crustal deformation along the altyn tagh fault system western china from gps we collected gps data from the southern tarim basin the qaidam basin and the western kunlun shan region between 1993 and 1998 to determine crustal deformation along the altyn tagh fault system at the northern margin of the tibetan plateau we conclude from these data that the altyn tagh is a left lateral strike slip fault with a current slip rate of 9 mm yr in sharp contrast with geological estimates of 20 30 mm yr this contrast poses an enigma because the gps data cover a wider region than the geologic data they might be expected to reveal somewhat more slip we also find that the tarim and qaidam basins behave as rigid blocks within the uncertainty of our measurements rotating clockwise at a rate of 11 and 4 5 nrad yr respectively with respect to the eurasia plate the rotation of the tarim basin causes convergence across the tian shan increasing progressively westward from 6 mm yr at 87 e to 18 mm yr at 77 e our data and other gps data suggest that the indo asia collision is mainly accommodated by crustal shortening along the main himalayan thrust system 53 and the tian shan contractional belt 19 eastward extrusion of the tibetan plateau along the altyn tagh and kunlun faults accommodates only 23 of the indo asia convergence

slip rate measurements on the karakorum fault may imply secular variations in fault motion beryllium 10 surface exposure dating of offset moraines on one branch of the karakorum fault west of the gar basin yields a long term 140 to 20 thousand year right lateral slip rate of 10 7 0 7 millimeters per year this rate is 10 times larger than that inferred from recent insar analyses 1 3 millimeters per year that span 8 years and sample all branches of the fault the difference in slip rate determinations suggests that large rate fluctuations may exist over centennial or millennial time scales such fluctuations would be consistent with mechanical coupling between the seismogenic brittle creep and ductile shear sections of faults that reach deep into the crust

block models of crustal motion in southern california constrained by gps measurements 1 we estimate slip rates on major active faults in southern california using a block model constrained by global positioning system measurements of interseismic deformation the block model includes the effects of block rotation and elastic strain accumulation consistent with a simple model of the earthquake cycle our estimates of the right lateral strike slip rate on the san andreas fault vary by at least a factor of 5 from a high of 35 9 0 5 mm yr in the carrizo plain to a low of 5 1 1 5 mm yr through the san bernadino segment shortening across the puente hills thrust and left lateral slip on the raymond hill fault are consistent with both thickening and escape tectonics in the los angeles basin discrepancies between geodetic and geologic slip rate estimates along the san andreas and san jacinto faults as well as in the eastern california shear zone may be explained by a temporal change in fault system behavior we find no substantial evidence for long term postseismic relaxation and infer that the viscosity of the lower crust upper mantle may be relatively high 1019 pa s

contemporary crustal deformation in east asia constrained by global positioning system measurements global positioning system gps measurements collected since the early 90 s allow us to derive geodetic velocities at 16 permanent stations in east asia and 68 campaign mode sites in north china the resulting velocity field shows the following 1 contrary to the early inferences that the shanxi rift has accommodated significant right slip motion our results suggest that the rift system at least in its northern part in north china is under ese wnw extension at a rate of 4 2 mm yr the velocity field also suggests that an ese wnw trending left lateral shear zone deforming at a rate of 2 1 mm yr may exist along the north rim of north china at the latitude of 40 n separating actively extending north china in the south from relatively stable mongolia in the north 2 central and east china move at a rate of 8 11 mm yr east southeast with respect to siberia implying that the overall east southeastward motion is the dominant mode of deformation in east china 3 the india plate moves at a rate of 6 1 mm yr slower than the nuvel 1a model prediction relative to the eurasia plate 4 significant eastward motion 20 2 mm yr with respect to siberia occurs in southeastern tibet about half of this eastward motion 11 mm yr is absorbed by structures along the eastern boundary of the tibetan plateau

historical pattern and behavior of earthquake ruptures along the eastern boundary of the sichuan yunnan faulted block southwestern china abstract the eastern boundary of the sichuan yunnan faulted block in southwestern china which contains four major fault zones named xianshuihe anninghe zemuhe and xiaojiang behaves as a huge left lateral strike slip active fault system where the most frequent seismicity in continental china occurs to uncover the history of earthquake ruptures of this fault system we developed an empirical relation between rupture extent and seismic intensity distribution based on data of those earthquakes whose rupture extents and intensity distributions are well known through analyzing various types of data including distributions of damage or intensity of historical earthquakes as well as surface ruptures and aftershock zones of modern earthquakes we determined systematically the locations and spatial extents of ruptures for 36 main earthquakes and built up a spatial temporal pattern of the rupture history of the fault system for the last several hundred years the spatial temporal rupture pattern contains information of multi cycle and broad scale ruptures from which we find that for most fault segments scales of segment ruptures are time or cycle variable and only in two or three cases do scales of segment ruptures in successive cycles seem to be characteristic in infrequent cases several adjacent and connecting fault units may rupture simultaneously resulting in cascading ruptures triggering of ruptures is common along the fault system but differs in various periods even on a single fault zone triggered ruptures may not occur on fault segments adjacent to a preceding rupture of major earthquake but on other segments at some distance away from the preceding rupture implying that the rupture history determines whether a segment can be triggered or not recurrence intervals of major segment ruptures are longer on the anninghe and zemuhe fault zones and on the southernmost segment of the xiaojiang fault zone than that on the xianshuihe fault zone and the northern and middle segments of the xiaojiang fault zone probably due to the partitioning of slip along major and secondary faults and their complicated fault geometry four seismic gaps along the fault system are recognized where major earthquakes have been absent for a long time

