the atlantic water boundary current north of svalbard in late summer data from a shipboard hydrographic velocity survey carried out in september 2013 of the region north of svalbard in the nansen basin are analyzed to characterize the atlantic water aw boundary current as it flows eastward along the continental slope eight meridional transects across the current spanning an alongstream distance of 180 km allow for a detailed description of the current and the regional water masses during the survey the winds were light and there was no pack ice the mean section reveals that the boundary current was o 40 km wide surface intensified with a maximum velocity of 20 cm s its mean transport during the survey was 3 11 0 33 sv of which 2 31 0 29 sv was aw this suggests that the two branches of aw entering the arctic ocean via fram strait the yermak plateau branch and the svalbard branch have largely combined into a single current by 30 e at this location the boundary current meanders with a systematic change in its kinematic structure during offshore excursions a potential vorticity analysis indicates that the flow is baroclinically unstable consistent with previous observations of aw anticyclones offshore of the current as well as the presence of a near field cyclone in this data set our survey indicates that only a small portion of the boundary current is diverted into the kvitoya trough 0 17 0 08 sv and that the aw temperature salinity signal is quickly eroded within the trough

extrusion tectonics of the okhotsk plate northeast asia based on focal mechanism geologic and lineament data faulting in the chersky range northeast asia changes from right lateral transpression between north america and eurasia to left lateral strike slip between north america and the okhotsk plate the location of the okhotsk eurasia boundary is poorly constrained available data suggest this boundary is right lateral the okhotsk plate is being compressed and extruded from between north america and eurasia resulting in high levels of microseismic activity along the southern flanks of the chersky range

imprint of the north american plate in siberia revealed by gps 1 gps observations in east siberia combined with global observations collected 1995 2002 place constraints on the geometry and motions of the eurasian north american and pacific plates in east asia by comparing velocities relative to eurasia and to north america we conclude that east siberia to the east of the cherskiy range belongs to the north american plate hypothesized for three decades but not proven because of uncertainties with the plate boundary arising from the ambiguous seismicity smaller plates in east asia such as okhotsk and amurian can neither be resolved nor excluded by the gps velocities

plate dynamics near divergent boundaries geophysical implications of postrifting crustal deformation in ne iceland the bulk of a tectonic plate is thought to move continously at a rate consistent with the geologic average on the other hand movements are highly episodic at plate boundaries we study the plate dynamics that relate to these two different modes by modelling the displacements observed using the global positioning system in northeast iceland 1987 1990 these observations were made about 10 years after an episodic divergent movement between the north american and eurasian plates 1975 1981 the horizontal displacement field fits well a two dimensional model of postrupture stress relaxation assuming a thin elastic layer overlying a layer of newtonian viscosity this analysis indicates values of about 10 m2 s for the stress diffusivity and 0 3 2 1018 pa s for the newtonian viscosity of the lower layer however no significant correlation exists between the observed and modeled vertical displacements probably because of the relative inaccuracy of the vertical component observations assuming that contemporary plate motion is the sum of many displacements that have diffused from boundaries where episodic displacements occur periodically we simulate the spatial transition from episodic to continuous plate movements the plate boundary zone where movements are episodic or quasi episodic is of the order of 100 km wide depending on the stress diffusivity which may be fairly uniform throughout the world and the frequency of episodic movements

crustal extension in the baikal rift zone analysis of the gravity field along four profiles crossing the baikal rift zone permits an estimate of the amount of anomalous mass produced by 1 1 graben fill sediments 2 2 moho uplift and intrusion of mantle sills and dikes 3 3 an asthenospheric bulge crustal extension is evaluated based on the idea of mass and volume balance of material introduced into and removed from the initial volume of the crust extension in the baikal rift increases southwestward from 0 9 km in the chara depression to 19 3 km in the south baikal depression these values generally agree with the position of the euler pole determined from seismic data fault plane solutions average rotation velocity for the lithospheric plates separated by the rift zone is estimated to be 5 93 10 4 rad m y over about 30 m y

evidence for mechanically coupled lithosphere in central asia and resulting implications the recent dramatic increase in seismic anisotropy and surface global positioning system gps data for central asia permits a comprehensive examination of the mantle s role in mountain building a joint analysis of 178 shear wave splitting and 2000 gps observations using a new technique reveals that the crust and lithospheric mantle deform coherently arguing for crust mantle mechanical coupling during deformation the observed spatial variations in anisotropy refl ect the large scale pattern of lithospheric deformation as well as a change in deformational style from simple shear on the tibetan plateau transitioning to pure shear in surrounding regions

estimation of slip distribution using an inverse method based on spectral decomposition of green s function utilizing global positioning system gps data 1 an inverse method based on the spectral decomposition of the green s function was employed for estimating a slip distribution we conducted numerical simulations along the philippine sea plate ph boundary in southwest japan using this method to examine how to determine the essential parameters which are the number of deformation function modes and their coefficients japanese gps earth observation network geonet global positioning system gps data were used for three years covering 1997 1999 to estimate interseismic back slip distribution in this region the estimated maximum back slip rate is about 7 cm yr which is consistent with the philippine sea plate convergence rate areas of strong coupling are confined between depths of 10 and 30 km and three areas of strong coupling were delineated these results are consistent with other studies that have estimated locations of coupling distribution

late quaternary to decadal velocity fields in asia 1 fields of crustal velocity and strain rate within asia averaged over horizontal distances of 300 km are calculated from estimates of quaternary slip rates on faults and rates of change of lengths of baselines between gps sites the calculated fields fit strain rate components estimated from quaternary slip rates within 95 confidence limits and fit the gps data with an rms residual of 2 5 mm yr 1 the strain rate field constrained only by quaternary slip rates of faults differs from the combined solution at the level of 20 nstrain yr 1 and the differences are explicable by the limited accuracy of geological estimates of slip rate therefore the strain rate fields determined by geodetic measurements taken on the 10 year timescale are consistent with geological observations on the 104 year timescale the combined solution for velocities shows plate or block like motion within deforming asia only in tarim south china and the amurian region elsewhere the kinematics of rigid blocks does not provide a useful description of the motion in particular velocities relative to eurasia point at high angles to contours of their magnitudes not parallel to them as they would if large regions moved as rigid blocks the axes of principal horizontal compressional strain align with topographic gradients in agreement with previous suggestions that asia deforms as a continuum under the influence of gravity

