quantifying slip balance in the earthquake cycle coseismic slip model constrained by interseismic coupling the long term slip on faults has to follow on average the plate motion while slip deficit is accumulated over shorter timescales e g between the large earthquakes accumulated slip deficits eventually have to be released by earthquakes and aseismic processes in this study we propose a new inversion approach for coseismic slip taking interseismic slip deficit as prior information we assume a linear correlation between coseismic slip and interseismic slip deficit and invert for the coefficients that link the coseismic displacements to the required strain accumulation time and seismic release level of the earthquake we apply our approach to the 2011 m9 tohoku oki earthquake and the 2004 m6 parkfield earthquake under the assumption that the largest slip almost fully releases the local strain as indicated by borehole measurements our results suggest that the strain accumulated along the tohoku oki earthquake segment has been almost fully released during the 2011 m9 rupture the remaining slip deficit can be attributed to the postseismic processes similar conclusions can be drawn for the 2004 m6 parkfield earthquake we also estimate the required time of strain accumulation for the 2004 m6 parkfield earthquake to be 25 years confidence interval of 17 43 years consistent with the observed average recurrence time of 22 years for m6 earthquakes in parkfield for the tohoku oki earthquake we estimate the recurrence time of 500 700 years this new inversion approach for evaluating slip balance can be generally applied to any earthquake for which dense geodetic measurements are available

resolving depth dependent subduction zone viscosity and afterslip from postseismic displacements following the 2011 tohoku oki japan earthquake abstract we developed a 3 d viscoelastic finite element model of the m9 2011 tohoku oki japan earthquake capable of predicting postseismic displacements due to viscoelastic relaxation and afterslip we consider seismically inferred slab geometries associated with the pacific and philippine sea plate and a wide range of candidate viscoelastic rheologies for each case we invert for afterslip based on residual surface displacements observed gps minus that predicted due to viscoelastic relaxation to develop combined viscoelastic relaxation and afterslip models we are able to find a mechanical model that fully explains all observed geodetic on land and seafloor horizontal and vertical postseismic displacements we find that postseismic displacements are in about equal parts due to viscoelastic relaxation and afterslip but their patterns are spatially distinct accurately predicting both horizontal and vertical on land postseismic displacements requires a mantle wedge viscosity structure that is depth dependent reflecting the manner in which temperature pressure and water content influence viscosity no lateral heterogeneities within the mantle wedge viscosity structure beneath northern honshu are required westward directed postseismic seafloor displacements may be due flow via low temperature plastic creep within the lower half of a pacific lithosphere weakened by plate bending the distribution of afterslip is controlled by the location of coseismic slip from the tohoku oki and other regional historic earthquakes the paradigm by which afterslip is thought of as the dominant postseismic mechanism immediately following earthquakes with viscoelastic relaxation to follow in later years is shown to no longer be valid

introduction of covariance components in slip inversion of geodetic data following a non uniform spatial distribution and application to slip deficit rate estimation in the nankai trough subduction zone when spatial distribution of observation stations has bias in geodetic slip inversion modeling errors in the inversion scheme may result in significant unnatural short wave components in estimated slip distribution which overfit to data combined use of both land and seafloor geodetic data in slip inversion often leads to such situations to avoid overfitting i proposed a method to incorporate proper covariance components in the data covariance matrix originated by modeling errors in the geodetic slip inversion because linearity of the inversion problem is retained widely known approaches to introduce prior constraints to the inversion which assumes linear inversion are easily applied to the proposed method synthetic tests showed that the introduction of covariance components allowed for the estimation of slip distributions closer to the true one avoiding overfitting to geodetic data in biasedly distributed observation stations compared to a conventional approach that does not introduce covariance components i applied the proposed method to the estimation of the slip deficit rate in the nankai trough subduction zone using geodetic data of displacement rates provided by land gnss stations and seafloor gnss acoustic stations the proposed method estimated a reasonably smooth distribution of slip deficit rate compared to the conventional approach spatial distribution of residuals in the displacement rates suggested that the proposed method successfully avoids overfitting to the block motion at the south of the median tectonic line which the physical model i assumed here cannot describe

green s functions for post seismic strain changes in a realistic earth model and their application to the tohoku oki m w 9 0 earthquake based on a spherically symmetric self gravitating viscoelastic earth model we derive a complete set of green s functions for the post seismic surface strain changes for four independent dislocation sources strike slip dip slip and horizontal and vertical tensile point sources the post seismic surface strain changes caused by an arbitrary earthquake can be obtained by a combination of the above green s functions the post seismic surface strain changes in the near field agree well with the results calculated by the method in a half space earth model wang et al in comupt geosci 32 527 541 2006 which verifies our green s functions with an increase in the epicentral distance the effect of the curvature on both the co and post seismic strain changes clearly increases revealing the importance of our spherical theory for far field calculations next we use our green s functions to simulate the post seismic surface strain changes that were caused by the viscoelastic relaxation of the mantle over the 6 year period after the tohoku oki mw 9 0 earthquake based on continuous global positioning system gps observations around honshu island of japan northeastern china south korea and the russian far east we also deduce the post seismic strain changes caused by the tohoku oki mw 9 0 earthquake overall the distributions of the calculated and gps derived strain changes agree well each other finally we compare the relative error between the observed and simulated strain changes over the 3 0 4 5 year period after the earthquake in both the near and far field we find that the relative errors decrease as the epicentral distance increases which validates our green s functions for research in the far field

