accelerated pacific plate subduction following interplate thrust earthquakes at the japan trench interplate thrust earthquakes are usually followed by afterslips and they let the fore arc move slowly trenchward however we do not know if the subducting oceanic plate is accelerated landward after such earthquakes the westward velocity of global positioning system gps stations in ne japan show gradient decreasing from east to west reflecting the e w contractional strain built up by the inter plate coupling here we show that such coupling significantly enhanced 1 5 times after the 2003 tokachi oki earthquake mw 8 0 hokkaido in the segments adjacent to the ruptured fault the coupling seems to be further enhanced 3 times after the 2011 tohoku oki earthquake mw 9 0 it is unlikely that interplate friction suddenly increased over such a large region and relatively strong pre 2003 coupling there would not allow such enhancements even if full coupling is attained hence they are attributable to the temporary acceleration of the pacific plate subduction we propose a simple 2 dimensional model in which down dip acceleration of the slab let the force balance rapidly recover promoted by a thin low viscosity layer on the slab surface the accelerated subduction would account for temporary activations of regional interplate seismicity after megathrust earthquakes

seismic evidence for sharp lithosphere asthenosphere boundaries of oceanic plates the mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics and thus the understanding of the processes at the lithosphere asthenosphere boundary lab is fundamental to understand how our planet works it is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the lab data from borehole broadband ocean bottom seismometers show that the lab beneath the pacific and philippine sea plates is sharp and age dependent the observed large shear wave velocity reduction at the lab requires a partially molten asthenosphere consisting of horizontal melt rich layers embedded in meltless mantle which accounts for the large viscosity contrast at the lab that facilitates horizontal plate motions

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

predicting imminence of analog megathrust earthquakes with machine learning implications for monitoring subduction zones abstract subduction zones are monitored using space geodesy with increasing resolution with the aim of better capturing the deformation accompanying the seismic cycle here we investigate data characteristics that maximize the performance of a machine learning binary classifier predicting slip event imminence we overcome the scarcity of recorded instances from real subduction zones using data from a seismotectonic analog model monitored with a spatially dense continuously recording onshore geodetic network we show that a 70 85 km wide coastal swath recording interseismic deformation gives the most important information on slip imminence prediction performances are mainly influenced by the alarm duration amount of time that we consider an event as imminent with density of stations and record length playing a secondary role the techniques developed in this study are most likely applicable in regions of slow earthquakes where stick slip like failures occur at time intervals of months to years

temporal variation of large intraplate earthquakes in coupled subduction zones the focal mechanisms of intraplate earthquakes within subducting lithosphere are frequently used to infer large scale stress regimes induced by slab pull bending or unbending and lateral segmentation and undulations of the slab numerous studies have further postulated that the intraplate activity is influenced by transitory regional stress regimes such as those associated with interplate thrust events temporal variations of the latter type may potentially play an important role in assessing regions of uncertain seismic potential and possibly even in earthquake forecasting a systematic analysis of 1130 focal mechanisms for intraplate earthquakes with m b 5 0 in the depth range 0 300 km is conducted for nine circum pacific subduction zones all of which are known to have large interplate thrust events the spatial and temporal relationships of the earthquakes within the subducting slab to the large thrust events in each region are appraised the earthquake catalog assembled contains all published focal mechanisms and is probably complete for m b 6 5 for the years 1963 1986 for many of the localized regions considered in detail the catalog is complete to lower thresholds of m b 6 0 or m b 5 5 this analysis provides compelling evidence for a temporal link between large interplate thrust activity and intraplate seismicity for the seismically coupled regions considered here outer rise compressional events have occurred prior to several large thrust events or are associated with seismic gaps while outer rise tensional events generally only follow interplate ruptures in the intermediate depth range large down dip tensional events generally precede interplate thrusts and are often concentrated at the down dip edge of the coupled zone a transition to down dip compressional stress or diminished tensional activity at intermediate depth is observed after several large thrust events e g 1960 chile 1974 peru 1957 aleutian 1971 new britain these examples support the notion that the intraplate stress environment responds viscoelastically to the temporally varying interplate stress regime assuming that this concept is correct the seismic potential of several seismic gaps is considered on the basis of both outer rise and intermediate depth earthquake activity

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

interplate quasi static slip off sanriku ne japan estimated from repeating earthquakes 1 space time distribution of quasi static slip on the plate boundary off sanriku northeastern ne japan was estimated by using small repeating earthquakes we found 2509 repeating earthquakes occurring on the plate boundary for the last 17 years based on the interpretation that these events are caused by repeating slips of small asperities surrounded by stable sliding area we regarded these repeating events as creepmeters embedded on the plate boundary the results show that deeper portions of the plate boundary are sliding almost stably and earthquakes with magnitudes more than 6 are accompanied by quasi static slips in the surrounding areas

the tr method the use of slip preference to separate heterogeneous fault slip data in compressional stress regimes the surface rupture of the 1999 chi chi taiwan earthquake as a case study abstract synthetic contractional fault slip data have been considered in order to examine the validity of widely applied criteria such as the slip preference slip tendency kinematic p and t axes transport orientation and strain compatibility in different andersonian compressional stress regimes radial compression rc radial pure compression rc pc pure compression pc pure compression transpression pc trp and transpression trp are examined with the aid of the win tensor stress inversion software furthermore the validity of the recently proposed graphical tr method which uses the concept of slip preference for the separation of heterogeneous fault slip data is also examined for compressional stress regimes in these regimes only contractional faults can be activated and their slip preferences imply the distinction between real i e rc rc pc and pc and hybrid i e pc trp and trp stress regimes for slip tendency values larger than 0 6 the activated faults dip at angles from 10 to 50 but in the hybrid regimes faults can dip with even higher angles the application of the tr method is here refined by introducing two controlling parameters the coefficient of determination r2 of the final tensor ratio line ftrl and the normal or inverse distribution of the faults plotted within the final tensor ratio belt ftrb the application of the tr method on fault slip data of the 1999 chi chi earthquake taiwan allowed the meaningful separation of complex heterogeneous contractional fault slip data into homogeneous groups in turn this allowed the identification of different compressional stress regimes and the determination of local stress perturbations of the regional or far stress field generated by the 1999 chi chi earthquake this includes clear examples of stress permutation and stress partitioning caused by pre existing fault structures such as the n s trending chelungpu thrust and the ne sw trending shihkang shangchi fault zone

turbulence and entrainment in a buoyant surface plume in winter tidal outflow from the leschenault estuary forms a buoyant sheared stratified plume in koombana bay on each outgoing tide the turbulence in the plume and the local entrainment into the plume are examined based on measurements collected in an intensive field program coherency measurements between horizontally separated sensors are used to examine the anisotropy of the turbulence the effects of viscosity and buoyancy on the turbulence are studied using an activity diagram which is also an indicator of the mixing efficiency and total mixing the osborne cox model is tested and found to be valid in the plume

