eddy resolving observation of the north pacific subtropical mode water abstracthydrographic data obtained by high resolution shipboard observations and argo profiling floats have been analyzed to study the mesoscale structure and circulation of the north pacific subtropical mode water stmw the float data show that in the late winter of 2008 stmw having a temperature of approximately 18 8 17 7 and 16 6 c formed west of 140 e at 140 150 e and east of 150 e respectively in the recirculation gyre south of the kuroshio extension after spring the newly formed stmw gradually shift southward decreasing in thickness simultaneously the stmws of 16 6 and 17 7 c are gradually stirred and then mixed in terms of properties in late fall they seem to be integrated to form a single group of stmws having a temperature centered at 17 2 c such stmw circulation in 2008 is much more turbulent than that in 2006 which was investigated in a previous study the difference between the two years is attributed to the more variable state of the kuroshio extension in 2008 associate

in situ thermal conductivity of gas hydrate bearing sediments of the mallik 5l 38 well 1 detailed knowledge about thermal properties of rocks containing gas hydrate is required in order to quantify processes involving gas hydrate formation and decomposition in nature in the framework of the mallik 2002 program three wells penetrating a continental gas hydrate occurrence under permafrost were successfully equipped with permanent fiber optic distributed temperature sensing cables temperature data were collected over a 21 month period after completing the wells thermal conductivity profiles were calculated from the geothermal data as well as from a petrophysical model derived from the available logging data and application of mixing law models results indicate that thermal conductivity variations are mainly lithologically controlled with a minor influence from hydrate saturation average thermal conductivity values of the hydrate bearing sediments range between 2 35 and 2 77 w m 1 k 1 maximum gas hydrate saturations can reach up to about 90 at an average porosity of 0 3

multicore structure of the north pacific subtropical mode water from enhanced argo observations seventeen argo profiling floats with enhanced vertical and temporal sampling were deployed in the kuroshio recirculation gyre in the western north pacific in late march 2014 the subtropical mode water stmw observed in many profiles displays a multicore structure with more than one minima in potential vorticity pv corroborated by vertical covariations in apparent oxygen utilization aou these cores are classified into four submodes according to density and aou the submode waters are typically 100 m thick in which pv varies by 1 10 10 m 1 s 1 and aou by 10 mole kg the stmw multicore structure is most frequently observed in spring gradually taken over by single core profiles into summer the seasonal evolution is suggestive of vertical mixing especially in stmw of lower density

block modeling with connected fault network geometries and a linear elastic coupling estimator in spherical coordinates geodetic observations of interseismic deformation provide constraints on the partitioning of fault slip across plate boundary zones the spatial distribution of both elastic and inelastic strain accumulation and the nature of the fault system evolution here we describe linear block theory which decomposes surface velocity fields into four components 1 plate rotations 2 elastic deformation from faults with kinematically consistent slip rates 3 elastic deformation from faults with spatially variable coupling and 4 homogeneous intrablock strain elastic deformation rates are computed for each fault segment in a homogeneous elastic half space using multiple optimal planar cartesian coordinate systems to minimize areal distortion and triangular dislocation elements to accurately represent complex fault system geometry block motions fault slip rates elastic coupling and internal block strain rates are determined simultaneously using a linear estimator with constraints from both geodetically determined velocity fields and geologic fault slip rate estimates we also introduce algorithms for efficiently implementing alternative fault network geometries to quantify parameter sensitivity to nonlinear perturbations in model geometry

geodetic imaging of plate motions slip rates and partitioning of deformation in japan 1 interseismic deformation in japan results from the combined effects of tectonic processes including rotation of crustal blocks and the earthquake cycle process of elastic strain accumulation about upper plate faults and subduction zone interfaces we use spherical linear block theory constrained by geodetic observations from densely spaced global positioning system gps stations to estimate plate motions fault slip rates and spatially variable interplate coupling on the japan kuril sagami and nankai subduction zones the reference model developed in this paper consists of 20 blocks produces a mean residual velocity magnitude of 1 84 mm yr at 950 stations and accounts for 96 of the observed interseismic deformation signal we estimate fault slip rates in excess of 15 mm yr along the niigata kobe tectonic zone and itoigawa shizuoka tectonic line through central japan confirming their hypothesized roles as major tectonic boundaries oblique convergence across the nankai trough is partitioned with 3 4 of the 30 mm yr of trench parallel motion accommodated by strike slip motion on the subduction interface and the remaining 1 4 accommodated by right lateral slip on the median tectonic line in contrast our models suggest negligible slip partitioning in eastern hokkaido where oblique slip on the japan kuril subduction interface accommodates all of the trench parallel component of relative plate motion inferred spatial variations in the rake and magnitude of slip deficit on subduction zone interfaces reflect the influences of megathrust geometry and earthquake cycle processes such as enhanced elastic strain accumulation about seismic asperities and coseismic sense fault motion indicative of silent slip events or afterslip following large earthquakes

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

strain partitioning in the zone of transition from nankai subduction to izu bonin collision central japan implications for an extensional tear within the subducting slab abstract the izu bonin ridge collision with central japan is a type example of collision of two island arcs in a subduction context based on the analysis of active faults paleomagnetic data and recent seismicity in the northern tip of the izu bonin arc and the adjacent oceanic plate we propose a tectonic schema of the izu collision system and its transition to the nankai subduction to the west the dense gps network deployed in central japan allows us to constrain the kinematics of the different blocks identified this new kinematic model demonstrates the essential role of strain partitioning there as the northward component of the izu bonin arc motion is locked in the collision zone 30 of the convergence between the philippine sea plate and central japan is accommodated within the philippine sea slab along the zenisu east izu deformation system we show that this pattern of deformation is related to an extensional tear of the philippine sea slab propagating southward along the volcanic arc we discuss the implications of this kinematic model on the seismogenic potential of the area and the dynamics of the central japan convergence zone

crustal deformation and interplate coupling in the shikoku district japan as seen from continuous gps observation abstract data from the nationwide gps continuous tracking network which has been operated by the geographical survey institute gsi of japan since april 1996 were used to study crustal deformation in the shikoku district japan the crustal deformation data are inverted to estimate interplate coupling between the subducting philippine sea phs plate and the overriding continental plate for this purpose we first extracted site coordinates from daily sinex files for the period from 1 april 1996 to 31 march 1998 and estimated average site velocities by linear regression estimated velocities under itrf96 are converted into a kinematic reference frame k heki j geophys res 101 1996 3187 3198 to discuss the crustal deformation relative to the stable interior of the eurasian eur plate to segregate the signal and noise in the thus obtained velocity vectors we employed the least squares prediction technique estimated signals displacement vectors were used to reconstruct the strains dilatations maximum shear strains principal axes of strains and to estimate the interplate coupling in the area results of crustal strains clearly portray tectonic straining of the shikoku island 1 dilatational strains show that the shikoku island is under a compressive strain regime induced by the subducting phs plate 2 maximum shear is high in the island which may be due to the oblique subduction 3 the principal axes of the strains indicate that the shikoku island is under the influence of the converging oceanic plate beneath the island in contrast the results of the inversion analysis show 1 there is a high coupled region extending from 10 to 30 km deep 2 the average back slip rate in this region reaches 43 5 mm yr and 3 the direction of the plate convergence at the nankai trough is n42 6 w

short and long term effects of gps measured crustal deformation rates along the south central andes in this study we present the contemporary crustal deformation field along the central and southern andes 17 42 s estimated from four global positioning sys tem gps campaigns conducted in 1994 97 we find that the majority of the observed crustal deformation field is relatively homogenous roughly parallel to the plate conver gence direction with decreasing velocities away from the trench we attribute this type of deformation pattern to the inter seismic phase of an earthquake deformation cycle caused by 100 locking of the thrust interface between the subducting nazca and the overrid ing south american plates we have also detected a strong post seismic deformation sig nal in the vicinity of the 1995 mw8 0 antofagasta 22 26 s and 1960 mw9 5 chile 38 43 s earthquakes this type of deformation can be described as short term in nature compared to geological timescales the above conclusions are based on the results of the 3 d andean elastic dislocation model aedm by subtracting the aedm predicted deformation rates from the observations we obtained a residual velocity field that high lights the post seismic as well as more long term deformation eects for example we find a strong evidence for the continuing crustal shortening across the back arc reach ing its maximum 4 mm yr in the very north of our study area in addition between latitudes 29 34 s there is an indication of e w oriented extension within the fore arc in accordance with the recent geologic findings for the n s oriented normal faulting

observing subsurface changes of two anticyclonic eddies passing over the izu ogasawara ridge eddy bathymetry interactions are common in the ocean but the full evolution of the interaction is difficult to observe below the surface using 17 iridium argo floats we continually track two anticyclonic eddies aes in the north pacific that migrate westward and encounter the izu ogasawara ridge based on over 5000 argo profiles following the two aes this study presents the first detailed descriptions of changes in eddy vertical structure and diapycnal mixing as the two aes pass the ridge there we find that isopycnals dome up and the eddy diameter increases while the diapycnal mixing is enhanced to the order of 10 4 m 2 s 1 or larger in comparison with an ambient of 10 5 m 2 s 1 the enhanced mixing around the ae center in the upper 1000m appears where the underlying bathymetry is shallower than 4000m and is mainly sustained by tidally generated internal waves