coseismic slip distribution of the 2011 off the pacific coast of tohoku earthquake m9 0 refined by means of seafloor geodetic data 1 on 11 march 2011 the devastating m9 0 tohoku earthquake occurred on the interface of the subducting pacific plate and was followed by a huge tsunami that killed about 20 000 people several geophysical studies have already suggested that the very shallow portion of the plate interface might have played an important role in producing such a large earthquake and tsunami however the sparsity of seafloor observations leads to insufficient spatial resolution of the fault slip on such a shallow plate interface for this reason the location and degree of the slip has not yet been estimated accurately enough to assess future seismic risks thus we estimated the coseismic slip distribution based on terrestrial gps observations and all available seafloor geodetic data that significantly improve the spatial resolution at the shallow portion of the plate interface the results reveal that an extremely large greater than 50 m slip occurred in a small about 40 km in width and 120 km in length area near the japan trench and generated the huge tsunami the estimated slip distribution and a comparison of it with the coupling coefficient distribution deduced from the analysis of the small repeating earthquakes suggest that the 2011 tohoku earthquake released strain energy that had accumulated over the past 1000 years probably since the jogan earthquake in 869 the accurate assessments of seismic risks on very shallow plate interfaces in subduction zones throughout the world can be obtained by improving the quality and quantity of seafloor geodetic observations

distributed fault slip model for the 2011 tohoku oki earthquake from gnss and grace goce satellite gravimetry the gravity recovery and climate experiment grace mission launched 2002 and the gravity field and steady state ocean circulation explorer goce mission march 2009 to november 2013 collected spaceborne gravity data for the preseismic and postseismic periods of the 2011 tohoku oki earthquake in addition the dense japan geonet global navigation satellite systems gnss network measured with approximately 1050 stations the coseismic and postseismic surface displacements we use a novel combination of gnss grace and goce observations for a distributed fault slip model addressing the issues with gravimetric and geometric change over consistent time windows our model integrates the coseismic and postseismic effects as we include goce observations averaged over a 2 year interval but their inclusion reveals the gravity change with unprecedented spatial accuracy the gravity gradient grid evaluated at goce orbit height of 265 km has an estimated formal error of 0 20 me which provides sensitivity to the mainly coseismic and integrated postseismic induced gravity gradient signal of 1 03 me we show that an increased resolution of the gravity change provides valuable information with goce gravity gradient observations sensitive to a more focused slip distribution in contrast to the filtered grace equivalent the 2 year averaging window of the observations makes it important to incorporate estimates of the variance covariance of unmodeled processes in the inversion the gnss and grace goce combined model shows a slip pattern with 20 m peak slip at the trench the total gravity change 200 gal and the spatial mapping accuracy would have been considerably lower by omitting the goce derived fine scale gravity field information

the geodetic signature of the earthquake cycle at subduction zones model constraints on the deep processes recent megathrust events in tohoku japan maule chile and sumatra indonesia were well recorded much has been learned about the dominant physical processes in megathrust zones partial locking of the plate interface detailed coseismic slip relocking afterslip viscoelastic mantle relaxation and interseismic loading these and older observations show complex spatial and temporal patterns in crustal deformation and displacement and significant differences among different margins a key question is whether these differences reflect variations in the underlying processes like differences in locking or the margin geometry or whether they are a consequence of the stage in the earthquake cycle of the margin quantitative models can connect these plate boundary processes to surficial and far field observations we use relatively simple cyclic geodynamic models to isolate the first order geodetic signature of the megathrust cycle coseismic and subsequent slip on the subduction interface is dynamically and consistently driven a review of global preseismic coseismic and postseismic geodetic observations and of their fit to the model predictions indicates that similar physical processes are active at different margins most of the observed variability between the individual margins appears to be controlled by their different stages in the earthquake cycle the modeling results also provide a possible explanation for observations of tensile faulting aftershocks and tensile cracking of the overriding plate which are puzzling in the context of convergence compression from the inversion of our synthetic gnss velocities we find that geodetic observations may incorrectly suggest weak locking of some margins for example the west aleutian margin

prevalence of viscoelastic relaxation after the 2011 tohoku oki earthquake seafloor global positioning system observations immediately after the great 2011 tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than just afterslip on the fault as is commonly assumed this paper presents revised estimates of the afterslip following the 2011 tohoku oki earthquake based on seafloor gps observations made immediately after the earthquake tianhaozhe sun et al obtain unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than elastic afterslip on the fault as is commonly assumed they conclude that models which erroneously assume an elastic earth substantially overestimate afterslip downdip of the rupture zone and underestimate afterslip updip after a large subduction earthquake crustal deformation continues to occur with a complex pattern of evolution1 this postseismic deformation is due primarily to viscoelastic relaxation of stresses induced by the earthquake rupture and continuing slip afterslip or relocking of different parts of the fault2 3 4 5 6 when postseismic geodetic observations are used to study earth s rheology and fault behaviour it is commonly assumed that short term a few years deformation near the rupture zone is caused mainly by afterslip and that viscoelasticity is important only for longer term deformation6 7 however it is difficult to test the validity of this assumption against conventional geodetic data here we show that new seafloor gps global positioning system observations immediately after the great tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation these data reveal fast landward motion of the trench area opposing the seaward motion of gps sites on land using numerical models of transient viscoelastic mantle rheology we demonstrate that the landward motion is a consequence of relaxation of stresses induced by the asymmetric rupture of the thrust earthquake a process previously unknown because of the lack of near field observations our findings indicate that previous models assuming an elastic earth will have substantially overestimated afterslip downdip of the rupture zone and underestimated afterslip updip of the rupture zone our knowledge of fault friction based on these estimates therefore needs to be revised