oceanic mesoscale eddies as revealed by lagrangian coherent structures 1 we demonstrate the feasibility of using dynamical systems tools to unambiguously identify mesoscale oceanic eddies from surface ocean currents derived using climatological hydrography and altimetry specifically our analysis is based on extracting lagrangian coherent structures lcss from finite time lyapunov exponent ftle fields the ftle fields reveal with unprecedented detail an intricate tangle of lcss which are hidden in ocean surface topography maps but sometimes are apparent in ocean color images these lcss delineate fluid domains with very different advective properties and thus their detection provides an objective i e frame independent means of identifying eddy boundaries the importance of considering lcss in quantifying transport by eddies is highlighted such a quantification does not rely on the common assumption which is shown to be generally not valid that transport is largely effected by the trapping and subsequent translation of water slugs inside eddies defined as the regions enclosed by sea height streamfunction contours within which rotation dominates over strain lcss are calculated for the whole globe and compared with satellite tracked drogue drifter trajectories within a selected region of the south atlantic

late quaternary activity of the zemuhe and xiaojiang faults in southwest china from geomorphological mapping abstract there has been limited detailed geomorphological research on the kangding fault system located along the eastern margin of the tibetan plateau despite the system containing active faults with high slip rates fault related landforms such as offset streams were mapped at selected sites along the zemuhe and xiaojiang faults in the central and southern sections of the kangding fault system the results permitted assessment of the mode and rate of late quaternary fault movement based on more comprehensive information than used in previous studies the left lateral strike slip of these faults reflects the large scale clockwise rotation of the southern tibetan plateau the estimated strike slip rate of the zemuhe fault is ca 5 9 mm yr 1 whereas that of the xiaojiang fault is ca 14 22 mm yr 1 these rates and the known slip rates of the adjacent faults indicate that in the northern and southern sections of the kangding fault system the regional tectonic stress from the clockwise rotation has been released mainly along the major faults whereas the stress in the central section has been released by both fault movement and deformation in surrounding areas the latter mechanism reflects a more complex geological structure in the central system of distinct thrusts and folds late quaternary vertical deformation along the zemuhe and xiaojiang faults has mostly resulted from local stresses associated with strike slip movement although the zemuhe fault has also undergone slow but consistent normal faulting since the early quaternary due to its orientation oblique to the direction of the clockwise rotation

contemporary crustal deformation around the southeast borderland of the tibetan plateau 1 we derive a detailed horizontal velocity field for the southeast borderland of the tibetan plateau using gps data collected from the crustal motion observation network of china between 1998 and 2004 our results reveal a complex deformation field that indicates that the crust is fragmented into tectonic blocks of various sizes separated by strike slip and transtensional faults most notably the regional deformation includes 10 11 mm yr left slip across the xianshuihe fault 7 mm yr left slip across the anninghe zemuhe xiaojiang fault zone 2 mm yr right slip across a shear zone trending northwest near the southern segment of the lancang river fault and 3 mm yr left slip across the lijiang fault deformation along the southern segment of the red river fault appears not significant at present time the region south and west of the xianshuihexiaojiang fault system whose eastward motion is resisted by the stable south china block to the east turns from eastward to southward motion with respect to south china resulting in clockwise rotation of its internal subblocks active deformation is detected across two previously unknown deformation zones one is located 150 km northwest of and in parallel with the longmenshan fault with 4 6 mm yr right slip and another is continued south southwestward from the xiaojiang fault abutting the red river fault with 7 mm yr left slip while both of these zones are seismically active the exact locations of faults responsible for such deformation are yet to be mapped by field geology comparing our gps results with predictions of various models proposed for tibetan plateau deformation we find that the relatively small sizes of the inferred microblocks and their rotation pattern lend support to a model with a mechanically weak lower crust experiencing distributed deformation underlying a stronger highly fragmented upper crust

geodetic measurement of crustal motion in southwest china global positioning system measurements performed over a 2 4 yr period confirm the xianshuihe xiaojiang fault system as one of the primary active structures in southwest china stations southwest of these faults show southerly motions of 5 15 mm yr relative to the western sichuan basin and stations in a 200 km geodetic network located northwest of the basin move at only 0 5 mm yr these results are consistent with clockwise rotation of southwestern sichuan and western yunnan about the eastern tibetan syntaxis accommodated by left lateral slip of 12 4 mm yr on the xianshuihe xiaojiang fault system the results imply that if eastward extrusion of crustal material from the plateau occurs at present it is not accommodated by east west shortening along the margin of the plateau and must involve wholesale eastward motion of low lying regions to the east

velocity field in asia inferred from quaternary fault slip rates and global positioning system observations we perform a joint inversion of quaternary strain rates and 238 global positioning system gps velocities in asia for a self consistent velocity field the reference frames for all geodetic velocity observations are determined in our inversion procedure india in moves relative to eurasia eu about a pole of rotation at 29 78 n 7 51 e 0 353 myr 1 which yields a velocity along the himalaya within india that is 73 76 of the magnitude of the in eu nuvel 1a velocity and a vector azimuth that is 8 10 clockwise of nuvel 1a in eu vector azimuth relative to eurasia south china moves at 9 11 mm yr in the direction 110 120 with a pole position 64 84 n 156 74 e 0 12 myr 1 amurian block motion has a pole position in a similar location but at a slower rate 64 61 n 158 23 e 0 077 myr 1 and most of the amurian eurasia motion is accommodated by extension across lake baikal tarim basin moves relative to eurasia about a pole of rotation at 39 24 n 98 2 e 0 539 myr 1 and 16 18 mm yr of shortening is accommodated across the west central tien shan there is distributed e w extension throughout both southern and north central tibet within southern tibet between the longitudes of 77 e to 92 e the deformation field accommodates 16 19 mm yr of e w extension we compare predicted seismic moment rates with those observed in this century in asia total observed seismic moment rates within the entire area of central and east asia 2 2 107 km2 in this century are 2 26 0 7 1020 n m yr 1 as compared with a predicted total rate of 2 03 0 066 1020 n m yr 1 comparisons between observed and predicted moment rates within 42 subregions reflect the generally unstable process of inferring long term seismic moment rates from a catalog of limited duration 94 years an observation period of 10 000 years would be required to reduce uncertainties in observed seismic moment rate to the same size as the uncertainties in model tectonic moment rates inferred from the joint inversion of gps and quaternary rates of strain we show that in general a better correlation with model tectonic moment rate is inferred from the seismicity catalog by considering the numbers of earthquakes above a cutoff magnitude mb 5 0 for the period january 1 1965 to january 1 1999

