a kinematic model for deformation of the lithosphere at subduction zones a subduction model that interprets the whole pattern of topography and gravity anomalies across the island arc trench system has been constructed on the basis of dislocation theory we model the lithosphere asthenosphere system by a gravitating stratified half space which consists of an elastic surface layer an intervening layer with maxwell viscoelasticily and an elastic substratum the steady subduction of the oceanic plate beneath the continental plate is represented by uniform slip at a constant rate over the plate interface which divides the elastic viscoelastic half space into two blocks using the limiting value theorem of the laplace transform we can show that the steady slip on the interface deeper than the lithosphere asthenosphere boundary does not contribute to surface deformation in the steady state accordingly the pattern of surface deformation associated with the steady state subduction depends only on the thickness of the lithosphere and the geometry of the plate interface shallower than the lithosphere asthenosphere boundary numerical results show that the pattern of vertical motion at subduction zones is characterized by steep uplift on the continental side sharp subsidence at the plate boundary and gentle uplift on the oceanic side this pattern bears a striking resemblance to the general pattern of topography across island arc trench systems the whole pattern of topography and gravity anomalies across the southern kurile arc is well matched by the subduction model with a lithosphere thickness of 50 km and a dip angle of 30 at depths

paleotsunami research along the nankai trough and ryukyu trench subduction zones current achievements and future challenges abstract located near japan s most densely populated and industrially active region the nankai trough subduction zone has long been highlighted as a high risk area for damaging earthquakes and tsunamis in contrast less attention has been paid the adjacent ryukyu trench because historical and geological records are scarce in order to develop better quantitative estimates of the timing and size of the earthquakes and tsunamis generated along these subduction zones comprehensive studies using geological seismological and historical methods have been conducted since the 1990s studies of tsunami deposits in this region have contributed to our current understanding of the history of tsunamis over the last 6000 years following the 2011 t hoku earthquake and tsunami paleotsunami research has especially focused on guiding and enhancing tsunami disaster management and mitigation measures the last nine years have seen a rapid increase in paleotsunami data from the nankai trough and ryukyu trench coasts these recent studies reveal that there are significant differences in the size and recurrence pattern of earthquakes and tsunamis along these subduction zones for instance large earthquakes have repeatedly occurred along the nankai trough every 100 200 years on the other hand large earthquakes and tsunamis may not have occurred over the last few thousand years at the junction between these subduction zones there is also no evidence for the occurrence of large earthquakes along the northern and central ryukyu trench over this time period large earthquakes and tsunamis may have occurred every few hundred years at the southern end of the ryukyu trench nevertheless data on the occurrence of these earthquakes are still insufficient both in quantity and quality to estimate the maximum size or recurrence pattern

finite element study of uplift and strain across vancouver island geological evidence for sudden coastal subsidence along the west coast of southern vancouver island points to the occurrence of great prehistorical subduction earthquakes contemporary uplift and crustal shortening patterns in southern vancouver island appear to indicate that the subduction megathrust fault is currently locked to understand better the dynamics of the observed surface deformation we develop a finite element model of earthquake cycles for the northern cascadia subduction zone across southern vancouver island using a linear viscoelastic rheology the model consists of the continental and oceanic lithospheres the asthenospheric mantle with a viscosity of 5 1019 pa s and a low viscosity 1018 pa s mantle wedge between the subducted oceanic plate and the overlying continental plate the shallow geometry of the subducted juan de fuca plate is well defined by the results of various geophysical surveys and the deep geometry is constrained by the results of seismic tomography the model me

spatiotemporal distribution of interplate coupling in southwest japan from inversion of geodetic data 1 we determine the spatiotemporal distribution of slip or slip deficit on the subduction interface of the nankai trough over an entire earthquake cycle using geodetic data including leveling triangulation and trilateration sea level and gps surveys obtained during the past 100 years in southwest japan we develop a new inversion method that accounts for long term crustal deformation coseismic earthquake displacements and stress relaxation of the viscoelastic asthenosphere from this analysis we obtain a model that shows postseismic afterslip on the deeper part of the plate interface following the 1946 nankaido earthquake significant afterslip is found beneath central shikoku that totals about 0 8 m the slip deficit rate during the interseismic period is 5 6 cm year in the n50 w n60 w direction which is consistent with the relative plate motion between the philippine and amurian plates a fully locked region is found in the shallower portion 30 km and the slip deficit rate has a maximum at a depth of about 20 km the plate interface deeper than 30 km is slowly slipping the amount of slip deficit reaches about 3 3 m off shikoku and about 2 m off the kii peninsula 50 years after the 1946 earthquake this suggests that fault healing and full interplate coupling has occurred by this time along the nankai trough

temporal change in plate coupling and long term slow slip events in southwestern japan abstract in the southwestern part of japan many large earthquakes have been reported and many geodetic or seismic observations have been performed to monitor crustal deformation due to the interaction between the subducting philippine sea plate and the overriding continental plate along the suruga nankai trough these precise observations provide insight into aseismic stress releasing processes such as slow slip events sses in this study i focus on the effect of sses on interplate coupling to reveal the overall temporal evolution of interplate states along the trough in southwestern japan i focus mainly on the western part of the subduction zone called the nankai region in this part three sses in 1997 2003 and 2010 were detected during the period in which observations are available interplate coupling recovered quickly after the sses terminated the eastern part of this region shows consistently strong coupling whether sses occur or not long term sses are distributed between the coupling area and the area where tremors occur i also examine the balance between stress accumulation and release at four points in the region below the eastern part of the strongly coupled area at a depth of 15 km constant coupling of about 7 cm yr takes place in the center of the sse region at a depth of 25 km 40 of the accumulated stress is released through sses with the rest contributing to the stress accumulation process

interseismic stress accumulation at the locked zone of nankai trough seismogenic fault off kii peninsula abstract a primary source of stress variation prior to great subduction zone earthquakes is the tectonic loading due to plate convergence we have calculated the elastic stress around the locked zone accumulated during an interseismic period numerically using a 2d plane strain finite element model in the nankai trough off kii peninsula and examined its dependence on elastic properties and some boundary conditions for the modeling we used the geometry of subducting plate interface determined previously through seismic surveys and the physical properties that were obtained through iodp scientific drilling offshore kii peninsula to construct a physically realistic model a dislocation along the plate interface is calculated from a 5 m displacement imposed on one side of the subducting plate with the locked zone defined at a depth of 10 to 25 km along the plate interface calculated shear stress is maximized at the downdip edge of the locked zone decreases exponentially seaward and is almost zero near the updip edge maximum shear stress is primarily proportional to the young s modulus of the overlying section comparing the maximum shear stress with the average stress drop for subduction earthquakes 3 4 mpa the most appropriate young s modulus and poisson s ratio ranges are 50 70 gpa and 0 3 respectively which are in good agreement with previous estimations from observed vp vs the stress accumulated during one seismic cycle can be reasonably explained by a linear elastic model with an appropriately sized locked region we found that the envelope of simulated horizontal displacement on the surface agrees well with gps velocity data which also supports this inference disturbance near the updip edge is no larger than 0 1 mpa of stress or 0 1 radian of tilt which are difficult to detect with current borehole measurement techniques and likely complex borehole conditions

three dimensional numerical modeling of temperature and mantle flow fields associated with subduction of the philippine sea plate southwest japan we investigated temperature and mantle flow distributions associated with subduction of the philippine sea phs plate beneath southwest japan by constructing a three dimensional parallelepiped model incorporating a past clockwise rotation the bathymetry of the philippine sea plate and distribution of the subducting velocity within its slab the geometry of the subducting plate was inferred from contemporary seismic studies and was used as a slab guide integrated with historical plate rotation into the 3 d simulation using the model we estimated a realistic and high resolution temperature field on the subduction plate interface which was constrained by a large number of heat flow data and attempted to clarify its relationship with occurrences of megathrust earthquakes long term slow slip events l sses and nonvolcanic low frequency earthquakes lfes results showed that the oblique subduction coupled with the 3 d geometry of subducting phs plate was a key factor affecting the interplate and intraplate temperature distributions leading to a cold anomaly in the plate interface beneath western shikoku the bungo channel and the kii peninsula temperatures in the slab core in these regions at a depth near the continental moho were nearly 200 c lower than that in eastern shikoku indicating a high thermal lateral heterogeneity within the subducting plate the geothermal control of the lfes beneath western shikoku was estimated to be within a range from 400 to 700 c and the interplate temperature for the l sses with a slip larger than 15 cm beneath the bungo channel was estimated to be approximately 350 500 c a large horizontal temperature gradient of 2 5 c km was present where the lfes occurred repeatedly the steep temperature change was likely to be related to the metamorphic phase transformation from lawsonite or blueschist to amphibolite of hydrous minerals of the mid ocean ridge basalt of the subducting phs plate

possible splay fault slip during the 1946 nankai earthquake this paper considers seafloor deformation associated with the 1946 nankai earthquake which occurred in the nankai trough subduction zone off the coast of southwest japan we note that recent high resolution determinations of the slip distribution assumed to be confined to the plate boundary result in a pronounced maximum in seafloor displacement midway between the coast of shikoku and the trough axis we show that this feature could be due to slip on a splay fault rather than the plate boundary such a model for the western part of the slip distribution is able to account for the main features of the tsunamigenic seafloor deformation obtained in previous studies with a maximum slip consistent with the plate convergent rate and history of earthquake recurrence at the nankai trough

global positioning system gps and gps acoustic observations insight into slip along the subduction zones around japan the global positioning system gps is one of the most powerful tools available for observation of earth s surface deformation in particular coseismic postseismic slow transient and interseismic deformation have all been observed globally by gps over the past two decades especially in subduction zones moreover gps acoustic techniques have been developed for practical use in the past decade allowing observation of offshore deformation immediately above slip regions here we describe the application of gps and gps acoustic observations to the detection of deformation due to plate boundary slip for interplate earthquakes as well as afterslip and slow slip events in subduction zones around japan where geodetic data coverage is particularly dense the data demonstrate temporally variable strain accumulation in the source region of the 2011 mw 9 0 tohoku oki earthquake and observation of the huge slip of the tohoku oki earthquake near the trench using gps acoustic methods has considerably advanced o

