geodetic and seismological observations author s liu chengli lay thorne brodsky emily e dascher cousineau kelian xiong xiong

complex rupture of an immature fault zone a simultaneous kinematic model of the 2019 ridgecrest ca earthquakes the july 4 2019 mw6 4 and subsequent july 6 2019 mw7 1 ridgecrest sequence earthquakes ruptured orthogonal fault planes in the little lake fault zone a low slip rate 1 mm yr dextral fault zone in the area linking the eastern california shear zone and walker lane this region accommodates nearly one fourth of plate boundary motion and has been proposed to be an incipient transform fault system that could eventually become the main tectonic boundary replacing the san andreas we investigate the rupture process of these events using a novel simultaneous kinematic slip method with joint inversion of high rate gnss strong motion gnss static offset and insar data we model the coulomb stress change to evaluate how the first mainshock may have affected the second our findings suggest complex interactions between several fault structures including dynamic and static triggering and provide important context for regional seismic source characterization and hazard models

advancement in source estimation techniques using broadband regional seismograms one important constraint on source retrieval from regional seismograms comes from the amplitude difference between various phases such as pnl surface wave sv sh because the misfit errors used in some waveform inversions are normalized by the data and synthetics the amplitude information in the data has not been fully utilized in this article we modify the cut and paste source estimation technique zhao and helmberger 1994 by removing this type of normalization it is shown that the modified method increases the stability and resolution of inversion when multiple stations at different distance ranges are used a distance scaling factor is introduced to compensate for the amplitude decay with distance by applying the technique to the terrascope data we have determined source mechanisms and depths of 335 southern californian events with m l 3 5 the amplitude decays with distance are r 1 13 for pnl r 0 55 for love waves and r 0 74 for rayleigh waves in contrast to generally shallow source depths reported by the southern california short period network the depth distribution from waveform inversion shows a strong peak around 12 km with few earthquakes occurring above 5 km and below 20 km

sem electron channelling analysis of dynamic recrystallization in a quartz grain abstract the sem electron channelling ec technique has been used to investigate the processes involved in the dynamic recrystallization of an individual quartz porphyroclast by using a combination of crystal axis polefigure diagrams and theoretical crystal axes dispersion paths for individual crystal slip systems it is possible to establish whether a relationship exists between recrystallized grains and parental grain it is then possible to distinguish between rotational and migrational dynamic recrystallization processes and to establish a dynamic recrystallization history for the porphyroclast dynamic recrystallization initiates as a subgrain rotation process initial rotation is accommodated by slip on individual systems leading to grain bending elongate polygonal subgrains and a systematic orientation relationship between subgrains and parent larger rotations and neoblast formation require more than one slip system but a systematic relationship between grains and parent can still be recognized rotational recrystallization produces an unstable microstructure which is stabilized by grainboundary migration

dynamic recrystallization of quartz under greenschist conditions abstract the sem electron channelling technique has been used to investigate the dynamic recrystallization of three quartz grains representative of optical textures observed in quartzite deformed under greenschist facies conditions the degree of recrystallization has been determined at 10 20 50 and 100 respectively we demonstrate that dynamic recrystallization is a sequential process involving subgrain grain rotation and grainboundary migration it initiates via subgrain polygonization on a single crystal slip system and continues via subgrain and neoblast rotation on several slip systems in the early stages of recrystallization

seismic b value anomalies in the sumatran region seismotectonic implications abstract the spatial variations in the seismic b value seismic moment bouguer gravity change and fault plane solution are estimated in the sumatran region based on homogeneous seismicity data from june 2005 to march 2012 to investigate the seismotectonic characteristics and tectonic activity between the 2004 sumatran earthquake and the 2012 east indian ocean earthquakes based on changes in the seismicity rate this time period is divided into five intervals with different earthquake distributions and faulting styles the seismic b values faulting mechanisms and seismic moment release values are mapped throughout the sumatran region and the gravity change every two years between the 2004 event and the 2012 events are determined from satellite grace gravity data the b values vary from 0 45 to 1 59 and an inverse correlation is observed between the b values and convergence rates low b values are located at depths between 20 km and 40 km in the subduction zone and between 20 km and 35 km in the oceanic plate the lowest b values are located at a depth of approximately 28 km in both regions which indicates a homogeneous fault system between them the areas with low b values are associated with megathrust and strike slip mechanisms while the area with the lowest b values is dominated by a megathrust mechanism seismically active regions have low b values associated with a high stress accumulation and high seismic moment release low b value areas are located mainly along the andaman sunda trench and andaman nicobar sumatra forearc temporal variations in the seismicity distribution and faulting style are recognized with temporal variations in the b values in each period relationships exist between the epicenter of the 2004 event and the location of the maximum bouguer gravity change in 2012 and between the epicenters of the 2012 events and the location of the maximum bouguer gravity change in 2004 furthermore a zone of continuous 2 year positive gravity change is located near the nicobar islands the 2004 event boost the 2012 events and intraplate seismicity via stress transfer the seismicity distributions in individual periods within the studied timeframe highlight the active and locked portions of the fault systems

