a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

the meandering gulf stream as seen by the geosat altimeter surface transport position and velocity variance from 73 to 46 w the surface geostrophic velocity field for the gulf stream region was analyzed for the position structure and surface transport of the gulf stream for 2 5 years of the geosat altimeter exact repeat mission synthetic data using a gaussian velocity profile were generated and fit to the sea surface residual heights to create a synthetic mean sea surface height field and profiles of absolute geostrophic currents most of cross track velocity variance was due to the meandering of the gulf stream rather than to rings or complicated velocity profiles which suggested that the simple model parameters are an efficient description of the gulf stream fluctuations an analysis of the model parameters and the actual geostrophic velocity profiles revealed two different flow regimes for the gulf stream connected by a narrow transition region coincident with the new england seamount chain the upstream region was characterized by relatively straight gulf stream paths long eulerian time scales and eastward propagating meanders the downstream region had more large meanders no consistent propagation direction and shorter eulerian time scales a 25 reduction in surface transport occurred in the transition region with a corresponding reduction in current speed and no change in gulf stream width a significant anomaly in surface transport near 69 w suggested the existence of small scale recirculation gyres there the highest variance empirical orthogonal functions of position and surface transport were significantly correlated with larger surface transports leading more northerly positions by a month

transport of the norwegian atlantic current as determined from satellite altimetry relatively warm and salty north atlantic surface waters flow through the faeroe shetland channel into the higher latitudes of the nordic seas preserving an ice free winter environment for much of the exterior coast of northern europe in this study we have monitored this flow along the norwegian coast using geosat altimetry on two ascending arcs during the exact repeat mission in 1987 1989 concurrent undertrack ctd surveys were used to fix a reference surface for the altimeter derived sea surface height ssh anomalies in effect creating time series of alongtrack surface dynamic height topographies climatologic ctd casts were then used with empirical orthogonal function eof analysis to derive relationships between historical surface dynamic heights and vertical temperature and salinity profiles applying these eof relationships to the altimeter signals we calculated mean transports of volume heat and salt at approximately 2 9 sverdrups 8 1 1011 kcal s and 1 0 108 kg s respectively although strong variability occurred a clear seasonal signal could be seen with summer to winter variations of about 50 of the means maximum transports occurred in february march and minimum in july august

high speed rupture in the first 20 s of the 2011 tohoku earthquake japan 1 the 2011 tohoku earthquake produced tens of meters of fault slip near the japan trench which generated devastating tsunami the rupture process before the huge slip is still unclear due to a lack of resolution here i perform a multiscale slip inversion analysis to examine the first 10 and 20 s of the rupture process and the whole rupture process at different scales the result shows that 4 s after the initiation this earthquake started with a relatively high speed rupture that had a peak slip rate faster than 1 m s and a rupture velocity comparable to 3 km s fourteen seconds after the initiation the rupture propagation direction changed from northward to westward near the edge of the m 7 3 foreshock coseismic slip area the stress release by the foreshock may contribute to the complex small scale rupture propagation which may appear to be slow rupture propagation when only looking at long period data

propagation of slow slip leading up to the 2011 mw 9 0 tohoku oki earthquake many large earthquakes are preceded by one or more foreshocks but it is unclear how these foreshocks relate to the nucleation process of the mainshock on the basis of an earthquake catalog created using a waveform correlation technique we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude mw 9 0 tohoku oki earthquake in japan the time history of quasi static slip along the plate interface based on small repeating earthquakes that were part of the migrating seismicity suggests that two sequences involved slow slip transients propagating toward the initial rupture point the second sequence which involved large slip rates may have caused substantial stress loading prompting the unstable dynamic rupture of the mainshock

global positioning system gps and gps acoustic observations insight into slip along the subduction zones around japan the global positioning system gps is one of the most powerful tools available for observation of earth s surface deformation in particular coseismic postseismic slow transient and interseismic deformation have all been observed globally by gps over the past two decades especially in subduction zones moreover gps acoustic techniques have been developed for practical use in the past decade allowing observation of offshore deformation immediately above slip regions here we describe the application of gps and gps acoustic observations to the detection of deformation due to plate boundary slip for interplate earthquakes as well as afterslip and slow slip events in subduction zones around japan where geodetic data coverage is particularly dense the data demonstrate temporally variable strain accumulation in the source region of the 2011 mw 9 0 tohoku oki earthquake and observation of the huge slip of the tohoku oki earthquake near the trench using gps acoustic methods has considerably advanced o

observations of atmosphere ocean coupling in midlatitude western boundary currents oceanographic fields derived from the geosat altimeter and atmospheric fields from the european centre for medium range weather forecasts ecmwf were examined for both the western north pacific ocean and the western north atlantic ocean to determine the nature of the coupling despite the short data records approximately 2 5 years correlation analyses of nonseasonal fluctuations showed similar relationships for both oceans correlations between the height difference across the jets surface transport and the path of the western boundary currents suggested that there is a structural change of the recirculation gyres associated with a path change with timescales of 5 9 months both wind stress and wind stress curl were clearly correlated with the surface transport and path in each ocean although net surface heat flux and wind stress were correlated there was no clear correlation between net surface heat flux from ecmwf and surface transport over the entire study region additional regional analyses of the north atlantic showed a consistent relationship between cooling sea surface temperature sst and surface transport west of 62 w anomalous cooling accompanied by cyclonic wind anomalies corresponds to a weaker sst gradient across the gulf stream and decreasing surface transport because the surface transport fluctuations to the west and east of 62 w in the western north atlantic are not correlated structural changes in the recirculation gyres which have their maximum variations east of 62 w may not be related to surface heat flux variations

a synthetic geoid validation of geosat mesoscale dynamic topography in the gulf stream region a validation study is carried out for the geosat altimeter in the gulf stream meander and ring region a synthetic geoid containing the medium scales of interest for mesoscale research is constructed by subtracting an independent estimate of the oceanographic mean dynamic topography from the altimetric sea surface the oceanographic mean dynamic topography which is concurrent with the altimetric mean is derived from a year of real time nowcasts and forecasts gulfcast based on assimilating a composite data set into a dynamical model using the synthetic geoid absolute dynamic topography from geosat and gulfcast for a year and 4 months in 1988 and 1989 compare very well in signal shape and feature locations sixteen cases of comparison of dynamic heights derived from axbts along geosat tracks in 1987 are made with geosat absolute topography the rms difference is less than 10 cm thus the comparison of these two independent data sets validates the altimeter and the synthetic geoid within the noise and error levels of the system

velocity and slip dependent weakening in simulated fault gouge implications for multimode fault slip in addition to the velocity dependence of friction slip dependence may play a major role before and during earthquake slip in fault zones we performed laboratory friction experiments on simulated fault gouges measuring both the velocity and slip dependence of friction in velocity step tests the pure velocity dependent component of friction measured over short displacements shows both velocity strengthening and velocity weakening friction depending on the amount of slip considered however we observe that increases in sliding velocity can induce slip weakening behavior which overwhelms the velocity dependence resulting in large overall weakening especially at rates 1 m s on natural tectonic faults this suggests that a velocity perturbation such as coseismic rupture propagating onto a fault patch could induce instability via large slip weakening therefore a fault which is experiencing a transient slip or slow earthquakes may be more easily induced to slip coseismically if a dynamic rupture from large earthquake propagates onto the fault

coseismic slip distribution of the 2011 off the pacific coast of tohoku earthquake m9 0 refined by means of seafloor geodetic data 1 on 11 march 2011 the devastating m9 0 tohoku earthquake occurred on the interface of the subducting pacific plate and was followed by a huge tsunami that killed about 20 000 people several geophysical studies have already suggested that the very shallow portion of the plate interface might have played an important role in producing such a large earthquake and tsunami however the sparsity of seafloor observations leads to insufficient spatial resolution of the fault slip on such a shallow plate interface for this reason the location and degree of the slip has not yet been estimated accurately enough to assess future seismic risks thus we estimated the coseismic slip distribution based on terrestrial gps observations and all available seafloor geodetic data that significantly improve the spatial resolution at the shallow portion of the plate interface the results reveal that an extremely large greater than 50 m slip occurred in a small about 40 km in width and 120 km in length area near the japan trench and generated the huge tsunami the estimated slip distribution and a comparison of it with the coupling coefficient distribution deduced from the analysis of the small repeating earthquakes suggest that the 2011 tohoku earthquake released strain energy that had accumulated over the past 1000 years probably since the jogan earthquake in 869 the accurate assessments of seismic risks on very shallow plate interfaces in subduction zones throughout the world can be obtained by improving the quality and quantity of seafloor geodetic observations