characteristics of a surface buoyant jet tidal outflow from leschenault estuary in winter forms an unsteady surface buoyant jet in koombana bay on each outgoing tide as the water moves away from the exit channel and spreads radially over the bay it assumes a plumelike nature the mean features of this buoyant outflow such as the plume shape frontal celerity internal circulation and the bulk entrainment were measured in an intensive field program these features are shown to compare favorably with results from previous laboratory investigations and predictions from a simple inertia buoyancy force balance which includes entrainment at the front the stability of the plume frontal region was examined and it is shown that subfronts were present but their behavior cannot be explained by reference to previous work

enhancement of alongshore freshwater transport in surface advected river plumes by tides abstracta recent numerical study by isobe showed that imposing alongshore tidal forcing on buoyant coastal discharge enhances the net freshwater transport in the coastal currents the mechanisms for this transport enhancement are studied using a three dimensional primitive equation ocean model regional ocean modeling system roms lagrangian drifters are used to trace the freshwater transport paths it is found that the river plume bulge circulation largely follows the rigid body motion i e constant vorticity the buoyant fluid near the bulge s outer edge is thinner and faster behaving as a baroclinic jet the bulge currents then split after impinging on the coast the outer fluid feeds the downshelf flowing coastal currents while the inner fluid recirculates to form the bulge the coastal current transport estimated from the present and prior studies corresponds well to a baroclinic jet theory with the incident angle of bulge currents at the coast being a key parameter without tides the bulg

two layer hydraulics at the river ocean interface liftoff is the hydraulically forced detachment of buoyant freshwater from the channel bottom or seabed that occurs as river water discharges into the coastal ocean it is a key feature of strongly stratified systems occurring well upstream in the channel or seaward of the river mouth under sufficiently strong forcing we present a two layer hydraulic solution for the river ocean interface that considers the river estuary and near field river plume as a single interlinked system extending previous work that considered them separately this unified approach provides a prediction of the liftoff location and free surface profile for a wide range of forcing conditions which are characterized in terms of the freshwater froude number f f equiv q b 0 sqrt g 0 prime h 0 3 here q is the river discharge b 0 is the channel width g 0 prime equiv unicode stix x0394 unicode stix x1d70c 0 unicode stix x1d70c 2 g is the reduced gravitational acceleration unicode stix x0394 unicode stix x1d70c 0 is the density contrast between fresh and ocean water and h 0 is the total water depth at the river mouth the solution is validated with laboratory experiments using an experimental apparatus consisting of a long sloping river channel that discharges into a deep wide saltwater basin the experiments simulate the full range of hydraulic behaviours predicted by the model from saltwater intrusion to offshore liftoff for f f 1 liftoff occurs in the estuary channel and our results show that the relationship between intrusion length and f f depends on the channel slope for f f 1 corresponding to flood conditions in many natural systems liftoff is forced outside the river mouth and the hydraulic coupling between the channel and shelf becomes more important for these conditions and for intermediate to steeply sloped shelves the offshore liftoff distance varies linearly with f f 1 a particularly simple scaling given the nonlinearity and relative complexity of the governing equations the model and experimental results support a conceptual description of the river ocean interface that relates the liftoff location free surface elevation and the spreading rate of the buoyant river plume

effect of the volcanic front migration on helium nitrogen argon and carbon geochemistry of hydrothermal magmatic fluids from hokkaido volcanoes japan abstract active volcanoes from hokkaido are distributed along the sw ne trending volcanic front where the subducting pacific plate changes direction from n s to wsw ese one exception is the tokachi volcano which is located approximately 50 km to the north west of the current volcanic front the tokachi oki slab cracking zone represents the transitional zone between the honshu and kurile trenches this change is responsible for the rapid lateral variation of the subduction angle and slab shape we investigate the consequence of this change on the chemical and isotopic compositions from hydrothermal magmatic fluids and mineral separates collected from three volcanoes of hokkaido northern japan namely tarumae tokachi and meakan our data show that these volcanoes have a distinct range of he n and c isotopic compositions meakan fumaroles have a 3he 4he ratio that ranges from 4 46ra to 6 88ra 15n from 2 2 to 3 5 and 13c co2 from 8 47 to 9 81 consistent with subducted sediment contribution tarumae fumaroles have a particularly low 3he 4he ratio 3 08ra in comparison with their hot springs up to 5 24ra and are associated with high co2 3he ratios 2 2 5 3 1011 hydrothermal crustal interactions from the dome or from a deeper hydrothermal system are the main mechanisms that control the 3he 4he and co2 3he ratios in tarumae fumaroles the 15n and 13c co2 values for tarumae volcano range from 0 6 to 3 1 and from 6 34 to 6 43 respectively tokachi fumaroles are characterized by high 3he 4he up to 7 38ra low 15n 2 4 0 1 and low 13c co2 up to 5 32 consistent with mantle contribution and minor subducted sediment contribution the limestone sediment mantle ratio shows a decreasing contribution from subducted sediments starting from tokachi 1 9 to meakan 3 4 and finally tarumae 5 3 this change of isotopic compositions from the sw ne of hokkaido is the result of the tokachi oki slab cracking zone slab dehydration under tokachi occurs at a deeper level 150 200 km than in other hokkaido volcanoes 100 km which produces the migration of the volcanic front therefore we argue that the isotopic signature of tokachi is the result of i a lower sediment contribution from the slab ii a deeper dehydration of the slab and iii a lower degree of partial melting

separating rapid relocking afterslip and viscoelastic relaxation an application of the postseismic straightening method to the maule 2010 cgps the postseismic deformation captured with continuous global positioning system cgps monitoring following many recent mega thrust events has been shown to be a signal composed of two dominant processes afterslip on the plate interface and viscoelastic relaxation of the continental and oceanic mantles in response to the coseismic stress perturbation following the south central chile 2010 maule mw 8 8 earthquake the time series from the regional cgps network show a distinct curvature in the pathway of the horizontal motion that is not easily fit by a stationary decaying pattern of afterslip in combination with viscoelastic relaxation here we show that with realistic assumptions about the long term decay of the afterslip signal the postseismic signal can be decomposed into three first order contributing processes plate interface re locking plate interface afterslip and mantle viscoelastic relaxation from our analyses we conclude that the plate interface recovers its interseismic locking state rapidly model space ranges between an instant recovery and a period of 1 year a finding that supports laboratory experimental evidence as well as some recent studies of aftershocks and postseismic surface deformation furthermore re locking is the main cause of the curvature in the cgps signal and this study presents a plausible range of geodetic re locking rates following a megathrust earthquake

estuarine plume a case study by satellite sar observations and in situ measurements estuary plumes on the western louisiana continental shelf in the gulf of mexico outside of constricted channels of the sabine and calcasieu lakes were observed on two radarsat 1 synthetic aperture radar sar images the in situ data showed a change in salinity of 2 3 psus across the front on the northwest edge of the plume corresponding to locations of vertical salinity variation of 5 5 7 5 psu velocity magnitude outside of the inlet reached more than 2 3 ms mathrm 1 seaward and a brackish lens in the upper 4 5 m of the water column the spread of which contributed to the development of a plume the volume of brackish water within the plume was estimated an order of magnitude larger than the volume output from the calcasieu river within an entire ebb tidal period this implies that the plume was formed during multiple tidal cycles and it sustained during the flood tides because only weak diurnal tides exist both satellite and in situ observations showed an interesting western intensification of the plume an analysis to the momentum vorticity equations suggests that the western intensification is due to the asymmetry of the vorticity divergence relationship under the coriolis force this can also be enhanced by an ambient coastal current that strengthens the convergence at the front estuary plumes are shown as bright and dark features in two sar images results from a radar model simulation and in situ water temperature data showed that the sar observed plume features were dominated by the water temperature differences

