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

fast recession of a west antarctic glacier satellite radar interferometry observations of pine island glacier west antarctica reveal that the glacier hinge line position retreated 1 2 0 3 kilometers per year between 1992 and 1996 which in turn implies that the ice thinned by 3 5 0 9 meters per year the fast recession of pine island glacier predicted to be a possible trigger for the disintegration of the west antarctic ice sheet is attributed to enhanced basal melting of the glacier floating tongue by warm ocean waters

mortality in england during the 1783 4 laki craters eruption 1783 4 has been recognised as a mortality crisis year in the population history of england this demographic incident coincides with the laki craters eruption iceland which began in june 1783 and fumigated many parts of europe with volcanic gases and particles many reports and proxy climate records implicate the volcanic cloud in meteorological anomalies including notably hot 1783 summer conditions in england and a severe subsequent winter we present here a detailed analysis of the geographical and temporal trends in english mortality data and interpret them in the light of the climatological records and observations of the pollutant cloud we show that there were two distinct crisis periods in august september 1783 and january february 1784 which together accounted for 20 000 extra deaths in both cases the east of england was the worst affected region possible causes for the two crisis periods are considered and we conclude that the timing and magnitude of the winter mortality peak can be explained by the severe cold of january 1784 the late summer mortality followed 1 2 months after the very hot july of 1783 and may also have been related to the weather with the time lag reflecting the relatively slow spread of enteric disease or the contraction of malaria however it is hard to explain the entire late summer anomaly by these high temperature causes we therefore consider that fine acid aerosol and or gases in the volcanic haze may also have contributed to the unusual august september mortality given that complex radiative and dynamical effects of the volcanic cloud are implicated in the climatic anomalies in 1783 4 it is likely that the laki craters eruption did play a role in the english mortality crises of the same period

monitoring landslides and tectonic motions with the permanent scatterers technique spaceborne differential synthetic aperture radar interferometry dinsar has already proven its potential for mapping ground deformation phenomena e g volcano dynamics however atmospheric disturbances as well as phase decorrelation have prevented hitherto this technique from achieving full operational capability these drawbacks are overcome by carrying out measurements on a subset of image pixels corresponding to pointwise stable reflectors permanent scatterers ps and exploiting long temporal series of interferometric data results obtained by processing 55 images acquired by the european space agency esa ers sar sensors over southern california show that the ps approach pushes measurement accuracy very close to its theoretical limit about 1 mm allowing the description of millimetric deformation phenomena occurring in a complex fault system a comparison with corresponding displacement time series relative to permanent gps stations of the southern california integrated gps network scign is carried out moreover the pixel by pixel character of the ps analysis allows the exploitation of individual phase stable radar targets in low coherence areas this makes spaceborne interferometric measurements possible in vegetated areas as long as a sufficient spatial density of individual isolated man made structures or exposed rocks is available the evolution of the ancona landslide central italy was analysed by processing 61 ers images acquired in the time span between june 1992 and december 2000 the results have been compared with deformation values detected during optical levelling campaigns ordered by the municipality of ancona the characteristics of ps gps and optical levelling surveying are to some extent complementary a synergistic use of the three techniques could strongly enhance quality and reliability of ground deformation monitoring d 2002 elsevier science b v all rights reserved

on the optimization of interferometric sar for topographic mapping spaceborne synthetic aperture radar sar provides the possibility of producing topographic maps and cartographically corrected radar images using an interferometric method the technique requires two sar images of the same area gathered from slightly separated positions the interferometric baseline may be optimized to minimize the topographic altitude error the altitude error caused by the radar system and the topography is discussed the simulation of an interferometric measurement based on ers 1 sar parameters is presented it is found that the terrain topography has a significant effect on the height error which in many cases is more severe than baseline decorrelation

x sar interferometry first results repeat pass interferometry data were acquired during the first and second sir c x sar missions in april and october 1994 this paper presents the first results from x sar interferometry at four different sites the temporal separations were one day and six months at two sites the coherence requirements were met resulting in high quality interferograms a digital elevation model in ground range geometry has been derived the limitations of the x sar interferometry are discussed

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

reducing ionospheric effects in insar data using accurate coregistration interferometric synthetic aperture radar insar is a valuable tool for the study of geophysical phenomena such as crustal deformation ice motion and structure and vegetation canopy depths but it is adversely affected by uncharacterized inhomogeneities in ionospheric propagation delay ionospheric disturbances distort both insar phase and correlation maps here we present a method to compensate ionospheric propagation variations using accurate image coregistration this significantly improves both the interferometric coherence and phase accuracy an azimuth gradient in the total electron content tec from a spatially variable ionosphere results in a range dependent azimuth phase gradient being added to the phase histories of the pixels being imaged these phase gradients are equivalent to doppler shifts and thus they cause azimuth offsets between the actual and imaged positions of the pixels measuring these offsets accurately permits estimation of the gradient and correction of the interferograms for much of the phase distortion resulting in more accurate estimates of coherence we show an example over greenland where the tec variation causes the correlation to drop from about 0 7 to about 0 2 in one region if spatially varying offsets are not accounted for it also adds an estimated 4 4 radians of interferometric phase over an 80 km insar scene after applying our algorithm we find that the correlation in regions affected by the ionospheric inhomogeneity becomes comparable to correlation in the rest of the image in a more challenging example over iceland we show that our method improves the correlation from 0 15 to 0 25 in some areas

paleomagnetism carried by crystal inclusions the effect of preferred crystallographic orientation abstract randomly oriented phlogopite crystals from a pegmatite contain submicroscopic inclusions of magnetite the inclusions have oblate magnetic fabrics subparallel to the ab crystal plane alternating field demagnetization of individual crystals shows that the remanence is influenced by the crystal symmetry of the phlogopite host the magnetizations isolated by alternating field demagnetization either cluster close to the a axis or scatter in the ab plane coarse grained igneous and metamorphic rocks can only record a paleofield direction accurately if there is a suitable orientation distribution of the rock forming minerals that host the ferromagnets an isotropic distribution of rock forming minerals is preferable but it is not obligatory rock forming minerals that have l fabrics or s fabrics with a strong l component are also suitable if they contain oblate inclusion fabrics of ferromagnets

satellite radar interferometry for monitoring ice sheet motion application to an antarctic ice stream satellite radar interferometry sri provides a sensitive means of monitoring the flow velocities and grounding line positions of ice streams which are indicators of response of the ice sheets to climatic change or internal instability the detection limit is about 1 5 millimeters for vertical motions and about 4 millimeters for horizontal motions in the radar beam direction the grounding line detected by tidal motions where the ice goes afloat can be mapped at a resolution of 0 5 kilometer the sri velocities and grounding line of the rutford ice stream antarctica agree fairly well with earlier ground based data the combined use of sri and other satellite methods is expected to provide data that will enhance the understanding of ice stream mechanics and help make possible the prediction of ice sheet behavior

norwegian sea surface palaeoenvironments of marine oxygen isotope stage 3 the paradoxical response of dinoflagellate cysts high resolution marine palynological data have been obtained from two very long sediment cores md952009 and md952010 retrieved from the southern norwegian sea the dinoflagellate cyst assemblages show pronounced fluctuations in composition which correlate strongly with magnetic susceptibility records and also mimic the 18 o signal of the gisp2 greenland ice core if focusing on the period from 48 to 30 cal kyr bp this correlation suggests a paradoxical response of the sea surface environments to the atmospheric conditions over greenland when the greenland 18 o signal reflects warm interstadial conditions the norwegian sea depicts cold sea surface temperatures with quasi perennial sea ice cover based on dinoflagellate cysts in contrast when the greenland 18 o records cold stadial periods the norwegian sea surface temperatures are warm based on dinoflagellate cysts probably linked to inflow of the north atlantic drift these results similar in both cores are contrary to those of previous studies and shed light on a possible decoupling of norwegian sea surface water conditions and atmospheric conditions over greenland this decoupling could be linked to an atmosphere ocean system behaving similar to that which the northern hemisphere is experiencing at present i e strongly variable owing to the north atlantic oscillation copyright 2002 john wiley sons ltd

confined aquifer head measurements and storage properties in the san luis valley colorado from spaceborne insar observations interferometric synthetic aperture radar insar a remote sensing technique for measuring centimeter level surface deformation is used to estimate hydraulic head in the confined aquifer of the san luis valley slv colorado reconstructing head measurements from insar in agricultural regions can be difficult as insar phase data are often decorrelated due to vegetation growth analysis of 17 l band alos palsar scenes acquired between january 2007 and march 2011 demonstrates that comprehensive insar deformation measurements can be recovered over the vegetated groundwater basin with an improved processing strategy local skeletal storage coefficients and time delays between the head change and deformation are estimated through a joint insar well data analysis insar subsidence estimates are transformed to head changes with finer temporal and spatial resolution than is possible using existing well records alone both insar and well data suggest that little long term water storage loss occurred in the slv over the study period and that inelastic compaction was negligible the seasonal head variations derived from insar are consistent with the existing well data at most locations where confined aquifer pumping activity dominates our results demonstrate the advantages of insar measurements for basin wide characterization of aquifer storage properties and groundwater levels over agricultural regions