fault interactions and triggering during the 10 january 2012 mw 7 2 sumatra earthquake the 10 january 2012 mw 7 2 sumatra earthquake in the wharton basin occurred 3 months before the great mw 8 6 and mw 8 2 earthquakes in the same region which had complex ruptures and are the largest strike slip earthquakes ever recorded teleseismic p wave back projection of the mw 7 2 earthquake images a unilateral rupture lasting 40 s without observable frequency dependency low frequency 0 05 0 3 hz high frequency 0 3 1 hz in addition to radiation bursts during the mw 7 2 main shock coherent energy releases from 50 to 75 s and from 100 to 125 s are observed about 143 km northeast of the main shock rupture and landward of the trench analysis of globally recorded p waves in both 0 02 0 05 hz velocity records and 1 5 hz stacked envelope functions confirms the presence of coherent sources during the time windows the observed energy bursts are likely to be large early aftershocks occurring on or near the subduction interface both dynamic and static triggering could have induced these early aftershocks as they initiated after the surface wave passed by and the coulomb stress perturbations from the mw 7 2 main shock promote earthquakes in the observed locations the earthquake sequence is a clear example of a seaward intraplate strike slip earthquake triggering landward intraplate earthquakes in the same region in contrast to previously reported normal reverse or reverse normal interactions at subduction zones

rupture process of the 2004 sumatra andaman earthquake the 26 december 2004 sumatra andaman earthquake initiated slowly with small slip and a slow rupture speed for the first 40 to 60 seconds then the rupture expanded at a speed of about 2 5 kilometers per second toward the north northwest extending 1200 to 1300 kilometers along the andaman trough peak displacements reached 15 meters along a 600 kilometer segment of the plate boundary offshore of northwestern sumatra and the southern nicobar islands slip was less in the northern 400 to 500 kilometers of the aftershock zone and at least some slip in that region may have occurred on a time scale beyond the seismic band

superficial simplicity of the 2010 el mayor cucapah earthquake of baja california in mexico the geometry of faults is usually thought to be more complicated at the surface than at depth and to control the initiation propagation and arrest of seismic ruptures the fault system that runs from southern california into mexico is a simple strike slip boundary the west side of california and mexico moves northwards with respect to the east however the m w 7 2 2010 el mayor cucapah earthquake on this fault system produced a pattern of seismic waves that indicates a far more complex source than slip on a planar strike slip fault here we use geodetic remote sensing and seismological data to reconstruct the fault geometry and history of slip during this earthquake we find that the earthquake produced a straight 120 km long fault trace that cut through the cucapah mountain range and across the colorado river delta however at depth the fault is made up of two different segments connected by a small extensional fault both segments strike n130 e but dip in opposite directions the earthquake was initiated on the connecting extensional fault and 15 s later ruptured the two main segments with dominantly strike slip motion we show that complexities in the fault geometry at depth explain well the complex pattern of radiated seismic waves we conclude that the location and detailed characteristics of the earthquake could not have been anticipated on the basis of observations of surface geology alone

teleseismic search for slow precursors to large earthquakes some large earthquakes display low frequency seismic anomalies that are best explained by episodes of slow smooth deformation immediately before their high frequency origin times analysis of the low frequency spectra of 107 shallow focus earthquakes revealed 20 events that had slow precursors 95 percent confidence level 19 were slow earthquakes associated with the ocean ridge transform system and 1 was a slow earthquake on an intracontinental transform fault in the east african rift system these anomalous earthquakes appear to be compound events each comprising one or more ordinary fast ruptures in the shallow seismogenic zone initiated by a precursory slow event in the adjacent or subjacent lithosphere

mantle control of plate boundary deformation the seismic wavefield propagating along the recently instrumented pacific north american plate boundary california displays remarkable variation with regional shear waves arriving at coastal stations up to 20 seconds earlier than equidistant stations in eastern california broadband modeling of this data reveals that coastal paths sample fast upper mantle typical of miocene aged ocean plate 50 km thickness inland paths sample slower uppermost mantle with the seismic lithosphere or lid measuring less than 5 km thick characteristic of the basin and range extensional province the boundary in the uppermost mantle between these provinces is sharp expressing the juxtaposition of the stronger pacific plate with weaker continental north america the lid step coincides with regionally maximum dextral strain rates measured with gps suggesting the uppermost mantle modulates long term regional scale continental margin deformation and evolution

scaling relations for seismic cycles on mid ocean ridge transform faults 1 mid ocean ridge transform faults rtfs have thermal structures that vary systematically with tectonic parameters resulting in predictable seismic characteristics and clear seismic cycles we develop a scaling relation for repeat time tr of the largest expected earthquake mc tr 1 2 3cmc1 3at1 4v 1 where is the shear modulus is the stress drop cmc is a constant at is the area above 600 c and v is the slip rate we identify repeating mc earthquakes by measuring differential arrival times of first orbit rayleigh waves to determine centroid offsets between pairs of events comparing our observations of tr 5 14 years for earthquakes on gofar and blanco rtfs with predictions from our scaling relation we can constrain rtf stress drops specific tests of this scaling relation are proposed for earthquakes on blanco gofar discovery and clipperton rtfs which are all expected to have large ruptures in the next few years

