active faulting at the eurasian north american and pacific plates junction abstract the active faults known and inferred in the area where the major pacific north american and eurasian plates come together group into two belts one of them comprises the faults striking roughly parallel to the pacific ocean margin the extreme members of the belt are the longitudinal faults of islands arcs in its oceanic flank and the faults along the continental margins of marginal seas in its continental flank the available data show that all these faults move with some strike slip component which is always right lateral we suggest that characteristic right lateral either partially or dominantly kinematics of the fault movements has its source in oblique convergence of the pacific plate with continental eurasian and north american plates the second belt of active faults transverses the extreme northeast asia as a continental extension of the active mid arctic spreading ridge the two active fault belts do not cross but come close to each other at the northern margin of the sea of okhotsk marking thus the point where the pacific north american and eurasian plates meet

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

low vp vs ratios in the crust and upper mantle beneath the sea of okhotsk inferred from teleseismic pmp smp and sms underside reflections from the moho 1 teleseismic ground motion recordings of deep earthquakes often contain clear seismic wave reflections from the free surface above the source pp sp ss with isolated precursors pmp smp and sms produced by underside reflections from the moho the crust mantle boundary below the free surface reflection points the waveforms of the depth phases and their precursors are readily modeled providing constraints for steep angles of incidence on integrated two way crustal travel times and moho shear and compressional impedance contrasts above deep earthquake source regions we model surface reflection waveforms in stacks of three component long period wwssn and digital broadband seismograms for signals traversing the crust and upper mantle beneath the sea of okhotsk which overlies deep earthquakes in the subducted kurile slab the crust beneath most of the sea of okhotsk is 19 25 km thick indicating a submerged continental margin with minor crustal thinning toward the kuril back arc basin where thin oceanic crust is found modeling pmp and sms phases that sample the same subregion provides tight constraints on the vp vs ratio in the crust and uppermost mantle assuming common density structure and consistent crustal thickness for p and s waves the absolute velocities are not constrained by the data we find unusually low vp vs ratios in the range 1 6 1 7 for the uppermost mantle under the sea of okhotsk and comparably low average vp vs ratios for the crust in several regions the presence of fluids and extensive silica enrichment possibly involving low temperature veining are viable explanations for the anomalous vp vs ratios this may represent an important process of continentalization taking place landward from the volcanic arc in subduction zones

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

active deformation of the continents whereas relatively narrow bands of deformation define oceanic plate boundaries in continental situations deformation is shown to be distributed over much broader zones the complex and heterogeneous nature of boundary regions between major plates is outlined with reference to the mediterranean and the himalayas relatively aseismic regions have traditionally been defined as microplates but although they are presently acting as rigid blocks undergoing slow deformation it is argued that this need not always have been the case and that deformation may simply have moved elsewhere broad zones of deformation surrounding rigid blocks are highlighted as fundamental to the analysis and interpretation of continental tectonics detailed theoretical consideration is given to the kinematics of distributed formation and the dynamics of continental deformation a j barker

explosion contamination of the northeast siberian seismicity catalog implications for natural earthquake distributions and the location of the tanlu fault in russia russian regional seismicity catalogs including those in the annual earthquakes of the ussr are contaminated by industrial explosions in northeastern russia explosions occur in tin coal and gold mines as well as in the construction of roads railways and dams most seismically recorded mining and construction related explosions have magnitudes of about 2 0 and occur during local daytime in addition explosions in placer mining areas are concentrated from midwinter to early spring when frozen placers are broken up for the summer processing season we analyzed the temporal variation of over 87 000 events occurring in northeast russia using a newly compiled seismicity catalog to identify areas where there may be explosion contamination areas with temporal biases indicative of mining or other explosions include the yana river delta and chukotka placers the southern amur district coal mining the trace of the baikal amur railroad construction lazo quarry the south yakutian gold fields and the kolyma gold belt the locations and estimates of the level of explosion contamination of the catalog suggest that the natural seismicity may be lower and not as diffuse along the plate boundaries in northeastern russia than previously thought use of only nighttime events from the seismicity catalog which should have a minimum of explosions helps to clarify the extension of the tanlu fault into russia and may ultimately help elaborate tectonics in other areas of eastern russia