flow of winter transformed pacific water into the western arctic abstract the dynamics of the flow of dense water through barrow canyon is investigated using data from a hydrographic survey in summer 2002 the focus is on the winter transformed bering water the highest volumetric mode of winter water in the chukchi sea which drains northward through the canyon in spring and summer the transport of this water mass during the time of the survey was 0 2 0 3 sv as the layer flowed from the head of the canyon to the mouth it sank decelerated and stretched strong cyclonic relative vorticity was generated on the seaward side of the jet which compensated for the stretching this adjustment was incomplete however in that it did not extend across the entire current possibly because of internal mixing due to shear instabilities the resulting vorticity structure of the flow at the canyon mouth was conducive for baroclinic instability and eddy formation multiple eddies of winter transformed bering water were observed along the chukchi beaufort shelfbreak those to the west of barrow canyon were in the process of being spawned by the eastward flowing shelfbreak current emanating from herald canyon while the single eddy observed to the east originated from the barrow canyon outflow it is argued that such an eddy formation is a major source of the ubiquitous cold core anti cyclones observed historically throughout the canada basin implications for the ventilation of the upper halocline of the western arctic are discussed

neogene and quaternary faulting in and along the qinling shan the structure of the qinling shan mountain range shaanxi china involves major east south east strike slip faults field observations made during two expeditions in 1983 and 1984 show that the faults are active and may have undergone several tens of kilometres of post eocene left lateral displacement the faults cut the morphology sharply and offset left laterally small channels their trace is marked by cataclastic to mylonitic non coaxial deformation zones at least 50 100 m wide the qinling faults allow the eastward extrusion of south china and may be considered the easternmost continuation of the altyn tagh fault system they link extensional tectonics in northeastern china to the himalayan collision

crustal strains in the japanese islands as deduced from dense gps array data from the nationwide continuous gps network operated by the geographical survey institute of japan were used to estimate crustal strains in the japanese islands we used horizontal velocity vectors at 610 sites for the period april 1996 to march 1997 and employed the least squares prediction method to interpolate the velocities to a uniform 7km 7km grid over japan the gridded velocities were then differentiated in space to calculate principal components of strains results clearly portray tectonic strainings of the japanese islands in one year 1 dilatational strains show that the japanese islands are under a compressive strain regime induced by the subducting oceanic plates 2 distribution of high maximum shear strains coincides with the regions of crustal activities and 3 principal axes of the strains indicate influences of e w and nw se compression due to the converging oceanic plates north south extension in kyushu is also visible

gulf stream meander propagation past cape hatteras the propagation and growth characteristics of gulf stream meanders past the stream s separation point at cape hatteras are analyzed using yearlong time series from a mooring program sponsored by the minerals management service which included moorings imbedded in the gulf stream cyclonic flank both upstream south and downstream north of cape hatteras in the upstream region energetic meanders of 3 8 day period 180 380 km wavelength propagate downstream along the gulf stream at speeds of 40 55 km day 21 this variability decays almost completely across the gulf stream separation with growth in lower frequency variability 30 120 day in the downstream direction wavelength and phase speed in the 3 8 day band are strong functions of frequency with increasing phase speed for increasing wavenumber phase speeds upstream from cape hatteras and across the gulf stream separation point are faster for a given wavenumber than downstream from cape hatteras in keeping with prior published estimates at the upstream end of the study site both baroclinic and barotropic mechanisms contribute to the decay of 3 8 day meanders and growth of lower frequency 30 120day variability in the downstream direction at the downstream end of the study region the reverse holds with both baroclinic and barotropic mechanisms contributing to growth of 3 8 day meanders and decay of lowerfrequency 30 120 day variability

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

geofem kinematic earthquake cycle simulation in southwest japan we construct a viscoelastic fem model with 3 d configuration of the subducting philippine sea plate in southwest japan to simulate recent 300 year kinematic earthquake cycles along the nankai suruga sagami trough based on the kinematic earthquake cycle model this 300 year simulation contains a series of three great interplate earthquakes the inclusion of viscoelasticity produces characteristic velocity field during earthquake cycles regardless of the assumed constant plate coupling throughout the interseismic period just after the occurrence of interplate earthquakes the viscoelastic relaxation creates the seaward motion in the inland region in the middle period the seaward motion gradually decreases and the resultant velocity field is similar to the elastic one later just before the next interplate earthquake displacements due to the interplate coupling in the viscoelastic material are distributed more broadly in the forearc region than in the purely elastic one since the viscoelastic relaxation due to the previous earthquake mostly disappears the effects of such interplate earthquake cycles on five major inland faults in southwest japan where large intraplate earthquakes occurred during this period are quantitatively evaluated using the coulomb failure function cff the calculated change in cff successfully predicts the occurrence of the 1995 kobe earthquake m 7 the occurrence of other inland earthquakes however cannot be explained by the calculated changes in cff and especially the 1891 nobi earthquake m 8 the largest inland earthquake in japan which occurred at the time close to the local minimum of cff this implies that further improvements are necessary for our fem modeling such as the modeling of steady east west compressive force and stress interactions between the inland faults

the amurian plate motion and current plate kinematics in eastern asia we use global positioning system gps velocity data to model eastern asian plate kinematics out of 15 stations in korea russia china and japan studied here three sites considered to be on the stable interior of the hypothetical amurian plate showed eastward velocities as fast as 9 10 mm yr with respect to the eurasian plate they were stationary relative to each other to within 1 mm yr and these velocity vectors together with those of a few additional sites were used to accurately determine the instantaneous angular velocity euler vector of the amurian plate the predicted movement between the amurian and the north american plates is consistent with slip vectors along the eastern margin of the japan sea and sakhalin which reduces the necessity to postulate the existence of the okhotsk plate the euler vector of the amurian plate predicts left lateral movement along its boundary with the south china block consistent with neotectonic estimates of the displacement at the qinling fault possibly the southern boundary of the amurian plate the amurian plate offers a platform for models of interseismic strain buildup in southwest japan by the philippine sea plate subduction at the nankai trough slip vectors along the baikal rift the boundary between the amurian and the eurasian plates are largely inconsistent with the gps based euler vector suggesting an intrinsic difficulty in using earthquake slip vectors in continental rift zones for such studies

