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

insar reveals coastal subsidence in the pearl river delta china summary the pearl river delta prd is one of the most important economic regions with the highest population densities in china with its dramatic increasing population and economy hazards associated with land subsidence frequently occur here that amplify the negative effect of sea level rise however land subsidence has not been regularly measured in this region here we use interferometric synthetic aperture radar insar to investigate the rate and extent of land subsidence in the prd region assuming purely vertical displacements multi track interferograms from different viewing geometries are combined to estimate the linear rate map and time series at a higher resolution in time than is possible with a single track the results show apparent subsidence along the coastal region of shenzhen associated with rapid urban development in recent years the average subsidence rate within 500 m of the coast is about 2 5 mm yr 1 and the maximum is up to about 6 mm yr 1 with respect to the central part of the city much of the land surface in the prd is less than 2 m above mean sea level high precision geodetic measurements throughout the prd region are therefore critical for conducting risk assessments considering the rate of about 2 3 mm yr 1 of current global sea level rise

greenland ice sheet surface melt extent and trends 1960 2010 observed meteorological data and a high resolution 5 km model were used to simulate greenland ice sheet surface melt extent and trends before the satellite era 1960 79 and during the satellite era through 2010 the model output was compared with passive microwave satellite observations of melt extent for 1960 2010 the average simulated melt extent was 15 5 for the period 1960 72 simulated melt extent decreased by an average of 6 whereas 1973 2010 had an average increase of 13 with record melt extent in 2010 the trend in simulated melt extent since 1972 indicated that the melt extent in 2010 averaged twice that in the early 1970s the maximum and mean melt extents for 2010 were 52 9 5 10 5 km 2 and 28 5 2 10 5 km 2 respectively due to higher than average winter and summer temperatures and lower than average winter precipitation for 2010 the southwest greenland melt duration was 41 60 days longer than the 1960 2010 average while the northeast greenland melt duration was up to 20 days shorter from 1960 to 1972 the melting period with a 10 melt extent decreased by an average of 3 days a 1 after 1972 the period increased by an average of 2 days a 1 indicating an extended melting period for the ice sheet of about 70 days 40 and 30 days in spring and autumn respectively

greenland coastal air temperatures linked to baffin bay and greenland sea ice conditions during autumn through regional blocking patterns variations in sea ice freeze onset and regional sea surface temperatures ssts in baffin bay and greenland sea are linked to autumn surface air temperatures sats around coastal greenland through 500 hpa blocking patterns 1979 2014 we find strong statistically significant correlations between baffin bay freeze onset and ssts and sats across the western and southernmost coastal areas while weaker and fewer significant correlations are found between eastern sats ssts and freeze periods observed in the neighboring greenland sea autumn greenland blocking index values and the incidence of meridional circulation patterns have increased over the modern sea ice monitoring era increased anticyclonic blocking patterns promote poleward transport of warm air from lower latitudes and local warm air advection onshore from ocean atmosphere sensible heat exchange through ice free or thin ice covered seas bordering the coastal stations temperature composites by years of extreme late freeze conditions occurring since 2006 in baffin bay reveal positive monthly sat departures that often exceed 1 standard deviation from the 1981 2010 climate normal over coastal areas that exhibit a similar spatial pattern as the peak correlations

toward mapping surface deformation in three dimensions using insar 1 one of the limitations of deformation measurements made with interferometric synthetic aperture radar insar is that an interferogram only measures one component of the surface deformation in the satellite s line of sight we investigate strategies for mapping surface deformation in three dimensions by using multiple interferograms with different imaging geometries geometries for both current and future missions are evaluated and their abilities to resolve the displacement vector are compared the north component is always the most difficult to determine using data from near polar orbiting satellites however a satellite with an inclination of about 60 120 would enable all three components to be well resolved we attempt to resolve the 3d displacements for the 23 october 2002 nenana mountain alaska earthquake the north component s error is much larger than the signal but proxies for eastward and vertical motion can be determined if the north component is assumed negligible inversions of hypothetical coseismic interferograms demonstrate that earthquake model parameters can be well recovered from two interferograms acquired on ascending and descending tracks

potential of small baseline sar interferometry for monitoring land subsidence related to underground coal fires wuda northern china case study uncontrolled coal fires can result in massive surface displacements due to the change in volume of burning coal and thermal effects in the adjacent rock mass simultaneously the resultant surface breakings provide greater access to air and water that in turn can aggravate the problem of underground coal seam burning in this case study we have investigated the feasibility and potential of detecting the land subsidence accompanying coal fires by means of satellite insar observations three groups of small baseline insar approaches psi stacking and 2 passdinsar were applied to the wuda coalfield northern china to reveal the spatial and temporal signals of the land subsidence in the areas affected by the coal fires the interferometric results agree well with gps observations and coal fire data obtained by field investigation which demonstrates that the small baseline insar techniques have remarkable potential to detect this land subsidence of interest in particular our results show that the development of coal fires can lead to new subsiding areas and also accelerate the ongoing surface subsidence typically within the areas of mature coal fires through a comparison of the interferometric observations and the multi temporal coal fire maps this timely and reliable information on land subsidence will be useful for the detection and mapping of the coal fire affected regions and thereby assist in fighting and controlling coal seam burning