spatial variations of stirring in the surface ocean a case study of the tasman sea abstract stirring in the tasman sea is examined using surface geostrophic currents derived from satellite altimeter measurements calculations of the distribution of finite time lyapunov exponents ftles indicate that the stirring in this region is not uniform and stretching rates over 15 days vary from less than 0 02 day 1 to over 0 3 day 1 these variations occur at both small 10 km and large 1000 km scales and in both cases are linked to dynamical features of the flow the small scale variations are related to the characteristics of coherent vortex structures and there are low ftles inside vortices and filaments of high ftles in strain dominated regions surrounding these vortices regional variations in the stirring are closely related to variations in mesoscale activity and eddy kinetic energy eke high values of mean ftle occur in regions of high eke highest mean values of around 0 2 day 1 occur in the east australia current separation region whereas small values occur in regions with low

unsettled earthquake nucleation detailed analyses of the source characteristics of two earthquake sequences lead to seemingly contradictory interpretations one study concludes that each earthquake triggers subsequent ones while the other favours a slow slip trigger

stirring of the northeast atlantic spring bloom a lagrangian analysis based on multisatellite data 1 the effect of the geostrophic stirring on phytoplankton variability during the northeast atlantic spring bloom is studied by analyzing satellite derived surface chlorophyll sea surface temperature and sea surface height the calculation of unstable manifolds is used as a diagnostic of the transport properties of the geostrophic velocity field calculated from the sea surface height we identify two mechanisms by which the geostrophic velocity field acts on chlorophyll patterns the first mechanism is a direct effect of the horizontal transport on already formed chlorophyll by acting as sticking transport barriers the unstable manifolds are shown to 1 modulate the fronts of already formed phytoplankton in lobular structures 2 create spiralling chlorophyll anomalies within eddies and 3 produce chlorophyll filaments the second mechanism is an indirect effect on in situ chlorophyll production mediated by nutrient upwelling supported by a recent study on the vertical velocities of the northeast atlantic legal et al 2006 we argue that the horizontal unstable manifolds also shape the filamentary vertical velocity cells and hence the patterns of in situ produced chlorophyll through submesoscale vertical nutrient injection

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

localized fault slip to the trench in the 2010 maule chile mw 8 8 earthquake from joint inversion of high rate gps teleseismic body waves insar campaign gps and tsunami observations the 27 february 2010 mw 8 8 maule earthquake ruptured 500 km along the plate boundary offshore central chile between 34 s and 38 5 s establishing whether coseismic fault offset extended to the trench is important for interpreting both shallow frictional behavior and potential for tsunami earthquakes in the region joint inversion of high rate gps teleseismic body waves interferometric synthetic aperture radar insar campaign gps and tsunami observations yields a kinematic rupture model with improved resolution of slip near the trench bilateral rupture expansion is resolved in our model with relatively uniform slip of 5 10 m downdip beneath the coast and two near trench high slip patches with 12 m displacements the peak slip is 17 m at a depth of 15 km on the central megathrust located 200 km north from the hypocenter and overlapping the rupture zone of the 1928 m 8 event the updip slip is 16 m near the trench another shallow near trench patch is located 150 km southwest of the hypocenter with a peak slip of 12 m checkerboard resolution tests demonstrate that correctly modeled tsunami data are critical to resolution of slip near the trench with other data sets allowing but not requiring slip far offshore large interplate aftershocks have a complementary distribution to the coseismic slip pattern filling in gaps or outlining edges of large slip zones two clusters of normal faulting events locate seaward along the plate motion direction from the localized regions of large near trench slip suggesting that proximity of slip to the trench enhanced extensional faulting in the underthrusting plate

global surface eddy diffusivities derived from satellite altimetry 1 velocities derived from aviso sea surface height observations adjusted to be nondivergent are used to simulate the evolution of passive tracers at the ocean surface eddy mixing rates are derived from the tracer fields in two ways first the method of nakamura is applied to a sector in the east pacific second the osborn cox diffusivity is calculated globally to yield estimates of diffusivity in two dimensions the results from the east pacific show weak meridional mixing at the surface in the southern ocean 1000 m2 s 1 consistent with previous results but higher mixing rates 3000 5000 m2 s 1 in the tropical ocean the osborn cox diagnostic provides a global picture of mixing rates and agrees reasonably well with the results from the east pacific it also shows extremely high mixing rates 104 m2 s 1 in western boundary current regions the osborn cox diffusivity is sensitive to the tracer initialization which we attribute to the presence of anisotropic mixing processes the mixing rates are strongly influenced by the presence of a mean flow nearly everywhere as shown by comparison with an eddy only calculation with the mean flow absent finally results are compared with other recent estimates of mixing rates using lagrangian and inverse methods