active faulting in and along the qinling range china inferred from spot imagery analysis and extrusion tectonics of south china abstract since the beginning of the india asia collision about 2500 km of convergence has been accommodated by crustal thickening in and around the tibetan plateau and by extrusion of tibetan blocks and of the south china block the relative amounts of convergence accommodated by the two mechanisms are however still largely a matter of debate the main purpose of the present study is to determine the rate of left lateral movement between south china and north china during the late cenozoic this movement is accommodated by offsets along the more than 1000 km long e w trending qinling fault system which separates the south china block from the north china block and terminates to the east in the right lateral ndashs trending tanlu fault zone physiographic features typical of active faulting such as triangular facets along scarps and drainage deviations have been observed on spot images throughout the qinling fault system recent active faulting involves both left lateral strike slip and normal dip slip which are partitioned laterally east of the weihe graben two major faults the luonan and danfeng faults of the qinling fault system slip left laterally a cumulative slip rate of about 7 2 2 2 mm yr between the qinling shan south china and the hua shan north china has been estimated using quaternary morphological offsets in contrast the qinling frontal fault which bounds the cenozoic weihe graben to the south exhibits abundant evidence of normal faulting that accommodated large post early eocene vertical displacement in the graben crustal extension estimated from published seismic profiles and boreholes across the weihe graben contributes to a late cenozoic rate of left lateral movement of 2 0 5 mm yr in a n140 e direction between the hua shan and the ordos block combining these yields a rate of left lateral movement of 8 5 2 5 mm yr in a n100 e direction between south china and the ordos block is achieved additionally the ordos block rotates counterclockwise relative to gobi mongolia resulting in nw se crustal extension along the yinchuandashhetao grabens this is estimated from published seismic sections and adds a component of left lateral movement of 4 1 mm yr in a n125 e direction between south china and gobi mongolia the total rate of left lateral movement of south china with respect to gobi mongolia is 12 4 mm yr in a n110 e direction the eastward decrease of the left lateral strike slip on the active qinling fault system may be explained by the partitioning of left lateral movement on the faults bounding the dabie shan to the south and north and by a book shelf mechanism of counterclockwise rotating blocks separated by active ne sw right lateral faults in the dabie shan

big mantle wedge anisotropy slabs and earthquakes beneath the japan sea abstract the japan sea is a part of the western pacific trench arc backarc system and has a complex bathymetry and intense seismic activities in the crust and upper mantle local seismic tomography revealed strong lateral heterogeneities in the crust and uppermost mantle beneath the eastern margin of the japan sea which was determined using p and s wave arrival times of suboceanic earthquakes relocated precisely with sp depth phases ambient noise tomography revealed a thin crust and a thin lithosphere beneath the japan sea and significant low velocity low v anomalies in the shallow mantle beneath the western and eastern margins of the japan sea observations with ocean bottom seismometers and electromagnetometers revealed low v and high conductivity anomalies at depths of 200 300 km in the big mantle wedge bmw above the subducting pacific slab and the anomalies are connected with the low v zone in the normal mantle wedge beneath ne japan suggesting that both shallow and deep slab dehydrations occur and contribute to the arc and back arc magmatism the pacific slab has a simple geometry beneath the japan sea and earthquakes occur actively in the slab down to a depth of 600 km beneath the ne asian margin teleseismic p and s wave tomography has revealed that the philippine sea plate has subducted aseismically down to the mantle transition zone mtz 410 660 km depths beneath the southern japan sea and the tsushima strait and a slab window is revealed within the aseismic philippine sea slab seismic anisotropy tomography revealed a nw se fast velocity direction in the bmw which reflects corner flows induced by the fast deep subduction of the pacific slab large deep earthquakes m 7 0 depth 500 km occur frequently beneath the japan sea western margin which may be related to the formation of the changbai and ulleung intraplate volcanoes a metastable olivine wedge is revealed within the cold core of the pacific slab at the mtz depth which may be related to the deep seismicity however many of these results are still preliminary due to the lack of seismic stations in the japan sea the key to resolving these critical geoscientific issues is seismic instrumentation in the japan sea for which international cooperation of geoscience communities in the east asian countries is necessary

three dimensional structure of p wave anisotropy beneath the tohoku district northeast japan 1 we retrieve three dimensional structures of isotropic and anisotropic velocities of p waves of the tohoku district from first p arrival time data assuming azimuthal anisotropy to be caused by hexagonal symmetry axes distributed horizontally in the earth the results show that the high velocity pacific slab is clearly imaged in the isotropic velocity structure even though the azimuthal anisotropy is taken into account in addition small scale low velocity regions and prominent low velocity anomalies are found just below the active volcanoes and in the mantle wedge above the high velocity pacific slab respectively the fast propagation axis of p waves is in mostly e w direction in the upper crust nearly n s and e w directions in the lower crust e w direction in the mantle wedge and n s direction in the descending pacific slab these features of the p wave anisotropy structure are consistent with those of lateral variations of the fast polarization directions measured previously by shear wave splitting observations the plausible factor that causes the crust anisotropy is interpreted as being alignment or preferred orientation of microcracks and crust minerals the mantle wedge anisotropy is attributed to lattice preferred orientation of the mantle minerals arising from present day mantle process such as the mantle wedge convection and the plate motion however the fast propagation axis of p waves in the slab is almost perpendicular to the magnetic lineation of the oceanic plate under the northwest pacific and thus the slab preserves the original anisotropic property that the pacific plate gained when it formed

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

integration of transient strain events with models of plate coupling and areas of great earthquakes in southwest japan we model the crustal deformation caused by two long term subduction slip transients in southwest japan which we refer to as the 2000 2004 tokai and the 2002 2004 bungo channel slow slip events sses we use re analysed geonet position time series and a kalman filter based network inversion method to image the spatiotemporal slip variation of the two events on the plate interface during the period of 1998 2004 67 and 2000 2005 both events are found to have complex slip histories with multiple subevents in addition to a newly identified slip subevent in 2002 2003 we find that the major event in the bungo channel sse initiated in early 2003 beneath the northeastern corner of the region and expanded southwestward in contrast to the slip characteristics suggested by other studies the re analysed gps data in the tokai region shows a renewed slip activity for the tokai sse in early 2003 2004 at a similar location as in the period of 2001 2002 the equivalent m w for both the tokai and bungo channel sses are about 7 0 our results show that the tokai sse appears to start before the miyaki kozu seismovolcanic event integrating plate coupling and sses shows that the transient slip zones are located in a region between the locked zones and the epicentres of the low frequency earthquakes lfes at least part of the interseismic slip deficit is released by episodic sses beneath the bungo channel region we find excellent temporal correspondence between transient slip and adjacent lfes for both sse suggesting that they are closely related and possibly reflect that long term slow slip may modulate the occurrence of lfes

