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

mass balance of east antarctic glaciers and ice shelves from satellite data thevelocityandmassdischarge of ninemajoreast antarcticglaciersnot draining into the ross or filchner ronne ice shelves is investigated using interferometric syntheticapertureradar insar datafromtheeuropeanremote sensingsatellite1and2 ers 1 2 andradarsat 1 theglaciersare david ninnis mertz totten scott denman lambert shiraseandstancomb wills insarisusedtolocatetheirgroundinglinewithpre cision ice velocity is measured with either insar or a speckle tracking technique ice thickness is deduced from prior determined ice shelf elevation assuming hydrostatic equi librium mass fluxes are calculated both at the grounding line and at a flux gate located downstream the grounding line flux is compared to a mass input calculated from snow accumulation to deduce the glacier mass balance the calculation is repeated at the flux gate downstream of the grounding line to estimate the average bottom melt rate of the ice shelf under steady state conditions the main results are 1 grounding lines are found several tens of km upstream of prior identified positions not because of a recent ice sheet retreatbutbecause of the inadequacy of prior determined grounding line positions 2 no gross imbalance between outflow and inflow is detected on the nine glaciersbeing investi gated with anuncertainty of 10 20 prior determined largely positive mass imbalances wereduetoanincorrectlocalizationofthegroundingline 3 highratesofbottommelting 24 7 micea 1 are inferred neargrounding zones where ice reaches the deepestdraft a few glaciers exhibit lower bottom melt rates 4 7 micea 1 bottom melting however appearsto be a major source of mass loss on antarctic ice shelves

pelagic smectite as an important factor in tsunamigenic slip along the japan trench the very large slip on the shallow portion of the subduction interface during the 2011 tohoku oki earthquake m w 9 0 caused a huge tsunami along the northeast coast of honshu japan in order to elucidate the mechanics of such tsunamigenic slip the integrated ocean drilling program expedition 343 japan trench fast drilling project jfast was carried out one year after the earthquake and succeeded in recovering rocks constituting the active plate boundary fault our mineralogical analyses using x ray diffraction reveal that the shallow portion of the fault zone that caused the earthquake is significantly enriched in smectite compared to the surrounding sediments which may be intimately linked to the tsunamigenic shallow faulting for comparison we also analyzed mineralogical features of incoming sediments just prior to subduction recovered on the outer rise of the japan trench site 436 deep sea drilling project leg 56 and found a characteristic smectite rich horizon in the uppermost 5 m of the pelagic clay layer this horizon should be mechanically weak and will become the future plate boundary fault as observed in the jfast cores the smectite rich deposits are broadly distributed in the northwestern pacific ocean and may therefore potentially enhance conditions for large shallow slip during earthquakes that occur over a broad area of the japan trench plate boundary which would result in large tsunamis for this region

scaling of the critical slip distance for seismic faulting with shear strain in fault zones theoretical and experimentally based laws for seismic faulting contain a critical slip distance1 5 dc which is the slip over which strength breaks down during earthquake nucleation on an earthquake generating fault this distance plays a key role in determining the rupture nucleation dimension6 the amount of premonitory and post seismic slip7 10 and the maximum seismic ground acceleration1 11 in laboratory friction experiments d c has been related to the size of surface contact junctions2 5 12 thus the discrepancy between laboratory measurements of dc 10 5m and values obtained from modelling earthquakes 10 2m has been attributed to differences in roughness between laboratory surfaces and natural faults5 this interpretation predicts a dependence of dc on the particle size of fault gouge2 breccia and wear material but not on shear strain here we present experimental results showing that dc scales with shear strain in simulated fault gouge our data suggest a new physical interpretation for the critical slip distance in which dc is controlled by the thickness of the zone of localized shear strain as gouge zones of mature faults are commonly 102 103 m thick12 17 whereas laboratory gouge layers are 1 10 mm thick our data offer an alternative interpretation of the discrepancy between laboratory and field based estimates of dc

implications of fault constitutive properties for earthquake prediction the rate and state dependent constitutive formulation for fault slip characterizes an exceptional variety of materials over a wide range of sliding conditions this formulation provides a unified representation of diverse sliding phenomena including slip weakening over a characteristic sliding distance dc apparent fracture energy at a rupture front time dependent healing after rapid slip and various other transient and slip rate effects laboratory observations and theoretical models both indicate that earthquake nucleation is accompanied by long intervals of accelerating slip strains from the nucleation process on buried faults generally could not be detected if laboratory values of dc apply to faults in nature however scaling of dc is presently an open question and the possibility exists that measurable premonitory creep may precede some earthquakes earthquake activity is modeled as a sequence of earthquake nucleation events in this model earthquake clustering arises from sensitivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and assigns physical interpretation to aftershock parameters the seismicity formulation predicts large changes of earthquake probabilities result from stress changes two mechanisms for foreshocks are proposed that describe observed frequency of occurrence of foreshock mainshock pairs by time and magnitude with the first mechanism foreshocks represent a manifestation of earthquake clustering in which the stress change at the time of the foreshock increases the probability of earthquakes at all magnitudes including the eventual mainshock with the second model accelerating fault slip on the mainshock nucleation zone triggers foreshocks