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

aseismic slip and seismogenic coupling along the central san andreas fault we use high resolution synthetic aperture radar and gps derived observations of surface displacements to derive the first probabilistic estimates of fault coupling along the creeping section of the san andreas fault in between the terminations of the 1857 and 1906 magnitude 7 9 earthquakes using a fully bayesian approach enables unequaled resolution and allows us to infer a high probability of significant fault locking along the creeping section the inferred discreet locked asperities are consistent with evidence for magnitude 6 earthquakes over the past century in this area and may be associated with the initiation phase of the 1857 earthquake as creeping segments may be related to the initiation and termination of seismic ruptures such distribution of locked and creeping asperities highlights the central role of the creeping section on the occurrence of major earthquakes along the san andreas fault

detection of aquifer system compaction and land subsidence using interferometric synthetic aperture radar antelope valley mojave desert california interferometric synthetic aperture radar insar has great potential to detect and quantify land subsidence caused by aquifer system compaction insar maps with high spatial detail and resolution of range displacement 10 mm in change of land surface elevation were developed for a groundwater basin 103 km2 in antelope valley california using radar data collected from the ers 1 satellite these data allow comprehensive comparison between recent 1993 1995 subsidence patterns and those detected historically 1926 1992 by more traditional methods the changed subsidence patterns are generally compatible with recent shifts in land and water use the insar detected patterns are generally consistent with predictions based on a coupled model of groundwater flow and aquifer system compaction the minor inconsistencies may reflect our imperfect knowledge of the distribution and properties of compressible sediments when used in conjunction with coincident measurements of groundwater levels and other geologic information insar data may be useful for constraining parameter estimates in simulations of aquifer system compaction

the displacement field of the landers earthquake mapped by radar interferometry geodetic data obtained by ground or space based techniques can be used to infer the distribution of slip on a fault that has ruptured in an earthquake although most geodetic techniques require a surveyed network to be in place before the earthquake1 3 satellite images when collected at regular intervals can capture co seismic displacements without advance knowledge of the earthquake s location synthetic aperture radar sar interferometry first introduced4 in 1974 for topographic mapping5 8 can also be used to detect changes in the ground surface by removing the signal from the topography9 10 here we use sar interferometry to capture the movements produced by the 1992 earthquake in landers california11 we construct an interferogram by combining topographic information with sar images obtained by the ers 1 satellite before and after the earthquake the observed changes in range from the ground surface to the satellite agree well with the slip measured in the field with the displacements measured by surveying and with the results of an elastic dislocation model as a geodetic tool the sar interferogram provides a denser spatial sampling 100 m per pixel than surveying methods1 3 and a better precision 3 cm than previous space imaging techniques12 13

glacial interglacial instabilities of the western boundary under current during the last 365 kyr from sm nd ratios of the sedimentary clay size fractions at odp site 646 labrador sea we present 40 sm nd isotope measurements of the clay size 2 m fractions of sediments from the sout hern greenland rise odp 646 that span the last 365 kyr these data track changes in the relative supply o f fine particles carried into the deep labrador sea by the western boundary under current wbuc back to the fourth glacial interglacial cycles earlier studies reveal ed three general sources of particles to the core s ite i precambrian crustal material from canada greenland and or scandinavia north american shield nas ii palaeozoic or younger crustal material from east gr eenland nw europe and or western scandinavia young crust yc and iii volcanic material from iceland and the mid atlantic ridge mar clay size fractions from glacial sediments have the lowest nd isotopic ratios supplies of young crustal particles were si milar during glacial oxygen isotope stages ois 2 6 and 10 i n contrast the mean volcanic contributions decrease d relative to old craton material from ois 10 to ois 6 and the n from ois 6 to ois 2 the glacial ois 8 interval d isplays a mean sm nd ratio similar to those of interglacials ois 1 5 and 9 compared with other interglacials ois 7 was marked by a higher yc contribution but a similar 3 0 mar supply the overall nas contribution dropped by a factor of 2 during each glacial interglacial tran sition with the mar contribution broadly replacing it during interglacials to decipher between higher supplies and or dilution particle fluxes from each end memb er were estimated glacial nas fluxes were systematically h igher than interglacial fluxes during the time int erval examined fine particle supplies to the labrador se a were strongly controlled by proximal ice margin e rosion and thus echoed the glacial stage intensity in con trast the wbuc carried mar supplies from the eastern basins did not change significantly throughout the last 36 5 kyr except for a marked increase in surface sedi ments that suggests unique modern conditions distal wbuc controlled inputs from the northern and ne north atlant ic seem to have been less variable than proximal suppl ies linked with glacial erosion rate

cenozoic alongslope processes and sedimentation on the nw european atlantic margin based on studies of sediment accumulations deposited from and erode by alongslope flowing ocean currents on the european continental margin from porcupine ireland to lofoten norway the evolution of the cenozoic paleocirculation was reconstructed as part of the stratagem project there is evidence of ocean current controlled erosion and deposition in the rockall trough in the faeroe shetland channel and on the voring plateau since the late eocene although the circulation pattern remains ambiguous the late palaeogene flow in the rockall trough was almost probably driven by southerly derived tethyan outflow water the extent and strength of any northerly derived flow is uncertain from the early neogene early mid miocene there was a massive regional expansion of contourite drift development both in the north atlantic and in the norwegian greenland sea this was most probably related to the development of the faroe conduit the opening of the fram strait and the general subsidence of the greenland scotland ridge these may have combined to cause a considerable acceleration in the exchange and overflow of deep waters between the arctic and atlantic oceans an early late neogene late early pliocene regional erosional event has been ascribed to a vigorous pulse of bottom current activity most probably the result of a global reorganisation of ocean currents associated with the closure of the central american seaway during the late neogene contourites and sediment drifts developed in deep water basins between units of glacigenic sediments as well as infill of several paleo slide scars these sediments were derived from areas of bottom current erosion as well as from the development of plio pleistocene prograding sediment wedges incorporating the extensive sediment supply derived from shelf wide ice sheets presently a profound winnowing prevails along the shelf and upper slope due to the inflowing currents of atlantic water depocentres of sediments derived from the winnowing are located locally in lower slope embayments and in slide scars

deep water bottom current evolution in the northern south china sea during the last 150 kyr evidence from sortable silt grain size and sedimentary magnetic fabric abstract deep water bottom current dwbc plays a central role in global climate relative to the atlantic due to poor preservation of marine carbonate in the pacific sediments the evolution of pacific deepwater circulation is still unclear the south china sea scs connection to the pacific through luzon strait at a depth of about 2400 m offers a unique opportunity to monitor the changes of western pacific deep water circulation we present a magnetic and grain size analysis of two sediment cores pc111 and pc83 located in xisha trough northern scs in order to reconstruct past changes of dwbc during the last 150 kyrs variations in the mean size of sortable silt are interpreted to indicate past changes of dwbc which suggest abrupt millennial scale increasing dwbc strength during heinrich stadials hs1 hs2 hs3 hs4 hs5 hs6 hs7 hs8 hs9 hs10 hs11 for past 150 kyr the flow orientation of dwbc revealed by the anisotropy of magnetic susceptibility ams are mostly nw se direction in core pc111 and core pc83 which are both parallel to the local topography combined with the published studies we suggest the increase bottom current in northern scs during the heinrich stadials hs1 to hs11 times of weak north atlantic deep water formation demonstrating the tight coupling between the atlantic and pacific oceans

atmospheric effects in interferometric synthetic aperture radar surface deformation and topographic maps interferogram images derived from repeat pass spaceborne synthetic aperture radar systems exhibit artifacts due to the time and space variations of atmospheric water vapor other tropospheric variations such as pressure and temperature also induce distortions but the effects are smaller in magnitude and more evenly distributed throughout the interferogram than the wet troposphere term spatial and temporal changes of 20 in relative humidity lead to 10 cm errors in deformation products and perhaps 100 m of error in derived topographic maps for those pass pairs with unfavorable baseline geometries in wet regions such as hawaii these are by far the dominant errors in the spaceborne imaging radar c and x band synthetic aperature radar sir c x sar interferometric products the unknown time delay from tropospheric distortion is independent of frequency and thus multiwavelength measurements such as those commonly used to correct radar altimeter and global positioning system gps ionospheric biases cannot be used to rectify the error in the topographic case the errors may be mitigated by choosing interferometric pairs with relatively long baselines as the error amplitude is inversely proportional to the perpendicular component of the interferometer baseline for the sir c x sar hawaii data we found that the best longest baseline pair produced a map supporting 100 m contouring whereas the poorest baseline choice yielded an extremely noisy topographic map even at this coarse contour interval in the case of deformation map errors the result is either independent of baseline parameters or else very nearly so here the only solution is averaging of independent interferograms so in order to create accurate deformation products in wet regions many multiple passes may be required rules for designing optimal data acquisition and processing sequences for interferometric analyses in nondesert parts of the world are 1 to use the longest radar wavelengths possible within ionospheric scintillation and faraday rotation limits 2 for topography maximize interferometer baseline within decorrelation limits and 3 for surface deformation use multiple observations and average the derived products following the above recipe yields accuracies of 10 m for digital elevation models and 1 cm for deformation maps even in very wet regions such as hawaii