first measurement of the displacement rate of the pacific plate near the japan trench after the 2011 tohoku oki earthquake using gps acoustic technique the subduction rate of an oceanic plate may accelerate after large earthquakes rupture the interplate coupling between the oceanic and overriding continental plates to better understand postseismic deformation processes in an incoming oceanic plate we directly measured the displacement rate of the pacific plate near the japan trench after the 2011 tohoku oki earthquake using a gps acoustic technique over a period of 2 years september 2012 to september 2014 the displacement rate was measured to be 18 0 4 5 cm yr 1 n302 0 e relative to the north american plate which is almost twice as fast as the predicted interseismic plate motion because the sum of steady plate motion and viscoelastic response to the tohoku oki earthquake roughly accounts for the observed displacement rate we conclude that viscoelastic relaxation is the primary mechanism responsible for postseismic deformation of the pacific plate and that significant subduction acceleration did not occur at least not during the observation period

analyses of internal solitary waves generated at the columbia river plume front using sar imagery 1 internal solitons generated at the columbia river plume front during ebb tide are displayed on a synthetic aperture radar sar image taken on 26 july 2004 at 14 24 22 utc scale analyses suggest that these internal solitons belong to the finite depth category a theoretical model relating the radar backscatter cross section to dynamic parameters of internal solitons in the continuous stratification is developed using the model and background stratification data collected by the river influences on shelf ecosystem rise project in july 2004 we extract the soliton dynamic parameters of the half width amplitude phase speed and average energy flux per crest length along a typical section across the internal solitons the observed stratification is simulated by using a theoretical model parameterized by pycnocline depth thickness and maximum buoyancy frequency the half width amplitude phase speed and energy flux of the leading soliton at the section are 119 3 m 9 3 m 0 69 m s 1 and 417 4 w m 1 with the uncertainty ranges of 14 7 m 2 6 m 0 10 m s 1 and 281 6 w m 1 respectively sensitivity analyses reveal that the extraction of the soliton half width from the sar image is not affected by the stratification the amplitude is less influenced by the pycnocline thickness than the depth and is independent of the maximum buoyancy frequency

a simplified energy and mixing budget for a small river plume discharge 1 the formation and evolution of a tidally modulated river plume that spreads and mixes into english channel waters is investigated by combining results from two observational studies remote sensing imagery showed a near semicircular plume expansion as its diameter increased linearly during the ebb tide subsequent ship surveys made repeated transects across the plume front and showed that regions of mixing and instability froude numbers 1 were confined to horizontal length scales 1 suggesting that a plume cannot form

initial expansion of the columbia river tidal plume theory and remote sensing observations 1 analysis of the columbia river tidal plume using lagrangian frontal equations provides a concise description of the evolution of frontal depth h velocity u reduced gravity g and frontal internal froude number fr because the estuary mouth is narrow the initial radial plume motion is supercritical fr 1 for up to 12 hours understanding this supercritical phase is vital because plume properties change rapidly with strong ecosystem impacts to analyze this expansion analytical and numerical models the latter with three mixing formulations were tested model results are compared to synthetic aperture radar images to verify that the predicted frontal properties are realistic lagrangian theory provides especially simple constraints independent of the mixing model on spatial variations in fr and ug h for parameters representative of the columbia river plume the plume spreads 10 35 km and thins to 25 60 of its initial depth before becoming subcritical after liftoff fr increases as the front accelerates and thins it then decreases to unity g decreases but more slowly than h and u h controlled by a balance between spreading and mixing first decreases then increases the strength of vertical mixing and the mixing efficiency ef ratio of buoyancy flux to dissipation both play a significant role in determining plume properties and it is important to include both the horizontal gradient in g and surface slope component of the pressure gradient a model with an ellison turner type entrainment scheme predicts the plume trajectory better than one that assumes a constant interfacial gradient richardson number

migrating pattern of deformation prior to the tohoku oki earthquake revealed by grace data understanding how and when far field continuous motions lead to giant subduction earthquakes remains a challenge an important limitation comes from an incomplete description of aseismic mass fluxes at depth along plate boundaries here we analyse earth s gravity field variations derived from grace satellite data in a wide space time domain surrounding the mw 9 0 2011 tohoku oki earthquake we show that this earthquake is the extreme expression of initially silent deformation migrating from depth to the surface across the entire subduction system our analysis indeed reveals large scale gravity and mass changes throughout three tectonic plates and connected slabs starting a few months before march 2011 before the tohoku oki earthquake rupture the gravity variations can be explained by aseismic extension of the pacific plate slab at mid upper mantle depth concomitant with increasing seismicity in the shallower slab for more than two years after the rupture the deformation propagated far into the pacific and philippine sea plate interiors suggesting that subduction accelerated along 2 000 km of the plate boundaries in march 2011 this gravitational image of the earthquake s long term dynamics provides unique information on deep and crustal processes over intermediate timescales which could be used in seismic hazard assessment deformation migrated from depth towards the surface in the months leading up to the 2011 tohoku oki earthquake according to analyses of satellite gravity data

a decadal scale deformation transient prior to the 2011 mw 9 0 tohoku oki earthquake gps time series in northeast japan exhibit nonlinear trends from 1996 to 2011 before the mw 9 0 2011 tohoku oki earthquake after removing reference frame noise we model time series as linear trends plus constant acceleration correcting for coseismic and postseismic effects from the numerous mw 6 5 earthquakes during this period we find spatially coherent and statistically significant accelerations throughout northern honshu large areas of japan outside the tohoku region show insignificant accelerations demonstrating that the observation is not due to network wide artifacts while the accelerations in northern tohoku sanriku area can be explained by decaying postseismic deformation from pre 1996 earthquakes the accelerations in south central tohoku appear unrelated to postseismic effects the latter accelerations are associated with a decrease in average trench normal strain rate and can be explained by increasing slip rate on the japan trench plate interface and or updip migration of deep aseismic slip in the decades before the 2011 tohoku oki earthquake