a comprehensive model of postseismic deformation of the 2004 sumatra andaman earthquake deduced from gps observations in northern sumatra abstract we investigate the postseismic deformation of the 2004 sumatra andaman earthquake sae using 5 years of global positioning system gps data located in northern sumatra continuous gps data from northern sumatra suggest that the relaxation time in the vertical displacement is longer than horizontal displacements this implies that there are multiple physical mechanisms that control the postseismic deformation which refer to afterslip and viscoelastic relaxation in this study we introduce an analysis strategy of postseismic deformation to simultaneously calculate multiple mechanisms of afterslip and viscoelastic relaxation the afterslip inversion results indicate that the distribution of the afterslip and the coseismic slip are compensatory of each other also afterslip has a limited contribution to vertical deformation in northern sumatra in our rheology model we use a gravitational maxwell viscoelastic response and the result indicates that the elastic layer thickness is 65 5 km and the maxwell viscosity is 8 0 1 0 1018 pa s we find that afterslip plus maxwell viscoelastic relaxation are appropriate to explain the deformation in northern sumatra we also find that our rheology model reproduces the long term features of the gps time series in thailand applying our rheology model to the data in andaman islands our afterslip estimation is located at the down dip part of the plate boundary finally we showed that our rheology model is applicable to the gps datasets of postseismic deformation of the 2004 sae located in northern sumatra thailand and andaman nicobar respectively

heterogeneous rheology controlled postseismic deformation of the 2011 tohoku oki earthquake using two dimensional finite element modeling we reproduced the observed postseismic deformation of the 2011 tohoku oki earthquake our model which accounts for the lithosphere asthenosphere boundary and weak zones beneath volcanoes was able to reproduce small scale 20 km perturbations in postseismic deformation observed by the dense geodetic network such as local subsidence around quaternary volcanoes the inverted afterslip has a peak at the downdip limit of the main rupture region on the subducting plate interface consistent with physical predictions the combination of afterslip and viscoelastic relaxation in a heterogeneous rheology model explains the observations well even on small scales

subsidence at cerro prieto geothermal field and postseismic slip along the indiviso fault from 2011 to 2016 radarsat 2 dinsar time series analysis we present radarsat 2 differential interferometric synthetic aperture radar dinsar observations of deformation due to fluid extraction at the cerro prieto geothermal field cpgf and afterslip on the 2010 m7 2 el mayor cucapah emc earthquake rupture during 2011 2016 advanced multidimensional time series analysis reveals subsidence at the cpgf with the maximum rate greater than 100 mm yr accompanied by horizontal motion radial contraction at a rate greater than 30 mm yr during the same time period more than 30 mm of surface creep occurred on the indiviso fault ruptured by the emc earthquake we performed inversions of dinsar data to estimate the rate of volume changes at depth due to the geothermal production at the cpgf and the distribution of afterslip on the indiviso fault the maximum coseismic slip due to the emc earthquake correlates with the coulomb stress changes on the indiviso fault due to fluid extraction at the cpgf afterslip occurs on the periphery of maximum coseismic slip areas time series analysis indicates that afterslip still occurs 6 years after the earthquake

small interseismic asperities and widespread aseismic creep on the northern japan subduction interface the canonical model of fault coupling assumes that slip is partitioned into fixed asperities that display stick slip behavior and regions that creep stably we show that this simple asperity model is inconsistent with gps derived deformation in northern japan associated with interseismic coupling on the subduction interface and the transient response to mw 6 3 7 2 earthquakes during 2003 2011 comparisons of gps data with simulations of earthquakes on asperities and associated velocity strengthening afterslip require that afterslip overlaps areas of the fault that ruptured in previous earthquakes including the 2011 mw 9 tohoku oki earthquake whereas about 55 of the plate interface ruptured in earthquakes during 2003 2011 we infer that only 9 of the plate interface was fully locked between earthquakes inferred locked asperities are roughly 25 the size of rupture areas determined by seismic source inversions these smaller asperities are consistent with interseismic strain accumulation in 2009 although more extensive locking is required a decade earlier in 1998

oxygen isotopic composition of relict olivine grains in cosmic spherules links to chondrules from carbonaceous chondrites most olivine relict grains in cosmic spherules selected for the present study are pristine and have not been disturbed during their atmospheric entry thereby preserving their chemical mineralogical and isotopic compositions in order to understand the origin of the particles oxygen isotope compositions of relict olivine grains in twelve cosmic spherules collected from deep sea sediments of the indian ocean were studied using secondary ion mass spectrometry most of the data lie close to the ccam carbonaceous chondrite anhydrous mineral line with 17 o ranging from 5 to 0 the data overlap oxygen isotopic compositions of chondrules from carbonaceous chondrites such as cv ck cr and cm which suggests that chondrules from carbonaceous chondrites are the source of relict grains in cosmic spherules chemical compositions of olivine in cosmic spherules are also very similar to chondrule olivine from carbonaceous chondrites several olivine relict grains in three cosmic spherules are 16 o rich 17 o 21 9 to 18 7 similar to oxygen isotopic compositions observed in calcium aluminium rich inclusions cais amoeboid olivine aggregates aoas and some porphyritic chondrules from carbonaceous chondrites these grains appear to have recorded the initial oxygen isotopic composition of the inner solar nebula three olivine grains from two cosmic spherules have 18 o values 20 which could be interpreted as mixing with stratospheric oxygen during atmospheric entry