tidally induced variations in vertical and horizontal motion on rutford ice stream west antarctica inferred from remotely sensed observations to better understand the influence of stress changes over floating ice shelves on grounded ice streams we develop a bayesian method for inferring time dependent 3 d surface velocity fields from synthetic aperture radar sar and optical remote sensing data our specific goal is to observe ocean tide induced variability in vertical ice shelf position and horizontal ice stream flow thus we consider the special case where observed surface displacement at a given location can be defined by a 3 d secular velocity vector a family of 3 d sinusoidal functions and a correction to the digital elevation model used to process the sar data using nearly 9 months of sar data collected from multiple satellite viewing geometries with the cosmo skymed 4 satellite constellation we infer the spatiotemporal response of rutford ice stream west antarctica to ocean tidal forcing consistent with expected tidal uplift inferred vertical motion over the ice shelf is dominated by semidiurnal and diurnal tidal constituents horizontal ice flow variability on the other hand occurs primarily at the fortnightly spring neap tidal period m sf we propose that periodic grounding of the ice shelf is the primary mechanism for translating vertical tidal motion into horizontal flow variability causing ice flow to accelerate first and most strongly over the ice shelf flow variations then propagate through the grounded ice stream at a mean rate of 29 km d and decay quasi linearly with distance over 85 km upstream of the grounding zone

the temporal and spatial variability of the confined aquifer head and storage properties in the san luis valley colorado inferred from multiple insar missions interferometric synthetic aperture radar insar data from multiple satellite missions were combined to study the temporal and spatial variability of head and storage properties in a confined aquifer system on a decadal time scale the area of study was a 4 500 km2 agricultural basin in the san luis valley slv colorado we had available previous analyses of c band ers 1 2 data from june 1992 to november 2000 and l band alos palsar data from october 2009 to march 2011 we used c band envisat data to fill in the time period from november 2006 to july 2010 in processing the envisat data we successfully employed a phase interpolation between persistent scatterer pixels to reduce the impact of vegetation decorrelation which can significantly reduce the quality of c band insar data over agricultural basins in comparing the results from the l band alos data and c band envisat data in a 10 month overlapping time period we found that the shorter wavelength of c band insar allowed us to preserve small deformation signals that were not detectable using l band alos data a significant result was the finding that the elastic storage properties of the slv confined aquifer system remained stable over the 20 year time period and vary slowly in space allowing us to combine insar data acquired from multiple missions to fill the temporal and spatial gaps in well data the insar estimated head levels were validated with well measurements which indicate little permanent water storage loss over the study time period in the slv

improvements in long core measurement techniques applications in palaeomagnetism and palaeoceanography we report on new developments in the long core measurement techniques using u channels in connection with new small access cryogenic magnetometers with these new instruments u channel samples allow us to measure a wide range of magnetic parameters along entire core length with a spatial resolution and accuracy virtually equivalent to that obtained using discrete cubic samples an additional advantage is that the sediment disturbance when sampling is significantly less when using u channels we present comparisons of results from both continuous and discrete measurements and examine the effectiveness of minimal deconvolution using various techniques examples of continuous measurements of low field susceptibility nrm arm irm hrc from north atlantic deep sea cores show that it is possible to generate logs of combination of parameters related to rock magnetic characteristics of the sediments useful in palaeoceanography in particular the continuous method allows us to rapidly detect core regions with fast changing magnetic parameters useful for correlation between cores and also for understanding changes in palaeo environmental conditions the fast scan also allows us to detect regions of the core where the rock magnetic parameters are suitable or not suitable for palaeomagnetic studies related to changes in the geomagnetic field such as the relative changes in palaeointensity

release of arsenic to deep groundwater in the mekong delta vietnam linked to pumping induced land subsidence deep aquifers in south and southeast asia are increasingly exploited as presumed sources of pathogen and arsenic free water although little is known of the processes that may compromise their long term viability we analyze a large area 1 000 km2 of the mekong delta vietnam in which arsenic is found pervasively in deep pliocene miocene age aquifers where nearly 900 wells at depths of 200 500 m are contaminated there intensive groundwater extraction is causing land subsidence of up to 3 cm y as measured using satellite based radar images from 2007 to 2010 and consistent with transient 3d aquifer simulations showing similar subsidence rates and total subsidence of up to 27 cm since 1988 we propose a previously unrecognized mechanism in which deep groundwater extraction is causing interbedded clays to compact and expel water containing dissolved arsenic or arsenic mobilizing solutes e g dissolved organic carbon and competing ions to deep aquifers over decades the implication for the broader mekong delta region and potentially others like it across asia is that deep untreated groundwater will not necessarily remain a safe source of drinking water

late folding related magnetic foliation in the active ferdows northeastern iran thrust fold system abstract in this work we present new ams and structural results from the ferdows active fold thrust system lut block central iran ams analyses show that the miocene units of the upper red formation have a well defined magnetic fabric of tectonic origin with both magnetic lineation and magnetic foliation oriented parallel to the regional fold axes in most of the cases the magnetic fabric acquired when the bedding was still horizontal is related to different degrees of lps shortening in some other cases the magnetic foliation is vertical and oblique to the bedding suggesting that in the ferdows thrust fold structure a cleavage system not visible at the outcrop scale has been developed as a consequence of later shortening related to the activity of the thrust system responsible of the recent earthquakes in the area results from this study establish a relationships between the recent tectonics of the area and the evolution of the magnetic fabric and demonstrate that a well defined magnetic fabric of pure tectonic origin can also develop in poorly deformed rocks lacking field evidence of pervasive internal deformation

geometric calibration of ers satellite sar images geometric calibration of the european remote sensing ers satellite synthetic aperture radar sar slant range images is important in relation to mapping areas without ground reference points and also in relation to automated processing the relevant sar system parameters are discussed and calibrated by using the european space agency esa transponders at flevoland the resulting accuracy of the slant range images corresponds to 10 m horizontally on the ground the results are verified by using runway intersections and corner reflectors surveyed with differential gps techniques based on a seven year ers 1 and a four year ers 2 time series the long term stability is found to be sufficient to allow a single calibration covering the entire mission period a descending and an ascending orbit tandem pair of the esa calibration site on flevoland suitable for calibration of ers sar processors is described to allow other researchers to geometrically calibrate their processing systems

physical properties of reykjanes ridge sediments and their linkage to high resolution greenland ice sheet project 2 ice core data five gravity cores taken from the reykjanes ridge have been used to establish a link between sediment physical properties and atmospheric records documented by 18o variations in greenland ice cores over the last 45 000 calendar years marine gamma ray attenuation porosity evaluator density and magnetic susceptibility variations could be linked with the ice core dansgaard oeschger and bond cycles this is supported by ice rafted detritus ird grain size the quartz feldspar ratio and carbonate isotopic and foraminiferal records the covariation of the sediment physical properties and 18o in greenland ice indicates a coupling of atmospheric temperature and paleocirculation variations gradual reduced bottom currents iceland scotland overflow water and enhanced iceberg discharges have been reconstructed for cold atmospheric periods relative to interstadial times in the study area the magnetic susceptibility signal is not related to the ice rafted detritus input but most probably reflects the variations of the iceland scotland overflow water intensity transporting titanomagnetite into the reykjanes ridge region

postseismic rebound in fault step overs caused by pore fluid flow near field strain induced by large crustal earthquakes results in changes in pore fluid pressure that dissipate with time and produce surface deformation synthetic aperture radar sar interferometry revealed several centimeters of postseismic uplift in pull apart structures and subsidence in a compressive jog along the landers california 1992 earthquake surface rupture with a relaxation time of 270 45 days such a postseismic rebound may be explained by the transition of the poisson s ratio of the deformed volumes of rock from undrained to drained conditions as pore fluid flow allows pore pressure to return to hydrostatic equilibrium

compaction and inclination shallowing in deep sea sediments from the pacific ocean progressive downcore shallowing of the remanent inclination has been observed in a 120 m section of marine sediments at deep sea drilling project site 578 in the northwest pacific representing the past 6 5 m y near the top of the section the average inclination corresponds to the expected geocentric axial dipole value of 53 but shallows down section by about 6 to 8 northward translation of the pacific plate accounts for only about a quarter of the inclination shallowing moreover no inclination shallowing was observed at neighboring site 576 which has considerably lower sedimentation rates and the last 5 m y are represented by a 26 m sedimentary section we correlate the inclination shallowing at site 578 with an average decrease in porosity of 3 4 the porosities in the top 26 m at site 576 are slightly higher than at site 578 and show no definite trend downhole we interpret these results to suggest that both the downhole inclination shallowing and decrease of porosity in site 578 are caused by sediment compaction compaction does not play a significant role for the section at site 576 due to its much shorter length