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

insar slip rate determination on the altyn tagh fault northern tibet in the presence of topographically correlated atmospheric delays 1 the interseismic strain across the altyn tagh fault at 85 e has been measured using 59 interferograms from 26 ers 1 2 sar acquisitions on a single track for the period 1993 2000 using an atmospheric delay correction that scales linearly with height we estimate the left lateral strike slip motion to be 11 1 5 mm yr assuming no relative vertical motion and a 15 km fault locking depth this is in agreement with sparse gps measurements the atmospheric delay corrections agree well with coarse contemporaneous modelled weather data reinforcing the importance of correcting for atmospheric delays in insar studies of interseismic strain accumulation particularly in areas of high topographic relief that strongly correlate with the expected tectonic signal we also find that in addition to the tropospheric water vapour wet delay the hydrostatic dry delay makes a significant contribution to the signal

constraints on surface deformation in the seattle wa urban corridor from satellite radar interferometry time series analysis summary we apply differential insar dinsar time series techniques to the urban corridor between tacoma seattle and everett wa using 93 interferograms from three satellites ers 1 ers 2 and radarsat 1 between 1992 and 2007 our goal is to study local tectonic geomorphic and groundwater processes consequently we remove long wavelength 50 100 km deformation signals from unwrapped interferograms by comparing surface velocities generated via the time series technique at more than two million points within the overlapping region between two independent ers tracks we estimate the uncertainty of relative surface velocity measurements to be 0 5 mm yr 1 in the vertical we estimate the uncertainty of relative displacement measurements to be 5 4 mm given our comparisons of dinsar derived time series to gps data a result that is consistent both with previous dinsar time series analysis and with the uncertainty expected from gps displacements projected onto the radar line of sight active tectonic deformation at shallow depths on the region s numerous east west structures is absent over the 11 5 yr of sar data examined assuming that the south dipping thrust beneath seattle and tacoma takes up 3 mm yr 1 of north south shortening our data indicate that the fault must be currently locked to a depth of greater than 10 km we also document extensive groundwater related deformation throughout much of the study region most notably we identify sharp linear deformation gradients near federal way wa and running between sumner wa and steilacoom wa these features may mark the locations of previously unmapped fault splays that locally control groundwater movement we find no slow landslide deformation on any of the numerous mapped slide complexes within seattle although regions of known active landsliding such as along perkins lane in seattle exhibit radar phase de correlation these observations are consistent with relatively infrequent and rapid landslide deformation within seattle

has arctic sea ice loss contributed to increased surface melting of the greenland ice sheet abstractin recent decades the greenland ice sheet has experienced increased surface melt however the underlying cause of this increased surface melting and how it relates to cryospheric changes across the arctic remain unclear here it is shown that an important contributing factor is the decreasing arctic sea ice reduced summer sea ice favors stronger and more frequent occurrences of blocking high pressure events over greenland blocking highs enhance the transport of warm moist air over greenland which increases downwelling infrared radiation contributes to increased extreme heat events and accounts for the majority of the observed warming trends these findings are supported by analyses of observations and reanalysis data as well as by independent atmospheric model simulations using a state of the art atmospheric model that is forced by varying only the sea ice conditions reduced sea ice conditions in the model favor more extensive greenland surface melting the authors find a positive feedba

interseismic slip rate of the northwestern xianshuihe fault from insar data 1 the xianshuihe fault is a highly active strike slip fault system near the eastern margin of the tibetan plateau we use a multi interferogram method to construct a map of line of sight deformation rate due to interseismic strain accumulation on the northwestern xianshuihe fault from a decade of sar data acquired by the ers 1 2 and envisat satellites the rate map shows a clear deformation gradient associated with the fault but slightly offset to the northeast from the surface trace joint inversion of insar rate map and gps data using monte carlo method we estimate a slip rate of 9 12 mm yr with a locking depth of 3 6 km at the 90 confidence level the slip rate agrees with the holocene fault slip rate and the historical earthquakes our results also suggest no significant across fault extension in the future insar data from both ascending and descending orbits may further constrain the 3 d fault slip rate on this fault

deciphering vertical deformation and poroelastic parameters in a tectonically active fault bound aquifer using insar and well level data san bernardino basin california summary using insar and hydrogeologic time series spanning 1995 to 2000 we characterize the elastic storage and surface deformation in the vicinity of the san bernardino basin california the region encompasses a complex major aquifer located at the junction of the san andreas and san jacinto faults that supplies groundwater to over 600 000 people we remove the elastic vertical surface displacement associated with changes in groundwater levels from the insar time series by a least squares inversion our method estimates a poroelastic ratio at 60 well sites which we normalize by basin depth allowing for comparison of the elastic response of the aquifer skeleton from site to site our method also estimates residual vertical displacement rates at each well site surface displacement not explained by observed trends in groundwater levels residual vertical displacement rates reveal patterns of subsidence and uplift across the basin over the 5 yr period from 1995 to 2000 in a narrow zone of observed residual subsidence near the san jacinto fault where many normalized poroelastic ratios trend higher than expected we find permanent compaction of clay rich strata to be the most likely explanation for 0 5 2 0 mm yr 1 of residual subsidence this permanent compaction is likely a result of delayed compaction due to previous overdraft conditions and or a result of the installation of deep production wells during the span of the insar time series observations of localized subsidence within stepovers of the san jacinto fault zone and relative uplift at the range fronts are consistent with current basin development models however interseismic strain modelling of the regional faults does not reproduce the surface displacement pattern or magnitude of these observations

the extreme melt across the greenland ice sheet in 2012 1 the discovery of the 2012 extreme melt event across almost the entire surface of the greenland ice sheet is presented data from three different satellite sensors including the oceansat 2 scatterometer the moderate resolution imaging spectroradiometer and the special sensor microwave imager sounder are combined to obtain composite melt maps representing the most complete melt conditions detectable across the ice sheet satellite observations reveal that melt occurred at or near the surface of the greenland ice sheet across 98 6 of its entire extent on 12 july 2012 including the usually cold polar areas at high altitudes like summit in the dry snow facies of the ice sheet this melt event coincided with an anomalous ridge of warm air that became stagnant over greenland as seen in melt occurrences from multiple ice core records at summit reported in the published literature such a melt event is rare with the last significant one occurring in 1889 and the next previous one around seven centuries earlier in the medieval warm period given its rarity the 2012 extreme melt across greenland provides an exceptional opportunity for new studies in broad interdisciplinary geophysical research

advanced interferometric synthetic aperture radar insar time series analysis using interferograms of multiple orbit tracks a case study on miyake jima 1 insar time series analysis is an effective tool for detecting spatially and temporally complicated volcanic deformation to obtain details of such deformation we developed an advanced insar time series analysis using interferograms of multiple orbit tracks considering only right or only left looking sar observations incidence directions for different orbit tracks are mostly included in a common plane therefore slant range changes in their interferograms can be expressed by two components in the plane this approach estimates the time series of their components from interferograms of multiple orbit tracks by the least squares analysis and higher accuracy is obtained if many interferograms of different orbit tracks are available additionally this analysis can combine interferograms for different incidence angles in a case study on miyake jima we obtained a deformation time series corresponding to gps observations from palsar interferograms of six orbit tracks the obtained accuracy was better than that with the sbas approach demonstrating its effectiveness furthermore it is expected that higher accuracy would be obtained if sar observations were carried out more frequently in all orbit tracks the deformation obtained in the case study indicates uplift along the west coast and subsidence with contraction around the caldera the speed of the uplift was almost constant but the subsidence around the caldera decelerated from 2009 a flat deformation source was estimated near sea level under the caldera implying that deceleration of subsidence was related to interaction between volcanic thermal activity and the aquifer