seismic structure of the upper mantle in a central pacific corridor the seismic structure of the tonga hawaii corridor has been investigated by combining two data sets revenaugh and jordan s reflectivity profile from scs reverberations which provides travel times to and impedance contrasts across the major mantle discontinuities and 1500 new observations of frequency dependent phase delays for the three component s ss and sss body waves and the r1 and g1 surface waves which constrain the velocity structure within this layered framework the shear waves turning in the upper mantle showed significant splitting of the sh and sv components indicative of shallow polarization anisotropy the data set was inverted in conjunction with attenuation and mineralogical constraints to obtain a complete spherically symmetric radially anisotropic structure the final model pa5 is characterized by a high velocity anisotropic lid bounded at 68 km depth by a large negative g discontinuity a low velocity anisotropic layer below g extending to a small l discontinuity at 166 km an isotropic steep gradient region between 166 km and 415 km and transition zone discontinuities at 415 507 and 651 km the depth of the radial anisotropy in pa5 is shallower than in most previous studies based on surface waves and higher modes the average value of radial shear anisotropy in the lid 3 7 is consistent with the magnitude expected from the spreading controlled models of olivine orientation while anisotropy in the low velocity zone which is required by our data set could be induced either by paleostrains that took place near the ridge crest or by shearing in the asthenosphere as a result of present day plate motions on the basis of recent work by hirth and kohlstedt we suggest that the g discontinuity is caused by a rapid increase in the water content of mantle minerals with depth marking the fossilized lower boundary of the melt separation zone active during crust formation the high gradient zone between 200 and 400 km is a characteristic feature of convecting oceanic upper mantle and is probably controlled by a steady decrease in the homologous temperature over this depth interval the average shear velocity gradient in the transition zone is lower than in most previous seismic models in better agreement with the predictions for a pyrolitic composition

transient rheology of the oceanic asthenosphere following the 2012 indian ocean earthquake inferred from geodetic data abstract postseismic motion in the middle field 100 500 km from the epicenter geodetic data resulting from the 2012 indian ocean earthquake exhibited rapid change during the two months following the rupture this pattern probably indicates multiple postseismic deformation mechanisms and might have been controlled by transient rheology therefore the relative contribution of transient rheology in the oceanic asthenosphere and afterslip in the oceanic lithosphere should be incorporated to explain short and long term transitional features of postseismic signals in this study using two years of post earthquake geodetic data from northern sumatra a three dimensional spherical earth finite element model was constructed based on a heterogeneous structure and incorporating transient rheology a rheology model combined with stress driven afterslip was estimated our best fit model suggests an oceanic lithosphere thickness of 75 km with oceanic asthenosphere viscosity values of 1 10 17 pa s and 2 10 18 pa s for the kelvin and maxwell viscosity models respectively the model results indicate that horizontal landward motion and vertical uplift in northern sumatra require viscoelastic relaxation of the oceanic asthenosphere coupled with afterslip in the lithosphere the present study demonstrates that transient rheology is essential for reproducing the rapidly changing motion of postseismic deformation in the middle field area

source parameters of the bay of bengal earthquake of 21 may 2014 and related seismotectonics of 85 e and 90 e ridges abstract source parameters of the bay of bengal earthquake of 21 may 2014 have been studied using full waveform inversion its source mechanism thus determined the orientation of the strike slip faulting as nw se ne sw the occurrence of past earthquakes along the ne sw nodal plane suggested its preference as the main fault which could result from the transmission of stresses from the indian plate boundary high stress drop of this earthquake 216 bar is attributed to its location in the intraplate region strike slip faulting and focus in the colder upper mantle comparison of the stress drop of deeper focus hindukush earthquakes with that of the bay of bengal earthquake showed a smaller felt radius due to fractured lithosphere in the himalayas vis a vis more efficient propagation of seismic waves in the peninsular region from the source region of this recent earthquake the seismological evidence presented for the 85 e and 90 e ridges shows the predominance of strike slip faulting with thrusting on both the ridges integrating their source mechanism with that of the may 2014 earthquake it could be inferred that the bay of bengal region excluding andaman sumatra subduction zone is characterised predominantly by strike slip faulting in the region north of latitude 20 n and strike slip with thrusting in the remaining portion

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

evidence of pervasive trans tensional deformation in the northwestern wharton basin in the 2012 earthquakes rupture area abstract the wharton basin in the indian ocean is one of the most extensively deforming ocean basins as confirmed by the occurrence of several very large earthquakes starting from january 12 2012 with mw 7 2 followed by the great earthquakes of april 11 2012 with mw 8 6 and mw 8 2 although the mw 7 2 and mw 8 2 earthquakes seem to have ruptured the re activated n s striking fracture zones the largest event mw 8 6 required the rupturing of several faults oblique to each other in a very complex manner in order to understand the nature of deformation in these earthquakes rupture zones we recently acquired 90 000 km2 of bathymetry 11 400 km of sub bottom profiling gravity and magnetic data covering the rupture areas of the 2012 earthquakes east of the ninety east ridge in the northwestern wharton basin these new data reveal six n8 e striking re activated fracture zones f5b f6a f6b f7a f7b and f8 where the fracture zone f6a can be followed for over 400 km and seems to be most active the epicenters of the mw 8 6 and mw 8 2 earthquakes lie on the fracture zones f6a and f7b respectively the newly observed fracture f5b in the east is short and has an extensional basin at its southern tip the fracture zone f8 defines the eastern boundary of the ninety east ridge the presence of en echelon faults and pull apart basins indicate left lateral motion along these fracture zones in between these fracture zones we observe pervasive 290 striking right lateral shear zones at 4 8 km intervals one of which has cut through a seamount that might have ruptured during the mw 8 6 earthquake we also observe another n20 e striking left lateral shear zones in the vicinity of f7b and f8 which is coincident with the strike of one of the nodal planes of the mw 8 6 focal mechanism these n20 e striking shear zones are interpreted as r riedel shears and the n290 e striking shear zones as r riedel shears these shear zones are formed by a series of n335 e striking en echelon normal faults our data also show the presence of n65 e striking thrust faults east of the ninety east ridge orthogonal to the regional principal direction of compression furthermore extensive bending related faulting is also observed close to the sumatra trench with normal faults also striking at n335 e similar to the normal faults that form the shear zones normal faults with a similar orientation are also present at the southern tip of f5b we explain all these observations with a single coherent model of deformation in the wharton basin where a dominant part of the regional nw se compressional stress is accommodated along the n8 e re activated fracture zones and the rest is distributed along shear zones thrust and normal faults between these fracture zones the thrust and normal faults are orthogonal to each other and define the direction of principal compressive and extensive stresses in the region whereas the two shear zone systems form a conjugate pair

