extracting time domain green s function estimates from ambient seismic noise 1 it has been demonstrated experimentally and theoretically that an estimate of the green s function between two seismic stations can be obtained from the time derivative of the long time average cross correlation of ambient noise between these two stations this tdgf estimate from just the noise field includes all tensor components of the green s function and these green s function estimates can be used to infer earth structure we have computed cross correlations using 1 to 30 continuous days of ambient noise recorded by over 150 broadband seismic stations located in southern california the data processing yielded thousands of cross correlation pairs for receiver separations from 4 500 km which clearly exhibit coherent broadband propagating dispersive wavetrains across frequency band 0 1 2 hz

source model of deformation at lazufre volcanic center central andes constrained by insar time series 1 recent interferometric synthetic aperture radar insar observations of the lazufre region central andes show large scale uplift at a rate of about 3 cm yr beginning between 1998 and 2002 the initiation of this activity during the ers satellite mission and its proximity to active volcanoes have made lazufre the focus of several studies aimed at understanding its source geometry its relation to nearby volcanoes and whether or not the source area is expanding there now exists a longer time series from multiple ers envisat satellite tracks that allows a more comprehensive examination of the source geometry and its temporal and spatial variation if any we processed 15 years of insar data from three separate tracks modeling the different look geometries provided greater resolution of source depth and geometry we conclude that the source is a shallowly dipping sill at a depth of about 8 km with no evidence of lateral expansion

tide model accuracy in the amundsen sea antarctica from radar interferometry observations of ice shelf motion 1 this study assesses the accuracy of tide model predictions in the amundsen sea sector of west antarctica tide model accuracy in this region is poorly constrained yet tide models contribute to simulations of ocean heat transfer and to the removal of tidal signals from satellite observations of ice shelves we use two satellite based interferometric synthetic aperture radar insar methods to measure the tidal motion of the dotson ice shelf at multiple epochs a single difference technique that measures tidal displacement and a double difference technique that measures changes in tidal displacement we use these observations to evaluate predictions from three tide models tpxo7 1 cats2008a opt and fes2004 all three models perform comparably well exhibiting root mean square deviations from the observations of 9 cm single difference technique and 10 cm double difference technique care should be taken in generalizing these error statistics because 1 the dotson ice shelf experiences relatively small semidiurnal tides and 2 our observations are not sensitive to all tidal constituents an error analysis of our insar based methods indicates measurement errors of 7 and 4 cm for the single and double difference techniques respectively a model based correction for the effect of fluctuations in atmospheric pressure yields an 6 improvement in the agreement between tide model predictions and observations this study suggests that tide model accuracy in the amundsen sea is comparable to other antarctic regions where tide models are better constrained these methods can be used to evaluate tide models in other remote antarctic waters

rapid disintegration of the wordie ice shelf in response to atmospheric warming the breaking up of ice shelves around the antarctic peninsula has been cited1 as a sign that a dangerous warming is beginning in antarctica here we present satellite images showing the disintegration of the wordie ice shelf which lies off the west coast of the antarctic peninsula fig 1 fracture either in the form of surface crevasses or rifts extending to the bottom of the ice shelf has been responsible for iceberg calving and weakening the central region of the ice shelf these fracture processes which led to retreat of the ice front were apparently enhanced by the presence of increased amounts of melt water resulting from a warming trend recorded in mean annual air temperatures in marguerite bay if this warming trend continues other nearby ice shelves on the antarctic peninsula may be at risk but substantial additional warming would be required before similar processes could initiate breakup of the ross and filchner ronne ice shelves which help stabilize the west antarctic ice sheet

surface deformation time series and source modeling for a volcanic complex system based on satellite wide swath and image mode interferometry the lazufre system central andes article i nfo the variable spatio temporal scales of earth s surface deformation in potentially hazardous volcanic areas pose a challenge for observation and assessment here we used envisat data acquired in wide swath mode wsm and image mode im from ascendingand descending geometry respectively to studytime dependent grounduplift at the lazufre volcanic system in chile and argentina a least squares adjustment was performed on 65 im interferograms that coveredthetimeperiod of 2003 2008 we obtaineda cleartrendofupliftreaching 15 16 cm in this 5 year interval using a joint inversion of ascending and descending interferograms we evaluated the geometry and time dependent progression of a horizontally extended pressurized source beneath the lazufre volcanicsystem ourresultshenceindicatethatanextendedmagmabodyatadepthbetween10and15kmwould accountformostofthegrounduplift themaximuminflationreachedupto 40cmduring2003 2008 thelateral propagation velocity of the intrusion was estimated to be nearly constant at 5 10 km yr during the observation time which has important implications for the physical understanding of magma intrusion processes

larsen ice shelf has progressively thinned the retreat and collapse of antarctic peninsula ice shelves in tandem with a regional atmospheric warming has fueled speculation as to how these events may be related satellite radar altimeter measurements show that between 1992 and 2001 the larsen ice shelf lowered by up to 0 27 0 11 meters per year the lowering is explained by increased summer meltwater and the loss of basal ice through melting enhanced ocean driven melting may provide a simple link between regional climate warming and the successive disintegration of sections of the larsen ice shelf