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

an improved mass budget for the greenland ice sheet extensive ice thickness surveys by nasa s operation icebridge enable over a decade of ice discharge measurements at high precision for the majority of greenland s marine terminating outlet glaciers prompting a reassessment of the temporal and spatial distribution of glacier change annualmeasurements for 178 outlet glaciers reveal that despite widespread acceleration only 15 glaciers accounted for 77 of the 739 29 gt of ice lost due to acceleration since 2000 and four accounted for 50 among the top sources of loss are several glaciers that have received little scientific attention the relative contribution of ice discharge to total loss decreased from 58 before 2005 to 32 between 2009 and 2012 as such 84 of the increase in mass loss after 2009 was due to increased surface runoff these observations support recentmodel projections that surface mass balance rather than ice dynamics will dominate the ice sheet s contribution to 21st century sea level rise

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

quantitative evidence that compaction of holocene sediments drives the present land subsidence of the po delta italy 1 deltas are highly dynamic coastal systems that over the last few decades have generally experienced a substantial area loss caused by trapping of river sediments in upland drainage basins as well as land subsidence due to natural and anthropogenic causes a major example is the po delta in the mediterranean in northeastern italy this area has experienced as much as 3 m of land subsidence from the 1930s to the 1970s primarily because of the extraction of gas bearing waters however present subsidence rates are largely unknown and the ground settlement is supposedly controlled by natural long term deep processes we have combined radar interferometric point target analysis ipta with previous geomorphological investigations on aerial satellite images and seismic surveys and geochronological data from core samples and geomechanical in situ tests to assess the current sinking of the delta and to understand the processes controlling the vertical movement the high density of the measurable point targets more than 15 000 allows characterization of the spatial variation in the vertical land motions vlm ranging from 1 to 15 mm yr we find that subsidence rates are significantly correlated with the age of highly compressible holocene deposits that compose the shallowest 30 40 m of the sedimentary sequence a typical log type consolidation equation applicable at the scale of the entire delta has been obtained we conclude that the consolidation of late holocene sediments is the major cause of the present land subsidence in the po river delta this finding has significant impact on the understanding of many other modern deltas that were formed in the lower holocene epoch

greenland ice sheet melt extent 1979 1999 analysis of melt extent on the greenland ice sheet is updated to span the time period 1979 1999 and examined along with its spatial and temporal variability using passive microwave satellite data to acquire the full record the issue of continuity between the previous passive microwave sensors smmr ssm i f 8 and ssm i f 11 and the most recent ssm i f 13 sensor is addressed the f 13 cross polarized gradient ratio melt classification threshold is determined to be 0 0154 results show that for the 21 year record a positive melt trend of nearly 1 yr is observed but this trend falls just below the 90 significance level the observed melt increase does appear to be driven by conditions in the western portion of the ice sheet rather than the east where melt appears to have decreased slightly moreover the eruption of mount pinatubo in 1991 is likely to have had some impact on the melt but not so much as previously suspected the 1992 melt anomaly is 1 7 standard deviations from the mean finally the relationship between coastal temperatures and melt extent suggests an increase in surface runoff contribution to sea level of 0 31 mm yr for a 1 c temperature rise

continental deformation in asia from a combined gps solution 1 after decades of research on continental tectonics there is still no consensus on the mode of deformation of continents or on the forces that drive their deformation in asia the debate opposes edge driven block models requiring a strong lithosphere with strain localized on faults to buoyancy driven continuous models requiring a viscous lithosphere with pervasive strain discriminating between these models requires continent wide estimates of lithospheric strain rates previous efforts have relied on the resampling of heterogeneous geodetic and quaternary faulting data sets using interpolation techniques we present a new velocity field based on the rigorous combination of geodetic solutions with relatively homogeneous station spacing avoiding technique dependent biases inherent to interpolation methods we find 1 unresolvable strain rates 3 109 yr over a large part of asia with current motions well described by block or microplate rotations and 2 internal strain possibly continuous limited to high elevation areas

interseismic strain accumulation and anthropogenic motion in metropolitan los angeles 1 we use global positioning system gps geodesy and synthetic aperture radar sar interferometry to distinguish between interseismic strain accumulation and anthropogenic motion in metropolitan los angeles we establish a relationship between horizontal and vertical seasonal oscillations of the santa ana aquifer use this relationship to infer cumulative horizontal anthropogenic motions from cumulative vertical motions caused by water and oil resource management and estimate horizontal interseismic velocities corrected for anthropogenic effects vertical anthropogenic rates from 1992 to 1999 are slower than 3 mm yr 1 in the santa ana and san gabriel aquifers and faster than 5 mm yr 1 in the chino aquifer and in many oil fields inferred horizontal anthropogenic velocities are faster than 1 mm yr 1 at 18 of 46 gps sites northern metropolitan los angeles is contracting with the 25 km south of the san gabriel mountains shortening at 4 5 1 mm yr 1 95 confidence limits the thrust fault in an elastic edge dislocation model of the observed strain is creeping at 9 2 mm yr 1 beneath and north of a position 6 2 km deep and 8 8 km north of downtown los angeles the model fault is near the los angeles segment of the puente hills thrust but south of the sante fe springs segment of the thrust disagreement between the 6 km locking depth in the model and the 15 km seismogenic depth inferred from earthquakes suggests that the elastic continuum model may be unsatisfactory models with different stiffnesses of sedimentary basin and crystalline basement must be investigated