full interseismic locking of the nankai and japan west kurile subduction zones an analysis of uniform elastic strain accumulation in japan constrained by permanent gps we analyze permanent global positioning system gps data obtained over japan between 1995 and 1997 to estimate the instantaneous interseismic coupling ratio of the seismogenic zones due to the subduction of the pacific and philippine sea plates below the japanese islands we first derive the gps strain rate fields that characterize the crustal deformation of southern and northern japan and invert them to determine the effective subduction velocity along the central nankai trough on one side and the japan west kurile trench on the other these reference free velocities are close to those predicted by plate motion models with respect to eurasia we conclude that the eurasian reference frame gives a good approximation to the subduction motion and that to first order both subduction zones were fully locked during the period of measurements we then test whether the coupling ratio shows local variations within the seismogenic zones to do this we divide the subduction interface into 35 km 30 km elements that we model by point source groups and we invert the gps velocity field referenced to eurasia to derive the coupling ratio between 0 and 1 on each fault element the results are coherent over the 3 years and confirm that both the central nankai and the japan west kurile seismogenic zones are homogeneously fully locked most of the coupling ratios are close to 1 and a few are close to 0 intermediate values are rare the zones of decoupling correspond either to strong postseismic afterslip associated with the 1994 sanriku oki interplate earthquake japan trench or to a small overestimation of the actual lower limit of the locked zone we conclude that within the resolution of the gps data and the model 1 partial coupling did not exist during these 3 years along the nankai and japan west kurile trenches 2 the small seismic coupling ratio previously derived from earthquakes analysis for the japan and kurile trenches may indicate that a significant part of the elastic energy is dissipated silently through slow earthquakes and postseismic afterslip and 3 the heterogeneous coseismic slip pattern observed for the large and great earthquakes that rupture both subduction zones is in great contrast to the homogeneous loading finally we discuss the nonelastic residual deformation within the frame of the long term deformation of the japanese islands

crustal deformation the earthquake cycle and models of viscoelastic flow in the asthenosphere summary the crustal deformation patterns associated with the earthquake cycle can depend strongly on the rheological properties of subcrustal material substantial deviations from the simple patterns for a uniformly elastic earth are expected when viscoelastic flow of subcrustal material is considered the detailed description of the deformation pattern and in particular the surface displacements displacement rates strains and strain rates depend on the structure and geometry of the material near the seismogenic zone in the past few years various viscoelastic models of crustal deformation have been published these models differ in their predictions concerning the temporal and spatial patterns of crustal deformation in some cases these differences are due to varying choices for the physical mechanism under study in other cases however the differences are the result of the details of the mathematical treatment or the choice of model parameters we seek to resolve the origin of some of these differences by analysing several different linear viscoelastic models with a common finite element computational technique the models involve strike slip faulting and include a thin channel asthenosphere model a model with a varying thickness lithosphere and a model with a viscoelastic inclusion below the brittle slip plane the calculations reveal that the surface deformation pattern is most sensitive to the rheology of the material that lies below the slip plane in a volume whose extent is a few times the fault depth if this material is viscoelastic the surface deformation pattern resembles that of an elastic layer lying over a viscoelastic half space when the thickness or breadth of the viscoelastic material is less than a few times the fault depth then the surface deformation pattern is altered and geodetic measurements are potentially useful for studying the details of subsurface geometry and structure distinguishing among the various models in best accomplished by making geodetic measurements not only near the fault but out to distances equal to several times the fault depth this is where the model differences are greatest these differences will be most readily detected shortly after an earthquake when viscoelastic effects are most pronounced for a thin channel asthenosphere model we have found that the predicted displacements are less than those for a half space asthenosphere this result is contrary to recently published results based on analytical approximations the deficiencies of the latter work result from ignoring material below the asthenosphere and in using thickness averaged deformation parameters although the displacements predicted for a thin channel asthenosphere are less than those for a half space asthenosphere the post seismic strain rates at intermediate distances from the fault are greater in an absolute value sense in the former model

a fault model of the 1946 nankaido earthquake derived from tsunami data abstract a fault model of the 1946 nankaido earthquake m 8 2 is determined by the use of tsunami records of uwajima shimotsu and hososhima which were located within or near the area of major coseismic crustal deformation synthetic tsunamis computed for various fault models are matched with the observed tsunamis to determine the fault parameters a low angle thrust model slightly revised from a previous model by ando is consistent with the observed tsunamis the duration of faulting is constrained as less than 10 min based upon the tsunami the fault is divided into an eastern and a western segment corresponding to areas associated with and without aftershocks respectively the fault area and dislocation for the western segment are 150 70 km2 and 6 m and those for the eastern segment are 150 70 km2 and 3 m respectively the total seismic moment is 4 7 1028 dyn cm significantly smaller than that obtained from a geodetic model by fitch and scholz but still larger than that of the seismic model by kanamori the discrepancy in seismic moment between the seismic and the present models ran2 could be interpreted in terms of a slow dislocation on the fault but this interpretation does not match the seismic intensity distribution and damage pattern and the slow slip model for the nankaido earthquake is rejected the discrepancy between the two seismic moments is considered insignificant within error involved in data and modeling assumptions if the revised geodetic model ran2 is modified the seismic moment required to explain the observed tsunamis would be reduced further by 30 if we consider the uncertainties involved in the fault model of kanamori and the fault finiteness effect affecting the amplitude of seismic waves the seismic moment required to interpret the seismic wave data could be increased possibly being more than twice that of kanamori thus the two seismic moments from the different data sets could be close to each other within allowable tolerance this implies that the rise time of the nankaido earthquake was short enough to generate short period seismic waves from both the western and the eastern fault segments

spatial and temporal evolution of stress and slip rate during the 2000 tokai slow earthquake 1 we investigate an ongoing silent thrust event in the tokai seismic gap along the suruga nankai trough central japan prior to the event continuous gps data from april 1996 to the end of 1999 show that this region displaced 2 cm yr to the northwest relative to the landward plate the gps time series show an abrupt change in rate in mid june 2000 that continues as of mid 2005 we model this transient deformation which we refer to as the tokai slow thrust slip event as caused by slip on the interface between the philippine sea and amurian plates the spatial and temporal distribution of slip rate is estimated with kalman filter based inversion methods our inversions reveal two slow subevents the first initiated in late june 2000 slightly before the miyake jima eruption the locus of slip then propagated southeast in the second half of 2000 with maximum slip rates of about 15 cm yr through 2001 a second locus of slip initiated to the northeast in early 2001 the depth of the slip zone is about 25 km which may correspond to the transition zone from a seismogenic to a freely sliding zone the cumulative moment magnitude of the slow slip event up to november 2002 is mw 6 8 we calculate shear stress changes on the plate interface from the slip histories stress change as a function of slip rate shows trajectories similar to that inferred for high speed ruptures however the maximum velocity is 8 orders of magnitude less than in normal earthquakes

the earthquake deformation cycle at the nankai trough southwest japan geodetic measurements made landward of the nankai trough site of great subduction zone thrust earthquakes in 1854 and 1946 provide a uniquely detailed picture of the strain buildup process supply constraints on the mechanism of strain accumulation and allow for improved estimates of earthquake recurrence provided the two most recent movement cycles are similar the observations dating from about 1890 may be used to reconstruct a single complete deformation cycle coseismic strain release postseismic transients interseismic strain accumulation very complete leveling and tidal gage data indicate that postseismic deformation extends more than 300 km inland from the plate boundary persists for at least 30 years and shows a clear tendency to become longer wavelength with increasing time the transient movements have two timescales the first of about a year or less corresponds to deformation largely uplift concentrated close to the coseismic fault and is most easily explained by aseismic slip or very localized deformation downdip of the earthquake rupture plane the second longer timescale is associated with a diffusion like spread of the deformation further landward an effect qualitatively similar to that first predicted by elsasser to be an expected consequence of faulting in an elastic plate overlying a viscoelastic asthenosphere cumulative uplift since 1890 correlates well with the distribution of uplifted marine terraces although average post 1890 tilt rates exceed late quaternary and holocene averages by at least a factor of three because of the nonlinearity of strain buildup and the significant permanent deformation simple recurrence calculations typically overestimate the true interval between great earthquakes by a factor of 2 to a factor of 3 strict application of the time predictable model assumed correct overcomes these difficulties provided the cumulative transient deformation and the proportion of permanent deformation per cycle can be estimated

depth distribution of coseismic slip along the nankai trough japan from joint inversion of geodetic and tsunami data coseismic slip distribution on the fault plane particularly in the downdip direction associated with large subduction earthquakes can be estimated by joint inversion of geodetic and tsunami data two large earthquakes the 1944 tonankai earthquake mw 8 1 and the 1946 nankaido earthquake mw 8 3 occurred on the nankai trough southwestern japan where the philippine sea plate is subducting beneath the eurasian plate the source areas of these events extended over both land and ocean coseismic crustal movements on land were measured by leveling while those in ocean were recorded as tsunami waveforms on tide gauges the coseismic slip distribution inverted from these data shows that the slip on the shallower part of the fault plane is comparable to that on the deeper parts this indicates that large coseismic slip can occur beneath an accretionary wedge where current seismicity is low the result has implications for other subduction zones having a similar tectonic environment such as for the pacific northwest region of the united states although the possibility of a large earthquake there is still debated should a large subduction earthquake occur in this region coseismic slip on the shallow part could be large and the potential for large tsunamis is high