rapid climatic variations during marine isotopic stage 3 magnetic analysis of sediments from nordic seas and north atlantic abstract the bulk magnetic parameters of seven deep sea cores distributed from the nordic seas 67 n to the north atlantic as far south as the bermuda rise 33 n exhibit short term variations which correlate with rapid climatic changes during marine isotopic stage 3 mis3 the magnetic mineralogy is uniformly dominated by well sorted low ti content magnetites indicating that these variations are due to variations in the relative amount of magnetic minerals because the magnetic minerals predominantly originate from one common source area the nordic basaltic province these changes arise from changes in the efficiency of the transport of the magnetic particles by deep currents from the source to the site of deposition these results therefore show that the fast climatic changes are related to coeval fast changes in the strength of the deep sea circulation the latter was active reduced during the interstadials stadials and heinrich events transporting the magnetic particles from the norwegian sea into the north atlantic ocean along a path similar to the present path of the nadw it is tentatively suggested that the faeroe shetland channel and the denmark strait were the only two active paths for the overflow water during mis3 the presence of magnetic oscillations in the bermuda rise core in phase with those from the north atlantic indicates that the activity of the southern newfoundland basin gyre was linked to that of the nadw during mis3

magnetic mineral diagenesis abstract reduction oxidation redox reactions occur during burial because sediments contain reactive mixtures of oxidised and reduced components diagenetic chemical reactions represent the approach of all sedimentary components toward equilibrium and control the long term stability of sedimentary iron bearing minerals magnetic minerals are sensitive indicators of sedimentary redox conditions and of changes in these conditions through time with diagenetic effects ranging from subtle to pervasive despite the importance of magnetic mineral diagenesis in paleomagnetism rock magnetism and environmental magnetism and the usefulness of these subjects in the earth and environmental sciences there is no systematic single published treatment of magnetic mineral diagenesis this paper is an attempt to provide such a treatment for the full range of diagenetic environments magnetic mineral diagenesis during early burial is driven largely by chemical changes associated with organic matter degradation in a succession of environments that range from oxic to nitrogenous to manganiferous to ferruginous to sulphidic to methanic where the free energy yielded by different oxidants decreases progressively in each environment in oxic environments the most important diagenetic processes involve surface oxidation of detrital minerals and precipitation of fe3 bearing minerals from solution in ferruginous environments the most reactive detrital and authigenic iron oxides undergo dissolution often mediated by dissimilatory iron reducing bacteria which releases fe2 that becomes available for other reactions the fe2 in solution can diffuse upward where it is oxidised to form new authigenic iron oxyhydr oxide minerals or it can become bioavailable to enable magnetotactic bacteria to biomineralise magnetite generally at the base of the overlying nitrogenous zone alternatively dissimilatory iron reducing bacteria can produce extracellular magnetite within ferruginous environments in sulphidic environments iron bearing detrital mineral assemblages undergo more radical alteration hydrogen sulphide which is a byproduct of bacterial sulphate reduction or of anaerobic oxidation of methane reacts with the fe2 released from iron mineral dissolution or directly with solid iron oxyhydr oxide minerals to form iron sulphide minerals mackinawite greigite and pyrite authigenic growth of ferrimagnetic greigite has important implications for paleomagnetic recording secondary iron sulphide formation can also occur as a result of anaerobic oxidation of methane methane migration through sediments in association with biogenic or thermogenic methane production or in association with gas hydrate dissociation can disrupt the diagenetic steady state and give rise to greigite and monoclinic pyrrhotite formation that remagnetises sediments most of the above described diagenetic processes occur below 50 c with continuing burial above 50 c but at sub metamorphic temperatures magnetic minerals can undergo further thermally induced chemical changes that give rise to a wide range of mineralogical transformations that affect the magnetic record of the host sediment these changes include remagnetisations magnetic analysis can provide much valuable information concerning diagenesis in environmental processes the range of processes discussed in this paper should assist researchers in analysing sediment magnetic properties for which the assessment of diagenetic effects has become a necessary component

rock magnetic properties of the gardar drift sedimentary sequence site iodp u1314 north atlantic implications for bottom current change through the mid pleistocene abstract the sediment obtained at integrated ocean drilling program iodp site u1314 on the gardar drift in the eastern flank of the reykjanes ridge was analyzed using rock magnetic techniques to study the depositional environment through the mid pleistocene climate transition the study area is under the influence of iceland scotland overflow water isow consequently the sedimentary record represents directly isow behavior over time a change in the depositional environment was documented as magnetic property changes that are the result of changes in concentration and grain size of magnetic minerals both of which decrease upward from around 0 9 ma because these shifts are accompanied by a change in magnetic fabrics which is interpreted as a change in bottom current directions from e w to nne ssw it is considered that the sedimentation pattern inferred from magnetic records at the site was modified by a change in the bottom current through the middle pleistocene

change of apparent segmentation of the san andreas fault around parkfield from space geodetic observations across multiple periods sequences of earthquakes are commonly represented as a succession of periods of interseismic stress accumulation followed by coseismic and postseismic phases of stress release because the recurrence time of large earthquakes is often greater than the available span of space geodetic data it has been challenging to monitor the evolution of interseismic loading in its entire duration here we analyze large data sets of surface deformation at different key episodes around the cholame parkfield and creeping segments of the san andreas fault that show evidence of significant deceleration of fault slip during the interseismic period we compare the average fault slip rates before and after the 2004 mw6 parkfield earthquake in the 1986 2004 and 2006 2012 periods respectively avoiding 2 years of postseismic deformation after 2004 using a combination of gps data from the plate boundary observatory the southern california earthquake center crustal motion map and the bay area velocity unification networks and interferometric synthetic aperture radar from the advanced land observing satellite alos and envisat satellites we show that the area of coupling at the transition between the parkfield and cholame segments appears larger later in the interseismic period than it does earlier on while strong plate coupling is uniform across the parkfield and cholame segments in the 1986 2004 period creep occurs south of the 2004 epicenter after 2006 making segmentation of the san andreas fault south of parkfield more clearly apparent these observations indicate that analyses of surface deformation late in the earthquake cycle may overestimate the area of plate coupling a fault surface creeping much below plate rate may in some case be a region that does not promote earthquake nucleation but rather just be at a slower stage of its evolution our analysis also shows signs of large variation of slip velocity above and below plate rate in the creeping segment indicating that cycles of weakening and hardening can also be at play in dominantly aseismic areas

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

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

interferometric radar observations of glaciares europa and penguin hielo patagonico sur chile repeat pass l band interferometric synthetic aperture radar insar data for part of hielo patagonico sur chile were collected by the space shuttle based spaceborne imaging radar c sir c over a 4 day span in october 1994 three co registered complex sar images are used to generate phase coherence maps a digital elevation model dem and an ice velocity map the phase coherence maps indicate low coherence in the 5 15 km approaching the termini due to large displacements ice deformation and melting however the coherence is high over nearly all of the remaining imaged icefield ice velocity precision is greater than 2 cm d 1 while the dem is good to about 25 m a flow divide between two of the glaciers is mapped by locating a narrow band of near zero ice velocity horizontal ice surface velocity profiles calculated along flowlines show there is a high degree ofspatial variability reaching a peak value of 5 5 m d 1 located 3 5 km from the terminus of glaciar europa longitudinal strain rates along the center lines calculated from these velocities at the locations of the initiation of crevassing are used to compute the tensile strength of ice 169 224 kpa

accuracy and resolution of alos interferometry vector deformation maps of the father s day intrusion at kilauea we assess the spatial resolution and phase noise of interferograms made from l band advanced land observing satellite alos synthetic aperture radar sar data and compare these results with corresponding c band measurements from european space agency remote sensing satellite ers based on cross spectral analysis of phase gradients we find that the spatial resolution of alos interferograms is 1 3times better than ers interferograms the phase noise of alos i e line of sight precision in the 100 5000 m wavelength band is 1 6times worse than ers 3 3 mm versus 2 1 mm in both cases the largest source of error is tropospheric phase delay vector deformation maps associated with the june 17 2007 father s day intrusion along the east rift zone of the kilauea volcano were recovered using just four alos sar images from two look directions comparisons with deformation vectors from 19 continuous gps sites show rms line of site precision of 14 mm and rms azimuth precision flight direction of 71 mm this azimuth precision is at least 4times better than the corresponding measurements made at c band phase coherence is high even in heavily vegetated areas in agreement with previous results this improved coherence combined with similar or better accuracy and resolution suggests that l band alos will outperform c band ers in the recovery of slow crustal deformation