present day crustal deformation in china constrained by global positioning system measurements global positioning system gps measurements in china indicate that crustal shortening accommodates most of india s penetration into eurasia deformation within the tibetan plateau and its margins the himalaya the altyn tagh and the qilian shan absorbs more than 90 of the relative motion between the indian and eurasian plates internal shortening of the tibetan plateau itself accounts for more than one third of the total convergence however the tibetan plateau south of the kunlun and ganzi mani faults is moving eastward relative to both india and eurasia this movement is accommodated through rotation of material around the eastern syntaxis the north china and south china blocks east of the tibetan plateau move coherently east southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year respectively with respect to the stable eurasia

the long precursory phase of most large interplate earthquakes many earthquakes are preceded by foreshocks however the mechanisms that generate foreshocks and the reason why they occur before some earthquakes and not others are unknown here we use seismic catalogues from the best instrumented areas of the north pacific to analyse the foreshock sequences preceding all earthquakes there between 1999 and 2011 of magnitude larger than 6 5 and at depths shallower than 50 km the data set comprises 31 earthquakes at plate boundaries and 31 in plate interiors we find that there is a remarkable contrast between the foreshock sequences of interplate compared with intraplate earthquakes most large earthquakes at plate interfaces in the north pacific were preceded by accelerating seismic activity in the months to days leading up to the mainshock in contrast foreshocks are much less frequent in intraplate settings we suggest that at plate boundaries the interface between the two plates begins to slowly slip before the interface ruptures in a large earthquake this relatively long precursory phase could help mitigate earthquake risk at plate boundaries

interpreting energy and tracer spectra of upper ocean turbulence in the submesoscale range 1 200 km submesoscale 1 200km wavenumber spectra of kinetic and potential energy and tracer variance are obtained from in situ observations in the gulf stream region and in the eastern subtropical north pacific in the gulf stream region steep kinetic energy spectra at scales between 200 and 20km are consistent with predictions of interior quasigeostrophic turbulence theory both in the mixed layer and in the thermocline at scales below 20km the spectra flatten out consistent with a growing contribution of internal wave energy at small scales in the subtropical north pacific theenergyspectraareflatterand inconsistentwith predictionsofinteriorquasigeostrophic turbulence theory the observed spectra and their dependence on depth are also inconsistent with predictions of surface quasigeostrophic turbulencetheoryfortheobservedoceanstratification itappearsthatunbalancedmotions most likely internal tides at large scales and the internal wave continuum at small scales dominate the energy spectrum throughout the submesoscale range spectra of temperature variance along density surfaces which are not affected by internal tides are also inconsistent with predictions of geostrophic turbulence theories reasons for this inconsistency could be the injection of energy in the submesoscale range by small scale baroclinic instabilities or modifications of the spectra by coupling between surface and interior dynamics or by ageostrophic frontal effects

geometry and deformation features of the most recent co seismic surface ruptures along the xiaojiang fault and its tectonic implications for the tibetan plateau abstract the anninghe zemuhe xiaojiang and daliangshan faults bound the southeastern margin of the tibetan plateau which has almost been entirely ruptured by strong earthquakes during the past 500 years the geometry and deformation features of the most recent co seismic surface ruptures show not only the surface morphology of the source seismogenic fault but also the structural characteristics of the upper crust as well as the pre existing tectonic environment hence the most recent co seismic surface ruptures along the xiaojiang fault zone reveal the surface deformation of the southeastern tibetan plateau our investigation reveal that the 1833 songming rupture zone is about 150 km with maximum co seismic offset of 8 4 m and the re evaluated moment magnitude is about m 7 5 7 6 which is lower than previously estimated m 8 0 the 1500 yiliang rupture zone is about 80 km with maximum co seismic offset of 8 0 m and the re evaluated moment magnitude of m 7 2 7 5 which is higher than previously demonstrated m 7 0 the spatial distribution of the surface rupture zones along xiaojiang fault shows an arcuate geometry our findings also reveal that strong earthquakes rupture not only the two major strands but also the en echelon faults between them the arcuate geometry of the fault zone and the development of these en echelon faults are consistent with the clockwise rotation of the southeastern tibetan plateau

contemporary crustal deformation within the pamir plateau constrained by geodetic observations and focal mechanism solutions we used an updated data set of 192 gps derived surface velocities and 393 earthquake focal mechanisms mw 3 0 hypocenter depths 30 km to evaluate the spatial variations in the surface strain rate and crustal stress regime throughout the pamir plateau and its surrounding regions the strain rate field was estimated using the spline in tension approach that solves for the surface velocity in a rectangular grid and the stress field was predicted from focal mechanism solutions using the damped regional scale stress inversion drssi method of hardebeck and michael journal of geophysical research https doi org 10 1029 2005jb004144 2006 the results show that the crustal stress field around the pamir plateau is predominantly characterized by nnw sse compression and e w extension which is consistent with the principal orientations of the two dimensional surface strain rate tensor this agreement supports the notion that the pamir and southwestern tien shan are uniformly strained blocks in particular the fan shaped rotational pattern between text shmax and the strain rate from the western pamir to the tajik basin shows that the counterclockwise rotation of the text shmax orientation is associated with vertical deformation which is consistent with the idea of schurr et al tectonics 33 8 2014tc003576 2014 concerning the gravitational collapse and westward extrusion of the crust in the western pamir we propose that such a stress strain pattern dominated by nnw ese oriented compression and e w trending extension originated from a combination of the northward push of the indian continent and the southward subduction of the tien shan