modeling short and long term slow slip events in the seismic cycles of large subduction earthquakes 1 slow slip events sses occur in the deeper extents of areas where large interplate earthquakes are expected in subduction zones such as the nankai region of japan and the cascadia region of north america in the nankai region sses are divided into long and short term sses depending on their duration and recurrence interval we modeled and examined the occurrence of long and short term sses and changes in their behavior during the seismic cycles of large interplate earthquakes in these numerical simulations we adopted a rate and state dependent friction law with cutoff velocities and assumed that the distribution of pore fluid controls the recurrence interval of both long and short term sses the recurrence intervals of reproduced short term sses decrease during a long term sse as observed in western shikoku in the nankai region the recurrence intervals of both types of sses become shorter in the later stages of interseismic periods large interplate earthquakes nucleate between the region where sses occur and the locked region of the large earthquakes as suggested from observations of the 1944 tonankai earthquake our numerical results suggest that the stress buildup process in a seismic cycle affects the recurrence behavior of sses

modeling of postseismic relaxation following the great 1857 earthquake southern california abstract repeated first order triangulation measurements made from 15 monuments in central and southern california are used to explore the structure of the crust and upper mantle beneath southern california as well as to estimate the distribution of slip during the great 1857 earthquake the monuments are divided into two subnetworks with repeated observations covering the respective time intervals from 1884 to 1923 and from 1898 to 1923 the angle changes occurring within these times are modeled as a sum of two contributions postseismic displacements following the 1857 earthquake and plate tectonic loading the postseismic displacements have been calculated using a elastic viscoelastic coupling model that for any fault geometry yields the exact displacements on a spherically stratified earth the southern california crust and upper mantle are modeled as an upper elastic plate underlain by a viscoelastic asthenosphere for several different combinations of structural parameters inversions are performed for the slip distribution of the 1857 earthquake in general the best fits to the data are achieved with a triangular slip distribution an elastic plate thickness of 16 km a crustal thickness of 16 to 33 km and a mantle viscosity of 0 4 to 0 8 10 19 pa s although these inversions identify the best rheological models they lead to observed residuals that are inconsistent with a normally distributed data set a preferred model of slip is constructed that accounts for the budget of total slip during the earthquake cycle and satisfies a normally distributed data set the preferred slip distribution is similar in shape to the mapped surface slip distribution but is greater in amplitude by a factor of 1 5 to 2 in addition the san jacinto fault which has no known surface slip associated with the 1857 earthquake is inferred to have accommodated 1 to 3 m of slip during the 1857 earthquake and appears to be the favored site for tectonic strain accumulation since 1857 inferred fault slip exceeding known surface slip implies either unrecognized secondary faulting or a slip deficit at the surface relative to the slip at depth

thermal constraints on the seismogenic portion of the southwestern japan subduction thrust for coastal cities an important factor in earthquake hazard from subduction zone earthquakes is the landward extent of the seismogenic portion of the subduction thrust fault in this study we test the hypothesis that the maximum downdip extent is defined by a critical temperature we have developed a transient thermal model for the nankai subduction zone of southwest japan to allow comparison of the thermally estimated downdip extent of the seismogenic zone with that from 1 seismicity and tsunami data for two great subduction earthquakes 2 the coseismic faulting extent of these events estimated from geodetic deformation data and 3 the interseismic locked zone determined from interseismic geodetic data the nankai margin has extensive heat flow and heat production data to control thermal models and thus crustal temperatures it has earthquake tsunami and geodetic data that constrain the coseismic rupture portion of the subduction thrust fault for past great earthquakes and the portion of the thrust fault that is locked and storing interseismic elastic strain on the nankaido margin off shikoku island the thermal model indicates that a temperature of 350 c taken to be the limit for seismic initiation from laboratory and field data is reached on the subduction thrust fault 150 km from the trench a transition zone into which rupture may extend with decreasing offset taken to be 450 c extends an additional 45 km downdip the thermal model results are in excellent agreement with the maximum downdip extent of coseismic displacement for the 1946 nankaido ms 8 2 earthquake off shikoku island and with the downdip extent of the present locked zone in the region of the 1944 tonankai ms 8 2 earthquake to the northeast the subduction angle is much steeper and the thermal models indicate a narrower downdip seismogenic extent the seismogenic locked zone from earthquake and geodetic data is also narrower thus our analysis of the southwest japan margin indicates that all three constraints on the downdip extent of the seismogenic zone thermal coseismic and interseismic geodetic data are in general agreement the study also supports the hypothesis that the seismogenic portion of subduction thrust faults is limited primarily by temperature the thermal control implies that subduction thrust faults with shallow dip have wider seismogenic zones compared to those with steep dip the subducting plate age and thus heat flow and the thickness of the insulating sediments on the incoming plate are also very important to the thermal regime and thus to the seismogenic width the relation of the maximum seismic rupture area to the interseismic locked zone is particularly important for earthquake hazard estimation on subduction margins such as cascadia where there have been no great historical events

displacement fields due to the 1946 nankaido earthquake in a laterally inhomogeneous structure with the subducting philippine sea plate a three dimensional finite element approach abstract the displacement fields associated with the 1946 nankaido earthquake have been investigated in detail taking into account the configuration of the philippine sea plate subducting beneath southwest japan we used a three dimensional finite element method for the elastic problem to examine the effects of three dimensionally inhomogeneous structure some differences in the displacement patterns between homogeneous and inhomogeneous media have been identified the amounts of displacements are large in low rigidity portions such as in the crust and mantle wedge and are small in a high rigidity portion composed of the subducting plate the inhomogeneity affects horizontal displacements at the earth s surface more than vertical displacements if the rigidity and the poisson ratio given here to southwest japan are appropriate the fault parameters of the earthquake which have been estimated from simple dislocation models in a homogeneous semi infinite medium need to be modified somewhat the present computations indicate that larger dip angles and smaller fault slips are more appropriate fault parameters when structural inhomogeneity is taken into account this suggests that the discrepancy in the obtained total seismic moment between the geodetic and seismic models of the nankaido earthquake could be reduced

dynamic rupture scenarios of anticipated nankai tonankai earthquakes southwest japan 1 we investigated dynamic rupture scenarios of anticipated megathrust earthquakes on the nankai tonankai subduction zone southwest japan to improve the scenario reliability the model parameters should be constrained by available data or derived from their analysis we employed the three dimensional plate interface geometry and the slip deficit rate on the interface accumulated slip deficit was used to obtain the stress drop distribution of anticipated earthquakes the estimated stress drop distribution is consistent with the seismogenic asperity locations known from the analysis of past earthquakes fault friction constitutive parameters however had to be assumed from indirect observations because they cannot be constrained directly by the data based on various geophysical observations we defined three regions where larger fracture energy is required these are the eastern edge of the tonankai area the western edge of the nankai area and the region between the tonankai and nankai areas beneath the kii peninsula such lateral heterogeneity promoted the segmented rupture along the nankai trough with predefined stress drop and constitutive parameters various rupture scenarios for tonankai and nankai asperities were obtained for different initiation locations in some cases a single segment is ruptured while in other cases all the segments are broken due to dynamic linkage at the segment boundary causing a giant earthquake the initiation location is a critical parameter that controls the rupture propagation across the segment boundary these scenarios will be extremely useful to evaluate deterministically the strong ground motions and tsunami hazards caused by the next major earthquakes in southwest japan

assessing the contribution of off fault deformation to slip rate estimates within the taupo rift new zealand using 3 d ground penetrating radar surveying and trenching we demonstrate that conventional palaeoseismic trenching and mapping techniques that do not account for the effects of off fault deformation can significantly underestimate a fault s slip rate using combined interpretations of 3 d ground penetrating radar gpr and palaeoseismic trench data we show that drag folding and hangingwall and footwall horizontal axis rotations have accommodated up to 41 of total extension across a normal fault within the taupo rift new zealand over the past 24 6 1 0 cal ka bp our results may explain why geologically determined fault slip rates for the central and southern taupo rift are anomalously low when compared with geodetic estimates we suggest that a combination of gpr surveying and palaeoseismic trenching may help resolve differences between geodetically and geologically determined strain rates observed across active extensional regimes worldwide

seismicity at the eastern end of the 1944 tonankai earthquake rupture area the rupture areas of the large interplate thrust earthquakes along the nankai trough offshore southwestern japan are divided into several segments the 1944 tonankai earthquake ruptured one of the segments off of the kii peninsula in 2005 we conducted an ocean bottom seismograph experiment at the eastern end of the rupture area of the 1944 earthquake little seismic activity was observed on the plate interface most earthquake activity was within the subducting and overriding plates aftershocks of the 2004 off kii peninsula earthquake which was an intraplate earthquake in the subducting philippine sea plate were mainly located in the subducting oceanic crust and uppermost mantle however several earthquakes at the eastern end of the rupture area of the 1944 earthquake were in the sedimentary wedge with a focal mechanism indicating deformation by a subducting seamount the earthquakes and faults in the sedimentary wedge show deformation related to the irregular topography of the subducting oceanic crust to the east of the rupture area of the 1944 tonankai earthquake in contrast few earthquakes were observed in the sedimentary wedge in the rupture area of the 1944 earthquake difference in topography of the subducting oceanic crust in the two areas might have caused spatial variations of interplate coupling which in turn caused the observed differences in the deformation of the sedimentary wedge the spatial variation of interplate coupling may affect rupture propagation during large interplate earthquakes and cause the segmentation of large interplate earthquakes along the nankai trough