permanent scatterer insar reveals seasonal and long term aquifer system response to groundwater pumping and artificial recharge received 4 may 2007 revised 30 july 2007 accepted 10 october 2007 published 5 february 2008 1 permanent scatterer insar psinsark p rovides an ew high resolution methodology for detecting and precisely measuring long term and seasonal aquifer system response to pumping and recharge in contrast to conventional insar the permanent scatterer methodology utilizes coherent radar phase data from thousands of individual radar reflectors on the ground to develop displacement time series and to produce velocity field maps that depict aquifer system response with a high degree of spatial detail in this study we present the first results of a prototype study in las vegas valley nevada that demonstrate how this methodology can be utilized in heavily pumped groundwater basins to analyze aquifer system response to long term and seasonal pumping we have developed a series of velocity field maps of the valley for the 1992 1996 1996 2000 and 2003 2005 time periods that show that despite rising water levels associated with an artificial recharge program long term residual inelastic aquifer system compaction subsidence is continuing in several parts of the valley in other areas however long term subsidence has been arrested and locally reversed the seasonal elastic responses to alternating pumping and recharge cycles were segregated from the long term trends and analyzed for spatial and temporal patterns the results show oscillations in which the maximum seasonal responses are associated with the late stages of the annual artificial recharge cycles and that similar seasonal subsidence signals are related to summer pumping cycles the differentiation of the seasonal response through the use of time series data further allows the estimation of elastic and inelastic skeletal storage coefficients providing a basis for future work that could characterize the storage properties of an aquifer system with a high degree of spatial resolution

the 1994 sefidabeh eastern iran earthquakes revisited new evidence from satellite radar interferometry and carbonate dating about the growth of an active fold above a blind thrust fault in 1994 three shallow earthquakes of mw 6 occurred close together on blind thrusts near sefidabeh in eastern iran in an earlier study of the teleseismic waveforms the geomorphology and the faulting in the epicentral region it was suggested that these earthquakes were associated with the growth of a ridge above a blind thrust fault system whose activity could be detected by its effect on the surface drainage in this study we present a sar interferogram that precisely determines the location and amount of coseismic surface displacements showing that the earthquakes in the sefidabeh sequence probably occurred on en echelon fault segments associated with three stepping ridges we also present u th dates of 100 ka for lake deposits uplifted by the growing ridge from the cumulative dated uplift and knowledge of the surface displacements due to an earthquake sequence we estimate that 120 such events have occurred in the past 100 ka with an average recurrence interval of 830 yr and an average convergence rate of 1 5 mm yr 1 on the sefidabeh thrust each estimate has an uncertainty of a factor of two either way we argue that the sefidabeh fault originally formed by coalescence of many small fault segments and has grown in length at about 2 cm yr 1 in the past 100 ka though the coseismic surface deformation observed in the sar interferogram closely resembles folding the overall topography does not because of inherited topography associated with earlier geological deformation in spite of this the activity of the buried thrust fault can easily be detected by its effect on the surface drainage a significant lesson when interpreting landscapes that are not entirely due to the present day deformation

recent changes in arctic sea ice melt onset freezeup and melt season length 1 in order to explore changes and trends in the timing of arctic sea ice melt onset and freezeup and therefore melt season length we developed a method that obtains this information directly from satellite passive microwave data creating a consistent data set from 1979 through present we furthermore distinguish between early melt the first day of the year when melt is detected and the first day of continuous melt a similar distinction is made for the freezeup using this method we analyze trends in melt onset and freezeup for 10 different arctic regions in all regions except for the sea of okhotsk which shows a very slight and statistically insignificant positive trend 0 4 d decade 1 trends in melt onset are negative i e toward earlier melt the trends range from 1 0 d decade 1 for the bering sea to 7 3 d decade 1 for the east greenland sea except for the sea of okhotsk all areas also show a trend toward later autumn freeze onset the chukchi beaufort seas and laptev east siberian seas observe the strongest trends with 7 d decade 1 for the entire arctic the melt season length has increased by about 20 days over the last 30 years largest trends of over 10 d decade 1 are seen for hudson bay the east greenland sea the laptev east siberian seas and the chukchi beaufort seas those trends are statistically significant at the 99 level

a sea ice free summer arctic within 30 years an update from cmip5 models interpreted as sea ice extent less than 1 0 million km 2 w e consider this estimate to be still valid based on projections of updated climate models cmip5 and observational data similar to previous models cmip3 cmip5 still shows a wide spread in hindcast and projected sea ice loss among different models further there is no consensus in the scientific literature for the cause of such a spread in results for cmip3 and cmip5 while cmip5 model mean sea ice extents are closer to observations than cmip3 the rates of sea ice reduction in most model runs are slow relative to recent observations all cmip5 models do show loss of sea ice due to increased anthropogenic forcing relative to preindustrial control runs applying the same technique of model selection and extrapolation approach to cmip5 as we used in our previous paper the interval range for a nearly sea ice free arctic is 14 to 36 years with a median value of 28 years relative to a 2007 baseline this suggests a nearly sea ice free arctic in the 2030s citation wang m and j e overland 2012 a sea ice free summer arctic within 30 years an update from cmip5 models geophys res lett 39 l18501

the melting arctic and midlatitude weather patterns are they connected abstractthe potential of recent arctic changes to influence hemispheric weather is a complex and controversial topic with considerable uncertainty as time series of potential linkages are short 10 yr and understanding involves the relative contribution of direct forcing by arctic changes on a chaotic climatic system a way forward is through further investigation of atmospheric dynamic mechanisms during several exceptionally warm arctic winters since 2007 sea ice loss in the barents and kara seas initiated eastward propagating wave trains of high and low pressure anomalous high pressure east of the ural mountains advected arctic air over central and eastern asia resulting in persistent cold spells blocking near greenland related to low level temperature anomalies led to northerly flow into eastern north america inducing persistent cold periods potential arctic connections in europe are less clear variability in the north pacific can reinforce downstream arctic changes and arctic amplification

