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

microstructure and fabric development in ice lessons learned from in situ experiments and implications for understanding rock evolution abstract in this contribution we present a review of the evolution of microstructures and fabric in ice based on the review we show the potential use of ice as an analogue for rocks by considering selected examples that can be related to quartz rich rocks advances in our understanding of the plasticity of ice have come from experimental investigations that clearly show that plastic deformation of polycrystalline ice is initially produced by basal slip interaction of dislocations play an essential role for dynamic recrystallization processes involving grain nucleation and grain boundary migration during the steady state flow of ice to support this review we describe deformation in polycrystalline standard water ice and natural ice samples summarize other experiments involving bulk samples and use in situ plane strain deformation experiments to illustrate the link between microstructure and fabric evolution rheological response and dominant processes most terrestrial ice masses deform at low shear stresses by grain size insensitive creep with a stress exponent n 3 however from experimental observations it is shown that the distribution of plastic activity producing the microstructure and fabric is initially dominated by grain boundary migration during hardening primary creep followed by dynamic recrystallization during transient creep secondary creep involving new grain nucleation with further cycles of grain growth and nucleation resulting in near steady state creep tertiary creep the microstructural transitions and inferred mechanism changes are a function of local and bulk variations in strain energy i e dislocation densities with surface grain boundary energy being secondary except in the case of static annealing as there is a clear correspondence between the rheology of ice and the high temperature deformation dislocation creep regime of polycrystalline quartz we suggest that lessons learnt from ice deformation can be used to interpret polycrystalline quartz deformation different to quartz ice allows experimental investigations at close to natural strain rate and through in situ experiments offers the opportunity to study the dynamic link between microstructural development rheology and the identification of the dominant processes

influence of the subtropical andes on baroclinic disturbances a cold front case study abstract the andes cordillera produces a significant disruption to the structure and evolution of the weather systems that cross south america in particular cold fronts tend to be channeled to the north immediately to the east of the andes fostering the advance of cold air incursions cold surges well into subtropical and sometimes tropical latitudes in contrast active cold fronts hardly reach subtropical latitudes along the western side of the andes pacific sea border instead as a cold front moves equatorward along the east side of the andes a marked low level warming tends to appear along the west side of the subtropical andes leading to the formation of a mesoscale coastal low or trough in this region to further understand the processes that lead to a contrasting evolution of the cold front at each side of the andes a typical frontal passage is studied in this work using synoptic observations and a regional model eta centro de previsao de tempo e estudos climaticos cptec simula

segmented lateral dyke growth in a rifting event at barðarbunga volcanic system iceland crust at many divergent plate boundaries forms primarily by the injection of vertical sheet like dykes some tens of kilometres long1 previous models of rifting events indicate either lateral dyke growth away from a feeding source with propagation rates decreasing as the dyke lengthens2 3 4 or magma flowing vertically into dykes from an underlying source5 6 with the role of topography on the evolution of lateral dykes not clear here we show how a recent segmented dyke intrusion in the bar arbunga volcanic system grew laterally for more than 45 kilometres at a variable rate with topography influencing the direction of propagation barriers at the ends of each segment were overcome by the build up of pressure in the dyke end then a new segment formed and dyke lengthening temporarily peaked the dyke evolution which occurred primarily over 14 days was revealed by propagating seismicity ground deformation mapped by global positioning system gps interferometric analysis of satellite radar images insar and graben formation the strike of the dyke segments varies from an initially radial direction away from the bar arbunga caldera towards alignment with that expected from regional stress at the distal end a model minimizing the combined strain and gravitational potential energy explains the propagation path dyke opening and seismicity focused at the most distal segment at any given time and were simultaneous with magma source deflation and slow collapse at the bar arbunga caldera accompanied by a series of magnitude m 5 earthquakes dyke growth was slowed down by an effusive fissure eruption near the end of the dyke lateral dyke growth with segment barrier breaking by pressure build up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries

flow of anisotropic ice from the epica core a new test apparatus our objective is to measure the mechanical properties of anisotropic ice of the epica ice core from dome concordia antarctica through the full depth of the borehole in deformation experiments under simulated ice sheet conditions of temperature and pressure we propose to undertake experiments on the epica core using both a conventional triaxial test apparatus and a new true triaxial test apparatus incorporating automated tomographic imaging of the ice fabric evolution during deformation we present the design of this new apparatus together with our testing methodology for epica ice the new apparatus is capable of deforming an ice specimen up to 200 mm x 100 mm x 40 mm under servo controlled biaxial loading with a superimposed confining pressure of 50 mpa and at temperatures down to 40 degreesc highly unusual problems arising from the true triaxial nature of the apparatus and tomographic imaging are discussed

