persistent scatterer interferometric synthetic aperture radar for crustal deformation analysis with application to volcan alcedo galapagos 1 while conventional interferometric synthetic aperture radar insar is a very effective technique for measuring crustal deformation almost any interferogram includes large areas where the signals decorrelate and no measurement is possible persistent scatterer ps insar overcomes the decorrelation problem by identifying resolution elements whose echo is dominated by a single scatterer in a series of interferograms existing ps methods have been very successful in analysis of urban areas where stable angular structures produce efficient reflectors that dominate background scattering however man made structures are absent from most of the earth s surface furthermore existing methods identify ps pixels based on the similarity of their phase history to an assumed model for how deformation varies with time whereas characterizing the temporal pattern of deformation is commonly one of the aims of any deformation study we describe here a method for ps analysis stamps that uses spatial correlation of interferogram phase to find pixels with low phase variance in all terrains with or without buildings prior knowledge of temporal variations in the deformation rate is not required for their identification we apply stamps to volcan alcedo where conventional insar fails because of dense vegetation on the upper volcano flanks that causes most pixels to decorrelate with time we detect two sources of deformation the first we model as a contracting pipe like body which we interpret to be a crystallizing magma chamber the second is downward and lateral motion on the inner slopes of the caldera which we interpret as landsliding

sea ice motion in response to geostrophic winds it is an old rule of thumb that sea ice moves with a speed of about 2 of the surface wind and about 45 to the right of the wind a similar relationship between the ice velocity and the geostrophic wind is examined here it is found that only about half of the long term several month average ice motion is directly related to the geostrophic wind the other half being due to the mean ocean circulation on shorter time scales and in all seasons more than 70 of the variance of the ice velocity in the central arctic ocean is explained by the geostrophic wind within about 400 km of the coasts the geostrophic wind is less successful in explaining the ice motion the spatial variations in ice velocity are also partly explained by the geostrophic wind about half of the variance in the large scale ice vorticity and shear are accounted for on the other hand none of the large scale ice divergence can be explained by the wind the long term average ocean current is estimated by subtracting the share of the ice motion caused by the wind from the total ice motion

surface rupture of the 2005 kashmir pakistan earthquake and its active tectonic implications to provide a detailed record of a relatively rare thrust surface rupture and examine its active tectonic implications we have conducted field mapping of the surface rupture associated with the 2005 m w 7 6 kashmir earthquake despite the difficulty arising from massive earthquake induced landslides along the surface rupture we found that typical pressure ridges and warps extend northwestward for a distance of 70 km with a northeast side up vertical separation of up to 7 m neither the main frontal thrust nor the main boundary thrust is responsible for the earthquake but three active faults or fault segments within the sub himalaya collectively called the balakot bagh fault compose the causative fault although the fault exhibits substantial geomorphic expression of repeated similar surface ruptures only a part of it had been mapped as active before the earthquake the location of the hypocenter suggests that the rupture was initiated at a deep portion of the northern central segment boundary and propagated bilaterally to eventually break all three segments our obtained surface rupture traces and the along strike slip distribution are both in good agreement with results of prompt analyses of satellite images indicating that space geodesy can greatly aid in time consuming field mapping of surface ruptures assuming that the extensive fill terrace in the meizoseismal area was abandoned during 10 30 ka we tentatively estimate the earthquake recurrence interval and shortening rate on the balakot bagh fault to be 1000 3300 yr and 1 4 4 1 mm yr respectively these estimates indicate that the balakot bagh fault is not a main player of himalayan contraction accommodation graphic 1 selected field photographs and arcgis files of the mapped surface rupture traces and measured vertical separations are available in the electronic supplement to this article 1 embed inline graphic 1 gif

observations and modeling of coseismic and postseismic deformation due to the 2015 mw 7 8 gorkha nepal earthquake we use space geodetic data to investigate coseismic and postseismic deformation due to the 2015 mw 7 8 gorkha earthquake that occurred along the central himalayan arc because the earthquake area is characterized by strong variations in surface relief and material properties we developed finite element models that explicitly account for topography and 3 d elastic structure we computed the line of sight displacement histories from three tracks of the sentinel 1a b interferometric synthetic aperture radar insar satellites using persistent scatter method insar observations reveal an uplift of up to 70 mm over 20 months after the main shock concentrated primarily at the downdip edge of the ruptured asperity gps observations also show uplift as well as southward movement in the epicentral area qualitatively similar to the coseismic deformation pattern kinematic inversions of gps and insar data and forward models of stress driven creep suggest that the observed postseismic transient is dominated by afterslip on a downdip extension of the seismic rupture a poroelastic rebound may have contributed to the observed uplift and southward motion but the predicted surface displacements are small we also tested a wide range of viscoelastic relaxation models including 1 d and 3 d variations in the viscosity structure models of a low viscosity channel previously invoked to explain the long term uplift and variations in topography at the plateau margins predict opposite signs of horizontal and vertical displacements compared to those observed our results do not preclude a possibility of deep seated viscoelastic response beneath southern tibet with a characteristic relaxation time greater than the observation period 2 years

surface deformation and lower crustal flow in eastern tibet field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern tibetan plateau since about 4 million years ago instead central eastern tibet has been nearly stationary relative to southeastern china southeastern tibet has rotated clockwise without major crustal shortening and the crust along portions of the eastern plateau margin has been extended modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle this model also predicts east west extension on the high plateau without convective removal of tibetan lithosphere and without eastward movement of the crust east of the plateau

dominant afterslip of the 2010 m w 6 9 yushu tibetan plateau earthquake as derived from gps observations implication for seismic hazard assessment the mw 6 9 yushu earthquake occurred on 14 april 2010 rupturing the yushu segment of the previously mapped left lateral strike slip ganzi yushu fault southeastern tibet we constructed eight temporary gps benchmarks across the faulting belt in a quick mode within 1 week after the mainshock the newly constructed benchmarks and seven pre existing ones were observed in campaign mode with each session lasting for 3 consecutive days the entire observations spanned a period of 250 days until the end of 2010 capturing early post seismic transients induced by the yushu earthquake the gps derived post seismic motions generally had the same orientations as the coseismic displacements the post seismic displacement time series are modeled with a logarithmic function obtaining a characteristic decay time scale of 6 7 0 2 days using the gps site displacements we investigated the possible mechanism of the stress relaxation process the estimated surface displacements due to possible poroelastic rebound did not agree with the observed displacements multiple tests with various viscoelastic models including the burgers model standard linear solid rheology and maxwell relaxation model show that the viscoelastic deformation in the early post seismic phase was possibly insignificant thus afterslip was deemed dominant in the process of stress relaxation we identified that the afterslip was primarily located at the northwestern and southeastern flanks of coseismic slip distribution anti correlated with the coseismic slip spatially moreover we found that the time dependent afterslip decays rapidly with time with moments released by the aftershocks and afterslip taken into account we derived a new recurrence period of 124 452 years for an m 7 class earthquake similar to the yushu earthquake in the ganzi yushu fault the newly derived recurrence interval benefits the seismic hazard assessment in the southeastern tibetan plateau

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

el mayor cucapah mw 7 2 earthquake early near field postseismic deformation from insar and gps observations el mayor cucapah earthquake occurred on 4 april 2010 in northeastern baja california just south of the u s mexico border the earthquake ruptured several previously mapped faults as well as some unidentified ones including the pescadores borrego paso inferior and paso superior faults in the sierra cucapah and the indiviso fault in the mexicali valley and colorado river delta we conducted several global positioning system gps campaign surveys of preexisting and newly established benchmarks within 30 km of the earthquake rupture most of the benchmarks were occupied within days after the earthquake allowing us to capture the very early postseismic transient motions the gps data show postseismic displacements in the same direction as the coseismic displacements time series indicate a gradual decay in postseismic velocities with characteristic time scales of 66 9 days and 20 3 days assuming exponential and logarithmic decay respectively we also analyzed interferometric synthetic aperture radar insar data from the envisat and alos satellites the main deformation features seen in the line of sight displacement maps indicate subsidence concentrated in the southern and northern parts of the main rupture in particular at the indiviso fault at the laguna salada basin and at the paso superior fault we show that the near field gps and insar observations over a time period of 5 months after the earthquake can be explained by a combination of afterslip fault zone contraction and a possible minor contribution of poroelastic rebound far field data require an additional mechanism most likely viscoelastic relaxation in the ductile substrate

mapping of sea ice production in the arctic coastal polynyas 1 high ice production in coastal polynyas over the continental shelves in the arctic ocean is responsible for the formation of cold saline water which contributes to the maintenance of the arctic ocean halocline the accurate detection of coastal polynyas including an estimate of thin ice thickness is essential for the estimation of sea ice production this paper presents an algorithm that estimates thin ice thickness using special sensor microwave imager ssm i data in the arctic ocean detection and estimation of sea ice thicknesses of 0 15 m are based on the ssm i 85 and 37 ghz polarization ratios pr85 and pr37 through a comparison with sea ice thicknesses estimated from the advanced very high resolution radiometer avhrr data in the three different arctic coastal polynyas thus for the entire arctic ocean the algorithm can be used for the detection of coastal polynyas and for the estimation of sea ice production through combination with heat flux calculation this study provides the first circumpolar mapping of sea ice production in coastal polynyas over the entire arctic ocean high ice production is confined to the major arctic coastal polynyas with the highest ice production rate being in the north water polynya this study also presents the interannual variability of sea ice production in the 10 major coastal polynyas from 1992 to 2007 in general interannual variability in sea ice production has good correlation with polynya extent rather than surface air temperature the mapping also provides surface heat and salt flux conditions in the ice covered region which have not been well understood to date