interpretation of offshore crustal movements following the 2011 tohoku oki earthquake by the combined effect of afterslip and viscoelastic stress relaxation on the 11th march 2011 a megathrust event called the tohoku oki earthquake occurred at the north american pacific plate interface off northeast japan transient crustal movements following this earthquake were clearly observed by a dense gps network geonet on land and a sparse gps acoustic positioning network on seafloor the observed crustal movements are in accordance with ordinary expectations on land but not on seafloor that is slowly decaying landward movements above the main rupture area and rapidly decaying trench ward movements in its southern extension to reveal the cause of such curious offshore crustal movements we analyzed the coseismic and postseismic gps array data on land with a sequential stepwise inversion method considering viscoelastic stress relaxation in the asthenosphere and obtained the following results the afterslip of the tohoku oki earthquake rapidly proceeds for the first 1 year on a high angle downdip extension of the main rupture which occurred on the low angle offshore plate interface the theoretical patterns of seafloor horizontal movements due to the afterslip and the viscoelastic relaxation of coseismic stress changes in the asthenosphere are essentially different both in space and time inshore trench ward movements and offshore landward movements for the afterslip while overall landward movements for the viscoelastic stress relaxation general agreement between the computed horizontal movements and the gps acoustic observations demonstrates that the postseismic curious offshore crustal movements can be ascribed to the combined effect of afterslip on a high angle downdip extension of the main rupture and viscoelastic stress relaxation in the asthenosphere

space time distribution of afterslip following the 2003 tokachi oki earthquake implications for variations in fault zone frictional properties 1 gps time series following the september 25 2003 ut tokachi oki earthquake m w 8 0 reveal significant deformation we use the network inversion filter to invert for the spatial and temporal evolution of afterslip in the 30 days following the earthquake afterslip is concentrated adjacent to the coseismic rupture zone between the 2003 rupture and the inferred source regions of the 1968 tokachi oki and the 1973 nemuro oki earthquakes the inversion shows a rapid decay of slip rate in the 2003 rupture zone with slower deceleration in the surrounding regions the stress velocity paths for the afterslip regions approximately follow d d in v 0 6 mpa suggestive of steady state velocity strengthening friction the complementary spatial pattern of coseismic rupture and afterslip may indicate along strike spatial variations of frictional properties although other interpretations can not be ruled out

asthenospheric viscosity inferred from correlated land sea earthquakes in north east japan the viscosity of the earth s mantle has been estimated from studies of post glacial rebound1 2 post seismic deformations of the ground following large earthquakes3 4 and aftershock sequences5 7 here we derive a value for the viscosity of the asthenosphere from a correlation found in the historical catalogue of subduction induced seismicity between the intraplate land and interplate sea earthquakes in north east japan the correlation persists since the time of reliably reported earthquakes in ad 1600 land events precede sea events by 36 yr with a mean distance between land sea pairs of 200 km because of the visocoelastic coupling of the lithosphere to the asthenosphere a plausible mechanism to explain the correlation is stress migration governed by the viscosity of the asthenosphere large land shocks generate diffuse like stress pulses which sweep past and unlock the thrust fault in the subduction zone thus triggering the sea events the correlation time and distance provide a measure of the speed of diffusion 5 6 km yr 1 and hence an estimate of the viscosity 7 1018 pa s

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

emergence and disappearance of interplate repeating earthquakes following the 2011 m9 0 tohoku oki earthquake slip behavior transition between seismic and aseismic depending on the loading rate we investigated spatiotemporal change in the interplate seismic activity following the 2011 tohoku oki earthquake m9 0 in the region where interseismic interplate coupling was relatively weak and large postseismic slip was observed we classified earthquakes by their focal mechanisms to identify the interplate events and conducted hypocenter relocation to examine the detailed spatiotemporal distribution of interplate earthquakes in the mostly creeping area the results show that many interplate earthquakes including m 6 events emerged immediately after the tohoku oki earthquake in areas where very few interplate earthquakes had been observed in the 88 previous years the emergent earthquakes include repeating sequences and the extremely long quiescence of small to moderate earthquakes before the tohoku oki earthquake suggests that the source areas for the post m9 events slipped aseismically during the quiescence the repeaters magnitudes decayed over time following the tohoku oki earthquake and some sequences disappeared within a year the emergence of interplate earthquakes suggests that areas where aseismic slip had been dominant before the tohoku oki earthquake started to cause seismic slip after the earthquake probably due to the increased loading rate from the afterslip the magnitude decrease and disappearance of repeaters can be interpreted as shrinkage in seismic areas around the repeaters sources as the loading rate decreased due to the afterslip decay over time these observations suggest that changes in the loading rate can cause slip behavior transition between seismic and aseismic this indicates that such loading rate dependent slip behavior plays an important role in the spatiotemporal distribution of earthquakes in interplate seismogenic zones