stress modeling of tectonic blocks at cape kamchatka russia using principal stress proxies from high resolution sar new evidence for the komandorskiy block abstract a new data set of 851 lineaments mapped from european remote sensing satellites 1 and 2 full resolution synthetic aperture radar sar data are interpreted as geological proxies for stresses resulting from plate and block collision near the cape kamchatka region of the kamchatka peninsula using a geographical information systems based analysis numerical manifold method nmm analysis is used to model the stress field within the cape kamchatka region resulting from the collision of lithospheric plates and blocks results of our nmm model using different plate motion and plate configuration in the region are compared with orientation data for the mapped set of lineaments these data suggest that the lineaments observed in sar cannot be fully explained by a simple two plate model in this in the cape kamchatka region as an alternative we propose that the data can be explained by the existence of the previously proposed komandorskiy block recent global positioning satellite measurements in the aleutian islands support our lineament derived model and show that the near islands komandorskiy island block of the extreme western aleutians is moving independently of the north american plate

coastal atmospheric forcing in the northern gulf of alaska a comparison of winds over the northern gulf of alaska found measured winds to be significantly weaker than calculated geostrophic winds the latter required more than the standard 30 reduction to correct for frictional effects in the maritime boundary layer an additional 11 is calculated based on principal axis analysis a counterclockwise rotation of the instantaneous geostrophic wind vectors of 44 59 total beyond the standard 15 was required to align them with those measured at a coastal weather station however events in these two wind sets were well correlated throughout the year and the rotary coherence was significant for frequencies lower than 0 895 cpd on the basis of empirical orthogonal function analysis most of the seasonal variability in this coastal current is associated with wind changes freshwater discharge is also important in driving the alongshore baroclinic flow and a secondary cross shelf flow

the nearshore current along a high rainfall trade wind coast nicaragua abstract runoff from abundant rainfall on the watersheds along the east coast of nicaragua results in a well defined nearshore current extending 20 40 km out from the coast important terms in the controlling dynamical balance are the coriolis forces and eddy frictional forces calculations of the diabathic surface slope 0 10 5 show a smooth setup of 4 5 cm from the outer edge of the current to the shoreline a longshore surface slope of 0 10 8 appears to be set up by the longshore wind stress and further computations allow an estimate of 6 gr cm 1 s 1 for the dynamic eddy viscosity an analytical expression including diabathic surface slope and density gradient parabathic surface slope wind stress and quadratic bottom friction reproduces the salient observed features of the nearshore current these include the pronounced maximum in the parabathic along shelf current about 10 km off the coast a complex diabathic velocity structure and a shelf countercurrent just seaward of the outer edge further calculations suggest that the dominant driving arises from the freshwater induced density gradients accounting for upward of 80 of the flow velocity as suggested by royer 1982 the prevailing trade wind exerts an onshore wind stress that serves the important role of maintaining the integrity of the density gradients via the convergence of a surface ekman layer toward the coast

geodynamic implications of paleomagnetic data from tertiary sediments in sakhalin russia nw pacific 1 n s trending right lateral strike slip faults which were active in the tertiary transect sakhalin russia while mesozoic forearc and accretionary rocks testify to an earlier period of subduction several kinematic models have been proposed for the region but the details required to constrain these models such as the timing of the transition from subduction to strike slip tectonics in sakhalin are still unknown even first order tectonic features such as the boundaries of the plates with which sakhalin evolved during the tertiary are poorly known paleomagnetic results from around sakhalin were obtained to constrain the geodynamic evolution of the region comparison of paleomagnetic inclination data with the apparent polar wander paths for the eurasian pacific and north american plates suggests that sakhalin probably evolved with the north american plate although a history including the eurasian plate cannot be ruled out paleomagnetic declination data suggest that significant clockwise vertical axis rotation has occurred in sakhalin since the mid paleocene it is likely that this rotational deformation was accommodated by tertiary activity on right lateral strike slip faults which may be associated with the opening of the japan sea tatar strait and kuril basin these data contradict a published kinematic model for eastern sakhalin where counterclockwise vertical axis rotations were predicted for neogene basins in the east sakhalin mountains agreement is better however with published paleomagnetic data from southern sakhalin where clockwise vertical axis rotations were documented