heat budget in the kuroshio extension region 1993 99 abstract processes responsible for the seasonal and interannual variations of the sea surface temperature as well as of the heat content of the upper ocean 0 400 m in the kuroshio extension region are examined from a 3d advection diffusion model in finite elements with an embedded bulk mixed layer the geostrophic velocity is specified externally from topex poseidon altimeter data and ekman velocity is specified from ncep wind stress the thermal field from the model shows good agreement with observations while both atmospheric and oceanic processes are required to explain observed nonseasonal sst changes the interannual heat storage rate is dominated by horizontal advection in particular the transition between an elongated and a contracted state of the kuroshio caused by geostrophic advection has a clear signature in the sst there is an indication that this process is accompanied by consistent changes in nonseasonal entrainment when the kuroshio is in an elongated state and warmer waters are pr

co and postseismic deformation of the 28 march 2005 nias mw 8 7 earthquake from continuous gps data 1 global positioning system gps measurements registered up to 5m of coseismic displacements during the 28 march 2005 mw 8 7 nias earthquake indonesia the vertical offsets put tight constraints on the northern and southern limit of the rupture the inferred coseismic slip distribution indicates high slip patches near the epicenter and near the southern extent of the 26 december 2004 aceh andaman rupture where aftershocks have been abundant six months of postseismic time series are better fit with a logarithmic instead of exponential function suggesting that the postseismic deformation is likely controlled by afterslip our inversion model predicts afterslip to be concentrated both up and down dip from patches of maximum coseismic slip where aftershocks are sparse the shallow afterslip adds further evidence that the earthquake probably did not break the surface with implications for tsunami generation and instead caused aseismic deformation in shallow parts of the subduction zone after the event

seasonal axis migration of the upstream kuroshio extension associated with standing oscillations the topex poseidon altimeter data from october 1992 to october 1998 are analyzed to investigate the seasonal cycle of the sea surface height ssh in the upstream region of the kuroshio extension after removing steric height changes caused by surface buoyancy fluxes two maxima of the seasonal ssh amplitude are found around the crest and trough of the quasi stationary meanders as standing waves accompanied with nodes of amplitude minima seasonal variations are identified in the subsurface temperature at 400 m depth similar to those of ssh in amplitude and phase associated with the standing waves the current follows a straight path in fall and then changes to a meandering path in spring from a composite map of the seasonal kuroshio extension axes nodes of minimum displacement are found one node is located over the izu ridge while the others are located in the areas where meridional acceleration is large the seasonal axis migration of the upstream kuroshio extension is regulated by these nodes

altimetric signal and three dimensional structure of the sea in the channel of sicily the 1996 altimeter synoptic mesoscale plancton experiment alt symplex was specifically designed to perform in situ measurements simultaneous with the passage of topex poseidon t p and ers 2 over selected tracks in the central and eastern sicily channel this experiment made it possible to have for the first time a validation of altimetry with in situ data over the mediterranean where weak dynamics results in a modest sea elevation rarely exceeding 10 cm historical infrared and altimetric satellite data were first analyzed in order to study the variability of the circulation in the area the comparative and integrative analysis of simultaneous satellite data and in situ measurements permitted investigation of the relation between the altimeter derived surface topography and the three dimensional structure of the sea the pearson correlation coefficients between altimeter data and dynamic heights along track resulted to be 0 72 0 89 t p and 0 88 ers 2 when using conventional repeat track analysis for t p a correlation value of 0 87 was found for time differences computed basing on a collinear analysis technique this analysis also led to the identification of a strong barotropic component of the velocity field located near the sicilian continental shelf where it is responsible for approximately 60 of the signal

seasonal and interannual variations in geostrophic velocity in the middle atlantic bight 1 more than 6 years of measurements from the topex poseidon t p altimeter are used to study the seasonal and interannual variations of the geostrophic velocity anomalies in the middle atlantic bight region geostrophic velocities from t p data are compared with the simultaneous low pass filtered current meter data the correlations are all above 95 significance for the three current meter observations at the 1000 m 2210 m and 2990 m isobaths the seasonal mean geostrophic currents from 63 75 w show coherent variations along isobaths with seasonal reversals toward the southwest during the winter and toward the northeast during the summer the eof analysis indicates that the seasonal reversals disappeared during 1996 this disruption is part of the intensification of the slope sea gyre and is related to the southward shift of the gulf stream which acts as the boundary between the subpolar and subtropical gyres the gulf stream moved farther south during 1996 1998 the variations in the gulf stream position may be caused by the wind stress wind stress curl change

the effect of the new england seamounts on gulf stream meandering as observed from satellite ir imagery abstract it is commonly held belief that meandering of the gulf stream increases dramatically downstream of the new england seamount chain in fact this appears not to be the case the envelope of gulf stream northern edges derived from 30 months of satellite data remains constant from 65 to 58 w only the mean of the integrated path length normalized by the mean path length appears to increase downstream of the seamounts but at very nearly the same rate as upstream of them

synoptic gulf stream velocity profiles through simultaneous inversion of hydrographic and acoustic doppler data data from a shipborne acoustic profiling device have been combined with conductivity temperature depth o 2 sections across the gulf stream to form estimates of the absolute flow fields the procedure for the combination was a form of inverse method the results suggest that at the time of the observations june 1982 the net gulf stream transport off hatteras was 107 11 sv and that across a section near 72 5ow it had increased to 125 6 sv subject to further uncertainty from the definition of the stream the transport of the deep western boundary current was 9 3 sv these and other transport estimates are plausibly close to previous calculations but we do not claim that they represent the temporal mean for comparison purposes we have done an inversion using the hydrographic o 2 data alone as in previously published results and obtained qualitative agreement with the combined inversion inversion of the acoustic measurements alone when corrected for instrument biases leaves unacceptably large mass transport residuals in the deep water our conclusion is that the inversion of the combined data sets produces results much improved over those from using either acoustic or hydrographic chemical constraints in isolation the procedures are close analogues to those which can be used with satellite altimeters and are a procedure for obtaining very accurate geoid slope measurements

profiling the gulf stream with a current meter mooring a current meter mooring was deployed for one year at the mean position of the gulf stream at 68 w with instruments from 400 m to 4000 m it provides the first unambiguous evidence that the gulf stream extends from top to bottom of the water column using the strong cross stream temperature structure to derive a horizontal coordinate related to temperature we estimate the width and transport of the gulf stream for four individual events and we determine an average profile of the vertical and cross stream structure of the gulf stream a conservative estimate of transport for this average profile indicates that the gulf stream has a transport of 103 106 m s 1 at 68 w

spatial distribution of the faulting types of small earthquakes around the 2011 tohoku oki earthquake a comprehensive search using template events we developed a new method to classify the faulting types of small earthquakes using interevent waveform similarity and applied it to earthquakes in the northeast japan subduction zone in the method we used separate time windows for p and s waves and established a relationship between waveform similarity and differences in focal mechanisms from event pairs whose focal mechanisms we know then we applied the relationship to many pairs of such focal mechanism known events 5607 from the moment tensor catalogue and 3623 events from the interplate repeating earthquakes catalogue and focal mechanism unknown events for the period from 1984 to 2013 as a result 8984 earthquakes were newly classified into interplate n 5401 noninterplate thrust n 631 normal n 1070 and strike slip faulting earthquakes n 165 from the new data set which doubles the number of mechanism types we confirmed that there have been almost no interplate earthquakes in the area of large coseismic slip of the tohoku oki earthquake since that event we also saw that this trend continued until at least the end of 2013 suggesting a nearly complete stress release and slow interplate stress recovery the abundant interplate aftershocks also indicate the precise spatial extent of postsesimic slip which is usually difficult to obtain from land based geodetic data the postseismic slip also suggests stress concentration at the asperities of the 1968 tokachi oki m7 9 and 1994 sanriku oki m7 6 earthquakes the present day faulting types offshore tohoku correlated well with the static stress change from the tohoku oki earthquake suggesting a stress state change during the earthquake cycle of megathrust earthquakes