helicopter borne observations with portable microwave radiometer in the southern ocean and the sea of okhotsk accurately measuring and monitoring the thickness distribution of thin ice is crucial for accurate estimation of ocean atmosphere heat fluxes and rates of ice production and salt flux in ice affected oceans here we present results from helicopter borne brightness temperature tb measurements in the southern ocean in october 2012 and in the sea of okhotsk in february 2009 carried out with a portable passive microwave pmw radiometer operating at a frequency of 36 ghz the goal of these measurements is to aid evaluation of a satellite thin ice thickness algorithm which uses data from the spaceborne advanced microwave scanning radiometer earth observing system amsr e or the advanced microwave scanning radiometer ii amsr ii amsr e and amsr ii tb agree with the spatially collocated mean tb from the helicopter borne measurements within the radiometers precision in the sea of okhotsk in february 2009 the amsr e 36ghz tb values are closer to the mean than the modal tb values measured by the helicopter borne radiometer in an antarctic coastal polynya in october 2012 the polarization ratio of 36ghz vertical and horizontal tb is estimated to be 0 137 on average our measurements of the tb at 36ghz over an iceberg tongue suggest a way to discriminate it from sea ice by its unique pmw signature

on the effects of thermally weakened ductile shear zones on postseismic deformation 1 we present three dimensional 3 d numerical models of postseismic deformation following repeated earthquakes on a vertical strike slip fault our models use linear maxwell burgers and temperature dependent power law rheology for the lower crust and upper mantle we consider effects of viscous shear zones that result from thermomechanical coupling and investigate potential kinematic similarities between viscoelastic models incorporating shear zones and elastic models incorporating rate strengthening friction on a deep aseismic fault root we find that the thermally activated shear zones have little effect on postseismic relaxation in particular the presence of shear zones does not change the polarity of vertical displacements in cases of rheologies that are able to generate robust postseismic transients stronger rheologies can give rise to an opposite polarity of vertical displacements but the amplitude of the predicted transient deformation is generally negligible we conclude that additional to thermomechanical coupling mechanisms of strain localization are required for a viscoelastic model to produce a vertical deformation pattern similar to that due to afterslip on a deep extension of a fault we also investigate the discriminating power of models incorporating burgers and power law rheology these rheologies were proposed to explain postseismic transients following large m7 earthquakes in the mojave desert eastern california numerical simulations indicate that it may be difficult to distinguish between these rheologies even with high quality geodetic observations for observation periods less than a decade longer observations however may potentially allow discrimination between the competing models as illustrated by the model comparisons with available gps and interferometric synthetic aperture radar data

estimation of sea ice thickness and volume in the sea of okhotsk based on icesat data sea ice thickness in the sea of okhotsk is estimated for 2004 2008 from icesat derived freeboard under the assumption of hydrostatic balance total ice thickness including snow depth h t o t averaged over 2004 2008 is 95 cm the interannual variability of h t o t is large from 77 5 cm 2008 to 110 4 cm 2005 the mode of h t o t varies from 50 60 cm 2007 and 2008 to 70 80 cm 2005 ice thickness derived from icesat data is validated from a comparison with that observed by electromagnetic induction instrument em aboard the icebreaker soya near hokkaido japan annual maps of h t o t reveal that the spatial distribution of h t o t is similar every year ice volume of 6 3 10 11 m 3 is estimated from the icesat derived h t o t and amsr e derived ice concentration a comparison with ice area demonstrates that the ice volume cannot always be represented by the area solely despite the fact that the area has been used as a proxy of the volume in the sea of okhotsk the ice volume roughly corresponds to that of annual ice production in the major coastal polynyas estimated based on heat budget calculations this also supports the validity of the estimation of sea ice thickness and volume using icesat data

steady state laboratory flow laws alone fail to explain postseismic observations abstract we test whether laboratory derived steady state flow laws for wet olivine can be used to explain postseismic relaxation in the upper mantle following the 1999 hector mine earthquake this is accomplished using rate changes in gps observed displacement time series at far field stations as constraints on the parameters associated with laboratory derived temperature and stress dependent flow laws for diffusion and dislocation creep of olivine we primarily concentrate on the influences of temperature grain size and background strain rate to explain observed fast early displacement rates that slow rapidly in the 7 years of postseismic observations we find that a reasonable fit to the observed time series cannot be achieved by any combination of flow law parameters and plausible assumptions for the tectonic environment of the mantle beneath the mojave desert we conclude that postseismic relaxation within the mantle following the hector mine earthquake likely includes an initial transient weakening phase suggesting that steady state flow laws by themselves are insufficient to characterize the flow of mantle rocks when stress conditions evolve

thickness distribution texture and stratigraphy and a simple probabilistic model for dynamical thickening of sea ice in the southern sea of okhotsk 1 sea ice thickness data and sea ice samples were analyzed to examine the characteristics of the ice thickness distribution and ice texture and to understand ice growth processes in the southern sea of okhotsk ice thickness data and samples were obtained aboard the icebreaker soya in early february the ice growth season ice thickness data which were obtained with a video monitoring system installed on the side deck of the ship each winter from 1991 to 2000 except 1995 show that the average thickness ranges from 19 7 to 55 23 cm and that it matches the characteristics of a poisson distribution ice structure analysis reveals that granular texture occupies about three quarters of the total ice thickness and that the ice exhibits a layered structure with unit thickness averaging 5 to 10 cm stratigraphy and stable isotopic composition of the ice indicate that snow ice accounts for 10 and frazil ice accounts for 64 of the total ice thickness this suggests that dynamic ice thickening processes such as frazil ice growth and piling up are more significant than congelation growth on the basis of these characteristics which resemble more those of antarctic than arctic sea ice we propose a conceptual model for the ice thickening process in this region it is shown that this model can explain the shape of the ice thickness distribution well and is analogous with the concept of the pancake cycle and multiple rafting of antarctic sea ice growth and thickening

finite element model predictions of static deformation from dislocation sources in a subduction zone sensitivities to homogeneous isotropic poisson solid and half space assumptions 1 dislocation models can simulate static deformation caused by slip along a fault these models usually take the form of a dislocation embedded in a homogeneous isotropic poisson solid half space hipshs however the widely accepted hipshs assumptions poorly approximate subduction zone systems of converging oceanic and continental crust this study uses three dimensional finite element models fems that allow for any combination including none of the hipshs assumptions to compute synthetic green s functions for displacement using the1995 mw 8 0 jalisco colima mexico subduction zone earthquake and associated measurements from a nearby gps array as an example fem generated synthetic green s functions are combined with standard linear inverse methods to estimate dislocation distributions along the subduction interface loading a forward hipshs model with dislocation distributions estimated from fems that sequentially relax the hipshs assumptions yields the sensitivity of predicted displacements to each of the hipshs assumptions for the subduction zone models tested and the specific field situation considered sensitivities to the individual poisson solid isotropy and homogeneity assumptions can be substantially greater than gps measurement uncertainties forward modeling quantifies stress coupling between the mw 8 0 earthquake and a nearby mw 6 3 earthquake that occurred 63 days later coulomb stress changes predicted from static hipshs models cannot account for the 63 day lag time between events alternatively an fem that includes a poroelastic oceanic crust which allows for postseismic pore fluid pressure recovery can account for the lag time the pore fluid pressure recovery rate puts an upper limit of 10 17 m2 on the bulk permeability of the oceanic crust

the production of ice and dense shelf water in the okhotsk sea polynyas this paper examines the ice and dense water production in the okhotsk sea coastal polynyas for the 1990 1995 winters the dominant polynyas occur on the northwest and northern shelves and in shelikhov bay we use an algorithm developed for the special sensor microwave imager ssm i to derive for each polynya the area and composition of thin ice and open water and a heat flux algorithm to derive the ice and brine production historic oceanographic observations show that the northwest shelf is the only north pacific region where the 26 8 potential density surface outcrops to the surface and is also that part of the okhotsk shelf where the densest water is observed to occur in support of these observations we find that the northwest shelf polynya is the dominant ice and brine producer contributing on average about 55 of the total production shelikhov bay is the second largest producer with about 25 of the total this region has been previously neglected by both oceanographic and remote sensing studies using a combination of two dense water production models we find that the 6 year average dense water production lies between 0 2 0 4 sv the ice and brine production for the dominant northwest shelf vary interannually by a factor of 3 while the production from all the northern polynyas varies by factor of 2 the source of the variability for the northwest shelf comes from the fact that the southwest to northeast trend of the coastline and the mean winter geostrophic wind velocities are roughly parallel which means that small variations in the wind direction yield large changes in the ice production

genesis of the northeast brazil upper tropospheric cyclonic vortex a primitive equation barotropic instability study abstract the primitive equation barotropic unstable linear normal modes are computed using an eigenvalue approach for daily latitudinal profiles of zonal flow in the upper tropospheric layer of 100 350 hpa before and after formation of cyclonic vortices during january 1993 and november 2001 off the coast of northeast brazil the wave kinetic energy equation for u and motion is presented equations are derived to isolate the contribution of divergence and other dynamical processes in the movement and growth of unstable modes numerical accuracy and physical nature of unstable modes are tested in a short span of 2 3 days prior to formation of vortices a progressive and a sharp intensification of the basic flow shear zone and its barotropic instability are seen with time the horizontal structure momentum transport and zonal and meridional scales of the most unstable normalized wave are obtained and compared with the vortex extracted from the 200 hpa observed winds using a bandpass smoother a close

dense water production on the northern okhotsk shelves comparison of ship based spring summer observations for 1996 and 1997 with satellite observations for the northern okhotsk sea polynyas five russian ctd surveys taken during 1995 to 1997 are used to examine the evolution of the polynya dense water the surveys show that consistent with other investigations the largest potential densities are 26 99 and the densest water occurs in sakhalin and shelikhov bays the surveys also suggest that the shelikhov water drains directly into the deep okhotsk while on the northern shelves gravity currents transport the dense water west to sakhalin bay for comparison determination of the polynya sizes and ice production from satellite passive microwave and meteorological observations shows that polynyas occur on the northwest shelf nws between ayan and okhotsk city on the northern shelf between okhotsk city and magadan and in shelikhov bay in contrast the observations show that sakhalin bay is a region of land fast ice with no polynyas so that the dense water observed here cannot form locally for all polynyas the satellite observations show that the nws contributes 60 to 70 of the total ice production and due to the warmer 1997 air temperatures the 1996 production is about 1 5 times the 1997 value an estimate of the ice production from the surveys shows a similar regional distribution and enhancement of the 1996 production with the satellite and ship estimates in agreement within their error bars finally analysis of the dense water outflow shows that the upper okhotsk sea mode water has a renewal time of about 4 years the lower part about 14 years