age spreading rates and spreading asymmetry of the world s ocean crust we present four companion digital models of the age age uncertainty spreading rates and spreading asymmetries of the world s ocean basins as geographic and mercator grids with 2 arc min resolution the grids include data from all the major ocean basins as well as detailed reconstructions of back arc basins the age spreading rate and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments the age uncertainties for grid cells coinciding with marine magnetic anomaly identifications observed or rotated to their conjugate ridge flanks are based on the difference between gridded age and observed age the uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges resulting in ridge jumps toward hot spots we also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age depth relationships the new set of grids helps to investigate prominent negative depth anomalies which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow a combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems

the 2018 m w 7 9 gulf of alaska earthquake multiple fault rupture in the pacific plate a major m w 7 9 intraplate earthquake ruptured the pacific plate seaward of the alaska subduction zone near kodiak island on 23 january 2018 the aftershock seismicity is diffuse with both nnw and ene trending distributions while long period point source moment tensors have near horizontal compressional and tensional principal strain axes and significant non double couple components backprojections from three large aperture networks indicate sources of short period radiation not aligned with the best double couple fault planes a suite of finite fault rupture models with one to four faults was considered and a four fault model dominated by right lateral slip on an sse trending westward dipping fault is compatible with most seismic gps and tsunami data however the precise geometry timing and slip distribution of the complex set of faults is not well resolved the sequence appears to be the result of intraplate stresses influenced by slab pull the 1964 alaska earthquake and collision of the yakutat terrane in northeastern alaska

a complete structural model and kinematic history for distributed deformation in the wharton basin abstract the equatorial eastern indian ocean hosts a diffuse plate boundary where widespread deformation accommodates the relative motion between the indian australian and capricorn sub plates we integrate iodp expedition 362 borehole data which for the first time provides an accurate ground truthed chronostratigraphy of the sedimentary sequence east of the ninety east ridge ner with 2d seismic reflection profiles and multibeam bathymetry to assess the styles of faulting between the ner and the sunda subduction zone timing of activity and comparison with physical and rheological properties we identify four distinct fault sets east of the ner in the northern wharton basin n s 350 010 orientated faults associated with the n s fracture zones formed at the now extinct wharton spreading centre are still active and have been continuously active since at least 10 ma nne and wnw trending fault fabrics develop between the fracture zones the orientations and likely sense of displacement on these three sets of faults defines a riedel shear system responding to nne ssw left lateral strike slip activity at depth demonstrated by the recent 2012 great intraplate earthquakes we also find evidence of ne sw reverse faults similar in style to e w reverse faults observed west of the ner where reverse faulting is more dominant we show that the activity of this strike slip system increased ca 7 9 ma contemporaneous with reverse faulting and intraplate deformation west of the ner

locating earthquakes with surface waves and centroid moment tensor estimation traditionally p wave arrival times have been used to locate regional earthquakes in contrast the travel times of surface waves dependent on source excitation and the source parameters and depth must be determined independently thus surface wave path delays need to be known before such data can be used for location these delays can be estimated from previous earthquakes using the cut and paste technique ambient seismic noise tomography and from 3d models taking the chino hills event as an example we show consistency of path corrections for 10 s love and rayleigh waves to within about 1 s obtained from these methods we then use these empirically derived delay maps to determine centroid locations of 138 southern california moderate sized 3 5 m w 5 7 earthquakes using surface waves alone it appears that these methods are capable of locating the main zone of rupture within a few 3 km accuracy relative to southern california seismic network locations with 5 stations that are well distributed in azimuth we also address the timing accuracy required to resolve non double couple source parameters which trades off with location with less than a km error required for a 10 compensated linear vector dipole resolution

stress driven relaxation of heterogeneous upper mantle and time dependent afterslip following the 2011 tohoku earthquake stress driven relaxation of heterogeneous upper mantle and time dependent afterslip following the 2011 tohoku earthquake yan hu 1 roland burgmann 1 naoki uchida 2 paramesh banerjee 3 and jeffrey t freymueller 4 university of california berkeley berkeley ca united states graduate school of science tohoku university japan earth observatory of singapore nanyang technological university singapore singapore university of alaska fairbanks fairbanks ak united states corresponding author yan hu earth and planetary science university of california berkeley 307 mccone hall berkeley ca 94720 usa yhu seismo berkeley edu this article has been accepted for publication and undergone full peer review but has not been through the copyediting typesetting pagination and proofreading process which may lead to differences between this version and the version of record please cite this article as doi 10 1002 2015jb012508 2015 american geophysical union all rights reserved

