forward and inverse modelling of post seismic deformation we consider a new approach to both the forward and inverse problems in post seismic deformation we present a method for forward modelling post seismic deformation in a self gravitating heterogeneous and compressible earth with a variety of linear and nonlinear rheologies we further demonstrate how the adjoint method can be applied to the inverse problem both to invert for rheological structure and to calculate the sensitivity of a given surface measurement to changes in rheology or time dependence of the source both the forward and inverse aspects are illustrated with several numerical examples implemented in a spherically symmetric earth model

near surface dynamical structure of the kuroshio extension 1 lagrangian data from 657 svp drifters cnes aviso archiving validation and interpretation of satellite oceanographic data time variable satellite altimeter sea level anomaly and levitus 98 hydrographic data are used to develop 0 25 spatial resolution maps of the mean and eddy circulations in the northwestern pacific during the 1990s drifter velocities at 15 m depth and 200 m temperature data clearly indicate in the kuroshio extension ke jet two prominent meanders that culminate in a 300 km northward deflection east of the shatsky rise at 160 e the interannual trends of aviso mesoscale variance are absent along the path of the meandering ke jet three anticyclonic recirculations can be identified south or southeast of the kuroshio the southernmost around daito island being a new discovery about 3 of the drifters with drogues attached crossed the kuroshio front the aviso currents are correlated at 0 8 with drifter geostrophic velocity the aviso geostrophic currents are adjusted in amplitude to the contemporaneous drifter observations and are further used to compute an unbiased mean geostrophic circulation and the quasi geostrophic reynolds stresses in the ke region the principal axes of the eddy reynolds stresses are oriented along the unbiased mean velocity vectors within the meandering ke jet the time mean horizontal momentum balance that includes both the mean and eddy momentum convergences is used to compute absolute sea level map and its uncertainty at 145 e the 2000 m depth absolute dynamic height referenced to the sea level reveals a heretofore unknown 70 dynamic cm drop from 25 to 42 n

lower crustal structure in northern california implications from strain rate variations following the 1906 san francisco earthquake 1 it is well known that geodetic data from a single instant in time cannot uniquely characterize structure or rheology beneath active seismogenic zones nevertheless comparison of spatial and temporal variations in deformation rate with time dependent mechanical models can place valuable constraints on fault zone geometry and rheology we consider postseismic strain rate transients by comparing geodetic data from north of san francisco bay obtained between 1906 and 1995 to predictions from viscoelastic finite element models models include 1 an elastic plate over a viscoelastic half space 2 distributed shear within a viscoelastic layer 3 discrete shear zones within an otherwise elastic layer 4 discrete shear zones in combination with distributed viscoelastic shear and 5 midcrustal detachment surfaces we vary as applicable locking depth elastic thickness depth to the top and bottom of the distributed shear layer distributed shear relaxation time discrete shear zone relaxation time and discrete shear zone width the best fitting physically reasonable elastic plate over viscoelastic half space models 1 do a poor job simultaneously predicting spatial and temporal variations in the data the best fitting distributed shear models 2 do a poor job predicting spatial variations in the deformation rate although they fit the geodetic data recent findings from seismic reflection refraction studies in northern california argue against models with shallow subhorizontal detachments 5 models incorporating discrete shear zones 3 4 provide the best fit to the geodetic data and are consistent with seismic studies that argue for discrete fault zones extending through the entire crust

dynamics of izmit earthquake postseismic deformation and loading of the duzce earthquake hypocenter we have developed dynamic finite element models of izmit earthquake postseismic deformation to evaluate whether this deformation is better explained by afterslip via either velocity strengthening frictional slip or linear viscous creep or by distributed linear viscoelastic relaxation of the lower crust we find that velocity strengthening frictional afterslip driven by coseismic shear stress loading can reproduce time dependent global positioning system data better than either linear viscous creep on a vertical shear zone below the rupture or lower crustal viscoelastic relaxation our best frictional afterslip model fits the main features of postseismic slip inversions in particular high slip patches at and below the hypocenter and on the western karadere segment and limited afterslip west of the hersek delta burgmann et al 2002 the model requires a weakly velocity strengthening fault that is either low effective normal stress in the slipping regions or a smaller value for the parameter describing rate dependence of friction a b than is indicated by laboratory experiments our best afterslip model suggests that the coulomb stress at the duzce hypocenter increased by 0 14 mpa 1 4 bars during the izmit earthquake assuming right lateral slip on a surface dipping 50 to the north and by another 0 1 mpa during the 87 days between the izmit and duzce earthquakes in the marmara sea region within about 160 km of the izmit earthquake rupture this model indicates that the coulomb stresses increased by 15 25 of the coseismic amount during the first 300 days after the earthquake three hundred days after the earthquake postseismic contributions to coulomb stressing rate on the maramara region faults had fallen to values equal to or less than the inferred secular stress accumulation rate our estimates of postseismic coulomb stress are highly model dependent in the marmara region the linear viscous shear zone and viscoelastic lower crust models predict greater postseismic coulomb stresses than the frictional afterslip model near field stress and fault zone rheology estimates are sensitive to the earth9s elastic structure when a layered elastic structure is incorporated in our model it yields a coulomb stress of 0 24 mpa at the duzce hypocenter significantly more than the 0 14 mpa estimated from the uniform elastic model because of the higher near field coseismic stresses the layered elastic model requires a higher value of velocity strengthening parameter a b a b times effective normal stress r to produce comparable postseismic slip a b is estimated at 0 4 and 0 2 mpa respectively for the layered and uniform elastic models these results highlight the importance of understanding the earth9s elastic structure and the mechanism for postseismic deformation if we wish to accurately model coseismic and postseismic crustal stresses

relating viscosities from postseismic relaxation to a realistic viscosity structure for the lithosphere summary models of geodetic observations of postseismic relaxation most often represent the lithosphere with only a few layers with constant viscosity this is surpr ising because rock mechanical experiments consistently demonstrate that we should expect a profound vertical gradient in lithospheric viscosities due to the geothermal gradient i n this thermal boundary layer we isolate the effect of lower crustal flow where the effect of visc osity gradients has the largest impact on surface deformation we therefore explore postseismic deformation in models with realistic vertical viscosity gradients and seek to illustrate th e differences between these models and those with idealized uniform viscosity layers by means of synthetic experiments with a semianalytical viscoelastic relaxation model we show how for a given earthquake the averaged viscosity value obtained for a thick viscoelastic layer is d ependent on both the layout of the geodetic network and on the observation time window

seasonal variation and instability nature of the north pacific subtropical countercurrent and the hawaiian lee countercurrent 1 the relation between baroclinic instability of the north pacific subtropical countercurrent stcc and the hawaiian lee countercurrent hlcc and seasonal evolution of mesoscale sea surface height ssh variability was investigated by using historical hydrographic data and altimeter derived ssh anomaly data during 1992 2000 the annual and monthly mean dynamic height climatologies show two robust eastward flowing countercurrents the stcc extends typically along 24 n from 130 e to 160 w and slightly shifts to the north as it flows toward the east and the hlcc is located typically along 20 n and extends from about 150 e to just west of the hawaiian islands seasonal variations of the stcc in the western north pacific and the hlcc west of the hawaiian island where the eddy variability is relatively larger than the background were quite different the stcc hlcc is strong in winter summer to summer winter and weak in fall spring in contrast seasonal evolution of mesoscale ssh variability has almost the same cycle in the two countercurrent regions the eddy kinetic energy eke is a maximum in spring and a minimum in fall the dominant zonal scales are shortest in late winter and become longer with time a linear quasigeostrophic stability analysis using a three layer model indicates that instability properties are very similar between the two countercurrent regions the stcc and the hlcc become baroclinically more unstable during winter and late fall to winter respectively due to strong vertical velocity shear and weak stratification between the stcc hlcc and underlying westward flow and the most unstable wave during this season has an e folding timescale of about 2 3 months and a zonal wavelength of about 300 400 km the same behavior of the seasonal evolution of the mesoscale variability in the two countercurrent regions is a manifestation of these similarities in terms of increasing nonlinearity of the unstable waves and an inverse cascade of the eddy energy we discussed generation processes of the mesoscale ssh disturbances