processes controlling the advance and retreat of sea ice in the sea of okhotsk using defense meteorological satellite program dmsp special sensor microwave imager ssm i sea ice data and meteorological data we investigate processes controlling the advance and retreat of sea ice in the sea of okhotsk for this investigation we apply a new algorithm to the ssm i data which is capable of calculating ice concentration and distinguishing sea ice types this algorithm is confirmed by comparison with national oceanic and atmospheric administration noaa advanced very high resolution radiometer avhrr imagery our investigations show that there exists a locality for the areas of new ice formation and the ice formation near the ice edge always occurs as a recovery after sea ice has retreated suddenly we also reveal that the speed of ice edge advance fairly coincides with that predicted by 2 of the geostrophic wind furthermore there exists a good correspondence between the times when the overall advance and retreat of ice cover begin and the decrease and increase of air temperature begin we conclude that the advance of the ice cover in the sea of okhotsk occurs primarily through ice advection by wind and that the interannual variation in the maximum sea ice extent can be interpreted by that in wind and air temperature conditions

postseismic relaxation in kashmir and lateral variations in crustal architecture and materials thirty horizontal displacement time series from gps sites in the area around the 2005 kashmir earthquake show lateral spatial variations in displacement magnitude and relaxation time for the postseismic interval from 2005 to 2012 the observed spatial pattern of surface displacements can only be reproduced by finite element models of postseismic deformation in elastic over viscoelastic crust that include lateral differences in both the thickness of the elastic layer and the viscosity of the viscoelastic layer solutions reproducing the sign of horizontal displacements everywhere in the epicentral region also require afterslip on the portion of the fault dislocation in the viscoelastic layer but not in the elastic lid although there are substantial tradeoffs among contributions to postseismic displacements of the surface the observations preclude both crustal homogeneity and shallow afterslip in the best family of solutions the thickness of the elastic upper crust differs by a factor of 5 and the viscosity of the middle and lower crust by an order of magnitude between domains north and south of a suture zone containing the main boundary thrust and main mantle thrust

probing the mechanical properties of seismically active crust with space geodesy study of the coseismic deformation due to the 1992 mw7 3 landers southern california earthquake 1 the coseismic deformation due to the 1992 m w 7 3 landers earthquake southern california is investigated using synthetic aperture radar sar and global positioning system gps measurements the ers 1 satellite data from the ascending and descending orbits are used to generate contiguous maps of three orthogonal components east north up of the coseismic surface displacement field the coseismic displacement field exhibits symmetries with respect to the rupture plane that are suggestive of a linear relationship between stress and strain in the crust interferometric synthetic aperture radar insar data show small scale deformation on nearby faults of the eastern california shear zone some of these faults in particular the calico rodman and pinto mountain faults were also subsequently strained by the 1999 m w 7 1 hector mine earthquake i test the hypothesis that the anomalous fault strain represents essentially an elastic response of kilometer scale compliant fault zones to stressing by nearby earthquakes fialko et al 2002 the coseismic stress perturbations due to the landers earthquake are computed using a slip model derived from inversions of the insar and gps data calculations are performed for both homogeneous and transversely isotropic half space models the compliant zone model that best explains the deformation on the calico and pinto mountain faults due to the hector mine earthquake successfully predicts the coseismic displacements on these faults induced by the landers earthquake deformation on the calico and pinto mountain faults implies about a factor of 2 reduction in the effective shear modulus within the similar to 2 km wide fault zones the depth extent of the low rigidity zones is poorly constrained but is likely in excess of a few kilometers the same type of structure is able to explain high gradients in the radar line of sight displacements observed on other faults adjacent to the landers rupture in particular the lenwood fault north of the soggy lake has likely experienced a few centimeters of left lateral motion across 1 km wide compliant fault zone having the rigidity reduction of more than a factor of 2 the inferred compliant fault zones are interpreted to be a result of extensive damage due to past earthquakes

space geodetic investigation of the coseismic and postseismic deformation due to the 2003 mw7 2 altai earthquake implications for the local lithospheric rheology 1 we use envisat advanced synthetic aperture radar data and spot optical imagery to investigate the coseismic and postseismic deformation due to the 27 september 2003 mw7 2 altai earthquake which occurred in the chuya basin near the russia china mongolia border on the basis of the synthetic aperture radar sar and spot data we determined the rupture location and developed a coseismic slip model for the altai earthquake the inferred rupture location is in a good agreement with field observations and the geodetic moment from our slip model is consistent with the seismic moment determined from the teleseismic data while the epicentral area of the altai earthquake is not optimal for radar interferometry in particular due to temporal decorrelation we were able to detect a transient signal over a time period of 3 years following the earthquake the signal is robust in that it allows us to discriminate among several commonly assumed mechanisms of postseismic relaxation we find that the postearthquake interferometric sar data do not warrant poroelastic rebound in the upper crust the observed deformation also disagrees with linear viscoelastic relaxation in the upper mantle or lower crust giving rise to a lower bound on the dynamic viscosity of the lower crust of the order of 1019 pa s the data can be explained in terms of fault slip within the seismogenic zone on the periphery of areas with high coseismic slip most of the postseismic deformation can be explained in terms of seismic moment release in aftershocks some shallow slip may have also occurred aseismically therefore the observed postseismic deformation due to the altai earthquake is qualitatively different from deformation due to other similarly sized earthquakes in particular the landers and hector mine earthquakes in the mojave desert southern california the observed variations in the deformation pattern may be indicative of different rheologic structure of the continental lithosphere in different tectonically active areas

structure and evolution of the large scale flow and an embedded upper tropospheric cyclonic vortex over northeast brazil horizontal structure and evolution of large scale flow and an embedded synoptic scale cyclonic vortex over northeast brazil as separate systems and dynamical interaction between them are studied at 200 hpa a quasistationary cyclonic vortex with its average position at 10 8s and 358w that formed and remained active during 5 10 january 1993 is selected for the investigation the evolution of large scale flow in the prevortex period 1 4 january is also explored an efficient and effective scale separation technique is developed and used to separate the large scale flow and embedded synoptic scale vortex it is shown that a strong positive shear zone developed in the latitude domain 17 58 7 58s within the south atlantic trough region before the vortex formation the shear zone has a characteristic meridional zonal scale of 1000 km 3000 km and satisfies strongly the necessary condition for barotropic instability it is identified that the development of a strong shear zone is associated with the intensification of a bolivian anticyclone and associated ridge and their eastward shift and intensification of the south atlantic trough east west orientation of the atlantic trough and the presence of a transient trough over the equatorial atlantic ocean the average structure of vortex including zonal and meridional characteristic scales is computed from the synoptic bandpass flow the vortex is identified as a nonlinear wave packet with an average zonal wavelength of 2750 km and it is confined to a latitude belt of about 17 58 the vortex shows a strong westward tilt with latitude the convergence zone is located to its southwest and it is a weak cold cored system maximum cyclonic vorticity of the vortex is 23 24 3 1025 s 21 which is comparable to the value for embedding flow the momentum transports due to the vortex large scale eddy and the vortex large scale eddy interaction are computed it is found that the vortex and vortex large scale eddy westerly momentum transports are southward down the gradient of embedding zonal flow and their divergence convergence is located over the latitudes of large scale westerlies easterlies the sensible heat transports are weak it is noted that the vortex large scale flow interaction leads to the weakening of the shear zone and restoration of the large circulation features to their january 1993 mean configuration which have undergone significant deviation during the prevortex period the signature of vortex large scale interaction is also seen in the evolution of dynamical parameters y and n2 q square of refractive index parameter

a preliminary study of summertime tropospheric circulation patterns over south america estimated from cloud winds abstract cloud winds obtained from sms i geostationary satellite images for the southern hemisphere summer time are used to describe the tropospheric circulation over tropical and subtropical south america these data provide good spatial and temporal coverage over south america for at least two levels in the troposphere the summertime circulation derived from cloud winds is similar in pattern to that obtained from sparse conventional winds but is more intense the major features of the time averaged circulation at the upper level 300 100 mb are an intense quasi stationary anticyclone trough system extending over most of south america north of 35 s a band of easterly flow near 10 s and strong cross equatorial northward flow between 60 and 80 w longitudes at the lower level 900 700 mb the major features are the northerly and northwesterly jet type flow along the eastern slopes of the central andes and northeasterly trades over much of the remainder of the continental region to the north and cast

estimation of thin sea ice thickness from noaa avhrr data in a polynya off the wilkes land coast east antarctica antarctic coastal polynyas are major areas of intense ocean atmosphere heat and moisture flux and associated high sea ice production and dense water formation their accurate detection including an estimate of thin ice thickness is therefore very important in this paper we apply a technique originally developed in the arctic to an estimation of sea ice thickness using us national oceanic and atmospheric administration noaa advanced very high resolution radiometer avhrr data and meteorological data in the vincennes bay polynya off wilkes land east antarctica the method is based upon the heat flux calculation using sea ice surface temperature estimates from the satellite thermal infrared data combined with global objective analysis european centre for medium range weather forecasts ecmwf data the validity of this method is assessed by comparing results with independent ice surface temperature and ice thickness data obtained during an australian led research cruise to the region in 2003 in thin ice polynya regions ice thicknesses estimated by the heat flux calculation using avhrr and ecmwf data show reasonable agreement with those estimated by a applying the heat flux calculation to in situ radiation thermometer and meteorological data and b in situ observations the standard deviation of the difference between the avhrr derived and in situ data is 0 02 m comparison of the avhrr ice thickness retrievals with coincident satellite passive microwave polarization ratio data confirms the potential of the latter as a means of deriving maps of thin sea ice thickness on the wider scale uninterrupted by darkness and cloud cover