detailed observations of a naturally occurring shear instability simultaneous profiles of microstructure horizontal velocity and acoustic backscatter allow one of the most complete descriptions of a naturally occurring shear instability to date shear increased rapidly after passing through a lateral constriction which formed a hydraulic control a kilometer long set of 20 m tall billows grew on a middepth density interface where the richardson number fell below 0 25 the velocity interface thickened steadily after the billows formed consistent with rapid momentum mixing across a shear layer with a reynolds number of 3 106 the billows generated large density overturns and dissipation rates greater than 10 5 w kg 1 even within the first large overturn indicating that these structures were fully turbulent early in their development as the billows grew a well mixed layer developed at the interface and survived as an actively turbulent layer for up to 6 buoyancy periods 3 times longer than in laboratory studies at low reynolds number variations in the mean density of the billows lead us to infer that the vertical offset of the velocity and density interfaces varied with time where the billows first formed with data from the large overturns within the shear layer we find e n2 3 104 an average root mean square overturn scale lrms of 2 6 m and a buoyancy scale lb of 2 7 m despite having sampled the billows at varying stages of their evolution we find no indication that the ratio lrms lb is ever significantly different than 1 for this shear instability

convergence and downwelling at a river plume front abstract the small scale structure of the circulation and hydrography at the frontal boundary of the connecticut river plume in long island sound has been resolved using a novel combination of instruments a towed acoustic doppler current profiler adcp and a rigid array of current meters and conductivity temperature sensors observations were made during the latter half of the eastward ebb tide when the river plume was well established and the front was moving to the west at approximately 0 3 m s 1 two across front transects revealed a horizontal convergence rate in the across front velocity components at 0 6 m of 0 05 0 1 s 1 this was associated with a salt induced horizontal density gradient of 10 2 kg m4 observations obtained during a period in which the towed adcp was caught in the zone of maximum surface convergence showed significant downwelling with a near surface maximum of 0 2 m s 1 vertical velocities of this magnitude are consistent with observed magnitudes of the convergence rate at 0 6

seismic evidence for deep water transportation in the mantle we report seismic evidence for the transportation of water into the deep mantle in the subduction zone beneath northeastern japan our data indicate that water is released from the hydrated oceanic crust at shallow depths approximately 100 kilometers and then forms a channel of hydrated mantle material on top of the subducting plate that is the pathway for water into the deep mantle our result provides direct evidence that shows how water is transported from the ocean to the deep mantle in a cold subduction zone environment

the super interseismic phase of the megathrust earthquake cycle in chile along a subduction zone great megathrust earthquakes recur either after long seismic gaps lasting several decades to centuries or over much shorter periods lasting hours to a few years when cascading successions of earthquakes rupture nearby segments of the fault we analyze a decade of continuous global positioning system observations along the south american continent to estimate changes in deformation rates between the 2010 maule m8 8 and 2015 illapel m8 3 chilean earthquakes we find that surface velocities increased after the 2010 earthquake in response to continental scale viscoelastic mantle relaxation and to regional scale increased degree of interplate locking we propose that increased locking occurs transiently during a super interseismic phase in segments adjacent to a megathrust rupture responding to bending of both plates caused by coseismic slip and subsequent afterslip enhanced strain rates during a super interseismic phase may therefore bring a megathrust segment closer to failure and possibly triggered the 2015 event

relating river plume structure to vertical mixing abstract the structure of a river plume is related to the vertical mixing using an isohaline based coordinate system salinity coordinates offer the advantage of translating with the plume as it moves or expanding as the plume grows this coordinate system is used to compare the relative importance of different dynamical processes acting within the plume and to describe the effect each process has on the structure of the plume vertical mixing due to inertial shear in the outflow of a narrow estuary and wind mixing are examined using a numerical model of a wind forced river plume vertical mixing and the corresponding entrainment of background waters is greatest near the estuary mouth where inertial shear mixing is large this region is defined as the near field with the more saline far field plume beyond wind mixing increases the mixing throughout the plume but has the greatest effect on plume structure at salinity ranges just beyond the near field wind mixing is weaker at high salinity classes tha

viscosity of oceanic asthenosphere inferred from remote triggering of earthquakes a sequence of large interplate earthquakes from 1952 to 1965 along the aleutian arc and kurile kamchatka trench released accumulated stresses along nearly the entire northern portion of the pacific plate boundary the postseismic stress evolution across the northern pacific and arctic basins calculated from a viscoelastic coupling model with an asthenospheric viscosity of 5 x 10 17 pascal seconds is consistent with triggering of oceanic intraplate earthquakes temporal patterns in seismicity at remote plate boundaries and space based geodetic measurements of anomalous velocity over an area 7000 by 7000 kilometers square during the 30 year period after the sequence

space time distribution of afterslip following the 2003 tokachi oki earthquake implications for variations in fault zone frictional properties 1 gps time series following the september 25 2003 ut tokachi oki earthquake m w 8 0 reveal significant deformation we use the network inversion filter to invert for the spatial and temporal evolution of afterslip in the 30 days following the earthquake afterslip is concentrated adjacent to the coseismic rupture zone between the 2003 rupture and the inferred source regions of the 1968 tokachi oki and the 1973 nemuro oki earthquakes the inversion shows a rapid decay of slip rate in the 2003 rupture zone with slower deceleration in the surrounding regions the stress velocity paths for the afterslip regions approximately follow d d in v 0 6 mpa suggestive of steady state velocity strengthening friction the complementary spatial pattern of coseismic rupture and afterslip may indicate along strike spatial variations of frictional properties although other interpretations can not be ruled out

transient rheology of the oceanic asthenosphere following the 2012 indian ocean earthquake inferred from geodetic data abstract postseismic motion in the middle field 100 500 km from the epicenter geodetic data resulting from the 2012 indian ocean earthquake exhibited rapid change during the two months following the rupture this pattern probably indicates multiple postseismic deformation mechanisms and might have been controlled by transient rheology therefore the relative contribution of transient rheology in the oceanic asthenosphere and afterslip in the oceanic lithosphere should be incorporated to explain short and long term transitional features of postseismic signals in this study using two years of post earthquake geodetic data from northern sumatra a three dimensional spherical earth finite element model was constructed based on a heterogeneous structure and incorporating transient rheology a rheology model combined with stress driven afterslip was estimated our best fit model suggests an oceanic lithosphere thickness of 75 km with oceanic asthenosphere viscosity values of 1 10 17 pa s and 2 10 18 pa s for the kelvin and maxwell viscosity models respectively the model results indicate that horizontal landward motion and vertical uplift in northern sumatra require viscoelastic relaxation of the oceanic asthenosphere coupled with afterslip in the lithosphere the present study demonstrates that transient rheology is essential for reproducing the rapidly changing motion of postseismic deformation in the middle field area

gold metallogeny associated with craton destruction a geophysical perspective from the north china craton abstract currently ranking as the largest producer of gold in the world china s gold reserves are spread over 200 major gold deposits and several minor deposits a large part of these belong to the late mesozoic gold deposits in the north china craton ncc that occur along craton margins as well as within the cratonic interior in reactivated paleo sutures and show a close spatio temporal relationship with zones of lithospheric thinning and craton destruction here we integrate and evaluate geophysical information from the ncc through an analysis of receiver function and tomography that suggest mantle upwelling accompanied by lower crustal or lithospheric delamination our results identify that the major gold belts in the ncc are largely located above zones of mantle upwelling and craton destruction the faults and paleo sutures provided the pathways for migration of ore bearing fluids with the granitoids offering favorable conditions for gold deposition