brittle rotational faults and the associated shear heating abstract brittle faulting related shear heating is important in petroleum geosciences tectonics and seismic studies temporal variation of shear heat related temperature rise for rotational and roto translational faults are investigated in this work for planar fault planes devoid of gouge and any secondary faulting temperature rise is proportional to the coefficient of friction and rate of angular slip tectonically realistic physical parameters for rotational faults especially prolonged faulting can significantly increase temperature by shear heating at shallow crustal depth capable of thermal maturity of hydrocarbons

estimating mean dynamic topography in boundary currents and the use of argo trajectories a mean dynamic topography mdt is required to estimate mean transport in the ocean to combine with altimetry to derive instantaneous geostrophic surface velocities and to estimate transport from shipboard hydrography a number of mdts are now available globally but differ most markedly in boundary currents and the antarctic circumpolar current we evaluate several mdts in two boundary currents off new zealand in the subtropical western boundary current system east of the country and in the subantarctic front to the south using satellite hydrographic and argo observations near two altimeter tracks argo float trajectories are combined with estimates of shear to produce new mdts along both altimeter tracks sufficiently high numbers of argo floats travel in both boundary currents to allow a useful estimate of the mean flow at 1000 m depth and conservation of potential vorticity is used to account for more realistic flow paths in finding a mdt we show the uncertainties in the estimates of velocity differences between 1000 m and the surface from density climatologies while often not estimated need to be considered the mdt computed from the argo trajectories is generally consistent with the cls09 mdt in both boundary currents and in some locations distinctly different from the mdt using a level of no motion assumption the comparison suggests velocities from argo trajectories can be usefully combined with other observations to improve estimates of flows and mdt in boundary currents

a kuroshio extension system model study decadal chaotic self sustained oscillations abstract a model study of the kuroshio extension system in which forcing is provided by a time independent climatological wind yields a mean meandering path and a decadal variability of the jet in significant agreement with in situ and altimetric measurements a reduced gravity primitive equation ocean model is implemented in a box spanning the whole north pacific including a schematic coastline at the western side and an analytical wind forcing is determined according to the ecmwf and comprehensive ocean atmosphere data set coads climatologies the modeled time averaged kuroshio extension shows meanders northern and southern recirculation regions and a jet penetration that are in good agreement with the corresponding observed climatological features this result suggests that intrinsic nonlinear mechanisms are likely to play a major role in determining the meander pattern of the mean flow the internal low frequency variability is found to be a chaotic bimodal self sustained oscillation between a

dynamic topography estimates using geosat data and a gravimetric geoid in the gulf stream region summary a gravimetric geoid undulation on a 3 x 3 grid has been calculated in the gulf stream region 30 5 i 45 278 5 i 5 318 these undulations were calculated using two 360 potential coefficient models land ship and altimeter derived gravity anomalies and bathymetric data least squares collocation and fast fourier transform procedures were used with various data selection and gridding procedures results from five different undulation computations are described with comparisons made with synthetic geoid undulations along geosut tracks in the region the standard deviation of the undulation differences was f14cm when a cubic polynomial was used to model long wavelength errors a point verification of the geoid undulation at the laser tracking station on bermuda was also made with a discrepancy ground truth minus model undulation of 40 cm within the predicted standard deviation the gravimetric geoid undulation was used to compute dynamic topography along geosat tracks for comparison with existing estimates based on hydrographic data in the gulf stream region the agreement between these two estimates is on the order of f15 cm although the discrepancies can reach 60 cm the larger differences are usually associated with a location on a track that passes near a seamount where the gravity data may be inadequate to represent the high frequency variations in the geoid undulations this effect will be represented in the undulation standard deviations that have been calculated using the least squares collocation procedure the average accuracy is fl6cm with the range from f14 to f48cm the dynamic height derived from the gravimetric undulations and altimeter data has been used to calculate characteristics of the gulf stream width velocity centre location height profile using an implied velocity model for the set the results are compared with previous estimates with generally good agreement however the maximum velocities and the jump function are approximately 30 per cent larger than previous studies that used an average of altimeter tracks to define the geoid undulation the dynamic topography was calculated for the entire region using a mean sea surface based on geos 3 seasat and geosat data the results are compared with two hydrographic estimates due to martel wunsch and letraon mercier the agreement is at the f25cm level with the best correlation coefficient reaching 0 72 with the martel wunsch model

western boundary currents and frontal air sea interaction gulf stream and kuroshio extension abstract in the northern hemisphere midlatitude western boundary current wbc systems there is a complex interaction between dynamics and thermodynamics and between atmosphere and ocean their potential contribution to the climate system motivated major parallel field programs in both the north pacific kuroshio extension system study kess and the north atlantic climate variability and predictability clivar mode water dynamics experiment climode and preliminary observations and analyses from these programs highlight that complexity the gulf stream gs in the north atlantic and the kuroshio extension ke in the north pacific have broad similarities as subtropical gyre wbcs but they also have significant differences which affect the regional air sea exchange processes and their larger scale interactions the 15 yr satellite altimeter data record which provides a rich source of information is combined here with the longer historical record from in situ data to describe and compare the curr

existence of interplane earthquakes and neutral stress boundary between the upper and lower planes of the double seismic zone beneath tohoku and hokkaido northeastern japan abstract using data from the recently constructed nationwide dense seismic network we determined the hypocenters and focal mechanisms of many intermediate depth intraslab earthquakes within the pacific slab beneath northeastern japan the results show that in addition to the upper and lower planes of the double seismic zone a considerable number of intraslab earthquakes also occur between the two planes this interplane earthquake activity is not homogeneously distributed in space being high beneath eastern hokkaido and the fore arc regions of southeast and central tohoku the focal mechanisms of the interplane earthquakes tend to be of the down dip compressional type dc in tohoku and the hokkaido corner but down dip tensional type de in eastern hokkaido upper plane earthquakes are characterized by dc type stress while lower plane earthquakes are de type in both tohoku and eastern hokkaido the existence of interplane earthquakes enables estimation of the position of the neutral plane between the upper plane dc stress and the lower plane de stress we did so by applying stress tensor inversions to focal mechanism data obtained in the present study and japan meteorological agency jma data the results show that the neutral plane is located about 22 km beneath the upper plate interface beneath tohoku but only about 10 km beneath the upper surface beneath eastern hokkaido this difference in the location of the neutral plane may be due to the difference in buoyancy force exerted by the less dense metastable olivine wedge that is a result of the oblique plate subduction beneath hokkaido comparison of large intraslab earthquakes beneath the two regions shows that their aftershock areas are limited by the neutral plane suggesting that large earthquake ruptures are confined to either the dc or de stress field and do not go beyond the neutral plane

estimation of seismic centroid moment tensor using ocean bottom pressure gauges as seismometers we examined the dynamic pressure change at the seafloor to estimate the centroid moment tensor solutions of the largest and second largest foreshocks mw 7 2 and 6 5 of the 2011 tohoku oki earthquake combination of onshore broadband seismograms and high frequency 20 200 s seafloor pressure records provided the resolution of the horizontal locations of the centroids consistent with the results of tsunami inversion using the long period 10 min seafloor pressure records although the depth was not constrained well whereas the source locations were poorly constrained by the onshore seismic data alone also the waveforms synthesized from the estimated cmt solution demonstrated the validity of the theoretical relationship between pressure change and vertical acceleration at the seafloor the results of this study suggest that offshore pressure records can be utilized as offshore seismograms which would be greatly useful for revealing the source process of offshore earthquakes