on the maintenance of the subtropical front and its associated countercurrent abstract in the north pacific and atlantic oceans the subtropical countercurrent is an eastward flow across the subtropical gyre at a latitude where a classical wind driven circulation theory would predict a westward flow it is in geostrophic balance with the subtropical front a zonal density front which runs across the ocean basin from previous numerical models it is argued that convergence of ekman transports can hardly be the primary reason for the existence of such a phenomenon and that thermodynamic effects play a crucial role to elucidate how them may be responsible for the frontal structure a very simple analytical model is constructed where the dynamics yield motions consisting of a nondivergent wind driven sverdrup current and a geostrophic thermal flow that is divergent on a beta plane the surface temperature is governed by a nonlinear hyperbolic equation for which the corresponding characteristics intersect separating the basin into two distinct regions limited by a temperature discon

postseismic and interseismic displacements near a strike slip fault a two dimensional theory for general linear viscoelastic rheologies 1 we present an analytic solution for the deformation near an infinite strike slip fault in an elastic layer overlying a linear viscoelastic half space the theory is valid for any linear viscoelastic rheology and any earthquake sequence this is a generalization of the work of j c savage and colleagues which only holds for models with a uniform shear modulus maxwell viscoelastic lower half space and periodic rupture recurrence we demonstrate the theory for models of an elastic layer over a maxwell standard linear solid burgers and triviscous half space for each of these models we calculate example postseismic displacements interseismic displacements in a periodic earthquake sequence and interseismic displacements for a nonperiodic earthquake sequence our solution is for a simple geometry however the model presents an elegant tool to explore the evolution of displacements for relatively complex rheologies and rupture recurrence histories

detection of a locked zone at depth on the parkfield california segment of the san andreas fault the parkfield california segment of the san andreas fault is transitional in character between the creeping segment of the fault to the northwest and the locked carrizo plain segment to the southeast the rate of shallow fault slip decreases from 25 30 mm yr northwest of the epicenter of the 1966 parkfield earthquake to zero at the southeastern end of the 1966 rupture zone data from a network of trilateration lines spanning the san andreas fault near parkfield and extending to the pacific coast near san luis obispo shed light on the rate of fault slip at depth since the 1966 earthquake in this study average rates of line length change and shallow fault slip were inverted to determine the slip rate at depth on the parkfield fault segment the fault is taken to be a vertical surface with unknown distribution of strike slip displacement in an elastic half space a striking result of the inversions is that all solutions providing acceptable fits to the data exhibit a locked zone essentially coincident with the rupture surface of the 1966 parkfield earthquake the data require that the locked zone extend nearly as far north as the 1966 epicenter however the vertical extent of the locked zone is not well resolved over much of the parkfield segment the fault is slipping faster at the earth s surface than it is at seismogenic depths in order to fit the trilateration measurements it is necessary to include a component of contraction normal to the trend of the san andreas the inversion results suggest a spatially uniform normal strain of 0 06 strain yr the orientation of the contraction is compatible with geologic and seismic evidence of active folding and reverse faulting in the region the magnitude of the contraction is consistent with convergence rates inferred from global plate motion models

stress dependent power law flow in the upper mantle following the 2002 denali alaska earthquake abstract far field continuous global positioning system gps time series data following the 2002 m7 9 denali alaska earthquake imply that mantle viscoelastic rheology is stress dependent a linear viscous mantle cannot explain fast early displacement rates at the surface that rapidly decay with time whereas a power law rheology where strain rate is proportional to stress raised to the power of 3 5 0 5 provides decay rates and spatial patterns in agreement with observations this is consistent with laboratory measurements for hot wet olivine implying a hydrated mantle and a relatively thin 60 km thick lithosphere beneath south central alaska these results suggest that the viscous strength of the lithosphere varies both spatially and temporally and that effective viscosities inferred from different loading events or observational time periods can differ by up to several orders of magnitude thus the very conditions that enable the inference of rheologic strength transient loading and unloading events significantly alter the effective viscosity

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

three subtropical fronts in the north pacific observational evidence for mode water induced subsurface frontogenesis 1 subsurface fronts in the subtropical north pacific were investigated by constructing a high resolution temperature climatology three distinct subtropical fronts stfs are identified which are the southern northern and eastern stfs according to their relative geographical locations the southern stf extends along 19 21 n west of the dateline while the northern and eastern stfs appear along 21 24 n and 26 n in the western and central subtropical gyre respectively our analysis showed that each of these stfs is associated with large negative meridional potential vorticity pv gradient in the thermocline below the front the northern stf is located on the southern edge of the kuroshio recirculation where the negative pv gradient occurs within a narrow density range and is maintained by the low pv core of the subtropical mode water stmw on the other hand the negative pv gradient at the eastern and southern stfs spans over a wide density range the eastern stf forms near the center axis of the subtropical gyre north of which the upper and lower portions of the central mode water cmw converge forming a thick low pv pool that maintains the negative pv gradient on the front similarly at the southern stf the negative pv gradient is due to a low pv pool to the north with the southernmost portion of the stmw stacked above the upper cmw advected from the central subtropical gyre it is concluded that the mode waters are essential for the north pacific stfs

geodetic displacements and aftershocks following the 2001 mw 8 4 peru earthquake implications for the mechanics of the earthquake cycle along subduction zones we analyzed aftershocks and postseismic deformation recorded by the continuous gps station areq following the m w 8 4 23 june 2001 peru earthquake this station moved by 50 cm trenchward in a n235 e direction during the coseismic phase and continued to move in the same direction for an additional 15 cm over the next 2 years we compare observations with the prediction of a simple one dimensional 1 d system of springs sliders and dashpot loaded by a constant force meant to simulate stress transfer during the seismic cycle the model incorporates a seismogenic fault zone obeying rate weakening friction a zone of deep afterslip the brittle creep fault zone bcfz obeying rate strengthening friction and a zone of viscous flow at depth the ductile fault zone dfz this simple model captures the main features of the temporal evolution of seismicity and deformation our results imply that crustal strain associated with stress accumulation during the interseismic period is probably not stationary over most of the interseismic period the bcfz appears to control the early postseismic response afterslip and aftershocks although an immediate increase by a factor of about 1 77 of ductile shear rate is required placing constraints on the effective viscosity of the dfz following a large subduction earthquake displacement of inland sites is trenchward in the early phase of the seismic cycle and reverse to landward after a time t i for which an analytical expression is given this study adds support to the view that the decay rate of aftershocks may be controlled by reloading due to deep afterslip given the ratio of preseismic to postseismic viscous creep we deduce that frictional stresses along the subduction interface account for probably 70 of the force transmitted along the plate interface