geodetic imaging of thermal deformation in geothermal reservoirs production depletion and fault reactivation abstract we investigate thermally induced surface deformation in geothermal systems to define source mechanisms at depth we assess the mechanical process of subsurface deformation by assuming a spherically cooled fractured reservoir in an infinite medium and derive relations that define magnitudes of thermal contraction stress change and permeability evolution the magnitude of thermal deformation in typical geothermal system is larger than anticipated and suggests two different modalities of surface subsidence thermal contraction and fault reactivation here surface deformation vertical displacement surface tilt and horizontal strain induced by the two different modalities are assessed with mogi contraction and okada slip models and compared with instrumental sensitivity of high precision surface geodetic tools we show that 1 year of geothermal operation at 10 mw with a power plant conversion efficiency of 12 can yield 3 0 104 m3 of subsurface volume change for a reservoir at 2000 m depth this induces 1 7 mm of vertical surface displacement 800 nano radians of surface tilt and 900 nano strains of surface strain this result implies that typically observed magnitudes of surface subsidence order of cm year are naturally expected in massive 100 mw scale geothermal operations and observed surface subsidence may largely be the result of thermal contraction conversely thermal unloading can trigger fault reactivation analysis with an okada slip model shows these shear offsets on pre existing faults can also result in surface deformations of considerable magnitude our analysis of field operational data from various geothermal projects suggests that both thermal contraction and slow fault reactivation may contribute to the observed large surface deformation comparison of predicted deformation with instrumental sensitivity of high precision surface tools confirms that geodetic signals especially tilt and strain are indeed sufficiently large to describe reservoir evolution and to potentially deconvolve reservoir parameters of interest such as permeability

mesoscale forcing of a boundary layer jet along the california coast mesoscale numerical model simulations were examined to investigate the thermal and topographic forcing of a boundary layer jet along the northern california coast from 0000 utc may 2 to 1200 utc may 3 1990 routine surface and upper air observations satellite and higher resolution coastal observations r v point sur and doppler wind profiler data documented the diurnal evolution of a coastal marine atmospheric boundary layer mabl coastal cloud structure and mesoscale features such as the coastal jet and land sea breeze circulations that were reasonably well forecast by the numerical model sensitivity model simulations to coastal baroclinicity showed that the diurnal development and intensification of the coastal mabl jet located north of the san francisco bay area was a result of thermal forcing due to differential land sea heating simulations in which the coastal baroclinicity was held fixed in time at a minimal strength showed no diurnal development of the mabl jet the strength of the jet was approximated well by the thermal wind relationship with the jet core located in the sloping marine inversion layer within one rossby radius of deformation from the coastline the steepness of the marine inversion at the coastline was enhanced by regions of strong mabl divergence just offshore and strong convergence onshore resulting from the sea breeze circulation modifications to coastal terrain in two separate sensitivity model simulations illustrated that the primary effect of coastal topography was to act as a barrier to the onshore intrusion of higher momentum offshore air this blocking was due to a topographically forced vertical circulation with a strong descending branch located at the coast this downslope flow and adiabatic warming steepened the mabl inversion at the coast and enhanced the coastal baroclinicity and the coastal jet simulations without coastal terrain showed a jet structure that was spatially diffuse across the coastline and displaced more shoreward simulations in which coastal valleys were removed and replaced by a larger coastal mountain range resulted in little modification to the coastal jet intensity or offshore displacement

geodynamics of iceland and the signatures of plate spreading abstract iceland rising to more than 2 km above sea level originates from the interaction of a mid oceanic ridge and excessive mantle upwelling the plate boundary between the north american and eurasian plates traverses iceland as a series of seismic and volcanic rift zones the building blocks of the volcanic zones are about 32 volcanic systems typically consisting of a central volcano often with a caldera and an associated fissure swarm one or more recent revision of geometry and nature of the volcanic systems include new constraints on the fissure swarms of western volcanic zone and the one active in 2014 2015 associated to the bar arbunga central volcano countrywide seismic network and historical earthquake activity shows that seismicity is most pronounced in transform zones in south and north iceland and at central volcanoes undergoing volcanic unrest in a two year period 2015 2016 the most seismically active volcanoes were katla and bar arbunga measurements of ground deformation using both gps geodesy and interferometric analysis of synthetic aperture radar images acquired by satellites insar reveal well the present day plate spreading process in iceland geodetically measured spreading rate across iceland is consistent with global plate motion models morvel2010 18 19 mm yr in direction n 100 105 e accommodated by a single rift zone in north iceland overlapping rifts in south iceland and a highly oblique rift on the reykjanes peninsula glacial isostatic adjustment gia in response to ice retreat since 1890 is an additional important processes on a regional scale in iceland responsible for rise of central part of iceland of 30 mm year

recent advances in sar interferometry time series analysis for measuring crustal deformation abstract synthetic aperture radar sar interferometry is a technique that permits remote detection of deformation at the earth s surface and has been used extensively to measure displacements associated with earthquakes volcanic activity and many other crustal deformation phenomena analysis of a time series of sar images extends the area where interferometry can be successfully applied and also allows detection of smaller displacements through the reduction of error sources here we review recent advances in time series sar interferometry methods that further improve accuracy this is particularly important when constraining displacements due to processes with low strain rates such as interseismic deformation we include examples of improved algorithms applied to image deformation associated with the 2010 eruption of eyjafjallajokull volcano in iceland slow slip on the guerrero subduction zone in mexico and tectonic deformation in western anatolia turkey

modelled stress distributions at the dome summit south borehole law dome east antarctica a comparison of anisotropic ice flow relations in this study we compare the anisotropic flow relations for polycrystalline ice of azuma and goto azuma 1996 thorsteinsson 2002 placidi and others 2010 and budd and others 2013 observations from the dome summit south dss ice coring site at law dome east antarctica are used to model the vertical distribution of deviatoric stress components at the borehole site the flow relations in which the anisotropic rheology is parameterized by a scalar function so that the strain rate and deviatoric stress tensor components are collinear provide simple shear and vertical compression deviatoric stress profiles that are most consistent with laboratory observations of tertiary creep in combined stress configurations those flow relations where 1 the anisotropy is derived from the magnitude of applied stresses resolved onto the basal planes of individual grains and 2 the macroscopic deformation is obtained via homogenization of individual grain responses provide stress estimates less consistent with laboratory observations this is most evident in combined simple shear and vertical compression flow regimes where shear is dominant our results highlight the difficulties associated with developing flow relations which incorporate a physically based description of microdeformation processes in particular this requires that all relevant microdeformation recrystallization and recovery processes are adequately parameterized