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

characteristics of the active xiaojiang fault zone in yunnan china a slip boundary for the southeastward escaping sichuan yunnan block of the tibetan plateau abstract the xiaojiang fault zone within the yunnan province china is one of the most active fault zones of the southeastern edge of the tibetan plateau this n s trending 400 km long fault zone defines the southern part of the eastern boundary of the sichuan yunnan block which is escaping southeastward from the tibet plateau and rotating around the eastern himalayan syntaxis the middle section of the fault zone splits into two branches each branch fault consists of several en echelon faults basins of various ages have developed on the step overs between the secondary faults the left lateral strike slip rate along the eastern branch is up to 9 mm a and that on the western branch is 7 mm a more than 10 m 6 historic earthquakes have occurred along the fault zone the largest was the 1833 songming earthquake of m 8 four earthquake rupture zones were discovered along the fault zone 15 trenches have been excavated along every major segment of the fault zone and 4 5 paleoearthquakes have been distinguished along the xiaojiang fault zone the average strong earthquake recurrence interval is 2000 2500 years

stratospheric tracer spectra abstract the combined effects of advection and diffusion on the equilibrium spatial structure of a tracer whose spatial variation is maintained by a large scale forcing are considered motivated by the lower stratosphere the flow is taken to be large scale time dependent and purely horizontal but varying in the vertical with the vertical shear much larger than horizontal velocity gradients as a result the ratio between horizontal and vertical tracer scales is large for the lower stratospheric surf zone has been shown to be about 250 the diffusion parameterizes the mixing effects of small scale processes the three space dimensions and the large range between the forcing scale and the diffusive scale mean that direct numerical simulation would be prohibitively expensive for this problem instead an ensemble approach is used that takes advantage of the separation between the large scale of the flow and the small scale of the tracer distribution this approach which has previously been used i

on the circulation in the bay of bengal during northern spring inter monsoon march april 1987 abstract temperature and salinity data collected from the bay of bengal 22 march 28 april 1987 northern spring inter monsoon identified the seasonal anticyclonic gyre acg at 16 n 86 e characterized by warm 24 c and low salinity 34 85 psu at their cores the velocity of wbbc increased from 0 40 ms 1 at 12 n to 0 70 ms 1 at 17 5 n where it left the coast and turned eastward the mean northward transport of the wbbc in the upper 200 m was 12 sv 1 sv 10 6 m 3 s 1 these circulation features the acg wbbc and cyclonic eddies are well depicted in the maps of sea surface height ssh topography derived from the residual sshs of geosat altimeter for the period 12 february 28 april 1987 the results show that the wbbc flowed against the northeasterly winds during february and that the current sets up almost three months ahead of the wind reversal the acg and in turn the wbbc intensified with the wind reversal in april when the wind stress curl attained a negative maximum the ssh maps further indicate that formation of the acg started in february and reached its maximum intensity during april with the coalescence of two anticyclonic cells

mixing structures in the mediterranean sea from finite size lyapunov exponents 1 we characterize horizontal mixing and transport structures in the surface circulation of the mediterranean sea as obtained from a primitive equation circulation model we calculate the finite size lyapunov exponents fsles of the velocity data set which give a direct measure of the local stirring by proper election of the fsle parameters we focus on the mesoscale structures locating a number of vortices embedded in an intricate network of high stretching lines these lines control transport in the system at the edge of the vortices a dense tangle of line intersections appears identifying strong mixing the spatial distribution of fsles averaged over one year allows to classify areas in the mediterranean basin according by their mixing activity the space average of fsles on selected geographical regions gives a measure for quantifying and comparing the mixing seasonal variability

a revised dislocation model of interseismic deformation of the cascadia subduction zone 1 cas3d 2 a new three dimensional 3 d dislocation model is developed to model interseismic deformation rates at the cascadia subduction zone the model is considered a snapshot description of the deformation field that changes with time the effect of northward secular motion of the central and southern cascadia forearc sliver is subtracted to obtain the effective convergence between the subducting plate and the forearc horizontal deformation data including strain rates and surface velocities from global positioning system gps measurements provide primary geodetic constraints but uplift rate data from tide gauges and leveling also provide important validations for the model a locked zone based on the results of previous thermal models constrained by heat flow observations is located entirely offshore beneath the continental slope similar to previous dislocation models an effective zone of downdip transition from locking to full slip is used but the slip deficit rate is assumed to decrease exponentially with downdip distance the exponential function resolves the problem of overpredicting coastal gps velocities and underpredicting inland velocities by previous models that used a linear downdip transition a wide effective transition zone etz partially accounts for stress relaxation in the mantle wedge that cannot be simulated by the elastic model the pattern of coseismic deformation is expected to be different from that of interseismic deformation at present 300 years after the last great subduction earthquake the downdip transition from full rupture to no slip should take place over a much narrower zone

intraseasonal variability of sea surface height in the bay of bengal intraseasonal variability isv of sea surface height ssh over the bay of bengal bob is studied using altimetry data and an eddy resolving ocean model in both the model hindcast and satellite observations large ssh isv is found along the eastern and northern coasts of the bob in the western bob and in a zonal band across the bay centered near 5 degrees n the isv displays a clear seasonality in the western bob it reaches its annual maximum in spring whereas it does so in summer and autumn southeast of sri lanka driven by equatorial intraseasonal winds equatorial kelvin waves propagate eastward reach the western coast of sumatra and reflect there to propagate around the perimeter of the bob as coastally trapped waves two distinct bands of high eddy activity are detected in the western and central bob respectively in both bands isolated eddies propagate southwestward eddy formation in the eddy train in the central bay is linked to the coastal wave as it bends around the corner of the irrawaddy delta off myanmar eddy activity contributes to the high isv in the central bay to some extent an energetics analysis indicates that high total eddy energy in the western bob is due to barotropic baroclinic instability of the mean current citation cheng x s p xie j p mccreary y qi and y du 2013 intraseasonal variability of sea surface height in the bay of bengal j geophys res oceans 118 816 830 doi 10 1002 jgrc 20075

