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

a high resolution micromorphological record of changing landscapes and climates on the western loess plateau of china during oxygen isotope stage 5 abstract the micromorphological characteristics of a continuous set of block samples from 24 38 m depth in a well section on jiuzhoutai mountain lanzhou china are described the shape of the magnetic susceptibility curve together with previously published radiocarbon luminescence and geomagnetic dates indicates that this sample set encompasses the whole of the last interglacial s1 palaeosol complex and extends into the overlying and underlying loess l1 and l2 units seven pedosedimentary units are recognised on the basis of trends in the bulk properties and the key micromorphological indicators excrements textural concentrations shell fragments and calcite and gypsum features high rates of loess deposition with significant cryogenic activity gypsum precipitation and only weak bioturbation characterised oxygen isotope stage ois 6 and ois 4 at lanzhou depositional rates were moderately high in ois 5d and 5b with slightly higher bioturbation and no significant cryogenesis or gypsum precipitation ois 5e 5c and 5a were marked by low rates of accretion more extensive bioturbation and limited leaching this reconstruction reflects the pedosedimentary responses to fluctuating dominances of monsoonal controls during this period of global climatic change comparison of earlier micromorphological results from sites to west and east of lanzhou along a dry to humid climatic gradient indicate a clear regional pattern with reduced loess accumulation rates and enhanced bioturbation and leaching in the humid east tianshui and xian clay translocation occurred only in ois 5e at xian the warmest and most humid site on the transect

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

3 d modelling of plate interfaces and numerical simulation of long term crustal deformation in and around japan we developed a 3 d simulation model for long term crustal deformation due to steady plate subduction in and around japan by incorporating viscoelastic slip response functions into a realistic 3 d plate interface model constructed on the basis of the topography of ocean floors and hypocenter distributions of earthquakes the lithosphere asthenosphere system is modelled by an elastic surface layer overlying a maxwellian viscoelastic half space kinematic interaction at plate interfaces is rationally represented by the increase of tangential displacement discontinuity fault slip across the interfaces with this model giving the steady slip rates at plate interfaces calculated from nuvel 1a we simulated long term crustal deformation due to steady plate subduction in and around japan the simulated crustal deformation pattern is characterized by steep uplift at island arcs sharp subsidence at ocean trenches and gentle uplift at outer rises the numerical results show the strong dependence of the deformation pattern on the 3 d geometry of plate interfaces

effects of three dimensional inhomogeneous viscoelastic structures on postseismic surface deformations associated with the great 1946 nankaido earthquake we investigated the effects of various viscoelastic structures on postseismic surface displacement and principal strain fields associated with the great 1946 nankaido earthquake which occurred on the plate boundary between the subducting philippine sea plate and the continental eurasian plate for this purpose we constructed two kinds of three dimensional structural models using the finite element method one is the layered model in which a semi infinite maxwell viscoelastic material is underlying an elastic layer and the other is the more realistic plate model in which the three dimensional configuration of the subducted philippine sea plate is taken into account we also considered two cases with different thicknesses of the elastic layer 50 and 33km for the respective models the difference between the two models in postseismic surface deformations is significant for the case with the thinner elastic layer in this case the horizontal surface displacement and principal strain for the layered model is two to three times larger than those for the plate model downward surface deformation tends to be dominant for the layered model while the change in the pattern for the plate model is less marked the spatial extent of uplift and subsidence for the plate model is broader than that for the layered model postseismic vertical displacements in shikoku were found to be strongly dependent on the viscoelastic structures from these results we suggest that the estimates of the viscosity of the uppermost mantle interplate coupling and the area and the amount of after slip following the 1946 nankaido earthquake which have been estimated based on simple layered viscoelastic models should be re evaluated using realistic three dimensionally heterogeneous viscoelastic structures

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

high vp vs zone accompanying non volcanic tremors and slow slip events beneath southwestern japan abstract in southwestern japan the philippine sea plate subducts beneath the eurasian plate non volcanic tremors and slow slow slip events are observed beneath southwestern japan seismic tomography based on the data obtained from the dense seismic network revealed the velocity structure in and around the subducting philippine sea plate the oceanic crust of the philippine sea plate subducting from the suruga and nankai troughs can be imaged clearly beneath the tokai region and the kii peninsula non volcanic tremors and short term slow slip events may occur in the high vp vs zones owing to the fluid dehydrated from the subducting plate where the oceanic crust of the philippine sea plate encounters the serpentinized wedge mantle of the eurasian plate these tremors and short term slow slip events occur in the high vp vs zone at depths of 30 40 km beneath the tokai region the landward edge of the high vp vs zone beneath the kii peninsula and eastern shikoku region and the seaward edge of the high vp vs zone beneath the western shikoku region long term slow slip events were observed beneath the tokai region and the bungo channel and both these events are located on the seaward side of a high vp vs zone these long term slow slip events are considered to be caused at the plate boundary between the oceanic crust of the philippine sea plate and the lower crust of the eurasian plate by the high pore fluid pressure caused by the fluid dehydrated from the subducting plate the existence of the high vp vs lower crust of the eurasian plate may control the occurrence of the long term slow slip events