influence of temperature and depth dependent viscosity structures on postseismic deformation predictions for the large 1946 nankai subduction zone earthquake abstract to investigate the influence of spatial change of viscosity on postseismic deformation associated with the interplate 1946 nankai earthquake m 8 0 at the nankai trough southwest japan we newly constructed a realistic viscoelastic structure model taking into account temperature and depth dependent viscosity of materials for this purpose we first compiled leveling and triangulation data during postseismic periods and clarified characteristics of the amount and spatial patterns of postseismic vertical displacement and principal strain fields then we calculated the spatial distributions of viscosity from temperature and flow fields which were obtained from 2d subduction models by incorporating the obtained viscosity structure into 3d viscoelastic finite element models we constructed a temperature and depth dependent viscosity structure model model p2 based on model p2 we constructed a viscoelastic structure model taking into account poisson s ratio for the oceanic plate and low velocity regions and the existence of low viscosity materials beneath the shikoku and chugoku districts model p3 which were revealed from seismic tomography we also constructed a conventional layered viscoelastic structure model model l1 and plate subduction model model p1 with constant viscosity for each region and evaluated the effects of different viscoelastic structures on postseismic surface deformations using the coseismic slip distribution obtained by inversion analyses of geodetic data we also compared the calculated surface deformations with the observed postseismic crustal deformations in and around shikoku the results show that postseismic surface deformation fields for the newly constructed model p2 are rather different from those for models l1 and p1 landward horizontal displacements for model p2 are smaller than those for models l1 and p1 seaward horizontal displacements are negligible and vertical displacement is characterized by small subsidence over shikoku the postseismic horizontal principal strain field for model p2 is characterized by contractions in the n s to nw se directions at amounts smaller than those for models l1 and p1 postseismic surface deformations for model p3 are almost the same as those for model p2 the observed postseismic vertical displacement and horizontal principal strain fields could not be explained by the viscoelastic response for the realistic viscoelastic structure models p2 and p3 this indicates that the effects of elastic and viscoelastic responses due to interplate coupling on the plate interface after slip at the extension of the coseismic slipped region and poroelasticity should be taken into account to precisely estimate postseismic surface deformation this also suggests that in order to evaluate postseismic crustal deformations derived from a large interplate subduction zone earthquake it is essential to use realistic temperature and depth dependent viscoelastic structure models

a dislocation model for the earthquake cycle at convergent plate boundaries summary a kinematic model for the earthquake cycle at convergent plate boundaries has been constructed on the basis of dislocation theory we model the lithosphere asthenosphere system by a stratified semi infinite medium under gravity consisting of an elastic surface layer an intervening layer with maxwell viscoelasticity and an elastic substratum the steady motion of plate convergence is naturally represented by uniform slip at a constant rate on the upper boundary of the descending oceanic plate the occurrence of interplate earthquakes is regarded as a perturbation of the steady state plate motion and represented by a periodic sequence of step slips on a finite seismic zone of the plate interface based on dislocation theory we can show that the steady slip on the interface deeper than the lithosphereasthenosphere boundary does not contribute to surface deformation in the steady state accordingly the surface deformation associated with the earthquake cycle is given by the superposition of viscoelastic responses to the steady slip on the interface shallower than the lithosphere asthenosphere boundary the steady backslip on the seismic zone and the periodic sequence of seismic slips we have computed cyclic patterns of vertical displacements at the free surface for two representative cases taking account of gravity effects the patterns of vertical displacements differ notably in the latter stage of the cycle depending on whether or not the seismic zone extends through the entire thickness of the lithosphere after the completion of one earthquake cycle our model yields a certain amount of permanent deformation resulting from the steady plate convergence the pattern of the permanent deformation that is characterized by steep uplift on the continental side sharp subsidence at the plate boundary and gentle uplift on the oceanic side is irrespective of the cyclic process of stress accumulation and release repeated on the seismic zone the earthquake cycle model developed here provides a possible explanation for the formation of earthquake origin marine terraces

comparison of characteristic and gutenberg richter models for time dependent m 7 9 earthquake probability in the nankai tokai subduction zone japan summary earthquake forecasts are usually underinformed and can be plagued by uncertainty in terms of the most appropriate model and parameter values used in that model in this paper we explore the application of two different models to the same seismogenic area the first is a renewal model based on the characteristic earthquake hypothesis that uses historical palaeoseismic recurrence times and fixed rupture geometries the hazard rate is modified by the coulomb static stress change caused by nearby earthquakes that occurred since the latest characteristic earthquake the second model is a very simple earthquake simulator based on plate motion or fault slip rates and adoption of a gutenberg richter magnitude frequency distribution this information is commonly available even if historical and palaeoseismic recurrence data are lacking the intention is to develop and assess a simulator that has a very limited parameter set that could be used to calculate earthquake rates in settings that are not as rich with observations of large earthquake recurrence behaviour as the nankai trough we find that the use of convergence rate as a primary constraint allows the simulator to replicate much of the spatial distribution of observed segmented rupture rates along the nankai tonankai and tokai subduction zones although we note rate differences between the two forecast methods in the tokai zone we also see enough similarities between simulations and observations to suggest that very simple earthquake rupture simulations based on empirical data and fundamental earthquake laws could be useful forecast tools in information poor settings

asymmetric radiation of seismic waves from an atoll nuclear tests in french polynesia seismic records of nuclear tests detonated in the mururoa atoll in french polynesia show large unpredicted arrivals 2 2 and 4 5 seconds x1 and x2 after the p wave at the australian warramunga array these arrivals are not observed at the canadian yellowknife array x1 and x2 are also absent on warramunga array recordings of tests carried out at the fangataufa atoll situated 40 km sse of mururoa array analysis shows that x1 and x2 are produced within the source area the layered crustal structure of the atoll significant local inhomogeneities and focusing effects due to the elongated shape and the steep flanks of the mururoa atoll are most likely responsible for x1 and x2 the form of mururoa 28 10 km and its east west orientation is due to its location on the austral fracture zone afz the fangataufa atoll on the other hand is almost circular 10 km diameter and is unaffected by the dynamics along the afz our observations demonstrate that complicated structures in the source area can significantly alter the wave field at teleseismic distances and produce a large magnitude mb bias a better understanding of the exact cause of these unusual seismic observations will only become possible if the coordinates of the tests and information on the detailed 3 d structure of the atolls are released

interplate coupling in the kanto district central japan deduced from geodetic data inversion and its tectonic implications abstract interplate coupling between the philippine sea phs the north american nam and the pacific pac plates in the kanto district central japan has been investigated through the inversion analysis of geodetic data using akaike s bayesian information criterion abic the data used for the analysis are annual rates of level changes 1972 1985 and horizontal length changes 1973 1990 which presumably represent average crustal movements during the interseismic period disregarding effects of steady plate subduction we may ascribe the observed crustal movements to the effects of locking or faulting on some parts of the plate boundaries in our model the effect of locking is represented by back slip on the plate boundary and that of faulting by forward slip the results of the inversion analysis show the existence of a strongly coupled area on the southwestern shallower part of the nam phs plate boundary which almost coincides with the faulting area of the 1923 kanto earthquake m 7 9 and a notable faulting area on the northeastern deeper part of the phs pac plate boundary in the southwestern strongly coupled area the rate of back slip reaches 3 5 cm yr and its direction is oriented n33 w which is almost opposite to the direction of fault slip s29 e at the time of the 1923 event this suggests that tectonic stress accumulation for the next large event is effectively proceeding there and its recurrence time is roughly estimated as 245 years the strongly coupled region is also recognized as corresponding to a recent seismic gap the inverted forward slip distribution on the phs pac plate boundary which has the average rate of 1 9 cm yr and the average direction of n56 e may be explained by aseismic northeastward slip in relation to the process to form a peculiar configuration of downward bend of the phs plate beneath the kanto district

distribution of seismic coupling on the subducting plate boundary in northeastern japan inferred from gps observations abstract many global positioning system gps stations of the geographical survey institute and tohoku university in northeastern japan observed clear coseismic and postseismic deformations associated with the m7 5 1994 far off sanriku earthquake applying the geodetic inversion algorithm given by yabuki and matsu ura geophys j int 1992 109 363 376 to the observed gps data we estimate in this paper the spatial distributions of the coseismic and postseismic slip on the boundary between the subducting pacific plate and the overriding continental plate it is noted that the coseismic slip estimated in this paper denotes the slip for a period between the day before and the day after the main shock the inversion for coseismic slip shows that the main shock was thrust faulting typical for interplate earthquakes which is consistent with the results of other seismological studies the short term postseismic deformation std observed for a period of ca 10 days between the main shock and its largest aftershock shows that the initially high deformation rate was lowered rather rapidly in comparison with the subsequent long term deformations ltd lasting longer than 1 year which decreased at an almost constant low rate the observed data of std can be explained by postseismic slip distributed approximately on the same region as the faulting area of the main shock where the moment release during this period is ca 16 of that estimated for the coseismic slip the region of the sliding causing ltd is found to have significantly expanded southward and downward or westward on the plate boundary the moment released by the postseismic sliding for nearly 1 year amounts approximately to 80 of that released by the coseismic slip in addition to the contribution from uniform steady sliding due to the relative plate motion furthermore we find from the inversion analysis a locked region to the south of the long term postseismic sliding region on the plate boundary the amount of nominal back slip estimated is so large that the locked region of the plate boundary is considered to have been tightly coupled for the year of 1995 this study demonstrates that the gps observation only for ca 1 year can distinguish the decoupled region due to the postseismic sliding around the source area of the main shock from the coupled one of the plate boundary

repetitive long term slow slip events beneath the bungo channel southwestern japan identified from leveling and sea level data from 1979 to 2008 1 leveling and sea level data for the period from 1979 to 2008 around the bungo channel southwestern japan were investigated to characterize vertical deformation patterns we found evidence of discrete events that may have occurred beneath the bungo channel before the two most recent long term slow slip events sses 1996 1997 and 2003 detected from gps data gps derived steady state vertical displacements related to ongoing subduction of the philippine sea plate were subtracted from the vertical displacements observed by leveling surveys the spatial pattern of the residual vertical displacements observed by leveling was similar to that observed by gps in the periods including recent long term sses this suggests that discrete vertical displacements which might represent long term sses have occurred in each of four intervals between leveling surveys before gps deployment we calculated differences of sea level between tidal stations near the bungo channel after some corrections and then cross correlated them with the gps derived vertical displacements of the recent long term sse to estimate the timing of the events these cross correlations and the discrete vertical displacements derived from leveling suggest that long term sses may have occurred around 1980 around 1985 1986 and around 1991