afterslip and viscoelastic relaxation model inferred from the large scale post seismic deformation following the 2010 mw 8 8 maule earthquake chile

simulation of postseismic deformations caused by the 1896 riku u earthquake northeast japan re evaluation of the viscosity in the upper mantle we examine the postseismic deformations which are induced by an inland earthquake at a subduction zone and investigate especially the effect of the viscoelastic heterogeneity through finite element method fem we estimate the viscosity of the upper mantle beneath the northeast japan with realistic structures based on the leveling data which includes the postseismic deformations due to the 1896 riku u earthquake for this purpose we construct two 3 d fem models with different viscoelastic structures namely layered model and plate model the results show that spatial patterns of the postseismic deformations differ considerably depending on the two viscoelastic structures postseismic deformations are strongly controlled by the effective thickness of the viscoelastic medium above descending plate at the surface if the structure is complicated the relaxation time is outwardly longer and varies significantly with position considering the plate structure the profile of surface deformation and decaying subsidence rate constrain the maxwell time of the upper mantle to be 5 years which is shorter than the value of 10 years estimated by thatcher et al 1980 assuming the layered structures

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

three dimensional viscoelastic finite element model for postseismic deformation of the great 1960 chile earthquake 2 5 10 19 pa s for the continental upper mantle the model well explains the gps observations numerical tests suggest that the continental mantle viscosity value is reasonably well constrained the model shows the prolonged postseismic seaward motion of the inland area to be a unique feature of earthquakes with very long rupture along strike and large coseismic fault slip for short rupture and small coseismic slip the motion will stop very quickly after the earthquake explaining why this phenomenon is not more commonly observed with an oceanic mantle viscosity of 10 20 pa s the model also provides an explanation for tide gauge constrained postseismic uplift 200 km from the trench that had previously been explained using a model of prolonged afterslip of a deep segment of the chile subduction fault index terms 1236 geodesy and gravity rheology of the lithosphere and mantle 8160 1242 geodesy and gravity seismic deformations 7205 3230 mathematical geophysics numerical solutions 7209 seismology earthquake dynamics and mechanics 7260 seismology theory and modeling keywords postseismic deformation viscoelastic stress relaxation gps finite element modeling chile subduction zone upper mantle viscosity

poroelastic rebound along the landers 1992 earthquake surface rupture maps of surface displacement following the 1992 landers california earthquake generated by interferometric processing of ers 1 synthetic aperture radar sar images reveal effects of various postseismic deformation processes along the 1992 surface rupture the large scale pattern of the postseismic displacement field includes large lobes mostly visible on the west side of the fault comparable in shape with the lobes observed in the coseismic displacement field this pattern and the steep displacement gradient observed near the emerson camp rock fault cannot be simply explained by afterslip on deep sections of the 1992 rupture models show that horizontal slip occurring on a buried dislocation in a poisson s material produces a characteristic quadripole pattern in the surface displacement field with several centimeters of vertical motion at distances of 10 20 km from the fault yet this pattern is not observed in the postseismic interferograms as previously proposed to explain local strain in the fault step overs peltzer et al 1996b we argue that poroelastic rebound caused by pore fluid flow may also occur over greater distances from the fault compensating the vertical ground shift produced by fault afterslip such a rebound is explained by the gradual change of the crustal rocks poisson s ratio value from undrained coseismic to drained postseismic conditions as pore pressure gradients produced by the earthquake dissipate using the poisson s ratio values of 0 27 and 0 31 for the drained and undrained crustal rocks respectively elastic dislocation models show that the combined contributions of afterslip on deep sections of the fault and poroelastic rebound can account for the range change observed in the sar data and the horizontal displacement measured at global positioning system gps sites along a 60 km long transect across the emerson fault savage and svarc 1997 using a detailed surface slip distribution on the homestead valley kickapoo and johnson valley faults we modeled the poroelastic rebound in the homestead valley pull apart a poisson s ratio value of 0 35 for the undrained gouge rocks in the fault zone is required to account for the observed surface uplift in the 3 5 years following the earthquake this large value implies a seismic velocity ratio vp vs of 2 1 consistent with the observed low vs values of fault zone guided waves at shallow depth li et al 1997 the sar data also reveal postseismic creep along shallow patches of the eureka peak and burnt mountain faults with a characteristic decay time of 0 8 years coseismic dilatant hardening locking process followed by post seismic pore pressure controlled fault creep provide a plausible mechanism to account for the decay time of the observed slip rate along this section of the fault

preceding coseismic and postseismic slips of the 2011 tohoku earthquake japan 1 we estimated the spatial and temporal evolution of the preceding aseismic slip from january 2003 to january 2011 the coseismic slip of the tohoku earthquake and the postseismic slip after the earthquake based on global positioning system gps data time dependent analysis indicates aseismic slip offshore of miyagi and fukushima prefectures from 2004 associated with a series of subduction earthquakes that overlap the aseismic slip area these preceding aseismic and coseismic slip areas are centered between the centers of the coseismic and afterslip areas of the tohoku earthquake offshore of miyagi prefecture while they overlap the coseismic and afterslip areas of the tohoku earthquake off fukushima prefecture the timing of moment magnitude nine mw9 class earthquakes appears to be controlled by multiple preceding slip events smaller earthquakes and their afterslip the preceding aseismic and coseismic slip decreased the coupling rate off the tohoku coast suggesting the possibility that the preceding slip represented a precursive stage of the tohoku earthquake the afterslip of the tohoku earthquake occurred in an area where the coseismic slip was not large complementing the large coseismic slip zone the afterslip along iwate miyagi extends up to 80 km in depth and is currently the sole mechanism of strain release in this depth range the source region of the anticipated miyagi oki earthquake shows small postseismic slip after the tohoku earthquake reflecting the energy release at the time of the earthquake aftershock activity is roughly governed by an afterslip process