geodetically accurate insar data processor we present a new interferometric synthetic aperture radar insar processing approach that capitalizes on the precise orbit tracking that is available with modern radar satellites our method uses an accurate orbit information along with motion compensation techniques to propagate the radar echoes to positions along a noninertial virtual orbit frame in which the location and focusing equations are particularly simple so that images are focused without requiring autofocus techniques and are computed efficiently motion compensation requires two additional focus correction phase terms that are implemented in the frequency domain if the images from an interferometric pair or stack are all computed along the same reference orbit flat earth topographic correction is not needed and image coregistration is simplified obviating many difficulties that are often encountered in insar processing we process several data sets collected by the alos palsar instrument and find that the geodetic accuracy of the radar images is 10 20 m with up to 20 m of additional image distortion needed to align 100 km 100 km scenes with reference digital elevation models we validated the accuracy by using both known radar corner reflector locations and by the registration of the interferograms with digital maps the topography corrected interferograms are free from all geometric phase terms and they clearly show the geophysical observables of crustal deformation atmospheric phase and ionospheric phase

a high resolution holocene record of the east asian summer monsoon variability in sediments from mountain ganhai lake north china abstract a high resolution environmental magnetic records from a sediment profile in mountain ganhai lake has provided new insights into modulation of the east asian summer monsoon easm on climatic changes in north china from the final period of last deglacial stage to holocene large pseudo single domain psd to multidomain md detrital magnetite grains are identified in the lake samples the upwards decreasing magnetic susceptibility and anhysteretic remanent magnetic susceptibility arm are consistent with the dominant vegetation changes grassland 13 0 10 5 ka under dry and cold conditions shrub forest grassland 10 5 5 8 ka in a warm and humid climate and forest where the pinus trees increase rapidly to be the dominant taxa indicating the climate changes from warm and humid to cooler but drier between 5 8 ka and 4 0 ka the lower s 100mt and s 300mt ratios coincide with the higher degree of soil stability and a stable lake stage at 11 8 6 5 ka changes in magnetic anisotropy are also linked to environmental and climatic changes with t parameters showing higher values during warm interglacial periods the anisotropy patterns indicate three different stages of the lake evolution 1 an early stage of the lake accompanied by a disturbed high energy flow a coarse average mineral particle diameter mpd distribution 16 28 m and scattered subvertical minimum direction k3 at 13 0 11 8 ka 2 a fairly stable lake environment between 11 8 ka and 6 5 ka indicated by a low energy flow finer mpd 9 69 m and subvertical k3 axes 3 an unstable high energy flow and coarse mpd 20 03 m with tilted k3 axes thus indicating a transition from lake center to lakeside 6 5 4 0 ka these multi proxy records reveal a weak easm activity in the final period of the last deglaciation 13 0 11 8 ka a high easm intensity in the early mid holocene 11 8 4 8 ka an easm maxima in the mid holocene 8 0 5 8 ka which then generally weakens at 4 3 4 2 ka overall this study suggests the anisotropy and climatic changes in the alpine lake are significantly affected by the insolation driven easm

magnetic anisotropy of some phyllosilicates magnetic susceptibility anisotropy of susceptibility and hysteresis of single microcrystals of chlorite biotite phlogopite muscovite zinnwaldite and fuchsite were measured in low and high magnetic fields with an alternating gradient force magnetometer micromag their properties are sufficient to account for the low field susceptibility ams of most micaceous rocks nearly all samples show some ferromagnetic contribution at low fields due to inclusions of pseudosingle domain and multidomain magnetite the paramagnetic contribution isolated at high fields usually exceeds the ferromagnetic contribution the paramagnetic susceptibility is intrinsic to the silicate lattice and agrees with values predicted from chemical composition within the limits of error the minimum susceptibility is nearly parallel to c another axis is parallel to b and the third susceptibility usually the maximum is close to a the paramagnetic susceptibility has a disk shaped magnitude ellipsoid with strong anisotropy p 2 the ferromagnetic contributions at low fields have more variably shaped ellipsoids with greater eccentricity p 5 the silicate lattice does not constrain their orientation our technique cannot determine the principal axes of the ferromagnetic component however its principal values usually correspond with the paramagnetic principal susceptibilities in order of magnitude thus the combined paramagnetic ferromagnetic anisotropy recognised in routine studies of ams should faithfully represent the petrofabric of most micaceous rocks nevertheless nearly 10 of our samples have incompatible anisotropy ellipsoids for the silicate host and magnetite inclusions these yield a net inverse ams that does not correctly represent the orientation of the silicate lattice therefore some caution is necessary in petrofabric ams studies of micaceous rocks

a tectonic origin of magnetic fabric in the shemshak group from alborz mts northern iran abstract the magnetic lineation observed in undeformed sedimentary units has been interpreted either as an indication of paleoflow direction or as a result of tectonic overprint which progressively modifies the original sedimentary fabric related to compactional processes distinguishing between the two processes is not always easy in fact most studies of the anistropy of magnetic susceptibility ams of undeformed sequences have been carried out in fine grained sediments from foredeep sequences which are characterized by sedimentary flow directions which are almost parallel to the main deformation structures like thrust faults and folds in the alborz mts the upper triassic lower jurassic shemshak group was deposited in a foreland to molassic basin of the eo cimmerian orogen and now outcrops in several folds which are oriented parallel to the curved chain paleoflow directions are generally oblique to the main tectonic structures being directed ssw to sse and showing negligible changes in their orientation along the alborz mountains we have therefore the opportunity to distinguish between tectonic or sedimentary related origins of the magnetic lineation the ams results show that magnetic lineations of the shemshak group are oriented almost parallel to the main fold axes and thrust structures which follow the alborz mts curved trend suggesting that magnetic lineation is of tectonic origin in fine to medium grained mostly massive sandstones and confirming that ams is a valuable tool to study deformation processes in sedimentary rocks

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

are paleomagnetic records from u channels appropriate for studies of reversals and excursions sampling of sediment cores using plastic u channels has made possible the acquisition of detailed records of paleomagnetic secular variation geomagnetic polarity environmental magnetic studies and relative paleointensity over the past several million years u channel measurements provide the great advantage of rapid measurements of long sediment cores but the signal resolution is attenuated by the response function of the magnetometer sensors which therefore restrains the recovery of rapid and large amplitude field changes here we focus on the suitability of the dynamics of reversals and excursions derived from u channel measurements we compare successive individual paleomagnetic directions of 1 5 cm 1 5 cm 1 5 cm cubic discrete samples with those of a 1 5 m equivalent u channel sample train obtained by placing the samples adjacent to each other we use varying excursion and transition lengths and generate transitional directions that resemble those of the most detailed paleomagnetic records excursions with opposite polarity directions recorded over less than 7 5 cm are barely detected in u channel measurements regarding reversals u channel measurements smooth the signal of low resolution records and generate artificial transitional directions despite producing misleading similarities with the overall structure of transition records longer transitional intervals fail also to reproduce the complexity of field changes finally we test the convolution of magnetization by different response functions the simulation reveals that even small response function changes can generate significant differences in results keywords geomagnetic reversals geomagnetic excursions paleomagnetic measurements

ice flow dynamics of the greenland ice sheet from sar interferometry synthetic aperture radar sar interferograms produced from esa s ers 1 satellite provide the first synoptic view of ice flow dynamics of the western sector of the greenland ice sheet glacial motion is detected in the radar ranging direction at millimetric scales across a complete sequence of snow accumulation and melting regimes despite significant variations in their radar scattering properties ice flow evolves from a slow regular motion at the higher elevations at lower elevations motion is strongly convoluted by meter scale undulations in surface topography which have a unique interferometric signature that enables a novel approach for retrieving flow direction inferred flow directions combined with surface displacements in the radar ranging direction yield ice velocity estimates that are within 6 of in situ measurements gathered along a 40 km survey line application of repeat pass sar interferometry to the entire greenland ice sheet should enable precise mapping of its ice flow dynamics at an unprecedented level of spatial detail

insar detects increase in surface subsidence caused by an arctic tundra fire wildfire is a major disturbance in the arctic tundra and boreal forests having a significant impact on soil hydrology carbon cycling and permafrost dynamics this study explores the use of the microwave interferometric synthetic aperture radar insar technique to map and quantify ground surface subsidence caused by the anaktuvuk river fire on the north slope of alaska we detected an increase of up to 8 cm of thaw season ground subsidence after the fire which is due to a combination of thickened active layer and permafrost thaw subsidence our results illustrate the effectiveness and potential of using insar to quantify fire impacts on the arctic tundra especially in regions underlain by ice rich permafrost our study also suggests that surface subsidence is a more comprehensive indicator of fire impacts on ice rich permafrost terrain than changes in active layer thickness alone

changes in the strength of the iceland scotland overflow water in the last 200 000 years evidence from magnetic anisotropy analysis of core su90 33 abstract results from a high resolution study of magnetic anisotropy combined with mineral magnetic analysis clay analysis and oxygen isotopes stratigraphy are reported for core su90 33 located 60 34 4n 22 05 1w at 2400 m water depth along the iceland scotland overflow water isow a branch of the north atlantic deep water nadw this core covers the last 6 climatic stages the main magnetic mineral is low ti content magnetite with very slight changes in the grain size the susceptibility record corrected for the carbonate content indicates down core variations in the amount of magnetite which largely co vary with the changes in the proportion of smectite in the clay fraction both parameters are climatically controlled with lower values during glacial than during interglacial periods the measurements of the anisotropy of magnetic susceptibility document down core changes in the degree of anisotropy with significantly higher values during interglacial periods than during glacial times these changes appear to be related to differences in the degree of alignment of the magnetic particles and not to changes in grain shape providing evidence that they arise from changes in strength of the bottom water circulation therefore the strength of the contour current associated to the transport of the isow appears to have been significantly larger during climatic stages 5 3 and 1 than during stages 6 4 and 2