a revised dislocation model of interseismic deformation of the cascadia subduction zone 1 cas3d 2 a new three dimensional 3 d dislocation model is developed to model interseismic deformation rates at the cascadia subduction zone the model is considered a snapshot description of the deformation field that changes with time the effect of northward secular motion of the central and southern cascadia forearc sliver is subtracted to obtain the effective convergence between the subducting plate and the forearc horizontal deformation data including strain rates and surface velocities from global positioning system gps measurements provide primary geodetic constraints but uplift rate data from tide gauges and leveling also provide important validations for the model a locked zone based on the results of previous thermal models constrained by heat flow observations is located entirely offshore beneath the continental slope similar to previous dislocation models an effective zone of downdip transition from locking to full slip is used but the slip deficit rate is assumed to decrease exponentially with downdip distance the exponential function resolves the problem of overpredicting coastal gps velocities and underpredicting inland velocities by previous models that used a linear downdip transition a wide effective transition zone etz partially accounts for stress relaxation in the mantle wedge that cannot be simulated by the elastic model the pattern of coseismic deformation is expected to be different from that of interseismic deformation at present 300 years after the last great subduction earthquake the downdip transition from full rupture to no slip should take place over a much narrower zone

depth extent of the long term slow slip event in the tokai district central japan a new insight 1 temporal changes to interplate coupling and long term aseismic slip in the tokai region of central japan from july 1996 to june 2009 are statically inverted using continuous global positioning system gps data and leveling observations and examined using a new interpretation of aseismic slip in this interpretation the interplate coupling and the aseismic slip should be inferred and compared with reference to a state of no coupling on the plate interface rather than assuming steady state interplate coupling before the occurrence of the aseismic event as previous works have done for this purpose we used original time series data without subtracting any linear trends the inferred distribution shows that the entire period can be divided into three subperiods based on the existence of the aseismic slip area from 2000 to 2005 the strength of the interplate coupling does not change throughout the observed period even though the distribution narrows along the dip direction after the aseismic slip terminates the aseismic slip area inferred in this study based on the no coupling reference was determined to be deeper than the area where the long term slow slip event sse defined as the slip corresponding to the residual displacement from the steady state was hypothesized to have occurred in numerous previous studies the total seismic moment released by the aseismic slip is equivalent to a mw 6 6 earthquake while the sse in previous works was considered to be equivalent to a mw 7 0 to 7 1 earthquake this difference can be attributed primarily to the effects on the interplate coupling which previous studies did not take into account when defining the sse the aseismic slip area coincides well with the distribution of other types of plate interactions such as short term slow slip events and low frequency earthquakes

nonlinear strain buildup and the earthquake cycle on the san andreas fault two contrasting models of the earthquake deformation cycle on strike slip faults predict significant temporal declines in shear strain rate near the fault accompanied by a progressive broadening of the zone of deformation adjacent to it in the thin lithosphere model transient deformation results from flow in the asthenosphere due to stress relaxation following faulting through most or all of the lithosphere for an earth model with a thick elastic lithosphere plate thickness depth of seismic slip transient motions are due to postearthquake aseisrnic slip below the coseismic fault plane data from the san andreas fault indicate a long term temporal decrease in strain rate that persists for at least 30 years and may extend through the entire earthquake cycle observations support a cycle long rate decrease and a temporal spreading of the deformation profile only if movement cycles on the northern and southern locked sections of the fault are basically similar if so the usually lower strain rates and broader deformation zone currently observed on the southern san andreas represent a later evolutionary stage of the northern locked section where a great earthquake is a more recent occurrence although the data allow some extreme models to be discarded no sufficiently strong constraints exist to decide between the thin and thick lithosphere models regardless of the appropriate model the geodetic observations themselves indicate that strain buildup is sufficiently nonlinear to cause significant departures from recurrence estimates based on linear strain accumulation and the time predictable model

postseismic deformation following the 1906 san francisco earthquake we have reevaluated triangulation data from northern california following the 1906 san francisco earthquake thereby increasing the temporal and spatial resolution of postseismic deformation following that event we have calculated uniform shear strain rates and average station velocities at point arena using data from 1906 1907 1929 1930 and 1973 1975 and for the point reyes petaluma arc using data from 1929 1930 1938 1939 and 1960 1961 with the addition of recent geodetic data we infer an effective relaxation time for long term postseismic deformation following the 1906 earthquake of 36 16 years the point arena data are satisfactorily fit with accelerated afterslip at depth along the san andreas fault plane for a 10 km deep 25 km wide afterslip zone the average slip rate between 1906 and 1930 is 11 2 cm yr between 1929 and 1975 it is 4 6 cm yr deformation in the point reyes petaluma arc is clearly asymmetric with respect to the trace of the san andreas fault especially between 1929 and 1939 after inverting for the range of acceptable accelerated deep afterslip and horizontal detachment models a detailed analysis using geologically reasonable geometries revealed that both model types have trouble explaining the spatial variations in the deformation field through time in particular accelerated deep afterslip models cannot reproduce the breadth of the observed deformation field to the northeast of the san andreas fault as a result more complex time varying deformation mechanisms are required to explain the point reyes petaluma arc observations

secular crustal deformation and interplate coupling of the japanese islands as deduced from continuous gps array 1996 2001 abstract data from the nation wide gps continuous tracking network that has been operated by the geographical survey institute of japan since april 1996 were used to study crustal deformation in the japanese islands we first extracted site coordinate from daily sinex files for the period from april 1 1996 to february 24 2001 since raw time series of station coordinates include coseismic and postseismic displacements as well as seasonal variation we model each time series as a combination of linear and trigonometric functions and jumps for episodic events estimated velocities were converted into a kinematic reference frame heki k 1996 horizontal and vertical crustal movements from three dimensional very long baseline interferometry kinematic reference frame implication for reversal timescale revision j geophys res 101 3187 3198 to discuss the crustal deformation relative to the stable interior of the eurasian plate a least squares prediction technique has been used to segregate the signal and noise in horizontal as well as vertical velocities estimated horizontal signals horizontal displacement rates were then differentiated in space to calculate principal components of strain dilatations maximum shear strains and principal axes of strain clearly portray tectonic environments of the japanese islands on the other hand the interseismic vertical deformation field of the japanese islands is derived for the same gps data interval the gps vertical velocities are combined with 31 year tide gage records to estimate absolute vertical velocity the results of vertical deformation show that 1 the existence of clear uplift of about 6 mm yr in shikoku and kii peninsula whereas pattern of subsidence is observed in the coast of kyushu district this might reflect strong coupling between the philippine sea plate and overriding plate at the nankai trough and weak coupling off kyushu 2 no clear vertical deformation pattern exists along the pacific coast of northeastern japan this might be due to the long distance between the plate boundary japan trench and overriding plate where gps sites are located 3 significant uplift is observed in the southwestern part of hokkaido and in northeastern tohoku along the japan sea coast this is possibly due to the viscoelastic rebound of the 1983 japan sea mw 7 7 and the 1993 hokkaido nansei oki mw 7 8 earthquakes and or associated with distributed compression of incipient subduction there we then estimate the elastic deformation of the japanese islands caused by interseismic loading of the pacific and philippine sea subduction plates the elastic models account for most of the observed horizontal velocity field if the subduction movement of the philippine sea plate is 100 locked and if that of the pacific plate is 70 locked however the best fit for vertical velocity ranges from 80 to 100 coupling factor in southwestern japan and only 50 in northeastern japan since horizontal data does not permit the separation of rigid plate motion and interplate coupling because horizontal velocities include both contributions we used the vertical velocities to discriminate between them so we can say there is strong interplate coupling 80 100 over the nankaido subduction zone whereas it is about 50 only over the kurile japan trench

slow slip events and seismic tremor at circum pacific subduction zones 1 it has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements however only recently has a fuller spectrum of strain release processes including normal slow and silent earthquakes or slow slip events and continuous and episodic slip been observed and generated by numerical simulations of the earthquake cycle despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive the concurrence of seismic tremor with slow slip episodes in cascadia and southwestern japan provides insight into the process of slow slip a perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface alternatively evidence is accumulating to support the notion that tremor results from shear failure during slow slip global observations of the location spatial extent magnitude duration slip rate and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation most slow slip events occur just downdip of the seismogenic zone consistent with rate and state dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation at a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault bringing it closer to or farther from earthquake failure respectively this paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide with a focus on circum pacific subduction zones trends in global observations of slow slip events suggest that 1 slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it 2 different frictional properties likely control fast versus slow slip 3 the depth range of slow slip may be related to the thermal properties of the plate interface and 4 the equivalent seismic moment of slow slip events is proportional to their duration mo different from the mo 3 scaling observed for earthquakes

the influence of preferential flow on pressure propagation and landslide triggering of the rocca pitigliana landslide abstract the fast pore water pressure response to rain events is an important triggering factor for slope instability the fast pressure response may be caused by preferential flow that bypasses the soil matrix currently most of the hydro mechanical models simulate pore water pressure using a single permeability model which cannot quantify the effects of preferential flow on pressure propagation and landslide triggering previous studies showed that a model based on the linear diffusion equation can simulate the fast pressure propagation in near saturated landslides such as the rocca pitigliana landslide in such a model the diffusion coefficient depends on the degree of saturation which makes it difficult to use the model for predictions in this study the influence of preferential flow on pressure propagation and slope stability is investigated with a 1d dual permeability model coupled with an infinite slope stability approach the dual permeability model uses two modified darcy richards equations to simultaneously simulate the matrix flow and preferential flow in hillslopes the simulated pressure head is used in an infinite slope stability analysis to identify the influence of preferential flow on the fast pressure response and landslide triggering the dual permeability model simulates the height and arrival of the pressure peak reasonably well performance of the dual permeability model is as good as or better than the linear diffusion model even though the dual permeability model is calibrated for two single pulse rain events only while the linear diffusion model is calibrated for each rain event separately in conclusion the 1d dual permeability model is a promising tool for landslides under similar conditions