mantle flow at a slab edge seismic anisotropy in the kamchatka region the junction of the aleutian island and the kamchatka peninsula defines a sharp turn in the boundary of the pacific and north american plates terminating the subduction zones of the northwest pacific the regional pattern of shear wave birefringence near the junction indicates that trench parallel strain follows the seismogenic benioff zone but rotates to trench normal beyond the slab edge asthenospheric mantle is inferred to flow around and beneath the disrupted slab edge and may influence the shallowing dip of the benioff zone at the aleutian junction

ancient subduction zone in sakhalin island abstract the northern part of sakhalin island is an area of recent intensive tectonic movements and hydrothermal processes as well as a place of accumulation of useful minerals the deep structure of the lithosphere beneath the region of the neftegorsk earthquake of may 27 1995 in north sakhalin which killed residents and caused significant destruction is examined in this paper our geodynamic model shows that north sakhalin consists of the north sakhalin basin deryugin basin and an ophiolite complex located between them the deryugin basin was formed in place of an ancient deep trench after subducting the okhotsk sea plate under sakhalin in the late cretaceous paleogene the north sakhalin basin was formed on the side of the back arc basin at that time the ophiolite complex is fixed in the position of ancient subduction zone that was active in the late cretaceous paleogene approximately in the miocene the subduction of the okhotsk lithosphere apparently ceased the remains of the subduction zone in the form of an ophiolite complex have been identified from geological and geophysical data on the surface the subduction zone is manifested as deep faults stretched along sakhalin it is probable that the neftegorsk earthquake was a result of activation of this ancient subduction zone

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

physical processes and sedimentation on a broad shallow bank an integrated study of the meteorology physical oceanography sedimentationand coastal morphology on the broad shallow miskito bank off the eastern coast of nicaragua has uncovered systematic interrelationships between driving forces bank geometry and sedimentologic environments on the bank extremely high rainfall results from an interaction between meteorological processes over the bank and topographic effects along the coast both acoustic and radio sounding of the lower atmosphere have documented the feedback between convective plumes inversion layers and the incessant rainfall which brings three times more freshwater and 15 times more sediment down to a unit length of coast than on the u s atlantic shore the resultant brackish turbid coastal water moves as a highly organized band of water parallel to the coast seaward of this coastal boundary layer offshore water from the caribbean current rides up on the bank and provides an environment ideal for carbonate production a zone of fine grained terrigenous sediment underlying the coastal boundary current merges abruptly into a smooth carbonate plain covering most of the surface of the bank these central bank carbonates are composed primarily of the disintegration products of prolific calcareous green algae a trend of high relief luxuriant coral reef growth is aligned along the steep dropoff at the bank edge a zone of observed upwelling of cooler and saltier basin water a threefold southerly increase in wave energy at the shoreline due to the decreasing width of the shallow shelf results in wave dominated coastal morphologies in the south compared to fluvial domination in the north and a systematic change from straight linear bars and beaches in the north to rhythmic topography in the south

earthquake recurrence and magnitude and seismic deformation of the northwestern okhotsk plate northeast russia 1 recorded seismicity from the northwestern okhotsk plate northeast asia is currently insufficient to account for the predicted slip rates along its boundaries due to plate tectonics however the magnitude frequency relationship for earthquakes from the region suggests that larger earthquakes are possible in the future and that events of mw 7 5 which should occur every 100 350 years would account for almost all the slip of the plate along its boundaries due to eurasia north america convergence we use models for seismic slip distribution along the bounding faults of okhotsk to conclude that relatively little aseismic strain release is occurring and that larger future earthquakes are likely in the region our models broadly support the idea of a single okhotsk plate with the large majority of tectonic strain released along its boundaries