plate boundary deformation and man made subsidence around geothermal fields on the reykjanes peninsula iceland abstract we present interferometric synthetic aperture radar insar data from 1992 1999 and 2003 2008 as well as gps data from 2000 2009 for the active plate boundary on the reykjanes peninsula southwest iceland the geodetic data reveal deformation mainly due to plate spreading anthropogenic subsidence caused by geothermal fluid extraction and possibly increasing pressure in a geothermal system subsidence of around 10 cm is observed during the first 2 years of production at the reykjanes geothermal power plant which started operating in may 2006 we model the surface subsidence around the new power plant using point and ellipsoidal pressure sources in an elastic halfspace short lived swarms of micro earthquakes as well as aseismic fault movement are observed near the geothermal field following the start of production possibly triggered by the stresses induced by geothermal fluid extraction

estimating source parameters from deformation data with an application to the march 1997 earthquake swarm off the izu peninsula japan we have applied two monte carlo optimization techniques simulated annealing and random cost to the inversion of deformation data for fault and magma chamber geometry these techniques involve an element of randomness that permits them to escape local minima and ultimately converge to the global minimum of misfit space we have tested the monte carlo algorithms on two synthetic data sets we have also compared them to one another in terms of their efficiency and reliability we have applied the bootstrap method to estimate confidence intervals for the source parameters including the correlations inherent in the data additionally we present methods that use the information from the bootstrapping procedure to visualize the correlations between the different model parameters we have applied these techniques to gps tilt and leveling data from the march 1997 earthquake swarm off of the izu peninsula japan using the two monte carlo algorithms we have inferred two sources a dike and a fault that fit the deformation data and the patterns of seismicity and that are consistent with the regional stress field

deformation due to geothermal exploitation at reykjanes iceland abstract ground deformation in utilized geothermal areas is often attributed either to pressure decrease or temperature decrease in the geothermal reservoir a new geothermal power plant at reykjanes began operation in may 2006 and local deformation caused by geothermal utilization was observed shortly thereafter we use images acquired by the envisat and terrasar x tsx satellites between 2003 and 2016 as well as available gnss data to derive constraints on the cumulative ground displacement at the reykjanes geothermal area iceland and compare these results to production data acquired from observation wells in this region we employ interferometric analysis of synthetic aperture satellite radar images insar using a combined persistent scatterer and small baseline approach on both ascending and descending envisat and tsx satellite tracks covering the 2003 2016 period time series of range change along line of sight los from the ground to the satellite show the characteristics of on going ground deflation in the vicinity of the reykjanes power plant in the 2005 2008 period the main area of deformation was 4 km long by 2 5 km wide aligned along the reykjanes fissure swarm but in the period 2009 2016 it is more circular in shape and 2 km wide los displacement rates have remained relatively steady in time although slightly faster in the 2005 2008 period than the 2009 2016 period the average los velocities from ascending and descending tracks are decomposed into estimates of near vertical and near east displacements the inferred maximum subsidence since the start of production is 260 mm horizontal displacements show contraction towards the center of deflation of up to 140 mm geodetic modeling is undertaken using sources of simple geometry within an elastic halfspace to determine the optimal sources for the observed contraction throughout 2005 2016 for the earlier period modeled utilizing envisat interferograms 16 june 2005 16 august 2008 the optimal source is a yang model with a strike of 58 and a source depth of 2 2 km the calculated volume change associated with the observed contraction is 2 3 106 m3 for the latter period utilizing tsx interferograms 24 september 2009 17 august 2016 the preferred source is a mogi type model at a depth of 1 2 km and the modeled volume change is 1 106 m3

deformation at krafla and bjarnarflag geothermal areas northern volcanic zone of iceland 1993 2015 abstract the krafla volcanic system has geothermal areas within the krafla caldera and at bjarnarflag in the krafla fissure swarm 9 km south of the krafla caldera arrays of boreholes extract geothermal fluids for power plants in both areas we collected and analyzed insar gps and leveling data spanning 1993 2015 in order to investigate crustal deformation in these areas the volcanic zone hosting the geothermal areas is also subject to large scale regional deformation processes including plate spreading and deflation of the krafla volcanic system these deformation processes have to be taken into account in order to isolate the geothermal deformation signal plate spreading produces the largest horizontal displacements but the regional deformation pattern also suggests readjustment of the krafla system at depth after the 1975 1984 krafla rifting episode observed deformation can be fit by an inflation source at about 20 km depth north of krafla and a deflation source at similar depth directly below the krafla caldera deflation signal along the fissure swarm can be reproduced by a 1 km wide sill at 4 km depth closing by 2 4 cm per year these sources are considered to approximate the combined effects of vertical deformation associated with plate spreading and post rifting response local deformation at the geothermal areas is well resolved in addition to these signals insar shows that deformation at bjarnarflag is elongated along the direction of the krafla fissure swarm 4 km by 2 km while it is circular at krafla 5 km diameter rates of deflation at krafla and bjarnarflag geothermal areas have been relatively steady average volume decrease of about 6 6 10 5 m 3 yr for krafla and 3 9 10 5 m 3 yr for bjanarflag are found at sources located at 1 5 km depth when interpreted by a spherical point source of pressure this volume change represents about 8 10 3 m 3 ton of the mass of geothermal fluid extracted per year indicating important renewal of the geothermal reservoir by water flow