basal mass budget of ross and filchner ronne ice shelves antarctica derived from lagrangian analysis of icesat altimetry traditional methods of deriving temporal variability of antarctic ice shelf elevation from satellite altimetry use a fixed eulerian reference frame where the measured changes include advection of ice thickness gradients between measurement epochs we present a new method which removes advection effects by using an independent velocity field to compare elevations in a moving lagrangian reference frame applying the technique to icesat laser altimetry for the period 2003 2009 over the two largest antarctic ice shelves ross and filchner ronne we show that the lagrangian approach reduces the variability of derived elevation changes by about 50 compared to the eulerian approach and reveals clearer spatial patterns of elevation change the method simplifies the process of estimating basal mass budget from the residual of all other processes that contribute to ice shelf elevation changes we use field data and icesat measurements over ice rises and the grounded ice sheet to account for surface accumulation and changes in firn air content and remove the effect of ice flow divergence using surface velocity and ice thickness data the results show highest basal melt rates 5 m a 1 near the deep grounding lines of major ice streams but smaller melt rates 5 m a 1 near the ice shelf fronts are equally important to total meltwater production since they occur over larger areas integrating over the entire ice shelf areas we obtain basal mass budgets of 50 64 gt a 1 for ross and 124 66 gt a 1 for filchner ronne with changes in firn air content as the largest error source

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

very low frequency earthquakes within accretionary prisms are very low stress drop earthquakes 1 we report characteristic p wave spectra and stress drops of very low frequency vlf earthquakes that occurred within the accretionary prism along the nankai trough southwestern japan although many vlf earthquakes showed no distinct phases on a raw seismogram a few showed slightly distinct phases the arrival times of some phases were consistent with the calculated p wave arrival times the corner frequencies of the vlf earthquakes were calculated using the stacked p wave spectra assuming an omega square spectrum stress drops were very low i e in the range of 0 1 10 kpa which corresponds to 0 1 1 of those of ordinary earthquakes such extremely low stress drops of the vlf earthquakes suggest that the fault strength within the accretionary prism may have weakened due to the existence of a fluid within the thrust fault system of the accretionary prism

low temperature frictional characteristics of chlorite epidote amphibole assemblages implications for strength and seismic style of retrograde fault zones in retrograde faults exhuming mafic rocks shearing occurs in metamorphic and or hydrothermally altered mineral assemblages whose frictional properties are not well known here we present the results of laboratory shearing experiments on chlorite schist epidotite and hornblende dominated amphibolite and mixtures of these rocks and evaluate their frictional properties and microstructures the experiments were conducted on powdered rock samples with starting grain size of 125 m at room temperature under fluid saturated conditions and applied normal stress of 10 mpa the results show that chlorite schist is relatively weak friction coefficient of 0 36 whereas epidotite and amphibolite are strong friction coefficients of 0 63 and 0 67 respectively the friction of chlorite schist epidotite and chlorite schist amphibolite mixtures decreases nearly linearly with increasing chlorite content chlorite schist exhibits velocity strengthening behavior epidotite is velocity weakening and the amphibolite shows mostly velocity weakening friction mixtures show intermediate strength and velocity dependence of friction well developed striations formed on slip surfaces in samples with 50 chlorite schist the epidotite slip surface exhibits a mixture of very fine particles and coarser crystals amphibolite slip surfaces have less very fine grains and are composed of subhedral to euheral needles few intragranular fractures are preserved and we infer wear at contact asperities to be the likely cause of velocity weakening in our epidote gouges addition of chlorite to epidotite and amphibolite produces a striated slip surface and disrupts contacts between harder grains therefore retrograde chlorite growth is expected to facilitate frictional weakening and stable slip in higher grade mineral assemblages exhumed to low temperature conditions

deep glacial troughs and stabilizing ridges unveiled beneath the margins of the antarctic ice sheet the antarctic ice sheet has been losing mass over past decades through the accelerated flow of its glaciers conditioned by ocean temperature and bed topography glaciers retreating along retrograde slopes that is the bed elevation drops in the inland direction are potentially unstable while subglacial ridges slow down the glacial retreat despite major advances in the mapping of subglacial bed topography significant sectors of antarctica remain poorly resolved and critical spatial details are missing here we present a novel high resolution and physically based description of antarctic bed topography using mass conservation our results reveal previously unknown basal features with major implications for glacier response to climate change for example glaciers flowing across the transantarctic mountains are protected by broad stabilizing ridges conversely in the marine basin of wilkes land east antarctica we find retrograde slopes along ninnis and denman glaciers with stabilizing slopes beneath moscow university totten and lambert glacier system despite corrections in bed elevation of up to 1 km for the latter this transformative description of bed topography redefines the high and lower risk sectors for rapid sea level rise from antarctica it will also significantly impact model projections of sea level rise from antarctica in the coming centuries a high resolution update of antarctic bed topography using mass conservation reveals broad stabilizing ridges for glaciers flowing across the transantarctic mountains and stabilizing slopes beneath moscow university totten and lambert glacier system

force perturbation analysis of recent thinning and acceleration of jakobshavn isbrae greenland observations between 1997 and 2001 of a 30 velocity increase and up to 60 m thinning of downstream parts of jakobshavn isbrae greenland immediately following calving of about 4 km of its 15 km floating ice tongue suggest that acceleration may have been initiated by the calving assuming that the force perturbation associated with such weakening is swiftly transmitted far up glacier i develop equations to estimate the perturbation initially the observed changes are consistent with the comparatively small perturbation associated with the calving thereafter it was probably sustained by thinning of the remaining ice tongue at rates of about 80 m a 1 otherwise the force perturbation would soon have been balanced by reduction in the hydrostatic driving force for longitudinal creep as the glacier thinned with velocities dropping to their former values the calculated force perturbation increases to a maximum about 10 km inland of the grounding line consistent with decreasing weight forces as the glacier thins over bedrock that slopes uphill seawards further inland it progressively decreases probably because marginal drag increased as the glacier accelerated both here and on the floating tongue marginal ice appears to have been softened by the influence of locally intense shear on ice temperature and or fabric more recent observations show continued acceleration and thinning and most of the remaining ice tongue calved away in april 2003 so thinning is likely to continue