gulf stream surface transport and statistics at 69 w from the geosat altimeter geosat altimeter height measurements for the gulf stream for three subtracks from the exact repeat mission were processed to remove the geoid and mean gulf stream height a gaussian model for the gulf stream velocity profile was used to predict the form of the residual height profiles seen by geosat and the mean height profile using estimates of the width and position derived from the height residuals estimates of the maximum surface velocity and the surface transport were obtained by a least squares fit of the synthetic height profiles to the data location statistics from the geosat data were in good agreement with values obtained from infrared images of the gulf stream maximum surface velocities were typically between 1 2 and 2 0 m s 1 the time series showed that surface transport is correlated primarily with the magnitude of the surface velocities although an anomalously large increase in surface transport in the winter of 1987 1988 was caused by an increase in the width of the gulf stream an analysis of the average annual signal in transport showed maximum values in the late fall and minimum transport in the late spring maximum minimum surface transport generally occurred when the gulf stream was north south of its mean position

on the meridional surface profile of the gulf stream at 55 w nine month records from nine inverted echo sounders iess are analyzed to describe the mean baroclinic gulf stream at 55 w ies acoustic travel times are converted to thermocline depth which is optimally interpolated kinematic and dynamic parameters gulf stream meridional position velocity and vorticity are calculated primary gulf stream variability is attributed to meandering and changes in direction a mean stream coordinate relative to gulf stream instantaneous position and direction meridional profile is derived and compared with results presented by other investigators the mean velocity is estimated at 0 84 m s 1 directed 14 to the right of eastward and the thermocline 12 c drops 657 m north to south corresponding to a baroclinic rise of the surface of 0 87 m the effect of gulf stream curvature on temporal mean profiles is found to be unimportant and of minimal importance overall the derived downstream current profile is well represented by a gaussian function and is about 190 km wide where it crosses zero surface baroclinic transport is estimated to be 8 5 104 m2 s 1 and maximum shear flanking the maximum is 1 2 10 5 s 1 results compare well with other in situ observational results from the same time period on the other hand analyses by others of concurrent satellite altimetry geosat suggest a considerably narrower more intense mean gulf stream

seasonal variations of the large scale geostrophic flow field and eddy kinetic energy inferred from the topex poseidon and jason 1 tandem mission data 1 geostrophic surface velocity anomalies are used to analyze the annual variations of the large scale geostrophic currents and of the eddy kinetic energy eke field of the ocean circulation the underlying geostrophic currents were estimated from the jason 1 topex poseidon jtp tandem altimetric sea surface height data using the parallel track approach with a 10 km along track resolution however because of the given separation of the tracks of the two satellites only large mesoscale eddies are resolved by the tandem measurements the analysis covers the entire 3 year period of the tandem mission 109 repeat cycles from september 2002 to september 2005 the analysis of the seasonal flow changes reveals annual changes of all major current systems but especially of the zonal flow field in low latitudes leading to zonal jets on the annual cycle in the southern pacific atlantic and indian oceans in middle and high latitudes indications of a seasonally modulated strength of the sverdrup circulation emerge from the analysis the eke field also shows changes in its amplitude on the annual period in low latitudes those can be rationalized as resulting from seasonally modulated currents in middle and high latitudes changes in the wind driven barotropic circulation loom large which are not represented in other altimetric velocity products results shown suggest that velocity time series of the jtp tandem mission should be continued through similar constellations e g of jason 1 and jason 2

low frequency variability in regions of the kuroshio extension and the gulf stream using sea surface height data collected by the topex poseidon altimeter we studied the low frequency variability in the kuroshio extension and gulf stream the most significant signals are the basin wide background seasonal cycle and low frequency wave activity generated over major bottom bathymetry and subsequent westward propagation in both regions the spatial structures of the seasonal cycle in the two regions are quite different in the kuroshio extension the seasonal cycle has a northeast southwest orientation and lies closer to the western boundary whereas it has an east west orientation and lies more offshore in the gulf stream the close relationship between the low frequency wave activity and major bottom bathymetry features is discussed through both empirical orthogonal functional eof analysis and calculation of eddy kinetic energy and reynolds stress the spatial structures of these eddy statistics are fundamentally different from those of high frequency mesoscale variability they are not in the proximity of maximum time mean flow but rather they lie mostly to the west of major bottom bathymetry the close association of the clusters of local maximum eddy properties with major bottom topographic features in both regions wave generation over the major bottom topographic features and subsequent westward propagation and difference of the eddy statistics from that associated with high frequency mesoscale variability all suggest that unlike in the case with high frequency mesoscale variability generation in which internal dynamics of the background mean flow such as nonlinear instability plays a fundamental role external forcing through bottom topography must play a fundamental role in generating the low frequency wave activity

seismic activity preceding the 2011 m w 9 0 tohoku earthquake japan analyzed with multidimensional template matching the observation of a transient slip 1 month before the rupture of the 2011 tohoku earthquake is a conandrum since the area was supposedly fully coupled a better understanding of the mechanisms at work during the preseismic phase is thus fundamental however the configuration of the pacific plate and the location of the tohoku rupture zone 200 km from the coast make it difficult to detect microseismic events in this study we use a multidimensional template matching mdtm technique to detect earthquakes that are hidden in the noise the temporal distribution of these 395 newly detected earthquakes provides new insights on the slip history of the megathrust earthquake epicentral zone the detected events can be separated into two groups 187 low frequency detections below 5 hz that well recorded the episodes of earthquake migration prior to the tohoku earthquake and 208 high frequency detections above 10 hz that occurred close to the rupture zones of the m 4 8 6 earthquakes that struck between the 9 march 2011 m7 3 foreshock and the 30 november 2010 tohoku oki earthquake the seismic rate of these high frequency detection events starts to increase on 30 november 2010 until the tohoku earthquake

determination of the surface geostrophic velocity field from satellite altimetry 1 presently available marine geoid models are not accurate enough to extract the mean surface circulation directly from satellite altimetry a novel method for estimating the mean velocity field of major ocean current systems is derived from the free surface boundary condition with a given quasi geostrophic balance for the horizontal surface flow a scaling analysis of this boundary condition indicates that although the vertical velocity w is mostly balanced by the local change of the free surface t useful information on the mean current is contained in a small ageostrophic departure t w our method consists in the development of a simple algebraic equation with two unknowns and an adjustable parameter associated with t assuming that the latter is proportional to t w most interestingly t and all other coefficients of the equation can be determined from altimetry the altimeter data used is combined topex poseidon ers gridded data and the solution is obtained by least squares minimizing the contribution from the time variable part of the parameter and prescribing the zonal direction of the mean current the method which is found to be particularly useful for quasi zonal high energy current systems has been validated against direct observations in the gulf stream and southern ocean comparisons with direct observations and monte carlo experiments suggest an overall solution error of about 10 cm s 1 once calibrated against regional velocity statistics this method will be able to determine from altimetry the mean or instantaneous surface velocity field down to the frontal scale with a realism that has been inaccessible because of the geoid constraint

episodic slow slip events in the japan subduction zone before the 2011 tohoku oki earthquake abstract we describe two transient slow slip events that occurred before the 2011 tohoku oki earthquake the first transient crustal deformation which occurred over a period of a week in november 2008 was recorded simultaneously using ocean bottom pressure gauges and an on shore volumetric strainmeter this deformation has been interpreted as being an m6 8 episodic slow slip event the second had a duration exceeding 1 month and was observed in february 2011 just before the 2011 tohoku oki earthquake the moment magnitude of this event reached 7 0 the two events preceded interplate earthquakes of magnitudes m6 1 december 2008 and m7 3 march 9 2011 respectively the latter is the largest foreshock of the 2011 tohoku oki earthquake our findings indicate that these slow slip events induced increases in shear stress which in turn triggered the interplate earthquakes the slow slip event source area on the fault is also located within the downdip portion of the huge coseismic slip area of the 2011 earthquake this demonstrates episodic slow slip and seismic behavior occurring on the same portions of the megathrust fault suggesting that the faults undergo slip in slow slip events can also rupture seismically