time dependent land uplift and subsidence in the santa clara valley california from a large interferometric synthetic aperture radar data set 1 we invert 115 differential interferograms derived from 47 synthetic aperture radar sar scenes for a time dependent deformation signal in the santa clara valley california the time dependent deformation is calculated by performing a linear inversion that solves for the incremental range change between sar scene acquisitions a nonlinear range change signal is extracted from the ers insar data without imposing a model of the expected deformation in the santa clara valley cumulative land uplift is observed during the period from 1992 to 2000 with a maximum uplift of 41 18 mm centered north of sunnyvale uplift is also observed east of san jose seasonal uplift and subsidence dominate west of the silver creek fault near san jose with a maximum peak to trough amplitude of 35 mm the pattern of seasonal versus long term uplift provides constraints on the spatial and temporal characteristics of water bearing units within the aquifer the silver creek fault partitions the uplift behavior of the basin suggesting that it acts as a hydrologic barrier to groundwater flow while no tectonic creep is observed along the fault the development of a low permeability barrier that bisects the alluvium suggests that the fault has been active since the deposition of quaternary units

radar interferometry and its application to changes in the earth s surface geophysical applications of radar interferometry to measure changes in the earth s surface have exploded in the early 1990s this new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times the resulting interferogram is a contour map of the change in distance between the ground and the radar instrument these maps provide an unsurpassed spatial sampling density 100 pixels km 2 a competitive precision 1 cm and a useful observation cadence 1 pass month 1 they record movements in the crust perturbations in the atmosphere dielectric modifications in the soil and relief in the topography they are also sensitive to technical effects such as relative variations in the radar s trajectory or variations in its frequency standard we describe how all these phenomena contribute to an interferogram then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments including the four satellites currently in orbit ers 1 ers 2 jers 1 and radarsat the next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement respecting the limits of the technique assessing its uncertainty recognizing artifacts and discriminating different types of signal we then review the geophysical applications published to date most of which study deformation related to earthquakes volcanoes and glaciers using ers 1 data we also show examples of monitoring natural hazards and environmental alterations related to landslides subsidence and agriculture in addition we consider subtler geophysical signals such as postseismic relaxation tidal loading of coastal areas and interseismic strain accumulation we conclude with our perspectives on the future of radar interferometry the objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it

instruments and methods a simple and updated pneumatic method for uniaxial ice compression in the laboratory experimental settings and creep test results on glacier ice creep tests provide invaluable data to better understand the physical properties of ice under various conditions we describe here a simple updated pneumatic apparatus for experimental studies of

ice flow relations for stress and strain rate components from combined shear and compression laboratory experiments the generalized glen flow relation for ice involving the second invariants of the stress deviator and strain rate tensors is only expected to hold for isotropic polycrystalline ice previous single stress experiments have shown that for the steady state flow which develops at large strains the tertiary strain rate is greater than the minimum secondary creep value by an enhancement factor which is larger for shear than compression previous experiments combining shear with compression normal to the shear plane have shown that enhancement of the tertiary octahedral strain rate increases monotonically from compression alone to shear alone additional experiments and analyses presented here were conducted to further investigate how the separate tertiary shear and compression strain rate components are related in combined stress situations it is found that tertiary compression rates are more strongly influenced by the addition of shear than is given by a glen type flow relation whereas shear is less influenced by additional compression a scalar function formulation of the flow relation is proposed which fits the tertiary creep data well and is readily adapted to a generalized form that can be extended to other stress configurations and applied in ice mass modelling

deformation properties of subfreezing glacier ice role of crystal size chemical impurities and rock particles inferred from in situ measurements to improve understanding of the deformation properties of subfreezing polycrystalline glacier ice and in particular the role of crystal size chemical impurities and rock particle impurities we analyze in situ strain rates of the basal layers of meserve glacier antarctica strain rates were monitored on the walls of a subglacial tunnel where down flow shear stress is relatively uniform and ice properties were measured texture fabric and impurity content we propose a simple empirical model describing strain rate variations due to variations in crystal size and impurity content and we use all relevant meserve data to constrain model parameters we conclude that there is a direct dependence of strain rate on crystal size which reflects an important role for a grain size sensitive deformation mechanism such as grain boundary sliding or diffusion chemical impurities are found to enhance the grain size sensitive deformation and are found to be an important control on strain rate variations in the very impure ices of meserve glacier however the per molar sensitivity of strain rate to chemical impurity content is shown to be very low such that in the ice age ices of the greenland ice sheet there is probably an immeasurable contribution of chemical impurities to strain rate enhancement though we cannot exclude chemical enhancements as high as 1 3 there our analyses detect no direct rheologic effect of rock particles in the meserve ices which suggests that rock content is not directly responsible for the low viscosity of dirty basal layers