a new mixing diagnostic and gulf oil spill movement chaotic advection has served as the paradigm for mixing in fluid flows with simple time dependence its skeletal structure is based on analysis of invariant attracting and repelling manifolds in fluid flows here we develop a finite time theory for two dimensional incompressible fluid flows with arbitrary time dependence and introduce a new mixing diagnostic based on it besides stretching events around attracting and repelling manifolds this allows us to detect hyperbolic mixing zones we used the new diagnostic to forecast the spatial location and timing of oil washing ashore in plaquemines parish and grand isle louisiana and pensacola florida in may 2010 and the flow of oil toward panama city beach florida in june 2010

the benthic silica cycle in the northeast atlantic annual mass balance seasonality and importance of non steady state processes for the early diagenesis of biogenic opal in deep sea sediments within the framework of the eu funded bengal programme the effects of seasonality on biogenic silica early diagenesis have been studied at the porcupine abyssal plain pap an abyssal locality located in the northeast atlantic ocean nine cruises were carried out between august 1996 and august 1998 silicic acid dsi increased downward from 46 2 to 213 m mean of 27 profiles biogenic silica bsi decreased from ca 2 near the sediment water interface to 1 at depth benthic silicic acid fluxes as measured from benthic chambers were close to those estimated from non linear dsi porewater gradients some 90 of the dissolution occurred within the top 5 5 cm of the sediment column rather than at the sediment water interface and the annual dsi efflux was close to 0 057 mol si m 2 yr 1 biogenic silica accumulation was close to 0 008 mol si m 2 yr 1 and the annual opal delivery reconstructed from sedimentary fluxes assuming steady state was 0 065 mol si m 2 yr 1 this is in good agreement with the mean annual opal flux determined from sediment trap samples averaged over the last decade 0 062 mol si m 2 yr 1 thus ca 12 of the opal flux delivered to the seafloor get preserved in the sediments a simple comparison between the sedimentation rate and the dissolution rate in the uppermost 5 5 cm of the sediment column suggests that there should be no accumulation of opal in pap sediments however by combining the bengal high sampling frequency with our experimental results on bsi dissolution we conclude that non steady state processes associated with the seasonal deposition of fresh biogenic particles may well play a fundamental role in the preservation of bsi in these sediments this comes about though the way seasonal variability affects the quality of the biogenic matter reaching the seafloor hence it influences the intrinsic dissolution properties of the opal at the seafloor and also the part played by non local mixing events by ensuring the rapid transport of bsi particles deep into the sediment to where saturation is reached

mixing by low and high resolution surface geostrophic currents 1 the nature of mixing near the ocean s surface is investigated by considering passive tracer advection by currents derived geostrophically using sea surface height fields that differ in their spatiotemporal resolution one is a low resolution field that can be thought of as being derived using current generation groundtrack altimetric measurements the other is a high resolution field that may be envisioned as derived using hypothetical next generation wideswath altimetric measurements the investigation is carried out in two world ocean regions with quite distinct characteristics and which have been the focus of recent studies on mixing by altimetry derived currents one region corresponds to an ample domain in the south atlantic which is traversed by vortices shed from the agulhas current the other region corresponds to a portion of the pacific sector of the southern ocean which is dominated by multiple zonal jets associated with the antarctic circumpolar current it is argued that while altimetry derived currents capture the most salient characteristics of surface ocean mixing deterministic lagrangian calculations may be improved by considering surface geostrophic currents with greater spatiotemporal resolution this is supported on analysis of probability distribution functions of finite time lyapunov exponents ftles inspection of lagrangian coherent structures or lcss which constitute distinguished material fluid curves that organize mixing computation of kinetic energy and ftle variance spectra and realization of explicit passive tracer advection experiments

automatic imaging of earthquake rupture processes by iterative deconvolution and stacking of high rate gps and strong motion seismograms by combining the complementary advantages of conventional network inversion and backprojection methods we have developed an iterative deconvolution and stacking ids approach for imaging earthquake rupture processes with near field complete waveform data this new approach does not need any manual adjustment of the physical empirical constraints such as restricting the rupture time and duration and smoothing the spatiotemporal slip distribution therefore it has the ability to image complex multiple ruptures automatically the advantages of the ids method over traditional linear or nonlinear optimization algorithms are demonstrated by the case studies of the 2008 wenchuan and 2011 tohoku earthquakes for such large earthquakes the ids method is considerably more stable and efficient than previous inversion methods additionally the robustness of this method is demonstrated by comprehensive synthetic tests indicating its potential contribution to tsunami and earthquake early warning and rapid response systems it is also shown that the ids method can be used for teleseismic waveform inversions for the two major earthquakes discussed here the ids method can provide without tuning any physical or empirical constraints teleseismic rupture models consistent with those derived from the near field gps and strong motion data