deformation of the japanese islands and seismic coupling an interpretation based on gsi permanent gps observations summary the entire area of the japanese islands has been covered by the permanent gps observation network of the geographical survey institute since 1994 in this paper we use a solution for the vectors of motion during 1995 for a selection of 116 stations to discuss the origin of the observed deformation field we refer the displacement field to eurasia using the vlbi determined motion of kashima and demonstrate that other choices such as the okhotsk or north american plates for north japan are not compatible with the data 1 yr gps velocities are much higher than geological constraints would allow because these short term measurements include transient elastic deformation however the good qualitative agreement between the observed geodetic deformation tensors and those inferred from active faults and earthquakes suggests that the quaternary permanent deformation is essentially the result of the transfer of part of the subduction induced elastic deformation into permanent plastic deformation we then compute the elastic deformation of the japanese islands caused by interseismic loading of the pacific and philippine subduction planes the geometry of the coupled zone and its downward extension are determined from the distribution of earthquakes for the pacific slab for the philippine slab we use the geometry proposed by hyndman et al 1995 these elastic models account for most of the observed velocity field if the subduction movement of the philippine sea plate is 100 per cent locked and if that of the pacific plate is 75 85 per cent locked we note that the boundaries of the areas where significant elastic deformation is predicted more than 10 mm yr 1 of motion with respect to eurasia coincide with the main zones of permanent deformation the eastern japan sea deformation zone for the pacific subduction elastic deformation field and the setouchi mtl deformation zone for the nankai field each zone probably accommodates 10 15 mm yr 1 of motion in the long term convergence in the eastern japan sea strike slip in the setouchi mtl zone to account for this deformation the evect of elastic loading from the trench must be combined with 5 10 mm yr 1 of motion of the amur plate with respect to eurasia because loading during the subduction earthquake cycle causes an increase in stress in the eastern japan sea and setouchi mtl deformation zones the probability of earthquake occurrence in these zones may be higher near the end of the cycle

tectonic evolution of the japanese island arc system abstract growth of the japanese arc system which has mainly taken place along the continental margin of asia since the permian is the result of subduction of the ancient pacific ocean floor backarc basin formation in the tertiary shaped the present day arc configuration the neotectonic regime which is characterized by strong east west compression has been triggered by the eastward motion of the amur plate in the quaternary the tectonic evolution of the japanese arc system includes formation of rock assemblages common in most orogenic belts because the origin and present day tectonics of these assemblages are better defined in the case of the japanese arc system study of the system provides useful insight into orogenesis and continental crust evolution

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

observations related to tetrahydrofuran and methane hydrates for laboratory studies of hydrate bearing sediments the interaction among water molecules guest gas molecules salts and mineral particles determines the nucleation and growth behavior of gas hydrates in natural sediments hydrate of tetrahydrofuran thf has long been used for laboratory studies of gas hydrate bearing sediments to provide close control on hydrate concentrations and to overcome the long formation history of methane hydrate from aqueous phase methane in sediments yet differences in the polarizability of thf polar molecule compared to methane nonpolar molecule raise questions about the suitability of thf as a proxy for methane in the study of hydrate bearing sediments from existing data and simple macroscale experiments we show that despite its polar nature thf s large molecular size results in low permittivity prevents it from dissolving precipitated salts and hinders the solvation of ions on dry mineral surfaces in addition the interfacial tension between water and thf hydrate is similar to that between water and methane hydrate the processes that researchers choose for forming hydrate in sediments in laboratory settings e g from gas liquid or ice and the pore scale distribution of the hydrate that is produced by each of these processes likely have a more pronounced effect on the measured macroscale properties of hydrate bearing sediments than do differences between thf and methane hydrates themselves

incipient subduction and deduction along the eastern margin of the japan sea the eastern margin of the japan sea has been under convergent tectonics since sometime after the pliocene the suture line is on the ocean continent boundary between the japan yamato basins and the tohoku northeast japan arc incipient subduction and obduction of the oceanic and sub oceanic crust are observed along the suture line with the occurrence of numerous n s trending fault bounded ridges and troughs focal mechanism solutions of several compressional type earthquakes with magnitudes of m 6 9 to 7 7 which have occurred along the zone are consistent with the observation of geological thrust faults the convergent stresses in the japan sea may be due to india eurasia collision and its associated intra plate or inter microplate movements in east asia the eastward movement of the amurian plate causes baikal extension along its western margin and the japan sea convergence along its eastern margin

plate convergence measured by gps across the sundaland philippine sea plate deformed boundary the philippines and eastern indonesia summary the western boundary of the philippine sea ph plate in the philippines and eastern indonesia corresponds to a wide deformation zone that includes the stretched continental margin of sundaland the philippine mobile belt pmb extending from luzon to the molucca sea and a mosaic of continental blocks around the ph australia sunda triple junction the gps geodyssea data are used to decipher the present kinematics of this complex area in the philippines the overall scheme is quite simple two opposing rotations on either side of the left lateral philippine fault clockwise to the southwest and counterclockwise to the northeast transfer 55 per cent of the ph sundaland convergence from the manila trench to the northwest to the philippine trench to the southeast further south 80 per cent of the ph sunda convergence is absorbed in the double subduction system of the molucca sea and less than 20 per cent along both continental margins of northern borneo finally within the triple junction area between the sundaland ph and australia plates from sulawesi to irian jaya preferential subduction of the celebes sea induces clockwise rotation of the sulu block which is escaping toward the diminishing celebes sea oceanic space from the eastwardadvancing ph plate to the south we identify an undeformed banda block that rotates counterclockwise with respect to australia and clockwise with respect to sundaland the kinematics of this block can be defined and enable us to compute the rates of southward subduction of the banda block within the flores trench and of eastward convergence of the makassar straits with the banda block the analysis made in this paper confirms that this deformation is compatible with the eastward motion of sundaland with respect to eurasia determined by the geodyssea programme but is not compatible with the assumption that sundaland belongs to eurasia as was often assumed prior to this study

intraplate deformation in the japanese islands a kinematic study of intraplate deformation at a convergent plate margin relative motions within the deforming japanese islands with respect to the sea of japan are determined using earthquake records over the last 414 years slip rates on quaternary faults and angular change rates obtained from triangulation in the last century we use a least squares inversion method to match the strain rates on the surface of the earth with continuous spline functions to recover the velocity gradient tensors the directions of the principal strain axes obtained from seismic geological and geodetic data are in general agreement with each other with the maximum shortening axis oriented in a wnw direction principal strain rate magnitudes obtained from the geodetic data are about 3 5 times larger than the principal strain rates obtained from the seismic and geological data intraplate deformation in southwestern japan determined from the seismic data accommodates a velocity of5 5 2 l mm yr in a direction parallel to the nankai trough which is about 25 of the plate motion velocity component parallel to the nankai trough between the philippine sea and eurasian plates in northern honshu the velocity vectors from the seismic data are nearly parallel to the plate motion vector at the japan trench and the intraplate deformation accommodates about 6 of the total pacific eurasian or north american plate motion velocity the velocity vector at kashima northern honshu calculated from the geodetic data is about 9 12 mm yr in a direction of n55 w n76 w which is about half of the very long baseline interferometry velocity calculated in the eurasian reference frame suggesting that the sea of japan may not be rigidly attached to the assumed rigid eurasian plate

mesoscale eddy effects on the subduction of north pacific mode waters mesoscale eddy effects on the subduction of north pacific mode waters are investigated by comparing observations and ocean general circulation models where eddies are either parameterized or resolved the eddy resolving models produce results closer to observations than the noneddy resolving model there are large discrepancies in subduction patterns between eddy resolving and noneddy resolving models in the noneddy resolving model subduction on a given isopycnal is limited to the cross point between the mixed layer depth mld front and the outcrop line whereas in eddy resolving models and observations subduction takes place in a broader zonally elongated band within the deep mixed layer region mesoscale eddies significantly enhance the total subduction rate helping create remarkable peaks in the volume histogram that correspond to north pacific subtropical mode water stmw and central mode water cmw eddy enhanced subduction preferentially occurs south of the winter mean outcrop with an anticyclonic eddy to the west and a cyclonic eddy to the east the outcrop line meanders south and the thermocline mld shoals eastward as eddies propagate westward the mld shoals shielding the water of low potential vorticity from the atmosphere the southward eddy flow then carries the subducted water mass into the thermocline the eddy subduction processes revealed here have important implications for designing field observations and improving models

seismic coupling and structure of the hellenic subduction zone in the ionian islands region abstract the western hellenic arc has been commonly considered as a largely aseismic subduction zone from the comparison of a small rate of shortening derived from the seismic moment release with a large rate of convergence inferred from geology complete seismic coupling would instead be expected from models that consider a control by plate tectonic forces because of the trenchward velocity of the hellenic aegean upper plate now confirmed with gps measurements in the region of the ionian islands a subduction interplate boundary has been recently imaged and its seismogenic downdip width suggested to be moderate from reflection seismic profiling and local earthquake tomography in the appropriate model for such an earthquake source region which considers a single interplate fault and takes into account these features the moderate seismic moment release is found consistent with complete seismic coupling of this subduction the shallow downdip limit of the seismogenic zone can be interpreted as due to the interplate boundary being overlain there by the ductile deeper crust of the orogenically thickened hellenides

interplate coupling in the tohoku district japan deduced from geodetic data inversion the spatial distribution and the temporal change of the strength of interplate coupling between the subducting pacific plate and overlying continental plate in the tohoku district northeast japan have been investigated through the inversion analysis of geodetic data the geodetic data used for this analysis are the rates of vertical 1966 1995 and horizontal 1979 1991 displacements which presumably represent average crustal movements during the interseismic period we incorporate smoothing constraints on back slip distribution into the observed data the degree of the constraints is controlled by hyperparameters whose optimal values are determined by minimizing akaike s bayesian information criterion abic under the assumption of abic we can obtain a unique solution the result of the inversion analysis shows that there are two regions of high coupling the first extending from 20 to 45 km in the north 40 5 n and the second extending from 25 to 55 km in the south 38 5 n the average back slip rate in the northern region reaches 55 11 mm yr 1 and in the southern region 41 14 mm yr 1 also the inversion analysis shows that the direction of the plate convergence at the japan trench is n71 3 w in the northern region and n48 5 w in the southern region the interplate coupling becomes weaker toward the shallower and deeper portions and exhibits significant temporal variation