evaluation of regional climate models using regionally optimized grace mascons in the amery and getz ice shelves basins antarctica author s mohajerani y velicogna i rignot e abstract 2019 american geophysical union all rights reserved we develop regionally optimized gravity recovery and climate experiment grace solutions to evaluate the mass balance of the drainage basins of amery ice shelf east antarctica and getz ice shelf west antarctica we find that the amery region is near balance while the getz region is rapidly losing mass we compare the results with the mass budget method mbm combining ice discharge along the periphery with surface mass balance derived from three regional climate models 1 regional atmospheric climate model racmo 2 3p1 and 2 2 3p2 and 3 modele atmospherique regional 3 6 41 for amery mbm racmo2 3p1 agrees with grace while mbm racmo2 3p2 and mbm mar3 6 41 suggest a positive mass balance for getz all estimates agree with a mass loss and the grace results are robust to uncertainties in glacial isostatic adjustment derived from an ensemble 128 000 forward models over the period april 2002 to november 2015 the mass loss of the getz drainage basin is 22 9 10 9 gt yr with an acceleration of 1 6 0 9 gt yr2

quantitative measure of the variation in fault rheology due to fluid rock interactions we analyze friction data from two published suites of laboratory tests on granite in order to explore and quantify the effects of temperature t and pore water pressure pp on the sliding behavior of faults rate stepping sliding tests were performed on laboratory faults in granite containing gouge granite powder both dry at 23 to 845 c lockner et al 1986 and wet pp 100 mpa at 23 to 600 c blanpied et al 1991 1995 imposed slip velocities v ranged from 0 01 to 5 5 m s and effective normal stresses were near 400 mpa for dried granite at all temperatures and wet granite below 300 c the coefficient of friction shows low sensitivity to v t and pp for wet granite above 350 drops rapidly with increasing t and shows a strong positive rate dependence and protracted strength transients following steps in v presumably reflecting the activity of a water aided deformation process by inverting strength data from velocity stepping tests we determined values for parameters in three formulations of a rate and state dependent constitutive law one or two state variables were used to represent slip history effects each velocity step yielded an independent set of values for the nominal friction level five constitutive parameters transient parameters a b1 and b2 and characteristic displacements dc1 and dc2 and the velocity dependence of steady state friction ss ln v a b1 b2 below 250 data from dry and most wet tests are adequately modeled by using the slip law ruina 1983 and one state variable a 0 003 to 0 018 b 0 001 to 0 018 dc 1 to 20 m dried tests above 250 can also be fitted with one state variable in contrast wet tests above 350 require higher direct rate dependence a 0 03 to 0 12 plus a second state variable with large negative amplitude b2 0 03 to 0 14 and large characteristic displacement dc2 300 to 4000 m thus the parameters a b1 and b2 for wet granite show a pronounced change in their temperature dependence in the range 270 to 350 c which may reflect a change in underlying deformation mechanism we quantify the trends in parameter values from 25 to 600 c by piecewise linear regressions which provide a straightforward means to incorporate the full constitutive response of granite into numerical models of fault slip the modeling results suggest that the succeptibility for unstable stick slip sliding is maximized between 90 and 360 c in agreement with laboratory observations and consistent with the depth range of earthquakes on mature faults in the continental crust

on the short term grounding zone dynamics of pine island glacier west antarctica observed with cosmo skymed interferometric data using radar satellite data from the italian cosmo skymed csk constellation and the german tandem x formation we present comprehensive measurements of the bi weekly grounding line dynamics of pine island glacier west antarctica from august to december 2015 the one day repeat cycle of csk reveals tidally induced grounding line migration on the scale of kilometers and extensive seawater intrusion within the grounding zone which significantly exceeds that predicted for a stiff bed but are consistent with that calculated for a deformable bed the deformable bed also explains the continuous draining filling of subglacial lakes proximal to the grounding line after correction for oceanic tides we estimate a retreat rate for 2011 2015 of 0 3 km yr at the glacier center and 0 5 km yr on the sides which is three times slower than for 1994 2011 1 2 km yr at the center we attribute the decrease in retreat rate to colder ocean conditions in 2012 2013 relative to 2000 2011

four decades of antarctic ice sheet mass balance from 1979 2017 we use updated drainage inventory ice thickness and ice velocity data to calculate the grounding line ice discharge of 176 basins draining the antarctic ice sheet from 1979 to 2017 we compare the results with a surface mass balance model to deduce the ice sheet mass balance the total mass loss increased from 40 9 gt y in 1979 1990 to 50 14 gt y in 1989 2000 166 18 gt y in 1999 2009 and 252 26 gt y in 2009 2017 in 2009 2017 the mass loss was dominated by the amundsen bellingshausen sea sectors in west antarctica 159 8 gt y wilkes land in east antarctica 51 13 gt y and west and northeast peninsula 42 5 gt y the contribution to sea level rise from antarctica averaged 3 6 0 5 mm per decade with a cumulative 14 0 2 0 mm since 1979 including 6 9 0 6 mm from west antarctica 4 4 0 9 mm from east antarctica and 2 5 0 4 mm from the peninsula i e east antarctica is a major participant in the mass loss during the entire period the mass loss concentrated in areas closest to warm salty subsurface circumpolar deep water cdw that is consistent with enhanced polar westerlies pushing cdw toward antarctica to melt its floating ice shelves destabilize the glaciers and raise sea level