surface melt induced acceleration of greenland ice sheet flow ice flow at a location in the equilibrium zone of the west central greenland ice sheet accelerates above the midwinter average rate during periods of summer melting the near coincidence of the ice acceleration with the duration of surface melting followed by deceleration after the melting ceases indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice bedrock interface interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting with larger increases accompanying higher amounts of summer melting the indicated coupling between surface melting and ice sheet flow provides a mechanism for rapid large scale dynamic responses of ice sheets to climate warming

a borehole flowmeter investigation of small scale hydraulic conductivity variation in the biscayne aquifer florida geostatistical analysis of closely spaced borehole flowmeter measurements was used to estimate the variance 2 53 and vertical and horizontal correlation lengths of ln k 0 57 and 7 3 m in the biscayne aquifer a limestone aquifer critical for florida s water supply and for everglades restoration efforts the variance and correlation lengths of the biscayne aquifer are similar to some of the values for unconsolidated siliciclastic sediments especially those at columbus mississippi the larger h for the biscayne aquifer 7 3 m is thought to be due at least in part to the lower lateral variability of the carbonate platform depositional environment compared to the fluvial environments in which the siliciclastic sediments were deposited an improved down hole packer would allow for data with finer vertical resolution the current system is adequate for work inside well screens but cannot adequately seal many spots in open irregular rock boreholes research in rock presents additional logistical difficulties but is important for addressing fundamental questions about solute transport in a wider range of geological media beyond unconsolidated siliciclastic deposits

multi interferogram method for measuring interseismic deformation denali fault alaska summary studies of interseismic strain accumulation are crucial to our understanding of continental deformation the earthquake cycle and seismic hazard by mapping small amounts of ground deformation over large spatial areas insar has the potential to produce continental scale maps of strain accumulation on active faults however most insar studies to date have focused on areas where the coherence is relatively good e g california tibet and turkey and most analysis techniques stacking small baseline subset algorithm permanent scatterers etc only include information from pixels which are coherent throughout the time span of the study in some areas such as alaska where the deformation rate is small and coherence very variable it is necessary to include information from pixels which are coherent in some but not all interferograms we use a three stage iterative algorithm based on distributed scatterer interferometry we validate our method using synthetic data created using realistic parameters from a test site on the denali fault alaska and present a preliminary result of 10 5 5 0 mm yr 1 for the slip rate on the denali fault based on a single track of radar data from ers1 2

greenland ice sheet surface melt and its relation to daily atmospheric conditions abstractmelt area is one of the most reliably monitored variables associated with surface conditions over the full greenland ice sheet gris surface melt is also an important indicator of surface mass balance and has potential relevance to the ice sheet s global sea level contribution melt events are known to be spatially heterogeneous and have varying time scales to understand the forcing mechanisms it is necessary to examine the relation between the existing conditions and melt area on the time scales that melt is observed here we conduct a regression analysis of atmospheric reanalysis variables including sea level pressure near surface winds and components of the surface energy budget with surface melt the regression analysis finds spatial heterogeneity in the associated atmospheric circulation conditions for basins in the southern gris there is an association between melt area and high pressure located south of the denmark strait which allows for southerly flow over the western half of th

multiscale insar time series mints analysis of surface deformation 1 we present a new approach to extracting spatially and temporally continuous ground deformation fields from interferometric synthetic aperture radar insar data we focus on unwrapped interferograms from a single viewing geometry estimating ground deformation along the line of sight our approach is based on a wavelet decomposition in space and a general parametrization in time we refer to this approach as mints multiscale insar time series the wavelet decomposition efficiently deals with commonly seen spatial covariances in repeat pass insar measurements since the coefficients of the wavelets are essentially spatially uncorrelated our time dependent parametrization is capable of capturing both recognized and unrecognized processes and is not arbitrarily tied to the times of the sar acquisitions we estimate deformation in the wavelet domain using a cross validated regularized least squares inversion we include a model resolution based regularization in order to more heavily damp the model during periods of sparse sar acquisitions compared to during times of dense acquisitions to illustrate the application of mints we consider a catalog of 92 ers and envisat interferograms spanning 16 years in the long valley caldera ca region mints analysis captures the ground deformation with high spatial density over the long valley region

geomorphologic changes in the lower pearl river delta 1850 2015 largely due to human activity abstract we use 165 years of navigational and bathymetric data and 60 years of sediment discharge data to document and explain geomorphic changes in the pearl river delta prd and its estuary which in recent years has experienced rapid urbanization and explosive economic growth a series of british and chinese navigation charts dating back to 1850 show that since then the prd has gained 1160 km2 of new land most of it reclaimed land derived from disposal of dredge spoils accordingly the prd estuary has decreased by 35 in ocean area and by 39 in water volume changes were most dramatic in the western part of the delta where the modaomen and huangmao seas decreased in ocean area by 62 and 39 respectively to the east upper lingding bay ldb decreased in ocean area by 36 in contrast the lower part of ldb decreased by only 3 in area although shoaling more by than 2 m some of which may come via influx of sediment from the south china sea since 1995 the rate of land accretion in the prd has declined to 40 of what it was over the previous 145 years and to