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

field study of a highly active fault zone the xianshuihe fault of southwestern china the xianshuihe fault of western sichuan province china is one of the world s most active faults having produced 4 earthquakes during this century of magnitude 7 along a 350 km length of the fault at least 8 such events have occurred since 1725 in the more limited 150 km long segment including luhuo and daofu major earthquakes in 1904 1923 1973 and 1981 m 7 7 7 6 6 9 were associated with overlapping surficial fault ruptures and with individual left lateral displacements as large as 3 6 m field studies indicate that this high degree of activity is typical of the fault s longer term history the holocene left lateral slip rate on the north western segment of the fault has been 15 5 mm yr decreasing to about 5 mm yr on its southeastern segment based on radiometrically dated offset stream channel and terrace deposits and on offset glacial moraines physiographic features of active faulting are fully as diagrammatic as those of california s san andreas fault mainly because of high altitude preservation and the absence of cultural modification on this eastern margin of the tibetan plateau detailed en echelon tensional and pushup features resulting from surface ruptures in 1973 1955 1923 and 1893 can still be recognized today and new data have been collected bearing on the offsets and fault rupture lengths during these and other events the locations and magnitudes of historic earthquakes suggest that the characteristic earthquake model may apply to the xianshuihe fault obvious geometric segmentation of the fault has controlled the initiation and termination of ruptures in some events whereas segmentation control for others remains obscure based on the historic record repeat times estimated from slip rates and current seismic gaps two segments are particularly likely sites for m 7 earthquakes in the near future the 65 km long segment between daofu and qianning and the 135 km long segment bracketing kangding continuing creep has been documented along some segments of the fault and this together with the high degree of activity and other unique attributes makes the xianshuihe fault one of the most promising sites in the world for earthquake prediction and hazard evaluation studies

rupture model of the 2011 mineral virginia earthquake from teleseismic and regional waveforms 1 we independently invert teleseismic p waveforms and regional crustal phases to examine the finite fault slip model for the 2011 mw 5 8 mineral virginia earthquake theoretical and empirical green s functions are used for the teleseismic and regional models respectively both solutions show two distinct sources each about 2 km across and separated by 2 5 km the source at the hypocenter is more localized in the regional model leading to a higher peak slip of 130 cm and higher average stress drop of 250 bars compared with 86 cm and 150 bars for the same source in the teleseismic model both sources are centered at approximately 8 km depth in the regional model largely below the aftershock distribution in the teleseismic model the sources extend updip to approximately 6 km depth into the depth range of the aftershocks the rupture velocity is not well resolved but appears to be near 2 7 km s

crustal shortening in the andes why do gps rates differ from geological rates gps data indicate 30 40 mm yr 1 present day crustal shortening across the andes whereas geological evidence shows crustal shortening concentrated in the sub andean thrust belt at a much lower rate 15 mm yr 1 we reconcile the discrepancy between the geodetic and the geological crustal shortening using geodynamic modeling that includes timescale dependent crustal deformation the gps velocities reflect the instantaneous deformation in the andes that includes both permanent deformation and elastic deformation that will be recovered during future earthquakes whereas the lower geological rates reflect only the permanent deformation the three dimensional viscoelastic model predicts nearly uniform short term velocity gradients across the andes similar to the gps results and concentrated long term crustal shortening in the sub andean thrust zone consistent with geological observations

stirring in the global surface ocean 1 global variations of stirring in the surface ocean are quantified using finite time lyapunov exponents ftles calculated from currents derived from satellite altimetry it is shown that the stirring is highly non uniform and the probability distribution functions pdfs of the ftles are broad asymmetric and have long high stretch tails the characteristics of the pdfs vary with mesoscale activity and integration time there are larger values and broader pdfs in regions of high strain rates and eddy kinetic energy eke e g western boundary currents and the antarctic circumpolar current and for shorter integration times the pdfs have a near universal relationship with the mean strain of a region and are reasonably well fit by weibull distributions the above variations in the stirring may help our understanding of the distribution and spatial heterogeneities of biogeochemical tracers and raise the possibility of developing a parameterization of the stirring based on the easily calculated eke

seasonality of surface stirring by geostrophic flows in the bay of bengal abstract stirring of passive tracers in the bay of bengal driven by altimetry derived daily geostrophic surface currents is studied on subseasonal timescales to begin with hovmoller plots wavenumber frequency diagrams and power spectra confirm the multiscale nature of the flow advection of latitudinal and longitudinal bands highlights the chaotic nature of stirring in the bay via repeated straining and filamentation of the tracer field an immediate finding is that stirring is local i e of the scale of the eddies and does not span the entire basin further stirring rates are enhanced along the coast of the bay and are relatively higher in the pre and post monsoonal seasons indeed finite time lyapunov exponent ftle and finite size lyapunov exponent fsle maps in all the seasons are patchy with minima scattered through the interior of the bay further these maps bring out a seasonal cycle wherein rapid stirring progressively moves from the northern to southern bay during pre and post monsoonal periods respectively the non uniform stirring of the bay is reflected in long tailed probability density functions of ftles that become more stretched for longer time intervals quantitatively advection for a week shows the mean ftle lies between 0 13 0 07 day 1 while extremes reach almost 0 6 day 1 averaged over the bay relative dispersion initially grows exponentially followed by a power law at scales between approximately 100 and 250 km which finally transitions to an eddy diffusive regime quantitatively below 250 km a scale dependent diffusion coefficient is extracted that behaves as a power law with cluster size while above 250 km eddy diffusivities range from 6 10 3 1 6 10 4 m2s 1 in different regions of the bay these estimates provide a useful guide for resolution dependent diffusivities in numerical models that hope to properly represent surface stirring in the bay