mass loss of totten and moscow university glaciers east antarctica using regionally optimized grace mascons author s mohajerani y velicogna i rignot e abstract 2018 american geophysical union all rights reserved totten and moscow university glaciers in the marine based sector of east antarctica contain enough ice to raise sea level by 5 m obtaining precise measurements of their mass balance is challenging owing to large area of the basins and the small mass balance signal compared to west antarctic glaciers here we employ a locally optimized processing of gravity recovery and climate experiment grace harmonics to evaluate their mass balance at the sub basin scale and compare the results with mass budget method mbm estimates using regional atmospheric climate model version 2 3 racmo2 3 or modele atmospherique regional version 3 6 4 mar3 6 4 the sub basin mass loss estimate for april 2002 to november 2015 is 14 8 4 3 gt yr which is weakly affected by glacial isostatic adjustment uncertainties 1 4 gt yr this result agrees with mbm racmo2 3 15 8 2 0 gt yr whereas mbm mar3 6 4 underestimates the loss 6 6 1 6 gt yr for the entire drainage the mass loss for april 2002 to august 2016 is 18 5 6 6 gt yr or 15 4 of its ice flux these results provide unequivocal evidence for mass loss in this east antarctic sector

evidence for subglacial water transport in the west antarctic ice sheet through three dimensional satellite radar interferometry 1 radarsat data from the 1997 antarctic mapping mission are used interferometrically to solve for the 3 dimensional surface ice motion in the interior of the west antarctic ice sheet wais an area of 125 km2 in a tributary of the kamb ice stream slumped vertically downwards by up to 50 cm between september 26 and october 18 1997 areas in the bindschadler ice stream also exhibited comparable upward and downward surface displacements as the uplift and subsidence features correspond to sites at which the basal water apparently experiences a hydraulic potential well we suggest transient movement of pockets of subglacial water as the most likely cause for the vertical surface displacements these results and related lidar observations imply that imaging the change in ice surface elevation can help reveal the key role of water in the difficult to observe subglacial environment and its important influence on ice dynamics

dynamic thinning of antarctic glaciers from along track repeat radar altimetry since 2002 the envisat radar altimeter has measured the elevation of the antarctic ice sheet with a repeat cycle of 35 days this long and regular time series is processed using an along track algorithm to depict in detail the spatial and temporal pattern of elevation change for the whole ice sheet we use this dataset to examine the spatial and temporal pattern of pine island glacier pig thinning and compare it to the neighbouring glaciers we also examine additional areas especially in east antarctica whose mass balance is poorly known one advantage of the finer along track spacing of measurements is that it reveals places of dynamic thinning in regions of rapid ice flow we observe the acceleration of thinning on pig over the entire basin the volume loss increased from 7 km3 a 1 during 2002 06 to 48 km3 a 1 during 2006 10 we also observe accelerated thinning on the lower tens of kilometres of thwaites glacier with a mean thinning of 0 18 m a 1 over its entire basin during our observation period we confirm the dynamic thinning of totten glacier but we do not detect significantly accelerated thinning on any glacier elsewhere than on the coast of the amundsen sea

grounding line retreat of pope smith and kohler glaciers west antarctica measured with sentinel 1a radar interferometry data we employ sentinel 1a c band satellite radar interferometry data in terrain observation with progressive scans mode to map the grounding line and ice velocity of pope smith and kohler glaciers in west antarctica for the years 2014 2016 and compare the results with those obtained using earth remote sensing satellites ers 1 2 in 1992 1996 and 2011 we observe an ongoing rapid grounding line retreat of smith at 2 km yr 40 km since 1996 an 11 km retreat of pope 0 5 km yr and a 2 km readvance of kohler since 2011 the variability in glacier retreat is consistent with the distribution of basal slopes i e fast along retrograde beds and slow along prograde beds we find that several pinning points holding dotson and crosson ice shelves disappeared since 1996 due to ice shelf thinning which signal the ongoing weakening of these ice shelves overall the results indicate that ice shelf and glacier retreat in this sector remain unabated

the mechanisms behind jakobshavn isbrae s acceleration and mass loss a 3 d thermomechanical model study the mechanisms causing widespread flow acceleration of jakobshavn isbrae west greenland remain unclear despite an abundance of observations and modeling studies here we simulate the glacier s evolution from 1985 to 2016 using a three dimensional thermomechanical ice flow model the model captures the timing and 90 of the observed changes by forcing the calving front basal drag in the trough is low and lateral drag balances the ice stream s driving stress the calving front position is the dominant control on changes of jakobshavn isbrae since the ice viscosity in the shear margins instantaneously drops in response to the stress perturbation caused by calving front retreat which allows for widespread flow acceleration gradual shear margin warming contributes 5 to 10 to the total acceleration our simulations suggest that the glacier will contribute to eustatic sea level rise at a rate comparable to or higher than at present

new antarctic gravity anomaly grid for enhanced geodetic and geophysical studies in antarctica gravity surveying is challenging in antarctica because of its hostile environment and inaccessibility nevertheless many ground based airborne and shipborne gravity campaigns have been completed by the geophysical and geodetic communities since the 1980s we present the first modern antarctic wide gravity data compilation derived from 13 million data points covering an area of 10 million km2 which corresponds to 73 coverage of the continent the remove compute restore technique was applied for gridding which facilitated levelling of the different gravity datasets with respect to an earth gravity model derived from satellite data alone the resulting free air and bouguer gravity anomaly grids of 10 km resolution are publicly available these grids will enable new high resolution combined earth gravity models to be derived and represent a major step forward towards solving the geodetic polar data gap problem they provide a new tool to investigate continental scale lithospheric structure and geological evolution of antarctica