on the mechanics of earthquake afterslip we propose a model for earthquake afterslip based on rate and state variable friction laws in the model afterslip is attributed to the interaction of a velocity weakening region at depth within which earthquakes nucleate with an upper region of velocity strengthening frictional behavior the existence of this upper region is supported by independent seismologic observations and the results of laboratory friction experiments in our model afterslip is the result of relaxation of a stress perturbation within the velocity strengthening region which arises when an earthquake propagates into that region from below we derive the stress perturbation and its decay from the friction constitutive law using a simple 1 degree of freedom approximation for the elastic interaction between the fault and its surroundings this approximation is based on thickness averaged displacements and slip velocities within the velocity strengthening region which is assumed to slip as a rigid block coseismic and postseismic slip are coupled through the thickness averaged stiffness k of the velocity strengthening region we assume k to be inversely proportional to the thickness of this region which means that thicker velocity strengthening regions have a greater tendency to arrest coseismic slip we model the afterslip time histories of the 1966 parkfield and 1987 superstition hills earthquakes and relate the model parameters to physical parameters which may govern the rheologic behavior of the faults in accord with field observations our model predicts 1 that afterslip on some faults scales with the thickness of the unconsolidated sedimentary cover and 2 that proportionally more afterslip occurs for earthquakes in which coseismic surface slip is small compared with coseismic slip at depth velocity strengthening frictional behavior is to be expected for faults within poorly consolidated sediments and for those that contain significant gouge zones about 500 m within their shallow regions 3 5 km combining our results with those of recent laboratory friction studies indicates that relatively young faults with little accumulated fault gouge should exhibit little afterslip

far reaching effects of the hawaiian islands on the pacific ocean atmosphere system using satellite data we detected a wind wake trailing westward behind the hawaiian islands for 3000 kilometers a length many times greater than observed anywhere else on earth this wind wake drives an eastward ocean current that draws warm water from the asian coast 8000 kilometers away leaving marked changes in surface and subsurface ocean temperature standing in the path of the steady trade winds hawaii triggers an air sea interaction that provides the feedback to sustain the influence of these small islands over a long stretch of the pacific ocean

ventilated thermocline strongly affected by a deep mixed layer a theory for subtropical countercurrent abstract the mixed layer thickness generally increases in the northward direction but its change seems to occur rather sharply in a narrow transition zone referred to as a mixed layer front here the author investigates the effects of the mixed layer front on the ventilated thermocline structure especially focusing on the generation mechanism of the subtropical countercurrent if the mixed layer front is not parallel to the surface density contour the fluid with minimum isopycnal potential vorticity is formed around the intersection of the mixed layer front and outcrop line if the mixed layer front slants northeastward and surface density is zonally uniform as seen in a numerical experiment carried out by kubokawa and inui in which the subtropical countercurrent was reproduced the minimum potential vorticity on a high density isopycnal occurs in the east while that in a low density isopycnal occurs in the west in the present study analytic solutions for a simple three layer model are presented f

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

postseismic relaxation and transient creep 1 postseismic deformation has been observed in the epicentral area following the 1992 landers m 7 3 1999 chi chi m 7 6 1999 hector mine m 7 1 2002 denali m 7 9 2003 san simeon m 6 5 and 2004 parkfield m 6 0 earthquakes the observations consist of repeated gps measurements of the position of one monument relative to another separation 100 km the early observations t 0 1 year are well fit by the function a c log t where t is the time after the earthquake and a and c are constants chosen to fit the data because a log t time dependence is characteristic of transient primary creep the early postseismic response may be governed by transient creep as benioff proposed in 1951 that inference is provisional as the stress conditions prevailing in postseismic relaxation are not identical to the constant stress condition in creep experiments the observed logarithmic time dependence includes no characteristic time that might aid in identifying the micromechanical cause

coupled afterslip and viscoelastic flow following the 2002 denali fault alaska earthquake summary models of postseismic deformation following the 2002 m 7 9 denali fault alaska earthquake provide insight into the rheologic structure of the alaskan lithosphere and the physical processes activated following a large earthquake we model coseismic gps displacements and 4 yr of postseismic gps position time series with a coupled model of afterslip on the fault in the lithosphere and distributed viscous flow in the asthenosphere afterslip is assumed to be governed by a simplified version of a laboratory derived rate strengthening friction law that is characterized with a single parameter a b where is the effective normal stress on the fault and a b is a dimensionless empirical parameter afterslip is driven by coseismic stress changes on the fault generated by the main shock the lithosphere is modelled as an elastic plate overlying a linear maxwell viscoelastic asthenosphere we devise a scheme to simultaneously estimate the distributions of coseismic slip and afterslip friction parameters lithosphere thickness and asthenosphere viscosity the postseismic gps time series are best reproduced with a 45 85 km thick elastic lithosphere overlying an asthenosphere of viscosity 0 6 1 5 1019 pa s the 45 85 km elastic lithosphere thickness is greater than or equal to the average crustal thickness in the region suggesting that distributed postseismic flow occurs largely within the mantle while postseismic deformation in the crust is confined largely to slip on a discrete fault penetrating the entire crust and perhaps into the uppermost mantle for typical laboratory values of a b of order 10 2 at temperatures corresponding to the inferred depth of afterslip the estimated effective normal stress on the fault is 50 mpa which is about an order of magnitude lower than effective normal stresses at hydrostatic pore pressure previous studies showed that models with linear newtonian rheology cannot reproduce the observed gps time series but that models incorporating non linear or biviscous flow of the mantle do fit the data we show that a model with afterslip governed by a non linear fault zone rheology coupled to newtonian mantle flow is sufficient to reproduce the gps time series

subthermocline eddies observed by rapid sampling argo floats in the subtropical northwestern pacific ocean in spring 2014 in spring 2014 two subthermocline eddies stes were observed by rapid sampling argo floats in the subtropical northwestern pacific stnwp the first one is a warm salty and oxygen poor lens with its temperature salinity dissolved oxygen t s do anomalies reaching 1 16 c 0 21 practical salinity unit psu 29 9 mol kg respectively near the 26 62 0 surface the other is a cold fresh and oxygen rich lens with its t s do anomalies reaching 1 95 c 0 34 psu 88 0 mol kg respectively near the 26 54 0 surface the vertical extent of the water mass anomalies in the warm cold ste is about 190 m 150 m and its horizontal length scale is 22 7 km 18 10 km according to their water mass properties we speculate that the warm and cold stes are generated in the north pacific subtropical and subarctic front region respectively the observed stes may play an important role in modifying the intermediate layer water properties in the stnwp and this needs to be confirmed by more focused observations in the future

decadal changes in the north pacific oceanic frontal zones as revealed in ship and satellite observations 1 influence of decadal climate changes upon the north pacific subarctic and subtropical oceanic frontal zones np safz and np stfz respectively is documented both satellite and ship measured sea surface temperature sst data reveal the strong confinement of wintertime decadal sst anomalies to those frontal zones the satellite data indicate that the wintertime np safz tended to be narrow and shift northward under the weakened surface westerlies during a warm event in the early 1990s the opposite was the case under the enhanced westerlies during a cool event in the mid 1980s decadal scale modulations in the frontal intensity are also evident in the satellite data a diagnosis based on a simple linearized mixed layer model suggests that the observed anomalous frontal intensity was contributed by the sign reversal of anomalous wind stress curl through the ekman processes and by an anomaly dipole of the net heat flux around the safz these decadal scale modulations in the np safz and their relationships with decadal fluctuations in the local surface westerlies are confirmed in the ship measured data over the 4 recent decades it is found that the safz happens to be a region where the decadal variability in the surface westerlies are unlikely to be masked by the higher frequency fluctuations as it almost coincides with the ridge trough line of the remote atmospheric response to the el nino southern oscillation

strengthening kuroshio observed at its origin during november 2010 to october 2012 direct measurements of kuroshio at its origin 18 degrees n east of the luzon island are conducted from november 2010 to october 2012 it is found that the depth averaged kuroshio between 200 and 700 m has increased over 15 cm s 1 during the 2 year observational period and it is accompanied by the pronounced southward shift of the north equatorial current nec bifurcation further analysis indicates that the kuroshio s strengthening is confined to the upstream segment east of the luzon island while the kuroshio decreased as it passed the luzon strait due to a dipole like sea surface height ssh trend between 15 degrees n and 23 degrees n it is demonstrated that the 2 year strengthening of the kuroshio as well as the dipole like ssh trend can be adequately reproduced by a 1 5 layer nonlinear reduced gravity model suggesting an important role of upper ocean response to low frequency wind forcing in the western pacific salinity at 500 m depth is also found to increase during the concurrent 2 years this subthermocline salinity increase is a combined outcome of vertical basin scale isopycnal surface movement and horizontal advections i e strengthened kuroshio due to changes in the large scale wind driven ocean circulation