near surface salinity and stratification in the north bay of bengal from moored observations a thin layer of fresh water from summer monsoon rain and river runoff in the bay of bengal bob has profound influence on air sea interaction across the south asian region but the mechanisms that sustain the low salinity layer are as yet unknown using the first long time series of high frequency observations from a mooring in the north bob and satellite salinity data we show that fresh water from major rivers is transported by large scale flow and eddies and shallow salinity stratification persists from summer through the following winter the moored observations show frequent 0 2 1 2 psu salinity jumps with time scales of 10 min to days due to o 1 10 km submesoscale salinity fronts moving past the mooring in winter satellite sea surface temperature shows 10km wide filaments of cool water in line with moored data rapid salinity and temperature changes at the mooring are highly coherent suggesting slumping of salinity dominated fronts based on these observations we propose that submesoscale fronts may be one of the important drivers for the persistent fresh layer in the north bob

nucleation of the 1999 izmit earthquake by a triggered cascade of foreshocks much of what we know about the nucleation of earthquakes comes from the temporal and spatial relationship of foreshocks to the initiation point hypocentre of the mainshock the 1999 mw 7 6 izmit turkey earthquake was preceded by a 44 minute long foreshock sequence which built in intensity as the time of the mainshock approached here we apply a series of high resolution methods to the sparse seismological observations to determine the spatial and temporal relation of the foreshocks to the mainshock hypocentre we find that the foreshocks form a contiguous series of ruptures that progressed systematically from west to east towards the mainshock hypocentre located at the extreme eastern edge of the foreshocks the izmit foreshock sequence occurred as a triggered cascade in which one foreshock loads the adjacent fault patch causing it to fail with the mainshock initiation no different than another foreshock we find no evidence to support a hypothesized precursory aseismic driving process if we are to resolve the role of aseismic deformation and possible role of fluid overpressure in the earthquake nucleation process it will likely require measurements made in the near field of the hypocentre the magnitude 7 6 izmit earthquake that struck turkey in 1999 was nucleated by an eastward migrating cascade of foreshocks according to high resolution analyses of seismic data

on eddy viscosity energy cascades and the horizontal resolution of gridded satellite altimeter products motivated by the recent interest in ocean energetics the widespread use of horizontal eddy viscosity in models and the promise of high horizontal resolution data from the planned wide swath satellite altimeter this paper explores the impacts of horizontal eddy viscosity and horizontal grid resolution on geostrophic turbulence with a particular focus on spectral kinetic energy fluxes p k computed in the isotropic wavenumber k domain the paper utilizes idealized two layer quasigeostrophic qg models realistic highresolution ocean general circulation models and present generation gridded satellite altimeter data adding horizontal eddy viscosity to the qg model results in a forward cascade at smaller scales in apparent agreement with results from present generation altimetry eddy viscosity is taken to roughly represent coupling of mesoscale eddies to internal waves or to submesoscale eddies filtering the output of either the qg or realistic models before computing p k also greatly increases the forward cascade such filtering mimics the smoothing inherent in the construction of present generation gridded altimeter data it is therefore difficult to say whether the forward cascades seen in present generation altimeter data are due to real physics represented here by eddy viscosity or to insufficient horizontal resolution the inverse cascade at larger scales remains in the models even after filtering suggesting that its existence in the models and in altimeterdata is robust however themagnitudeofthe inverse cascadeis affectedbyfiltering suggestingthat the wide swath altimeter will allow a more accurate determination of the inverse cascade at larger scales as well as providing important constraints on smaller scale dynamics

relative motion across the eastern tibetan plateau contributions from faulting internal strain and rotation rates abstract a kinematic model comprising 14 rotating elastic plastic blocks is used to represent the modern deformation of eastern tibet and neighboring regions block rotations fault slip rates and permanent strain rates within the blocks are constrained by inverting gps velocities slip vector azimuths derived from earthquakes and fault slip rates derived from geology the calculated internal strain rates of blocks in eastern tibet amounts to 10 to 30 10 9 yr in contrast to relatively low rates

seismic risk on the northern xiaojiang fault implied by the latest and nearest gps observations on the basis of the continuous and dense gps observations covering the northern segment of the xiaojiang fault zone n xjfz from march 2012 to march 2016 we present the velocity field spatiotemporal deformation slip rate and locking depth of the n xjfz the results provide strong support for achieving a better understanding of the deformation behavior of this fault the heterogeneity of the gps velocity field and relatively nonuniform distribution of seismicity suggest that the observational area is fragmented shear strain has been accumulating with an almost constant azimuth which is consistent with the trends of the mapped major faults the 2014 ms 6 5 ludian earthquake produced a sudden change in the dilatational strain which was almost constant prior to the event and an increase in the shear strain rate the near field deformation of the n xjfz estimated with the near field data was larger than expected revealing that the n xjfz is becoming more locked these results imply that the seismic risk in the study area is currently rising and that similar to the 2014 ms 6 5 ludian earthquake future earthquakes will possibly occur away from mapped faults

source rupture process of the tecoman colima mexico earthquake of 22 january 2003 determined by joint inversion of teleseismic body wave and near source data the spatial and temporal slip distribution of the tecoman colima mexico earthquake is estimated from near source strong motion and teleseismic body wave data to perform a stable inversion we applied smoothing constraints and determined their optimal relative weights on the observed data using an optimized akaike s bayesian information criterion abic the source parameters are as follows strike dip slip 300 20 93 seismic moment m 2 3 1020 n m source duration 30 sec along strike distance 35 km along dip distance 70 km we found that the rupture process can be divided into three stages the rupture nucleated near the hypocenter stage i then it broke the first asperity centering about 15 km southwest from the epicenter stage ii and the rupture propagated to the northeast and the second asperity was broken stage iii we also estimated the shear stress change due to the rupture process of the mainshock on and around the major fault zone it appears that one cluster of aftershocks for the first 5 days which took place in and adjacent to the zones of stress increased due to the fault rupture during the mainshock but overall correlation between the aftershock location and the stress pattern is not clear manuscript received 14 may 2003