australian southerly busters part i analysis of a numerically simulated case study abstract a diagnostic study of the australian southerly buster is performed using a numerical weather prediction model it is demonstrated that the model run at 50 km resolution is capable of capturing the transition of a cold front into a southerly buster as it traverses the cut coast of the australian continent the main features of the modified front am identified through comparison of the simulation with an adiabatic simulation from which precipitation and surface processes including orography have been removed from this comparison the southerly buster effect is defined in terms of the deformation of the front from its adiabatic ostentation and in terms of enhancement of temperature gradients and southerly winds along the coastal strip sensitivity experiments are then analyzed with a view to objectively determining the relative roles of mountains precipitation and land sea contrasts of heating and friction in bringing about these perturbations the major conclusions are that i the primary e

crustal deformation from 1992 to 1995 at the mid atlantic ridge southwest iceland mapped by satellite radar interferometry satellite radar interferometry observations of the reykjanes peninsula oblique rift in southwest iceland show that the reykjanes central volcano subsided at an average rate of up to 13 millimeters per year from 1992 to 1995 in response to use of its geothermal field interferograms spanning up to 3 12 years also include signatures of plate spreading and indicate that the plate boundary is locked at a depth of about 5 kilometers below that depth the plate movements are accommodated by continuous ductile deformation which is not fully balanced by inflow of magma from depth causing subsidence of the plate boundary of about 6 5 millimeters per year

synthetic aperture radar interferometry to measure earth s surface topography and its deformation synthetic aperture radar interferometry insar from earth orbiting spacecraft provides a new tool to map global topography and deformation of the earth s surface radar images taken from slightly different viewing directions allow the construction of digital elevation models of meter scale accuracy these data sets aid in the analysis and interpretation of tectonic and volcanic landscapes if the earth s surface deformed between two radar image acquisitions a map of the surface dis placement with tens of meters resolution and subcentimeter accuracy can be con structed this review gives a basic overview of insar for earth scientists and presents a selection of geologic applications that demonstrate the unique capabilities of insar for mapping the topography and deformation of the earth

forward modeling of ice topography on mars to infer basal shear stress conditions 1 understanding the history of ice caps on mars could reveal important information about martian geologic and climatic history to do this an ice reconstruction model is needed that operates over complex topography and can be constrained with a limited number of free parameters in this study we developed a threshold sliding model for ice cap morphology based on the classic model of nye later incorporated into the models of reeh and colleagues we have updated the nye reeh model with a new numerical algorithm although the model was originally developed to model perfectly plastic deformation it is applicable to any ice body that deforms when a threshold basal shear stress is exceeded the model requires three inputs a digital elevation model of bed topography a mask grid that defines the position of the ice terminus and a function defining the threshold basal shear stress to test the robustness of the model the morphology of the greenland ice sheet is reconstructed using an empirical equation between threshold basal shear stress and ice surface slope the model is then used to reconstruct the morphology of ice draping impact craters on the margins of the south polar layered deposits using an inferred constant basal shear stress of 0 6 bar for the majority of the examples this inferred basal shear stress value is almost 1 3 of the average basal shear stress calculated for the greenland ice sheet what causes this lower basal shear stress value on mars is unclear but could involve the strain weakening behavior of ice

dynamic inland propagation of thinning due to ice loss at the margins of the greenland ice sheet cryospheric sciences branch nasa goddard space flight center greenbelt md usaabstract mass balance analysis of the greenland ice sheet based on surface elevation changesobserved by the european remote sensing satellite ers 1992 2002 and ice cloud and land elevationsatellite icesat 2003 07 indicates that the strongly increased mass loss at lower elevations 2000m of the ice sheet as observed during 2003 07 appears to induce interior ice thinning athigher elevations in this paper we perform a perturbation experiment with a three dimensionalanisotropic ice flow model aif model to investigate this upstream propagation observed thinningrates in the regions below 2000m elevation are used as perturbation inputs the model runs withperturbation for 10 years show that the extensive mass loss at the ice sheet margins does in fact causeinterior thinning on short timescales i e decadal the modeled pattern of thinning over the ice sheetagrees with the observations which implies that the strong mass loss since the early 2000s at lowelevations has had a dynamic impact on the entire ice sheet the modeling results also suggest that evenif the large mass loss at the margins stopped the interior ice sheet would continue thinning for 300 yearsand would take thousands of years for full dynamic recovery

ground deformation due to steam cap processes at reykjanes sw iceland effects of geothermal exploitation inferred from interferometric analysis of sentinel 1 images 2015 2017

the general viscous relation for the response of ice and its implications in the reduced model for ice sheet flow analyses of confined and unconfined compression combined with shear and of biaxial stress laterally confined or unconfined are presented for a general deviatoric viscous relation describing the response of an incompressible material at present numerical models for ice sheet flow commonly adopt a very simple viscous law throughout the ice sheet in which the deviatoric stress is coaxial with the strain rate and the single response function depends on only one invariant and is determined by single stress component tests which cannot verify the validity of the simplification the analysis presented here is concerned with two stress component experimental configurations which could determine the general quadratic form of a viscous relation with two response functions depending on two invariants it is shown that the two combined compression and shear tests can also check the consistency of a viscous fluid assumption but not so the biaxial stress tests each test allows a direct assessment of the significance of the quadratic term it is then shown that a significant quadratic term changes the relative stress magnitudes in the commonly adopted reduced model for ice sheet flow and that the crucial simplifications are not achieved