a new tide model for the antarctic ice shelves and seas we describe a new tide model for the seas surrounding antarctica including the ocean cavities under the floating ice shelves the model uses data assimilation to improve its fit to available data typical peak to peak tide ranges on ice shelves are 1 2 m but can exceed 3 m for the filchner ronne and larsen ice shelves in the weddell sea spring tidal ranges are about twice these values model performance is judged relative to the 5 10 cm accuracy that is needed to fully utilize ice shelf height data that will be collected with the geoscience laser altimeter system scheduled to be launched on the ice cloud and land elevation satellite in late 2002 the model does not yet achieve this level of accuracy except very near the few high quality tidal records that have been assimilated into the model some improvement in predictive skill is expected from increased sophistication of model physics but we also require better definition of ice shelf grounding lines and more accurate water column thickness data in shelf seas and under the ice shelves long duration tide measurements bottom pressure gauge or gps in critical data sparse areas particularly near and on the filchner ronne and ross ice shelves and pine island bay are required to improve the performance of the data assimilation model

the 2011 tohoku oki earthquake displacement reaching the trench axis we detected and measured coseismic displacement caused by the 11 march 2011 tohoku oki earthquake moment magnitude mw 9 0 by using multibeam bathymetric surveys the difference between bathymetric data acquired before and after the earthquake revealed that the displacement extended out to the axis of the japan trench suggesting that the fault rupture reached the trench axis the sea floor on the outermost landward area moved about 50 meters horizontally east southeast and 10 meters upward the large horizontal displacement lifted the sea floor by up to 16 meters on the landward slope in addition to the vertical displacement

slip weakening as a mechanism for slow earthquakes slow earthquakes form part of a spectrum of fault behaviour between steady creep and fast rupture during a normal earthquake laboratory simulations of slow slip in rock samples taken from the nankai subduction zone japan reveal similar characteristics to fast earthquakes implying that some slow slip events could be prematurely arrested earthquakes

elastic dynamics and tidal migration of grounding lines modify subglacial lubrication and melting 1 we combine the dynamics of ice bed and ocean in a new elastic model for the tidal timescale migration of grounding lines on deformable foundations previous interpretations of tidal flexure using models of elastic ice shelves with fixed grounding lines were found to be inconsistent suggesting an elasticity of ice that varies spatially and temporally and that is significantly smaller than measured experimentally we argue here that with our model a consistent purely elastic interpretation can be made combining this new approach with remote sensing measurements we show that the grounding line migrates several kilometers during a tidal cycle that we can infer the effective elastic properties of the bed and that the elastic pressure of the ice leads to a hydrological barrier near the grounding line that controls subglacial hydrology our findings imply that subglacial lubrication and melting induced by the ocean thermal forcing can increase substantially during high tide

episodic slow slip events and rate and state friction 1 there are several ways of generating episodic slow slip events in models of rate and state friction here i explore the possibility that they arise on velocity weakening faults whose length is tuned in some sense unlike spring block sliders which have a unique critical stiffness for instability elastically deformable faults have multiple length scales stiffnesses relevant to nucleation slow slip events occur when the fault is large enough to initiate an event but too small for that event to reach dynamic instability the available window of lengths depends upon the effective fracture energy of the growing nucleation zone for the aging evolution law this fracture energy increases rapidly with slip speed and the range of permissible lengths increases nearly as b b a where a and b are the coefficients of the velocity and state dependence of the frictional strength this range becomes very large for faults that are near velocity neutral a b however existing lab data firmly favor the slip law as a predictor of nucleation style and for this law the effective fracture energy increases much less rapidly with slip speed the range of fault lengths capable of hosting slow slip events in this case seems too small to explain why they are common to so many subduction zones slow slip can be stabilized over an exceedingly large range of fault lengths if the fracture energy increases with slip speed much more rapidly than for the aging law an appealing mechanism is inelastic dilation of the fault zone coupled with pore pressure reduction and diffusive recovery

a dynamic early east antarctic ice sheet suggested by ice covered fjord landscapes the east antarctic ice sheet has played a fundamental part in modulating climate and sea level during the past 30 million years understanding its history is crucial to evaluating its future behaviour and response to global warming airborne ice penetrating radar studies now reveal a fjord like landscape beneath several kilometres of ice in the east antarctic aurora subglacial basin the data confirm and provide a new constraint on the magnitude and dynamics of the oscillations of the east antarctic ice sheet during the late cenozoic which had previously been supported only by marine cores the first cenozoic ice sheets initiated in antarctica from the gamburtsev subglacial mountains1 and other highlands as a result of rapid global cooling 34 million years ago2 in the subsequent 20 million years at a time of declining atmospheric carbon dioxide concentrations2 and an evolving antarctic circumpolar current2 sedimentary sequence interpretation3 and numerical modelling4 suggest that cyclical periods of ice sheet expansion to the continental margin followed by retreat to the subglacial highlands occurred up to thirty times these fluctuations were paced by orbital changes and were a major influence on global sea levels5 ice sheet models show that the nature of such oscillations is critically dependent on the pattern and extent of antarctic topographic lowlands here we show that the basal topography of the aurora subglacial basin of east antarctica at present overlain by 2 4 5 km of ice is characterized by a series of well defined topographic channels within a mountain block landscape the identification of this fjord landscape based on new data from ice penetrating radar provides an improved understanding of the topography of the aurora subglacial basin and its surroundings and reveals a complex surface sculpted by a succession of ice sheet configurations substantially different from today s at different stages during its fluctuations the edge of the east antarctic ice sheet lay pinned along the margins of the aurora subglacial basin the upland boundaries of which are currently above sea level and the deepest parts of which are more than 1 km below sea level although the timing of the channel incision remains uncertain our results suggest that the fjord landscape was carved by at least two iceflow regimes of different scales and directions each of which would have over deepened existing topographic depressions reversing valley floor slopes