coastal fresh water discharge in the northeast pacific very high annual rates of precipitation in the coastal mountains that border the northeast pacific ocean produce large fresh water discharges 23000 m3 s 1 this discharge has been ignored previously since it does not enter the ocean in the form of large rivers but instead the water enters by way of numerous small rivers and streams thus it acts as a line source instead of a point source this coastal discharge contributes at least 40 of the fresh water that enters the northeast pacific from the atmosphere the discharge is comparable to the mean annual discharge of the mississippi river system the fresh water creates a cross shelf density gradient that drives an alongshore baroclinic jet the width of this jet is less than 25 km with speeds in excess of 100 cm s 1 it extends along the coast from southeast alaska to at least kodiak island apparently the flow is maintained as a narrow current adjacent to the coast by wind stress that causes downwelling conditions here throughout most of the year

ocean currents along a nearshore frontal zone on the continental shelf of the southeastern united states abstract river and estuarine discharges mix to form a frontal zone along a 400 km length of the coast of the south eastern united states the frontal width extends from the coast outward 10 20 km two ships anchored across the frontal zone during autumn obtained simultaneous hourly profiles of currents and density for five consecutive tidal cycles the frontal zone contained a baroclinic coastal current flowing southward the flow was strongly convergent more water entered on the coastal side than exited on the seaward side much of the inflow was apparently turned southward thus the frontal zone acted as a dynamic barrier that inhibited the advection of mixed river discharge farther offshore a thermal wind relationship suitably predicted vertical shear through the frontal zone bottom friction seemed to play only a secondary role data suggest that the baroclinic coastal current was modified by the presence of a barotropic current seaward of the frontal zone the force responsible for the barotrop

paleomagnetism of a late cretaceous island arc complex from south sakhalin east asia convergent boundaries far away from the asian continental margin the hokkaido sakhalin fold system stretches for 1500 km along the eastern coast of asia and consists of several n s trending tectonic belts studies in south sakhalin show that the northern part of the tonino aniva peninsula ozersk unit is a counterpart of the tokoro belt on hokkaido japan in the eastern part of the ozersk unit 195 hand samples were sampled at 20 sites from campanian maastrichtian tuffaceous siltstones and sandstones of the chayka formation of island arc affinity stepwise thermal demagnetization isolates a postfolding low to intermediate temperature component b of normal polarity a high temperature component a is isolated from about half the samples because of strong overlap of unblocking temperature spectra of these two components in other samples direct observations and remagnetization circles were combined for calculation of site mean directions component a is mostly of reversed polarity a few samples of normal polarity are found at three sites the presence of two polarities with approximately antipodal directions and the positive fold test imply a prefolding and most probably primary origin of component a a formation mean inclination of 45 0 6 4 calculated with the aid of inclination only statistics corresponds to a latitude of 26 6 5 2 n a similar inclination is derived from a late cretaceous island arc complex from the tokoro belt on hokkaido since both mean inclinations are 30 lower than the coeval eurasian reference value a large scale northward transport of the entire tokoro island arc is inferred we exclude the possibility of displacement with the kula plate and coast parallel transport instead intra oceanic motion with the pacific plate and docking at the eurasian margin at circa 30 ma are inferred combined paleomagnetic data from the tokoro belt the nemuro belt and kamchatka region imply that a system of intra oceanic island arcs existed in the northwest pacific in late cretaceous time