a transient subduction zone slip episode in southwest japan observed by the nationwide gps array 1 we investigate the spatiotemporal variation of fault slip on the subduction interface in southwest japan following the two 1996 hyuganada earthquakes m 6 7 using continuous gps observations a silent thrust slip event has been reported by hirose et al 1999 following these earthquakes approximately 100 km to the north beneath the bungo channel we employ the network inversion filter to rigorously invert for the fault slip distribution in space and time the gps time series is modeled as a sum of 1 secular deformation 2 coseismic station displacements 3 transient fault slip 4 random benchmark motion 5 reference frame shifts and 6 observational errors nonnegativity constraints effectively prohibit normal faulting on the subduction interface spatial and temporal smoothing parameters are estimated by the extended kalman filter the estimated fault slip rate images postseismic slip following the two hyuganada earthquakes slip associated with the silent thrust event began roughly 1 month after the second earthquake but initiated 100 km to the northeast of the hyuganada earthquakes the slow event propagated southwest and downdip beneath the bungo channel lasting approximately 1 year with maximum slip rates of 0 6 m yr the equivalent seismic moment was mw 7 2 we can rule out the possibility that slip propagated from the source region of the hyuganada earthquakes to the location of the silent earthquake however the timing of the events suggests a causal connection perhaps due to static stress transfer this kind of transient event or silent earthquake may reflect different fault zone characteristics and may be responsible for accommodating strain that would otherwise be released in large earthquakes

independent active microplate tectonics of northeast asia from gps velocities and block modeling 1 independent okhotsk and amurian microplate motions are tested using velocities from 123 gps sites 80 from within the proposed okh and amu plate boundaries used to constrain the plate kinematics of northeast asia a block modeling approach is used to incorporate both rigid block rotation and near boundary elastic strain accumulation effects in a formal inversion of the gps velocities models include scenarios with and without independent okh and amu plate motion our modeling favors scenarios with independent okh and amu motion based on the application of f test statistics the independent okh plate rotates 0 231 deg myr clockwise with respect to north america about a pole located north of sakhalin the modeled amu plate rotates 0 298 deg myr counterclockwise with respect to nam about a pole located west of the magadan region the plate motion parameters of the independent plates are consistent with the kinematics inferred from earthquake focal mechanism solutions along their boundaries

earthquake strain rates and instantaneous relative motions within central and eastern asia summary we use the spatial distribution of moment tensors of earthquakes in this century to estimate the velocity field in asia within a eurasian reference frame in a least squares inversion strain rates on the surface of the earth are matched with continuous spline functions in order to recover the velocity gradient tensor associated with the seismic moment release in asia earthquakes account for 40 60 per cent of the expected motion of india relative to eurasia with the missing component of strain rate equivalent to about 20 mm yr 1 of n s shortening between siberia and india in this solution south china rotates counterclockwise and moves eastwards relative to siberia using rigid plate constraints we next investigate the characteristics of the complete horizontal strain field in asia that accommodates plate motions our strain rate solutions are analogous to the response of a newtonian thin viscous sheet in which the rate of work done by the straining medium in accommodating the velocity boundary conditions is a minimum in these solutions the euler pole for india relative to eurasia is constrained nuvel 1a demets et al 1994 but in the process of fitting the vlbi velocity at shanghai china ward 1994 heki et al 1995 the euler pole for south china is determined in the inversion a solution that both fits the velocity at shanghai china and yields a strain rate field consistent with the earthquake mechanisms is one where the south china block has a motion relative to siberia described by the pole at 51 n 131 e 0 3 deg myr 1 comparison of the complete strain field that accommodates plate motion with the seismic strains indicates that earthquake moment release rates in this century within mongolia are about a factor of 4 larger than the long term rate within gansu ningxia the earthquake moment rates have been about a factor of 2 higher than the long term rate the strike slip faulting within mongolia gansu ningxia western sichuan and yunnan is possibly a direct result of velocity boundary conditions imposed on the south china block by forces unrelated to continental collision of india and eurasia such as forces associated with subduction along the margins of south eastern asia verification of this requires a better understanding of the role of pre existing zones of weakness within the asian continental lithosphere

short term afterslip in the 1994 sanriku haruka oki earthquake the sanriku haruka oki earthquake that occurred on december 28 1994 at the japan trench as a typical interplate thrust event was followed by year long afterslip as large as the slip in the high speed rupture heki et al 1997 here we report on the transition between these inferred from crustal movements during the five days interval before and after the earthquake since this timescale is too long for seismometers but not suitably long for global positioning system gps we rely primarily on strainmeter data taken 200 km southwest of the epicenter to confirm that the recorded strain changes are not local disturbances we compare them with crustal movements derived by high time resolution analyses of gps data in the same period the transition to the long term afterslip was gradually achieved by slow fault slip with a time constant of a few hours the cumulative slow slip in 24 hours amounts to 1 3 of the coseismic slip i e we may overestimate the coseismic displacement if we look at gps data time series composed of daily solutions the result presented here indicates that a single earthquake could have multiple aspects in its slowness visible with different seismological and geodetic tools and we need to use all such data to understand fully such a hybrid earthquake

global plate velocities from the global positioning system we have analyzed 204 days of global positioning system gps data from the global gps network spanning january 1991 through march 1996 on the basis of these gps coordinate solutions we have estimated velocities for 38 sites mostly located on the interiors of the africa antarctica australia eurasia nazca north america pacific and south america plates the uncertainties of the horizontal velocity components range from 1 2 to 5 0 mm yr with the exception of sites on the pacific and nazca plates the gps velocities agree with absolute plate model predictions within 95 confidence for most of the sites in north america antarctica and eurasia the agreement is better than 2 mm yr we find no persuasive evidence for significant vertical motions 3 standard deviations except at four sites three of these four were sites constrained to geodetic reference frame velocities the gps velocities were then used to estimate angular velocities for eight tectonic plates absolute angular velocities derived from the gps data agree with the no net rotation nnr nuvel 1a model within 95 confidence except for the pacific plate our pole of rotation for the pacific plate lies 11 5 west of the nnr nuvel 1a pole with an angular speed 10 faster our relative angular velocities agree with nuvel 1a except for some involving the pacific plate while our pacific north america angular velocity differs significantly from nuvel 1a our model and nuvel 1a predict very small differences in relative motion along the pacific north america plate boundary itself our pacific australia and pacific eurasia angular velocities are significantly faster than nuvel 1a predicting more rapid convergence at these two plate boundaries along the east pacific rise our pacific nazca angular velocity agrees in both rate and azimuth with nuvel 1a