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

rapid bottom melting widespread near antarctic ice sheet grounding lines as continental ice from antarctica reaches the grounding line and begins to float its underside melts into the ocean results obtained with satellite radar interferometry reveal that bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed the melting rate is positively correlated with thermal forcing increasing by 1 meter per year for each 0 1 c rise in ocean temperature where deep water has direct access to grounding lines glaciers and ice shelves are vulnerable to ongoing increases in ocean temperature

aseismic slip transients emerge spontaneously in three dimensional rate and state modeling of subduction earthquake sequences 1 to investigate the possible physical mechanisms of recently observed aseismic slip events in the cascadia japan and mexico subduction zones we apply a dieterich ruina rate and state friction law to a three dimensional model of a shallow subduction fault that is loaded by imposed steady plate slip rate far downdip along the thrust interface friction properties are temperature and hence depth dependent such that sliding is stable at depths below about 30 km the system is perturbed into a significantly nonuniform slip mode along strike by introducing small along strike variations in the constitutive parameters a and a b in addition to large heterogeneous earthquake slip at seismogenic depths and associated postseismic transients we found that slip events which have clearly aseismic slip rates emerge spontaneously around the downdip end of the seismogenic zone both transients which start well after a seismic event and those which are triggered by other transients are observed from the simulations the slip velocity depth range and sometimes along strike migration speed of simulated transients are similar to the observations from natural subduction zones unstable stable transitional friction properties near the downdip end of the seismogenic zone are suggested to be an ingredient allowing such transients simulated transients can weaken the locking intensity of the updip seismogenic zone while enhancing that of the transition zone spatial temporal correlation of aseismic transients and nearby seismicity in the guerrero mexico area suggests that transients may signal a period of increased probability for nucleating their high frequency counterparts as damaging subduction thrust events

antarctic grounding line mapping from differential satellite radar interferometry 1 the delineation of an ice sheet grounding line i e the transition boundary where ice detaches from the bed and becomes afloat in the ocean is critical to ice sheet mass budget calculations numerical modeling of ice sheet dynamics ice ocean interactions oceanic tides and subglacial environments here we present 15 years of comprehensive high resolution mapping of grounding lines in antarctica using differential satellite synthetic aperture radar interferometry dinsar data from the earth remote sensing satellites 1 2 ers 1 2 radarsat 1 and 2 and the advanced land observing system alos palsar for years 1994 to 2009 dinsar directly measures the vertical motion of floating ice shelves in response to tidal oceanic forcing with millimeter precision at a sample spacing better than 50 m simultaneously over areas several 100 km wide in contrast with earlier methods that detect abrupt changes in surface slope in satellite visible imagery or altimetry data on stagnant and slow moving areas we find that breaks in surface slope are reliable indicators of grounding lines but on most fast moving glaciers and ice streams our dinsar results reveal that prior mappings have positioning errors ranging from a few km to over 100 km a better agreement is found with icesat s data also based on measurements of vertical motion but with a detection noise one order of magnitude larger than with dinsar overall the dinsar mapping of antarctic grounding lines completely redefines the coastline of antarctica

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

the international bathymetric chart of the southern ocean ibcso version 1 0 a new bathymetric compilation covering circum antarctic waters the international bathymetric chart of the southern ocean ibcso version 1 0 is a new digital bathymetric model dbm portraying the seafloor of the circum antarctic waters south of 60 degrees s

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

frontal wedge deformation near the source region of the 2011 tohoku oki earthquake 1 we report an uplift of 5 m with a horizontal displacement of more than 60 m due to the 2011 tohoku oki earthquake the uplift was measured by an ocean bottom pressure gauge installed before the earthquake on a frontal wedge which formed an uplift system near the japan trench horizontal displacements of the frontal wedge were measured using local benchmark displacements obtained by acoustic ranging before and after the earthquake the average displacements at the frontal wedge were 58 m east and 74 m east southeast these results strongly suggest a huge coseismic slip beneath the frontal wedge on the plate boundary the estimated magnitude of the slip along the main fault was 80 m near the trench our results suggest that the horizontal and vertical deformations of the frontal wedge due to the slip generated the tremendous tsunami that struck the coastal area of northeastern japan