postseismic deformation following the 2010 m 7 2 el mayor cucapah earthquake observations kinematic inversions and dynamic models due to its location on a transtensional section of the pacific north american plate boundary the salton trough is a region featuring large strike slip earthquakes within a regime of shallow asthenosphere high heat flow and complex faulting and so postseismic deformation there may feature enhanced viscoelastic relaxation and afterslip that is particularly detectable at the surface the 2010 m 7 2 el mayor cucapah earthquake was the largest shock in the salton trough since 1892 and occurred close to the us mexico border and so the postseismic deformation recorded by the continuous gps network of southern california provides an opportunity to study the rheology of this region three year postseismic transients extracted from gps displacement time series show four key features 1 1 2 cm of cumulative uplift in the imperial valley and sim 1 cm of subsidence in the peninsular ranges 2 relatively large cumulative horizontal displacements 150 km from the rupture in the peninsular ranges 3 rapidly decaying horizontal displacement rates in the first few months after the earthquake in the imperial valley and 4 sustained horizontal velocities following the rapid early motions that were still visibly ongoing 3 years after the earthquake kinematic inversions show that the cumulative 3 year postseismic displacement field can be well fit by afterslip on and below the coseismic rupture though these solutions require afterslip with a total moment equivalent to at least a m 7 2 earthquake and higher slip magnitudes than those predicted by coseismic stress changes forward modeling shows that stress driven afterslip and viscoelastic relaxation in various configurations within the lithosphere can reproduce the early and later horizontal velocities in the imperial valley while newtonian viscoelastic relaxation in the asthenosphere can reproduce the uplift in the imperial valley and the subsidence and large westward displacements in the peninsular ranges we present two forward models of dynamically coupled deformation mechanisms that fit the postseismic transient well a model combining afterslip in the lower crust newtonian viscoelastic relaxation in a localized zone in the lower crust beneath areas of high heat flow and geothermal activity and newtonian viscoelastic relaxation in the asthenosphere and a second model that replaces the afterslip in the first model with viscoelastic relaxation with a stress dependent viscosity in the mantle the rheology of this high heat flow high strain rate region may incorporate elements of both these models and may well be more complex than either of them

implications of deformation following the 2002 denali alaska earthquake for postseismic relaxation processes and lithospheric rheology 1 during the first 2 years following the 2002 mw 7 9 denali alaska strike slip earthquake a large array of global positioning system gps receivers recorded rapid postseismic surface motions extending at least 300 km from the rupture and at rates of more than 100 mm yr in the near field here we use three dimensional 3 d viscoelastic finite element models to infer the mechanisms responsible for these postseismic observations we consider afterslip both from an inversion of gps displacements and from stress driven forward models poroelastic rebound and viscoelastic flow in the lower crust and upper mantle several conclusions can be drawn 1 no single mechanism can explain the postseismic observations 2 significant postseismic flow below a depth of 60 km is required to explain observed far field motions best explained by a weak upper mantle with a depth dependent effective viscosity that ranges from 1019 pa s at the moho 50 km depth to 3 4 1018 pa s at 100 km depth 3 shallow afterslip within the upper crust occurs adjacent to and beneath the regions of largest coseismic slip 4 there is a contribution from deformation in the middle and lower crust from either lower crustal flow or stress driven slip afterslip is preferred over broad viscoelastic flow owing to the existence of seismic velocity discontinuities across the fault at depth though our modeling does not favor either mechanism if the process is viscoelastic relaxation the viscosity is a factor of 3 greater than the inferred mantle viscosity 5 poroelastic rebound probably contributed to the observed postseismic deformation in the immediate vicinity of the denali totschunda junction these conclusions lead us to infer an alaskan mechanical lithosphere that is about 60 km thick overlying a weak asthenosphere and a denali fault that cuts through the entire lithosphere with shear accommodated by faulting in the top 20 km and time dependent aseismic shear below

variability and frontogenesis in the large scale oceanic frontal zones sea surface temperature sst from weekly global advanced very high resolution radiometer data for the period of 1982 1992 and estimates of the surface forcing due to wind stress and net heat flux are used to investigate a global monthly climatology of large scale oceanic frontal zones ofzs the variability of sst gradient in several frontal zones and the meridional frontogenesis in the north pacific subpolar frontal zones are identifiable in the sst gradient field throughout the whole year while subtropical frontal zones appear as seasonal phenomena in the northern hemisphere the magnitude and position of subtropical fronts were found to vary synchronously in both hemispheres with maximum intensity in november to march during this period subtropical fronts in the northern hemisphere become clearly identifiable separate features while in the southern hemisphere their southern boundaries tend to merge with the subpolar front in the northern hemisphere the northward shift of the subtropical frontal zones during late boreal spring results in a merger of the subpolar and subtropical zones by august in the southern hemisphere subtropical fronts separate from the subpolar front during this period and become clearly distinguishable though less intense singular spectrum analysis of the 11 year time series of sst gradient in several ofzs revealed a seasonal signal as well as interannual variations that in the equatorial zone are related to el nino events the amplitude of the annual cycle is comparable in the subtropical and subpolar north pacific but the subtropics leads the subpolar zone by about 4 months combined forcing due to wind stress and net surface heat flux was found to be sufficient to describe most of the observed frontogenesis variability in north pacific midlatitudes on seasonal timescales but not on shorter timescales in the subtropical zone the ekman convergence alone was not sufficient to provide the observed frontogenesis frontolysis on seasonal time scales in fact when the maximum frontogenesis associated with ekman convergence occurs in late spring early summer this is counteracted by the frontolytic effect of ekman pumping and the dominating frontolytic effect of surface heat forcing in summer ekman convergence is more important in the subpolar area where it is enhanced by the smaller frontogenetic effect of both ekman pumping and surface heat forcing surface forcing due to wind stress and heat flux considered in this study does not explain the high amplitude intraseasonal frontogenesis variations especially in the subpolar region

viscoelastic earthquake cycle models with deep stress driven creep along the san andreas fault system 1 we develop a two dimensional boundary element earthquake cycle model including deep interseismic creep on vertical strike slip faults in an elastic lithosphere coupled to a viscoelastic asthenosphere uniform slip on the upper part of the fault is prescribed periodically to represent great strike slip earthquakes below the coseismic rupture the fault creeps in response to lithospheric shear stresses within a narrow linear viscous fault zone the model is applied to the gps contemporary velocity field across the carrizo plain and northern san francisco bay segments of the san andreas fault as well as triangulation measurements of postseismic strain following the 1906 san francisco earthquake previous analysis of these data using conventional viscoelastic coupling models without stress driven creep segall 2002 shows that it is necessary to invoke different lithosphere asthenosphere rheology in northern and southern california in order to explain the data we show that with deep stress driven interseismic creep on the san andreas fault the data can be explained with the same rheology for northern and southern california we estimate elastic thickness in the range 44 100 km 95 confidence level fault zone viscosity per unit width of 0 5 8 2 1017 pa s m and asthenosphere relaxation time of 24 622 years 0 1 2 9 1020 pa s for northern and southern california we estimate a slip rate of 21 27 mm yr and recurrence time of 188 315 years for the northern san francisco bay san andreas fault and slip rate of 32 42 mm yr with recurrence time of 247 536 years for the carrizo plain