implications of recent asperity failures and aseismic creep for time dependent earthquake hazard on the hayward fault abstract the probability of large seismic events on a particular fault segment may vary due to external stress changes imparted by nearby deformation events including other earthquakes and aseismic processes such as fault creep and postseismic relaxation the hayward fault hf undergoing both seismic and aseismic fault slip provides a unique opportunity to study the mutual relation of seismic and aseismic processes on a fault system we use surface deformation data obtained from insar interferometric synthetic aperture radar creepmeters and alinement arrays together with constraints provided by repeating earthquakes to investigate the kinematics of fault creep on the northern hf and its relation to two seismic clusters m w 4 1 in october 2011 and march 2012 and an m w 4 2 event in july 2007 recurrences of nearby repeating earthquakes show that these episodes involved both seismic and aseismic slip we model the stress changes due to fault creep and the recent seismic activity on the locked central asperity of the hf which is believed to be the rupture zone of past and future m 7 earthquakes the results show that the shallow fault creep stresses the major locked central patch at an average rate of 0 001 0 003 mpa yr in addition to background stressing at 0 01 0 015 mpa yr given the time dependent nature of the creep occasional deviations from this stressing rate occur we find that the 2011 seismic cluster occurred in areas on the fault that are stressed up to 0 01 mpa yr due to aseismic slip on the surrounding segments suggesting that the occurrence of these events was encouraged by the fault creep changes in the probability of major earthquakes can be estimated from the imparted stress from the recent earthquakes and associated fault creep transients we estimate that the 1 day probability of a large event on the hf only increased by up to 0 18 and 0 05 due to the static stress increase and stressing rate change by the 2011 and 2012 clusters for the july 2007 south oakland event m w 4 2 the estimated increase of short term probabilities is 50 highlighting the importance of short term probability changes due to transient stress changes

estimating the surface transport of meandering oceanic jet streams from satellite altimetry surface transport estimates for the gulf stream and kuroshio extension abstract a method has been developed to detect the location width maximum velocity and suffice transport of a meandering oceanic jet stream from satellite altimetry ale method is based on a nonlinear least squares scheme in which gaussian shaped velocity profiles are fitted to explain the observed current variability in the meandering region the method has been applied to 25 geosat tracks in the kuroshio extension and gulf stream for the first you of the geosat exact repeat mission a reasonably smooth circulation pattern has emerged for the surface transport for both currents at opposed to the widely varying direct transport estimates after leaving the coast both currents have surface strength of the order of 90 103 m2 a 1 equivalent to a 90 cm height jump i e the sea surface height difference across the jet they continue to gain strength downstream until a maximum of the order of 130 10 3 m2 a 1 is reached near 150 e for the kuroshio and 63 w for the gulf stream the gulf stream the

observations on the long period variability of the gulf stream downstream of cape hatteras to examine the long period variability of the gulf stream sea level residuals relative to a 2 year mean sea level in the gulf stream downstream of cape hatteras between 75 w and 60 w longitude are used residuals as derived from geosat altimetry between november 1986 and december 1988 were gridded in space and time at a temporal resolution of 10 days and spatial resolution of 1 4 complex empirical orthogonal function ceof analysis was applied to the data set to extract the spatially correlated signal with the original data sub sampled to 1 2 in addition to determining the space time scales and propagation characteristics of the different modes wavenumber frequency spectral techniques were used to separate the variability into propagating and stationary components the ceof technique applied to the data set indicated that the first four ceof modes accounted for 60 of the variability and were found to be above the noise level 99 of the time ceof 1 was associated with westward propagation at 5 km d at a wavelength of 2000 km and eastward propagation at 1 2 km d centered at a 500 km wavelength this first ceof is in good agreement with thin jet equivalent barotropic models which predict westward propagation for wavelengths greater than 1130 km a deflection of the wavelike pattern at 65 w also indicates a possible topographic effect a simple scaling of the effect of topography indicates that for length scales longer than the internal rossby radius of deformation the topographic term is at least of the same order of magnitude as the beta effect the second ceof was more broadbanded in wavenumber space with eastward propagation occurring in a wavenumber frequency band between 300 and 1400 km and 0 5 and 2 0 cycles yr the third ceof is similar in structure to the first but with less energy ceof 4 was clearly identifiable with higher frequencies than the first three with westward propagation at 4 km d the spatial location of this mode along with the westward propagation indicates possible influences from eddy stream interactions thus topography rossby wave dynamics and eddy stream interactions all appear to have a significant role in determining the space time scales and propagation properties of the long period response of sea level in the gulf stream

gulf stream variability and ocean atmosphere interactions abstract time series of gulf stream position derived from the topex poseidon altimeter from october 1992 to november 1998 are used to investigate the lead and lag relation between the gulf stream path as it leaves the continental shelf and the changes in sea level pressure surface wind stress and sea surface temperature sst as given by the ncep reanalysis the dominant signal is a northward southward displacement of gulf stream axis 11 to 18 months after the north atlantic oscillation nao reaches positive negative extrema a sst warming cooling peaking north of the gulf stream is also seen to precede the latitudinal shifts but it is a part of the large scale sst anomaly tripole that is generated by the nao fluctuations there is no evidence that the gulf stream shifts have a direct impact onto the large scale atmospheric circulation a fast passive response of the gulf stream to nao forcing is also suggested by a corresponding analysis of the yearly mean gulf stream position estimated from

coseismic slip model of offshore moderate interplate earthquakes on march 9 2011 in tohoku using tsunami waveforms abstract we estimated the coseismic slip distribution associated with the mw 7 2 and 6 5 foreshocks of the 2011 tohoku oki earthquake based on analysis of the tsunami waveform records obtained just above their focal areas the results show that the main rupture areas of each of the foreshocks do not overlap with each other and show a distribution that is complementary to the postseismic slip area of the first mw 7 2 foreshock as well as to the epicenters of smaller earthquakes during foreshock activity after the second largest foreshock seismicity increased in the area between the rupture area of the second largest foreshock and the mainshock epicenter suggesting propagation of aseismic slip towards the mainshock epicenter the calculated stress drop of the second largest foreshock was smaller than the largest one implying strength reduction during the postseismic period of the largest foreshock based on a comparison of coastal tsunami records it is suggested that the asperity ruptured in the m 7 0 earthquake in 1981 ruptured again during the largest foreshock in 2011 but it expanded to the updip side of the 1981 rupture area and became larger in magnitude exemplifying the irregularity of earthquake recurrence in the area

an estimate of global absolute dynamic topography abstract we estimate the absolute dynamic topography of the world ocean from the largest scales to a short wavelength cutoff of about 6700 km for the period july through september 1978 the data base consisted of the time averaged sea surface topography determined by seasat and geoid estimates made at the goddard space flight center the issues are those of accuracy and resolution use of the altimetric surface as a geoid estimate beyond the short wavelength cutoff reduces the spectral 1eakage in the estimated dynamic topography from erroneous small scale geoid estimates without contaminating the low wavenumbers comparison of the result with a similarly filtered version of levitus historical average dynamic topography shows good qualitative agreement there is quantitative disagreement but it is within the estimated errors of both methods of calculation

the 2014 cephalonia earthquakes finite fault modeling fault segmentation shear and thrusting at the nw aegean arc greece we present refined finite fault models ffm for the 2014 cephalonia keffalinia kefalonia seismic sequence mw 6 0 at the nw edge of the aegean arc ionian sea the area represents the seismically most active part of europe and a continental promontory in which fault modeling is a challenge because of structural complexity and poor coverage by seismological gps and insar data inversion was based on gps data and a new algorithm permitting fusion of slip vectors of individual earthquakes and of their cumulative dislocation and accepting constraints and collocation type analysis of uncertainties computed ffm which correspond to an essentially strike slip fault and a blind shallow oblique slip thrust were assessed by sensitivity analysis and insar data and are consistent with the tectonic fabric of the area they can also explain the observed extreme peak ground accelerations the 2014 faults in combination with ffms of the 2003 and 2015 leucas lefkada lefkas earthquakes farther ne and of the 1983 m7 0 earthquake farther sw constrain a 100 km long immature strike slip fault zone along close to the cephalonia leucas coasts this fault pattern previously regarded as a poorly documented cephalonia transform fault consists of occasionally overlapping oblique slip segments with variable geometric and kinematic characteristics in a shear zone landwards of the plate interface as evidence from seismic profiles reveals this pattern may explain the enigmatic superimposition of shear and compression in the nw edge of the aegean arc