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

a microphysical model for strong velocity weakening in phyllosilicate bearing fault gouges 1 previous rotary shear experiments performed on a halite muscovite fault gouge analogue system have shown that the presence of phyllosilicates under conditions favoring the operation of cataclasis and pressure solution in the matrix phase can have major effects on the frictional behavior of gouges while 100 halite and 100 muscovite samples exhibit rate independent frictional brittle behavior the strength of mixtures containing 10 30 muscovite is both normal stress and sliding velocity dependent at high sliding velocities 1 m s 1 such mixtures show unusually marked velocity weakening along with the development of a structureless cataclastic microstructure in the present paper a micromechanical model is developed in an attempt to explain this behavior the model assumes a granular flow process involving competition between intergranular dilatation and compaction by pressure solution the predictions of the model agree favorably with the experimental results extension of the model to quartz mica systems implies that the presence of phyllosilicates plus the operation of pressure solution can strongly promote unstable velocity weakening behavior at rapid slip rates on natural faults under midcrustal conditions static stress drop predictions based on the model agree reasonably well with estimates from seismic observations our results may help explain the discrepancy between laboratory derived rate and state friction parameter values obtained for dry low strain and or single phase rock systems and the values for natural fault rocks inferred from seismological data

seafloor geodetic constraints on interplate coupling of the nankai trough megathrust zone seafloor geodetic data from the nankai trough off southwestern japan show that most offshore sites in this earthquake prone region have high slip deficit rates revealing previously unknown locations that could be important for the mitigation of future earthquake and tsunami associated disasters yusuke yokota et al have used seafloor geodetic observations to visualize the seismogenic zone along the nankai trough off southwestern japan which is thought to be one of the most dangerous megathrust zones in the world they suggest that most offshore sites in this region have positive slip deficit rates revealing previously unknown locations that could be potential sources of future earthquakes and tsunamis low slip deficit rates are observed in other regions consistent with distributions of shallow slow earthquakes and subducting seamounts interplate megathrust earthquakes have inflicted catastrophic damage on human society such an earthquake is predicted to occur in the near future along the nankai trough off southwestern japan an economically active and densely populated area in which megathrust earthquakes have already occurred1 2 3 4 5 megathrust earthquakes are the result of a plate subduction mechanism and occur at slip deficit regions also known as coupling regions 6 7 where friction prevents plates from slipping against each other and the accumulated energy is eventually released forcefully many studies have attempted to capture distributions of slip deficit rates sdrs in order to predict earthquakes8 9 10 however these studies could not obtain a complete view of the earthquake source region because they had no seafloor geodetic data the hydrographic and oceanographic department of the japan coast guard jhod has been developing a precise and sustainable seafloor geodetic observation network11 in this subduction zone to obtain information related to offshore sdrs here we present seafloor geodetic observation data and an offshore interplate sdr distribution model our data suggest that most offshore regions in this subduction zone have positive sdrs specifically our observations indicate previously unknown regions of high sdr that will be important for tsunami disaster mitigation and regions of low sdr that are consistent with distributions of shallow slow earthquakes and subducting seamounts this is the first direct evidence that coupling conditions might be related to these seismological and geological phenomena our findings provide information for inferring megathrust earthquake scenarios and interpreting research on the nankai trough subduction zone

rapid subsurface warming and circulation changes of antarctic coastal waters by poleward shifting winds the southern hemisphere westerly winds have been strengthening and shifting poleward since the 1950s this wind trend is projected to persist under continued anthropogenic forcing but the impact of the changing winds on antarctic coastal heat distribution remains poorly understood here we show that a poleward wind shift at the latitudes of the antarctic peninsula can produce an intense warming of subsurface coastal waters that exceeds 2 c at 200 700 m depth the model simulated warming results from a rapid advective heat flux induced by weakened near shore ekman pumping and is associated with weakened coastal currents this analysis shows that anthropogenically induced wind changes can dramatically increase the temperature of ocean water at ice sheet grounding lines and at the base of floating ice shelves around antarctica with potentially significant ramifications for global sea level rise

sensitivity of pine island glacier west antarctica to changes in ice shelf and basal conditions a model study we use a finite element model of coupled ice stream ice shelf flow to study the sensitivity of pine island glacier west antarctica to changes in ice shelf and basal conditions by tuning a softening coefficient of the ice along the glacier margins and a basal friction coefficient controlling the distribution of basal shear stress underneath the ice stream we are able to match model velocity to that observed with interferometric synthetic aperture radar insar we use the model to investigate the effect of small perturbations on ice flow we find that a 5 5 13 reduction in our initial ice shelf area increases the glacier velocity by 3 5 10 at the grounding line the removal of the entire ice shelf increases the grounding line velocity by 70 the changes in velocity associated with ice shelf reduction are felt several tens of km inland alternatively a 5 reduction in basal shear stress increases the glacier velocity by 13 at the grounding line by contrast softening of the glacier side margins would have to be increased a lot more to produce a comparable change in ice velocity hence both the ice shelf buttressing and the basal shear stress contribute significant resistance to the flow of pine island glacier

migrating tremor off southern kyushu as evidence for slow slip of a shallow subduction interface detection of shallow slow earthquakes offers insight into the near trench part of the subduction interface an important region in the development of great earthquake ruptures and tsunami generation ocean bottom monitoring of offshore seismicity off southern kyushu japan recorded a complete episode of low frequency tremor lasting for 1 month that was associated with very low frequency earthquake vlfe activity in the shallow plate interface the shallow tremor episode exhibited two migration modes reminiscent of deep tremor down dip of the seismogenic zone in some other subduction zones a large scale slower propagation mode and a rapid reversal mode these similarities in migration properties and the association with vlfes strongly suggest that both the shallow and deep tremor and vlfe may be triggered by the migration of episodic slow slip events