a numerical study of a southeast australian coastal ridging event abstract a numerical study of the 9 11 november 1982 southeast australian coastal ridging event is presented the mesoscale coastal features of this event have been previously described as a coastally trapped disturbance ctd however the analysis presented in this paper shows that the model coastal trapping is of secondary importance in generating the coastal ridging given the potential controversy particular emphasis in this paper is placed on identifying the causes of the ridging the paper follows a previous study by the authors in which a colorado state university regional atmospheric modeling system simulation of this event was validated in this event contributions to ridging along the southeastern australian coast came from both synoptic and mesoscale phenomena in the model a southern ocean anticyclone that tracked east from the great australian bight toward the southern tasman sea led to a large scale steady pressure increase over the entire southeast australian region ridging at the victo

importance of horizontal seafloor motion on tsunami height for the 2011 mw 9 0 tohoku oki earthquake abstract it is now clear that the 2011 tohoku oki earthquake ruptured the subduction interface all the way to the japan trench however there is significant disagreement about just how much slip occurred at the trench with most geodetic studies locating only a small fraction of the maximum slip there whereas broadband seismic studies put the majority of the slip near the trench measurements of seafloor displacement near the trench also imply more slip there than is estimated by the geodetic studies here by means of a joint inversion of displacement measurements and seafloor pressure data we show that it is possible to reconcile geodetic and seismic studies and that a considerable amount of slip indeed occurred at the trench with slip magnitudes reaching 57 74 of the maximum slip the seafloor displacement predicted by our model agrees very well with independent measurements made close to the trench we also find good agreement between our tsunami model and independent measurements of tsunami height in the ocean and on land re running of the inversion without the near field pressure gauge data however leads to underprediction of the flooding on land even when the seafloor geodetic data are still included thus even if the seafloor geodetic measurements had been available in real time they would still not have allowed reliable prediction of near field tsunami inundation close to the trench the dip of the plate interface is shallow which serves to decrease the vertical motion of the sea floor for any given slip however the horizontal motion is conversely larger because the ocean floor slopes steeply near the trench it acted like a giant wedge converting the horizontal motion of the ground into an uplift of the water column and causing the peak initial tsunami wave height to be twice as high as it would have been from vertical displacement alone

geology and structure of the reykjanes volcanic system iceland abstract the reykjanes peninsula is a trans tensional plate boundary with several volcanic systems from the centers of which fissure swarms extend to the ne and sw the fissure swarms accommodate the extensional component whereas north south trending strike slip faults accomodate the transform component the fissure swarms release stress during volcano tectonic episodes that occur at intervals of several hundred years stress is released by the strike slip faults by microearthquake swarms at intervals of a few decades the fissure swarms are segmented along their trend the segments include a volcanic center with a clustering of fissure eruptions and extensional faults a proximal zone of 20 40 km follows were faults become dominant with distance from the center linear anomalies of a high geothermal gradient extend further still into the marginal area of early quaternary to miocene rocks indicating dyke propagation for another 30 40 km beyond visible faults the reykjanes volcanic center is nested in a 5 6 km wide rift zone with boundary faults of just over 20 m visible throw volcanic production keeps pace with extension and subsidence to fill the rift the last three volcano tectonic episodes occurred at reykjanes in the 13th century about 2000 years ago and about 3200 years ago the lavas from these three fissure eruptions cover 2 3 of reykjanes by area largely smoothing over faults of the rift floor during the weichselian glacial maximum the ice margin may have reached 75 100 km beyond reykjanes it had become ice free 14 500 years ago there is evidence of at least 10 eruptions on the reykjanes volcanic system since of which the first ones were of lava shield type a similar eruption frequency may have prevailed at reykjanes during its postglacial time interval there are three volcanic fissure zones within the reykjanes center the middle zone of 1 5 km2 hosts the main geothermal resource of the system recently the western zone proved to host an exploitable resource also it may be restricted to a narrow zone of dykes the reservoir temperatures of these two lie in the range 280 310 c the eastern zone has not proved productive so far it has erupted olivine rich shield lavas on most of its trace whereas the others have erupted slightly evolved tholeiite feed zones in the main production zone have been correlated partly with the axis of the eastern of two tindars they cluster also in near horizontal intervals which may suggest that density controlled offshots also play a role

repeated magmatic intrusions at el hierro island following the 2011 2012 submarine eruption abstract after more than 200 years of quiescence in july 2011 an intense seismic swarm was detected beneath the center of el hierro island canary islands culminating on 10 october 2011 in a submarine eruption 2 km off the southern coast although the eruption officially ended on 5 march 2012 magmatic activity continued in the area from june 2012 to march 2014 six earthquake swarms indicative of magmatic intrusions were detected underneath the island we have studied these post eruption intrusive events using gps and insar techniques to characterize the ground surface deformation produced by each of these intrusions and to determine the optimal source parameters geometry location depth volume change source inversions provide insight into the depth of the intrusions 11 16 km and the volume change associated with each of them between 0 02 and 0 13 km 3 during this period 20 cm of uplift was detected in the central western part of the island corresponding to approximately 0 32 0 38 km 3 of magma intruded beneath the volcano we suggest that these intrusions result from deep magma migrating from the mantle trapped at the mantle lower crust discontinuity in the form of sill like bodies this study using joint inversion of gps and insar data in a post eruption period provides important insight into the characteristics of the magmatic plumbing system of el hierro an oceanic intraplate volcanic island