plate tectonics and crustal deformation around the japanese islands we analyze over a century of geodetic data to study crustal deformation and plate motion around the japanese islands using the block fault model for crustal deformation developed by matsu ura et al 1986 in this model crustal deformation corresponds to the sum of relative movement among designated blocks and displacement due to dislocations along the locked parts of designated faults we model the area including the japanese islands with 19 crustal blocks and 104 faults based on the distribution of active faults and seismicity three kinds of data are used rates of change of angles and lengths and average velocities of very long baseline interferometry stations with the inversion of these geodetic data we obtain block motions and average slip rates of faults this geodetic model predicts that the pacific plate moves n69 2 w at about 80 3 mm yr relative to the eurasian plate which is much lower than that predicted in geologic models substantial aseismic slip occurs on the subduction boundaries the block containing the izu peninsula may be separated from the rigid part of the philippine sea plate the faults on the coast of japan sea and the western part of the median tectonic line have slip rates exceeding 4 mm yr while the fossa magna does not play an important role in the tectonics of the central japan the geodetic model requires the division of northeastern japan contrary to the hypothesis that northeastern japan is a part of the north american plate owing to rapid convergence the seismic risk in the nankai trough may be larger than that of the tokai gap

transient and permanent deformation of central japan estimated by gps 1 interseismic loading and subduction kinematics abstract we analyze continuous global positioning system gps data to estimate the kinematics of the philippine sea plate subduction below southern central japan using a back slip dislocation model we invert the strain rate tensors derived from the gps velocity field to obtain the velocity of the downgoing slab with respect to the tokai and kanto forearcs along the eastern nankai suruga and sagami troughs respectively in both cases these velocities are smaller and slightly rotated with respect to the philippine sea plate subduction velocity in central nankai this result implies strain partitioning between the subduction thrusts and on land and or offshore deformation zones in both the eastern nankai suruga and the sagami area in southern kanto we predict 20 mm yr 1 of dextral shear in agreement with motion observed along the boso strike slip fault in the tokai region the slip deficit accumulated since the last earthquake 1854 ranges between 6 and 3 m considering the extent of the locked zone it would correspond to a magnitude m w 8 15 earthquake if the slip deficit were to be released now during a single event

interpretation of interseismic deformations and the seismic cycle associated with large subduction earthquakes abstract the deformations of the overriding and subducting plates during the seismic cycle associated with large subduction earthquakes are modelled using 2d and 3d finite element techniques a particular emphasis is put on the interseismic velocities and on the impact of the rheology of the asthenosphere the distance over which the seismic cycle perturbs significantly the velocities depends upon the ratio of the viscosity in the asthenosphere to the period of the seismic cycle and can reach several thousand km for rheological parameters deduced from the first years of deformation after the aceh earthquake for a same early postseismic velocity a burger rheology of the asthenosphere implies a smaller duration of the postseismic phase and thus smaller interseismic velocities than a maxwell rheology a low viscosity wedge lvw modifies very significantly the predicted horizontal and vertical motions in the near and middle fields in particular with a lvw the peak in vertical velocity at the end of the cycle is predicted to be no longer above the deep end of the locked section of the fault but further away above the continentward limit of the lvw the lateral viscosity variations linked to the presence at depth of the subducting slab affect substantially the results the north south interseismic compression predicted by this preliminary 2d model over more than 1500 km within the sunda block is in good agreement with the pre 2004 velocities with respect to south china inferred from gps observations in thailand malaysia and indonesia in japan before the tohoku earthquake the eastern part of northern honshu was subsiding while the western part was uplifting this transition from subsidence to uplift so far away from the trench is well fitted by the predictions from our models involving a lvw most of the results obtained here in a 2d geometry are shown to provide a good estimate of the displacements for fault segments of finite lateral extent with a 3d spherical geometry as long as the displacements during the seismic cycle are normalised by the coseismic displacement

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

structural geodetic and seismological evidence for tectonic escape in sw taiwan abstract recent structural geodetic and seismological data in sw taiwan are analysed and discussed in terms of present day tectonic escape occurring in response to the active n100 collisional shortening the escaping area corresponds to the onland extension of the manila accretionary wedge this region comprises a rheologically weak thick muddy cover which is decoupled from the underlying basement by a decollement and which deforms mainly by aseismic creep it is separated from the northern actual collisional area by a major wnw to nw trending structural and kinematic transition zone oblique to the structural grain of the belt the chishan transfer fault zone geodetic data are further used to define several poorly deforming blocks undergoing nearly uniform displacement velocities and bounded by kinematic discontinuities that fit the major faults and to determine the present day across strike and along strike motions on these major faults although direct onland structural evidence of tectonic escape is poor reconstruction of quaternary paleostress patterns demonstrate that this escape probably began during the late pleistocene later than in northeastern taiwan as a result of the southward migration of the collision through time offshore structural data help to constrain the geometry and the southern extension of the escaping blocks finally a tentative model of lateral extrusion in sw taiwan is proposed

spatial and temporal strain rate variations at the northern hikurangi margin new zealand we have calculated shear strain rates in the northeastern part of the north island of new zealand using geodetic data collected in the mid 1920s and 1995 in addition we use observations from a part of the network across raukumara peninsula measured in 1976 to look for temporal variation in shear strain rates in that area the strain rates were estimated using a simultaneous reduction method assuming uniform strain in space and time within each subnetwork we find the largest spatial variation in shear strain rates from the mid 1920s to 1995 occurs across raukumara peninsula increasing from 0 06 0 04 ppm yr in the west to 0 18 0 03 ppm yr in the east 1 confidence the orientation of the azimuth of relative extension shows significant temporal variation across raukumara peninsula from the mid 1920s to 1976 the maximum shear strain rate was 0 22 0 05 ppm yr with the azimuth of relative extension oriented at 129 7 from 1976 to 1995 the maximum shear strain rate was 0 14 0 05 ppm yr with the azimuth of relative extension oriented at 13 12 we show that a model where the subduction interface is locked down to 15 or 30 km depth and slipping at nuvel ia plate rates below that depth can explain the strain rates and orientation observed during 1976 1995 to fit the observations from the mid 1920s to 1976 we suggest that additional dip slip occurred on the shallow part of the subduction zone above 30 km from this we conclude that the plate boundary below raukumara peninsula is locked down to 15 or 30 km depth and the aseismic shallow slip episode that occurred during the mid 1920s 1976 was an isolated event possibly induced by m 7 historical earthquakes in the area

coeval blueschist exhumation along thousands of kilometers implications for subduction channel processes we herein focus on understanding what controls the detachment and migration of oceanic crustal slices along subduction zones we provide evidence for the coeval middle to late cretaceous exhumation of oceanic blueschists in the same neotethyan subduction zone across more than 3000 km from depths around 30 40 km over a short time interval similar to 25 ma compared to the duration of subduction 100 ma we stress the importance of such a geodynamic process and suggest that this exhumation was promoted by a regional scale change in the long term interplate mechanical coupling on the basis of geological and geophysical evidence we propose that the upward migration of oceanic fragments in subduction zones is normally inhibited and only occurs discontinuously as the subduction channel opens up in response to a major change in plate geodynamics slab geometry and dynamics mantle wedge and slab hydration or a combination of these

thermal conductivity of hydrate bearing sediments 1 a thorough understanding of the thermal conductivity of hydrate bearing sediments is necessary for evaluating phase transformation processes that would accompany energy production from gas hydrate deposits and for estimating regional heat flow based on the observed depth to the base of the gas hydrate stability zone the coexistence of multiple phases gas hydrate liquid and gas pore fill and solid sediment grains and their complex spatial arrangement hinder the a priori prediction of the thermal conductivity of hydrate bearing sediments previous studies have been unable to capture the full parameter space covered by variations in grain size specific surface degree of saturation nature of pore filling material and effective stress for hydrate bearing samples here we report on systematic measurements of the thermal conductivity of air dry water and tetrohydrofuran thf saturated and thf hydrate saturated sand and clay samples at vertical effective stress of 0 05 to 1 mpa corresponding to depths as great as 100 m below seafloor results reveal that the bulk thermal conductivity of the samples in every case reflects a complex interplay among particle size effective stress porosity and fluid versus hydrate filled pore spaces the thermal conductivity of thf hydrate bearing soils increases upon hydrate formation although the thermal conductivities of thf solution and thf hydrate are almost the same several mechanisms can contribute to this effect including cryogenic suction during hydrate crystal growth and the ensuing porosity reduction in the surrounding sediment increased mean effective stress due to hydrate formation under zero lateral strain conditions and decreased interface thermal impedance as grain liquid interfaces are transformed into grain hydrate interfaces

a model with rigid rotations and slip deficits for the gps derived velocity field in southwest japan abstract we interpret the gps derived velocity field in southwest japan by a superposition of the elastic deformation caused by fault interactions slips or slip deficits on the rigid motion of tectonic blocks or plates based on the strain rate field and crustal seismicity we apply a model with three blocks inner arc outer arc and the northern ryukyu block and slip deficits along the block boundaries several characteristics of the synthesized contributions are found 1 westward motion of the outer arc relative to the amurian plate and the inner arc 2 southeastward motion of the northern ryukyu block relative to the amurian plate 3 2 4 mm yr deficits of left lateral slip rates along the boundary at 32 n in southern kyushu 4 0 8 mm yr deficits of right lateral slip rates along the median tectonic line and the beppu shimabara graben 5 slip deficit rates on the plate interface smaller than those in the case without any consideration for rigid block motions 6 clockwise deflection of slip deficit rate vector on the plate interface from that estimated when not taking rigid block motions into consideration