3d characterization of microbially induced carbonate precipitation in rock fracture and the resulted permeability reduction abstract a new seepage control method for fractured rock is biogrouting through a microbially induced calcite precipitation micp process a study on the spatial distribution of biogrout in a rock fracture and its effect on permeability reduction is presented in this paper a series of experiments together with 3d scanning and 3d flow simulation were performed on rock fractures with various initial apertures treated by bio grouting a lognormal distribution of micp precipitates along the flow direction in a fracture was observed the 3d flow simulation of biogrouted fracture has revealed that the routinely adopted parallel plate model cubic law for estimating permeability of channel flow is no longer applicable when the fracture aperture is less than the critical value of 0 7 mm based on this study this is because partially clogging will occur when the fracture aperture is less than the critical value resulting in a transition of the flow type from surface flow to channel flow a semi empirical equation which can account for the effect of flow type has been proposed for estimating the permeability reduction due to bio grouting for rock fractures

satellite radar interferometry time series analysis of surface deformation for los angeles california 1 the los angeles california metropolitan area is a tectonically active region with surface deformation that is a combination of fault related tectonics plus a variety of natural and anthropogenic signals we apply the small baseline subset sbas algorithm to produce an interferometric synthetic aperture radar insar time series analysis for the los angeles area using data acquired by the ers satellites from late 1995 into 2002 the result is a space time deformation product that can be exploited to view not only the smoothly varying long term surface motion but also its time varying patterns large seasonal oscillations of the santa ana aquifer observed in southern california integrated gps network scign data are accurately matched in the insar time series moreover correlations of the insar time series with an annual sinusoid allows us to investigate the dynamics of the hydrologic system index terms 1243 geodesy and gravity space geodetic surveys 1294 geodesy and gravity instruments and techniques 1803 hydrology anthropogenic effects citation lanari r p lundgren m manzo and f casu 2004 satellite radar interferometry time series analysis of surface deformation for los angeles california geophys res lett 31 l23613 doi 10 1029 2004gl021294

impact of anthropogenic subsidence on relative sea level rise in the fraser river delta subsidence is a common cause of amplified relative sea level rise flooding and erosion in coastal environments in particular subsidence due to sediment consolidation can play a significant role in relative sea level rise in large deltas we use a combination of insar interferometric synthetic aperture radar leveling and global positioning system data to map absolute vertical land motion in the fraser river delta western canada we show that primary consolidation of shallow holocene sediments is the main cause for the slow subsidence 1 to 2 mm a affecting the delta lowlands in addition parts of the delta undergo increased anthropogenic subsidence rapid subsidence rates 3 to 8 mm a are associated with recent artificial loads and exhibit a first order exponential decrease with a time constant of 20 years consistent with the theory of consolidation assuming two sea level rise scenarios of 30 or 100 cm by the end of the twenty first century natural subsidence will augment relative sea level rise in the fraser holocene lowlands by 50 or 15 anthropogenic subsidence will augment relative sea level rise by 130 or 40 potentially raising it to as much as 1 2 m in deltaic lacustrine and alluvial environments anthropogenic sediment consolidation can result in significant amplification and strong spatial variations of relative sea level rise that need to be considered in local planning

measurement of interseismic strain accumulation across the north anatolian fault by satellite radar interferometry in recent years interseismic crustal velocities and strains have been determined for a number of tectonically active areas through repeated measurements using the global positioning system the terrain in such areas is often remote and difficult and the density of gps measurements relatively sparse in principle satellite radar interferometry can be used to make millimetric precision measurements of surface displacement over large surface areas in practice the small crustal deformation signal is dominated over short time intervals by errors due to atmospheric topographic and orbital effects here we show that these effects can be overcome by stacking multiple interferograms after screening for atmospheric anomalies effectively creating a new interferogram that covers a longer time interval in this way we have isolated a 70 km wide region of crustal deformation across the eastern end of the north anatolian fault turkey the distribution of deformation is consistent with slip of 17 32 mm yr below 5 33 km on the extension of the surface fault at depth if the gps determined slip rate of 24 1 mm yr is accepted the locking depth is constrained to 18 6 km

spatial and temporal patterns of deformation at the tendaho geothermal prospect ethiopia abstract observations of ground deformation in east africa have been fundamental for unveiling the tectonics of continental rifting assessing the seismic and volcanic hazard to development and identifying geothermal resources here we investigate the active natural and anthropogenic processes in the tendaho graben afar using interferometric synthetic aperture radar insar collected by the envisat satellite in 2004 2010 we used the poly interferometric rate and time series estimation rate method to calculate displacement in satellite line of sight and a least square inversion to decompose the line of sight displacement into vertical and rift perpendicular components we observe two zones of deformation a 20 km wide circular region of subsidence located 10 km northeast of the town of semera with a maximum displacement rate of 5 cm yr and elongated zone 50 km of subsidence in the area of the geothermal prospect maximum rate of 4 cm yr the temporal characteristics of subsidence varies between these zones with an increase in subsidence rate observed in the circular region in august 2008 we used a bayesian inversion to find the best fitting source models and compared this to locations of seismicity and other geophysical observations the pattern of deformation is consistent with a combination of magmatic and geothermal processes but there does not appear to be a direct link to a sequence of dyke intrusions during 2005 2010 at manda hararo graben 60 km away but dynamic stress changes or deep crustal flow could account for the observations

melt induced speed up of greenland ice sheet offset by efficient subglacial drainage fluctuations in surface melting are known to affect the speed of glaciers and ice sheets but their impact on the greenland ice sheet in a warming climate remains uncertain although some studies suggest that greater melting produces greater ice sheet acceleration others have identified a long term decrease in greenland s flow despite increased melting here we use satellite observations of ice motion recorded in a land terminating sector of southwest greenland to investigate the manner in which ice flow develops during years of markedly different melting although peak rates of ice speed up are positively correlated with the degree of melting mean summer flow rates are not because glacier slowdown occurs on average when a critical run off threshold of about 1 4 centimetres a day is exceeded in contrast to the first half of summer when flow is similar in all years speed up during the latter half is 62 16 per cent less in warmer years consequently in warmer years the period of fast ice flow is three times shorter and overall summer ice flow is slower this behaviour is at odds with that expected from basal lubrication alone instead it mirrors that of mountain glaciers where melt induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient a model of ice sheet flow that captures switching between cavity and channel drainage modes is consistent with the run off threshold fast flow periods and later summer speeds we have observed simulations of the greenland ice sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage a simple model of basal lubrication alone misses key aspects of the ice sheet s response to climate warming