seasonal and interannual changes in the north atlantic subpolar gyre from geosat and topex poseidon altimetry sea surface slopes from the altimetric satellites geosat and topex poseidon are used to calculate eddy kinetic energy of the north atlantic subpolar gyre 40 65 n 60 5 w using two years of data from each satellite december 1986 to december 1988 and october 1992 to september 1994 respectively interannual differences in the north atlantic current nac are revealed in regions of strong currents the eddies are driven by baroclinic instability of the mean flow are not seasonally varying and may therefore be used as a surrogate for the mean flow itself wind stress curl fields for the same periods show that the northward and southward shifts in the current branches across the mid atlantic ridge are related to interannual differences in the winter wind stress curl pattern when the zero in wind stress curl is well defined and wind stress is at a maximum outside the nac the eddies are driven primarily by wind stress indicated by a significant seasonality time series of eddy kinetic energy and wind stress are generated for the 4 years and the magnitude phase and significance of annual and semiannual signals are determined interannual changes in the timing of the maximum eddy kinetic energy are associated with that of the maximum wind stress with each being shifted by a month or two later or earlier throughout much of the northern north atlantic a significant annual signal in eddy kinetic energy is observed lagging the wind stress by on average 6 weeks a negligible lag is found in the region of the east greenland current and irminger sea whereas the greatest lag about 2 months is found in the labrador sea

coseismic slip propagation on the tohoku plate boundary fault facilitated by slip dependent weakening during slow fault slip slow slip phenomena including earthquake afterslip and discrete slow slip events sse may have a major effect on megathrust earthquakes in subduction zones however the nature of this effect is still incompletely understood here we report that in friction experiments using samples from the plate boundary fault zone in the 2011 tohoku oki earthquake an increase in sliding velocity can induce a change from steady state frictional strength or slip strengthening friction to slip weakening frictional behavior specifically significant slip weakening is caused by velocity steps with initial slip rates consistent with afterslip observed after the largest tohoku earthquake foreshock on march 9th 2011 this suggests that the foreshock afterslip which is slightly faster than discrete sses is favorable for fault weakening that may have contributed to the large coseismic slip during the mainshock on the shallow plate boundary fault during the tohoku oki earthquake

eddy flow characteristics and mean flow interactions in the north pacific the strength shape orientation mean flow interactions and propagation characteristics of the time varying eddy flow determined from topex poseidon altimeter data in the north pacific are investigated using equivalent barotropic diagnostic calculations as presented by hoskins et al 1983 separate calculations for low and high pass flow fields distinguished by periods greater than and less than 6 months respectively are performed and revealed a fundamental difference between the eddy characteristics of the two the areas with largest values of surface eddy kinetic energy occur in the vicinity of the kuroshio extension and the subtropical front near the kuroshio extension the low pass surface eddy kinetic energy is greater than the high pass energy but in the subtropical frontal area the high pass eddy flow accounts for more energy than the low pass flow for both areas the values of eddy kinetic energy are larger in summer than during winter low pass eddy flow tends to be aligned zonally and the high pass eddy flow is aligned meridionally near the subtropical front the ratio of major to minor axis length is typically 1 5 1 whereas near the kuroshio extension that ratio increases to values near 2 1 along the southern boundary of the subtropical gyre the high pass eddy flow tends to propagate eastward relative to the mean flow tending to decrease the gyre strength however the low pass eddy flow propagates westward relative to the mean flow and tends to increase the gyre strength an additional computation of surface heat transport is used to deduce vertical propagation tendencies of the eddy flow and indicates that the low pass flow field transports more heat than the high pass flow with the largest eddy transports occurring near the coast of honshu the sign of the transport indicates a preference for upward energy propagation of the eddy flow there many of the characteristics such as the orientation and propagation tendencies of the eddy flow are similar to eddy flow in the atmosphere and accentuate a similarity between the general circulations of the atmosphere and ocean

persistent westward flow in the azores current as seen from altimetry and hydrography temporal and spatial variability of the eastward flowing jet like azores current is investigated by applying a new method for combining altimetry with hydrography in order to produce absolute surface geostrophic currents challenor et al 1996 the altimeter surface measurements contain information about both the geoid and the geostrophic ocean circulation the geoid signal dominates and is generally not sufficiently well known at the small length scales required to identify the mesoscale ocean signal in this study hydrography is used to distinguish the mean ocean signal from the geoid along an ers 1 satellite track south of the azores during both 3 day repeat phases and thereby determine cross stream absolute dynamic topography of the azores current at high temporal resolution hydrographic data collected near 28 w in march 1992 is combined with ers 1 altimeter data from january march 1992 and january to early april 1994 time series of 3 day repeat profiles of absolute surface geostrophic velocity perpendicular to the altimeter cruise track are examined the azores current absolute velocity profile along this track is rather coherent the current variability is less than the mean surprisingly a persistent westward flow of 25 cm s 1 is observed near 35 n 28 w this flow appears to be a retroflection from the main eastward flowing current an isopycnal analysis reveals the westward flow to be cooler by 0 5 c and fresher by 0 15 practical salinity units than the main body of the azores current the flow appears to persist throughout each of the above 3 month periods in late winter early spring but the question of whether this is a seasonal feature or more permanent remains open it is suggested that the westward flow is topographically controlled

geodetic constraints on afterslip characteristics following the march 9 2011 sanriku oki earthquake japan 1 a magnitude 7 3 foreshock occurred at the subducting pacific plate interface on march 9 2011 51 h before the magnitude 9 0 tohoku earthquake off the pacific coast of japan we propose a coseismic and postseismic afterslip model of the magnitude 7 3 event based on a global positioning system network and ocean bottom pressure gauge sites the estimated coseismic slip and afterslip areas show complementary spatial distributions the afterslip distribution is located up dip of the coseismic slip for the foreshock and northward of hypocenter of the tohoku earthquake the slip amount for the afterslip is roughly consistent with that determined by repeating earthquake analysis carried out in a previous study the estimated moment release for the afterslip reached magnitude 6 8 even within a short time period of 51h a volumetric strainmeter time series also suggests that this event advanced with a rapid decay time constant compared with other typical large earthquakes

meridional displacement of the antarctic circumpolar current observed long term warming trends in the southern ocean have been interpreted as a sign of increased poleward eddy heat transport or of a poleward displacement of the entire antarctic circumpolar current acc frontal system the two decade long record from satellite altimetry is an important source of information for evaluating the mechanisms governing these trends while several recent studies have used sea surface height contours to index acc frontal displacements here altimeter data are instead used to track the latitude of mean acc transport altimetric height contours indicate a poleward trend regardless of whether they are associated with acc fronts the zonally averaged transport latitude index shows no long term trend implying that acc meridional shifts determined from sea surface height might be associated with large scale changes in sea surface height more than with localized shifts in frontal positions the transport latitude index is weakly sensitive to the southern annular mode but is uncorrelated with el nino southern oscillation

episodic subsidence and active deformation of the forearc slope along the japan trench near the epicenter of the 2011 tohoku earthquake abstract to investigate the present day geological deformation occurring off the pacific coast of tohoku japan we obtained high resolution multichannel seismic reflection and bathymetric data in 2007 the study area is located along the japan trench near the epicenter of the 2011 off the pacific coast of tohoku earthquake the seismic profiles do not show active structures indicative of compressional stress on the forearc slope instead recent tectonic deformation is characterized by extensional subsidence and the occurrence of normal faults within a series of small basins on the slope to a water depth of 3000 m these isolated basins are thickest 525 m 0 7 s two way travel time in regions underlying areas of flat bathymetry the isolated basins range in width from several to 40 km and are covered by stratified sediments onlapping at the termination of concave down reflectors the seismic units below the basins show continuous subparallel internal reflectors suggesting that the subsidence related deformation started abruptly and recently the thickness of sediments overlying the unconformity at the top of the cretaceous is roughly constant in the upper slope area however lenticular internal reflection patterns occur locally the lenticular sedimentary units are similar to the isolated basins in terms of their widths and internal reflection patterns we infer that episodes of extensional deformation of the overriding plate in the form of isolated basins have occurred over geological time we suggest that the geological structures of the forearc slope along the japan trench are typical of those resulting from subduction erosion and propose that the episodic subsidence accompanied by normal faulting is the most recent deformation