enigmatic highly active left lateral shear zone in southwest japan explained by aseismic ridge collision global positioning system gps site velocities and earthquake focal mechanisms reveal an active left lateral shear zone cutting across kyushu in southwest japan surprisingly no active faults have been identified in association with this zone of rapid contemporary deformation to explain the existence of this shear zone we propose a model comprising subduction of an aseismic ridge kyushu palau ridge at the southwest end of the nankai trough because of rapid 40 mm yr along strike migration of the ridge we suggest that the ridge subduction point and resulting left lateral shear zone is never in one place long enough to enable the development of a through going fault zone that can be identified at the ground surface reconciling the mismatch between the gps seismological and geological data in this region our conceptual model is supported by numerical modeling results we also suggest that the along strike change in subducting plate buoyancy explains the recent counterclockwise rotation of the kyushu forearc documented in paleomagnetic studies as is found in many other western pacific subduction margins

multiple scs probing of the ontong java plateau abstract we use multiple scs phases recorded at pohnpei from a 1996 deep earthquake under the solomon islands to investigate the shear velocity and attenuation characteristics of the upper mantle under the ontong java plateau in the western equatorial pacific cross correlation results indicate a vertical one way travel time under the plateau 3 s slow with respect to prem in agreement with previously obtained tomographic results which revealed the existence of an anomalously slow root under the plateau additionally the study of stacked spectral ratios suggests an unusually high qscs 366 with a lower limit of qscs 253 this value is considerably higher than elsewhere in the pacific suggesting the absence of an asthenospheric layer under the edifice the combination of slow shear wave speed and lower than average shear attenuation rules out a temperature anomaly as the source of the ontong java plateau ojp root which must then be related to a chemical or mineralogical heterogeneity

imaging the seismic lithosphere asthenosphere boundary of the oceanic plate 1 the seismic lithosphere asthenosphere boundary lab or g discontinuity a seismologically characterized abrupt drop in wave speed in the uppermost mantle is one of the key issues in current geodynamics although plate tectonics started as a theory for the ocean reports on lab for normal oceanic regions are scarce due to paucity of seismic data and whether or not the oceanic lab grows with age is the key issue to be resolved we conduct a systematic survey for the oceanic lab using s to p converted seismic waves along three margins of oceanic plates whose crustal age ranges from 10 myr to 130 myr and we observe laterally continuous oceanic lab images the thickness of the oceanic plate estimated from labs increases with the plate age though scattered suggesting that the evolution of oceanic lithosphere is predominantly governed by temperature and that the oceanic seismic lab represents a boundary that grows with age

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

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

rupture process of the 1944 tonankai earthquake ms 8 1 from the inversion of teleseismic and regional seismograms 1 we digitized teleseismic and regional records of the 1944 tonankai earthquake we used the multiple time window method to invert these records for the spatial and temporal distribution of slip and rake we assume a 220 140 km fault with a spacing of 20 20 km and a maximum rupture velocity of 2 5 km s the inversion resolved an asperity along the accretionary wedge and under the shima and atsumi peninsulas the rupture propagated from southwest to northeast and there was little slip near the hypocenter consistent with the absence of uplift in the overlying submarine forearc basin the peak slip is 2 3 m and the total seismic moment is 2 4 1028 dyn cm mw 8 2 we compared the predicted and observed vertical geodetic displacements and inferred that the limit of rupture is consistent with the change from subsidence to uplift west of the atsumi peninsula this suggested that the earthquake did not rupture the plate interface in the tokai gap we modeled the tsunami using sea bottom displacements generated from this slip model the tide gauge amplitudes and frequency content are consistent with those predicted resolution tests from inverting synthetic seismograms computed using a simplified slip model indicated that the combination of teleseismic and regional data sets best recovers the asperity locations and peak slips given similar station geometry and degrees of freedom an inversion of the synthetic regional data set indicates that slip artifacts can occur early in the rupture process due to many clipped records while the inversion of synthetic teleseismic data set had less resolution and recovered only 50 of the peak slip