space geodetic observation of deep basal subduction erosion in northeastern japan abstract observation of tectonic erosion von huene and scholl rev geophys 29 1991 279 316 in a subduction zone has been difficult as it leaves little geological and geophysical evidence three dimensional velocity profiles of crustal movement obtained by global positioning system across ne and sw japan agree well with those predicted by the elastic loading of the subducting slabs however vertical velocities in the ne japan forearc show significant negative deviation relative subsidence this may indicate loss of material at the plate interface that can be attributed to the erosion of the upper plate by the underthrusting slab basal subduction erosion the estimated rate 15 mm yr down to a slab depth of 90 km is somewhat faster than the geological average the erosion speed may be variable being controlled by the surface roughness of subducting slabs

coastal river plumes collisions and coalescence abstract plumes of buoyant river water spread in the ocean from river mouths and these plumes influence water quality sediment dispersal primary productivity and circulation along the world s coasts most investigations of river plumes have focused on large rivers in a coastal region for which the physical spreading of the plume is assumed to be independent from the influence of other buoyant plumes here we provide new understanding of the spreading patterns of multiple plumes interacting along simplified coastal settings by investigating i the relative likelihood of plume to plume interactions at different settings using geophysical scaling ii the diversity of plume frontal collision types and the effects of these collisions on spreading patterns of plume waters using a two dimensional hydrodynamic model and iii the fundamental differences in plume spreading patterns between coasts with single and multiple rivers using a three dimensional hydrodynamic model geophysical scaling suggests that coastal margins with numerous small rivers watershed areas 2 such as found along most active geologic coastal margins were much more likely to have river plumes that collide and interact than coastal settings with large rivers watershed areas 100 000 km 2 when two plume fronts meet several types of collision attributes were found including refection subduction and occlusion we found that the relative differences in pre collision plume densities and thicknesses strongly influenced the resulting collision types the three dimensional spreading of buoyant plumes was found to be influenced by the presence of additional rivers for all modeled scenarios including those with and without coriolis and wind combined these results suggest that plume to plume interactions are common phenomena for coastal regions offshore of the world s smaller rivers and for coastal settings with multiple river mouths in close proximity and that the spreading and fate of river waters in these settings will be strongly influenced by these interactions we conclude that new investigations are needed to characterize how plumes interact offshore of river mouths to better understand the transport and fate of terrestrial sources of pollution nutrients and other materials in the ocean

high pressure creep of serpentine interseismic deformation and initiation of subduction the supposed low viscosity of serpentine may strongly influence subduction zone dynamics at all time scales but until now its role could not be quantified because measurements relevant to intermediate depth settings were lacking deformation experiments on the serpentine antigorite at high pressures and temperatures 1 to 4 gigapascals 200 to 500 c showed that the viscosity of serpentine is much lower than that of the major mantle forming minerals regardless of the temperature low viscosity serpentinized mantle at the slab surface can localize deformation impede stress buildup and limit the downdip propagation of large earthquakes at subduction zones antigorite enables viscous relaxation with characteristic times comparable to those of long term postseismic deformations after large earthquakes and slow earthquakes antigorite viscosity is sufficiently low to make serpentinized faults in the oceanic lithosphere a site for subduction initiation

super interseismic periods redefining earthquake recurrence precise geodetic measurements made over broad swaths of tectonically active regions record patterns of interseismic strain accumulation providing key insights into the locus and timing of pending earthquakes recent studies of geodetic position time series including that of melnick et al 2017 illustrate temporal variation in the pattern of interseismic deformation these authors propose that the 2010 mw 8 8 maule chile earthquake enhanced coupling on the andean subduction zone adjacent to the rupture including on the portion of the megathrust that broke 5 years later in the mw 8 3 illapel event

frontogenesis in mixed layers abstract a unified theory of frontogenesis in mixed layers is proposed analytical solutions of the nonlinear mass and density balances in a mixed layer are found in the lagrangian frame for a wide class of entrainment parameterizations these solutions show mixed layer depth and density to be functions of particle position and separation where mixing is represented by an integral over time following a particle thus given a knowledge of only the crossfront velocity field the likelihood of frontal formation can be predicted both surface convergence and divergence in conjunction with vertical mixing can be frontogenetic three different types of fronts distinguished by their associated crossfront velocity fields are discussed large scale fronts such as the subtropical front are described by a convergent surface flow acting upon an initial horizontal density gradient the powerful divergence caused by an offshore ekman flow forced to zero at a coast causes upwelling fronts the divergence associat

the columbia river plume study subtidal variability in the velocity and salinity fields a comprehensive study of the strongly wind driven midlatitude buoyant plume from the columbia river located on the u s west coast demonstrates that the plume has two basic structures during the fall winter season namely a thin 5 15 m strongly stratified plume tending west to northwestward during periods of southward or light northward wind stress and a thicker 10 40 m weakly stratified plume tending northward and hugging the coast during periods of stronger northward stress the plume and its velocity field respond nearly instantaneously to changes in wind speed or direction and the wind fluctuations have timescales of 2 10 days frictional wind driven currents cause the primarily unidirectional flow down the plume axis to veer to the right or left of the axis for northward or southward winds respectively farther downstream currents turn to parallel rather than cross salinity contours consistent with a geostrophic balance in particular during periods when the plume is separated from the coast currents tend to flow around the mound of fresher water at distances exceeding about 20 km from the river mouth the along shelf depth averaged flow over the inner to midshelf is linear and depth averaged acceleration is governed to lowest order by the difference between surface and bottom stress alone in this region along shelf geostrophic buoyancy driven currents at 5 m calculated from surface density and along shelf geostrophic wind driven currents computed from a depth averaged linear model are comparable in magnitude 10 25 cm s 1

strain budget of the ecuador colombia subduction zone a stochastic view the 2016 pedernales earthquake m w 7 8 ruptured a portion of the colombia ecuador subduction interface where several large historical earthquakes have been documented since the great 1906 earthquake m 8 6 considering all significant ruptures that occurred in the region it has been suggested that the cumulative moment generated co seismically along this part of the subduction over the last century exceeds the moment deficit accumulated inter seismically since 1906 such an excess challenges simple models with earthquakes resetting the elastic strain accumulated inter seismically in locked asperities these inferences are however associated with large uncertainties that are generally unknown the impact of spatial smoothing constraints on co seismic and inter seismic models also prevents any robust assessment of the strain budget we propose a bayesian kinematic slip model of the 2016 pedernales earthquake using the most comprehensive dataset to date including insar and gps offsets tsunami waveforms and kinematic records from high rate gps and strong motions in addition we use inter seismic geodetic velocities to produce a probabilistic inter seismic coupling model of the subduction interface our stochastic co seismic and inter seismic solutions include the ensemble of all plausible models consistent with our prior information and that fit the observations within uncertainties the analysis of these model ensembles indicates that an excess of co seismic moment during the 1906 2016 period is likely in central ecuador only if we assume that 1942 and 2016 earthquakes are colocated if this assumption is relaxed we show that this conclusion no longer holds given uncertainties in co and inter seismic processes the comparison of 1942 and 2016 teleseismic records reveals large uncertainties in the location of the 1942 event hampering our ability to draw strong conclusions on the unbalanced moment budget in the region our results also show a heterogeneous coupling of the subduction interface that coincides with two slip asperities in our co seismic model for the 2016 pedernales earthquake and with the location of historical ruptures in 1958 1979 and 1998 the spatial variability in coupling and complexity in earthquake history suggest strong heterogeneities in frictional properties of the subduction megathrust