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

initial results from wing the continuous gps network in the western pacific area to investigate tectonic deformation in the western pacific a continuous gps tracking network has been established and named the western pacific integrated network of gps wing between 1995 and march 1997 we establised ten new sites data for the period july 1995 to october 1996 were analyzed together with data from international gps service for geodynamics igs global sites to estimate daily coordinates a fiducial free approach was used to obtain the most accurate baseline estimates to fix the estimated coordinates to the terrestrial reference frame the tsukuba igs site is assumed to be moving westward relative to the stable eurasian continent at 2 cm yr according to heki s 1996 estimate we find that 1 velocities of sites well within oceanic plates are in good agreement with rigid plate motion models 2 sites close to plate boundaries are all affected by the deformation at those boundaries among which back arc rifting spreading is clearly visible at the mariana and okinawa troughs 3 sites in eastern asia are moving east to east southeast relative to the stable eurasian continent suggesting long distance effects of the northward collision of india with asia

the 12 july 1993 hokkaido nansei oki japan earthquake effects of source complexity on surface wave radiation abstract we present an analysis of the data dependency of surface wave inversions for source parameters of the 12 july 1993 hokkaido nansei oki japan earthquake this dependency is demonstrated by differences between source mechanisms obtained from different data sets particularly from rayleigh waves or love waves although inversions of various data sets yield unanimously thrust fault mechanisms for the inversion of rayleigh waves the mechanism is characterized by a shallow dipping west plunging nodal plane which is consistent with p wave first motion data and the distribution of aftershocks close to the hypocenter however for the inversion of both rayleigh and love waves the mechanism is characterized by a shallow dipping east plunging nodal plane several numerical experiments were carried out to test a hypothesis that the data dependency is attributed to the effects of source complexity on the surface wave radiation with the source complexity being characterized by tempo spatial changes in focal mechanism and moment release during the rupture process the experiments show that source parameters obtained from inversions of surface waves with periods as long as a few hundred seconds can be largely affected by using various models of source complexity proposed previously for the hokkaido earthquake and the effects on love waves tend to be systematically different from those on rayleigh waves our preferred source model is characterized by significant tempo spatial changes in focal mechanism the experiments based on this model provide a good explanation for the data dependency although our analysis cannot completely reject the alternative explanation that attributes the dependency to the manifestation of errors in modeling the surface wave propagation and or inversion instability the model is consistent with the data of body waves and long period surface waves for a very broad frequency band implying the existence of weak zones with various fault geometries along the eastern margin of the japan sea

the three dimensional secondary circulation in developing gulf stream meanders from june 1988 until august 1990 an array of 12 inverted echo sounders ies 12 additional ies with pressure gauges to measure the abyssal pressure signal and 12 tall current meter moorings instrumented at depths 400 m 700 m 1000 m and 3500 m was deployed in the gulf stream near 688w the current meter array spanned an area of approximately 260 km by 200 km with nominal horizontal instrument spacing of 56 km in the cross stream direction and 65 km in the downstream direction six events were observed during the two year deployment during which a steep gulf stream meander trough and an abyssal cyclone developed concurrently two of the meander troughs eventually pinched off to form cold core rings as the abyssal flows spun up they became nearly barotropic with strong o 30 cm s21 swirl speeds that advected the main thermocline and helped steepen the meanders although the geostrophic barotropic flow played a large role in the development of the system ageostrophic flow was also required in this study the three dimensional mesoscale ageostrophic flow within the main thermocline is diagnosed during two steep meander trough events and one steep meander crest event it is shown that in addition to the alongstream horizontal ageostrophic flow associated with the curvature of the main jet cyclostrophic speeds greater than 25 cm s21 are not unusual on trough axes there is significant horizontal cross stream ageostrophic flow cross stream ageostrophic flow as high as 18 cm s 21 is diagnosed vertical momentum advection is also shown to be an important contributor to cross stream ageostrophic flow with values as high as 7 cm s 21 diagnosed the patterns of the ageostrophic flow are shown to be tied to the phasing between the upper level meander and the abyssal vortex both rotational and divergent patterns in the ageostrophic flow are evident for parcels on main thermocline isopycnals the ageostrophic flow provides an asymmetric cross frontal flow relative to the symmetric cross frontal flow associated with the barotropic vortices

on the nature and variability of the east greenland spill jet a case study in summer 2003 abstractresults from a high resolution 2 km numerical simulation of the irminger basin during summer 2003 are presented the focus is on the east greenland spill jet a recently discovered component of the circulation in the basin the simulation compares well with observations of surface fields the denmark strait overflow dso and the hydrographic structure of typical sections in the basin the model reveals new aspects of the circulation on scales of o 0 1 10 days and o 1 100 km the model spill jet results from the cascade of dense waters over the east greenland shelf spilling can occur in various locations southwest of the strait and it is present throughout the simulation but exhibits large variations on periods of o 0 1 10 days the spill jet sometimes cannot be distinguished in the velocity field from surface eddies or from the dso the vorticity structure of the jet confirms its unstable nature with peak relative and tilting vorticity terms reaching twice the planetary vorticity term the

western arctic shelfbreak eddies formation and transport abstract the mean structure and time dependent behavior of the shelfbreak jet along the southern beaufort sea and its ability to transport properties into the basin interior via eddies are explored using high resolution mooring data and an idealized numerical model the analysis focuses on springtime when weakly stratified winter transformed pacific water is being advected out of the chukchi sea when winds are weak the observed jet is bottom trapped with a low potential vorticity core and has maximum mean velocities of o 25 cm s 1 and an eastward transport of 0 42 sv 1 sv 106 m3 s 1 despite the absence of winds the current is highly time dependent with relative vorticity and twisting vorticity often important components of the ertel potential vorticity an idealized primitive equation model forced by dense weakly stratified waters flowing off a shelf produces a mean middepth boundary current similar in structure to that observed at the mooring site the model boundary current is also highly v