rupture process of the 2014 iquique chile earthquake in relation with the foreshock activity the rupture process of the 2014 iquique chile earthquake is inverted from teleseismic p wave data applying a novel formulation that takes into account the uncertainty of green s function which has been a major error source in waveform inversion the estimated seismic moment is 1 5 1021 nm mw 8 1 associated with a 140 km long and 140 km wide fault rupture along the plate interface the source process is characterized by unilateral rupture propagation during the first 20 s the dynamic rupture front propagated from the hypocenter to the large asperity located about 50 km southward crossing a remarkably active foreshock area at high velocity of about 3 0 km s but small and irregular seismic moment release rate our result may suggest that the 20 s long initial phase was influenced by the stress drop due to the foreshock activity near the main shock hypocenter moreover the 2 week long swarm like foreshock activity migrating roughly at 5 km day toward the main shock hypocenter and possibly associated slow slip contributed to the stress accumulation prior to the mw 8 1 megaquake the main shock initial rupture phase might have triggered the rupture of the large asperity which had large fracture energy

episodic tremor and slip near the japan trench prior to the 2011 tohoku oki earthquake change in the rates of aseismic deformation prior to large earthquakes is a major area of interest in earthquake physics here we present evidence that episodic tremor and slip occurred in the shallow subduction zone within the source region of the 2011 tohoku oki earthquake prior to the main shock ocean bottom seismometers near the japan trench recorded some excitations in amplitude of ambient noise level accompanying both the 2008 and 2011 slow slip events the observed signals show that low frequencies of 5 8 hz dominated suggesting that the excitations were due to small low frequency tremors accompanying the slow slip events the largest amplitude tremor was observed just before the 2011 event the estimated sources of tremors were possibly distributed within the coseismic slip area of the 2011 event suggesting the shallow plate boundary thrust near the trench is a general location of slow earthquakes

mean sea surface height of the antarctic circumpolar current from geosat data method and application the mean sea surface height across the antarctic circumpolar current has been reconstructed from height variability measured by the geosat altimeter without assuming prior knowledge of the geoid for this study an automated technique has been developed to estimate mean sea surface height for each satellite ground track using a meandering gaussian jet model and errors have been estimated using monte carlo simulation the results are objectively mapped to produce a picture of the mean subantarctic and polar fronts which together comprise the major components of the antarctic circumpolar current the meandering jet model explains between 40 and 70 of the height variance along the jet axes the results show that the fronts are substantially steered by topography and that the jets have an average gaussian width of about 44 km in the meridional direction and meander about 75 km to either side of their mean locations the average height difference across the subantarctic front saf is 0 7 m and across the polar front pf 0 6 m the mean widths of the fronts are correlated with the size of the baroclinic rossby radius

preliminary estimates of gulf stream characteristics from topex data and a precise gravimetric geoid topex sea surface height data has been used with a gravimetric geoid to calculate sea surface topography across the gulf stream this topography was initially computed for nine tracks seven descending and two ascending on cycles 21 to 29 due to inaccurate geoid undulations on one track results for eight tracks are reported in the paper the sea surface topography estimates were used to calculate parameters that describe gulf stream characteristics from two models of the gulf stream one model was based on a gaussian representation of the velocity while the other was a hyperbolic representation of velocity or the sea surface topography the parameters of the gaussian velocity model fit were a width parameter a maximum velocity value and the location of the maximum velocity the parameters of the hyperbolic sea surface topography model were the width the height jump position and the sea surface topography at the center of the stream both models were used for the eight tracks and nine cycles studied comparisons were made between the width parameters the maximum velocities and the height jumps for one track d04 near 36 n 73 w the average width parameter was 69 15 km based on the gaussian velocity fitting and 75 14 km based on the hyperbolic sea surface topography fit with a 10 km smoothing function along the same track the average maximum velocity was 164 30 cm s using the velocity fit and 163 37 cm s with the hyperbolic sea surface topography fit some of the parameter estimates were found to be highly 0 9 correlated when the hyperbolic sea surface topography fit was carried out but such correlations were reduced for either the gaussian velocity fits or the hyperbolic velocity model fit a comparison of the parameters derived from 1 year of topex data showed good agreement with values derived by kelly 1991 using 2 5 years of geosat data near 38 n 66 w longitude width 78 22 km this paper 82 25 km kelly height jump 115 28 cm 123 19 cm maximum velocity 171 59 cm s 1 179 46 cm s 1 the accuracy of the geoid undulations used in the calculations was of the order of 16 cm with the accuracy of a geoid undulation difference equal to 15 cm over a 100 km line in areas with good terrestrial data coverage the north edge of the gulf stream was studied with topex data from cycles 1 to 37 the north edge was located at the position corresponding to the half width of the gulf stream north of the center of the stream along each track with all parameters estimated from the gaussian velocity fit procedure the location of the north edge along one track generally agreed with the location defined by national oceanic and atmospheric administration national ocean survey noaa nos maps based on advanced very high resolution radiometer avhrr data and with a north wall location provided by cornillon at 2 day intervals the results for this topex track showed the north edge at the highest 37 8 n latitude in october november 1992 falling to the lowest 36 9 n latitude in february march 1993 after which the stream moves north a second track 550 km to the east of the first track showed consistent agreement with the cornillon data for the edge location when such data were available in one case with the noaa data there was a 77 km discrepancy between the topex and noaa estimates of the north edge analysis of the sea surface topography suggested the noaa avhrr location may be inaccurate at this one location and time this paper demonstrates that our knowledge of geoid undulations and undulation differences in a portion of the gulf stream region is sufficiently accurate to determine characteristics of the jet when used with topex altimeter data the method used here has not been shown to be more accurate than methods that average altimeter data to form a reference surface used in analysis to obtain the gulf stream characteristics however the results in the paper show the geoid approach may be used in areas where lack of current meandering reduces the accuracy of the average surface procedure

the time mean circulation in the agulhas region determined with the ensemble smoother the time mean circulation in the agulhas retroflection area is determined by combining topex poseidon data and a two layer quasi geostrophic model using the ensemble smoother by taking the time mean circulation as the unknown in the data assimilation procedure the time varying altimeter signal is used to constrain the time mean field the quasi geostrophic model is applied as a strong constraint with only the time mean circulation containing errors inspection of the posterior penalty function showed that the inversion was successful the errors in the time mean sea surface topography reduced from about 10 to about 3 cm a cyclonic recirculation cell over the agulhas plateau was found related to the northward meander of the agulhas return current another cyclonic recirculation cell was found west of africa probably related to the passage of anticyclonic agulhas rings south of it the new field is compared with advanced very high resolution radiometer infrared satellite data confirming the northward meander of the agulhas return current

afterslip and only afterslip following the 2004 parkfield california earthquake 1 an analysis of the first two years of postseismic surface deformations from gps reveals that afterslip is the only mechanism significantly contributing to postseismic deformation following the 2004 m6 parkfield california earthquake finite element modeling shows this event to have been too small to significantly stress the lower crust and upper mantle thus viscoelastic relaxation did not lead to detectable surface displacements similarly coseismically induced pressure changes in the upper crust were not sufficient to induce a measurable poroelastic response from 10 days to two years after the parkfield earthquake postseismic displacements at all gps stations experience the same characteristic decay time 2 weeks this suggests that only afterslip was activated and the distribution of slip remained unchanged in this time period afterslip was found to be broadly distributed in the upper 15 km of the crust and associated with a moment release of much greater magnitude than the coseismic rupture