a high resolution model for eurasia north america plate kinematics since 20 ma summary we derive the first chronologically detailed model of eurasia north america plate motion since 20 ma from ship and airplane surveys of the well expressed magnetic lineations along this slowly spreading plate boundary including previously unavailable dense russian magnetic data from the southern reykjanes ridge and northern mid atlantic ridge near the charlie gibbs fracture zone from more than 7000 crossings of 21 magnetic anomalies from anomaly 1n 0 78 ma to anomaly 6n 19 7 ma we estimate best fitting finite rotations and realistic uncertainties linear regressions of total opening distances versus their reversal ages at different locations along the plate boundary show that reversal boundaries are shifted systematically outwards from the spreading axis with respect to their idealized locations with the outward shift ranging from more than 5 km between iceland and the charlie gibbs fracture zone to 2 km elsewhere this outward displacement which is a consequence of the finite zone of seafloor accretion degrades estimates of the underlying plate motion and is thus removed for the ensuing kinematic analysis the corrected plate motion rotations reveal surprising previously unrecognized features in the relative motions of these two plates within the uncertainties motion was steady from 20 to 8 ma around a pole that was located 600 km north of the present pole with seafloor spreading rates that changed by no more than 5 per cent 1 mm yr 1 along the reykjanes ridge during this period seafloor spreading rates decreased abruptly by 20 2 per cent at 7 5 6 5 ma coinciding with rapid southward migration of the pole of rotation and a5 10 counter clockwise change in the plate slip direction eurasia north america plate motion since 6 7 ma has remained remarkably steady with an apparently stationary axis of rotation and upper limit of 2 per cent on any variations in the rate of angular rotation during this period based on the good agreement between seismotectonic constraints on present deformation in northeast asia and directions of motion that are predicted by our 6 7 ma to present pole we hypothesize that motion has remained steady to the present and attempt to test this hypothesis with published gps estimates for eurasia north america motion we find however that gps estimates that are tied to recent versions of the international geodetic reference frame and rely principally on station velocities from europe give implausible estimates of recent motion with the most recently published gps model predicting convergence along the southern gakkel ridge and in the laptev sea where seafloor spreading occurs an alternative gps estimate that is not tied to the international terrestrial reference frame and employs gps station velocities from northeastern asia is marginally consistent with our 6 7 0 ma motion estimate

asymmetric deformation in the backarc region of the kuril arc northwest pacific new insights from analogue modeling 1 the eocene to middle late miocene tectonic evolution of the kuril arc and backarc region has been simulated with analogue experiments the experiments simulate asymmetric deformation in the overriding plate due to anticlockwise rollback of the subducting pacific plate the results show the formation of a n s to ne sw oriented dextral shear zone near the far edge of the retreating boundary analogous to the sakhalin hokkaido dextral shear zone contemporaneously normal faults and grabens form striking parallel to the retreating boundary near the far edge but striking more oblique near the hinge point and away from the retreating boundary this is similar to extensional structures observed in the kuril basin and the sea of okhotsk furthermore the model shows that the amount of extension progressively decreases away from the retreating boundary this appears to have also happened in the kuril okhotsk region as evidenced by crustal thickness variation in the region finally the model results show that extension is increasingly accommodated by the region close to the retreating boundary with progressive deformation this can account for the eocene early miocene extension in the sea of okhotsk followed by miocene spreading in the kuril basin

tectonics of the laptev sea and moma rift systems northeastern ussr abstract examination of the topography seismicity focal mechanisms and structure of the extension of the arctic mid ocean ridge into the laptev sea suggests that the present day features of the upper crust are consistent with an asymmetric simple shear extensional system on a large scale the topographically high upper plate side alternates from severnaya zemlya and taimyr peninsula across the rift zone to the new siberian islands and then back across to the kharaulakh range and the omoloi river basin the activity of this system is indicated by moderate size normal faulting earthquakes and the extensive development of extensional structural features a weakly developed axial graben with a few teleseismic earthquakes is developed in the eastern laptev sea further south a nw striking pliocene rift system commonly known as the moma rift extends through the northern cherskii range although there is a broad zone of elevated heat flow and isolated volcanoes this system is transpressional at the present time the zone of major seismicity passes south of the rift system near the indigirka river and indicates that the rift is not acting as the plate boundary the moma rift is also asymmetric but with the lower plate southwest side being topographically higher the moma system is inactive along most of its length and only reached an early stage of development before activity ceased

the latest cretaceous early paleogene rapid growth of accretionary complex and exhumation of high pressure series metamorphic rocks in northwestern pacific margin episodic growth of accretionary complexes along the northwestern pacific margin is well documented from detailed biostratigraphy and radiometric dating of metamorphic rocks the latest cretaceous to early paleogene rapid growth of the accretionary complexes observed in hokkaido and sakhalin islands was caused by the supply of a large amount of terrigenous sediments from an intracontinent collision zone the mongolia okhotsk zone in the northern asian continent rapid growth of the accretionary prism resulted in episodic tectonic events in the forearc and magmatic arc rapid underplating caused uplift and exhumation of previously accreted complexes along with high pressure series metamorphic rocks now exposed as the kamuikotan complex in hokkaido and the susunai complex in sakhalin the forearc basin shallowed as a result of the uplift the uplift collapsed the old accretionary complex and supplied olistoliths onto the forearc region magmatic activity along the continental margin was also active at the same time subduction of a large amount of terrigenous sediments into the mantle may have contributed to active magmatism at that time a large supply of water trapped in the subducted sediments entered the mantle and increased partial melting of the mantle wedge