gravitational viscoelastic postseismic relaxation on a layered spherical earth viscoelastic relaxation of a ductile asthenosphere underlying a purely elastic plate is a strong candidate process for explaining anomalous rates of crustal deformation observed following large earthquakes the nongravitational treatment of pollitz 1992 which is valid on a global scale and includes the effects of compressibility is here extended to permit the calculation of gravitational viscoelastic relaxation for a specified spherically layered viscoelastic rheology following an earthquake in an elastic layer the simple approximations we adopt make the resulting treatment particularly suitable for near field calculations for an asthenosphere with a maxwell rheology the effect of gravitational coupling is manifested only many relaxation times after the earthquake as obtained by previous investigators its effect is generally to speed up the long wavelength component of the relaxation process and attenuate the overall vertical displacement pattern several subtle features common to the relaxation behavior from several different fault types thrust rift and strike slip are identified the effect of gravitational coupling on horizontal displacements is consistent with flexure of the upper elastic plate driven by the corresponding effects on the vertical displacement stress diffusion away from the source region generally exhibits pulse like behavior which is dispersive in both space and time if the asthenosphere is confined to a relatively narrow channel then the dispersion branches governing relaxation are radically altered and stress diffusion effects far from the coseismic rupture zone exhibit a complicated time dependence reflecting the competing tendencies of toroidal and spheroidal mode relaxation

transient rheology of the uppermost mantle beneath the mojave desert california abstract geodetic data indicate that the m7 1 hector mine california earthquake was followed by a brief period a few weeks of rapid deformation preceding a prolonged phase of slower deformation we find that the signal contained in continuous and campaign global positioning system data for 2 5 years after the earthquake may be explained with a transient rheology quantitative modeling of these data with allowance for transient linear biviscous rheology in the lower crust and upper mantle demonstrates that transient rheology in the upper mantle is dominant its material properties being typified by two characteristic relaxation times 0 07 and 2 years the inferred mantle rheology is a jeffreys solid in which the transient and steady state shear moduli are equal consideration of a simpler viscoelastic model with a linear univiscous rheology 2 fewer parameters than a biviscous model shows that it consistently underpredicts the amplitude of the first 3 months signal and allowance for a biviscous rheology is significant at the 99 0 confidence level another alternative model deep postseismic afterslip beneath the coseismic rupture predicts a vertical velocity pattern opposite to the observed pattern at all time periods considered despite its plausibility the advocated biviscous rheology model is non unique and should be regarded as a viable alternative to the non linear mantle rheology model for governing postseismic flow beneath the mojave desert

relationships between total alkalinity in surface water and sea surface dynamic height in the pacific ocean improved spatial and temporal representation of total alkalinity ta is expected to be an important component in monitoring changes in the oceanic carbon cycle and acidification over the coming decades for this reason previous authors have sought to develop and apply empirical methods to characterize ta in the surface ocean however there are regions such as the north pacific that have proven difficult to successfully represent through empirical relationships based on temperature and salinity with linear regression here we propose a new empirical approach for reconstructing ta for the pacific basin using sea surface salinity and sea surface dynamic height ssdh we propose five zones of the pacific basin where the empirical relationships are applied separately the root mean square error of the fittings of these equations to the measured ta is 7 8 mol kg 1 the ssdh based empirical equation helps especially to represent the ta in the north pacific subtropical subarctic frontal zone where salinity normalized ta as well as other oceanographic variables exhibits a large meridional gradient and sizeable formation of central mode water and subtropical mode water occurs

decadal variability of the kuroshio extension observations and an eddy resolving model hindcast abstract low frequency variability of the kuroshio extension ke is studied using observations and a multidecadal 1950 2003 hindcast by a high resolution 0 1 eddy resolving global ocean general circulation model for the earth simulator ofes in both the ofes hindcast and satellite altimeter observations low frequency sea surface height ssh variability in the north pacific is high near the ke front an empirical orthogonal function eof analysis indicates that much of the ssh variability in the western north pacific east of japan is explained by two modes with meridional structures tightly trapped along the ke front the first mode represents a southward shift and to a lesser degree an acceleration of the ke jet associated with the 1976 77 shift in basin scale winds the second mode reflects quasi decadal variations in the intensity of the ke jet both the spatial structure and time series of these modes derived from the hindcast are in close agreement with observations a linear rossby wave

interannual variations of kuroshio transport in the east china sea and its relation to the pacific decadal oscillation and mesoscale eddies results of a data assimilative ocean model jcope2 from 1993 to 2012 were used to examine the correlation between the pacific decadal oscillation pdo index and interannual variations of the kuroshio transport in the east china sea ecs and the influences of mesoscale eddies on this correlation in a period from 1993 to 2002 the kuroshio transport estimated from the jcope2 reanalysis has a positive correlation with the pdo index this well known correlation became weak or even disappeared when the analysis period was extended from 1993 2002 to 1993 2012 this occurs because the variation range of the pdo index became small during enhanced mesoscale eddy activity southeast of taiwan in years after 2002 the eddies caused a larger variation in the kuroshio transport in the years after 2002 than before 2002 and therefore changed the correlation between the pdo index and kuroshio transport in the ecs the influence of mesoscale eddies on the kuroshio transport has strong regional dependence the kuroshio transport from the area east of taiwan to the midway along the shelf break in the east china sea depends mainly on eddies arriving from southeast of taiwan while transport from the midway along the shelf break to the tokara strait depends mainly on the eddies arriving from northeast of okinawa island the combination of pdo related signals and eddy related signals determines the interannual variations of the kuroshio transport in the ecs and sufficient attention must be paid to the spatial dependence of the kuroshio transport in the ecs on eddies

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

frictional afterslip following the 2005 nias simeulue earthquake sumatra continuously recording global positioning system stations near the 28 march 2005 rupture of the sunda megathrust moment magnitude m w 8 7 show that the earthquake triggered aseismic frictional afterslip on the subduction megathrust with a major fraction of this slip in the up dip direction from the main rupture eleven months after the main shock afterslip continues at rates several times the average interseismic rate resulting in deformation equivalent to at least a m w 8 2 earthquake in general along strike variations in frictional behavior appear to persist over multiple earthquake cycles aftershocks cluster along the boundary between the region of coseismic slip and the up dip creeping zone we observe that the cumulative number of aftershocks increases linearly with postseismic displacements this finding suggests that the temporal evolution of aftershocks is governed by afterslip

postseismic relaxation across the central nevada seismic belt 1 two gps geodetic surveys across the basin and range br province of western north america have detected an anomalous compression east of the central nevada seismic belt cnsb the first network installed by the u s geological survey along an east west trending transect across the br at approximately 40 n consisted of 63 monuments observed campaign style in 1992 1996 and 1998 the second network installed by the california institute of technology consisted of 50 continuously operating gps receivers 18 of which were roughly along the same transect as the campaign survey we have used a viscoelastic postseismic relaxation model of the four largest earthquakes in the cnsb on the pleasant valley fault in 1915 the cedar mountain fault in 1932 and on the fairview peak and dixie valley faults in 1954 to interpret the geodetic velocities observed across the cnsb a model of postseismic relaxation with a lower crustal maxwell viscosity of 5 50 1018 pa s can explain the apparent compression regardless of the assumed mantle viscosity the geodetic velocities that we determined after removing the postseismic contribution indicate that within current gps detection limits the br is stable east of the cnsb and is undergoing rapid right lateral shear west of the cnsb