the east greenland spill jet high resolution hydrographic and velocity measurements across the east greenland shelf break south of denmark strait have revealed an intense narrow current banked against the upper continental slope this is believed to be the result of dense water cascading over the shelf edge and entraining ambient water the current has been named the east greenland spill jet it resides beneath the east greenland irminger current and transports roughly 2 sverdrups of water equatorward strong vertical mixing occurs during the spilling although the entrainment farther downstream is minimal a vorticity analysis reveals that the increase in cyclonic relative vorticity within the jet is partly balanced by tilting vorticity resulting in a sharp front in potential vorticity reminiscent of the gulf stream the other components of the irminger sea boundary current system are described including a presentation of absolute transports

a reappraisal of the 1950 mw 6 9 mondy earthquake siberia and its relationship to the strain pattern at the south western end of the baikal rift zone the precise nature of the transition between the present day compressional tectonics in central mongolia and extensional deformation in the central baikal rift has still to be determined for that purpose we have built a comprehensive earthquake focal mechanism data base for the mongolia southern siberia area from which we map the variations of the stress field we focus our detailed investigations on the largest seismic event in the transition zone the 1950 mw 6 9 mondy earthquake for which several discordant focal mechanisms have been proposed using a new approach in source inversion we resolve the focal mechanism left lateral strike slip type on a steep south dipping fault and depth 14 3 km of the mondy earthquake with a satisfactory accuracy this seismological information combined with the geological observations allows us to decipher the connections between the 1950 mainshock the local stress tensor and the active faults which strongly suggest a partitioning of the deformation between two faults namely the mondy and ikhe ukghun faults

present day kinematics of asia derived from geologic fault rates active fault geometry available quaternary rates on major faults and the far field plate motion are used to determine crustal kinematics in the collision zone between india and asia using a finite element formalism to construct a spherical shell model of the asian continent with embedded faults we seek a velocity solution approaching the motion of rigid blocks by minimizing the elastic strain energy in the fault bounded blocks by doing so we test the assumption that long term deformation within continents is mostly localized into major faults in the solution fault motion accounts for more than 80 of the deformation allowing us to describe our velocity model in terms of quasi rigid block rotations on the sphere south china is rotating clockwise about a pole located southwest of borneo implying an e ese velocity vector of 11 mm yr for a point at shanghai in agreement with the velocity vector determined by very long baseline interferometry heki et al 1995 the eastward movement of south china is accommodated by oblique extension along the red river fault at a rate of 10 5 mm yr in the south and by the combination of left lateral strike slip motion on the qinling dabie shan fault and the counterclockwise rotation of the ordos and adjacent blocks in the north the tarim rotates clockwise with respect to dzungaria about a pole located at 44 n 92 e consistent with increasing crustal shortening toward the west throughout the tien shan assuming incompressibility a crustal volume budget over a domain encompassing the tertiary mountain ranges in asia shows that over the last 10 000 years 73 4 of the north south shortening between india and asia has been absorbed by thickening of the lithosphere and 27 has been accommodated by lateral extrusion of continental blocks the present day predominance of thickening in asia results from the relatively slow eastward motion of south china controlled by strike slip faulting in the qinling shan and oblique extension in northeastern china

comment on high latitude paleomagnetic poles from middle jurassic plutons and moat volcanics in new england and the controversy regarding jurassic apparent polar wander for north america by mickey c van fossen and dennis v kent

coseismic crustal deformation from the 1994 hokkaido toho oki earthquake monitored by a nationwide continuous gps array in japan using a brand new nationwide continuous gps array we monitored coseismic displacements from the october 4 1994 hokkaido toho oki kurile islands earthquake mjma 8 1 based on 2 week time series of site coordinates of 21 gps stations we present a coseismic deformation field of whole hokkaido within 1 cm precision for example the station at nemuro 170 km west of the epicenter moved 44 cm to the east and subsided 10 cm even stations in southern hokkaido 600 km apart from the epicenter moved a few cm horizontally toward the epicenter we compare the gps result with displacements calculated from two preliminary models assuming fault planes parallel or perpendicular to the kurile trench since the observed were far field displacements on land both models can explain the gps result

two configurations of the western arctic shelfbreak current in summer abstractdata from a closely spaced array of moorings situated across the beaufort sea shelfbreak at 152 w are used to study the western arctic shelfbreak current with emphasis on its configuration during the summer season two dynamically distinct states of the current are revealed in the absence of wind with each lasting approximately one month the first is a surface intensified shelfbreak jet transporting warm and buoyant alaskan coastal water in late summer this is the eastward continuation of the alaskan coastal current it is both baroclinically and barotropically unstable and hence capable of forming the surface intensified warm core eddies observed in the southern beaufort sea the second configuration present during early summer is a bottom intensified shelfbreak current advecting weakly stratified chukchi summer water it is baroclinically unstable and likely forms the middepth warm core eddies present in the interior basin the mesoscale instabilities extract energy from the mean flow such

no net rotation model of current plate velocities incorporating plate motion model nuvel 1 we present nnr nuvel1 a model of plate velocities relative to the unique reference frame defined by requiring no net rotation of the lithosphere while constraining relative plate velocities to equal those in global plate motion model nuvel 1 demets et al 1990 differences between nnr nuvel1 and no net rotation plate motion model am0 2 minster and jordan 1978 are as large as 15 mm yr in nnr nuvel1 the pacific plate rotates in a right handed sense relative to the no net rotation reference frame at 0 67 m y about 63 s 107 e this rotation nearly parallels but is 32 slower than the pacific hotspot euler vector of hs2 nuvel1 which is a global model of plate hotspot velocities constrained to consistency with nuvel 1 gripp and gordon 1990 at hawaii the pacific plate moves relative to the no net rotation reference frame at 70 mm yr which is 25 mm yr slower than the pacific plate moves relative to the hotspots differences between nnr nuvel1 and hs2 nuvel1 are described completely by a right handed rotation of 0 33 m y about 49 s 65 e the 99 confidence ellipsoids for plate hotspot motion in model hs2 nuvel1 exclude the corresponding euler vectors from model nnr nuvell thus the no net rotation reference frame differs significantly from the hotspot reference frame if the difference between reference frames is caused by motion of the hotspots relative to a mean mantle reference frame then hotspots beneath the pacific plate move with coherent motion towards the east southeast alternatively the difference between reference frames may show that the uniform drag no net torque reference frame which is kinematically equivalent to the no net rotation reference frame is based on a dynamically incorrect premise possible exceptions to the assumption of uniform drag include a net torque on the lithosphere due to attached subducting slabs and greater resistance to plate motion beneath continents than beneath oceans