deformation cycles of subduction earthquakes in a viscoelastic earth subduction zones produce the largest earthquakes over the past two decades space geodesy has revolutionized our view of crustal deformation between consecutive earthquakes the short time span of modern measurements necessitates comparative studies of subduction zones that are at different stages of the deformation cycle piecing together geodetic snapshots from different subduction zones leads to a unifying picture in which the deformation is controlled by both the short term years and long term decades and centuries viscous behaviour of the mantle traditional views based on elastic models such as coseismic deformation being a mirror image of interseismic deformation are being thoroughly revised snapshots of subduction zones using space geodesy reveal that the viscous behaviour of the mantle controls crustal deformation requiring the revision of traditional elastic models for earthquake risk assessment space geodesy the use of satellites to monitor earth has revolutionized our view of crustal deformation between consecutive earthquakes however the brevity of such measurements means that studies must be done by comparing multiple subduction zones at different stages of the earthquake cycle by piecing together geodetic snapshots from the sumatra chile and cascadia subduction zones this review presents a unifying picture in which deformation is controlled by the viscous behaviour of the mantle in both the short term years and the long term decades to centuries

offshore postseismic deformation of the 2011 tohoku earthquake revisited application of an improved gps acoustic positioning method considering horizontal gradient of sound speed structure

dominant controls of downdip afterslip and viscous relaxation on the postseismic displacements following the mw7 9 gorkha nepal earthquake author s zhao b burgmann r wang d tan k du r zhang r abstract 2017 american geophysical union all rights reserved we analyze three dimensional gps coordinate time series from continuously operating stations in nepal and south tibet and calculate the initial 1 year postseismic displacements we first investigate models of poroelastic rebound afterslip and viscoelastic relaxation individually and then attempt to resolve the trade offs between their contributions by evaluating the misfit between observed and simulated displacements we compare kinematic inversions for distributed afterslip with stress driven afterslip models the modeling results show that no single mechanism satisfactorily explains near and far field postseismic deformation following the gorkha earthquake when considering contributions from all three mechanisms we favor a combination of viscoelastic relaxation and afterslip alone as poroelastic rebound always worsens the misfit the combined model does not improve the data misfit significantly but the inverted afterslip distribution is more physically plausible the inverted afterslip favors slip within the brittle ductile transition zone downdip of the coseismic rupture and fills the small gap between the mainshock and largest aftershock slip zone releasing only 7 of the coseismic moment our preferred model also illuminates the laterally heterogeneous rheological structure between india and the south tibet the transient and steady state viscosities of the upper mantle beneath tibet are constrained to be greater than 1018 pa s and 1019 pa s whereas the indian upper mantle has a high viscosity 1020 pa s the viscosity in the lower crust of southern tibet shows a clear trade off with its southward extent and thickness suggesting an upper bound value of 8 1019 pa s for its steady state viscosity

two decades of spatiotemporal variations in subduction zone coupling offshore japan spatial patterns of interplate coupling on global subduction zones can be used to guide seismic hazard assessment but estimates of coupling are often constrained using a limited temporal range of geodetic data here we analyze 19 years of geodetic observations from the geonet network to assess time dependent variations in the spatial distribution of coupling on the subduction zones offshore japan we divide the position time series into five 3 75 year epochs each decomposed into best fit velocity annual periodic signals coseismic offsets and postseismic effects following seven major earthquakes nominally interseismic velocities are interpreted in terms of a combination of tectonic block motions and earthquake cycle activity the duration of the inferred postseismic activity covaries with the linear velocity to address this trade off we assume that the nominally interseismic velocity at each station varies minimally from epoch to epoch this approach is distinct from prior time series analysis across the earthquake cycle in that position data are not detrended using preseismic velocity which inherently assumes that interseismic processes are spatially stable through time but rather the best fit velocity at each station may vary between epochs these velocities reveal significant consistency since 1996 in the spatial distribution of coupling on the nankai subduction zone with variation limited primarily to the tokai and bungo channel regions where long term slow slip events have occurred and persistently coupled regions coincident with areas that slipped during historic great earthquakes on the sagami subduction zone south of tokyo we also estimate relatively stable coupling through time on the japan kuril trench we image significant coupling variations owing to effects of the 1994 mw 7 7 sanriku oki 2003 mw 8 2 tokachi oki and 2011 mw 9 0 tohoku oki earthquakes in particular strong coupling becomes more spatially extensive following the 1994 event until 2011 coseismic sense slip precedes the tohoku oki event and coupling offshore northern honshu is reduced after the 2011 earthquake despite the occurrence of the 2003 tokachi oki earthquake persistent coupling offshore hokkaido suggests ongoing seismic hazard possibly similar to past mw 9 class earthquakes interpreted from coastal paleoseismic records this time dependent analysis of interseismic deformation illuminates rich diversity in the distribution of subduction zone coupling including spatiotemporal stability in coupling effective reduction in strongly coupled regions due to aseismic thrust sense slip events and broad changes in the distribution of coupling following major earthquakes