tidal asymmetry in an estuarine pycnocline depth and thickness tidal variations in estuarine stratification are revealed by the depth and thickness of the density interface the depth of the interface may be predicted using an inviscid two layer model that combines baroclinic estuarine circulation with barotropic tidal currents helfrich 1995 here we present results from a two layer model modified to include the effects of bottom friction and interfacial mixing modeled layer thickness and speed compare favorably with prior analytic studies farmer and armi 1986 pratt 1986 we use a bulk richardson number criterion to estimate the thickness of the pycnocline from two layer model results the predicted pycnocline depth and thickness compare remarkably well with observations we also investigate the effects of changing bottom friction and barotropic currents on the pycnocline thickness

earthquake swarms slow slip and fault interactions at the western end of the hellenic subduction system precede the mw 6 9 zakynthos earthquake greece the month to year long deformation of the earth s crust where active subduction zones terminate is poorly explored here we report on a multidisciplinary dataset that captures the synergy of slow s

the role of turbulence stress divergence in decelerating a river plume 1 turbulence controls the composition of river plumes through mixing and alters the plume s trajectory by diffusing its momentum while believed to play a crucial role in decelerating river source waters the turbulence stress in a near field river plume has not previously been observationally quantified in this study finely resolved density velocity and turbulence observations are combined with a control volume technique to describe the momentum balance in the columbia river s near field plume during 10 tidal cycles that encompass both large and small river flow turbulence stress varies by 2 3 orders of magnitude both within a given ebb and between ebbs with different tidal or river forcing its magnitude scales with the strength of the instantaneous ebb outflow i e high stresses occur during peak flow of strong ebbs during these periods the momentum equation is represented by a balance between stress divergence and plume deceleration as the flow relaxes the stress divergence weakens and other terms pressure gradient and coriolis may become appreciable and influence plume deceleration while the momentum balance could not be closed during these weaker flow periods during strong tidal pulses the time scale for decay based on observed stress is significantly less than a tidal half period indicating that stress divergence plays a fundamental role in the initial deceleration of the plume

preceding coseismic and postseismic slips of the 2011 tohoku earthquake japan 1 we estimated the spatial and temporal evolution of the preceding aseismic slip from january 2003 to january 2011 the coseismic slip of the tohoku earthquake and the postseismic slip after the earthquake based on global positioning system gps data time dependent analysis indicates aseismic slip offshore of miyagi and fukushima prefectures from 2004 associated with a series of subduction earthquakes that overlap the aseismic slip area these preceding aseismic and coseismic slip areas are centered between the centers of the coseismic and afterslip areas of the tohoku earthquake offshore of miyagi prefecture while they overlap the coseismic and afterslip areas of the tohoku earthquake off fukushima prefecture the timing of moment magnitude nine mw9 class earthquakes appears to be controlled by multiple preceding slip events smaller earthquakes and their afterslip the preceding aseismic and coseismic slip decreased the coupling rate off the tohoku coast suggesting the possibility that the preceding slip represented a precursive stage of the tohoku earthquake the afterslip of the tohoku earthquake occurred in an area where the coseismic slip was not large complementing the large coseismic slip zone the afterslip along iwate miyagi extends up to 80 km in depth and is currently the sole mechanism of strain release in this depth range the source region of the anticipated miyagi oki earthquake shows small postseismic slip after the tohoku earthquake reflecting the energy release at the time of the earthquake aftershock activity is roughly governed by an afterslip process

acceleration of regional plate subduction beneath kanto japan after the 2011 tohoku oki earthquake two oceanic plates the pacific pa and philippine sea ph subduct beneath the land plate and they forms deeper ph pa and shallower land ph plate boundaries beneath kanto remarkably enhanced seismicity was observed in the densely populated area after the 2011 tohoku oki earthquake which cannot simply be explained by the southern expansion of the postseismic slip of the earthquake we examine interplate repeating earthquakes to constrain the relative plate motion across aseismically slipping faults the repeater slip rates show creep rates in the deeper and shallower boundaries respectively increased to 2 4 6 6 times and 1 3 6 2 times the pre tohoku oki rates in addition the repeater slip directions show no change larger than 4 degree in the deeper boundary the interplate creep rates and slip directions suggest regional movements of both the two plates had accelerated they probably caused the seismicity increase frequent slow slips on the shallower boundary and enhanced probability of larger earthquakes

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

months long thousand kilometre scale wobbling before great subduction earthquakes megathrust earthquakes are responsible for some of the most devastating natural disasters1 to better understand the physical mechanisms of earthquake generation subduction zones worldwide are continuously monitored with geophysical instrumentation one key strategy is to install stations that record signals from global navigation satellite systems2 3 gnss enabling us to track the non steady surface motion of the subducting and overriding plates before during and after the largest events4 6 here we use a recently developed trajectory modelling approach7 that is designed to isolate secular tectonic motions from the daily gnss time series to show that the 2010 maule chile moment magnitude 8 8 and 2011 tohoku oki japan moment magnitude 9 0 earthquakes were preceded by reversals of 4 8 millimetres in surface displacement that lasted several months and spanned thousands of kilometres modelling of the surface displacement reversal that occurred before the tohoku oki earthquake suggests an initial slow slip followed by a sudden pulldown of the philippine sea slab so rapid that it caused a viscoelastic rebound across the whole of japan therefore to understand better when large earthquakes are imminent we must consider not only the evolution of plate interface frictional processes but also the dynamic boundary conditions from deeper subduction processes such as sudden densification of metastable slab

a simple theory for the fate of buoyant coastal discharges abstract a simple theory that predicts the vertical structure and offshore spreading of a localized buoyant inflow onto a continental shelf is formulated the theory is based on two competing mechanisms that move the buoyant fluid offshore 1 the radial spread of the lighter water over the ambient water being deflected by the coriolis force and producing an anticyclonic cyclostrophic plume and 2 offshore transport of buoyant water in the frictional bottom boundary layer that moves the entire plume offshore while maintaining contact with the bottom the surface expression of the cyclostrophic plume moves offshore a distance ys 2 3g h0 2i 2g h0 2i 1 2f where g is reduced gravity based on the inflow density anomaly h0 is the inflow depth i is the inflow velocity and f is the coriolis parameter the plume remains attached to the bottom to a depth given by hb 2l ih0f g 1 2 where l is the inflow width both scales are based solely on parameters of the buoyant inflow at its source there