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

bias in estimates of lithosphere viscosity from interseismic deformation 1 the estimation of uniform viscosities representing the lower crust and uppermost mantle from postseismic or interseismic deformation i e apparent viscosities is inherently biased with respect to a depth dependence of the viscosities within each layer estimates are biased toward a more viscous lower crust or a less viscous lithospheric mantle depending on the relative geometric mean viscosities of the two layers when there is a low viscosity shear zone beneath the fault apparent viscosities are close to that of the shear zone immediately after the earthquake although the apparent viscosities increase significantly during the later interseismic period inferences made from interseismic deformation that the lower crust is more viscous than the upper mantle may be entirely consistent with depth dependent viscosity profiles that have a significant increase in viscosity from the lowermost crust to the uppermost mantle

time dependent distributed afterslip on and deep below the izmit earthquake rupture surface deformation transients measured with the global positioning system during the 87 days between the 17 august 1999 izmit earthquake and the 12 november 1999 duzce earthquake indicate rapidly decaying aseismic fault slip on and well below the coseismic rupture elastic model inversions for time dependent distributed fault slip using a network inversion filter approach show that afterslip was highest between and below the regions of maximum coseismic slip and propa gated downward to or even below the base of the crust maximum afterslip rates decayed from greater than 2 m yr immediately after the i zmit earthquake to about 1 2 m yr just prior to the duzce earthquake maximum afterslip occurred below the eastern karadere rupture segment and near the i zmit hypocenter afterslip in the upper 16 km decayed more rapidly than that below the seismogenic zone these observations are consistent with a phase of rapid aseismic fault slip concentrated near the base of the seismogenic zone continued loading from the rapid deep afterslip along the eastern rupture zone is a plausible mechanism that helped trigger the nearby mw 7 2 12 november duzce earthquake

mixed layers and fronts in simple ocean circulation models abstract a three dimensional regime with a differentially heated mixed layer on top of an ideal fluid interior is considered in a situation which corresponds to the interior of the well known wind driven model by stommel 1948 although the transport field in this case is continuous and simple the same is not necessarily true for the density and velocity fields if the mixed layer is weakly coupled to the atmosphere a front is generated at the line of a maximum downwelling another front is expected at the line of a zero downwelling

postseismic deformation following the june 2000 earthquake sequence in the south iceland seismic zone 1 we observe postseismic deformation on two spatiotemporal scales following mw 6 5 earthquakes in the south iceland seismic zone on 17 and 21 june 2000 we see a rapidly decaying deformation transient lasting no more than 2 months and extending about 5 km away from the two main shock ruptures this local month scale transient is captured by several radar interferograms and is also observed at a few campaign gps sites located near the faults a slower transient with a characteristic timescale of about a year is detected only by gps measurements the month scale deformation pattern has been explained by poroelastic rebound due to postearthquake pore pressure changes in contrast the year scale deformation can be explained by either afterslip at 8 14 km depth or viscoelastic relaxation of the lower crust and upper mantle in response to the coseismic stress changes the optimal viscoelastic models have lower crustal viscosities of 0 5 1 1019 pa s and upper mantle viscosity of 3 1018 pa s because of the limitations of our gps campaign data we consider both afterslip and viscoelastic relaxation as plausible mechanisms explaining the deformation field both types of postseismic deformation models suggest that the areas of large coseismic stress increase east of the 17 june and west of the 21 june ruptures continue to be loaded by the postseismic deformation

poroelastic rebound along the landers 1992 earthquake surface rupture maps of surface displacement following the 1992 landers california earthquake generated by interferometric processing of ers 1 synthetic aperture radar sar images reveal effects of various postseismic deformation processes along the 1992 surface rupture the large scale pattern of the postseismic displacement field includes large lobes mostly visible on the west side of the fault comparable in shape with the lobes observed in the coseismic displacement field this pattern and the steep displacement gradient observed near the emerson camp rock fault cannot be simply explained by afterslip on deep sections of the 1992 rupture models show that horizontal slip occurring on a buried dislocation in a poisson s material produces a characteristic quadripole pattern in the surface displacement field with several centimeters of vertical motion at distances of 10 20 km from the fault yet this pattern is not observed in the postseismic interferograms as previously proposed to explain local strain in the fault step overs peltzer et al 1996b we argue that poroelastic rebound caused by pore fluid flow may also occur over greater distances from the fault compensating the vertical ground shift produced by fault afterslip such a rebound is explained by the gradual change of the crustal rocks poisson s ratio value from undrained coseismic to drained postseismic conditions as pore pressure gradients produced by the earthquake dissipate using the poisson s ratio values of 0 27 and 0 31 for the drained and undrained crustal rocks respectively elastic dislocation models show that the combined contributions of afterslip on deep sections of the fault and poroelastic rebound can account for the range change observed in the sar data and the horizontal displacement measured at global positioning system gps sites along a 60 km long transect across the emerson fault savage and svarc 1997 using a detailed surface slip distribution on the homestead valley kickapoo and johnson valley faults we modeled the poroelastic rebound in the homestead valley pull apart a poisson s ratio value of 0 35 for the undrained gouge rocks in the fault zone is required to account for the observed surface uplift in the 3 5 years following the earthquake this large value implies a seismic velocity ratio vp vs of 2 1 consistent with the observed low vs values of fault zone guided waves at shallow depth li et al 1997 the sar data also reveal postseismic creep along shallow patches of the eureka peak and burnt mountain faults with a characteristic decay time of 0 8 years coseismic dilatant hardening locking process followed by post seismic pore pressure controlled fault creep provide a plausible mechanism to account for the decay time of the observed slip rate along this section of the fault

decadal variability of the subtropical front of the western north pacific in an eddy resolving ocean general circulation model 1 we examined decadal variability of the subtropical front stf of the western north pacific by using a north pacific ocean general circulation model ogcm comparing the results of three simulations with different horizontal resolutions in the long term mean fields the eddy resolving model 10 km was able to simulate the distributions of the stf and the associated subtropical countercurrent stcc between 20 n and 30 n better than either the non eddy resolving model 100 km or the eddy permitting model 20 km because it simulated the kuroshio recirculation gyre more realistically the simulated stf intensity exhibited significant decadal scale variations it was stronger in the late 1970s and weaker in the early 1990s during these two periods the simulated mode waters showed corresponding differences in their potential vorticity minima density and paths we also investigated the relationship between the decadal scale stf variability and atmospheric forcing the results suggest that the decadal scale stf variability can be largely explained by changes in the mode waters formed in the western north pacific and advected to north of the stf by the subtropical gyre in response to a change in surface westerly winds that occurred in the mid 1970s

mesoscale eddies in the northwestern subtropical pacific ocean statistical characteristics and three dimensional structures mesoscale eddy properties in the northwestern subtropical pacific ocean are investigated by analyzing 22 567 cyclonic eddies ces and 26 365 anticyclonic eddies aes detected from 19 year altimetric sea level records eddy occurrence frequency and kinetic energy are prevailingly high in the subtropical countercurrent zonal band between 19 degrees n and 26 degrees n and further elevated near the luzon taiwan coast a general superiority of aes is observed at most latitudes except between 19 degrees n and 22 degrees n where the ce number is larger the modal radius and mean lifespan of the ces aes are 134km and 11 2weeks 121km and 10 9weeks respectively after generation most eddies propagate westward with a mean speed of 7 2cms 1 and deflect northward following the kuroshio along the luzon taiwan coast three dimensional eddy structures are further explored with composite eddy images in five subregions constructed by surfacing argo temperature salinity data into altimeter detected eddy areas due to the existence of mode waters in the main thermocline eddy induced temperature anomaly exhibits a double core vertical structure which is especially evident in ce images because of the vertical water mass distribution salinity anomaly features a sandwich like pattern which is more evident in ae images also revealed is the significant structure difference in these five subregions eddies are greatly intensified as they approach the western boundary inducing larger temperature and salinity anomalies and influencing deeper ocean along the luzon taiwan coast aes are preferentially strengthened by the northward background flow