challenging the rate state asperity model afterslip following the 2011 m9 tohoku oki japan earthquake 1 prior to the 2011 m9 tohoku oki earthquake subduction at the japan trench was characterized by m7 8 earthquakes sometimes rupturing the same source regions seismic asperities followed by extensive afterslip detected by gps measurements a physically based model consisting of velocity weakening asperities surrounded by aseismic creep on velocity strengthening regions the rate state asperity model became the prevailing conceptual model for earthquakes in this region theory and numerical simulation indicates that velocity weakening areas do not exhibit sustained afterslip while velocity strengthening regions do not accumulate stress interseismically here we demonstrate that the rate state asperity model is contradicted by models of postseismic deformation following the tohoku oki earthquake afterslip in the first eight months either occurred on historical seismic asperities or stress accumulated in regions surrounding the asperities unsmoothed inversions of cumulative 8 month postseismic gps displacements that restrict afterslip to areas outside of historical ruptures cannot fit the data without afterslip exceeding the slip that fully relaxes the coseismic stress change in contrast similarly constrained inversions allowing slip within historical ruptures can satisfactorily fit the postseismic displacements these results require a modification of the rate state asperity model and raise new questions about physical processes and properties of the subduction interface

afterslip and viscoelastic relaxation following the 2011 tohoku oki earthquake mw9 0 inferred from inland gps and seafloor gps acoustic data we simultaneously estimate 2 5 years of afterslip and viscoelastic relaxation as well as coseismic slip for the 2011 tohoku oki earthquake displacements at inland gps and seafloor gps acoustic stations are inverted using viscoelastic green s functions for a model with an upper elastic layer and lower viscoelastic substrate the result shows that afterslip is isolated from the rupture area and possibly asperities of historical earthquakes and has almost decayed by 10 september 2013 2 5 years after the main shock the inversion result also suggests that observed landward postseismic displacements at the seafloor gps acoustic stations are caused by the viscoelastic relaxation whereas trenchward displacements at inland stations are mainly an elastic response to afterslip

azimuthal seismic anisotropy in the upper crust of the japanese islands induced by the 2011 tohoku oki megathrust earthquake

a secondary zone of uplift due to megathrust earthquakes the 1960 m9 5 valdivia and 1964 m9 2 alaska earthquakes caused a decimeters high secondary zone of uplift a few hundred kilometers landward of the trench we analyze gps data from the 2010 m8 8 maule and 2011 m9 0 tohoku oki earthquakes to reveal the persistent existence of a secondary zone of uplift due to great earthquakes at the megathrust interface this uplift varies in magnitude and location but consistently occurs at a few hundred kilometers landward from the trench and is likely mainly coseismic in nature this secondary zone of uplift is systematically predicted by our 2d visco elasto plastic seismo thermo mechanical numerical simulations which model both geodynamic and seismic cycle timescales through testing hypotheses in both simple and realistic setups we propose that a superposition of two physical mechanisms could be responsible for this phenomenon first a wavelength is introduced through elastic buckling of a visco elastically layered fore arc that is horizontally compressed in the interseismic period the consequent secondary zone of interseismic subsidence is elastically rebound during the earthquake into a secondary zone of relative uplift second absolute and broader uplift is ensured through a mass conservation driven return flow following accelerated slab penetration due to the megathrust earthquake the dip and width of the seismogenic zone and resulting deep coseismic slip seem to have the largest affect on location and amplitude of the secondary zone of uplift these results imply that subduction and mantle flow do not occur at constant rates but are rather modulated by earthquakes this suggests a link between deep mantle and shallow surface displacements even at time scales of minutes

characteristics of selected petroleum source rocks xianjiang uygur autonomous region northwest china 1 the sedimentary basins of xinjiang uygur autonomous region china are moderately to poorly explored for petroleum volumetric adequacy of petroleum source rocks is a critical exploration risk in these basins particularly because source rock data are limited this study provides new source rock data and speculatively assesses the source rock potential of xinjiang basins the junggar zhungaer basin the best explored of the xinjiang basins and containing a giant oil field is underlain in many areas by an upper permian lacustrine oil shale sequence remarkable for its organic richness and oil source quality depending on its position in the basin the permian section ranges from immature to overmature and is inferred to be the principal source of oil in the basin upper triassic middle jurassic coal measures including lacustrine rocks constitute a secondary source rock sequence in the basin the smaller intermontane turpan tulufan basin contains a very similar upper triassic middle jurassic sequence which where sufficiently buried probably comprises the only significant oil source sequence in the basin the vast tarim talimu basin offers the greatest variety of potential source rocks of all xinjiang basins but remains the least well documented from limited but geologically planned and focused sampling cambrian carboniferous and permian strata are not considered major oil contributors in the dominantly shallow marine paleozoic section of the northern tarim basin only ordovician black shales appear to have significant potential the upper triassic middle jurassic sequence of the northern tarim basin is similar to that of the junggar and turpan basins a section rich in coal and lacustrine shale that constitutes another potentially significant oil source due to the size stratigraphic packaging and structural relief of the northern tarim basin paleozoic and mesozoic potential il source beds range from immature to overmature