evolution of the freshwater coastal current at the southern tip of greenland abstractshipboard hydrographic and velocity measurements collected in summer 2014 are used to study the evolution of the freshwater coastal current in southern greenland as it encounters cape farew

present day tectonic plate motions and crustal deformations from the doris space system doppler orbitography and radiopositioning integrated by satellite doris data acquired between january 1993 and december 1996 from the spot 2 spot 3 and topex poseidon satellites have been analyzed to determine velocities for 45 sites on eight major tectonic plates for 28 sites far from deformation zones the velocity estimates agree with plate model predictions least squares computation of poles of rotation which model the plate motions shows that for eurasia africa pacific and south america plates the agreement is better with nuvel 1 while for australia antarctica nazca and north america plates the doris euler vectors are closer to ntjvel 1a in general doris results do not differ significantly from other space geodetic techniques determinations but provide better estimates for plates poorly or inhomogeneously covered by global positioning system gps very long baseline interferometry vlbi and satellite laser ranging slr networks such as africa the doris coverage of this plate allows discussion of intraplate deformations due to the motion of the eastern africa part which constitues the somalia plate sites located in deformation zones such as western eurasia boundaries central asia southwestern america coast south east asia show motion with respect to their own plates comparisons with other geodetic measurements for colocated stations or with regional geodynamical models show the interest of doris in active zones where global plate models are not valid

crustal deformation at the nankai subduction zone southwest japan derived from gps measurements the interseismic strain accumulation process at the nankai subduction zone the plate boundary region between the philippine sea and the eurasian plates off southwest japan has been revealed by gps measurements spanning five years large strains characterized by a contraction of 2 2 3 4 10 7 yr have accumulated in a narrow region extending parallel to the strike of the plate boundary the contraction axes lie in a northwest southeast direction nearly parallel to the direction of relative motion of the philippine sea plate with respect to the eurasian plate gps derived deformation data including both rate and direction are consistent with the expected earthquake deformation cycle at the nankai subduction zone current interplate coupling in this zone is strong much of the relative plate motion has been taken up by deformation of the marginal parts of the eurasian plate

synthesizing the gulf stream thermal structure from xbt data abstract thirty six xbt temperature profiles have been used in a parametric model introduced by hendry to model the gulf stream s thermal structure at 65 w between 200 and 1200 dbar with an rms residual error of 0 56 c velocity has been computed geostrophically relative to 1200 dbar and has been included in calculating potential vorticity analytically from the model the resulting potential vorticity section for 65 w has been compared with the analogous result from hendry s parametric model at 59 w as well as observed potential vorticity sections from 68 to 55 w there is a significant feature in the potential vorticity structure at 65 w not found at 59 w namely a relative minimum in potential vorticity along isopycnals centered at the gulf stream s axis and 350 dbar the modeled potential vorticity sections are consistent with the observation including the downstream disappearance of this feature the dynamical implications of these results are briefly discussed

on the effect of topography and wind on warm water inflow an idealized study of the southern weddell sea continental shelf system an idealized eddy resolving numerical model with topographic features common to the southern weddell sea is constructed to study mechanisms through which warm deep water enters a wide continental shelf with a trough the open ocean represented by a 1700 m deep channel is connected to a 400 m deep shelf with a continental slope the shelf is narrow 50 km in the east but widens to 300 km at the center of the model domain over the narrow shelf the slope front is balanced by wind driven ekman downwelling and counteracting eddy overturning favoring on shelf transport of warm water in summer scenarios when fresher surface water is present over the wide shelf the ekman downwelling ceases and the mesoscale eddies relax the front inflow of warm water is sensitive to along shelf salinity gradients and is most efficient when denser water over the wide shelf favors up slope eddy transport along isopycnals of the v shaped slope front inflow along the eastern side of the trough cannot penetrate the sill region due to potential vorticity constraints while along the western trough flank eddy induced inflow crosses the sill and reaches the ice front the warm inflow into the trough is sensitive to the density of the outflowing dense shelf water for weaker winds absence of the dense water outflow leads to a reversal of the trough circulation and a strong inflow of warm water while for stronger winds baroclinic effects become less important and the inflow is similar to experiments including dense water outflow this article is protected by copyright all rights reserved

crustal deformation in the baikal rift from gps measurements three years and four campaigns of global positioning system gps measurements 1994 1997 in the baikal rift zone largest active continental rift system in eurasia show crustal extension at a rate of 4 5 1 2 mm yr in a wnw ese direction a comparison with moment release of large historical earthquakes suggests that elastic strain is currently accumulating in the baikal rift zone along active faults that currently have the potential for a m 7 5 earthquake the gps derived extension rate in the baikal rift zone is at least two times greater than the prediction of most deformation models of asia this result could reflect the dynamic contribution of the pacific eurasia subduction to intracontinental deformation in asia in addition to the effect of the india eurasia collision

geodynamics of the baikal rift zone and plate tectonics of asia the baikal rift zone stretches from the southern termination of lake baikal as far as 118 e and includes the baikal basin and the barguzin upper angara and muysk grabens that form its easterly continuation coincident with the rift zone is a narrow seismic belt which extends further east along the stanovoy range to the okhotsk sea this belt can be considered as the boundary between the eurasian and amurian lithospheric plates earthquake focal mechanism solutions that show a consistent orientation of extensional axes across the strike of the rift zone indicate the behaviour of the eurasian and amurian plates as rigid bodies from 83 focal mechanism solutions the pole of rotation of the eurasian and amurian plates was computed to lie at the point 56 95n 117 45e the angular rate estimated from the amount of baikal opening is about 1 10 7 deg year the position of the pole at the eastern termination of the rift zone accounts for the dying out of the rift zone and for the appearance east of the pole of compressive structures in the stanovoy range to the southwest the baikal rift zone is replaced by the mosaic of microplates in central asia that occupy the space between the eurasian and indian lithospheric plates prominent are the mongolian dzungarian alashan tarim tibetan and pamir microplates earthquakes in central asia are dispersed although higher concentrations of earthquakes associated with microplate boundaries are prominent the tectonics of central asia are considered to be due to the interaction of rigid microplates assuming that plastic deformations occur within the relatively wide zones along the microplate boundaries by considering the strike slip faults to define the trajectories of microplate motions the parameters of relative movements of the microplates have been computed the microplate mosaic of central asia is moving northeasterly as a result of the collision and continued convergence of india and eurasia the mosaic acts as a wedge splitting off the amurian plate from eurasia causing it to rotate counterclockwise so opening the baikal rift