a comparison between rate and state friction and microphysical models based on numerical simulations of fault slip rate and state friction rsf is commonly used for the characterisation of laboratory friction experiments such as velocity step tests however the rsf framework provides little physical basis for the extrapolation of these results to the scales and conditions of natural fault systems and so open questions remain regarding the applicability of the experimentally obtained rsf parameters for predicting seismic cycle transients as an alternative to classical rsf microphysics based models offer means for interpreting laboratory and field observations but are generally over simplified with respect to heterogeneous natural systems in order to bridge the temporal and spatial gap between the laboratory and nature we have implemented existing microphysical model formulations into an earthquake cycle simulator through this numerical framework we make a direct comparison between simulations exhibiting rsf controlled fault rheology and simulations in which the fault rheology is dictated by the microphysical model even though the input parameters for the rsf simulation are directly derived from the microphysical model the microphysics based simulations produce significantly smaller seismic event sizes than the rsf based simulation and suggest a more stable fault slip behaviour our results reveal fundamental limitations in using classical rate and state friction for the extrapolation of laboratory results the microphysics based approach offers a more complete framework in this respect and may be used for a more detailed study of the seismic cycle in relation to material properties and fault zone pressure temperature conditions

grounding line retreat of totten glacier east antarctica 1996 to 2013 2015 american geophysical union all rights reserved totten glacier east antarctica a glacier that holds a 3 9 m sea level change equivalent has thinned and lost mass for decades we map its grounding line positions in 1996 and 2013 using differential radar interferometry insar data and develop precise high resolution topographies of its ice surface and ice draft using nasa operation icebridge data insar data and a mass conservation method we detect a 1 to 3 km retreat of the grounding line in 17 years the retreat is asymmetrical along a two lobe pattern where ice is only grounded a few 10 m above sea level or ice plain which may unground further with only modest amounts of ice thinning the pattern of retreat indicates ice thinning of 12 m in 17 years or 0 7 0 1 m yr at the grounding line on average sustained thinning will cause further grounding line retreat but may not be conducive to a marine instability key points grounding line of totten glacier is retreating not as fast as west antarctica retreat pattern explained by the newly inferred bed geometry if ice thinning maintains bed geometry conducive to further retreat

improved representation of east antarctic surface mass balance in a regional atmospheric climate model this study evaluates the impact of a recent upgrade in the physics package of the regional atmospheric climate model racmo2 on the simulated surface mass balance smb of the antarctic ice sheet the modelled smb increases in particular over the grounded ice sheet of east antarctica 44 gt a 1 with a small change in west antarctica this mainly results from an increase in precipitation which is explained by changes in the cloud microphysics including a new parameter ization for ice cloud supersaturation and changes in large scale circulation patterns which alter topographically forced precipitation the spatial changes in smb are evaluated using 3234 in situ smb observations and ice balance velocities and the temporal variability using grace satellite retrievals the in situ observations and balance velocities show a clear improvement of the spatial representation of the smb in the interior of east antarctica which has become considerably wetter no improvements are seen for west antarctica and the coastal regions a comparison of model smb temporal variability with grace satellite retrievals shows no significant change in performance

implications of basal micro earthquakes and tremor for ice stream mechanics stick slip basal sliding and till erosion abstract the whillans ice plain wip is unique among antarctic ice streams because it moves by stick slip the conditions allowing stick slip and its importance in controlling ice dynamics remain uncertain local basal seismicity previously observed during unstable slip is a clue to the mechanism of ice stream stick slip and a window into current basal conditions but the spatial extent and importance of this basal seismicity are unknown we analyze data from a 2010 2011 ice plain wide seismic and gps network to show that basal micro seismicity correlates with large scale patterns in ice stream slip behavior basal seismicity is common where the ice moves the least between unstable slip events with small discrete basal micro earthquakes happening within 10s of km of the central stick slip nucleation area and emergent basal tremor occurring downstream of this area basal seismicity is largely absent in surrounding areas where inter slip creep rates are high the large seismically active area suggests that a frictional sliding law that can accommodate stick slip may be appropriate for ice stream beds on regional scales variability in seismic behavior over inter station distances of 1 10 km indicates heterogeneity in local bed conditions and frictional complexity wip unstable slips may nucleate when stick slip basal earthquake patches fail over a large area we present a conceptual model in which basal seismicity results from slip weakening frictional failure of over consolidated till as it is eroded and mobilized into deforming till

on the physical mechanism of silent slip events along the deeper part of the seismogenic zone 1 to investigate the mechanism of recently observed silent slip events we simulated earthquake preparation processes using the dieterich ruina rate and state dependent friction law to ensure realistic modeling of the unstable stable transition we considered small cut off velocity to an evolution effect in the friction law for the transition zone when the cut off velocity to the evolution effect is significantly smaller than that of a direct effect steady state friction behaves as velocity weakening at low slip velocity and velocity strengthening at high slip velocity this frictional behavior was experimentally and theoretically confirmed for the unstable stable transition zone the results of our numerical simulations show that silent slips of which velocity is higher than the velocity of relative plate motion eventually propagates horizontally along the unstable stable transition over a period of several years silent slip events can be interpreted as being caused by the transitional behavior of the fault constitutive law

an eddy permitting southern ocean state estimate abstract an eddy permitting general circulation model of the southern ocean is fit by constrained least squares to a large observational dataset during 2005 06 data used include argo float profiles ctd synoptic sections southern elephant seals as oceanographic samplers seaos instrument mounted seal profiles xbts altimetric observations envisat geosat jason 1 and ocean topography experiment topex poseidon and infrared and microwave radiometer observed sea surface temperature an adjoint model is used to determine descent directions in minimizing a misfit function each of whose elements has been weighted by an estimate of the observational plus model error the model is brought into near agreement with the data by adjusting its control vector here consisting of initial and meteorological boundary conditions although total consistency has not yet been achieved the existing solution is in good agreement with the great majority of the 2005 and 2006 southern ocean observations and better repr