postseismic relaxation driven by brittle creep a possible mechanism to reconcile geodetic measurements and the decay rate of aftershocks application to the chi chi earthquake taiwan we evaluate the effect of coseismic stress changes on the fault slip at midcrustal depth assuming a velocity strengthening brittle creep rheology we show that this model can help reconcile the time evolution of afterslip as measured from geodesy with aftershocks decay we propose an analytical expression for slip of the brittle creeping fault zone bcfz that applies to any dynamic or static stress perturbation including shear stress and normal stress changes the model predicts an initial logarithmic increase of slip with time postseismic slip rate decays over a characteristic time t r a that does not depend on the amplitude of the stress perturbation and it asymptotically joins the long term creep imposed by interseismic stress buildup given that the seismicity rate might be considered proportional to the sliding velocity of the bcfz the model predicts a decay rate of aftershocks that follows omori s law with a mathematical formalism identical to that of dieterich 1994 although based on a different mechanical rationale our model also differs from dieterich s model in that it requires that aftershock sequences and deep afterslip as constrained from geodetic measurements should follow the same temporal evolution we test this for the 1999 chi chi earthquake m w 7 6 and find that both sets of data are consistent with a model of afterslip due to the response of the bcfz the inferred relaxation time t r 8 5 years requires a value for a log v being the coefficient of friction in the range between 1 3 10 3 and 10 2

estimation of the thin ice thickness and heat flux for the chukchi sea alaskan coast polynya from special sensor microwave imager data 1990 2001 1 one of the largest arctic polynyas occurs along the alaskan coast of the chukchi sea between cape lisburne and point barrow for this polynya a new thin ice thickness algorithm is described that uses the ratio of the vertically and horizontally polarized special sensor microwave imager ssm i 37 ghz channels to retrieve the distribution of thicknesses and heat fluxes at a 25 km resolution comparison with clear sky advanced very high resolution radiometer data shows that the ssm i thicknesses and heat fluxes are valid for ice thicknesses less than 10 20 cm and comparison with several synthetic aperture radar sar images shows that the 10 cm ice ssm i ice thickness contour approximately follows the sar polynya edge for the twelve winters of 1990 2001 the ice thicknesses and heat fluxes within the polynya are estimated from daily ssm i data then compared with field data and with estimates from other investigations the results show the following first our calculated heat losses are consistent with 2 years of over winter salinity and temperature field data second comparison with other numerical and satellite estimates of the ice production shows that although our ice production per unit area is smaller our polynya areas are larger so that our ice production estimates are of the same order because our salinity forcing occurs over a larger area than in the other models the oceanic response associated with our forcing will be modified index terms 4540 oceanography physical ice mechanics and air sea ice exchange processes 3360 meteorology and atmospheric dynamics remote sensing 4504 oceanography physical air sea interactions 0312 4572 oceanography physical upper ocean processes 4207 oceanography general arctic and antarctic oceanography keywords chukchi sea coastal polynya remote sensing

displacement field and slip distribution of the 2005 kashmir earthquake from sar imagery 1 the 8th october 2005 kashmir earthquake mw 7 6 involved primarily thrust motion on a ne dipping fault sub pixel correlation of envisat sar images gives the location of the 80 km long fault trace within 300 800 m and a 3d surface displacement field with a sub metric accuracy covering the whole epicentral area the slip distribution inverted using elastic dislocation models indicates that slip occurs mainly in the upper 10 km between the cities of muzaffarabad and balakot the rupture reached the surface in several places in the hanging wall horizontal motions show rotation from pure thrust to oblique right lateral motion that are not observed in the footwall a segmentation of the fault near muzaffarabad is also suggested north of the city of balakot slip decreases dramatically but a diffuse zone of mainly vertical surface displacements which could be post seismic exists further north where most of the aftershocks occur aligned along the nw se indus kohistan seismic zone

coseismic displacement field and slip distribution of the 2005 kashmir earthquake from sar amplitude image correlation and differential interferometry the coseismic surface displacement field and slip distribution at depth due to the kashmir earthquake mw 7 6 2005 have been analysed by different authors using subpixel correlation of synthetic aperture radar sar images and optical images teleseismic analysis gps measurements as well as in situ field measurements in this paper first we use 23 sets of measurement from subpixel correlation of sar images and differential interferometry to retrieve the 3 d coseismic surface displacement field the obtained horizontal and vertical components along the fault trace are then compared respectively to equivalent measurements obtained from subpixel correlation of two optical aster images and in situ field measurements second the coseismic fault geometry parameters and slip distribution at depth are estimated in addition to the one segment slip model as reported in previous work a two segments slip model that better fits the surface fault break is proposed the improvement of the two segments slip model in interpreting the measured displacement field is highlighted through comparison of residuals of both slip models taking advantage of differential interferometry measurements that provide precise and continuous information in the far field of the fault firstly a wedge thrust according to bendick et al to the northwest of the main rupture built on our two segments model is tested according to the obtained results the residual of the two segments main rupture plus wedge thrust model is slightly smaller than the residual of the two segments model to the northwest of the balakot bagh fault secondly we test the sensitivity of our slip model to the presence of slip along a decollement as evidenced by jouanne et al through post seismic analysis the results indicate that the estimations of the coseismic displacement field and slip distribution in this paper are not significantly biased by such post seismic displacement and that most coseismic displacement is located on a 40 ne dipping fault as previously reported

post seismic motion following the 1997 manyi tibet earthquake insar observations and modelling summary on november 8 1997 a mw 7 6 earthquake occurred in the manyi region of northern tibet near the western end of the kunlun fault over 7 m of left lateral slip occurred on a 200 kmlong fault here we use insar observations of post seismic surface deformation following the manyi earthquake to investigate possible causal mechanisms time series of deformation are constructed from 26 interferograms covering the entire length of the fault for nearly 4 yr after the earthquake three different modelling approaches are used to try and understand the observed variations in surface displacement first order poroelastic models predict displacement fields which do not match those observed modelling of viscoelastic stress relaxation in a half space with standard linear solid rheology beneath an elastic lid provides a reasonable fit to the observations and demonstrates that two relaxation times are needed to characterize the post seismic transient the best fitting viscosity is 4 10 18 pa s and the fully relaxed shear modulus is 32 per cent of the purely elastic value a model with a maxwell viscoelastic halfspace underlying the lid cannot explain the observations at later times larger viscosities are required than at earlier times this increase in effective viscosity with time may be consistent with stress relaxation occurring in a power law rheology the time series are also inverted for distributed afterslip on an extension of the coseismic rupture along strike correlation of coseismic and post seismic slip maxima suggests that afterslip is a plausible mechanism the maximum slip in the afterslip model is 0 72 m after 3 yr and the equivalent moment release is approximately 20 per cent of the coseismic moment this study shows that it is possible to rule out certain mechanisms as the dominant post seismic process but with the current insar data set it is difficult to distinguish between other plausible options

static stress change from the 8 october 2005 m 7 6 kashmir earthquake 1 we calculated static stress changes from the devastating m 7 6 earthquake that shook kashmir on 8 october 2005 we mapped coulomb stress change on target fault planes oriented by assuming a regional compressional stress regime with greatest principal stress directed orthogonally to the mainshock strike we tested calculation sensitivity by varying assumed stress orientations target fault friction and depth our results showed no impact on the active salt range thrust southwest of the rupture active faults north of the main boundary thrust near peshawar fall in a calculated stress decreased zone as does the raikot fault zone to the northeast we calculated increased stress near the rupture where most aftershocks occurred the greatest increase to seismic hazard is in the indus kohistan seismic zone near the indus river northwest of the rupture termination and southeast of the rupture termination near the kashmir basin

rapid afterslip following the 1999 chi chi taiwan earthquake 1 postseismic displacements of as much as 14 cm were recorded by gps measurements in the 3 months following the mw 7 6 1999 chi chi taiwan earthquake data from 35 continuous and 90 campaign surveyed stations which show continued east over west thrusting are analyzed to estimate the postseismic slip distribution and fault geometry assuming the shallow fault dips 24 e as determined by numerous studies of the mainshock we invert for the deeper fault structure our results show that the fault dip shallows with depth below the hypocenter merging into a nearly horizontal decollement at a depth of 8 12 km the afterslip distribution shows a maximum slip of 25 cm in the hypocentral region at 7 12 km depth as well as significant slip on the lower decollement afterslip is notably absent in the region of maximum coseismic slip consistent with the afterslip being driven by the mainshock stress change

probing fault frictional properties during afterslip updip and downdip of the 2017 mw 7 3 sarpol e zahab earthquake with space geodesy we use interferometric synthetic aperture radar insar data collected by the sentinel 1 mission to study the co and postseismic deformation due to the 2017 mw 7 3 sarpol e zahab earthquake occurr

subsidence at cerro prieto geothermal field and postseismic slip along the indiviso fault from 2011 to 2016 radarsat 2 dinsar time series analysis we present radarsat 2 differential interferometric synthetic aperture radar dinsar observations of deformation due to fluid extraction at the cerro prieto geothermal field cpgf and afterslip on the 2010 m7 2 el mayor cucapah emc earthquake rupture during 2011 2016 advanced multidimensional time series analysis reveals subsidence at the cpgf with the maximum rate greater than 100 mm yr accompanied by horizontal motion radial contraction at a rate greater than 30 mm yr during the same time period more than 30 mm of surface creep occurred on the indiviso fault ruptured by the emc earthquake we performed inversions of dinsar data to estimate the rate of volume changes at depth due to the geothermal production at the cpgf and the distribution of afterslip on the indiviso fault the maximum coseismic slip due to the emc earthquake correlates with the coulomb stress changes on the indiviso fault due to fluid extraction at the cpgf afterslip occurs on the periphery of maximum coseismic slip areas time series analysis indicates that afterslip still occurs 6 years after the earthquake