continuous gps array and present day crustal deformation of japan a gps array with about 1 000 permanent stations is under operation in japan the gps array revealed coseismic deformations associated with large earthquakes and ongoing secular deformation in the japanese islands based on daily coordinate data of the gps stations strain rate distribution is estimated most regions with a large strain rate are related to plate boundaries and active volcanoes in addition the niigata kobe tectonic zone nktz is recognized as a region of large strain rate along the japan sea coast and in the northern chubu and kinki districts this newly found tectonic zone may be related to a hypothetical boundary between the eurasian or amurian and the okhotsk or north america plates precise observation of crustal deformation provides important boundary conditions on numerical modeling of earthquakes and other crustal activities appropriate computation methods of continuous deformation field are directly applicable to data assimilation for such numerical simulations

segmentation and holocene surface faulting on the median tectonic line southwest japan the median tectonic line mtl active fault system is a 300 km long arc parallel right lateral strike slip fault related to oblique subduction of the philippine sea plate beneath the eurasian plate at the nankai trough southwest japan the fault on shikoku island has a slip rate of 5 10 mm yr one of the highest in onshore japan we identified 12 geometric segments along the mtl separated by discontinuities such as en echelon steps bends changes in strike and gaps in the surface trace a chronology of latest holocene surface faulting on the mtl was constructed based on previously published and new work including trenching geomorphic mapping and acoustic profiling and piston coring of the submarine extension of the fault zone the mtl probably does not rupture along its entire length in a single earthquake but instead consists of multiple earthquake segments that rupture independently of one another the recurrence interval and surficial offset for surface rupturing earthquakes at four individual sites on the mtl in shikoku island are 1000 3000 years and 5 8 m respectively the relatively long recurrence interval and large surficial offset per earthquake suggest large seismic moment release during surface rupturing earthquakes on the mtl as commonly observed for japanese moderate to large intraplate earthquakes because the predicted rupture lengths based on empirical relations between surface displacement and rupture length are considerably larger than those of individual segments large earthquakes on the mtl probably rupture multiple geometrically defined segments the fault was previously thought to be unruptured at least in the past 1000 years based on the absence of historical evidence for destructive earthquakes however trench excavations show that part of the mtl ruptured most recently during or after the 16th century a d with at least 6 9 0 7 m of slip along the main fault trace this rupture may be correlated to the 1596 keicho kinki earthquake but further geological and historical investigations are needed to confirm this hypothesis

contiguous rupture areas of two nankai trough earthquakes revealed by high resolution tsunami waveform inversion 1 we have developed a new method for inverting tsunami waveforms that reveals considerable detail in megathrust slip during subduction zone earthquakes previous methods have ensured compliance with the shallow water theory used to compute tsunami waveforms by using large subfaults that generate only long wavelength seafloor deformation we show that a better approach is to use small subfaults coupled with a smoothing criterion that ensures compliance with the shallow water approximation in an application of the method to historical earthquakes in the nankai trough southwestern japan we find that the areas with slip 1 m for the earthquakes of 1944 and 1946 which ruptured adjacent segments of the subduction zone are separated by a sharp non overlapping boundary this establishes that interseismic accumulation of strain energy extends very close to the boundary between rupture zones and strongly suggests that this boundary is associated with a physical barrier to rupture

temporal change of interplate coupling in northeastern japan during 1995 2002 estimated from continuous gps observations summary temporal change of deformation in northeastern japan is clarified by continuous global positioning system gps observations from 1995 april to 2002 march the observed gps velocity is approximately parallel to the direction of plate convergence on east and west plate boundaries of northeastern japan and shows post seismic transient deformation around source regions of the mw 7 8 1993 hokkaido nansei oki and the mw 7 7 1994 sanriku haruka oki earthquakes we interpret the source of the observed deformation as contemporary interplate coupling on the east subducting boundary to the pacific plate and the west collision boundary to the amurian plate using elastic dislocation theory we inverted horizontal and vertical velocities of 212 gps stations to estimate interplate coupling on both boundaries the estimated coupling during 1995 2002 is spatially heterogeneous however it is temporally almost constant except for the region around the 1993 and 1994 earthquakes after slip of the 1994 earthquake occurred over the coseismic rupture area and its downdip extension on the plate boundary for 0 3 1 3 yr after the earthquake after slip continued only in the downdip extension for later periods and decayed with time weak coupling was recovered in the eastern part of the coseismic rupture area 3 3 yr after the earthquake interplate coupling on the pacific plate was strong in two regions miyagi oki and tokachi oki the west plate boundary is tightly coupled except for the source areas of three large earthquakes that occurred in 1964 1983 and 1993 the apparent decoupling of the source areas of these earthquakes implies long term post seismic deformation as a result of viscoelastic relaxation in the subseismogenic lithosphere

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

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