countrywide observations of plate spreading and glacial isostatic adjustment in iceland inferred by sentinel 1 radar interferometry 2015 2018

exploring the influence of loading geometry on the plastic flow properties of geological materials results from combined torsion axial compression tests on calcite rocks abstract for technical reasons virtually all plastic deformation experiments on geological materials have been performed in either pure shear or simple shear these special case loading geometries are rather restrictive for those seeking insight into how microstructure evolves under the more general loading geometries that occur during natural deformation moreover they are insufficient to establish how plastic flow properties might vary with the 3rd invariant of the deviatoric stress tensor j 3 which describes the stress configuration and so applications that use those flow properties e g glaciological and geodynamical modelling may be correspondingly compromised we describe an inexpensive and relatively straightforward modification to the widely used paterson rock deformation apparatus that allows torsion experiments to be performed under simultaneously applied axial loads we illustrate the performance of this modification with the results of combined stress experiments performed on carrara marble and solnhofen limestone at 500 600 c and confining pressures of 300 mpa the flow stresses are best described by the drucker yield function which includes j 3 dependence however that j 3 dependence is small hence for these initially approximately isotropic calcite rocks flow stresses are adequately described by the j 3 independent von mises yield criterion that is widely used in deformation modelling loading geometry does however have a profound influence on the type and rate of development of crystallographic preferred orientation and hence of mechanical anisotropy the apparatus modification extends the range of loading geometries that can be used to investigate microstructural evolution as well as providing greater scope for determining the shape of the yield surface in plastically anisotropic materials

experimental work on the effect of pre existing anisotropy on fabric development in glaciers abstract localization of deformation in ice is known to be important at all scales in deforming glaciers however relatively little is known of the significance of shear localization and the influence of fabric development in anisotropic ice at microscopic scales c axis preferred orientation and the inclination of the primary layering in anisotropic ice masses during both plane strain compression and combined simple shear compression have been examined a series of creep tests in the temperature range of 5 to 1 c over a range of shortening strains varying from 10 to 40 and compressive stresses ranging from 0 to 0 7 mpa have been undertaken significant variations in the strain rate and microstructural development have been observed in the plane strain compression experiments that reflects the varying orientations of the anisotropy and its relationship to easy glide directions in the ice mass in the unconfined combined compression and shear experiments minimum shear stress rates vary between the variously oriented anisotropic ice masses and deviate from the normal power flow law for isotropic ice where annealing occurs such ice masses preserve the pre existing c axis fabric and hence may reflect a contribution from both the recrystallized and inherited ice components

episodic ground deformation associated with geothermal energy production at the guayabo caldera costa rica abstract the ground response to the production of energy in geothermal fields can be observed in the form of ground displacement and seismic activity changes in the temperature volume pressure of the reservoir can culminate in surface deformation and in seismicity at the reservoir edges and or near the production wells identifying the origin of the ground response enables controlled management of the reservoir and can help prevent damage to structures satellite remote sensing insar permits the study of the deformation at these sites with high spatial and temporal resolution however central america has a dynamic atmosphere with considerable water vapour and constant growth of vegetation all year long which leads to decorrelation between sar images here we study the dr alfredo mainieri protti geothermal field located near miravalles volcano in the northern costa rica volcanic arc we measure the deformation associated with geothermal energy production using data from two satellites alos 2 and sentinel 1 between january 2015 and january 2017 the alos 2 data was used to obtain the extent of the affected area and two stamps multi temporal methods persistent scatter ps insar and small baselines sb were applied to the sentinel 1 data to obtain the temporal pattern of the ground displacements results show a direct response of the ground to the extraction of fluids the pattern of deformation obtained with alos 2 is spatially correlated with the geothermal field and with the recorded seismicity between april 2015 to october 2016 periods of uplift and subsidence were observed with values between 2 0 to 3 0 cm every 120 days linked to changes in the amount of fluids extracted from the reservoir the results also show the ability of the reservoir to recover rapidly following a decrease in extraction rate this work has shown that even in this tropical region it is possible to monitor anthropogenic ground motion using insar this is beneficial for the central american region as satellite images are becoming more frequently acquired and available and can be used to boost the monitoring of seismic regions volcanic activity and anthropogenic activities

crustal deformation at the oblique spreading reykjanes peninsula sw iceland gps measurements from 1993 to 1998 in 1993 and 1998 a 38 point gps network was surveyed on the reykjanes peninsula sw iceland according to the nuvel 1a plate motion model the spreading rate of the north american and eurasian plates in sw iceland is 18 9 0 5 mm yr toward n102 7 1 1 e highly oblique to the plate boundary instead of oblique spreading the measurements indicate left lateral shear strain accumulation parallel to the reykjanes peninsula seismic zone n76 e at the rate of about eyx 0 2 strain yr tensor shear strain subsidence is generally observed toward the seismic zone a local maximum subsidence of 60 mm was measured in the svartsengi geothermal area subsidence in this area has previously been detected with geodetic measurements and is considered a result of geothermal usage expansion was observed in the area of the hengill triple junction this is probably a result of magma accumulation beneath mount hromundartindur as previous seismic and geodetic measurements have indicated using a simple screw dislocation model we fit the majority of the data assuming a left lateral shear zone at depth along the seismic zone we estimate locking depth of 6 5 km and deep slip rate of 16 5 mm yr the maximum left lateral displacement predicted by the screw dislocation model 11 85 0 06 mm yr is consistent with the observed value of 11 9 0 5 mm yr if the hengill area is excluded little extension is observed across the peninsula the discrepancy between the nuvel 1a oblique spreading and the observed transcurrent motion is thought to be caused by lack of magma intrusion into the crust during this time period