equivalent strike slip earthquake cycles in half space and lithosphere asthenosphere earth models by virtue of the images used in the dislocation solution the deformation at the free surface produced throughout the earthquake cycle by slippage on a long strike slip fault in an earth model consisting of an elastic plate lithosphere overlying a viscoelastic half space asthenosphere can be duplicated by prescribed slip on a vertical fault embedded in an elastic half space for the case in which each earthquake ruptures the entire lithosphere thickness h the half space equivalent slip rate is as follows depth interval 0 h slip identical to that in lithosphere asthenosphere model i e abrupt coseismic slip and no subsequent slip depth interval 2n 1 h to 2n 1 h n 1 2 slip rate uniform in space and dependent upon time as fn t exp t a where fn is a n 1 degree polynomial in t a is twice the asthenosphere relaxation time and t is measured from the instant after the preceding earthquake the slip rate averaged over the seismic cycle in each depth interval equals the secular rate of relative plate motion for reasonable values of a slip rates below 5h do not vary much from that mean value and can be treated as constant thus the surface deformation due to the earthquake cycle in the lithosphere asthenosphere model can be calculated very simply from the half space model with time dependent slip in the two depth intervals h 3h and 3h 5h and uniform slip at a rate equal to the secular relative plate velocity below depth 5h inversion of 1973 1988 geodetic measurements of deformation across the segment of the san andreas fault in the transverse ranges north of los angeles for the half space equivalent slip distribution suggests no significant slip on the fault above 30 km and a uniform slip rate of 36 mm yr below 30 km one equivalent lithosphere asthenosphere model would have a 30 km thick lithosphere and an asthenosphere relaxation time greater than 33 years but other models are possible

the contribution of alaskan siberian and canadian coastal polynyas to the cold halocline layer of the arctic ocean numerous arctic ocean circulation and geochemical studies suggest that ice growth in polynyas over the alaskan siberian and canadian continental shelves is a source of cold saline water which contributes to the maintenance of the arctic ocean halocline the purpose of this study is to estimate for the 1978 1987 winters the contributions of arctic coastal polynyas to the cold halocline layer of the arctic ocean the study uses a combination of satellite oceanographic and weather data to calculate the brine fluxes from the polynyas then an oceanic box model is used to calculate their contributions to the cold halocline layer of the arctic ocean this study complements and corrects a previous study of dense water production by coastal polynyas in the barents kara and laptev seas recurrent polynyas form on the canadian and alaskan coasts from banks island to the bering strait and on the siberian coast from the bering strait to the new siberian islands in the bering sea polynyas form in norton sound south and west of st lawrence island and in the gulf of anadyr two regions that account for almost 50 of the total dense water production are the siberian coastal polynyas in the adjacent regions of the gulf of anadyr and anadyr strait and the alaskan coastal polynyas which occur along the coast from cape lisburne to point barrow for all of the western arctic coastal regions examined the mean annual total brine flux is 0 5 0 2 sv combination of this flux with the contribution from the barents kara and laptev seas which is recalculated from data in the earlier study shows that over the entire arctic coastal polynyas generate about 0 7 1 2 sv of dense water this compares well with the theoretical estimates of 1 1 5 sv because an unknown fraction of the barents kara and laptev brine flux must go to the eurasian basin deep water the coastal polynyas alone cannot renew the halocline layer other potential brine generation mechanisms include overall freezing on the shelves and the response of the ice to infrequent violent storms for example during february 1982 an intense storm generated a large region of low ice concentration in the eastern chukchi sea over barrow canyon the refreezing of the region was followed by the flow of a dense plume down barrow canyon although the ocean dynamical response to this refreezing needs to be established the possible response of a barrow canyon flow to this refreezing event suggests that the overall refreezing in response to infrequent violent storms may be a potential source of the additional brine needed to maintain the arctic ocean halocline

nonlinear subsidence rate estimation using permanent scatterers in differential sar interferometry discrete and temporarily stable natural reflectors or permanent scatterers ps can be identified from long temporal series of interferometric sar images even with baselines larger than the so called critical baseline this subset of image pixels can be exploited successfully for high accuracy differential measurements the authors discuss the use of ps in urban areas like pomona ca showing subsidence and absidence effects a new approach to the estimation of the atmospheric phase contributions and the local displacement field is proposed based on simple statistical assumptions new solutions are presented in order to cope with nonlinear motion of the targets

investigations of newly formed sea ice in the cape bathurst polynya 2 microwave emission 1 this study examines the role of newly formed sea ice geophysical state on microwave emission coincident with sea ice geophysical sampling ship based passive microwave emission data dual polarized at 19 37 and 85 ghz were collected in the cape bathurst polynya during 18 october and 13 november 2003 using polarization ratios prs we found that bare thin ice was separable from snow covered ice thin snow equal to 0 02 0 13 m thickness is significantly correlated with the spectral gradient ratios grv 85 19 r2 0 55 p value 0 2 the relationship between atmospherically corrected r37 and bare ice thickness showed an exponential relationship very comparable to that reported by martin et al 2004 which is ascribed to the reduction of bare ice surface salinity based on both observational and modeling studies however the relationship quickly becomes invalid for even thin snow covered ice due to significant impact of thin wet liquid water fraction 0 02 0 04 snow on microwave emission our results suggest that the sea ice algorithms nasa team and nasa team 2 could underestimate total ice concentration over thin bare ice by 35 on average while both algorithms underestimate the total ice concentration by 20 over snow covered ice using pr 85 sea ice could be delineated from open water using a properly adjusted threshold value accounting for cloud or fog effects possibly with the exception of dark nilas and or bare consolidated pancakes

postseismic deformation associated with the 2015 mw 7 8 gorkha earthquake nepal investigating ongoing afterslip and constraining crustal rheology abstract the 2015 mw 7 8 gorkha earthquake has not only imposed effective constraints on the geometrical structures friction behaviours and seismogenic patterns of the nepal himalaya thrust systems but has also provided valuable insights into the uplift mechanism and lithosphere rheology of the tibetan plateau here 1 6 year gps observations are used to reveal the postseismic deformation characteristics following the gorkha earthquake investigate the ongoing aseismic afterslip on the main himalayan thrust mht fault and constrain the crustal rheology of the southern tibetan plateau first afterslip is considered to be solely responsible for the postseismic deformation afterslip only model the results show that afterslip is anticorrelated with peak coseismic slip areas one high afterslip concentration area with a peak of 24 cm is distributed downdip of the coseismic rupture as well as in two other regions one partially overlapping the mainshock rupture and the other next to the mw 7 3 aftershock area second the gps postseismic observations are inverted to jointly investigate afterslip and viscoelastic deformation multiple mechanism model the afterslip inversion results of the above two models are highly consistent indicating the dominant contribution of afterslip to surface deformation during the 1 6 year postseismic period considering the interseismic fault coupling and historical seismicity no appreciable fault slip associated with the gorkha earthquake is found to occur both updip and west of the mainshock rupture areas this reveals that the gorkha earthquake only unzipped the lower edge of the locked portion of the mht leaving the shallow portion and western segment of the seismogenic zone still locked and the nepal region under high seismic risk the viscoelastic mechanism contributes minorly to surface deformation during the 1 6 year postseismic period the middle lower crust is assumed to comprise maxwell material beneath an elastic 25 km thick upper crust and the optimal viscosity is conservatively estimated to be 1 6 1019 pa s beneath the southern tibetan plateau which should be robustly constrained with more long term observations more effective spatial constraints and more detailed crustal models

sea ice thickness in the southwestern sea of okhotsk revealed by a moored ice profiling sonar 1 using a moored ice profiling sonar along with a moored acoustic doppler current profiler a total spatial section of draft across 3334 km of sea ice was obtained in the southwestern sea of okhotsk near hokkaido in the winters of 1999 2001 using this draft data set the average draft and keel statistics are discussed in this sea for the first time the mean draft was 0 60 m which corresponds to the thickness of 0 71 m over the three winters with the range of 0 49 0 72 m for each winter the classification of level and deformed ice reveals a small range of the monthly mean level ice draft 0 18 0 27 m and the dominance of the deformed ice in terms of volume 80 the mean draft varied with the areal ratio of the deformed ice fairly well these results suggest that dynamic processes such as ridging and rafting are important for the evolution of draft in the region of observation the observed draft probability density distribution and keel statistics show that the thick ice ratio and keel frequency are lower than the similar data in polar regions and closer to those observed in davis strait west of greenland along with the ice concentration and speed derived from the satellite data the southward ice transport to the southwestern sea of okhotsk is estimated on the basis of the observed sea ice thickness the estimated ice transport ranged from 15 to 70 km3 in each winter the heat and freshwater transport associated with the ice transport ranged from 3 9 1017 to 1 8 1018 j and from 12 to 57 km3 respectively

fault slip distribution of the 1999 mw 7 1 hector mine california earthquake estimated from satellite radar and gps measurements we use a combination of satellite radar and gps data to estimate the slip distribution of the 1999 m w 7 1 hector mine earthquake a right lateral strikeslip earthquake that occurred on a northwest southeast striking fault in the southern california mojave desert the data include synthetic aperture radar interferograms insar from both ascending and descending orbits radar amplitude image offset fields sario for both ascending and descending azimuth directions and campaign gps observations from 55 stations provided by agnew et al 2002 we model the fault with nine segments derived from the field mapped fault rupture the sario data and aftershock locations we first estimate the dip of each fault segment as well as a single constant strike slip component across each segment resulting in an average dip of 83 to the northeast and slip of up to 5 6 m then we fix the optimal fault segment dip discretize the fault segments into 1 5 km 1 5 km patches and solve for the variable slip distribution using a nonnegative least squares method that includes an appropriate degree of smoothing our preferred solution has both right lateral strike slip and reverse faulting the estimated geodetic moment is 5 93 10 19 n m m w 7 1 similar to seismological estimates indicating that there are insignificant interseismic and postseismic deformation signals in the data we find strike slip displacements of up to 6 0 m and reverse faulting of up to 1 6 m with the maximum slip located just northwest of the epicenter most of the slip is concentrated northwest and south of the epicenter little slip is found on the northeastern branch of the fault the sario data and our modeling indicate that the amount and extent of surface fault rupture were underestimated in the field