extremely thin crust in the indian ocean possibly resulting from plume ridge interaction the thickness of the crust created at ocean spreading centres depends on the spreading rate and melt production in the mantle it is 5 8 km for a crust formed at slow and fast spreading centres and 2 4 km at ultra slow spreading centres away from hotspots and mantle anomalies the crust is generally thin at the fracture zones and thick beneath hotspots and large igneous provinces here we present results for the crust generated at the fast wharton spreading centre 55 58 ma ago using seismic reflection and refraction data we find that the crust over a 200 km segment of the wharton basin is only 3 5 4 5 km thick the thinnest crust ever observed in a fast spreading environment a thin crust could be produced by the presence of depleted and or cold mantle numerical simulations and recent laboratory experiments studying the impact of a hot plume under a lithosphere show that a curtain of weak cold downwellings of depleted mantle material is likely to develop around the edges of the hot plume pond because of a strongly temperature dependent viscosity of lithospheric material the hotter therefore less viscous bottom of the lithosphere can be mobilized by an impinging plume if sampled by a spreading centre the locally cold and depleted mantle should result in low production of melt we suggest that the observed thin crust in the wharton basin is likely to have been formed by the interaction between the kerguelen mantle plume and the wharton spreading centre 55 ma ago

source estimation from broadband regional seismograms recently developed source inversion techniques do not take full advantage of the broadband nature of regional seismograms the reason is that green s functions generated from flat layered models are not correct for the complicated propagational phenomena associated with realistic crustal structure the inversion is usually performed by removing short periods and inverting only selected portions of the records in this article we introduce a source estimation technique that allows for better use of the entire broadband record when only imperfect green s function are available the procedure desensitizes the timing between the principal crustal arrivals by fitting portions of the green s functions independently the preferred source is the orientation that minimizes the average l1 and l2 norms in term of the four parameters m 0 strike dip and rake the l2 error emphasizes the longer period surface waves while the l1 error weights the shorter period body waves we obtain estimates of duration by modeling long period and broadband signals the depth determination can be obtained directly from the surface reflected phases sp mp or ss ms or by cycling through the depth dependent green s functions in addition to the source parameters we obtain t phase alignments shifts that can be used as green s function corrections for relocating other events or as a guide to deriving new crustal models

pervasive deformation of an oceanic plate and relationship to large mw 8 intraplate earthquakes the northern wharton basin indian ocean large magnitude intraplate earthquakes within the ocean basins are not well understood the mw 8 6 and mw 8 2 strike slip intraplate earthquakes on 11 april 2012 while clearly occurring in the equatorial indian ocean diffuse plate boundary zone are a case in point with disagreement on the nature of the focal mechanisms and the faults that ruptured we use bathymetric and seismic reflection data from the rupture area of the earthquakes in the northern wharton basin to demonstrate pervasive brittle deformation between the ninetyeast ridge and the sunda subduction zone in addition to evidence of recent strike slip deformation along approximately north south trending fossil fracture zones we identify a new type of deformation structure in the indian ocean conjugate riedel shears limited to the sediment section and oriented oblique to the north south fracture zones the riedel shears developed in the miocene at a similar time to the onset of diffuse deformation in the central indian ocean however left lateral strike slip reactivation of existing fracture zones started earlier in the paleocene to early eocene and compartmentalizes the wharton basin modeled rupture during the 11 april 2012 intraplate earthquakes is consistent with the location of two reactivated closely spaced approximately north south trending fracture zones however we find no evidence for wnw ese trending faults in the shallow crust which is at variance with most of the earthquake fault models

the 2 march 2016 wharton basin mw 7 8 earthquake high stress drop north south strike slip rupture in the diffuse oceanic deformation zone between the indian and australian plates the diffuse deformation zone between the indian and australian plates has hosted numerous major and great earthquakes during the seismological record including the 11 april 2012 m w 8 6 event the largest recorded intraplate earthquake on 2 march 2016 an m w 7 8 strike slip faulting earthquake occurred in the northwestern wharton basin in a region bracketed by north south trending fracture zones with no previously recorded large event nearby despite the large magnitude only minor source finiteness is evident in aftershock locations or resolvable from seismic wave processing including high frequency p wave backprojections and love wave directivity analysis our analyses indicate that the event ruptured bilaterally on a north south trending fault over a length of up to 70 km with rupture speed of 2 km s and a total duration of 35 s the estimated stress drop 20 mpa is high comparable to estimates for other large events in this broad intraplate oceanic deformation zone

analysis of regional slope characteristics on venus and earth regional slope values for earth and venus are calculated for each 3 o x 3 o region of topography and the global characteristics of these magnitudes are examined and compared the effects on terrestrial regional slope due to ocean loading are treated by approximating the component of seafloor depth due to the weight of the overlying water column and removing this component from the ocean topography although regional slopes on venus and earth span the same range 0 00 2 4 o 0 07o the slope frequency distributions for the two planets differ significantly the most abundant regional slope values for the terrestrial cases earth and unloaded earth are 0 0 o and reflect the presence of vast plains associated with the continental interiors and ocean abyssal plain in contrast venus exhibits a peak in slope frequency at approximately 0 09 o perhaps indicating less effective planation processes in the absence of a hydrosphere surfaces with regional slope values of 0 07o 0 24 o are substantially more common on venus than on earth slopes in this range are associated with discrete features in the lowland and upland rolling plains provinces of venus and may be indicative of a geologic process that is not commonly observed on earth only 14 1 of all venus surfaces have regional slopes above 0 24 o compared to 26 1 for earth when mean regional slope is calculated as a function of elevation a distinctive positive correlation is expressed on venus in contrast the terrestrial cases exhibit a complex relationship marked by four modes related to the presence on earth of an active hydrosphere driven weathering regime a distinctive crustal dichotomy and plate tectonics the distinctions in the regional slope characteristics between venus and earth point to a simpler less diversified geology on venus