three dimensional isoneutral potential vorticity structure in the indian ocean the three dimensional isoneutral potential vorticity structure of the indian ocean is examined using world ocean circulation experiment and national oceanic and atmospheric administration conductivity temperature depth data and historical bottle data the distribution of the potential vorticity is set by the indian ocean s source waters and their circulation inside the basin the lower thermocline has a high potential vorticity signal extending westward from northwest of australia and a low signal from the subantarctic mode water in the south the antarctic intermediate water inflow creates patches of high potential vorticity at intermediate depths in the southern indian ocean below which the field becomes dominated by planetary vorticity indicating a weaker meridional circulation and weaker potential vorticity sources wind driven gyre depths have lower potential vorticity gradients primarily due to same source waters homogenization and western shadow zones are not observed the effect dominates the effect of the somali current and the red sea water on the potential vorticity distribution isopleths tilt strongly away from latitude lines in the deep and abyssal waters as the circumpolar deep water fills the basins in deep western boundary currents indicating a strong meridional circulation north of the antarctic circumpolar current the lower gradient intermediate layer surrounded vertically by layers with higher meridional potential vorticity gradients in the subtropical indian ocean suggests that rossby waves will travel 1 3 times faster than standard theory predicts to the south several pools of homogenized potential vorticity appear in the upper 2000 m of the southern ocean where gyres previously have been identified south of australia the abyssal potential vorticity structure is set by a combination of the antarctic circumpolar current and the bathymetry

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

crustal deformation and stress localization in kanto tokai central japan revealed by gps summary horizontal deformation associated with plate interaction in the kanto tokai district central japan has been determined using the japanese permanent global positioning system gps array with an accuracy of better than 2 5 mm yr 1 previous analysis of the gps observations mainly focused on the pattern of deformation or strain and did not attempt to assess stress change associated with plate subduction in this study using the gps observations and the geometry of subducting slabs as constraints we constructed a 3 d kinematic model to simulate the subduction of the philippine sea plate at the suruga and sagami troughs and the pacific plate at the japan trench the model incorporating the effects of major plate driving forces ridge push slab pull and drag force associated with plate subduction provides an overall fit to the horizontal deformation observed by gps during 1996 2001 in the kanto tokai region the horizontal motion of the philippine sea plate is estimated to be 41 5m m yr 1 60 5 nw consistent with that ca 43 50 mm yr 1 inferred from earthquake slip vectors and geological data the horizontal motion of the pacific plate is estimated to be 78 6m m yr 1 84 5 nw close to that ca 73 79 mm yr 1 deduced from earthquake slip vectors after extracting the regional deformation associated with subduction of the philippine sea and pacific plates from the gps observations two types of motion trends are revealed for the northern part of the kanto tokai region the southeastward motion of the gps stations revealed by the residual displacements in northern tokai indicates a possible resistance force from the north in northern kanto the west southwestward residual motion of the gps stations indicates the motion of the north american plate relative to the eurasian plate the distinct boundary between these two different types of motion trends provides strong support for the presence of the north american plate in the region which demonstrates that the model has delineated the main characteristics of plate interaction further a stress analysis indicates that stress is accumulating on the suruga trough at a rate of approximately 0 7 bar yr 1 at a depth of 15 km our results indicate that the pattern of stress localization is mainly controlled by the kinematic characteristics of the subducted slabs geometry and slip distribution and the persistent stress concentration is responsible for repeated large interplate earthquakes in the region

interplate coupling along the nankai trough off southwest japan derived from gps measurements we investigate interplate coupling between the philippine sea and the eurasian plates at the nankai trough off southwest japan during the interseismic period plate coupling is modeled by imaginary backward normal slip superposed on the steady state subduction we divide the plate interface into several segments and estimate coupling on each segment from gps horizontal velocity data estimated coupling is in general agreement with the rate of steady state subduction predicted from a plate motion model this implies that current coupling at the nankai trough is so strong that much of the relative plate motion is taken up by shortening of the leading edge of the overriding plate it seems that stronger interseismic coupling is realized on the segment where larger coseismic dislocation occurred and vice versa time fluctuation of plate coupling from 1995 to 1996 is found on a small segment

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

plate convergence and long term crustal deformation in central japan surveys by continuous global positioning system in and around japan revealed that the amurian plate collides with the north american plate in central japan by 2 cm yr long term crustal deformation seems to be influenced mainly by this collision although subduction of oceanic plates governs short term elastic deformation over the arc here we study the long term deformation field by carefully removing the short term signals inferred from a priori plate convergence vectors and coupling strengths predicted by a thermal model the obtained field shows that the change in velocities occurs along the longitude 135 137 and there exist a relatively rigid block and zones accommodating strains characteristic compressional deformation is found northwest of izu due possibly to the collision of the izu bonin arc with honshu plate convergence rate along the nankai suruga trough is considerably smaller in eastern parts due partly to the transition from the amurian to the north american plate of the landward side and partly to the motion of the izu microplate relative to the philippine sea plate this accounts for longer recurrence intervals of interplate earthquakes in the suruga trough where the tokai earthquake is anticipated to occur

a rigid block rotation model for the gps derived velocity field along the ryukyu arc abstract using a gps derived velocity field we try to estimate the kinematic features of the ryukyu arc and discuss its implications to the spreading of the okinawa trough the gps derived strain rate field implies that internal deformation within the ryukyu arc is not significant therefore we adopt a rigid block rotation model for the motion of the ryukyu arc the velocity field in the ryukyu arc is best explained by a model with three blocks rather than one with only one block the estimated block rotations predict the spreading along the okinawa trough the predicted spreading is slow 10 mm per year in the north and fast 50 mm per year in the southwest the direction of the predicted spreading is normal to the okinawa trough n170 e n180 e in the southwest while in the north the direction of the spreading is oblique to the okinawa trough n150 e n180 e