crustal deformation at long valley caldera eastern california 1992 1996 inferred from satellite radar interferometry satellite radar interferometric images of long valley caldera show a pattern of surface deformation that resembles that expected from analysis of an extensive suite of ground based geodetic data images from 2 and 4 year intervals respectively are consistent with uniform movement rates determined from leveling surveys synthetic interferograms generated from ellipsoidal inclusion source models based on inversion of the ground based data show generally good agreement with the observed images two interferograms show evidence for a magmatic source southwest of the caldera in a region not covered by ground measurements poorer image quality in the 4 year interferogram indicates that temporal decorrelation of surface radar reflectors is progressively degrading the fringe pattern in the long valley region

saw tooth pattern of north atlantic current speed during dansgaard oeschger cycles revealed by the magnetic grain size of reykjanes ridge sediments at 59 n detailed mineral rock magnetic measurements including high resolution magnetic hysteresis loops were carried out on three sediment cores recovered from the reykjanes ridge in the north atlantic supported by physical grain size analyses titanomagnetite grain size variations form a proxy of the speed of near bottom currents and reveal a cyclic saw tooth pattern between dansgaard oeschger cycles 8 and 5 the magnetic grain size data suggest that these dansgaard oeschger cycles were characterized by gradual intensification of the near bottom current speed while other paleoceanographic proxies indicate escalating iceberg discharge and declining sea surface temperatures these observations are contrary to the frequently assumed and strictly applied positive relationship between high latitude warmth and north atlantic deep water formation within the confines of temporal control however it would appear that peaks in iceberg discharge and slow near bottom current speeds were synchronous the magnetic hysteresis data also demonstrate that magnetic concentration parameters such as magnetic susceptibility do not necessarily provide direct evidence of paleocirculation less

changes in grain size and magnetic fabric at blake bahama outer ridge during the late pleistocene marine isotope stages 8 10 abstract odp sites 1055 1062 on the blake bahama outer ridge bbor are characterized by high sedimentation rates which allow high resolution analyses to reconstruct the behavior of the deep western boundary current dwbc as a function of depth along the bbor the odp sites provide an intermediate and deep water transect from 1800 to 4760 m water depths we focused on the time interval from 350 to 250 ka marine isotope stages mis 10 2 8 3 grain size and magnetic properties were analyzed with centennial to millennial scale time resolution integrating the results of grain size analyses lightness and magnetic properties the changes in the vertical position and the intensity of the dwbc core were inferred during glacial periods mis 10 2 and 8 4 8 3 the dwbc core was located at around 2200 m water depth whereas it deepened to 3000 m or more during warm periods interglacial stage 9 3 and interstadial 8 5 between these periods the dwbc core moved to shallower depth 2500 3000 m and its intensity increased which generally provided coarser sediments to a broad depth range from 2100 to 4800 m furthermore the magnetic properties imply that the dwbc supplied carbonate material other than terrigenous sediments to the deeper sites during mis 9 the depositional processes at site 1062 are characterized by sudden influxes of fine carbonate rich sediments which gradually decreased with time paleocurrent directions inferred from the direction of the great axis of the magnetic fabric are consistent with the modern topography at sites 1055 1056 1058 and 1060 during the relatively warm period from stages 9 3 to 8 5 at site 1062 the deepest site which exhibits a mud wave field the inferred flow direction is parallel to the bathymetric contours during warm periods while the nearly cross wave direction seemingly dominated during the other periods it appears that topographic position may have affected the scattering of azimuth plots moreover there is a possibility that the changes in flow direction correlate with climate changes

single baseline polarimetric sar interferometry examines the application of single baseline polarimetric sar interferometry to the remote sensing and measurement of structure over forested terrain for this a polarimetric coherent scattering model for vegetation cover suitable for the estimation of forest parameters from interferometric observables is introduced discussed and validated based on this model an inversion algorithm which allows the estimation of forest parameters such as tree height average extinction and underlying topography from single baseline fully polarimetric interferometric data is addressed the performance of the inversion algorithm is demonstrated using fully polarimetric single baseline experimental data acquired by dlr s e sar system at l band

on the derivation of coseismic displacement fields using differential radar interferometry the landers earthquake we present a map of the coseismic displacement field resulting from the landers california june 28 1992 earthquake derived using data acquired from an orbiting high resolution radar system we achieve results more accurate than previous space studies and similar in accuracy to those obtained by conventional field survey techniques data from the ers 1 synthetic aperture radar instrument acquired in april july and august 1992 are used to generate a high resolution wide area map of the displacements the data represent the motion in the direction of the radar line of sight to centimeter level precision of each 30 m resolution element in a 113 km by 90 km image our coseismic displacement contour map gives a lobed pattern consistent with theoretical models of the displacement field from the earthquake fine structure observed as displacement tiling in regions several kilometers from the fault appears to be the result of local surface fracturing comparison of these data with global positioning system and electronic distance measurement survey data yield a correlation of 0 96 thus the radar measurements are a means to extend the point measurements acquired by traditional techniques to an area map format the technique we use is 1 more automatic 2 more precise and 3 better validated than previous similar applications of differential radar interferometry since we require only remotely sensed satellite data with no additional requirements for ancillary information the technique is well suited for global seismic monitoring and analysis

interferometric estimation of three dimensional ice flow using ascending and descending passes satellite radar interferometry sri provides an important new tool for determining ice flow velocity interferometric measurements made from a single track direction are sensitive only to a single component of the three component velocity vector observations from along three different track directions would allow the full velocity vector to be determined a north south looking synthetic aperture radar sar could provide these observations over large portions of the globe but not over large areas of the polar ice sheets the authors develop and demonstrate a technique that allows the three component velocity vector to be estimated from data acquired along two track directions ascending and descending under a surface parallel flow assumption this technique requires that there are accurate estimates of the surface slope which are also determined interferometrically to demonstrate the technique the authors estimate the three component velocity field for the ryder glacier greenland their results are promising although they do not have yet ground truth data with which to determine the accuracy of their estimates

topographic phase recovery from stacked ers interferometry and a low resolution digital elevation model a hybrid approach to topographic recovery from ers interferometry is developed and assessed tropospheric ionospheric artifacts imprecise orbital information and layover are key issues in recovering topography and surface deformation from repeat pass interferometry previously we developed a phase gradient approach to stacking interferograms to reduce these errors and also to reduce the short wavelength phase noise see sandwell and price 1998 and appendix a here the method is extended to use a low resolution digital elevation model to constrain long wavelength phase errors and an iteration scheme to minimize errors in the computation of phase gradient we demonstrate the topographic phase recovery on 16 m postings using 25 ers synthetic aperture radar images from an area of southern california containing 2700 m of relief on the basis of a comparison with 81 gps monuments the ers derived topography has a typical absolute accuracy of better than 10 m except in areas of layover the resulting topographic phase enables accurate two pass real time interferometry even in mountainous areas where traditional phase unwrapping schemes fail as an example we form a topography free 127 m perpendicular baseline interferogram spanning 7 5 years fringes from two major earthquakes and aseismic slip on the san andreas fault are clearly isolated

correction for interferometric synthetic aperture radar atmospheric phase artifacts using time series of zenith wet delay observations from a gps network 1 radar interferograms provide precise millimeter level measurements of crustal deformation at fine resolution over wide areas the dominant error source in many interferograms results from spatial heterogeneity of the wet component of atmospheric refractivity resulting in excess path length of the radar signal propagating through the neutral atmosphere in this report we introduce a method to compensate for atmospheric phase artifacts in a radar interferogram using spatially interpolated zenith wet delay zwd data obtained from a network of global positioning system gps receivers in the region imaged by the radar our method based on taylor s frozen flow hypothesis uses gps data recorded prior to and after the individual radar acquisition times to infer denser spatial networks of control points for interpolation than is suggested by the sparse and irregular spatial distribution of gps receivers we test this approach by correcting phase fluctuations observed in a radar interferogram over an area covered by the southern california integrated gps network stations using maps of atmospheric delay interpolated from the denser network of gps zwd measurements generated by our method we find that the largest improvement results from removing an altitude dependent model derived from the gps data the uncorrected interferogram in our example has an rms fluctuation of 16 1 mm which falls to 8 6 mm after the altitude correction a map derived from zwd measurements recorded only at the instances of radar acquisition reduced overall fluctuations in the data from 8 6 to 8 1 mm rms while using the inferred denser network reduces the error further to 7 5 mm rms most of this residual variation is due to decorrelation of the signal and does not result from atmospheric propagation however after smoothing to remove decorrelation noise the residual drops from 4 7 to 3 9 mm gps stations only and then to 2 7 mm rms when the denser network algorithm is used