coseismic slip resolution along a plate boundary megathrust the nankai trough southwest japan geodetic survey measurements are used to estimate the coseismic slip distribution in the 1944 tonankai mw 8 1 and 1946 nankaido mw 8 3 earthquakes and to assess quantitatively the degree to which this slip is resolved on the plate boundary megathrust data used include 798 angle changes from triangulation surveys 328 leveling section differences and 5 coseismic tidal gage offsets many of the nominally coseismic triangulation data span 50 years nearly half the earthquake cycle and correction for interseismic deformation using post 1950 observations is applied microseismicity is used to define the configuration of the plate boundary interface and approximate it with a continuous multisegment fault model because the onshore geodetic data have very limited resolving power for offshore fault segments offshore coseismic slip was constrained by satake s 1993 estimation based on tsunami data the majority of the coseismic slip occurs between 15 and 25 km depth although resolution declines toward the trench axis it is sufficiently good to define two distinct high slip regions one off southeastern shikoku island 11 m maximum and the other offshore of kii peninsula 3 m maximum the slip magnitude off southeastern shikoku coupled with the plate convergence rate would imply an recurrence interval of about 270 years much longer than the average repeat time of 120 years for historical great earthquakes on the nankai trough however the maximum coseismic slip is sensitive to the assumed fault geometry and slippage on trough parallel splay faults could significantly decrease the maximum slip to about 6 m

mobility of continental mantle evidence from postseismic geodetic observations following the 1992 landers earthquake the crust around the rupture zone of the 1992 landers earthquake has continued to deform in the years following the earthquake at rates 3 times greater than pre earthquake rates we use a combination of global positioning system gps and synthetic aperture radar insar data collected during a 3 year epoch following the earthquake in order to investigate postseismic mechanisms responsible for the high transient velocities in order to maximize the potential signal from viscoelastic relaxation we evaluate and model postseismic relaxation following the first few months of documented accelerated deformation the combination of gps and insar data allows us to establish viscoelastic relaxation of the lower crust and upper mantle as the dominant postseismic process and to discriminate among possible viscoelastic models the data particularly require the presence of a highly ductile uppermost mantle beneath the central mojave domain with temperature between the wet and dry basalt solidus this is consistent with independent seismic and geochemical inferences of a regionally warm uppermost mantle further consideration of seismic velocity variations in conjunction with faulting patterns within the mojave desert suggests that the primary faulting characteristics of the mojave desert namely the pervasive late cenozoic deformation within the eastern california shear zone versus the near absence of faults in the western mojave domain are controlled by the rheology of the uppermost mantle

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

estimation of interplate coupling in the nankai trough japan using gps data from 1996 to 2006 we used three component surface velocities in southwest japan to estimate plate coupling on the subducting plate interface at the nankai trough we analyzed continuous gps data from the japanese geonet network from 1996 to 2006 using a consistent analysis strategy that generates bias fixed solutions for the entire network we applied systematic time series analysis methods to estimate common mode error which improved position solutions for the entire network to allow for differences in regional deformation sources we modelled the plate coupling on the plate interface beneath shikoku island to kii peninsula and the tokai suruga trough separately the results show strong coupling at a depth of 10 30 km off shikoku and kii peninsula the spatial variation in plate coupling coincides well with the coseismic rupture zones of the past large earthquakes maximum slip deficit rates of 2 3 cm yr 1 at the depth of 5 25 km are found beneath the tokai area consistent with results from other studies the downdip limits of the highly coupled areas and transition zones beneath shikoku and the kii peninsula correspond approximately to estimates of the 450 c isotherms good correlation is observed between the lateral variations of the slip deficit distribution low frequency earthquakes and coseismic slip this correlation suggests that temperature and possibly fluid variations contribute to such correlation in space the interplate slip deficit derived from the gps velocities over the 10 yr of observations is generally compatible with the results over shorter time spans suggesting that plate coupling in sw japan does not change significantly over the period of these gps measurements

temperature distribution of the upper surface of the subducted philippine sea plate along the nankai trough southwest japan from a three dimensional subduction model relation to large interplate and low frequency earthquakes summary the nankai subduction fault in southwest japan is a plate boundary along which large megathrust earthquakes have repeatedly occurred a previous 2 d thermal model suggested that the updip and downdip limits of the seismogenic zone are closely related to the temperature of the plate interface we estimated a new temperature distribution for the plate interface based on a 3 d thermal convection model that incorporates revised governing equations temporal changes in relative plate motion the shape of the subducted slab temperature variations related to basin evolution and more heat flow data and model regions than have been used in previous models the margin parallel spatial variation in the temperature of the plate interface was caused by spatio temporal changes associated with the cooling of the shikoku basin the updip limit of the thermally delineated seismogenic zone thermal seismogenic zone was approximately parallel to the trough axis due to a spreading rate that increased with distance from a fossil ridge although the margin parallel age dependency of the subducting plate was taken into account the downdip limit of the thermal seismogenic zone was determined by temperature except in eastern kyushu where it was determined by a boundary between the continental moho depth and the upper surface of the subducting plate the maximum coseismic slip associated with the 1944 tonankai m 7 9 and the 1946 nankai m 8 0 earthquakes and a strongly coupled region estimated from gps data inversion obtained by previous studies were both located in the thermal seismogenic zone on the plate interface low frequency earthquakes located at the downdip of the thermal seismogenic zone took place at temperatures of about 400 500 c this may be related to the phase transformation of hydrous minerals in oceanic crust from lawsonite blueschist jadeite to amphibole eclogite and the associated decreases in water content of approximately 2 4 wt the thermal seismogenic zone is narrowest off the kii peninsula where the hypocentres of the tonankai and nankai earthquakes were located the narrow seismogenic zone may have determined the rupture initiation points for these earthquakes as was previously demonstrated by numerical simulations of the earthquake cycle

difference in the maximum magnitude of interplate earthquakes off shikoku and in the hyuganada region southwest japan inferred from the temperature distribution obtained from numerical modeling the proposed hyuganada triangle abstract to clarify differences in the maximum magnitude of interplate earthquakes offshore of shikoku m 8 and in the western adjacent hyuganada region m 7 5 southwest japan where the oceanic philippine sea phs plate subducts beneath the continental amuria plate along the nankai trough we calculated the temperature distribution for the plate interface using a three dimensional thermal convection model we attribute the observed very low heat flow values less than approximately 45 mw m 2 in the southern part of the hyuganada region to the subduction of the kyushu palau ridge which is presumably older than the adjacent shikoku basin to the east trial and error methods suggest an age difference of about 20 myr between these two areas the heat flow calculated from the temperature distribution fits the observed heat flow in the hyuganada region well the results show that hyuganada earthquakes may take place in the newly proposed hyuganada triangle bounded by a southeastern isotherm of about 200 c on the plate interface a northwestern boundary between the upper surface of the subducting phs plate and the continental moho discontinuity a northern isotherm of about 350 c and a northeastern margin normal zone with a possible barrier or large friction parameter l interplate earthquakes in such a limited seismogenic zone may reach a maximum magnitude of m 7 5 our results also suggest that a seismic gap seaward of the hyuganada region may be caused by stable sliding arising from low temperature resulting in a deeper updip limit than that offshore of shikoku the seismic gap offshore southwest of southern kyushu along the ryukyu trench may result from the overlapping of two stable sliding regimes on the plate interface one with low temperature at shallower depths caused by the subduction of the old phs plate and the other a serpentinized mantle wedge at deeper depths

interplate coupling in the tokai district central japan deduced from continuous gps data i invert gps displacement rates in the tokai district to investigate strain accumulation associated with the anticipated tokai earthquake i apply a representation of interseismic strain accumulation at subduction zones by savage 1983 and estimate a distribution of virtual normal fault slip back slip on the plate boundary surface estimated back slip takes its maximum value of 30 40mm year under the sea of enshu this value is nearly equal to the relative plate motion there implying almost complete coupling back slip is smaller under suruga bay and its direction is different from the relative motion between the eurasian and the philippine sea plates localized deformation at the northern tip of the philippine sea plate may be responsible for this discrepancy partitioning tectonic strain due to the plate convergence into faults on both sides of the izu peninsula and also distributed strain inside the peninsula

contemporary deformation and seismicity analysis in southwest japan during 2010 2018 based on gnss measurements a significant amount of work has been conducted in the japanese islands on high precision positioning surveying natural disaster mitigation reference frame and datum definitions however there is substantial scope for exploring the current seismotectonic activity of japan which would provide further awareness of disaster management the short recurrence time of great inter plate earthquakes and well recorded geodetic observations provide one of the best examples to analyze the combination of contemporary deformation and seismic intensity in southwest sw japan in the current study we analyzed three districts of sw japan which include mainly kyushu district and parts of chugoku and shikoku districts we predicted global navigation satellite system gnss measurements based on amurian fixed reference frame aref velocities with the help of singular spectrum analysis ssa method and examined the regional deformation from april 01 2010 to december 31 2018 in addition we analyzed the earthquakes clustered calculated by the nearest neighborhood distance method which showed prominently bimodal seismicity of sw japan and revealed the existence of two statistically distinct earthquake populations the events inside a cluster were normally close to their nearest neighbors whereas events from distinct clusters were comparatively aloof from each other finally the paper provides the spatial strain and rotational rate variation for selected seismotectonic districts that are in relatively good agreement with the seismic deformation inferred from earthquake focal mechanisms we believe that our integrated approaches would provide a better insight into the active deformation of sw japan