on the formation of subtropical countercurrent to the west of the hawaiian islands 1 analysis of recent ocean model assimilation results suggest that the eastward countercurrent in the northern subtropical pacific may be divided into two branches one in the northwestern pacific 19 n 27 n to the west of 170 e and the other to the west of the hawaii islands to the west of the 158 w along 19 n 20 n two mechanisms contribute to the formation of the eastward countercurrent to the west of hawaii first the hawaiian islands blocks the easterly trade winds and generates a dipole of wind stress vorticity with positive wind curl to the north of the islands 20 n 23 n and with negative curl to the south 16 n 19 n this dipole of wind stress vorticity acts to create an eastward current jet to the west of the hawaii island through the sverdrup relation second the islands can directly block the westward north equator current nec to generate an eastward current to the west of the islands we use a numerical model to test these mechanisms for the generation of the eastward countercurrent to the west of the hawaii islands the results show that while the dipole of the wind stress vorticity is helpful in the forming of the eastward countercurrent and as the nec impinges upon the islands the westward traveling vortex streets formed in the ocean plays a key role in intensifying the eastward current to the west of the hawaiian islands

transient rheology of the upper mantle beneath central alaska inferred from the crustal velocity field following the 2002 denali earthquake the m7 9 2002 denali earthquake alaska is one of the largest strike slip earthquakes ever recorded the postseismic gps velocity field around the 300 km long rupture is characterized by very rapid horizontal velocity up to 300 mm yr for the first 0 1 years and slower but still elevated horizontal velocity up to 100 mm yr for the succeeding 1 5 years i find that the spatial and temporal pattern of the displacement field may be explained by a transient mantle rheology representing the regional upper mantle as a burghers body 1 infer steady state and transient viscosities of 1 2 8 x 10 18 pa s and 2 1 0 x 10 17 pa s respectively corresponding to material relaxation times of 1 3 and 0 05 years the lower crustal viscosity is poorly constrained by the considered horizontal velocity field and the quoted mantle viscosities assume a steady state lower crust viscosity that is 7 1 systematic bias in predicted versus observed velocity vectors with respect to a fixed north america during the first 3 6 months following the earthquake is reduced when all velocity vectors are referred to a fixed site this suggests that the post denali gps time series for the first 1 63 years are shaped by a combination of a common mode noise source during the first 3 6 months plus viscoelastic relaxation controlled by a transient mantle rheology

origins of eddy kinetic energy in the bay of bengal by analyzing satellite observational data and ocean general circulation model experiments this study investigates the key processes that determine the spatial distribution and seasonality of intraseasonal eddy kinetic energy eke within the bay of bengal bob it is revealed that a complicated mechanism involving both local and remote wind forcing and ocean internal instability is responsible for the generation and modulation of eke in this region high level eke mainly resides in four regions east of sri lanka region 1 the western bob region 2 northwest of sumatra region 3 and the coastal rim of the bob region 4 the high eke levels in regions 1 and 2 are predominantly produced by ocean internal instability which contributes 90 and 79 respectively prominent seasonality is also observed in these two regions with higher eke levels in boreal spring and fall due to enhanced instability of the east indian coast current and the southwest monsoon current respectively in contrast ocean internal instability contributes 49 and 52 of the total eke in regions 3 and 4 respectively whereas the atmospheric forcing of intraseasonal oscillations isos also plays an important role isos produce eke mainly through wind stress involving both the remote effect of equatorial winds and the local effect of monsoonal winds equatorial origin wave signals significantly enhance the eke levels in regions 3 and 4 in the form of reflected rossby waves and coastal kelvin waves respectively the local wind forcing effect through ekman pumping also has a significant contribution in regions 3 and 4 24 and 22 respectively

vertical structure of bottom ekman tidal flows observations theory and modeling from the northern adriatic 1 from september 2002 to may 2003 fifteen bottom mounted acoustic doppler current profilers measured currents of the northern adriatic basin tidal fluctuations at all seven of the major adriatic frequencies were synthesized from a response tidal analysis of these measurements most observed tidal current ellipses were nearly reversing but near the bottom tidal current ellipses all shortened and broadened semidiurnal currents led upper water column currents and diurnal tidal current ellipse orientations rotated counterclockwise toward the bottom theoretical solutions for a tidally forced bottom ekman layer with vertical eddy viscosity of the form az z k were least squares fit to the observations average values were 3 10 4 m s and k 5 10 4 m2 s the value of k was important in matching tidal orientation and phase changes and a nonzero was important in matching tidal amplitude changes the navy coastal ocean model ncom and the quoddy model were also compared to the observations the average rms errors for the bottom ekman layer were 0 22 cm s for the best fit theory 0 35 cm s for ncom and 0 36 cm s for quoddy az structures from ncom and quoddy show that time variation in az is relatively unimportant for adriatic tides the bottom shear stresses from theory were larger in magnitude than those from the bottom drag formulations in ncom and quoddy

postseismic deformation associated with the 1992 m ω 7 3 landers earthquake southern california following the 1992 m 7 3 landers earthquake a linear array of 10 geodetic monuments at roughly 5 km spacing was established across the emerson fault segment of the landers rupture the array trends perpendicular to the local strike of the fault segment and extends about 30 km on either side of it the array was surveyed by global positioning system 0 034 0 048 0 381 1 27 1 88 2 60 and 3 42 years after the landers earthquake to measure both the spatial and temporal character of the postearthquake relaxation the temporal behavior is described roughly by a short term decay time 84 23 days exponential relaxation superimposed upon an apparently linear trend because the linear trend represents motions much more rapid than the observed preseismic motions we attribute that trend to a slower decay time greater than 5 years postseismic relaxation the curvature of which cannot be resolved in the short run 3 4 years of postseismic data about 100 mm of right lateral displacement and 50 mm of fault normal displacement accumulated across the geodetic array in the 3 4 year interval covered by the postseismic surveys those displacements are attributed to postseismic right lateral slip in the depth interval 10 to 30 km on the downward extension of the rupture trace the right lateral slip amounted to about 1 m directly beneath the geodetic array and the fault normal displacement is apparently primarily a consequence of the curvature of the rupture these conclusions are based upon dislocation models fit to the observed deformation however no dislocation model was found with rms residuals as small as the expected observational error

seasonal modulations in the eddy field of the south pacific ocean abstract decade long satellite altimeter data from the ocean topography experiment topex poseidon and european remote sensing satellite 1 and 2 ers 1 2 missions are analyzed to investigate the eddy signals in the south pacific ocean high eddy kinetic energy eke bands with well defined annual cycles are detected along the eastward flowing surface currents of the south tropical countercurrent stcc between 21 29 s and the south equatorial countercurrent secc centered near 9 s overriding the westward flowing south equatorial current sec the stcc layer has the sign of its mean potential vorticity gradient opposite to that in the sec layer subjecting the vertically sheared stcc sec system to baroclinic instability in austral winter the stcc sec system is baroclinically more unstable than in other seasons because of the large vertical shear and weak stratification this seasonal variation in the intensity of baroclinic instability is responsible for the seasonal modulation of the stcc s eke fi

interannual variability of the north pacific subtropical countercurrent and its associated mesoscale eddy field interannual changes in the mesoscale eddy field along the subtropical countercurrent stcc band of 188 258n in the western north pacific ocean are investigated with 16 yr of satellite altimeter data enhanced eddy activities were observed in 1996 98 and 2003 08 whereas the eddy activities were below average in 1993 95 and 1999 2002 analysis of repeat hydrographic data along 1378e reveals that the vertical shear between the surface eastward flowing stcc and the subsurface westward flowing north equatorial current nec was larger in the eddy rich years than in the eddy weak years by adopting a 2 layer reduced gravity model it is shown that the increased eddy kinetic energy level in 1996 98 and 2003 08 is because of enhanced baroclinic instability resulting from the larger vertical shear in the stcc nec s background flow the cause for the stcc nec s interannually varying vertical shear can be sought in the forcing by surface ekman