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

a 4500 year record of emergence events at onnetoh hokkaido northern japan reconstructed using plant macrofossils abstract plant macrofossils vascular plants and mosses document six episodic emergence events during the late holocene at onnetoh eastern hokkaido northern japan four events were dated by the ams radiocarbon method to 4240 3910 3640 3360 1520 1260 and 790 660 cal year bp and another was dated by liquid scintillation spectrometry of radiocarbon to 2750 2430 cal year bp we attribute the three most recent and the two oldest periods of emergence events identified in this study to uplift associated with unusually large interplate earthquakes along the southwestern part of the kuril subduction zone

can the okhotsk plate be discriminated from the north american plate the plate geometry in northeast asia has been a long standing question with a major issue being whether the sea of okhotsk and northern japanese islands are better regarded as part of the north american plate or as a separate okhotsk plate this question has been difficult to resolve because earthquake slip vectors along the kuril and japan trenches are consistent with either pacific north america or pacific okhotsk plate motion to circumvent this difficulty we also use slip vectors of earthquakes along sakhalin island and the eastern margin of the japan sea and compare them to the predicted eurasia okhotsk and eurasia north america motions for a model with a separate okhotsk plate we invert 10 eurasia okhotsk and 255 pacific okhotsk slip vectors with pacific north america and eurasia north america nuvel 1 data alternatively for a model without an okhotsk plate those eurasia okhotsk and pacific okhotsk data are regarded as eurasia north america and pacific north america data respectively the model with an okhotsk plate fits the data better than one in which this region is treated as part of the north american plate because the improved fit exceeds that expected purely from the additional plate the data indicate that the okhotsk plate can be resolved from the north american plate the motions on the okhotsk plate s boundaries predicted by the best fitting euler vectors are generally consistent with the recent tectonics the eurasia okhotsk pole is located at northernmost sakhalin island and predicts right lateral strike slip motion on the nne striking fault plane of the may 27 1995 neftegorsk earthquake consistent with the centroid moment tensor focal mechanism and the surface faulting along the northern boundary of the okhotsk plate the north america okhotsk euler vector predicts left lateral strike slip consistent with the observed focal mechanisms on the nw boundary of the okhotsk plate the eurasia okhotsk euler vector predicts e w extension discordant with the limited focal mechanisms and geological data this misfit may imply that another plate is necessary west of the magadan region in southeast siberia but this possibility is hard to confirm without further data such as might be obtained from space based geodesy

on the use of dislocations to model interseismic strain and stress build up at intracontinental thrust faults creeping dislocations in an elastic half space are commonly used to model interseismic deformation at subduction zones and might also apply to major intracontinental thrust faults such as the main himalayan thrust here we compare such models with a more realistic 2 d finite element model that accounts for the mechanical layering of the continental lithosphere and surface processes and that was found to fit all available constraints on interseismic and long term surface displacements these can also be fitted satisfactorily from dislocation models the conventional back slip model commonly used for subduction zones may however lead to a biased inference about the geometry of the locked portion of the thrust fault we therefore favour the use of a creeping buried dislocation that simulates the ductile shear zone in the lower crust a limitation of dislocation models is that the mechanical response of the lithosphere to the growth of the topography by bending of the elastic cores and ductile flow in the lower crust cannot be easily introduced fortunately these effects can be neglected because we may assume to first order a stationary topography moreover we show that not only can dislocation models be used to adjust surface displacements but with some caution they can also provide a physically sound rationale to interpret interseismic microseismicity in terms of stress variations

gently north dipping median tectonic line mtl revealed by recent seismic reflection studies southwest japan abstract the median tectonic line mtl with a length of more 1000 km is the most significant fault in japan it juxtaposes the high p t sambagawa metamorphic rocks against the low p t metamorphic rocks of the ryoke belt the mtl was probably formed in the cretaceous with many subsequent reactivations the western segment of the mtl is still active with an almost pure right lateral sense of motion although a great amount of geological information on the mtl has been accumulated information about the subsurface especially the deep seated structure of the mtl is still insufficient it has been generally assumed that the mtl is vertical or steeply dipping at depth because of its straight surface trace and its recent lateral motion recently new geophysical data have suggested that the mtl dips gently northward at depth we have acquired a complementary set of geophysical profiles seismic reflection and refraction gravity and mt across the mtl in east shikoku our results confirm that the mtl dips northward at about 30 to 40 degrees from the surface to about 5 km depth where it becomes listric this fault geometry more reasonably explains the reactivation history of the mtl the motion has occurred on a listric type fault in so called oblique or lateral ramp manner

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

factors affecting seismic moment release rates in subduction zones the amount of shallow seismic activity in subduction zones varies greatly from region to region we quantify this seismicity by calculating seismic moment release rates and seismic slip rates for 24 subduction zones to calculate the moment release we sum the seismic moment for all interplate thrust type events with surface wave magnitude ms 7 0 occurring from 1904 to 1980 we present a time history plot of the seismic moment release for each subduction zone these exhibit the differences in the seismic release patterns for subduction zones where the time window of our study is not representative the total moment release is corrected using information on repeat times the moment release rates are compared with various subduction parameters in order to determine which factors influence the degree of coupling these parameters include the age of the subducting lithosphere absolute velocities of the upper and subducting plates convergence velocity and length maximum depth and dip of the wadati benioff zone the moment release rate decreases as the age of the subducting lithosphere increases when the zones belonging to a single subducting plate are considered this age versus moment release relation is consistent for the zones in which the pacific cocos philippine sea and indian plates are subducting the moment release rates for the subduction zones in which the pacific plate is subducting are much higher than for zones of other plates with similar age the age versus moment release relation holds among the zones which belong to one subducting plate however zones with similar ages but belonging to different plates do not have the same moment release rates this suggests that within a single plate the age is the dominating factor affecting the strength of seismic coupling but that each plate as a whole has a characteristic moment release budget zones with retreating upper plates tend to have lower moment release rates the moment release rate does not increase with convergence velocity no simple relationship was found between these two parameters the moment release rate depends most clearly on the age of the subducting lithosphere and the absolute velocity of the upper plate these are the two independent subduction zone parameters among the variables considered the other variables depend on these two parameters

variability of the kuroshio extension jet recirculation gyre and mesoscale eddies on decadal time scales abstract twelve years of sea surface height ssh data from multiple satellite altimeters are used to investigate the low frequency changes and the interconnections of the kuroshio extension ke jet its southern recirculation gyre and their mesoscale eddy field the dominant signal is characterized by the steady weakening of the ke jet recirculation gyre from 1993 to 1996 followed by a gradual strengthening after 1997 during the weakening period of 1993 96 the ke path migrated southward in general and this path migration reversed in direction during the strengthening period of the ke jet and recirculation gyre after 1997 by hindcasting the ssh signals using linear vorticity dynamics it was found that weakening strengthening in the ke jet and recirculation gyre is consistent with westward propagation of negative positive ssh anomalies generating in the eastern north pacific and strengthening during their westward propagation when the ke jet and recirculation gyre were in a weak mode during 19

3 d viscoelastic fem modeling of crustal deformation in northeast japan as a first step toward establishing a standard earthquake cycle model in japan we simulate the crustal deformation during the past 100 years in northeast japan using a 3 d fem based on the kinematic model then we compare the computed results with the observed long term leveling data and the recent gps data on the whole although the effect of the subducting pac is dominant coseismic deformation of the interplate earthquakes can be clearly seen in the inland moreover the postseismic deformation of the earthquakes due to the viscoelastic upper mantle seriously affects the inland movements and continues for a few decades our modeling including the effects of the interplate earthquakes and the three dimensional viscoelastic inhomogeneity reasonably explains the observed movement finally we stress that the viscoelastic effect should be taken into consideration in the analyses even if no earthquakes occur in the analyzed period

episodic emergence in the past 3000 years at the akkeshi estuary hokkaido northern japan at the akkeshi estuary rapid emergence interrupted holocene submergence at least four times in the past 3000 years each emergence event produced an upward change from estuarine mud to freshwater peat while the estuarine mud abounds in brackish and marine diatoms freshwater taxa dominate the peat emergence events occurred from 1700 to 2300 1000 to 1300 and 500 to 700 cal yr b p an additional emergence event predated by several decades a volcanic ash that erupted in a d 1694 at least three of the events produced contacts abrupt enough to represent uplift during earthquakes such uplift may reconcile seemingly conflicting records of vertical crustal movement in eastern hokkaido this tectonically active area which is being subducted by the pacific plate at 8 cm yr contains marine terraces that imply 0 1 0 5 mm yr of net uplift in the late quaternary however these terraces adjoin tide gages that recorded 8 9 mm yr of steady submergence in the 20th century the terrace uplift need not conflict with the gaged submergence if the region is subject to occasional coseismic uplift as during the emergence events implied by holocene geology near akkeshi

time dependent uplift of the kenai peninsula and adjacent regions of south central alaska since the 1964 prince william sound earthquake leveling global positioning system very long baseline interferometry and tide gauge observations indicate that time dependent uplift has occurred on the kenai peninsula and adjacent regions of southern alaska that subsided coseismically in the 1964 prince william sound earthquake these observations have been critically assessed and used along with seismological and geological information as constraints in various aseismic slip and viscoelastic flow models of crustal deformation the postseismic uplift rate in most of the region is significantly greater than the expected interseismic average some but not all of the data indicate that the uplift rate was quite rapid more than several centimeters per year in the years immediately following the earthquake and has slowed to a few centimeters per year or less since then the modeling shows that the uplift can be explained by aseismic slip at depth but not by viscoelastic flow the slip at depth since 1964 must have a transient as well as a steady component since the deduced slip is considerably greater than the roughly 1 5 m expected from north american pacific plate convergence since the 1964 event the minimum amount of slip required to fit the observations comes from an elastic model and is about 2 75 m viscoelastic models require more slip since the dominant effect of viscoelastic flow is to produce subsidence in the region that is uplifted a simple parameterization of the transient component using an amplitude and decay time is adequate to explain the observations while the parameters deduced from the viscoelastic models have some ambiguity the viscosity of models that best fit the observations cannot be much less than several times 1019 pa s when the thickness of the north american plate is taken to be about 90 km

a subsurface pathway for low potential vorticity transport from the central north pacific toward taiwan island 1 analysis of the simple ocean data assimilation product reveals that the central north pacific 28 n 35 n 150 e 170 w is one of the main formation regions for low potential vorticity water of density between 25 4 and 25 8 it is found that the low potential vorticity water is transported from the central north pacific toward the east of taiwan island along a subsurface pathway following the subtropical gyre circulation and it takes approximately 12 years propagation of pycnocline thickness anomalies is detected along the pathway in association with the decadal variability of the subduction rate