role of upslope soil pore pressure on lateral subsurface storm flow dynamics 1 the role of upslope soil pore water pressure on lateral subsurface storm flow dynamics is poorly understood further development of hillslope hydrologic models requires new understanding from field understanding in particular we need new quantifiable measures that link upslope soil pore pressure and water table dynamics to the timing and volume of subsurface storm flow here we examine the relationship between hillslope scale pore pressure and lateral outflow from slope base using the fine temporal resolution hydrometric data 10 min interval from two steep unchanneled concave hillslopes one hillslope fudoji covered by relatively high hydraulic conductivity sandy soil and the other toinotani covered by relatively low hydraulic conductivity clay soil in both hillslopes pore pressures in the area close to the slope base were only weakly related to subsurface storm flow dynamics during periods of storm flow production hillslope discharge was strongly related to the cross sectional area of the upslope saturated layer during slope seepage periods between events hillslope discharge from the highly permeable hillslope was still related to the upslope cross sectional subsurface saturated area however during this same period at the low permeability site hillslope discharge was not related to the upslope subsurface saturated area through intersite comparison we show that the soil matrix permeability has a large impact on the hydrological extension of preferential flow and hence the linkage between upslope pore pressure and subsurface storm flow dynamics

seafloor geodetic constraints on interplate coupling of the nankai trough megathrust zone seafloor geodetic data from the nankai trough off southwestern japan show that most offshore sites in this earthquake prone region have high slip deficit rates revealing previously unknown locations that could be important for the mitigation of future earthquake and tsunami associated disasters yusuke yokota et al have used seafloor geodetic observations to visualize the seismogenic zone along the nankai trough off southwestern japan which is thought to be one of the most dangerous megathrust zones in the world they suggest that most offshore sites in this region have positive slip deficit rates revealing previously unknown locations that could be potential sources of future earthquakes and tsunamis low slip deficit rates are observed in other regions consistent with distributions of shallow slow earthquakes and subducting seamounts interplate megathrust earthquakes have inflicted catastrophic damage on human society such an earthquake is predicted to occur in the near future along the nankai trough off southwestern japan an economically active and densely populated area in which megathrust earthquakes have already occurred1 2 3 4 5 megathrust earthquakes are the result of a plate subduction mechanism and occur at slip deficit regions also known as coupling regions 6 7 where friction prevents plates from slipping against each other and the accumulated energy is eventually released forcefully many studies have attempted to capture distributions of slip deficit rates sdrs in order to predict earthquakes8 9 10 however these studies could not obtain a complete view of the earthquake source region because they had no seafloor geodetic data the hydrographic and oceanographic department of the japan coast guard jhod has been developing a precise and sustainable seafloor geodetic observation network11 in this subduction zone to obtain information related to offshore sdrs here we present seafloor geodetic observation data and an offshore interplate sdr distribution model our data suggest that most offshore regions in this subduction zone have positive sdrs specifically our observations indicate previously unknown regions of high sdr that will be important for tsunami disaster mitigation and regions of low sdr that are consistent with distributions of shallow slow earthquakes and subducting seamounts this is the first direct evidence that coupling conditions might be related to these seismological and geological phenomena our findings provide information for inferring megathrust earthquake scenarios and interpreting research on the nankai trough subduction zone

prolonged post seismic deformation of the 1960 great chile earthquake and implications for mantle rheology 1 contemporary crustal deformation of the southern andean margin shows an interesting feature while nearly all coastal gps sites move landward consistent with inter seismic deformation near a locked subduction fault sites 300 400 km landward of the rupture region of the mw9 5 1960 chile earthquake are moving in the opposite direction we attribute the seaward motion of these inland sites to a prolonged crustal deformation due to mantle stress relaxation following the 1960 great earthquake in order to reproduce the observed seaward motion using a three dimensional finite element model we need to incorporate a mantle viscosity of about 3 1019 pa s the possibility that the seaward motion is caused by a silent slip event on the plate interface at large depths cannot be completely excluded and our analysis provides a working model for future field tests

rupture process of the 1946 nankai earthquake estimated using seismic waveforms and geodetic data the rupture process of the 1946 nankai earthquake mjma 8 0 was estimated using seismic waveforms from teleseismic and strong motion stations together with geodetic data from leveling surveys and tide gauges the results of joint inversion analysis showed that two areas with large slip are more confined than in previous studies in our inversion we assumed spatially varying strike and dip angles and depth of each subfault by fitting those to the actual complex shape of the upper surface of the philippine sea plate in the nankai trough region as a result we calculated the total seismic moment m0 5 5 1021 nm the moment magnitude mw 8 4 and a maximum slip of 5 1 m occurring at a point south of cape muroto the estimated slip distribution on the west side of the fault plane appears somewhat complicated but it explains well the vertical deformations at tosashimizu and in the vicinity of inomisaki arguments have been made that the westernmost part slipped slowly after the earthquake over a period of days or months as an afterslip because the seismic waveforms can be largely explained without the slip in this part however in order to explain the displacement recorded by the tide gauge at tosashimizu we conclude that the westernmost part slipped simultaneously with the earthquake splay faulting which was suggested in previous studies is not required in our model to explain the seismic waveforms and geodetic data

crustal velocity field of southwest japan subduction and arc arc collision we investigate crustal deformation in southwest japan over a 3 year period revealed by a permanent dense global positioning system gps array southwest japan is a part of the amurian plate a microplate moving about 10 mm yr toward the east with respect to the eurasian plate it overrides the philippine sea plate at the nankai trough and collides with the northeast japan arc in the central part of japan in this paper we first derive gps site velocities relative to the stable part of the amurian plate in order to isolate signals of crustal deformation caused by the subduction and or the collision the velocity field has a conspicuous feature indicating the interseismic elastic loading by the philippine sea plate slab at the nankai trough characterized by the northwestward movements of points throughout the studied area their amplitudes are the largest at the pacific coast and decay toward the japan sea coast with a subtle systematic shift of azimuths a model assuming an elastic half space the convergence rate at the nankai trough based on a refined euler vector and the strength of the coupling inferred from a thermal model could explain the velocity field in the western part of the studied area to a large extent those in the eastern part systematically deviate from them and the residual components there show east west shortening and north south extension this may represent crustal thickening and trenchward extrusion of crustal blocks caused by the collision between southwest and northeast japan this suggests that the collision between southwest and northeast japan gives rise to not only crustal thickening but also trenchward extrusion of crustal block a velocity contrast was found across the median tectonic line the largest inland active fault in japan but the current permanent gps network is not dense enough for us to discuss its coupling depth

possible slip history scenarios for the hyuga nada region and bungo channel and their relationship with nankai earthquakes in southwest japan based on numerical simulations the nankai earthquakes are great interplate earthquakes with recurrence intervals of 100 200 years occurring along the nankai trough southwestern japan new geological evidences suggest that the rupture area of the 1707 earthquake one of the largest extended farther westward than previously thought and similar magnitude events may have recurrence intervals of several hundred years west of the nankai earthquake segments in the bungo channel region slow slip events sses have occurred with recurrence intervals of several years since 1980 farther westward no m 7 5 interplate earthquakes have occurred except for one in 1968 in the northern hyuga nada region near the bungo channel we numerically simulated the generation cycles of nankai earthquakes hyuga nada earthquakes and bungo channel sses to obtain possible slip histories in these regions particularly during 1707 1980 we showed that the nankai and hyuga nada earthquakes occur mostly independently with average recurrence intervals of 151 and 117 years respectively an sse patch slipped coseismically during both the nankai and hyuga nada earthquakes the rupture of the nankai earthquakes extended to the hyuga nada region every 500 600 years and was followed by quiescence of sses for more than 200 years subsequently sses occurred repeatedly every 8 years current observational findings are generally consistent with the characteristics obtained from our scenarios except regarding the recurrence intervals of hyuga nada earthquakes for which few observations are available further evidence of the slip history in these regions will be required to use information from such simulations to forecast future earthquakes

time dependent triggered afterslip following the 1989 loma prieta earthquake we employ a modified version of the network inversion filter to investigate time dependent slip following the 1989 loma prieta earthquake previous analysis of global positioning system gps and leveling data suggests afterslip on the loma prieta rupture as well as aseismic slip on a thrust fault northeast of the san andreas fault which we identify with the foothills thrust belt we analyzed 173 daily gps solution files at 62 stations collected from 1989 8 to 1998 3 a total of 1 134 three dimensional relative baseline determinations the observed position changes are assumed to result from secular deformation random benchmark motions and temporally varying fault slip the data reveal temporal variations in slip rate but poorly resolve spatial variations in fault slip the amount of temporal smoothing is estimated by maximum likelihood conditional on this estimate reverse slip on the foothills thrust decays from 45 12 mm yr immediately after the earthquake to zero by 1992 reverse slip on the loma prieta rupture surface decays from 57 11 mm yr to zero by 1994 right lateral slip on the loma prieta rupture surface decays monotonically from 30 10 mm yr to zero by 1994 these results suggest that 1 triggered afterslip can occur off the main rupture zone on adjacent faults 2 shallow afterslip dominated the postseismic deformation for the 8 years following the earthquake and 3 postseismic slip on the foothills thrust may account for a significant portion of its total slip budget