interplate seismogenic zones along the kuril japan trench inferred from gps data inversion stress accumulation between earthquakes results from slip that is insufficient to fully accommodate plate movement an inverse analysis of gps data from the kuril japan trench reveals a trench parallel belt of stress accumulation with six peaks in the depth range of 10 40 km suggesting potential source regions for future earthquakes in the subduction zones around japan where four plates interact with one another large earthquakes have occurred repeatedly1 these interplate earthquakes are part of the process of tectonic stress accumulation and release that is driven by relative plate motion2 3 4 stress accumulation between earthquakes results from slip deficit slip that is insufficient to fully accommodate plate movement for the prediction of large earthquakes it is therefore important to monitor the distribution of slip deficit on plate interfaces here we apply an inversion method based on bayesian modelling using direct and indirect prior information on the magnitude and distribution of fault slip5 to horizontal and vertical velocities from global positioning system data for the seismically calm period between 1996 and 2000 we obtain a precise distribution of slip deficit rates on the interface between the north american and pacific plates around japan which reveals a trench parallel belt of slip deficit with six peaks in the depth range of 10 40 km these peaks agree with the source regions of past large interplate earthquakes along the kuril japan trench we conclude that the slip deficit zones identified with our method are potential source regions of large earthquakes

river islands change and impacting factors in the lower reaches of the yangtze river based on remote sensing abstract there are many developing river islands in the mawutong section of the yangtze river and their sizes change rapidly changes in eight river islands were studied using multi spectral scanner mss in 1979 and thematic maps tm in 1990 2001 2006 and 2009 the spectrum of typical objects in river islands was analyzed by isi921vf 256t field spectroradiometer bands combined and images interpreted by geometric correction subset images binarization processing convolution clump procedures and visual image interpretation a number of factors that were considered to influence the evolution of river islands were analyzed they include annual runoff annual sediment and soil particle composition of river islands the results show that 1 the isi921vf 256t field spectroradiometer can help to identify the correct spectrum of typical objects in river islands hence the selected bands three visible and one near infrared can be used to extract the variation of river islands area based on digital image processing and visual image interpretation 2 in general the eight river islands lengthened in 1979 2006 at various rates with the highest rate during 2001 2006 their sizes decreased rapidly in 2006 2009 except for two river islands 3 erosion and sediment deposition are two major physical processes that influence the evolution of river islands as no significant trend of annual total runoff in 1953 2010 was detected it is likely that the construction of large reservoirs upstream and hence the runoff dynamics and sediment loads in this region have more impact on the changes of river islands than do climate changes

characteristics of the great whale river plume observations of the motion field and dilution effects associated with the plume of great whale river in hudson bay are presented for both open water and ice covered conditions in the summer months a distinct plume of about 100 km2 in area is formed offshore which is characterized by a 1 2 m thickness and large velocities directed away from the river mouth in contrast to slower currents parallel to the shore in the ambient waters underneath surface drifter results suggest that the outer boundary of plume may be a zone of frontal convergence under ice covered conditions the plume was significantly thicker and extended much farther offshore in spite of a marked reduction in river runoff at this time

particle resuspension in the columbia river plume near field 1 measurements of suspended sediment concentration velocity salinity and turbulent microscale shear in the near field region of the columbia river plume are used to investigate the mechanisms of sediment resuspension and entrainment into the plume an east west transect was occupied during spring and neap tide periods in august 2005 and may 2006 corresponding to low and high river discharge conditions respectively during the high discharge period the plume is decoupled from the bottom and fine sediment resuspended from the bottom does not leave the benthic boundary layer the primary modes of sediment transport associated with the plume are advection of sediment from the estuary and removal of sediment from the plume by gravitational settling and turbulent mixing in contrast the plume is much less stratified during low discharge conditions and large resuspension events are observed that entrained sediment through the water column and into the plume our measurements indicate that two factors control the magnitude and timing of sediment resuspension and entrainment the supply of fine sediment on the seabed and the relative influence of tidal turbulence compared with buoyancy input from the river the latter is quantified in terms of the estuary richardson number rie the magnitude of vertical turbulent sediment flux is correlated with rie during the low flow period when there is a sufficient supply of bottom sediment in the near field region such sediment resuspension may be an important mechanism for the delivery of bioavailable micronutrients to the plume during the summer

two decades of spatiotemporal variations in subduction zone coupling offshore japan spatial patterns of interplate coupling on global subduction zones can be used to guide seismic hazard assessment but estimates of coupling are often constrained using a limited temporal range of geodetic data here we analyze 19 years of geodetic observations from the geonet network to assess time dependent variations in the spatial distribution of coupling on the subduction zones offshore japan we divide the position time series into five 3 75 year epochs each decomposed into best fit velocity annual periodic signals coseismic offsets and postseismic effects following seven major earthquakes nominally interseismic velocities are interpreted in terms of a combination of tectonic block motions and earthquake cycle activity the duration of the inferred postseismic activity covaries with the linear velocity to address this trade off we assume that the nominally interseismic velocity at each station varies minimally from epoch to epoch this approach is distinct from prior time series analysis across the earthquake cycle in that position data are not detrended using preseismic velocity which inherently assumes that interseismic processes are spatially stable through time but rather the best fit velocity at each station may vary between epochs these velocities reveal significant consistency since 1996 in the spatial distribution of coupling on the nankai subduction zone with variation limited primarily to the tokai and bungo channel regions where long term slow slip events have occurred and persistently coupled regions coincident with areas that slipped during historic great earthquakes on the sagami subduction zone south of tokyo we also estimate relatively stable coupling through time on the japan kuril trench we image significant coupling variations owing to effects of the 1994 mw 7 7 sanriku oki 2003 mw 8 2 tokachi oki and 2011 mw 9 0 tohoku oki earthquakes in particular strong coupling becomes more spatially extensive following the 1994 event until 2011 coseismic sense slip precedes the tohoku oki event and coupling offshore northern honshu is reduced after the 2011 earthquake despite the occurrence of the 2003 tokachi oki earthquake persistent coupling offshore hokkaido suggests ongoing seismic hazard possibly similar to past mw 9 class earthquakes interpreted from coastal paleoseismic records this time dependent analysis of interseismic deformation illuminates rich diversity in the distribution of subduction zone coupling including spatiotemporal stability in coupling effective reduction in strongly coupled regions due to aseismic thrust sense slip events and broad changes in the distribution of coupling following major earthquakes

observations at the tidal plume front of a high volume river outflow 1 we present shipboard observations of very strong convergence vertical velocities and mixing and near bed impacts associated with the leading edge front of the tidally pulsed columbia river plume with upwelling favorable winds and riverflow of 4900 m3s 1 the plume propagates as a buoyant gravity current with a rotary bore like vertical frontal circulation and downwelling as strong as 0 35 m s 1 in waters as deep as 65 m near bed currents intensify to as much as 1 0 m s 1 after frontal passage and are often associated with elevated acoustic backscatter mixing is locally strong with an eddy diffusivity of o 0 2 m2s 1 50 m behind the front and t s diagrams imply plume mixing with 10 m deep ocean water these observations indicate that the leading edge front of a surface advected plume can cause exchanges of a nutrients between cold subsurface shelf waters and the river plume and b nutrients and sediments across the sediment water interface