the effect of fluid compressibility and elastic rock properties on deformation of geothermal reservoirs a geothermal reservoir deforms when the extraction of pore fluid exceeds reservoir recharge causing a decrease in pore pressure the magnitude of this deformation is related to the amount of pore fluid that is extracted assuming compressible material properties in a homogeneous reservoir we derive an expression for the ratio of reservoir volume change per extracted fluid mass we show that this ratio depends on a number of parameters notably the compressibilities of reservoir rock and pore fluid we apply the obtained relationship to three different geothermal areas hellisheidi reykjanes and the geysers to illustrate under which circumstances the relation between reservoir deformation and the amount of extracted fluid is able to help us learn more about reservoir conditions we find that the fluid compressibility depending on whether the system is single phase or two phase may explain large differences in estimates of reservoir volume changes per mass of extracted fluid

anisotropic ice flow leading to the onset of ice stream d west antarctica numerical modelling based on the observations from byrd station borehole an ice sheet flowlinemodel is used to simulate the flow of ice along two particle paths toward the onset to ice stream d west antarctica one path is near the centre line of the main tributary to the ice stream while the second passes by the byrd station borehole site in this paper we analyze the flow of the moderately fast flowing tributaries in terms of ice fabric anisotropy and estimate the steady state ice flow regions with the compatible developed crystal orientation fabrics along two particle paths comparison between modelled isochrones and internal layers detected from radio echo sounding surveys in the area is used to suggest that flow upstream of the onset to ice stream d appears to have been stable since at least the last glacial maximum

effect of the andes cordillera on precipitation from a midlatitude cold front the effects of the andes cordillera the major mountain range in south america on precipitation patterns of baroclinic systems approaching from the southeast pacific remain largely unstudied this study focuses on a case in late may 2008 when an upper level trough and surface cold front produced widespread precipitation in central chile the primary goal was to analyze the physical mechanisms responsible for the structure and evolution of the precipitation weather research and forecasting wrf model simulations indicate that as an upper level trough approached central chile midtropospheric flow below 700 hpa was blocked by the high topography and deflected poleward in the form of a barrier jet this northerly jet had wind maxima in excess of 15 m s 21 was centered around 925 hpa and extended westward 200 km from the mountains it intersected the cold front which approached from the south near the coast thereby increasing convergence along the frontal surface slowing its equatorward progress and enhancing rainfall over central chile another separate region of heavy precipitation formed over the upwind slopes of the cordillera a trajectory analysis confirmed that the barrier jet moved low level parcels from their origin in the moist southeast pacific boundary layer to the coast when model topography was reduced to twenty percent of its original height the cold front advanced more rapidly to the northeast generated less precipitation in central chile between 338 and 368s and produced minimal orographic precipitation on the upwind andean slopes based on these findings the high topography appears responsible for not only orographic precipitation but also for substantially increasing precipitation totals over the central coast and valley

the 1993 superstorm cold surge frontal structure gap flow and tropical impact in the wake of the eastern united states cyclone of 12 14 march 1993 a cold surge originating over alaska and western canada brought northerlies exceeding 20 m s21 and temperature decreases up to 158c over 24 h into mexico and central america this paper addresses the multiscale aspects of the surge from the planetary scale to the mesoscale focusing on 1 the structure and evolution of the leading edge of the cold surge 2 the reasons for its extraordinary intensity and equatorward extent and 3 the impact of the surge on the tropics specifically on the strength of the trade winds and on the sea surface temperature in the eastern pacific the cold surge was initiated as a developing cyclone over the gulf of mexico and an upstream anticyclone east of the rockies caused an along barrier pressure gradient to form forcing topographically channeled northerlies along the rocky and sierra madre mountains to transport cold air equatorward on the mesoscale the leading edge of the cold surge possessed nonclassical frontal structure for example as the cold surge entered mexico the coldest air and the strongest wind arrived at about 900 hpa before affecting the surface suggestive of a tipped forward leading edge to the surge also satellite imagery and surface observations indicate that the leading edge appeared to be successively regenerated in the warm presurge air the cold surge had characteristics reminiscent of a kelvin wave a tipped forward cold front a pressure jump line a bore and a gravity current but none of these conceptual dynamical models was fully applicable associated with the cold surge gap winds up to 25 m s21 were observed in the gulfs of tehuantepec a tehuantepecer fonseca papagayo and panama owing to the strong cross mountain pressure gradient in the case of the tehuantepecer a rope cloud emanated from the isthmus of tehuantepec and turned anticyclonically consistent with an inertial oscillation on the synoptic and planetary scales the extraordinary equatorward extent of the cold surge was aided by topographic channeling similar to cold air damming by a low latitude upper tropospheric trough and by the lower branch of the secondary circulation associated with a confluent jet entrance region aloft the cold surge also impacted the tropical atmosphere and ocean by contributing to the strengthening of the northeast trade winds over the eastern pacific ocean and by inducing local cooling of the sea surface temperature in the gulfs of tehuantepec and papagayo by about 48 88c