interferometric synthetic aperture radar gps integration interseismic strain accumulation across the hunter mountain fault in the eastern california shear zone 1 the principal limitations of interferometric synthetic aperture radar insar to measure subtle long wavelength deformation are uncertainties associated with the satellite orbits we propose a method to remove orbital phase errors from the insar data by integrating insar and continuous gps time series we model the along track variation of the baseline errors as second order polynomials and estimate the coefficients using the continuous gps measurements we apply this method to a 600 km long region encompassing the basin and range and the eastern california shear zone comparison of the corrected insar velocities with independent gps data shows that this method removes the long wavelength insar errors the insar data reveal a region of sharp variation in the line of sight velocity across the hunter mountain fault we model the deformation as interseismic elastic strain accumulation across a strike slip fault the modeling suggests a fault slip rate of 4 9 0 8 mm yr and a locking depth of 2 0 4 km the shallow locking depth suggests that the hunter mountain fault is a transfer fault between low angle normal faults in the area

mining related ground deformation in crescent valley nevada implications for sparse gps networks 1 we use the small baseline subset sbas insar algorithm to obtain radar line of sight deformation velocities for two adjacent sar swaths and invert the data for the 2 d velocity field in vertical and ground range direction the analysis reveals areas of rapid deformation caused by mining and agricultural activities in the crescent valley nevada usa the los displacements of up to 25 centimeters during the 1992 2002 period are caused by vertical and horizontal deformation about 8 mm yr horizontal velocity is detected 10 km from the bargen gps site lewi suggesting that the gps station may be moving in response to the water pumping in the basin and range anthropogenic ground deformation can extend several tens of kilometers from the basins into the bedrock of the ranges

nonlinear rise in greenland runoff in response to post industrial arctic warming the greenland ice sheet gris is a growing contributor to global sea level rise1 with recent ice mass loss dominated by surface meltwater runoff2 3 satellite observations reveal positive trends in gris surface melt extent4 but melt variability intensity and runoff remain uncertain before the satellite era here we present the first continuous multi century and observationally constrained record of gris surface melt intensity and runoff revealing that the magnitude of recent gris melting is exceptional over at least the last 350 years we develop this record through stratigraphic analysis of central west greenland ice cores and demonstrate that measurements of refrozen melt layers in percolation zone ice cores can be used to quantifiably and reproducibly reconstruct past melt rates we show significant p 0 01 and spatially extensive correlations between these ice core derived melt records and modelled melt rates5 6 and satellite derived melt duration4 across greenland more broadly enabling the reconstruction of past ice sheet scale surface melt intensity and runoff we find that the initiation of increases in gris melting closely follow the onset of industrial era arctic warming in the mid 1800s but that the magnitude of gris melting has only recently emerged beyond the range of natural variability owing to a nonlinear response of surface melting to increasing summer air temperatures continued atmospheric warming will lead to rapid increases in gris runoff and sea level contributions

seasonal subsidence and rebound in las vegas valley nevada observed by synthetic aperture radar interferometry analyses of areal variations in the subsidence and rebound occurring over stressed aquifer systems in conjunction with measurements of the hydraulic head fluctuations causing these displacements can yield valuable information about the compressibility and storage properties of the aquifer system historically stress strain relationships have been derived from paired extensometer piezometer installations which provide only point source data because of the general unavailability of spatially detailed deformation data areal stress strain relations and their variability are not commonly considered in constraining conceptual and numerical models of aquifer systems interferometric synthetic aperture radar insar techniques can map ground displacements at a spatial scale of tens of meters over 100 km wide swaths insar has been used previously to characterize larger magnitude generally permanent aquifer system compaction and land subsidence at yearly and longer timescales caused by sustained drawdown of groundwater levels that produces intergranular stresses consistently greater than the maximum historical stress we present insar measurements of the typically small magnitude generally recoverable deformations of the las vegas valley aquifer system occurring at seasonal timescales from these we derive estimates of the elastic storage coefficient for the aquifer system at several locations in las vegas valley these high resolution measurements offer great potential for future investigations into the mechanics of aquifer systems and the spatial heterogeneity of aquifer system structure and material properties as well as for monitoring ongoing aquifer system compaction and land subsidence

mass balance of the greenland ice sheet from 1958 to 2007 we combine estimates of the surface mass balance smb of the greenland ice sheet for years 1958 to 2007 with measurements of the temporal variability in ice discharge d to deduce the total ice sheet mass balance during that time period we find a robust correlation r2 0 83 between anomalies in smb and in d which we use to reconstruct a continuous series of total ice sheet mass balance we find that the ice sheet was losing 110 70 gt yr in the 1960s 30 50 gt yr or near balance in the 1970s 1980s and 97 47 gt yr in 1996 increasing rapidly to 267 38 gt yr in 2007 multi year variations in ice discharge themselves related to variations in smb cause 60 20 more variation in total mass balance smb and therefore dominate the ice sheet mass budget copyright 2008 by the american geophysical union

radar interferogram filtering for geophysical applications the use of sar interferometry is often impeded by decorrelation from thermal noise temporal change and baseline geometry power spectra of interferograms are typically the sum of a narrow band component combined with broad band noise we describe a new adaptive filtering algorithm that dramatically lowers phase noise improving both measurement accuracy and phase unwrapping while demonstrating graceful degradation in regions of pure noise the performance of the filter is demonstrated with sar data from the ers satellites over the jakobshavns glacier of greenland

broadscale postseismic deformation and lower crustal relaxation in the central bayankala block central tibetan plateau observed using insar data abstract we have generated a more than 500 km long postseismic deformation rate map and cumulative displacement time series in the central bayankala block of the tibetan plateau using envisat asar data from 2003 to 2010 by the rate stacking algorithm this rate map spans a period of 7 2 years and reveals that postseismic motion of 2001 kokoxili earthquake exhibits a striking signal dominating crustal deformation of the central bayankala block with a cross fault magnitude 9 11 mm yr in line of sight los 93 1 e the southern and northern parts of the postseismic deformation field exhibit different patterns and variable magnitudes reflecting asymmetry of the displacement distribution postseismic motion affects eastward extrusion of the central bayankala block which reaches 15 km north of the ganzi yushu fault to further investigate viscoelastic relaxation of the lower crust in this area after approximately two years e m e m m and e s models are constructed the result shows that the best fit viscosity for the lower crust is about 1 1019 pa s comparison between cumulative displacements resolved by these three models shows that viscoelastic relaxation of the lower crust makes the most significant contribution to postseismic stress relaxation after 2001 event