transport and fate of river discharge on the continental shelf of the southeastern united states the authors analyzed 8 years of wind and salinity data from a frontal zone in a region of the inner continental shelf off the southeastern united states the changes in low salinity water stored in the frontal zone have been parameterized by analyzing the monthly rate of change in freshwater content when the rate of change in freshwater content was negative this was interpreted as a loss of low salinity water from the frontal zone when this parameter was compared with seasonally averaged alongshore wind stress the rate of loss was independent of the alongshore wind stress magnitude until threshold of about 0 1 dyne cm sup 2 was reached above the threshold there was a clear relationship between northward alongshore wind stress and rate of loss of freshwater from the inner shelf experimental evidence suggests that horizontal currents in the inner shelf frontal zone have cyclonic shear with increasing depth when wind stress is northward and offshore near surface low salinity water is transported offshore by ekman transport while near bottom high salinity water is transported shoreward 9 figures 2 tables

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

large scale deformation related to the collision of the aleutian arc with kamchatka the far western aleutian island arc is actively colliding with kamchatka westward motion of the aleutian arc is brought about by the tangential relative motion of the pacific plate transferred to major right lateral shear zones north and south of the arc early geologic mapping of cape kamchatka a promontory of kamchatka along strike with the aleutian arc revealed many similarities to the geology of the aleutian islands later studies support the notion that cape kamchatka is the farthest west aleutian island and that il has been accreted to kamchatka by the process of arc continent collision deformation associated with the collision onshore kamchatka includes gravimetrically determined crustal thickening and formation of a narrow thrust belt of intensely deformed rucks directly west of cape kamchatka the trend of the thrust faults is concave toward the collision zone indicating a radial distribution of maximum horizontal compressive stress offshore major crustal faults trend either oblique to the kamchatka margin or parallel to major aleutian shear zones these offshore faults are complex accommodating both strike slip and thrust displacements as documented by focal mechtmisms and seismic reflection data earthquake activity is much higher in the offshore region within a zone bounded to the north by the northernmost aleutian shear zone and to the west by an apparent aseismic front analysis of focal mechanisms in the region indicate that the present day arc continent contact zone is located directly east of cape kamchatka in modeling the dynamics of the coiiision zone using thin viscous sheet theory the rhealogical parameters are only partially constrained to values of n the effective power law exponent 2 3 and ar the argand number s 30 these values are consistent with a fnrcarc thermal profile of kamchatka previously determined from heat flow modeling the thin viscous sheet modeling also indicates that onshore thrust faulting is a consequence not only of compressive stresses resulting from the west directed collision but also of sediment induced coupling of the subducting pacific plate

cenozoic intracontinental dextral motion in the okhotsk japan sea region a right lateral shear zone trending northerly along more than 2000 km is recognized from central japan to northern sakhalin it was active mainly during the neogene and has accommodated several hundreds of kilometers of displacement the whole structure of sakhalin is built on this shear zone en echelon sigmoidal folds and thrusts en echelon narrow miocene basins and a major discontinuity which is observed along more than 600 km the tym poronaisk fault characterize the deformation there in hokkaido en echelon folds and thrusts and a ductile shear zone with high temperature metamorphism constitute the southern extension of this transpressional shear zone it continues to the south as a zone of transtensional deformation along the eastern margin of japan sea as en echelon basins and dextral transfer faults observed as far south as noto peninsula and yatsuo basin the style of the shear zone thus evolves from transpressional in the north far from the subduction zone to transtensional in the south in the back arc region strike slip motion along this shear zone was primarily responsible for the dextral pull apart opening of japan sea during the early and middle miocene dextral motion is still active in the north along the tym poronaisk fault in sakhalin as well as on the continental margin of japan sea korea and asia mainland active e w compression replaced the dextral motion along the eastern margin of japan sea in late miocene time and incipient subduction began in the early quaternary