thickness and production of sea ice in the okhotsk sea coastal polynyas from amsr e 1 from comparisons with thickness of sea ice from advanced very high resolution radiometer avhrr and ice profiling sonar data we have developed an advanced microwave scanning radiometer eos amsr e thin ice thickness algorithm for the sea of okhotsk this algorithm can estimate ice thickness of 0 2 m without snow using the polarization ratio of amsr e brightness temperature at a 36 5 ghz channel from a linear relationship with avhrr ice thickness when a snow cover exists on the thin ice surface as occurred a few times in each winter it is shown that the algorithm cannot detect the thin ice sea ice and dense shelf water dsw production in coastal polynya are estimated on the basis of heat flux calculation with the daily amsr e ice thickness for three winters december march of 2002 2003 to 2004 2005 the ice production is largest in the northwest shelf nws polynya which accounts for 45 of the sum of ice production in major coastal polynyas the ice production in major coastal polynyas would cover the maximum ice area of the okhotsk sea if the average ice thickness is assumed to be 1 m variability of the ice production is mainly modulated by air temperature in the nws polynya which is the main dsw production area the annual dsw formation rate is estimated to be 0 36 sv

evolution of the lorenz energy cycle in the intertropical convergence zone in the south american sector of the atlantic ocean abstractthe intertropical convergence zone itcz in the south american sector of the atlantic ocean is identified using outgoing longwave radiation olr data in order to investigate the evolution of the lorenz energy cycle in the region dominated by this large scale feature the ncep reanalysis data are utilized to calculate the zonal and eddy components denoted by z and e respectively of kinetic energy k and available potential energy a i e kz ke az and ae and their conversions on a daily basis a wavelet decomposition of the time series is performed to detect long term cycles trends in the atlantic itcz region this work also investigates trends in sea surface temperature sst and sea level pressure slp in the itcz region and connections between the itcz and the southern oscillation index soi a strong annual cycle in all the energy components with high peaks in austral summer is observed approximately 91 of the zonal component of energy is contained on decadal or longer time scales

estimation of sea ice production in the bering sea from amsr e and amsr2 data with special emphasis on the anadyr polynya

a new method for measuring deformation on volcanoes and other natural terrains using insar persistent scatterers 1 we present here a new insar persistent scatterer ps method for analyzing episodic crustal deformation in non urban environments with application to volcanic settings our method for identifying ps pixels in a series of interferograms is based primarily on phase characteristics and finds low amplitude pixels with phase stability that are not identified by the existing amplitude based algorithm our method also uses the spatial correlation of the phases rather than a well defined phase history so that we can observe temporally variable processes e g volcanic deformation the algorithm involves removing the residual topographic component of flattened interferogram phase for each ps then unwrapping the ps phases both spatially and temporally our method finds scatterers with stable phase characteristics independent of amplitudes associated with man made objects and is applicable to areas where conventional insar fails due to complete decorrelation of the majority of scatterers yet a few stable scatterers are present

rheology of the lithosphere inferred from postseismic uplift following the 1959 hebgen lake earthquake 1 we have modeled the broad postseismic uplift measured by geodetic leveling in the epicentral area of the 1959 mw 7 3 hebgen lake montana earthquake a normal faulting event in the northern basin and range province to fit the observed uplift we calculate synthetic postseismic deformation using the relaxation response of a gravitational viscoelastic earth to the earthquake for a model with an elastic plate overlying a viscoelastic half space we find that the elastic thickness is 38 8 km which is close to the local crustal thickness the half space viscosity is estimated at 4 1018 0 5 pa s the leveling data do not require a viscous lower crust but permit a lower bound viscosity of 1020 pa s the observed broad uplift cannot be explained by physically plausible afterslip on and below the coseismic fault however local deformation across the coseismic surface rupture requires shallow afterslip reaching the surface the postseismic deformation induced by the estimated viscoelastic structure decays exponentially with a time constant of 15 years because of coupling between the elastic layer and the viscoelastic substrate this relaxation time is significantly longer than the 2 year maxwell relaxation time of the viscous half space itself our result suggests the importance of postseismic relaxation in interpreting high precision global positioning system velocities for example our model results suggest that postseismic transient velocities from both the 1959 hebgen lake and the 1983 mw 6 9 borah peak earthquakes are currently as large as 1 2 mm yr

postseismic deformation in pakistan after the 8 october 2005 earthquake evidence of afterslip along a flat north of the balakot bagh thrust 1 the 8 october 2005 kashmir earthquake ruptured an out of sequence himalayan thrust known as the balakot bagh thrust the earthquake s hypocenter was located at a depth of 15 km on the ramp close to a possible ramp flat transition in the weeks following the earthquake a gps network was installed to measure postseismic displacement the initial measurements in november 2005 were followed by other campaigns in january and august 2006 in march and december 2007 and in august 2008 and 2009 two hypotheses were tested post seismic displacements controlled by viscous relaxation of the lower crust or by afterslip along a flat north of the ramp affected by the main shock a single newtonian viscosity for the different periods cannot be determined by numerical simulations of viscous relaxation which may indicate that the viscosity of the lower crust is non newtonian or that viscous relaxation does not control postseismic displacements numerical simulations using dislocations in a uniform elastic half space indicate afterslip north of the ramp of the earthquake along a flat connected to the ramp slip along the northwestern portion of the flat accrued to about 285 mm between november 2005 and august 2006 while slip along the southeastern portion accrued to 130 mm over the same time period residual misfit of the observed and predicted displacements clearly indicated that afterslip is a better explanation for the observations than the hypothesis of viscous relaxation the time evolution of the afterslip was found to be consistent with that predicted from rate strengthening frictional sliding

postseismic deformation following the 1999 chi chi earthquake taiwan implication for lower crust rheology on 1999 september 21 the mw 7 6 chi chi earthquake ruptured a segment of the chelungpu fault a frontal thrust fault of the western foothills of taiwan the stress perturbation induced by the rupture triggered a transient deformation across the island which was well recorded by a wide network of continuously operating gps stations the analysis of more than ten years of these data reveals a heterogeneous pattern of postseismic displacements with relaxation times varying by a factor of more than ten and large cumulative displacements at great distances in particular along the longitudinal valley in eastern taiwan where relaxation times are also longer we show that while afterslip is the dominant relaxation process in the epicentral area viscoelastic relaxation is needed to explain the pattern and time evolution of displacements at the larger scale we model the spatiotemporal behavior of the transient deformation as the result of afterslip on the decollement that extends downdip of the chelungpu thrust and viscoelastic flow in the lower crust and in the mid crust below the central range we construct a model of deformation driven by coseismic stress change where afterslip and viscoelastic flow are fully coupled the model is compatible with the shorter relaxation times observed in the near field which are due to continued fault slip and the longer characteristic relaxation times and the reversed polarity of vertical displacements observed east of the central range our preferred model shows a viscosity of 0 5 1 x 10 19 pa s at lower crustal depths and 5 x 10 17 pa s in the mid crust below the central range between 10 and 30 km depth the low viscosity zone at mid crustal depth below the central range coincides with a region of low seismicity where rapid advection of heat due to surface erosion coupled with underplating maintain high temperatures estimated to be between 300 c and 600 c from the modeling of thermo chronology and surface heat flow data

slip model of the 2015 mw 7 8 gorkha nepal earthquake from inversions of alos 2 and gps data we use surface deformation measurements including interferometric synthetic aperture radar data acquired by the alos 2 mission of the japanese aerospace exploration agency and global positioning system gps data to invert for the fault geometry and coseismic slip distribution of the 2015 mw 7 8 gorkha earthquake in nepal assuming that the ruptured fault connects to the surface trace of the main frontal thrust mft fault between 84 34 e and 86 19 e the best fitting model suggests a dip angle of 7 the moment calculated from the slip model is 6 08 1020 nm corresponding to the moment magnitude of 7 79 the rupture of the 2015 gorkha earthquake was dominated by thrust motion that was primarily concentrated in a 150 km long zone 50 to 100 km northward from the surface trace of the main frontal thrust mft with maximum slip of 5 8 m at a depth of 8 km data thus indicate that the 2015 gorkha earthquake ruptured a deep part of the seismogenic zone in contrast to the 1934 bihar nepal earthquake which had ruptured a shallow part of the adjacent fault segment to the east

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

space geodetic observations and models of postseismic deformation due to the 2005 m7 6 kashmir pakistan earthquake we use the l band advanced land observing satellite alos and c band envisat interferometric synthetic aperture data and campaign gps observations to study the postseismic deformation due to the 2005 magnitude 7 6 kashmir pakistan earthquake that occurred in the northwestern himalaya envisat data are available from both the descending and ascending orbits and span a time period of 4 5 years immediately following the earthquake 2005 2010 with nearly monthly acquisitions however the envisat data are highly decorrelated due to high topography and snow cover alos data are available from the ascending orbit and span a time period of 2 5 years between 2007 and 2009 over which they remain reasonably well correlated we derive the mean line of sight los postseismic velocity maps in the epicentral area of the kashmir earthquake using persistent scatterer method for envisat data and selective stacking for alos data los velocities from all data sets indicate an uplift decrease in radar range primarily in the hanging wall of the earthquake rupture over the entire period of synthetic aperture radar observations 2005 2010 models of poroelastic relaxation predict uplift of both the footwall and the hanging wall while models of viscoelastic relaxation below the brittle ductile transition predict subsidence increase in radar range in both the footwall and the hanging wall therefore the observed pattern of surface velocities indicates that the early several years of postseismic deformation were dominated by afterslip on the fault plane possibly with a minor contribution from poroelastic rebound kinematic inversions of interferometric synthetic aperture radar and gps data confirm that the observed deformation is consistent with afterslip primarily downdip of the seismic asperity to place constraints on the effective viscosity of the ductile substrate in the study area we subtract the surface deformation predicted by stress driven afterslip model from the mean los velocities and compare the residuals to models of viscoelastic relaxation for a range of assumed viscosities we show that in order to prevent surface subsidence the effective viscosity has to be greater than 1019 pa s

increase and decrease of sea ice area in the sea of okhotsk ice production in coastal polynyas and dynamic thickening in convergence zones 1 this paper examines the production and reduction of sea ice area in the sea of okhotsk analyses were carried out for 10 winters december april from 1991 1992 to 2000 2001 using daily data of sea ice velocity and concentration derived from images of the defense meteorological satellite program dmsp special sensor microwave imager ssm i first we mapped sea ice divergence which was calculated from the daily ice velocity field in the case of offshore winds high divergence was observed along the coastline while there existed a broad convergence area with inshore winds next we examined local changes in an area of sea ice as in the case of ice divergence ice production and reduction are strongly controlled by wind direction we found that a large amount of sea ice was produced in coastal areas under offshore wind conditions the geographical distribution of the ice production area agrees well with that of the well known coastal polynya areas our estimation shows that 8 7 105 km2 yr 1 of sea ice is produced in the northern coastal area and 3 7 105 km2 yr 1 in the sakhalin coastal area in contrast 7 4 105 km2 yr 1 of the ice area disappeared in shantarskiy bay this reduction of ice area is mainly caused by dynamic deformation of existing ice forming rafted ice or pressure ridges this dynamic deformation plays an important role not only in the reduction of okhotsk sea ice area but also in the thickening of ice