role of lower crust in the postseismic deformation of the 2010 maule earthquake insights from a model with power law rheology the surface deformation associated with the 2010 mw 8 8 maule earthquake in chile was recorded in great detail before during and after the event the high data quality of the continuous gps cgps observations has facilitated a number of studies that model the postseismic deformation signal with a combination of relocking afterslip and viscoelastic relaxation using linear rheology for the upper mantle here we investigate the impact of using linear maxwell or power law rheology with a 2d geomechanical numerical model to better understand the relative importance of the different processes that control the postseismic deformation signal our model results reveal that in particular the modeled cumulative vertical postseismic deformation pattern in the near field 50 km depth as suggested in previous studies the explanation for this difference is that in the model with power law rheology the relaxation of coseismically imposed differential stresses occurs mainly in the lower crust however even though the model with power law rheology probably has more potential to explain the vertical postseismic signal in the near field the uncertainty of the applied temperature field is substantial and this needs further investigations and improvements

geodetic data inversion using a bayesian information criterion for spatial distribution of fault slip summary we developed a new inversion method to reconstruct static images of seismic sources from geodetic data using akaike s bayesian information criterion abic coseismic surface displacements are generally related with a slip distribution on a fault surface by linear integral equations parametric expansion of the fault slip distribution by a finite number of known basis functions yields a set of observation equations expressed in a simple vector form incorporating prior constraints on the smoothness of slip distribution with the observation equations we construct a bayesian model with unknown hyperparameters the optimal values of the hyperparameters which control the structure of the bayesian model are objectively determined from observed data by using abic once the values of hyperparameters are determined we can use the maximum likelihood method to find the optimal distribution of fault slip we examined the validity of this method through a numerical experiment using theoretical data with random noise we analysed geodetic data associated with the 1946 nankaido earthquake ms 8 2 by using this method the result shows that the fault slip distribution of this earthquake has two main peaks of 4 and 6 m located off kii peninsula and muroto promontory these two high slip areas are clearly separated by a low slip zone extending along kii strait such a slip distribution corresponds with the fact that the rupture process of this earthquake in the western part is notably different from that in the eastern part

viscosity estimates for the crust and upper mantle from patterns of lacustrine shoreline deformation in the eastern great basin the deformed shorelines of lake bonneville constitute a classic source of information on lithospheric elastic thickness and upper mantle viscosity we describe and apply a new model to a recently augmented data set new data better constrain both the complex spatio temporal pattern of the lake load and the crustal deformation response to that load the history of lake level fluctuations has been significantly refined and somewhat modified this is due to both more radiocarbon dates from within the bonneville basin and to an improved calibration of the radiocarbon timescale itself the data which constrain the crustal deformation pattern consist of ages and shoreline elevations from several hundred points which sample three major levels of lake bonneville and corresponding elevations from the high stands of three smaller lakes situated to the west of lake bonneville the data from the smaller lakes help elucidate the pattern of deflection which occurred beyond the edge of the big lake the geometry of the earth model incorporates an arbitrary number of layers overlying a half space and the rheology of each level can accommodate an arbitrary number of maxwell viscoelastic elements in parallel the inverse modeling comprises three complementary approaches for the simplest configurations we performed a direct search of the parameter space and delineated the irregular boundary of the subspace of acceptable models for more complex configurations we constrained the elastic parameters to their seismically determined values and then solved for viscosity versus depth profiles by either expressing the log viscosity versus log depth profile as a series of specially constructed orthogonal polynomials or by allowing each of 8 10 layers plus the half space to have an independently determined viscosity we found that the data do not strongly support nor can they conclusively exclude a more complex rheology than simple maxwell viscoelasticity the orthogonal polynomial solution exhibits an essentially monotonic decrease in viscosity with depth the most rapid change occurs at shallow depths decreasing from 1023 pa s at 3 km to 102o pa s at 30 km the decrease is much more gradual below with only another factor of 5 decrease between 30 and 300 km depth the unconstrained solution exhibits a rapid decrease in viscosity with depth from 2x 10 24 pa s in the top 10 km to 4x 1017 pa s at a depth of 40 km a nearly isoviscous asthenospheric region extends from 40 to 150 km and is underlain by a mantle lithospheric region with increased viscosity 2x 102o pa s extending from 150 to 300 km depth and by a uniform viscosity 1019 pa s half space below

anomalous low velocity zone and linear alignment of seismicity along it in the subducted pacific slab beneath kanto japan reactivation of subducted fracture zone 1 a detailed investigation of the hypocenter distribution beneath kanto japan reveals a nw se trending linear alignment of seismicity within the subducted pacific slab we estimate the 3d seismic velocity structure in the pacific slab to understand the factors controlling the genesis of such intraslab earthquakes a narrow low velocity zone is imaged within the subducted slab over a length of 150 km which partly penetrates into the mantle portion of the slab the low velocity zone correlates in space with the nw se trending earthquake cluster a reactivation of hydrated fracture zone formed prior to subduction is probably related to the low velocity anomaly dehydration reactions of the hydrated oceanic mantle as well as the oceanic crust might lower the seismic velocity along the fossil fracture zone accompanied by intraslab earthquakes these observations support the hypothesis of dehydration embrittlement as the most viable mechanism for generating intraslab earthquakes