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

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

late cretaceous cenozoic deformation of northeast asia abstract the plate tectonic paradigm implies rigid plates and narrow plate boundaries in contrast diffuse plate boundaries are common both in the oceans and continents r g gordon annu rev earth planet sci 26 1998 615 642 and their history is difficult to constrain especially in remote tectonically complex areas such as northeast asia m e chapman s c solomon j geophys res 81 1976 921 930 here we show how extensive north atlantic marine magnetic r macnab et al eos 76 1995 449 458 and gravity data d t sandwell w h f smith j geophys res 102 1997 10039 10054 can be used to unravel with tight confidence limits successive periods of deformation over 80 million years along the diffuse continental eurasian north american plate boundary a period of compression in the late cretaceous 14 mm yr in the laptev sea to 20 mm yr in kamchatka led to thrusting in the verkhoyansk mountains and was followed by extension from 68 to 40 ma when 400 km of extension was accommodated by the formation of a series of grabens including the moma rift system since 40 ma time varying compression and transpression along the moma rift system created strike slip faults thrusts and folds at rates up to 6 3 mm yr in the laptev sea region 600 km of extension from latest late cretaceous to present created the laptev sea and lena rift systems the deformation predicted by our model fits most geological features formed in the laptev sea and central northeast asia during late cretaceous cenozoic times the most recent deformation late miocene pliocene is not very well constrained since our model lacks data younger than 11 ma the deformation that occurred in kamchatka reflects a complex tectonic setting and our model s predictions are only tentative

neogene strike slip faulting in sakhalin and the japan sea opening we describe structural data from a 2000 km n s dextral strike slip zone extending from northern sakhalin to the southeast corner of the japan sea satellite images field data and focal mechanisms of earthquakes in sakhalin are included in the interpretation since miocene time the deformation in sakhalin has been taken up by n s dextral strike slip faults with a reverse component and associated en echelon folds narrow en echelon neogene basins were formed along strike sup faults and were later folded in a second stage of deformation we propose a model of basin formation along extension al faults delimitating dominos between two major strike slip faults and subsequent counterclockwise rotation of the dominos in a dextral transpressional regime basins becoming progressively oblique to the direction of maximum horizontal compression and undergoing shortening the association of both dextral and compressional focal mechanisms of earthquakes indicates that the same transpressional regime still prevails today in sakhalin we present fault set measurements undertaken in noto peninsula and yatsuo basin at the southern end of the sakhalin east japan sea strike slip zone early and middle miocene formations recorded the same transtensional regime as observed along the west coast of ne honshu during the early and middle miocene the strike slip regime was transpressional to the north in sakhalin and hokkaido and transtensional to the south along the west coast of ne honshu as far as noto peninsula and yatsuo basin dextral motion accommodated the opening of the japan sea as a pull apart basin with the tsushima fault to the west the opening of the japan sea ceased at the end of the middle miocene when transtension started to change to e w compression in the japan arc subduction of the japan sea lithosphere under the japan arc started 1 8 ma ago the evolution of the stress regime from transtensional to compressional in the southern part of the strike slip zone is related to the inception of the subduction of the young philippine sea plate lithosphere under the japan arc during the late miocene subduction related extension is a necessary condition for the opening of the japan sea two possible mechanisms can account for dextral shear in this area 1 counterclockwise rotation of crustal blocks due to the collision of india with asia 2 extrusion of the okhotsk sea block squeezed between the north america and eurasia plates