magnetic anisotropy and environmental changes in two sedimentary cores from the norwegian sea and the north atlantic abstract we have studied the magnetic properties and the magnetic anisotropy ams and aarm of cores md95 2010 from the voering plateau and su90 33 from the south icelandic basin in the first core the study has been focussed on climatic stage 3 during which the record of magnetic susceptibility is correlated with the 18o signal from the greenland ice cores minima maxima in susceptibility anhysteretic remanent magnetization and isothermal remanent magnetization coincide with cold warm periods and reflect a modulation in the amount of deposited magnetite in the second core six climatic stages have been studied the ams and the aarm changes are tightly correlated showing that both are related to changes in the organization of magnetite grains in the sediment both magnetic fabrics are oblate and the variations of the degree of anisotropy are climatically controlled with higher values during short warm events or interglacial periods compared to cold periods different possible mechanisms leading to the observed fabrics are discussed it appears that although a differential compaction might have been active the fabrics mainly result from depositional effects in connection with climatic changes although the exact mechanisms of the link between magnetic fabrics and bottom current dynamics are as yet open to discussion the study of magnetic anisotropy which reflects the sedimentary structure may ultimately lead to a better understanding of the coupling between atmospheric temperature changes and paleocirculation pattern in the north atlantic and nordic seas

dynamics of slow moving landslides from permanent scatterer analysis high resolution interferometric synthetic aperture radar insar permanent scatterer data allow us to resolve the rates and variations in the rates of slow moving landslides satellite to ground distances range changes on landslides increase at rates of 5 to 7 millimeters per year indicating average downslope sliding velocities from 27 to 38 millimeters per year time series analysis shows that displacement occurs mainly during the high precipitation season during the 1997 1998 el nino event rates of range change increased to as much as 11 millimeters per year the observed nonlinear relationship of creep and precipitation rates suggests that increased pore fluid pressures within the shallow subsurface may initiate and accelerate these features changes in the slope of a hill resulting from increases in the pore pressure and lithostatic stress gradients may then lead to landslides

coherent patterns of ice rafted debris deposits in the nordic regions during the last glacial 10 60 ka we have synchronized records of ice rafted rock debris deposits of three sediment cores from the norwegian sea and the irminger basin during the last glacial period from 10 to 50 ka by combining the use of radiocarbon dates and adjustments of physical properties our synchronized records indicate that layers rich in ice rafted debris were deposited throughout the nordic regions at times near to synchronous with the major collapses of the laurentide ice sheet during the heinrich events there are also millennial scale coherent and near to synchronous deposits of ice rafted rock debris into the norwegian sea related to repetitive changes of the flux of icebergs from the fenno scandinavian the correlation with the cold phases of the dansgaard oeschger temperature record points to a close coupling between atmospheric temperature oscillations and variations of iceberg fluxes into the norwegian sea during the last glacial variations in atmospheric circulation patterns bringing moisture supply to high latitudes and the distribution of this moisture over the different northern hemisphere coastal ice sheets and ice shelves could be controlling both the timing of ice sheet advances and the flux of iceberg to the open ocean

oligo miocene magnetostratigraphy and rock magnetism of the xishuigou section subei gansu province western china and implications for shallow inclinations in central asia magnetostratigraphy of 222 remanent directions together with late oligocene to early miocene mammal and charophyte paleontology suggest that 2179 m of the xishuigou section subei gansu province china were deposited from 26 to 19 ma stratigraphic patterns of bulk susceptibility anisotropy of magnetic susceptibility parameters and natural and anhysteretic remanent magnetization intensities demonstrate that 1 faulting does not significantly affect the record 2 sediment deposition was relatively continuous 3 sediment source changed around 23 ma and 4 rapid uplift near subei occurred at 21 ma subei rotated 27 5 counterclockwise with respect to the 20 ma pole from the eurasian synthetic apparent polar wander path folding and rotation of the section took place after 19 ma the paleolatitude of subei is 14 less than at present and 19 3 less than predicted from the reference pole both rock magnetic and paleomagnetic data sets suggest that the unusually low paleolatitude is the result of synsedimentary inclination shallowing a phenomenon which has likely affected other paleomagnetic data from central asia

topographic mapping from interferometric synthetic aperture radar observations interferometric synthetic aperture radar observations provide a means for obtaining high resolution topographic terrain maps from data acquired simultaneously at two slightly displaced antennas calculation of the three dimensional coordinates of all the points in a radar image can be made from the combination of along track slant range and interferometer fringe measurements thus the result compensates for the layover exhibited by conventional radar maps and removes the false targets generated by multiple signal paths to a given object in the scene we have derived a topographic map of a portion of the san francisco bay area utilizing data that were recorded by a radar system mounted on a nasa cv990 aircraft and processed by a general purpose digital computer this map displays the height above sea level of a region approximately 11 km by 10 km in size sampled on an 11 m pixel grid uncertainties in the estimated height result from imprecise knowledge of the observational geometry radar bandwidth limitations and finite signal to noise ratios for our system each factor contributed approximately 3 4 m to a relative rms error of about 6 m additional global errors of the order of 10 m can result from inaccurate monitoring of aircraft attitude the statistical variation of the height measurements from the ocean portion of the map which we can presume to be quite flat is 2 10 m rms which is consistent with the theoretical estimate comparison of our results with u s geological survey contour maps indicates a high degree of correlation between the two sets of altitude data

climatic instability ice sheets and ocean dynamics at high northern latitudes during the last glacial period 58 10 ka bp abstract oxygen isotope magnetic susceptibility and foraminiferal distribution data are presented for a high resolution core enam93 21 located at the northeast faeroe margin this core recorded a rapid succession of faunistic sedimentologic and isotopic variations which paralleled the greenland ice core isotopic records with their typical succession of abrupt temperature rises and gradual coolings the dansgaard oeschger cycles the most notable feature was the contemporaneous changes in surface and bottom water conditions and circulation that appeared tightly coupled with the rapid climate fluctuations warm episodes interstadials were appeared with higher sea surface temperatures and thermohaline convection in the norwegian greenland sea the polar front was located north of the enam93 21 site cold episodes stadials were associated with an increase in the input of melting fennoscandian icebergs low sea surface temperature and salinity and no thermohaline convection in the norwegian greenland sea intermediate waters changed to an estuarine mode at the faeroe margin with a reversed flow pattern through the faeroe shetland channel the polar front was located south of the enam93 21 site

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

widespread uplift and trapdoor faulting on galapagos volcanoes observed with radar interferometry volcanic uplift caused by the accumulation of magma in subsurface reservoirs is a common precursor to eruptions1 2 but for some volcanoes uplift of metres or more has not yet led to an eruption3 here we present displacement maps of volcanoes in the galapagos islands constructed using satellite radar interferometry that might help explain this dichotomy we show that all but one of the seven volcanoes on the islands of isabela and fernandina deformed during 1992 99 cerro azul and fernandina erupted4 5 6 during the observation period and show evidence of inflation co eruptive deflation and shallow dyke intrusion in contrast the largest volcano sierra negra has not erupted yet exhibits spatially and temporally variable deformation with a maximum uplift of 2 7 m between 1992 and 1999 which can be modelled by a shallow inflating sill inflation during 1997 98 however was accompanied by trapdoor faulting on a steeply dipping fracture system within the caldera repeated trapdoor faulting over geological time has formed an arcuate intra caldera ridge within sierra negra and may have acted to relax stresses above the magma chamber inhibiting summit eruptions similar processes may help explain large uplift unaccompanied by eruptive activity at other volcanoes

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

rock magnetic detection of distal ice rafted debries clue for the identification of heinrich layers on the portuguese margin abstract high resolution measurements of concentration and grain size dependent magnetic parameters along a sedimentary sequence deposited on the portuguese margin 38 n during the last 120 ka allowed the detection of multiple thin layers slightly enriched by a coarse lithogenic fraction sizes mineralogy shapes and mode of deposition identify the material as ice rafted detritus ird the four most recent events dated by calibrated radiocarbon ages are contemporaneous with heinrich events he1 he4 older events can be identified as he5 he6 or with minor ird that occurred during stage 5 the resolution and sensitivity obtained with rock magnetic methods enable the detection of multiple secondary events showing that iceberg delivery was a frequent phenomenon directly linked to temperature variations over ice caps heinrich events representing the extreme cases

persistent scatterer selection using maximum likelihood estimation 1 we present here a new insar persistent scatterer selection method using maximum likelihood estimation to identify persistent scattering pixels which results in a denser network of reliable phase measurements than do existing methods we analyze the phase of each pixel in a series of interferograms and estimate the relative strength of any slowly fluctuating component of the radar echo from a dominant scatterer to the background scattering within a pixel we find a fairly dense network of scatterers with stable phase characteristics in areas where conventional insar fails due to decorrelation we examined data over two vegetated regions in the san francisco bay area the average phases of these pixels clearly show the slip along the hayward fault and set upper bounds on any slip along the bay area segment of the san andreas fault