a unified gps based earthquake catalog for the sumatran plate boundary between 2002 and 2013 we have compiled the first self consistent gps based earthquake catalog for the sumatran plate boundary using continuous daily position time series from the sumatran gps array sugar we document 30 earthquakes which occurred within or outside the sugar network from august 2002 through the end of 2013 and we provide estimates of both vertical and horizontal coseismic offsets associated with 1 m9 2 3 m8 6 m7 19 m6 and 1 m5 9 earthquakes as well as postseismic decay amplitudes and times associated with 9 m 7 earthquakes and 1 m6 7 earthquake for most of the previously studied earthquakes our geodetic catalog provides more complete coseismic displacements than those published showing consistent patterns of motion across a large range of distances for many of the moderate to large earthquakes we publish their coseismic displacements for the first time providing new constraints on their locations and slip distributions for the postseismic time series we have tackled the challenge of separating the signals for individual events from the overlapping effects of many other earthquakes as a result we have obtained either new or much longer time series than previously published based on our long time series we find logarithmic decay times ranging from several days to more than 20 years and sometimes a second decay time is needed suggesting that when studying large to great sumatran earthquakes we need to consider multiple postseismic mechanisms our geodetic catalog provides rich spatial and temporal sumatran earthquake cycle information for future studies of the physics and dynamics of the sumatran plate boundary

macrofracturing of oceanic lithosphere in complex large earthquake sequences major earthquakes in oceanic lithosphere seaward of the subduction zone outer trench slope are relatively uncommon but several recent occurrences have involved very complex sequences rupturing multiple nonaligned faults and or having high aftershock productivity with diffuse distribution this includes the 21 december 2010 m w 7 4 ogasawara bonin 11 april 2012 m w 8 6 indo australia 23 january 2018 m w 7 9 off kodiak island and 20 december 2018 m w 7 3 nikol skoye northwest pacific earthquakes major oceanic intraplate event sequences farther from plate boundaries do not tend to be as complex in faulting or aftershocks outer trench slope extensional faulting can involve complex distributed sequences particularly when activated by great megathrust ruptures such as 11 march 2011 m w 9 1 tohoku and 15 november 2006 m w 8 3 kuril islands intense faulting sequences also occur near subduction zone corners with many fault geometries being activated including some in nearby oceanic lithosphere as for the 29 september 2009 m w 8 1 samoa 6 february 2013 m w 8 0 santa cruz islands and 16 november 2000 m w 8 0 new ireland earthquakes the laterally varying plate boundary stresses from heterogeneous locking recent earthquakes or boundary geometry influence the specific faulting geometries activated in nearby major intraplate ruptures in oceanic lithosphere preexisting lithospheric structures and fabrics exert secondary influences on the faulting intraplate stress release in oceanic lithosphere near subduction zones favors distributed macrofracturing of near critical fault systems rather than localized single fault failures both under transient loading induced by plate boundary ruptures and under slow loading by tectonic motions and slab pull

modeling the 2012 wharton basin earthquakes off sumatra complete lithospheric failure a sequence of large strike slip earthquakes occurred west of sunda trench beneath the wharton basin first reports indicate that the main shock was extremely complex involving three to four subevents m w 8 with a maze of aftershocks we investigate slip models of the two largest earthquakes by joint inversion of regional and teleseismic waveform data using the m w 7 2 foreshock we developed hybrid green s functions for the regional stations to approximate the mixture of oceanic and continental paths the main shock fault geometry is defined based on the back projection results point source mechanisms aftershock distribution and fine tune of grid searches the fault system contains three faults labeled f1 89 289 for dip strike f2 74 20 and f3 60 310 the inversion indicates that the main rupture consisted of a cascade of high stress drop asperities up to 30 mpa extending as deep as 50 km the rupture propagated smoothly from one fault to the next f1 f2 and f3 in sequence with rupture velocities of 2 0 2 5 km s the whole process lasted about 200 s and the major moment release 70 took place on the n s oriented f2 the m w 8 2 aftershock happened about 2 h later on a n s oriented fault with a relatively short duration 60 s and also ruptured as deep as 50 km the slip distributions suggest that the earthquake sequence was part of a broad left lateral shear zone between the australian and indian plates and ruptured the whole lithosphere these earthquakes apparently reactivated existing fracture zones and were probably triggered by unclamping of the great sumatran earthquake of 2004

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

coseismic compression dilatation and viscoelastic uplift subsidence following the 2012 indian ocean earthquakes quantified from satellite gravity observations the 2012 indian ocean earthquake sequence mw 8 6 8 2 is a rare example of great strike slip earthquakes in an intraoceanic setting with over a decade of gravity recovery and climate experiment grace data we were able to measure and model the unanticipated large coseismic and postseismic gravity changes of these events using the approach of normal mode decomposition and spatial localization we computed the gravity changes corresponding to five moment tensor components our analysis revealed that the gravity changes are produced predominantly by coseismic compression and dilatation within the oceanic crust and upper mantle and by postseismic vertical motion our results suggest that the postseismic positive gravity and the postseismic uplift measured with gps within the coseismic compressional quadrant are best fit by ongoing uplift associated with viscoelastic mantle relaxation our study demonstrates that the grace data are suitable for analyzing strike slip earthquakes as small as mw 8 2 with the noise characteristics of this region