interpretations of a middle miocene and late quaternary steady dextral transpression in sw japan and the opening tectonics for the japan sea abstract an internal rotation hypothesis for the deformation of sw japan for middle miocene and recent times is studied rotations are known to have occurred from paleomagnetic data for the earlier case two geodetic flow field estimates as well as another tectonic study suggest that the rotations are also taking place at present a further examination of the geodetic flow models suggests that the rotations contained in these flow models are intrinsic to the deformation of sw japan which occurs in an e w dextral transpressive simultaneous pure and simple shear tectonic regime maps of rotation rates one half of vorticity and shear gradients the n s variation of the e w velocity field constructed from the geodetic flow models resemble one another in pattern the estimates of the directions of the principal strain rates from the geodetic models are on the whole n s contractional and or e w extensional which match the geodetic reference coordinate system used in the adjustment of the geodetic data these observations suggest that the vortical flow contained in the geodetic flow models is a frame independent shear induced vorticity as the material is rotating with respect to the principal directions of the strain rates and that the oblique motion of the philippine sea plate is partitioned between shear and arc normal convergence components the rotation rate is 10 12 ma furthermore the kinematical vorticity number estimates from the geodetic data correlate well with the first order tectonic fabric patterns in sw japan super simple shear deformation for large parts of sw japan where the median tectonic line and other large strike slip faults are found is also indicated in the internal kinematical vorticity number estimates a new model for the formation of the japan sea is proposed extrusion of japan due to the okhotsk eurasia collision this model agrees with the fundamental observations of the early middle miocene deformation in the region the application of an indentation extrusion model to the okhotsk eurasia collision results in a better agreement between the predicted and observed structures and leads to simpler more reasonable and coherent interpretations for the origin and development of the structures compared with the achievements of the previous models the nne trending early middle miocene rifts lying along the continental margin of western hokkaido formed as pull apart basins along a sinistral fault related to the collision of the okhotsk plate which segmented in a left handed sense because the collision was oblique the n s trending rifts and the normal faults found in the back arc domain of the ne honshu arc formed by eastward extrusion under the influence of the mariana type subduction in the japan trench these rift basins were subsequently left laterally displaced by movement along nw trending sinistral strike slip faults the shikoku basin opened from the east toward the west and dextral shear was imparted to the sw margin from the nankai trough leading to clockwise rotations in the middle miocene in sw japan the paleomagnetic rotations are accommodated as fully internal structural rotations in the new model for the origin of the japan sea the current episode of deformation in sw japan began 1 5 million years ago after a hiatus during a 15 5 ma interval and is likely a continuation of the middle miocene style of tectonics

crustal thickness of northeast russia abstract the first order crustal structure of the magadan region and northeast sakha republic yakutia northeast russia is obtained by simultaneously inverting for origin times and travel time curves a total of 1210 observations are used as an average a 37 km thick 5 992 0 007 km s crust overlying an 7 961 0 015 km s mantle provides an excellent fit to phase data listed in the materialy po seismichnosti sibiri bulletin travel time curves for individual stations are very close to this average though there are variations in both crustal thickness and velocities upper mantle velocities and crustal thickness appear to increase along the southern edge of the okhotsk chukotka volcanic belt and decrease in the upper kolyma river basin and along the trace of the proposed moma rift crustal thickness is greatest at khandyga on the siberian platform and lowest at yubileniya which may lie within the currently active laptev sea rift system

micro plate tectonics and kinematics in northeast asia inferred from a dense set of gps observations abstract the plate tectonics of northeast asia are very complex with diffuse and sparse seismicity in the broad plate deformation zones embedded by a number of micro plates particularly the controversial amurian plate now the increasingly dense gps networks in this area provide an important tool to investigate plate tectonic kinematics and to identify the approximate plate tectonic geometries in this paper we have processed gps data 1998 2005 collected by an extensive gps network china and south korea with more than 85 continuous sites and about 1000 campaign gps stations the kinematics of northeast asia is studied by modeling gps derived velocities with rigid block rotations and elastic deformation we find that the deformation in northeast asia can be well described by a number of rotating blocks which are independent of the eurasian plate motion with statistical significance above the 99 confidence level the tectonic boundary between the north china and amuria plates is the yin shan yan shan mountain belts with about 2 4 mm yr extension along the boundary between north china and south china the qinling dabie fault is moving left laterally at about 3 1 mm yr the amuria and south korea blocks are extending at about 1 8 mm yr the baikal rift between the amurian and eurasian plates is spreading at about 3 0 mm yr the 9 17 mm yr relative motion between the amuria and okhotsk blocks is accommodated at the east sea japan trench zone localized deformation near the qinling dabie fault and yin shan yan shan mountain belts may be elastic strain accumulation due to interseismic locking of faults

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

comment on the reply to the comment on thermal history modelling hefty vs qtqt by vermeesch and tian earth science reviews 2014 139 279 290

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