greenland ice sheet melt from modis and associated atmospheric variability daily june july melt fraction variations over the greenland ice sheet gis derived from the moderate resolution imaging spectroradiometer modis 2000 2013 are associated with atmospheric blocking forming an omega shape ridge over the gis at 500 hpa height blocking activity with a range of time scales from synoptic waves breaking poleward 5 days to full fledged blocks 5 days brings warm subtropical air masses over the gis controlling daily surface temperatures and melt the temperature anomaly of these subtropical air mass intrusions is also important for melting based on the years with the greatest melt 2002 and 2012 during the modis era the area average temperature anomaly of 2 standard deviations above the 14 year june july mean results in a melt fraction of 40 or more though the summer of 2007 had the most blocking days atmospheric temperature anomalies were too small to instigate extreme melting

drought driven transient aquifer compaction imaged using multitemporal satellite radar interferometry in unconsolidated heterogeneous aquifer systems low rates of pore pressure diffusion of applied effective stresses due to the drainage of thick low permeability clay rich layers with time constants of decades to centuries cause delayed residual permanent compaction and land subsidence current application of satellite differential radar interferometry dinsar differential interferometric synthetic aperture radar to estimate aquifer hydraulic properties compressibility and or storage in these systems is limited by the temporal availability of synthetic aperture radar data 1992 present in this paper we study the degree of aquifer compaction due to water extraction using dinsar through an example in southeast spain ground deformation data indicate large scale deformation and in particular the discovery of the highest rates of groundwater related land subsidence recorded in europe 10 cm yr affecting the guadalentin river basin 200 km 2 the largest tributary of the segura river modeling of the ground surface time series of the guadalentin basin indicates that deformation is mainly driven by nonlinear time delayed flow processes in the underlying aquifer after a drought period 1990 1995 the aquifer responded with an exponential decay of the land subsidence lasting 8 yr suggesting transient groundwater pore pressure flow we show that multitemporal satellite radar interferometry analysis and its modeling can be a stimulating way to study nonlinear soil mechanics and groundwater flows at aquifers a deeper understanding of such processes could help the management of water resources and land subsidence of unconsolidated coastal and quaternary alluvial aquifers in a highly evolving climate region the mediterranean sea and elsewhere

permanent scatterer investigation of land subsidence in greater cairo egypt summary land subsidence is a major geomorphic problem commonly associated with densely populated areas such as the greater cairo area prior to this study rates and patterns of land subsidence in greater cairo were not known the permanent scatterer interferometric approach has been applied in this study to detect and measure the magnitude and the spatial and temporal variations of subsidence in greater cairo thirty four interferometric synthetic aperture radar insar images acquired by the european radar satellites ers 1 and ers 2 during 1993 2000 have been used in this investigation the main contributing factors to the rate of land subsidence in greater cairo include natural sediment compaction tectonic activity and groundwater pumping however the measured rate of land subsidence is found significantly impacted by anthropogenic factors rather than natural factors the average measured rate of subsidence is approximately 7 mm yr 1 during the period of observation and the spatial and temporal patterns of land subsidence are demonstrated by a time series of surface deformation maps insar results show differential surface displacements along the major surface and subsurface faults and indicate pumping induced subsidence which is characterized by bowl shapes in districts of high population density the detected pattern of land subsidence in greater cairo implies a considerable contribution from the subway network as well the results from this interferometric investigation can be used to help mitigate the environmental impacts and potential consequences of land subsidence in the region

substantial contribution to sea level rise during the last interglacial from the greenland ice sheet during the last interglacial period the eemian global sea level was at least three metres and probably more than five metres higher than at present1 2 complete melting of either the west antarctic ice sheet or the greenland ice sheet would today raise sea levels by 6 7 metres but the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the west antarctic ice sheet3 with model studies attributing only 1 2 m of sea level rise to meltwater from greenland4 5 this result was considered consistent with ice core evidence4 although earlier work had suggested a much reduced greenland ice sheet during the last interglacial period6 here we reconsider the eemian evolution of the greenland ice sheet by combining numerical modelling with insights obtained from recent central greenland ice core analyses our results suggest that the greenland ice sheet was considerably smaller and steeper during the eemian and plausibly contributed 4 5 5 m to the sea level highstand during that period we conclude that the high sea level during the last interglacial period most probably included a large contribution from greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the west antarctic ice sheet

satellite geodetic imaging reveals internal deformation of western tibet 1 it is often assumed that the majority of the interseismic strain accumulates around the major mapped geological block boundaries however numerous recent earthquakes in the continents have occurred on faults that were previously unidentified existing deformation data from tibet are insufficiently dense to map the distribution of interseismic strain here we combine 265 interferograms formed from 166 radar images with gps data to constrain a high resolution velocity field covering 200 000 km2 of western tibet we confirm that the slip rate of the karakoram fault is low 6 mm yr but show that areas of focused strain do not coincide with the major fault structures some of this strain is due to postseismic relaxation after a mw 6 8 earthquake that occurred in 1996 on a structure that is difficult to identify in satellite imagery models of seismic hazard that rely on imperfect knowledge of the boundaries of crustal blocks can therefore underestimate hazard from unknown faults

glaciers dominate eustatic sea level rise in the 21st century ice loss to the sea currently accounts for virtually all of the sea level rise that is not attributable to ocean warming and about 60 of the ice loss is from glaciers and ice caps rather than from the two ice sheets the contribution of these smaller glaciers has accelerated over the past decade in part due to marked thinning and retreat of marine terminating glaciers associated with a dynamic instability that is generally not considered in mass balance and climate modeling this acceleration of glacier melt may cause 0 1 to 0 25 meter of additional sea level rise by 2100