source study of the 1906 san francisco earthquake all quality teleseismic recordings of the great 1906 san francisco earthquake archived in the 1908 carnegie report by the state earthquake investigation commission were scanned and digitized first order results were obtained by comparing complexity and amplitudes of teleseismic waveforms from the 1906 earthquake with well calibrated similarly located more recent earthquakes 1979 coyote lake 1984 morgan hill and 1989 loma prieta earthquakes at nearly co located modern stations peak amplitude ratios for calibration events indicated that a localized moment release of about 1 to 1 5 10 27 dyne cm was responsible for producing the peak the teleseismic body wave arrivals at longer periods 50 to 80 sec we found spectral amplitude ratios of the surface waves require a total moment release between 4 and 6 10 27 dyne cm for the 1906 earthquake comparable to previous geodetic and surface wave estimates thatcher 1975 we then made a more detailed source analysis using morgan hill s body waves as empirical green s functions in a finite fault subevent summation the morgan hill earthquake was deemed most appropriate for this purpose as its mechanism is that of the 1906 earthquake in the central portion of the rupture from forward and inverse empirical summations of morgan hill green s functions we obtained a good fit to the best quality teleseismic waveforms with a relatively simple source model having two regions of localized strong radiation separated spatially by about 110 km assuming the 1906 epicenter determined by bolt 1968 this corresponds with a large asperity on the order of the loma prieta earthquake in the golden gate san francisco region and one about three times larger located northwest along strike between point reyes and fort ross this model implies that much of the 1906 rupture zone may have occurred with relatively little 10 to 20 sec radiation consideration of the amplitude and frequency content of the 1906 teleseismic data allowed us to estimate the scale length of the largest asperity to be less than about 40 km with rough constraints on the largest asperity size and magnitude we produced a suite of estimated synthetic ground velocities assuming a slip distribution similar to that of the loma prieta earthquake but with three times as much slip for purposes of comparison with the recent abundant loma prieta strong motion data set we moved the largest 1906 asperity into loma prieta region peak ground velocity amplitudes are substantially greater than those recorded during the loma prieta earthquake and are comparable to those predicted by the attenuation relationship of joyner and boore 1988 for a magnitude m w 7 7 earthquake

breaking the oceanic lithosphere of a subducting slab the 2013 khash iran earthquake 1 large intermediate depth intraslab normal faulting earthquakes are a common dangerous but poorly understood phenomenon in subduction zones owing to a paucity of near field geophysical observations seismological and high quality geodetic observations of the 2013 mw7 7 khash iran earthquake reveal that at least half of the oceanic lithosphere including the mantle and entire crust ruptured in a single earthquake confirming with unprecedented resolution that large earthquakes can nucleate in and rupture through the oceanic mantle a rupture width of at least 55 km is required to explain both interferometric synthetic aperture radar observations and teleseismic waveforms with the majority of slip occurring in the oceanic mantle combining our well constrained earthquake slip distributions with the causative fault orientation and geometry of the local subduction zone we hypothesize that the khash earthquake likely occurred as the combined result of slab bending forces and dehydration of hydrous minerals along a preexisting fault formed prior to subduction

the 2012 mw 8 6 sumatra earthquake evidence of westward sequential seismic ruptures associated to the reactivation of a n s ocean fabric 1 the 11 april 2012 mw 8 6 earthquake offshore sumatra is the largest of the rare great intraplate earthquakes of the instrumental era this major strike slip event occurred in the diffuse zone of deformation that accommodates differential rotation between indian and australian plates we perform a back projection analysis calibrated with well located aftershocks of short period teleseismic p waves recorded by the european array to image the rupture process during the mainshock in complement a love wave analysis is conducted for tracking azimuthal change in the apparent global source duration due to the source spatio temporal extent the combined analysis reveals a complex rupture pattern characterized by three main episodes of energy release the latest being located 370 km west of the epicenter on the ninety east ridge with a delay of 120 s we interpret the 11 april 2012 mw 8 6 offshore sumatra earthquake as a complex westward propagating sequence of dynamically triggered strike slip fault ruptures associated to the reactivation of the inherited nne striking sea floor fabric the dynamic triggering mechanism could result from the interaction between transient surface wave stress perturbations and fluids

localized water reverberation phases and its impact on backprojection images coherent radiators imaged by back projections bp are commonly interpreted as part of the rupture process nevertheless artifacts introduced by structure related phases are rarely discriminated from the rupture process in this study we use a calibration event to discriminate between rupture and structure effects we re examine the waveforms and bp images of the 2012 mw 7 2 indian ocean earthquake and a calibration event mw 6 2 the p wave codas of both events present similar shape with characteristic period of approximately 10 s which are back projected as coherent radiators near the trench s wave bp doesn t image energy radiation near the trench we interpret those coda waves as localized water reverberation phases excited near the trench we perform a 2d waveform modeling using realistic bathymetry model and find that the steep near trench bathymetry traps the acoustic water waves forming localized reverberation phases these waves can be imaged as coherent near trench radiators with similar features as that in the observations we present a set of methodologies to discriminate between the rupture and propagation effects in bp images which can serve as a criterion of subevent identification