motion of the philippine sea plate consistent with the nuvel 1a model summary we determine euler vectors for 12 plates including the philippine sea plate ph relative to the fixed pacific plate pa by inverting the earthquake slip vectors along the boundaries of the philippine sea plate gps observed velocities and 1122 data from the nuvel 1 and the nuvel 1a global plate motion model respectively this analysis thus also yields euler vectors for the philippine sea plate relative to adjacent plates our results are consistent with observed data and can satisfy the geological and geophysical constraints along the caroline cr ph and pa cr boundaries the results also give insight into internal deformation of the philippine sea plate the area enclosed by the ryukyu trench nankai trough izu bonin trench and gps stations s102 s063 and okino torishima moves uniformly as a rigid plate but the areas near the philippine trench mariana trough and yap palau trench have obvious deformation

an andean model of interplate coupling and strain partitioning applied to the flat subduction zone of sw japan nankai trough abstract transcurrent motion is commonly observed in cases of oblique subduction yet the causes remain controversial a model of increased interplate coupling linked to flat subduction is proposed as a mechanism for producing strain partitioning at a great distance several hundred km from the trench the model originally developed for the north andean margin is applied to the geodynamics of sw japan here along the nankai trough and below adjacent sw honshu flat subduction occurs due to the relatively young age m 7 and nine additional m 6 earthquakes in the past 300 years dextral strike slip focal mechanisms for 15 modern and historical events indicate a significant degree of subduction related strain partitioning manifested by right lateral strike slip faulting along the adakitic volcanic arc some 400 km from the nankai trough

a role of eddies in formation and transport of north pacific subtropical mode water 1 hydrographic data acquired during 2001 by argo profiling floats deployed in the kuroshio recirculation region are used to verify the inference that mesoscale eddies prevailing in the recirculation region play an important role in the formation and transport of north pacific subtropical mode water npstmw that is the deeper winter mixed layer is formed preferentially where the thermocline is deeper in association with anticyclonic eddies in the succeeding seasons mesoscale eddies retain npstmw during their southwestward movement from the npstmw formation region so that anticylonic eddies contribute substantially to the npstmw transportation the spatial distributions of the mixed layer depth in winter and the npstmw thickness in the succeeding seasons based on the float data suggest that they are affected by mesoscale eddies the float data also provide the statistical relations of these quantities against the thermocline depth which are consistent with our inference

aperiodic recurrence of geologically recorded tsunamis during the past 5500 years in eastern hokkaido japan 1 along hokkaido s pacific coast near the town of kiritappu sandy deposits in a muddy lagoon and on a nearby beach ridge plain provide evidence for 15 tsunamis between 200 and 6000 years ago additional sand beds at the lagoon probably represent the historical tsunamis of a d 1843 and 1894 we observed the sequences of sandy deposits in continuous slices 2 to 4 m deep some of the deposits consist of just a single sand bed whereas others contain multiple units of sand muddy sand or sandy mud and mud caps including plant detritus we also found at the lagoon a 17th century tsunami deposit that thickens and thins regardless of elevation or distance inland we bracketed the ages of most of the inferred tsunamis by radiocarbon dating of detritus mainly seeds and leaves at the lagoon and charcoal at the beach ridge plain from pretsunami and posttsunami beds tsunami dates computed from the bracketing ages commonly have uncertainties spanning 2 to 4 centuries within these uncertainties the inferred sequence of 15 prehistoric tsunamis at the lagoon beginning almost 6000 years ago can be matched tsunami by tsunami with the inferred history at the beach ridge plain 15 km away the sand sheet extents suggest that most of these tsunamis were larger than any generated at hokkaido in the last 200 years the intervals between these inferred outsized tsunamis average nearly 400 years but range widely from about 100 to about 800 years

space time correlations between inland earthquakes in central japan and great offshore earthquakes along the nankai trough implication for destructive earthquake prediction abstract based on the tectonic framework of central japan including the surrounding submarine areas the space time relationship between destructive inland earthquakes of magnitudesm 6 4 or greater and great offshore earthquakes along the nankai trough was examined from east to west four tectonic lines are defined as lines linking active faults the itoigawa shizuoka tectonic line istl the tsurugawan isewan tectonic line titl the hanaore kongo fault line hkfl and the arima takatsuki tectonic line attl the titl divides central japan into the chubu and kinki districts and probably extends southward to the nankai trough the chubu district is subdivided into four blocks by boundary lines linking nw se trending active faults having left lateral strike slip in the kinki district n s trending active reverse steep dip faults are dominant in the triangular region north of the median tectonic line between the titl and hkfl forming a basin and range province starting from 1586 a d a seismic space time sequence of high seismic activity in the chubu district in which earthquake occurrence migrates from the eastern to western tectonic lines of central japan was identified the sequence also revealed that inland earthquakes preceded great offshore earthquakes which occurred along the nankai trough it was also found that a destructive earthquake tends to occur on the hkfl within 30 years after the occurrence on the titl and that the western nankai trough generated great earthquakes ofm 7 0 at intervals ranging from 8 to 49 years after the hkfl earthquakes if the eastern nankai trough is coupled with the western nankai trough a forthcoming greater earthquake measuringm 8 5 may be expected since such great earthquakes are always accompanied by large tsunamis much attention should be focussed on possible tsunami disasters along the pacific coast of central japan based on its tectonic structure a tectonic model of central japan is proposed the seismic space time sequence which attempts to explain the cause of the sequential earthquake generation is also discussed

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

transient and permanent deformation of central japan estimated by gps 2 strain partitioning and arc arc collision abstract deformation of central japan can be divided into two main components elastic deformation due to the interseismic locking of subduction thrusts and deformation associated with intra arc tectonics in a companion paper henry et al earth planet sci lett 2000 this issue we estimated an elastic deformation field based on the modeling of global positioning system gps strain rates in this study we show that the corrected field gps minus predicted elastic deformation is consistent with geological and seismological observations and should represent long term plastic deformation we use this corrected gps deformation field to describe the kinematics of partitioning of the philippine sea plate amurian plate amu convergence in relation with the izu bonin arc collision about one third of the relative philippine sea amur motion is transferred to the central japan crust north of the collision front this transfer induces high strain rates in southern kanto and in the northern japanese alps the latter region corresponds to the eastern boundary of the amu we propose that the independent motion of central japan results from the delamination and the underthrusting of the izu bonin arc lower crust and the upward bent oceanic slab

methane hydrate formation in partially water saturated ottawa sand bulk properties of gas hydrate bearing sediment strongly depend on whether hydrate forms primarily in the pore fluid becomes a load bearing member of the sediment matrix or cements sediment grains our compressional wave speed measurements through partially water saturated methane hydrate bearing ottawa sands suggest hydrate surrounds and cements sediment grains the three ottawa sand packs tested in the gas hydrate and sediment test laboratory instrument ghastli contain 38 1 porosity initially with distilled water saturating 58 31 and 16 of that pore space respectively from the volume of methane gas produced during hydrate dissociation we calculated the hydrate concentration in the pore space to be 70 37 and 20 respectively based on these hydrate concentrations and our measured compressional wave speeds we used a rock physics model to differentiate between potential pore space hydrate distributions model results suggest methane hydrate cements unconsolidated sediment when forming in systems containing an abundant gas phase

fluctuations in relative sea level during the past 3000 yr in the onnetoh estuary hokkaido northern japan this paper presents the results of a litho bio and chronostratigraphical study of the evidence for late holocene sea level change palaeoseismicity and coastal evolution at the onnetoh estuary northwest japan alternating peat and mud couplets record evidence for four falls in relative sea level since ca 2500 cal yr bp in the latest instance intertidal mud with a salt tolerant diatom and plant macrofossil flora is abruptly overlain by a freshwater peat containing abundant macrofossil remains of the conifer picea glehnii these stratigraphical changes record an abrupt change from tidal flat to upland with no intermediate transition through saltmarsh in the other three instances the stratigraphy records a more gradual fall in relative sea level as shown by gradational stratigraphical contacts and transitional diatom and plant macrofossil assemblages once established these freshwater peat communities are gradually submerged and become overlain by saltmarsh and then intertidal muds radiocarbon ages and tephra date the emergence events to 2700 1750 gradual 1350 950 gradual 650 300 gradual and ca 400 cal yr bp abrupt these ages are similar to a sequence of emergence events recorded at the akkeshi estuary 70 km to the west of the present study site the three falls in relative sea level may record coseismic or swift post seismic uplift caused by plate boundary subduction earthquakes on the kurile subduction zone the oldest relative sea level fall is correlated with the so called yayoi regression dated to 1500 3000 cal yr bp in other parts of japan copyright 2002 john wiley sons ltd