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

postseismic deformation following the april 25 2015 gorkha earthquake nepal afterslip versus viscous relaxation abstract the postseismic deformation consecutive to the april 25 2015 gorkha earthquake mw 7 9 is estimated in this paper based on a cgnss network installed prior to the earthquake and supplemented by 6 cgnss stations installed after the main shock postseismic displacement are obtained from daily time series corrected for interseismic deformation and seasonal variations the maximum postseismic displacement is found north of the rupture area where locally it reached 100 mm between the date of the earthquake and late 2016 the postseismic deformation affects the northern part of the rupture area but not the southern part along the southern part of the main himalayan thrust mht three hypotheses for the mechanisms controlling postseismic deformation are tested through numerical simulations of the postseismic time series i viscous relaxation ii afterslip or iii a combination of these two mechanisms we can exclude postseismic deformation controlled by viscous relaxation of a thick deformation zone along the northern and lower flat of the mht however it is impossible to discriminate between postseismic deformation controlled by either afterslip along the mht northern part of the rupture zone crustal ramp and lower flat of the mht or a combination of afterslip along the mht northern part of the rupture zone crustal ramp and viscous relaxation controlled by a thin 3 4 km thick low viscosity body centered on the lower flat of the mht the occurrence of afterslip along the northern part of the upper flat of the mht and its longitudinal variations have been established thanks to the densification of gnss network by our team presented in this paper

thin ice thickness from satellite thermal imagery sea ice thickness is an important parameter in the surface energy exchange and mass balance of the polar oceans remote sensing offers the opportunity to monitor thin ice routinely we combine measurements of surface temperature from an advanced very high resolution radiometer avhrr with a thermodynamic ice growth model to estimate thin ice and its thickness distribution during the cold season in a beaufort sea area of perennial ice we find that thin ice up to a meter thick had a concentration of 18 in december 1990 and 3 in april 1991 thin ice concentrations near the ice edge in the greenland sea range from 20 to 50 these avhrr derived estimates generally compare well with thickness observations from upward looking sonar given the uncertainties in all the model inputs estimated from avhrr such as radiative and turbulent heat flux components and surface albedo we find that ice thickness is estimated with an uncertainty of roughly 50 the uncertainty in the cumulative thickness distribution is about 3 for ice less than 20 cm thick and about 9 for ice around 1 m thick these magnitudes are significantly smaller than the variations in thin ice observed by satellite in different months and regions we conclude that avhrr is capable of resolving the regional and seasonal variations in thin ice to a level of accuracy useful both for establishing a climatology and for testing ice models

mobility of continental mantle evidence from postseismic geodetic observations following the 1992 landers earthquake the crust around the rupture zone of the 1992 landers earthquake has continued to deform in the years following the earthquake at rates 3 times greater than pre earthquake rates we use a combination of global positioning system gps and synthetic aperture radar insar data collected during a 3 year epoch following the earthquake in order to investigate postseismic mechanisms responsible for the high transient velocities in order to maximize the potential signal from viscoelastic relaxation we evaluate and model postseismic relaxation following the first few months of documented accelerated deformation the combination of gps and insar data allows us to establish viscoelastic relaxation of the lower crust and upper mantle as the dominant postseismic process and to discriminate among possible viscoelastic models the data particularly require the presence of a highly ductile uppermost mantle beneath the central mojave domain with temperature between the wet and dry basalt solidus this is consistent with independent seismic and geochemical inferences of a regionally warm uppermost mantle further consideration of seismic velocity variations in conjunction with faulting patterns within the mojave desert suggests that the primary faulting characteristics of the mojave desert namely the pervasive late cenozoic deformation within the eastern california shear zone versus the near absence of faults in the western mojave domain are controlled by the rheology of the uppermost mantle

postseismic mantle relaxation in the central nevada seismic belt holocene acceleration of deformation and postseismic relaxation are two hypotheses to explain the present day deformation in the central nevada seismic belt cnsb discriminating between these two mechanisms is critical for understanding the dynamics and seismic potential of the basin and range province interferometric synthetic aperture radar detected a broad area of uplift 2 to 3 millimeters per year that can be explained by postseismic mantle relaxation after a sequence of large crustal earthquakes from 1915 to 1954 the results lead to a broad agreement between geologic and geodetic strain indicators and support a model of a rigid basin and range between the cnsb and the wasatch fault

dominant controls of downdip afterslip and viscous relaxation on the postseismic displacements following the mw7 9 gorkha nepal earthquake author s zhao b burgmann r wang d tan k du r zhang r abstract 2017 american geophysical union all rights reserved we analyze three dimensional gps coordinate time series from continuously operating stations in nepal and south tibet and calculate the initial 1 year postseismic displacements we first investigate models of poroelastic rebound afterslip and viscoelastic relaxation individually and then attempt to resolve the trade offs between their contributions by evaluating the misfit between observed and simulated displacements we compare kinematic inversions for distributed afterslip with stress driven afterslip models the modeling results show that no single mechanism satisfactorily explains near and far field postseismic deformation following the gorkha earthquake when considering contributions from all three mechanisms we favor a combination of viscoelastic relaxation and afterslip alone as poroelastic rebound always worsens the misfit the combined model does not improve the data misfit significantly but the inverted afterslip distribution is more physically plausible the inverted afterslip favors slip within the brittle ductile transition zone downdip of the coseismic rupture and fills the small gap between the mainshock and largest aftershock slip zone releasing only 7 of the coseismic moment our preferred model also illuminates the laterally heterogeneous rheological structure between india and the south tibet the transient and steady state viscosities of the upper mantle beneath tibet are constrained to be greater than 1018 pa s and 1019 pa s whereas the indian upper mantle has a high viscosity 1020 pa s the viscosity in the lower crust of southern tibet shows a clear trade off with its southward extent and thickness suggesting an upper bound value of 8 1019 pa s for its steady state viscosity

mapping of sea ice production for antarctic coastal polynyas 1 active sea ice production in antarctic coastal polynyas causes dense water formation finally leading to antarctic bottom water aabw formation this study gives the first mapping of sea ice production in the antarctic ocean based on heat flux calculation with ice thickness data derived from satellite data the highest ice production occurs in the ross ice shelf polynya region the ice production there decreased by 30 from the 1990s to the 2000s which can be one candidate for causing the recent freshening of aabw the cape darnley polynya in east antarctica is found to be the second highest production area suggesting a possible aabw formation area according to our estimation around 10 of southern ocean sea ice is produced in the major antarctic coastal polynyas the mapping provides surface heat and salt flux conditions in the ice covered region which have not been well understood

lower crustal relaxation beneath the tibetan plateau and qaidam basin following the 2001 kokoxili earthquake summary in 2001 november a magnitude 7 8 earthquake ruptured a 400 km long portion of the kunlun fault northeastern tibet in this study we analyse over five years of post seismic geodetic data and interpret the observed surface deformation in terms of stress relaxation in the thick tibetan lower crust we model gps time series first year and insar line of sight measurements years two to five and infer that the most likely mechanism of post seismic stress relaxation is time dependent distributed creep of viscoelastic material in the lower crust since a single relaxation time is not sufficient to model the observed deformation viscous flow is modelled by a lower crustal burgers rheology which has two material relaxation times the optimum model has a transient viscosity 9 1017 pa s steady state viscosity 1 1019 pa s and a ratio of long term to maxwell shear modulus of 2 3 this model gives a good fit to gps stations south of the kunlun fault while displacements at stations north of the fault are over predicted we attribute this asymmetry in the gps residual to lateral heterogeneity in rheological structure across the southern margin of the qaidam basin with thinner crust higher viscosities beneath the basin than beneath the tibetan plateau deep afterslip localized in a shear zone beneath the fault rupture gives a reasonable match to the observed insar data but the slip model does not fit the earlier gps data well we conclude that while some localized afterslip likely occurred during the early post seismic phase the bulk of the observed deformation signal is due to viscous flow in the lower crust to investigate regional variability in rheological structure we also analyse post seismic displacements following the 1997 manyi earthquake that occurred 250 km west of the kokoxili rupture we find that viscoelastic properties are the same as for the kokoxili area except for the transient viscosity which is 5 1017 pa s the viscosities estimated for the manyi and kokoxili areas are consistent with constraints obtained from other earthquakes in the northwest and south central parts of the tibetan plateau

dense water formation on the northwestern shelf of the okhotsk sea 1 direct observations of brine rejection late february while the active brine rejection continued for several more weeks based on indirect evidence from water properties and ice cover this termination was possibly due to the onset of baroclinic instability of the density front at the polynya edge facilitating offshore eddy transport of the density anomaly observed periodic baroclinic tide intensification events are hypothesized to be an indicator of the presence of such baroclinic eddies no significant density increase was observed at the deeper offshore mooring indicating a robust demarcation of the offshore extent of newly formed dsw the relatively fresh water of the tidally mixed zone inshore of the shelf front was the precursor of the dsw aided by the late autumn offshore transition of the front index terms 4207 oceanography general arctic and antarctic oceanography 4219 oceanography general continental shelf processes 4540 oceanography physical ice mechanics and air sea ice exchange processes 4243 oceanography general marginal and semienclosed seas keywords okhotsk sea brine rejection dense water formation