interplate coupling in southwest japan deduced from inversion analysis of gps data abstract recently the geographical survey institute of japan completed the installation of a gps continuous observation network in japan which has enabled us to investigate real time crustal movements in this study we attempt to obtain spatial distribution of interplate coupling and relative plate motion between subducting and overriding plates in southwest japan using horizontal and vertical deformation rates which were observed at 247 gps observation stations during the period from april 6 1996 to march 20 1998 for this purpose we carried out an inversion analysis of geodetic data incorporating akaike s bayesian information criterion abic as a result strong interplate coupling was found off shikoku and kumanonada regions which corresponds well with the fault regions of the 1946 nankai m 8 1 and the 1944 tonankai m 8 0 earthquakes respectively we also found that interplate coupling becomes weak at depths deeper than about 30 to 40 km beneath the shikoku and kii peninsula the recurrence time of great trench type earthquakes was roughly estimated as 107 years which is consistent with previous research the direction of relative plate motion is oriented n53 w which is close to the direction predicted from the plate motion model on the other hand a large forward slip was found in the hyuganada region off southeast of kyushu since the coseismic displacements associated with the two 1996 hyuganada earthquakes m 6 6 m 6 6 are removed from the gps data this suggests that after slip occurred near the source region and or that kyushu moves southeastward stationarily due to other tectonic forces

temporal stability of deformation rates comparison of geological and geodetic observations hikurangi subduction margin new zealand abstract we examine how well contemporary horizontal velocity fields from global positioning system gps geodetic measurements describe long term deformation rates million year rates of extension shortening strike slip and vertical axis rotations are compared with modelling of gps velocities from the last 10 15 years in the hikurangi subduction margin new zealand within measurement uncertainties of mainly 50 the rates of deformation and vertical axis rotations for each time interval are usually indistinguishable the comparable deformation rates are consistent with the notion of near constant rates since 1 5 ma during this time oblique relative plate motion was partitioned with the majority 85 of margin normal motion accommodated on the plate interface and most 60 margin parallel motion by strike slip faulting and vertical axis rotations in the upper plate prior to 1 5 ma gps velocities cannot be reliably used to describe deformation and rotations of the hikurangi margin because at this time the taupo rift commenced opening the boundary between raukumara and wairoa rotational domains was abandoned and the rates of upper plate shortening increased the broad compatibility of gps and geological deformation and rotation rates since 1 5 ma suggests that the build up of contemporary elastic strains in the north island measured by gps is largely uniform for much of the duration of each seismic cycle the good agreement between the gps and geological deformation rates in the north island is consistent with the view that contemporary elastic strains will mainly be converted to permanent dip slip on the subduction thrust and to displacement on upper plate faults during future large magnitude earthquakes

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

interplate coupling along the nankai trough southwest japan inferred from inversion analyses of gps data effects of subducting plate geometry and spacing of hypothetical ocean bottom gps stations abstract we estimated the slip deficit rate distribution on the plate boundary between the subducting philippine sea plate and the continental amurian plate along the nankai trough southwest japan horizontal and vertical displacement rates were calculated from land based global positioning system gps data during the 5 year period from 1 january 2005 to 31 december 2009 we employed an inversion analysis of geodetic data using akaike s bayesian information criterion abic including an indirect prior constraint that slip distribution is smooth to some extent and a direct prior constraint that slip is mainly oriented in the plate convergent direction the results show that a large slip deficit exists at depths ranging from 15 to 20 km on the plate boundary in a belt like form the maximum slip deficit rate was identified off shikoku and reached 6 cm year the slip deficit rate differed by as much as 1 cm year when using a different geometric model of the subducting plate on the basis of the spatial distribution of estimation errors and the resolution of the obtained slip deficit rate on the plate boundary we also found that the offshore slip deficit rate cannot be estimated with sufficient accuracy using only land based gps data therefore we tested the improvement in results when introducing hypothetical ocean bottom gps stations the stations were arranged in four along arc and across arc spacings of 80 km and 40 km the ocean bottom data improved the estimation errors and resolutions and successful results were obtained for a checkerboard with each square 75 km 76 km our results indicate that 40 km along arc and across arc two dimensional spacing of ocean bottom gps stations is required to obtain reliable slip deficit distributions near the trough axis assuming the current estimation accuracy for ocean bottom horizontal displacement rates

interplate coupling in northeast japan deduced from inversion analysis of gps data abstract the spatial distribution of the strength of interplate coupling between the subducting pacific plate and the overlying continental plate in northeast japan was investigated through an inversion analysis of gps data employing akaike s bayesian information criterion the gps data used for the inversion analysis are rates of baseline length changes and vertical displacement rates of crustal movements during the period from april 6 1996 to march 20 1998 which were obtained at 161 continuous gps observation stations operated by the geographical survey institute of japan the result shows the average drag rates of the overriding plate on the model source regions off the tohoku and hokkaido districts are 6 7 cm yr and 6 8 cm yr respectively which are 0 85 and 0 87 as interplate coupling ratio these values are much higher than those in previous studies the average directions of drag rates are oriented n73 w 15 and n78 w 13 on the model source regions off the tohoku and hokkaido districts respectively these directions agree well with the direction of coseismic slip of the foot wall side n75 w of the 1978 miyagiken oki earthquake m 7 4 but differ slightly from the direction estimated from the plate motion model n65 w seno et al j geophys res 101 1996 11305 11315 we also found afterslip of 5 5 cm yr associated with the 1994 sanriku haruka oki earthquake m 7 5 off aomori prefecture interestingly enough large afterslip occurred on the plate boundary even when more than a year had passed after the sanriku haruka oki earthquake the amount of drag rate becomes dramatically small at depths greater than about 50 km on the model source regions indicating weak interplate coupling there

three dimensional elastic dislocation modeling of the postseismic response to the 1964 alaska earthquake 1 gps velocity observations from the kenai peninsula and kodiak island alaska display a pattern of spatial variability suggesting the presence of multiple active processes on the underlying pacific north american plate interface velocities of sites on the eastern kenai peninsula and kodiak island are consistent with elastic strain accumulation at the plate interface whereas velocities of sites on the western kenai peninsula and cook inlet are oriented in the opposite direction and suggest an ongoing postseismic response to the 1964 alaska earthquake we can reproduce the observed velocities using a three dimensional elastic dislocation model to estimate the variation in coupling between the pacific and north american plates two different inversion schemes are examined to check the robustness of the results we find that the gps data can be satisfied by the presence of a locked area near southwest prince william sound a locked area near southwest kodiak island and an area of postseismic reverse slip beneath and north of the western kenai peninsula the shallow plate interface trenchward of the western kenai peninsula does not appear to be locked the locked areas correspond to the prince william sound and kodiak island asperities that ruptured in 1964 and the area of postseismic slip lies downdip of the 1964 rupture area the correspondence between the present shallow coupling distribution and the 1964 slip distribution suggests that the locked regions repeat from one earthquake cycle to another

joint estimation of afterslip rate and postseismic relaxation following the 1989 loma prieta earthquake global positioning system gps data from campaigns carried out over the 5 years following the 1989 loma prieta earthquake and leveling data measured in 1990 and 1992 define the postseismic velocity field around the loma prieta rupture zone subtraction of a background velocity field yields a residual velocity pattern which we interpret as the product of two physical processes 1 slow afterslip along distinct planes in the upper cru st and 2 viscoelastic relaxation of the lower crust and upper mantle biirgmann et al 1997 previously derived an afterslip model involving uniform afterslip on two optimally determined planes in cluding oblique reverse slip on the coseismic rupture and reverse slip on a shallow thrust fault to the northeast of the san andreas fault we further consider models of distributed slip on these two fault planes plus a viscoelastic relaxation pattern which depends on a suitable cose ismic rupture model and crust and mantle viscosities several fault models from the literature were considered for the 1989 coseismic rupture with nearly identical impact on the results simultaneous maximum likelihood inversion of the gps and leveling data for afterslip distri bution and viscosity yields the following results 1 a good fit to the data is obtained by smooth afterslip distributions without any viscoelastic relaxation being required 2 tangible broad scale viscoelastic relaxation of the lower crust and upper mantle are present in this data set at 97 confidence and a lower crustal viscosity of 1029 pa s is obtained however the viscosity of both the lower crust and upper mantle are poorly constrained 3 for a given misfit 20 less integrated afterslip and smoother afterslip distributions result when viscoelas tic relaxation is included 4 maximum slip rates on the slip distributed models are 3 5 crn yr the dominant patches estimated on the two planes fill in the entire depth range 4 13 km without significant overlap and deeper afterslip is not required the afterslip distribution on the coseismic rupture plane is strongly dominated by reverse slip immediately southeast of the main center of coseismic reverse slip

study on coseismic and postseismic crustal movements associated with the 1923 kanto earthquake abstract the kanto earthquake of 1923 m 7 9 occurred in the southern part of the kanto district japan this earthquake was accompanied by the transient crustal movements which follow instantaneous elastic deformations at the time of faulting the coseismic and postseismic crustal movements associated with the kanto earthquake are well interpreted by a dislocation source model in a composite medium which consists of an elastic surface layer lithosphere an intervening maxwellian viscoelastic layer asthenosphere and an elastic substratum an optimum fault model of the kanto earthquake is obtained from the coseismic crustal movements by using a method of inversion analysis in which effects of systematic errors caused by the movements of reference points in geodetic measurement are taken into account it is found that the fault motion of this earthquake is a reverse right lateral slip of 4 8 m with a slip angle of 140 on a fault plane which dips 25 towards n24 e where the slip angle is measured counterclockwise from the fault strike the fault length the fault width and the depth to the upper fault edge are determined as 95 km 54 km and 2 0 km respectively the postseismic transient crustal movements are considered to be controlled by a quasi static relaxation process of stress changes due to faulting in the earth s asthenosphere in such a quasi static problem the surface motion caused by a dislocation source consists of instantaneous elastic deformation at the time of faulting and transient viscoelastic movement after the event the viscoelastic part of the surface displacement field is calculated for the optimum fault model in a three layered composite medium with an intervening viscoelastic layer and compared with the observed data the transient crustal movements after the kanto earthquake are adequately explained by the present model taking the thickness of the lithosphere as 60 km and the thickness and viscosity of the asthenosphere as 180 km and 1020 poise respectively