loci and maximum size of thrust earthquakes and the mechanics of the shallow region of subduction zones earthquakes do not extend updip along the plate interface at most subduction zones all of the way to the plate boundary at the trench axis or deformation front rather the shallowest part of that interface moves mainly through stable aseismic slip that part of the plate boundary referred to here as the aseismic zone occurs along the base of an accreted wedge of young sediments the probable primary cause for the existence of this aseismic zone is the stable slip properties of the unconsolidated and semiconsolidated sediments in that zone subducted sediment is progressively dewatered and underplated to the base of the overriding plate through this process more consolidated rocks eventually come into contact at depth across both sides of the plate boundary from the point where sufficiently hard rock is found across the plate interface that interface will change its slip behavior to unstable stick slip sliding which is characteristic of consolidated material under most conditions this type of motion is accommodated seismically as episodic slip in large earthquakes the location of this transition to seismic behavior referred to as the seismic front marks the deep end of the aseismic zone and the top of the seismogenic zone i e that part of the plate interface that moves primarily in thrust earthquakes several convergent plate margins are discussed to illustrate the seismic front and the aseismic zone we find that the seismic front defined by smaller earthquakes that occur during the interval between large events is nearly the same as that for large events as inferred from the locations of their aftershocks the location of the seismic front is important for making estimates of the maximum possible size of thrust earthquakes along the plate boundary because it delimits the trenchward limit of the potential rupture area of these events the size of large thrust earthquakes is proportional to rupture area and to at least the cube of the downdip width w of that area thus by defining the location of the seismic front for convergent margins it is possible to make better estimates of w and hence to deduce the maximum size of future interplate earthquakes the average repeat time of such events is also related to w and so better estimates of average repeat time are possible from improved knowledge of w the hypothesis that the location of the seismic front is related to the maximum depth of subduction of unconsolidated sediment has implications for forearc mechanics we use a mechanical analysis laboratory modeling and multichannel seismic information to develop a simple model explaining the growth of forearcs the outer arc high or trench slope break that occurs arcward of most accretionary wedges represents an abrupt change in the critical taper of the accretionary wedge we argue that that change is caused by a large arcward increase in the strength of the material within the overriding plate that stronger material is called the backstop our laboratory modeling experiments indicate that a backstop with a trenchward dipping upper surface results in the development of an overlying structure that includes all of the primary morphologic features observed in modern forearcs in our modeling an accretionary wedge develops trenchward of the backstop an outer arc high develops above the trenchward toe of the backstop and farther arcward a passive forearc basin forms above the stronger material of the backstop this model is consistent with the observation that earthquakes do not extend updip along the plate interface all the way to the trench axis we hypothesize that plate motion is accommodated seismically along the base of the consolidated backstop and mostly or entirely aseismically trenchward of the toe of the backstop along the base of the accretionary wedge at several margins the seismic front is approximately coincident with the outer arc high supporting this interpretation

precursory seismic activity before the 1944 tonankai japan earthquake focusing on the downward migration of seismic activity abstract based on the latest jma earthquake catalog the author investigated seismic activity around the time of the 1944 tonankai earthquake m 7 9 m w 8 1 and the 1946 nankaido earthquake m 8 1 m w 8 1 which were both great thrust type earthquakes along the nankai trough for about 20 years before these earthquakes their focal regions had been quiescent appearance of a seismic gap of the second kind and the surrounding areas had become increasingly active forming a doughnut pattern several years before these earthquakes occurred seismic activity increased at shallow depths of the area to the north this activity gradually migrated downwards and the tonankai earthquake occurred when it reached its limit a depth of approximately 70 km the author has previously reported on several cases of increased activity in the deep seismic plane at a depth of 300 500 km prior to large shallow earthquakes along the japan trench mogi 1973 this paper will demonstrate that a similar phenomenon occurs when the depth of the deep seismic plane is only about 70 km for several years before the tonankai earthquake there had been a slight increase in seismicity in the area along the trough which is where the plate subducts two or three days before tne earthquake marked ground tilt also proceeded at the northeastern tip of the focal region it is evident that the tonankai earthquake was preceded by various long term and short term precursory phenomena

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

observations of the subtropical mode water evolution from the kuroshio extension system study abstract properties and seasonal evolution of north pacific ocean subtropical mode water stmw within and south of the kuroshio extension recirculation gyre are analyzed from profiling float data and additional hydrographic and shipboard adcp measurements taken during 2004 the presence of an enhanced recirculation gyre and relatively low mesoscale eddy variability rendered this year favorable for the formation of stmw within the recirculation gyre stmw formed from late winter convection that reached depths greater than 450 m near the center of the gyre the lower boundary of stmw corresponding to 25 5 kg m 3 was set by the maximum depth of the late winter mixed layer properties within the deep portions of the stmw layer remained largely unchanged as the season progressed in contrast the upper boundary of the stmw layer eroded steadily as the seasonal thermocline deepened from late april to august vertical eddy diffusivity responsible for this erosion was estimated from a budget analysis of

deformation of an island arc rates of moment release and crustal shortening in intraplate japan determined from seismicity and quaternary fault data the historical record of large m 6 9 earthquakes and geologically determined rates of slip on quaternary faults in intraplate japan honshu and shikoku are used to estimate the average rate of seismic moment release m for the last 400 years and during the late quaternary respectively values of m estimated from the two data sets are similar in regions where seismic activity is concentrated on land we interpret this observation to suggest that m in intraplate japan has been constant during the late quaternary and is relatively free from secular variation when averaged over periods of several hundreds of years m in shikoku may be attributed almost solely to right lateral slip of the median tectonic line mtl the easterly strike of the mtl is consistent with a compressive stress field that trends northwest crustal shortening of the izu peninsula taken up on a set of strike slip faults that show north by northwest compression is 1 mm yr northeast honshu is characterized by a set of reverse type faults that trend northerly conversion of m in northeast japan to strain rates suggests that about 5 of the relative plate motion between japan and the pacific plate 9 7 cm yr is accommodated as a permanent east west shortening 5 mm yr of northeast honshu the predominant deformation in central and western honshu takes place as slip on a conjugate system of strike slip faults that strike northeast and southeast and show right lateral and left lateral motion respectively crustal shortening resulting from slip on faults in central and western honshu is 5 and 0 5 mm yr respectively in an easterly direction central and western honshu are in closest proximity to the nankai trough and hence the stress field in these regions cannot simply be attributed to the accommodation of the relative northwesterly convergence of the philippine sea plate the northward impingement of the izu peninsula into honshu may influence stresses in central and western japan but a conclusive explanation of the stress field in central and western honshu remains an enigma

lateral variations of interplate coupling along the mexican subduction interface relationships with long term morphology and fault zone mechanical properties although patterns of interseismic strain accumulation above subduction zones are now routinely characterised using geodetic measurements their physical origin persistency through time and relationships to seismic hazard and long term deformation are still debated here we use gps and morphological observations from southern mexico to explore potential mechanical links between variations in inter sse in between slow slip events coupling along the mexico subduction zone and the long term topography of the coastal regions from guerrero to oaxaca inter sse coupling solutions for two different geometries of the subduction interface are derived from an inversion of continuous gps time series corrected from slow slip events they reveal strong along strike variations in the shallow coupling i e at depths down to 25 km with high coupling zones coupling 0 7 alternating with low coupling zones coupling 0 7 and transitions to uncoupled steady slip at a relatively uniform sim 175 km inland from the trench along strike variations in the coast to trench distances are strongly correlated with the gps derived forearc coupling variations to explore a mechanical explanation for this correlation we apply coulomb wedge theory constrained by local topographic bathymetric and subducting slab slopes critical state areas i e areas where the inner subduction wedge deforms are spatially correlated with transitions at shallow depth between uncoupled and coupled areas of the subduction interface two end member models are considered to explain the correlation between coast to trench distances and along strike variations in the inter sse coupling the first postulates that the inter sse elastic strain is partitioned between slip along the subduction interface and homogeneous plastic permanent deformation of the upper plate in the second permanent plastic deformation is postulated to depend on frictional transitions along the subduction plate interface based on the location and friction values of the critical state areas identified by our coulomb wedge analysis we parameterise frictional transitions in plastic static models of deformation over several seismic cycles this predicts strong shear dissipation above frictional transitions on the subduction interface the comparison of modelled surface displacements over a critical zone at a frictional transition and over a stable area with no internal wedge deformation shows differences of long term uplift consistent with the observed along strike variations in the coast to trench distances our work favours a model in which frictional asperities partly control short term inter sse coupling as measured by geodesy and in which those asperities persist through time

recent crustal deformation and the earthquake cycle along the ecuador colombia subduction zone recent results from global positioning system gps measurements show deformation along the coast of ecuador and colombia that can be linked to the rupture zone of the earthquake in 1979 a 3d elastic boundary element model is used to simulate crustal deformation observed by gps campaigns in 1991 1994 1996 and 1998 deformation in ecuador can be explained best by 50 apparent locking on the subduction interface although there have not been any historic large earthquakes mw 7 south of the 1906 earthquake rupture zone 50 apparent elastic locking is necessary to model the deformation observed there in colombia only 30 apparent elastic locking is occurring along the subduction interface in the 1979 earthquake rupture zone mw 8 2 and no elastic locking is necessary to explain the crustal deformation observed at two gps sites north of there there is no evidence from seismicity or plate geometry that plate coupling on the subduction zone is reduced in colombia however simple viscoelastic models suggest that the apparent reduction in elastic locking can be explained entirely by the response of a viscous upper mantle to the 1979 earthquake these results suggest that elastic strain accumulation is occurring evenly throughout the study area but postseismic relaxation masks the true total strain rate

evolution of the north pacific subtropical mode water in anticyclonic eddies anticyclonic eddies aes trap and transport the north pacific subtropical mode water stmw but the evolution of the stmw trapped in aes has not been fully studied due to the lack of eddy tracking subsurface observations here we analyze profiles from special designed argo floats that follow two stmw trapping aes for more than a year the enhanced daily sampling by these argo floats swirling around the eddies enables an unprecedented investigation into the structure and evolution of the trapped stmw in the aes the upper lower thermocline domes up concaves downward and this lens shaped double thermocline encompasses the thick stmw within the eddy core the lighter stmw 25 0 25 2 trapped in aes dissipates quickly after the formation in winter because of the deepening seasonal thermocline but the denser stmw 25 2 25 4 remains largely unchanged except when the ae passes across the izu ridge the enhanced diapycnal mixing over the ridge weakens the denser stmw appreciably while many aes decay upon hitting the ridge some pass through a bathymetric gap between the hachijojima and bonin islands forming a cross ridge pathway for stmw transport by contrast the north pacific intermediate water npiw underneath is deeper than the eddy trapping depth 600 m and hence left behind east of the izu ridge in argo climatology the shallow stmw 400 m intrudes through the gap westward because of the eddy transport while the npiw 800 m is blocked by the izu ridge

interseismic horizontal deformation in northern honshu and its relationship with the subduction of the pacific plate in the japan trench we investigate the origin of the geodetically observed interseismic horizontal deformation in northern honshu by comparing shear strain rates principal strain rates and velocity fields determined from geodetic data with those calculated from the elastic dislocation models involving interplate motion at the japan trench the agreement between the observed and predicted directions of the principal strain axes indicates that the geodetic strain field in northern honshu is primarily elastic strain transmitted from the japan trench in order to match the strain rate tensors and velocity magnitudes obtained from the geodetic data the dislocation model requires that 35 to 60 of the nuvel1 a pacific north american plate motion is locked at the plate interface along the japan trench the down dip depth limit of the locked zone is inferred to be 55 km which is consistent with the seismic data in the japan trench