the 2005 mw 7 6 kashmir earthquake sub pixel correlation of aster images and seismic waveforms analysis we analyze the m w 7 6 kashmir earthquake of october 8 2005 using sub pixel correlation of aster images to measure ground deformation and modeling seismic waveforms the surface rupture is continuous over a distance of 75 km and cuts across the hazara syntaxis reactivating the tanda and the muzaffarabad faults north of muzaffarabad the surface rupture coincides approximately with the mbt on the southwestern flank of the syntaxis although the two faults have opposite dip angles the rupture terminates abruptly at the hairpin turn of the mbt showing a strong structural control the fault offset is 4 m on average and peaks to 7 m northwest of muzaffarabad the rupture lasted about 25 s and propagated updip and bi laterally 2 km s with a rise time of 2 5 s the shallowness and compactness of the rupture both in time and space provide an explanation for the intensity of destructions this kind of analysis could be achieved as soon as a post earthquake image is available and would provide key information for early assessment of damages the study sheds some light on seismic hazard in the himalaya and raises concern regarding the possibility of a repetition of the 1555 event which presumably ruptured the himalayan front south of the kashmir basin and may have reached a magnitude m w 8

hydrologic detection and finite element modeling of a slow slip event in the costa rica prism toe 1 we investigate transient fluid flux through the seafloor recorded near the costa rica trench during the 2000 costa rica seismogenic zone experiment using a 2 d fully coupled poroelastic finite element model we demonstrate that the observed hydrologic anomalies are consistent with a model of propagating slow slip at the subduction interface between the frontal prism and downgoing plate there are two sources of volumetric strain that drive fluid flux at the seafloor in response to fault slip at depth 1 compression and dilation in the vicinity of the tips of a slipping patch and 2 extension and compression due to flexure of the seafloor the superposition of these two effects results in distinctive spatial and temporal patterns of fluid flow through the seafloor in a forward modeling approach time series from shear ruptures with a range of fault length to depth ratios in a heterogeneous crust are generated and compared with flow rate observations assuming a constant propagation rate and an elliptical profile for the distribution of slip along the decollement the set of model predictions enables us to infer the probable rupture location extent propagation velocity and duration from a single flow rate time series the best fit model suggests that the slow slip event initiated within the toe at a depth of less than 4 km and propagated bilaterally at an average rate of 0 5 km d 1 this interpretation implies that stress in the shallow subduction zone is relieved episodically furthermore the costa rica data suggest that episodic slow slip events may initiate in the prism toe without being triggered by a seismic event further downdip

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

coseismic and postseismic deformation of the 2016 mw 6 2 lampa earthquake southern peru constrained by interferometric synthetic aperture radar

role of lower crust in the postseismic deformation of the 2010 maule earthquake insights from a model with power law rheology the surface deformation associated with the 2010 mw 8 8 maule earthquake in chile was recorded in great detail before during and after the event the high data quality of the continuous gps cgps observations has facilitated a number of studies that model the postseismic deformation signal with a combination of relocking afterslip and viscoelastic relaxation using linear rheology for the upper mantle here we investigate the impact of using linear maxwell or power law rheology with a 2d geomechanical numerical model to better understand the relative importance of the different processes that control the postseismic deformation signal our model results reveal that in particular the modeled cumulative vertical postseismic deformation pattern in the near field 50 km depth as suggested in previous studies the explanation for this difference is that in the model with power law rheology the relaxation of coseismically imposed differential stresses occurs mainly in the lower crust however even though the model with power law rheology probably has more potential to explain the vertical postseismic signal in the near field the uncertainty of the applied temperature field is substantial and this needs further investigations and improvements

distributions of dissolved organic carbon and nitrogen in the western okhotsk sea and their effluxes to the north pacific abstract the okhotsk sea is considered the only ventilation source area for north pacific intermediate water npiw which is widely distributed in the low and middle latitudes of the north pacific previous studies have confirmed high levels of dissolved organic carbon doc in npiw yet the amounts and the processes driving doc export from the okhotsk sea are poorly understood in this study concentrations of doc and dissolved organic nitrogen don were measured in the western okhotsk sea during the summer of 2006 and additional doc measurements were made during the late spring of 2010 results indicate that doc transport to the intermediate waters 26 7 27 0 occurs through two processes the first process involves the spread of water discharged from the continental shelf dense shelf water which contributes to a doc and turbidity maxima in the 250 300 m layer of okhotsk sea mode water osmw located off the eastern sakhalin coast the second process involves diapycnal mixing in the kuril basin and the bussol strait where doc is transported to a depth greater than 800 m the ratio of doc don in osmw was significantly higher in the kuril basin and bussol strait than off of the sakhalin coast which suggests that the transport of terrigenous organic matter from the bottom occurs in the former regions doc and don efflux from the okhotsk sea to the intermediate layer in the north pacific water 26 7 27 0 were estimated to be 68 72 tg c yr 1 and 5 4 tg n yr 1 respectively for which the doc transported by diapycnal mixing accounts for 37 we conclude that diapycnal mixing in the kuril basin and bussol strait regions could play a significant role in regulating the quality and quantity of doc exported to the intermediate water in the north pacific

freshening and dense shelf water reduction in the okhotsk sea linked with sea ice decline abstract a recently constructed hydrographic dataset from the okhotsk sea reveals a prominent freshening to depths of 500 m during the past four decades with the maximum in the northwestern part of the sea averaged over the sea this freshening corresponds to an input of 0 55 m of freshwater this leads to a decrease in density of the intermediate water and deepening of the isopycnals with the maximum deepening at 26 8 of 60 m averaged over the sea the intermediate water is significantly warmed along the pathway of dense shelf water dsw a simple box model shows that dsw production has decreased by 30 during the past four decades we propose that the freshening and dsw reduction are caused by the weakening of salt freshwater redistribution through sea ice decline as well as by the increase of excess precipitation over evaporation since the overturning in the north pacific originates from the okhotsk sea through the dsw these changes possibly weaken the shallow overturning of the north pacific

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities

coseismic deformation from the 1999 mw 7 1 hector mine california earthquake as inferred from insar and gps observations we use interferometric synthetic aperture radar insar and global positioning system gps observations to investigate static deformation due to the 1999 m w 7 1 hector mine earthquake that occurred in the eastern california shear zone interferometric decorrelation phase and azimuth offset measurements indicate regions of surface and near surface slip which we use to constrain the geometry of surface rupture the inferred geometry is spatially complex with multiple strands the southern third of the rupture zone consists of three subparallel segments extending about 20 km in length in a n45 w direction the central segment is the simplest with a single strand crossing the bullion mountains and a strike of n10 w the northern third of the rupture zone is characterized by multiple splays with directions subparallel to strikes in the southern and central the average strike for the entire rupture is about n30 w the interferograms indicate significant along strike variations in strain which are consistent with variations in the ground based slip measurements using a variable resolution data sampling routine to reduce the computational burden we invert the insar and gps data for the fault geometry and distribution of slip we compare results from assuming an elastic half space and a layered elastic space results from these two elastic models are similar although the layered space model predicts more slip at depth than does the half space model the layered model predicts a maximum coseismic slip of more than 5 m at a depth of 3 to 6 km contrary to preliminary reports the northern part of the hector mine rupture accommodates the maximum slip our model predictions for the surface fault offset and total seismic moment agree with both field mapping results and recent seismic models the inferred shallow slip deficit is enigmatic and may suggest that distributed inelastic yielding occurred in the uppermost few kilometers of the crust during or soon after the earthquake

gps measurement of postseismic deformation following the 1999 chi chi taiwan earthquake 1 in the 15 month period september 1999 to december 2000 after the 1999 chi chi taiwan earthquake mw 7 6 about 80 campaign surveyed gps stations in central taiwan were occupied up to seven times furthermore seven continuous gps stations were put into operation in the epicentral region mostly within three weeks after the main shock gps data from these near field stations and some pre existing far field stations were utilized to study the postseismic deformation following the chi chi earthquake the postseismic displacements of the gps stations were approximated by a combination of an exponential transient decay function with a relaxation time of 86 days and a postseismic linear rate change stations on the hanging wall displayed west northwesterly horizontal displacements of up to 252 mm and uplift as large as 229 mm postseismic displacements are much larger to the south near the epicenter of chi chi main shock than in the north where the maximum coseismic displacement occurred stations on the footwall show only small displacements the postseismic gps data were inverted to infer the deeper fault geometry and afterslip distribution based on a four segment fault model with its shallow part constrained by coseismic fault geometry deduced from gps and seismological studies the optimal model requires the lower fault segment to be a horizontal plane at a depth of 10 4 km consistent with a model based on gps data taken during the first three months after the main shock and other geological or geophysical studies the maximum afterslip 459 mm occurs in the hypocentral region and in the northern part of the decollement slip of about 430 mm also occurs in the southern part of the decollement the afterslip moment inferred from 15 months of gps data is 4 7 1019 n m approximately 2 3 times the seismic moment released by aftershocks this implies that a major part of the postseismic deformation is aseismic

observations of ice thickness and frazil ice in the st lawrence island polynya from satellite imagery upward looking sonar and salinity temperature moorings 1 for the 1999 winter this paper examines the behavior of the bering sea st lawrence island polynya using a combination of advanced very high resolution radiometer avhrr radarsat synthetic aperture radar sar meteorological data over winter moored upward looking sonars uls and seabird salinity temperature sensors we define a thermal ice thickness from the avhrr retrieval of ice surface temperature combined with meteorological observations and a heat flux model south of the island we compare the uls and thermal thicknesses for congelation and frazil ice when the satellites observe congelation ice over the ulss the uls and thermal ice thicknesses generally agree when sar observes langmuir plumes over the ulss which indicate frazil ice formation the ulss show scatterers at 5 20 m depths in the water column and the seawater temperatures are either within 0 01 c of freezing or are slightly supercooled this suggests that during frazil events crystals either nucleate at depth or are transported to depth by the langmuir circulation the combination of the sar imagery and uls observations also allow measurement of the pack ice advection velocity the polynya width and the downwind frazil accumulation thickness giving widths of 10 to 30 km and thicknesses of 0 1 0 2 m substitution of these observed values with the heat flux into the pease polynya model yields polynya widths that approximately agree with the observed