active tectonic deformation of the western indian plate boundary a case study from the chaman fault system abstract collision of the eurasian and indian plates has resulted in two spatially offset subduction zones the makran subduction zone to the south and the himalayan convergent margin to the north these zones are linked by a system of left lateral strike slip faults known as the chaman fault system 1200 km which spans along western pakistan although this is one of the greatest strike slip faults yet temporal and spatial variation in displacement has not been adequately defined along this fault system this study conducted geomorphic and geodetic investigations along the chaman fault in a search for evidence of spatial variations in motion four study areas were selected over the span of the chaman fault 1 tarnak rud area over the tarnak rud valley 2 spinatizha area over the spinatizha mountain range 3 nushki area over the nushki basin and 4 kharan area over the northern tip of the central makran mountains remote sensing data allowed for in depth mapping of different components and faults within the kohjak group wind and water gap pairs along with offset rivers were identified using high resolution imagery and digital elevation models to show displacement for the four study areas the mountain front sinuosity ratio valley height to width ratio and the stream length gradient index were calculated and used to determine the relative tectonic activity of each area these geomorphic indices suggest that the kharan area is the most active and the tarnak rud area is the least active gps data were processed into a stable indian plate reference frame and analyzed fault parallel velocity versus fault normal distance yielded a 8 10 mm yr displacement rate along the chaman fault just north of the spinatizha area insar data were also integrated to assess displacement rates along the fault system geodetic data support that ultra slow earthquakes similar to those that strike along other major strike slip faults such as the san andreas fault system are possible along the northern segments of the chaman fault zone geomorphic data suggest that the chaman fault along southern part is not very active now but may have gone through high tectonic activity in the past

displacement above the hypocenter of the 2011 tohoku oki earthquake the moment magnitude m w 9 0 2011 tohoku oki mega thrust earthquake occurred off the coast of northeastern japan combining global positioning system gps and acoustic data we detected very large sea floor movements associated with this event directly above the focal region an area with more than 20 meters of horizontal displacement that is four times larger than those detected on land stretches several tens of kilometers long along the trench the largest amount reaches about 24 meters toward east southeast just above the hypocenter furthermore nearly 3 meters of vertical uplift occurred contrary to observed terrestrial subsidence

post rifting stress relaxation at the divergent plate boundary in northeast iceland interaction of the elastic lithosphere with the underlying anelastic asthenosphere causes strain to propagate along the earth s surface in a diffusion like manner following tectonism at plate boundaries this process transfers stress between adjacent tectonic segments and influences the temporal tectonic pattern along a plate boundary observations of such strain transients have been rare and have hitherto been confined to strike slip and underthrusting plate boundaries1 here we report the observation of a strain transient at the divergent spreading plate boundary in iceland a global positioning system survey undertaken a decade after an episode of dyke intrusion accompanying several metres of crustal spreading reveals a spatially varying strain field with the expected diffusion pulse shape and an amplitude three times greater than the 5 7 cm that would be expected from the average spreading rate2 a simple one dimensional model with a thin elastic layer overlying a viscous layer fits the data well and yields a stress diffusivity of 1 1 a 0 3 m2s 1 combined with struc tural information from magnetotelluric measurements this implies a viscosity of 0 3 2 1019 pa s a value comparable to that derived for iceland from post glacial rebound23 but low compared with estimates for mantle viscosity obtained elsewhere3

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

estuary plumes and fronts in shelf waters a layer model abstract a layer model that treats fronts as discontinuities is developed to study the steady state behavior of shallow estuary plumes on the continental shelf the complete range of earth rotation effect is evaluated from small scale or nonrotating plumes kelvin number equal zero to large scale rotating plumes kelvin number equal order one supercritical flow is assumed in the outlet channel and the method of characteristics is used to compute the flow downstream nonrotating plumes have strong boundary fronts and concentrate their greatest layer depth and mass transport offshore near the front but form no coastal current rotating plumes have boundary fronts that weaken soon after discharge form a turning region where coriolis action deflects the flow toward shore and subsequently set up a coastal current soon after its formation this coastal current is bounded offshore by a strong front called the coastal front across which the momentum balance changes from nearly inertial in the turning regi

possibility of recovery of slip deficit rate between the north american plate and the pacific plate off sanriku northeast japan 1 the analysis of global positioning system gps data shows an increase in the westward ground velocity in iwate northeast japan from around 2003 after a period of roughly constant crustal deformation rate the spatiotemporal study of time series of displacements reveals that the westward slip deficit rate increased slightly from 2001 to 2003 at the deeper part of the source region of the 1994 sanriku oki earthquake the increase has been considerable since january 2003 and the area of increased slip deficit rate has expanded and now covers the source region of the 1994 sanriku oki earthquake this indicates that the restoration of the slip deficit rate which was affected by the 1994 earthquake was not completed in the period from 1994 to 2003

change in seismicity along the japan trench 1990 2011 and its relationship with seismic coupling we investigate the temporal evolution of the background seismicity rate related to the subduction of the pacific plate in northeast japan at latitudes 34o to 42o for the 1 1 1990 9 3 2011 period two declustering methods are used to identify robust features we find that the dominant behaviour is a lowering down of activity especially in the northern half of our studied area where changes appear related to the cycle of m7 5 earthquakes in particular the 1968 tokachi and the 1994 sanriku earthquakes acceleration of background seismicity is observed offshore the kanto region and could mark a long term decoupling of the pacific and the philippine sea plates over a 100 km long segment along the sagimi trough which cannot be simply explained by the earthquake cycle model our analysis further suggests that changes in background seismicity are plausibly related to changes in seismic coupling and thus further strengthens the recent observation that seismic coupling does vary at the time scales of tens of years for the japanese subduction zone

structure and dynamics of the columbia river tidal plume front 1 time dependent buoyant plumes form at the outflow of tidally dominated estuaries when estuary discharge velocity exceeds plume internal wave speed c a sharp front forms at the plume s leading edge that expands from the time dependent source using observations of the columbia river tidal plume from multiple tidal cycles we characterize time evolving plume structure and quantify front speed uf plume internal wave speed c front curvature and ultimate extent we identify three distinct stages of propagation 1 initially the plume is strongly influenced by shallow bathymetry near the river mouth 2 as the front advances offshore the plume detaches from the bottom and expands as a freely propagating gravity current with relatively constant uf c and frontal froude number f uf c ambient currents explain intracycle variability in uf and winds alter front shape variability in ambient stratification associated with previous cycles plume remnants leads to complex fronts and internal waves 3 finally the plume decelerates adjusts toward geostrophy and may radiate additional internal waves using a simple kinematic model we suggest that constant frontal propagation speed uf 0 9 0 1 m s during stage 2 is primarily controlled by linearly increasing volume flux from the columbia river mouth as this discharge rate subsides the plume expands as a fixed volume with decreasing front speed stage 3 the plume s final extent is controlled by the rossby radius which scales with a length based on the total volume discharged this provides an integral description of plume front evolution based on the time dependent estuary discharge