structural control on late miocene to quaternary volcanism in the ne honshu arc japan 1 volcanological and structural field data are used to define the tectonic control on the n s volcanic arc of ne honshu japan since late miocene during late miocene pliocene bimodal products were mainly erupted from along arc and ne sw aligned and elongated calderas the deformation pattern mostly consisted of n s dextral faults and subordinate ne sw extensional structures produced by ne sw compression this pattern because of the indentation of the kuril sliver is similar to that of oblique convergence settings magma rose and extruded along ne sw areas of localized extension created by the dextral faults these extensional areas were uncoupled with regard to those e w trending inferred to have focused the rise of melts from the subducting slab in the mantle during quaternary a larger amount of andesite was mainly erupted from along arc and e w aligned and elongated stratovolcanoes the deformation pattern mostly consisted of n s thrust faults and subordinate e w extensional structures produced by e w compression resulting from orthogonal convergence due to the variation in the absolute motion of the pacific plate the e w extensional structures are the shallowest expression of e w trending hot mantle fingers suggesting mantle crust coupling for the rise of magma such a coupling ensures 1 higher extrusion and 2 mixing between a deeper mafic and a shallower felsic magma generating the andesites the significantly larger volumes ma 1 200 km 1 of length of the arc of magma erupted during quaternary show that pure convergence conditions do not necessarily hinder the rise and extrusion of magma

microstructure measurements in the mid depth waters of the north pacific 1 microstructure measurements from the surface down to maximum depths of 2000 m were carried out at 28 locations in the interior of the north pacific special attention was directed to the diapycnal diffusivities k in the significant generation regions of the semidiurnal internal tide such as the aleutian ridge the hawaiian ridge and the izu ogasawara ridge in the profiles obtained near the aleutian ridge only a few turbulent patches with 10 9 wkg 1 were detected and k was generally less than 10 5 m2s 1 in the profiles obtained near the hawaiian ridge many turbulent patches with 10 9 wkg 1 were observed although k was generally of the order of 10 5 m2s 1 along the izu ogasawara trough running in parallel with the izu ogasawara ridge in contrast remarkably intense turbulent mixing 10 8 wkg 1 k 10 4 10 3 m2s 1 was common throughout the observed water depth

subduction zone paleoseismology along the pacific coast of northeast japan progress and remaining problems abstract this paper reviews recent progress in tsunami geology and the history of coastal uplift subsidence along the pacific coasts of hokkaido and tohoku facing the kuril and japan trenches respectively in the last 20 years research by tsunami geologists in northeast japan has focused on extending the record of tsunamis beyond the range of historical documents in the region which span too little time to reveal much of the earthquake history over the last millennia along the coast of hokkaido recurrent sandy deposits are evidence of historical and prehistoric large tsunamis at kiritappu marsh for example at least 15 identified tsunami deposits occurred between 200 and 6 000 years ago the spatial distribution of the most recent prehistoric tsunami deposit that of the so called 17th century earthquake and tsunami exceeds historical and recent tsunami inundations in eastern hokkaido numerical simulations of this event require a multi segment fault model with variable slip mw 8 8 encompassing both the tokachi oki and nemuro oki regions to reproduce the observed deposit distribution in eastern hokkaido the recurrence interval of such multi segment earthquakes along the southern kuril trench is estimated to be 100 800 years based on tephrochronological and radiocarbon evidence tsunami deposits are also associated with historical earthquakes in 1843 and 1894 in eastern hokkaido and with the 1640 komagatake eruption in western hokkaido the 17th century earthquake probably triggered postseismic coastal deformation diatom based transfer functions suggest rapid subsidence before the event and gradual uplift afterward and historical volcanic ash layers indicate that gradual postseismic uplift occurred over decades a simple dislocation model can explain such gradual uplift as an aseismic fault extension after the 17th century event in the tohoku region a tsunami deposit associated with the 869 jogan earthquake has been identified and the inundation area of this event has been constrained based on the lateral extent of the tsunami deposit and its stratigraphic position beneath the historical to a tephra 915 ce land level changes at odaka fukushima prefecture associated with the jogan event have been estimated based on changes of fossil diatom assemblages below and above the tsunami deposit numerical simulations based on geological evidence and observations of the 2011 tohoku tsunami deposit suggest that the jogan event was a plate boundary rupture at least 200 km long along the japan trench mw 8 3 8 6 the 1454 kyotoku tsunami is also considered to have been generated by a rupture area including the miyagi oki region part of the jogan rupture it remains unclear whether the 869 1454 and 2011 tsunamis were similar in size and source if they were the recurrence intervals of such events near sendai are less than 600 years and more regular than those for multi segment earthquakes along the kuril trench

tectonic stress state in ne japan as part of the okhotsk plate abstract an existing geodetic flow velocity model obtained by using an internal free network adjustment technique is used to derive estimates for various strain rates parameters in ne japan the greatest shortening rates of the principal strains trending e w are located in regions where much steady internal frame invariant plastic flow deformation is observed to be taking place the internal geodetic adjustment technique yielded the internal deformation in the tohoku arc most of the intraplate deformations including the much folding deformations observed in the inner zone are produced from within an interseismic transient elastic loading at a strongly coupled locked japan trench would not be needed the observed ongoing extensive ductile folding deformation in the inner zone of tohoku may mean that the geodetic strain rates causing shortening at 2 3 cm yr probably reflect the more correct level of the deformation which is steady permanent in ne japan as compared with seismic faulting data which indicate 0 5 cm yr shortening the calculated principal strain rates are used to make an interpretation for the origin of the deviatoric principal stresses within the greater regional plate tectonic framework the tectonic stress state in ne japan as part of the okhotsk plate could mostly be influenced by the okhotsk plate which is extruding southward to lessen the significant accumulated contractional deformation in ne asia in the verkhoyansk cherskii mountains the principal strain rates are n s extensional essentially everywhere in ne japan as a result of the southerly extrusion except in its southernmost leading edge in the uetsu fossa magna province where the japan alps rampart rises in front of the extrusion here an e w compressional stress state prevails a second e w contractional zone is found in north central tohoku extending from the sanriku province in the outer zone to the inner zone in the japan sea side being more prevalent in the latter zone the calculated rotation rates from the geodetic flow model are clockwise cw in both of the e w contractional regions ne japan extruding southward faces buttresses in 1 the oga ojika line ool and or a crustal weakness zone between the northern and the southern halves of tohoku approx at 38 5 n latitude and especially 2 the japanese alps rampart these obstacles cause the northern and southernmost tohoku to veer to its right and rotate cw thereby setting up the e w trending compressional deformation in their respective inner zones between the ool or the 38 5 n boundary and the kanto tectonic line ktl the sense of the differential rotations is counterclockwise ccw towards the ocean to the se the northern tohoku north of the ool and the southernmost tohoku south of the ktl cannot rotate ccw towards the ocean because of the izu block s collision in the south and the relatively strong coupling along the subduction interface beneath the japan trench in the north off sanriku the relatively stronger long term coupling between the northern tohoku and the pacific plate at the sanriku coast with respect to that in off fukushima is due to a flatter subduction of the pacific slab there increasing the plates interface contact area the flattening of the subduction dip angle was caused by ccw rotation and shifting of the northern tohoku along the dextral honjo matsushima line roughly corresponding to the ool towards the pacific and overriding of the subduction zone during the formation of the japan sea

the july 12 1993 hokkaido nansei oki japan earthquake coseismic slip pattern from strong motion and teleseismic recordings we employ a finite fault inversion scheme to infer the distribution of coseismic slip for the july 12 1993 hokkaido nansei oki earthquake using strong ground motions recorded by the japan meteorological agency within 400 km of the epicenter and vertical p waveforms recorded by the global digital seismograph network at teleseismic distances the assumed fault geometry is based on the location of the aftershock zone and comprises two fault segments with different orientations a northern segment striking at n20 e with a 30 dip to the west and a southern segment with an n20 w strike for the southern segment we use both westerly and easterly dip directions to test thrust orientations previously proposed for this portion of the fault the variance reduction is greater using a shallow west dipping segment suggesting that the direction of dip did not change as the rupture propagated south from the hypocenter this indicates that the earthquake resulted from the shallow underthrusting of hokkaido beneath the sea of japan static vertical movements predicted by the corresponding distribution of fault slip are consistent with the general pattern of surface deformation observed following the earthquake fault rupture in the northern segment accounts for about 60 of the total p wave seismic moment of 3 4 1020 n m and includes a large circular slip zone 4 m peak near the earthquake hypocenter at depths between 10 and 25 km slip in the southern segment is also predominantly shallower than 25 km but the maximum coseismic displacements 2 0 2 5 m are observed at a depth of about 5 km this significant shallow slip in the southern portion of the rupture zone may have been responsible for the large tsunami that devastated the small offshore island of okushiri localized shallow faulting near the island however may require a steep westerly dip to reconcile the measured values of ground subsidence

universality of the seismic moment frequency relation we analyze the seismic moment frequency relation in various depth ranges and for different seismic regions using flinn engdahl s regionalization of global seismicity three earthquake lists of centroid moment tensor data have been used the harvard catalog the usgs catalog and the huang et al 1997 catalog of deep earthquakes the results confirm the universality of the values and the maximum moment for shallow earthquakes in continental regions as well as at and near continental boundaries moreover we show that although fluctuations in earthquake size distribution increase with depth the values for earthquakes in the depth range of 0 500 km exhibit no statistically significant regional variations the regional variations are significant only for deep events near the 660 km boundary for declustered shallow earthquake catalogs and deeper events we show that the worldwide values have the same value of 0 60 0 02 this finding suggests that the value is a universal constant we investigate the statistical correlations between the numbers of seismic events in different depth ranges and the correlation of the tectonic deformation rate and seismic activity the number of earthquakes above a certain threshold level per year the high level of these correlations suggests that seismic activity indicates tectonic deformation rate in subduction zones combined with the universality of the value this finding implies little if any variation in maximum earthquake seismic moment among various subduction zones if we assume that earthquakes of maximum size are similar in different depth ranges and the seismic efficiency coefficient is close to 100 for shallow seismicity then we can estimate for deeper earthquakes for intermediate earthquakes 5 and 1 for deep events these results may lead to new theoretical understanding of the earthquake process and better estimates of seismic hazard