were glacial iceberg surges in the north atlantic triggered by climatic warming high resolution physical mineralogical sedimentological and micropalaeontological studies were carried out on north atlantic cores from the reykjanes ridge at 59degreesn and from the region southwest of the faeroe islands all core sites are situated along the pathway of iceland scotland overflow water isow and the various parameters measured display similar features previously identified carbonate oscillations keigwin and jones 1994 j geophys res 99 12397 12410 in the time span back to the marine isotope stage 5 4 transition and late glacial lithic events bond and lotti 1995 science 267 1005 1010 such as the heinrich ice rafting events are all represented in the core records long term trends and higher frequency changes in isow intensity were reconstructed on the basis of various independent proxy records the long term trends in circulation match theoretical orbitally forced insolation changes our observed links between ice rafted detritus ird input variations in sea surface temperature sst and circulation at greater depth point to the need to re examine the origin of ird events we suggest that these events may have been triggered by enhanced partly sub surface heat transport to the north enhanced northward heat transport may have caused bottom melting of floating outlet glaciers and ice shelves leading to increased iceberg discharge and ice sheet destabilization this discharge resulted in lower sst s and a lower temperature over greenland thus as shown by our records this scenario implies a temporary de coupling of surface processes and circulation at greater depth a key feature is the occurrence of a saw tooth pattern in the marine data which is similar to the greenland ice core records moreover the warming theory of ird events would explain the observed out of phase relationship between the greenland and antarctic ice core records and also the rapid establishment of higher temperatures over greenland immediately after the cold phases stadials of the dansgaard oeschger cycles less

estimation of marine sediment bulk physical properties at depth from seafloor geophysical measurements a combination of geophysical techniques can yield estimates of several physical properties versus depth an example is presented for a thick sequence of sediments in middle valley near the present spreading axis of the juan de fuca ridge we have computed the porosity temperature and thermal conductivity versus depth by combining the results of seafloor electrical and heat flow surveys the electrical resistivity of the sediments is empirically related to the porosity of the medium and to the pore fluid electrical conductivity which is in turn sensitive to the temperature the temperature profile is determined from the heat flow and the thermal conductivity the latter is determined from calculated porosity and estimates of the constituent mineral and pore fluid thermal conductivities the measured surface heat flow is assumed to be and the resistivity has been determined to be approximately constant with depth the computation of the variation of temperature porosity and thermal conductivity with depth yields physically realistic and reasonable results other physical properties void ratio bulk density water content compressional wave velocity are estimated from the porosity the shear wave velocity is calculated empirically from the compressional wave velocity and poisson s ratio is then computed from the compressional and shear wave velocities the results are in good agreement with values derived for similar rapidly deposited sediment sequences elsewhere but the model calculations indicate that deep sea drilling project measurements may be biased toward higher porosity samples

finite element modelling of the 2015 gorkha earthquake through the joint exploitation of dinsar measurements and geologic structural information abstract we investigate the co seismic effects of the mw 7 8 gorkha earthquake through a finite element modelling approach that jointly exploits space borne dinsar deformation measurements and geologic structural information our model permits to retrieve the coseismic displacements with a very good accuracy and to confirm the finding of earlier studies suggesting that the slip reaches a maximum value of about 7 m at a depth of 7 15 km along the main himalayan thrust mht and occurs in an area about 30 km northern of kathmandu in particular the main shock ruptured the deep part of the seismogenic zone of mht with rather small displacement values retrieved along the splay faults main frontal thrust mft main boundary thrust mbt in the southern region a relevant aspect of our results is the imaging of about 3 m of displacement in correspondence to the shallow portion of the main central thrust mct to the north and of the munsiari mahabharat thrust mt to the south this finding may be associated to a possible mechanism for accommodating the mht sourced deformation on the adjacent thrusts highlighting a passive role of the hinterland structures as receiver faults of the displacements transferred from earthquakes originating on the mht in addition the proposed model allow us to map the stress field distribution evaluated through von mises failure criteria associated to the main seismic event this result is in good agreement with the hypocentral distribution and mechanism of the investigated aftershocks

remote sensing measurements of thermokarst subsidence using insar thawing of ice rich permafrost followed by surface subsidence results in irregular depressed landforms known as thermokarst many remote sensing studies have identified thermokarst landforms and mapped their changes however the intrinsic dynamic thermokarst process of surface subsidence remains a challenge to quantify and is seldom examined using remote sensing methods in this study we used spaceborne interferometric synthetic aperture radar insar data to map surface subsidence trends at a thermokarst landform located near deadhorse on the north slope of alaska a pipeline access road constructed in the 1970s triggered the thawing of the permafrost causing subsequent expansion of the thermokarst landform using phased array type l band synthetic aperture radar images acquired by the advanced land observing satellite 1 our insar analysis reveals localized thermokarst subsidence of 2 8 cm yr between 2006 and 2010 equivalent to an ice volume loss of about 1 2 107 m3 yr comparisons between insar subsidence trends and lidar microtopography suggest a characteristic time of 8 years of thermokarst development we also quantitatively explain the difficulty uncertainties and possible biases in separating thermokarst induced irreversible subsidence from cyclic seasonal deformation our study illustrates that insar is an effective tool for mapping and studying active thermokarst processes and quantifying ice loss

fault creep along the southern san andreas from interferometric synthetic aperture radar permanent scatterers and stacking 1 interferometric synthetic aperture radar insar provides a practical means of mapping creep along major strike slip faults the small amplitude of the creep signal 10 mm yr combined with its short wavelength makes it difficult to extract from long time span interferograms especially in agricultural or heavily vegetated areas we utilize two approaches to extract the fault creep signal from 37 ers sar images along the southern san andreas fault first amplitude stacking is utilized to identify permanent scatterers which are then used to weight the interferogram prior to spatial filtering this weighting improves correlation and also provides a mask for poorly correlated areas second the unwrapped phase is stacked to reduce tropospheric and other short wavelength noise this combined processing enables us to recover the near field 200 m slip signal across the fault due to shallow creep displacement maps from 60 interferograms reveal a diffuse secular strain buildup punctuated by localized interseismic creep of 4 6 mm yr line of sight los 12 18 mm yr horizontal with the exception of durmid hill this entire segment of the southern san andreas experienced right lateral triggered slip of up to 10 cm during the 3 5 year period spanning the 1992 landers earthquake the deformation change following the 1999 hector mine earthquake was much smaller 1 cm and broader than for the landers event profiles across the fault during the interseismic phase show peak to trough amplitude ranging from 15 to 25 mm yr horizontal component and the minimum misfit models show a range of creeping locking depth values that fit the data

penetration depths inferred from interferometric volume decorrelation observed over the greenland ice sheet radar interferometry provides a novel way to study the subsurface of glaciers interferometric correlation since the two complex images that comprise the interferogram have slightly different incidence angles at each point on the ground a decorrelating phase noise with statistics related to the scattering medium is present in the interferogram the amount of surface decorrelation is increased by volume scatter the larger the vertical extent of the scatterers contributing to the radar echo the greater the decorrelation will be by modeling this effect the authors can estimate radio wave penetration depths within the upper layers of the glacier or ice sheet observations of the greenland ice sheet using ers data yield penetration depths one way 1 e point for power that range from 12 to 35 m due to the contribution of volume scatter the critical interferometer baseline is decreased and the authors find for the greenland data the baseline must be restricted to be less than 300 m the authors also compare penetration depths measured within the dry snow zone with those found in the percolation zone and coastal areas they find that as expected the rocky coastal areas evidence minimal penetration interestingly the penetration depths that the authors measure in the percolation zone spl sim 23 m indicate a large degree of volume scatter which is contrary to earlier results that found the scattering in the percolation zone dominated by structures in the first few meters this discrepancy may be due to unmodeled scattering behavior or the radar return may indeed include significant contributions from scatterers far beneath the surface

models of inclination shallowing during sediment compaction we construct microscopic models of compacting sediment which lead to inclination shallowing of the magnetic remanence the models can be classified as 1 rotation of elongated magnetic grains to more horizontal orientations 2 rotation toward the horizontal of flat nonmagnetic fabric grains to which smaller magnetic grains are attached 3 randomization of the sediment by grain rotations which lead to decreased intensity of magnetization and possibly also to inclination shallowing and 4 finally we show that the initial within sample dispersion of the magnetic moments dampens the amount of inclination shallowing of all the models and transforms any form of microscopic mechanism to an equation of a standardized form the physically realistic models give rise to different magnitudes of inclination shallowing which to the first order obey an equation of the form tan i i 1 a v tani where i is the inclination of the ambient field i is the inclination shallowing and v the compaction for these models we also calculate the effect of compaction on the intensity of magnetization and the results show that considerable randomization is needed to offset the increased intensity due to higher concentrations of magnetic particles caused by compaction if random rotations of the grains are biased toward rolling about horizontal axes and the randomization is sufficient to cancel the effect of greater concentrations then the random grain rolling due to the compaction would give rise to considerable inclination shallowing