determining the mean gulf stream and its recirculations through combining hydrographic and altimetric data the altimetric data from the first 2 5 year geosat exact repeat mission were used to estimate the mean sea surface height ssh field in the region of the gulf stream and its recirculation gyres assuming the instantaneous surface velocity field is composed of an eastward flowing jet and two westward recirculating flows we used the time varying surface data from the altimeter to determine the shape of the along track mean ssh profiles and the historical hydrographic data to constrain the net ssh difference across the gulf stream system the two dimensional mean ssh field was determined by objectively mapping the mean height profiles along the ascending and descending tracks the ssh jump across the mean gulf stream has a maximum of 1 15m around 65 w and drops to an almost constant 0 9m downstream of the new england seamount chain nesc while the ssh jump associated with the mean northern recirculating flow is mostly uniform we found that the gulf stream s southern recirculation has two local gyres that are separated by the nesc an attempt was then made to estimate the mean deep circulation in this region by comparing the mean ssh field derived from the altimetry data and the surface dynamic height field based on the historical hydrographic data despite the large uncertainties the mean deep flow pattern thus estimated agrees favorably with the overall circulation pattern from the long term current meter observations like the well defined northern recirculation gyre we found that a continuous southward flow exists along 57 5 w which follows closely along the deep layer potential vorticity contours to the south of the gulf stream the deep circulation consists of two separated recirculation gyres the recirculation gyre to the east of the nesc appears to be trapped around the corner rise

interannual variability of the kuroshio extension system and its impact on the wintertime sst field altimetry data from the first 7 yr topex poseidon t p mission october 1992 september 1999 are analyzed to investigate the interannual variability in regions of the kuroshio extension and its southern recirculation gyre large scale interannual changes of the kuroshio extension system are characterized by the oscillation between an elongated state and a contracted state in the elongated state the kuroshio extension has a larger eastward surface transport a greater zonal penetration and a more northerly zonal mean path all these characteristics are closely connected to the presence of an intense zonally elongated southern recirculation gyre in its contracted state the kuroshio extension has a smaller eastward surface transport a more southerly mean path and is accompanied by a weaker southern recirculation gyre during the t p period the kuroshio extension changed from the elongated state in 1992 93 to the contracted state in 1996 97 and back to the elongated state since late 1997 in addition to these large scale changes the mesoscale eddy field also exhibited prominent interannual changes in the kuroshio extension region in the upstream region between the izu ridge and the shatsky rise the eddy kinetic energy level was generally low while the kuroshio extension was in its elongated state and high while in the contracted state downstream of the shatsky rise on the other hand the eke level was high low when the kuroshio extension was in the elongated contracted state the large scale interannual changes in the kuroshio extension system have a significant impact on the regional wintertime sst anomaly field the warm cold wintertime sst anomalies tend to persist in years when the kuroshio extension is in its elongated contracted state a diagnostic analysis of the surface ocean heat balance indicates that the nonseasonal geostrophic advection by the ocean circulation works to reduce increase the wintertime sst anomalies when the kuroshio extension changes from an elongated contracted state to a contracted elongated state the sst anomalies associated with the large scale changes of the kuroshio extension have an area averaged peak topeak amplitude of 18c and appear independent of the interannual sst changes in the tropical pacific ocean

gulf stream variability in five oceanic general circulation models five non eddy resolving oceanic general circulation models driven by atmospheric fluxes derived from the ncep reanalysis are used to investigate the link between the gulf stream gs variability the atmospheric circulation and the atlantic meridional overturning circulation amoc despite the limited model resolution the temperature at the 200 m depth along the mean gs axis behaves similarly in most models to that observed and it is also well correlated with the north atlantic oscillation nao indicating that a northward southward gs shift lags a positive negative nao phase by 0 2 yr the northward shift is accompanied by an increase in the gs transport and conversely the southward shift with a decrease in the gs transport two dominant time scales appear in the response of the gs transport to the nao forcing a fast time scale less than 1 month for the barotropic component and a slower one about 2 yr for the baroclinic component in addition the two components are weakly coupled the gs response seems broadly consistent with a linear adjustment to the changes in the wind stress curl and evidence for baroclinic rossby wave propagation is found in the southern part of the subtropical gyre however the gs shifts are also affected by basin scale changes in the oceanic conditions and they are well correlated in most models with the changes in the amoc a larger amoc is found when the gs is stronger and displaced northward and a higher correlation is found when the observed changes of the gs position are used in the comparison the relation between the gs and the amoc could be explained by the inherent coupling between the thermohaline and the wind driven circulation or by the nao variability driving them on similar time scales in the models

geodetic data inversion using a bayesian information criterion for spatial distribution of fault slip summary we developed a new inversion method to reconstruct static images of seismic sources from geodetic data using akaike s bayesian information criterion abic coseismic surface displacements are generally related with a slip distribution on a fault surface by linear integral equations parametric expansion of the fault slip distribution by a finite number of known basis functions yields a set of observation equations expressed in a simple vector form incorporating prior constraints on the smoothness of slip distribution with the observation equations we construct a bayesian model with unknown hyperparameters the optimal values of the hyperparameters which control the structure of the bayesian model are objectively determined from observed data by using abic once the values of hyperparameters are determined we can use the maximum likelihood method to find the optimal distribution of fault slip we examined the validity of this method through a numerical experiment using theoretical data with random noise we analysed geodetic data associated with the 1946 nankaido earthquake ms 8 2 by using this method the result shows that the fault slip distribution of this earthquake has two main peaks of 4 and 6 m located off kii peninsula and muroto promontory these two high slip areas are clearly separated by a low slip zone extending along kii strait such a slip distribution corresponds with the fact that the rupture process of this earthquake in the western part is notably different from that in the eastern part

the mean sea surface height and geoid along the geosat subtrack from bermuda to cape cod measurements of near surface velocity and concurrent sea level along an ascending geosat subtrack were used to estimate the mean sea surface height and the earth s gravitational geoid velocity measurements were made on three traverses of a geosat subtrack within 10 days using an acoustic doppler current profiler adcp a small bias in the adcp velocity was removed by considering a mass balance for two pairs of triangles for which expendable bathythermograph measurements were also made because of the large curvature of the gulf stream the gradient wind balance was used to estimate the cross track component of geostrophic velocity from the adcp vectors this component was then integrated to obtain the sea surface height profile the mean sea surface height was estimated as the difference between the instantaneous sea surface height from adcp and the geosat residual sea level with mesoscale errors reduced by low pass filtering the error estimates were divided into a bias tilt and mesoscale residual the bias was ignored because profiles were only determined within a constant of integration the calculated mean sea surface height estimate agreed with an independent estimate of the mean sea surface height from geosat obtained by modeling the gulf stream as a gaussian jet within the expected errors in the estimates the tilt error was 0 10 m and the mesoscale error was 0 044 m to minimize mesoscale errors in the estimate the alongtrack geoid estimate was computed as the difference between the mean sea level from the geosat exact repeat mission and an estimate of the mean sea surface height rather than as the difference between instantaneous profiles of sea level and sea surface height in the critical region near the gulf stream the estimated error reduction using this method was about 0 07 m differences between the geoid estimate and a gravimetric geoid were not within the expected errors the rms mesoscale difference was 0 24 m rms

the hydrothermal system of volcan purace colombia this paper presents chemical and isotopic data for thermal waters gases and s deposits from volcan purace summit elevation 4600 m in sw colombia hot gas discharges from fumaroles in and around the summit crater and thermal waters discharge from three areas on its flanks the waters from all areas have d values of 75 1 indicating a single recharge area at high elevation on the volcano aircorrected values of3he 4he in thermal waters range from 3 8 to 6 7 ra and approach those for crater fumarole gas 6 1 7 1 ra indicating widespread addition of magmatic volatiles an economic s deposit el vinagre is being mined in the rio vinagre fault zone at 3600 m elevation sulfur isotopic data are consistent with a magmatic origin for s species in thermal waters and gases and for the s ore deposit isotopic equilibration between s species may have occurred at 220 40 c which overlaps possible equilibration temperatures 170 40 c determined by a variety of other geothermometers for neutral thermal waters apparent ch4 co2 equilibration temperatures for gases from thermal springs 400 50 c and crater fumaroles 520 60 c reflect higher temperatures deeper in the system hot magmatic gas ascending through the rio vinagre fault zone is though to have precipitated s and generated thermal waters by interaction with descending meteoric waters

real data assimilation for optimization of frictional parameters and prediction of afterslip in the 2003 tokachi oki earthquake inferred from slip velocity by an adjoint method