horizontal and vertical crustal movements from three dimensional very long baseline interferometry kinematic reference frame implication for the reversal timescale revision three dimensional kinematic reference frame of geodetic very long baseline interferometry vlbi stations tied to a geologic plate motion model was established using the glb907 solution by first selecting globally distributed stable plate interior stations and then applying a small translation and a rotation for the entire network in a three dimensional space so that the differences in the horizontal velocities between the vlbi observations and the model predictions are minimized since the vlbi network is global we only assume that the horizontal movements of technically stable stations obey a plate motion model we need not introduce any unwarranted constraints to the vertical velocities of specific stations to realize the frame a suggestive correlation was found between the estimated vertical velocities of north american stations and those predicted by a postglacial rebound model the revision of the magnetic polarity timescale mpts causes a uniform increase or decrease of the predicted velocities which could be detected as the small difference between the measured and the predicted relative plate velocities direct estimation of the correction suggests that the vlbi data fit best to the model when the nuvel1 model is corrected by 3 4 1 2 which differs significantly from the 4 5 deduced from the astronomical mpts calibration this was further confirmed by estimating the rotation rates for individual plate pairs

effects of mesoscale eddies on subduction and distribution of subtropical mode water in an eddy resolving ogcm of the western north pacific abstract the effects of mesoscale eddies on the subduction and distribution of the north pacific subtropical mode water stmw are investigated using an eddy resolving ocean general circulation model ogcm first the subduction rate is calculated and the contribution of eddies to the subduction of stmw is estimated it is found that eddy subduction significantly contributes to the total subduction of stmw second eddy thickness transport and diapycnal flux are directly diagnosed to investigate the large scale eddy induced transport process of stmw the large southward eddy thickness transport in the stmw core density is consistent with eddy subduction the eddy transport on the isopycnal surface of stmw is directed down the thickness gradient and traverses the mean flow the meridional eddy transport streamfunction indicates two eddy circulation cells south of 30 n associated with the circulation of stmw these cells flatten density surfaces similar to the effect of the gent and mcwilliams gm schem

triple seismic zone and the regional variation of seismicity along the northern honshu arc the regional variation of seismicity along the northern honshu arc japan is studied using accurate focal depths and focal mechanism types we use focal depths determined from pp p time intervals reported in the isc bulletins for submarine earthquakes depths are corrected by considering the pp phase reported in the bulletins as the pwp phase the reflection from the ocean surface out of more than 600 well located earthquakes selected from the isc bulletins we determine the types of the focal mechanisms of 184 events using p wave first motion data based on historical seismicity of great and large earthquakes we divide the zone of thrust type earthquakes at the plate interface into two regions the shallow thrust zone 0 40kin where great earthquakes ms 8 0 occur and the deep thrust zone 40 60km where large earthquakes ms 7 4 occur the activity of great or large earthquakes shows a variation along the are in some regions both the shallow and deep thrust zones are active and in other regions only one of the thrust zones is active the seismicity of recent moderate size earthquakes mb 4 combined with the focal mechanism type shows a variation along the are which reflects the variation of the activity of great or large earthquakes where large earthquakes do not occur in the deep thrust zone neither thrust type nor down dip compression tension type events occur in and beneath the deep thrust zone where large earthquakes do occur in the deep thrust zone we find a number of thrust type earthquakes further in the latter case in some regions the down dip compression and tension type events of the double seismic zones extend seaward just beneath the deep thrust zone and form a triple planed structure of seismicity the triple seismic zone this study confirms the hypothesis of previous workers seno and pongsawat 1981 on the causal relation between the strong seismic coupling of two converging plates at the deep thrust zone and extension of the double seismic zone i e the presence or absence of activity within the slab beneath the deep seismic zone occurs when the deep thrust zone has a strong or weak coupling respectively here the weak coupling could be interpreted as either aseismic slip or as low stress buildup since the last large event occurred at the deep thrust zone triple seismic zones are found offshore of miyagi prefecture where the deep thrust zone has been broken recently in 1978 and offshore of fukushima prefecture we expect a future large earthquake at the deep thrust zone offshore of fukushima prefecture because the presence of the triple seismic zone suggests stress has been accumulating and 40 years have passed since the deep thrust zone was ruptured in 1938

asthenospheric viscosity and stress diffusion a mechanism to explain correlated earthquakes and surface deformations in ne japan summary a significant correlation is found in both space and time between the intraplate land and interplate sea thrust zone only earthquakes in tohoku ne japan that has persisted since the times of reliably reported events in ad 1600 the correlation peaks at a land lead of about 36 yr with an average correlation distance of 200km with the implication of an average strain migration rate of 5 6 km yr 1 the correlation is highly significant 99 per cent both from formal statistics and from tests of random shuffles of the data additional analysis of the data as a point process confirms the results of the correlation analysis the sharpness of the correlation peak when compared to the individual times of occurrence of the land and sea events suggests a trigger mechanism to explain the correlation the general model ofsubduction rupture rebound is extended to include additional features the buckling of the land plate from the force of the subducting slab and the viscoelastic coupling of the plate to the underlying asthenosphere a buckle produces a high stress region in the continental plate where earthquakes are more prone to occur thus producing the spatial correlation in the data this may also explain the preferred location on land for the smaller modern day seismic events in ne japan the viscoelastic coupling controls the interaction between the land and sea events resulting in the temporal correlation in the data because of viscosity the model equations are diffuse like with strain pulses as solutions thus from the inferred strain migration rate it is possible to estimate asthenospheric viscosity 7 1018pa s using this model a large land shock generates a strain pulse that affects the locked fault at the thrust zone several decades later as the continental plate tends to pull away from the subducting slab the frictional force arising from the overburden pressure is reduced thus unlocking the fault and triggering a sea earthquake the viscoelastic model is also used to explain surface deformations measured by triangulation surveys in japan in 1904 and 1964 horizontal displacements which we believe are surface manifestations of the strain pulse from the large 1896 riku u land shock m 7 5 in ne japan are fit well by the model and provide a viscosity estimate 13 1018 pa s

effect of mesoscale eddies on subtropical mode water variability from the kuroshio extension system study kess abstract forty eight profiling floats have been deployed in the kuroshio extension ke region since may 2004 as part of the kuroshio extension system study kess project by combining the float temperature salinity measurements with satellite altimetry data this study investigates the role played by mesoscale eddies in controlling the property changes in north pacific subtropical mode water stmw following a 3 yr period of low eddy activity in 2002 04 the ke showed a transition to a high eddy kinetic energy state in 2005 this transition is the result of delayed oceanic response to the 2002 shift in the basin scale surface wind forcing in connection with the pacific decadal oscillation the high eddy kinetic energy state of the ke is characterized by successive shedding of strong cold core rings into the recirculation gyre resulting from the interaction of the ke jet with the shatsky rise or the preexisting cutoff rings by transporting northern origin high potential vorticity pv ke water into t

a test of present day plate geometries for northeast asia and japan alternative geometries for the present day configuration of plate boundaries in northeast asia and japan are tested using nuvel 1 and 256 horizontal earthquake slip vectors from the japan and northern kuril trenches statistical analysis of the slip vectors is used to determine whether the north american eurasian or okhotsk plate overlies the trench along the northern kuril trench sup vectors are well fit by the nuvel 1 pacific north america euler pole but are poorly fit by the pacific eurasia euler pole results for the japan trench are less conclusive but suggest that much of honshu and hokkaido are also part of the north american plate the simplest geometry consistent with the trench slip vectors is a geometry in which the north american plate extends south to 41 n and possibly includes northern honshu and southern hokkaido although these results imply that the diffuse seismicity that connects the lena river delta to sakhalin island and the eastern sea of japan records motion between eurasia and north america onshore geologic and seismic data define an additional belt of seismicity in siberia that cannot be explained with this geometry assuming that these two seismic belts constitute evidence for an okhotsk block two published kinematic models for motion of the okhotsk block are tested the first model which predicts motion of up to 15 mm yr 1 relative to north america is rejected because kuril and japan trench slip vectors are fit more poorly than for the simpler geometry described above the second model gives a good fit to the trench slip vectors but only if okhotsk north america motion is slower than 5 mm yr 1

new cnes cls09 global mean dynamic topography computed from the combination of grace data altimetry and in situ measurements 1 an accurate knowledge of the ocean mean dynamic topography mdt is mandatory for the optimal use of altimetric data including their assimilation into operational ocean forecasting systems a new global 1 4 resolution mdt was computed for the 1993 1999 time period with improved data and methodology compared to the previous rio05 mdt field first a large scale mdt is obtained from the cls01 altimetric mean sea surface and a recent geoid model computed from 4 5 years of grace gravity recovery and climate experiment data altimetric sea level anomalies and in situ measurements are then combined to compute synthetic estimates of the mdt and the corresponding mean currents while the rio05 mdt was based on 10 years of in situ dynamic heights and drifting buoy velocities the new field benefits from an enlarged data set of in situ measurements ranging from 1993 to 2008 and includes all hydrological profiles from the argo array moreover the processing of the in situ data has been updated a new ekman model was developed to extract the geostrophic velocity component from the drifting buoy measurements the handling of hydrologic measurements has also been revisited compared to the previous rio05 solution the new global mdt resolves much stronger gradients in western boundary currents with mean velocities being doubled in some places moreover in comparison to several other recent mdt estimates we find that the new cnes cls09 mdt is in better agreement with independent in situ observations

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