trans pacific upper mantle shear velocity structure 1 we use 50 tonga fiji events recorded at the broadband trinet array southern california to develop a pure path upper mantle shear velocity model across the pacific at the epicentral distances of 70 95 multibounce s waves up to s5 are observed including their triplicated branches which become particularly clear after stacking since these s wave multiples turn at various depths simultaneously modeling their differential traveltimes and waveforms provides strong constraints on the radial velocity structure we parameterize the velocity model according to a priori information from the previous oceanic models so that we can take a grid search approach to fully investigate possible interdependencies among the model parameters we construct synthetics with a reflectivity code and study both the sh and sv components by modeling the whole recordings from events at different depths with different mechanisms we are able to separate shallow low velocity zone lvz features from deeper structure our preferred model pac06 contains a fast lid vsh 4 78 km s 1 vsv 4 58 km s 1 with a thickness of 60 km the underlying lvz is prominent with the lowest velocities vsh 4 34 km s 1 and vsv 4 22 km s 1 occurring at a depth of 160 km these velocities are below the estimates of solid state lvz suggesting the presence of partial melt the anisotropy vsv vsh of pac06 extends to 300 km depth which is constrained by s5 turning at this depth besides the 406 km and 651 km discontinuities pac06 also has a small 1 velocity jump at 516 km we consider these main features of pac06 to be well determined since pac06 explains a large data set from various events therefore it is ideally suited for comparing with mineralogical models

highly heterogeneous pore fluid pressure enabled rupture of orthogonal faults during the 2019 ridgecrest mw7 0 earthquake here we show that the 2019 mw7 0 ridgecrest mainshock as well as its mw6 5 foreshock ruptured orthogonal conjugate faults we invert the waveforms recorded by the dense strong motion network at re

earthquake in a maze compressional rupture branching during the 2012 mw 8 6 sumatra earthquake seismological observations of the 2012 moment magnitude 8 6 sumatra earthquake reveal unprecedented complexity of dynamic rupture the surprisingly large magnitude results from the combination of deep extent high stress drop and rupture of multiple faults back projection source imaging indicates that the rupture occurred on distinct planes in an orthogonal conjugate fault system with relatively slow rupture speed the east southeast west northwest ruptures add a new dimension to the seismotectonics of the wharton basin which was previously thought to be controlled by north south strike slip faulting the rupture turned twice into the compressive quadrant against the preferred branching direction predicted by dynamic coulomb stress calculations orthogonal faulting and compressional branching indicate that rupture was controlled by a pressure insensitive strength of the deep oceanic lithosphere

the 2012 mw 8 6 indian ocean earthquake deep nucleation on a listric like fault abstract the 2012 mw 8 6 indian ocean earthquake the largest instrumentally recorded strike slip event has been described as a westward rupture on orthogonal faults that are part of the original oceanic fabric of the region reported estimates of its depth vary from 10 to 45 km while the maximum depth of its inferred rupture extends to 50 60 km the complexity of the earthquake is undeniable both in terms of fault geometry and rupture propagation with debates on the geometry of the causative faults results from recent seismic surveys enable a fresh look at the earthquake fault geometry nucleation depths and lithospheric rheology in the present study these new findings are incorporated into 22 forward models using a revised velocity structure and n s geometries that flatten with depth the rupture initiation is modeled in the uppermost mantle 25 30 km as well as in the upper mantle at 45 km the latter of which is 15 20 km below the commonly accepted values of maximum depth for frictional failure our study shows that the westward directionality of wave propagation is achieved for strike slip failure on a listric like fault in contrast to subvertical geometries as previously suggested this propagation is persistent for a strike slip failure only for events nucleating at upper mantle depths 45 km rather than for those set to originate at depths between 25 and 30 km however for a dip slip failure the westward propagation is found to be consistent at both nucleation depths on a listric like fault this study highlights a deep nucleation within the lithospheric mantle for the 2012 mw 8 6 earthquake that could be due to strain localization induced by fluid rock interaction and or mineral transformation crystallization near the 680 c isotherm at 45 km depth 1 4 gpa which correlates with deep serpentinization on faults

coherent seismic arrivals in the p wave coda of the 2012 m w 7 2 sumatra earthquake water reverberations or an early aftershock

seismic evidence for broken oceanic crust in the 2004 sumatra earthquake epicentral region the 2004 sumatra earthquake was one of the largest events to occur in a subduction zone in the past 50 years seismic reflection data for this subduction zone reveal thrust faults cutting across the entire oceanic crust this observation coupled with the hypocentres of aftershocks suggests that the megathrust the interface between the indo australian plate and the sunda plate currently lies in the oceanic mantle

source description of the 1999 hector mine california earthquake part ii complexity of slip history we present a rupture model of the hector mine earthquake m 7 1 determined from the joint inversion of strong motion records p and sh teleseismic body waves global positioning system gps displacement vectors and measured surface offset we solve for variable local slip rake angle rise time and rupture velocity of a finite fault model involving multiple segments the inversion methodology developed in a companion article ji et al 2002 combines a wavelet transform approach with a nonlinear simulated annealing algorithm the final model is checked by forward simulating the interferometric synthetic aperture radar insar data our estimation to the seismic moment is 6 28 10 19 n m which is distributed along three segments from north to south releasing 37 41 and 22 of the total moment respectively the average slip is 1 5 m with peak amplitudes as high as 7 m the fault rupture has an average rise time of 3 5 sec and a relatively slow average rupture velocity 1 9 km sec resulting in a 14 sec rupture propagation history our approach permits large variation in rupture velocity and rise time and indicates that rise time appears to be roughly proportional to slip and shorter rise times are associated with the initiation of asperity rupture we also find evidence for nearly simultaneous rupture of the two northern branches