postseismic deformation due to the mw 6 0 2004 parkfield earthquake stress driven creep on a fault with spatially variable rate and state friction parameters 1 we investigate the coseismic and postseismic deformation due to the m w 6 0 2004 parkfield california earthquake we produce coseismic and postseismic slip models by inverting data from an array of 14 continuous gps stations from the scign network kinematic inversions of postseismic gps data over a time period of 3 years show that afterslip occurred in areas of low seismicity and low coseismic slip predominantly at a depth of 5 km inversions suggest that coseismic stress increases were relaxed by predominantly aseismic afterslip on a fault plane the kinetics of afterslip is consistent with a velocity strengthening friction generalized to include the case of infinitesimal velocities we performed simulations of stress driven creep using a numerical model that evaluates the time dependent deformation due to coseismic stress changes in a viscoelastoplastic half space starting with a coseismic slip distribution we compute the time dependent evolution of afterslip on a fault plane and the associated displacements at the gps stations data are best explained by a rate strengthening model with frictional parameter a b 7 x 10 3 at a high end of values observed in laboratory experiments we also find that the geodetic moment due to creep is a factor of 100 greater than the cumulative seismic moment of aftershocks the rate of aftershocks in the top 10 km of the seismogenic zone mirrors the kinetics of afterslip suggesting that postearthquake seismicity is governed by loading from the nearby aseismic creep the san andreas fault around parkfield is deduced to have large along strike variations in rate and state frictional properties velocity strengthening areas may be responsible for the separation of the coseismic slip in two distinct asperities and for the ongoing aseismic creep occurring between the velocity weakening patches after the 2004 rupture

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

eddy transport of heat and thermocline waters in the north pacific a key to interannual decadal climate variability abstract high resolution xbt transects in the north pacific ocean at an average latitude of 22 n are analyzed together with topex poseidon altimetric data to determine the structure and transport characteristics of the mesoscale eddy field based on anomalies in dynamic height 410 eddies are identified in 30 transects from 1991 to 1999 including eddies seen in multiple transects over a year or longer their wavelength is typically 500 km with peak to trough temperature difference of 2 2 c in the center of the thermocline the features slant westward with decreasing depth by 0 8 of longitude on average from 400 m up to the sea surface this tilt produces a depth varying velocity temperature correlation and hence a vertical meridional overturning circulation in the mean 3 9 sv sv 106 m3 s 1 of thermocline waters are carried southward by the eddy field over the width of the basin balanced mainly by northward flow in the surface layer corresponding northward heat transport is 0 086 0 012 pw

interannual eddy kinetic energy modulations in the agulhas return current interannual variability in the mesoscale eddy field in the agulhas return current arc of 32 42 degrees s and 15 35 degrees e is investigated based on satellite altimeter observations and state estimate from the estimating the circulation and climate of the ocean phase ii from 1993 to 2016 it is found that the interannual modulation of eddy kinetic energy in the arc region is externally mediated by the wind stress forcing that generates the westward propagating sea surface height anomalies across the south indian ocean subtropical gyre the wind forced sea surface height anomalies influence the upstream agulhas current volume transports by modulating the intensity of barotropic instability of the arc mean flow centered around the retroflection region the agulhas current inflow variability leads to the downstream interannual eddy kinetic energy fluctuations in the arc region

mesoscale eddies northeast of the hawaiian archipelago from satellite altimeter observations 1 enhanced mesoscale eddy activity northeast of the hawaiian archipelago was investigated by using the high pass filtered satellite altimetric sea surface height ssh data of the past 16 years the level of eddy kinetic energy eke shows significant interannual variations which appear well correlated to the large scale atmospheric wind forcing associated with the pacific decadal oscillation index the eke levels in the area along the subtropical front zone in 1997 1998 and 2003 2005 for example were three times as large as those in the low eke years spectral analyses in the 3 latitude by 5 longitude subregions revealed the dominant mesoscale periods ranging from 90 days near 18 n to 180 days near 36 n a 3 layer quasi geostrophic model constrained by world ocean atlas 2005 climatologies was used to explore instability of the regional circulation the analysis shows a geographical match between baroclinic instability strength and the observed rms ssh variability and a temporal match between seasonally varying instability strength and the observed seasonal eke modulation and suggests that baroclinic instability by the vertically sheared regional mean circulation provides the energy source for the enhanced eddy variability northeast of the hawaiian archipelago

subtropical countercurrent in an idealized ocean gcm abstract in the north pacific there is a shallow eastward current called the subtropical countercurrent which flows across the central subtropical gyre the present article studies the generation mechanism of the subtropical countercurrent reproduced in an ocean general circulation model gcm with a simple geometry driven by surface wind stress and surface buoyancy forcing in the ocean gcm the deep mixed layer occurs in the northern part of subtropical gyre and shoals abruptly in the central subtropical gyre the mixed layer front the narrow transition zone of the mixed layer depth slants from the western central subtropical gyre to the northeast and the low potential vorticity fluid is formed at the intersection of the mixed layer front and the outcrop line since the surface density is almost zonally uniform and the mixed layer front slants northeastward the minimum potential vorticity fluids on denser isopycnals are formed in the northeastern region while those on lighter isopycnals are form

izmit earthquake postseismic deformation and dynamics of the north anatolian fault zone 1 we have modeled postseismic deformation from 1999 to 2003 in the region surrounding the 1999 izmit and duzce earthquake ruptures using a three dimensional viscoelastic finite element method our models confirm earlier findings that surface deformation within the first few months of the izmit earthquake is principally due to stable frictional afterslip on and below the izmit earthquake rupture a second deformation process is required however to fit the surface deformation after several months viscoelastic relaxation of lower crust and or upper mantle with a viscosity of the order of 2 to 5 1019 pa s improves the models fit to later gps site velocities however for a linear viscous rheology this range of values is inconsistent with highly localized interseismic deformation around the north anatolian fault zone nafz that was well observed prior to the earthquake sequence the simplest solution to this problem is to assume that the effective viscosity of the relaxing material increases with time after large earthquakes that is that it has a power law or burger s body transient rheology a burger s body rheology with two characteristic viscosities 2 to 5 1019 pa s and at least 2 1020 pa s in the mantle is consistent with deformation around the nafz throughout the earthquake cycle

nitric acid from volcanoes abstract atmospheric cycling of nitric acid and other nitrogen bearing compounds is an important biogeochemical process with significant implications for ecosystems and human health volcanoes are rarely considered as part of the global nitrogen cycle but here we show that they release a previously unconsidered flux of hno3 vapour to the atmosphere we report the first measurements of nitric acid vapour in the persistent plumes from four volcanoes masaya nicaragua etna italy and villarrica and lascar chile mean near source volcanic plume concentrations of hno3 range from 1 8 to 5 6 mol m 3 an enrichment of one to two orders of magnitude over background 0 1 1 5 mol m 3 using mean molar hno3 so2 ratios of 0 01 0 02 0 05 and 0 07 for villarrica masaya etna and lascar respectively combined with so2 flux measurements we calculate gaseous hno3 fluxes from each of these volcanic systems and extend this to estimate the global flux from high temperature non explosive volcanism to be 0 02 0 06 tg n yr 1 while comparatively small on the global scale this flux could have important implications for regional fixed n budgets the precise mechanism for the emission of this hno3 remains unclear but we suggest that thermal nitrogen fixation followed by rapid oxidation of the product no is most likely in explosive ash rich plumes no may result from or at least be supplemented by production from volcanic lightning rather than thermal n fixation we have calculated no production via this route to be of the order of 0 02 tg n yr 1