three dimensional shear velocity anisotropic model of piton de la fournaise volcano la reunion island from ambient seismic noise we cross correlate 4 years of seismic noise from the seismic network of piton de la fournaise volcano la reunion island to measure the group velocity dispersion curves of rayleigh and love waves we average measurements from vertical and radial components to obtain 577 rayleigh wave dispersion curves the transverse components provided 395 love wave dispersion curves we regionalize the group velocities measurements into 2 d velocity maps between 0 4 and 8 s finally we locally inverted these maps for a pseudo 3 d anisotropic shear velocity model down to 3 km below the sea level using a neighborhood algorithm the 3 d isotropic shear wave model shows three distinct high velocity anomalies surrounded by a low velocity ring the anomaly located below the present plaine des sables could be related to an old intrusive body at the location of the former volcanic center before it migrated toward its present location the second high velocity body located below the summit of the volcano likely corresponds to the actual preferential dyke intrusion zone as highlighted by the seismicity the third high velocity anomaly located below the grandes pentes and the grand brule areas and is an imprint of the solidified magma chamber of the dismantled les alizes volcano radial anisotropy shows two main anomalies positive anisotropy above sea level highlighting the recent edifice of piton de la fournaise with an accumulation of horizontal lava flows and the second one below the sea level with a negative anisotropy corresponding to the ancient edifice of piton de la fournaise dominated by intrusions of vertical dykes

residual ocean tide signals from satellite altimetry grace gravity fields and hydrodynamic modelling summary improvements of a global state of the art ocean tide model are identified and quantified by applying three independent approaches namely i empirical ocean tide analysis of multimission altimeter data ii evaluation of grace data and gravity field models and iii high resolution hydrodynamic modelling although these approaches have different capabilities to sense ocean tides they obtain results which are basically consistent one with each other the analysis of altimeter data clearly identifies significant residual amplitudes over shallow water for all major diurnal and semidiurnal constituents and the non linear tide m4 grace data and the time series of monthly gravity field models exhibit on a larger scale residual ocean tide signals over much the same areas the analysis of dynamic residuals of hydrodynamic modelling with data assimilation proves the validity of linear dynamics in the deep ocean and shows correlation of dynamic residuals with energy dissipation in these areas

stress tensor analysis of the 1998 1999 tectonic swarm of northern quito related to the volcanic swarm of guagua pichincha volcano ecuador the phreatic activity and the subsequent dacitic dome growth in 1998 1999 at guagua pichincha volcano ecuador were associated with two seismic swarms one located in the northern part of quito population 1 500 000 and another one just below the active volcano about 15 20 km sw from the first one quito swarm tectonic events have high frequencies from 1 to 10 15 hz we registered more than 3200 events among which 2354 events of 1 4 m l 4 2 between june 1998 and december 1999 at the 2 and 17 km depth the volcanic events below the guagua pichincha caldera have high from 1 to 10 15 hz and low less than 3 hz frequencies approximately 130 000 events were registered between september 1998 and december 1999 at the 2 4 and 3 5 km depth here we study the stress tensors of these two swarms deduced from the polarities of p first motions and compare them to the regional stress tensor deduced from cmt harvard focal mechanisms the quito swarm stress tensor is relatively close to the regional stress tensor the 1 axis was oriented n117 e close to the n102 e direction of the plate motion found by the gps measurement and 3 is nearly vertical the difference may be due to the action of the closely active guagua pichincha volcano the guagua pichincha stress tensor is very different from the regional tectonic one the 1 axis of the volcano is oriented n214 e almost perpendicular to the 1 of the swarm of quito and 3 is almost horizontal even if these two tensors are different they can be explained in a more general tectonic scheme the almost horizontal direction of 3 just below the volcano is compatible with an extensional horizontal direction that may be expected in the shallow extrados part of a compressional region and consistent with an opening of the top of the guagua pichincha volcano the movement of the fluids magma gas and or groundwater produced by the closely active guagua pichincha volcano seems to have an influence in the acceleration of the generation of seismic events

sulphur flows at lastarria volcano in the north chilean andes although several authors have suggested that sulphur plays an important role in the volcanism on the jovian moon io1 8 some deny the participation of elemental sulphur there at least in the form of cooled flows9 studies of volcanism on io have focused attention on the role of sulphur in terrestrial volcanism on earth fumarolic sulphur is very common in almost all active volcanoes but sulphur flows are rare having been reported only on siretoko iosan volcano in japan10 on sierra negra and azufre volcanoes in the galapagos islands11 12 and on mauna loa in hawaii13 14 of these the siretoko iosan example is the only natural molten sulphur flow to have been observed in the process of formation the others being rather poorly exposed i describe here a singularly well exposed example of sulphur lava flows on lastarria volcano in chile where the liquid sulphur appears to have been formed by melting of fumarolic sulphur deposits caused by a rise in the thermal gradient owing to the renewed activity of the magmatic source

ice shelf elevation changes due to atmospheric pressure variations the inverse barometer effect ibe is the isostatic response of ocean surface height to changes in atmospheric pressure p air at a rate of about 1 cm hpa 1 the ibe is a significant contributor to variability of ice shelf surface elevation ice as we demonstrate with simultaneous global positioning system measurements of ice and local measurements of p air from the amery brunt and ross ice shelves antarctica we find that an ibe correction is justified for frequencies covering the weather band 0 03 0 5 cpd cycles per day the ibe correction reduces the standard deviation of the weather band signal of ice from 9 cm to 3 cm with this correction the largest remaining high frequency error signal in ice is the inaccuracy of the present generation of antarctic tide models estimated to be of order 10 cm for most of antarctica

decadal volcanic deformation in the central andes volcanic zone revealed by insar time series 1 decadal trends of volcanic deformation in the central andes volcanic zone cvz are identified with interferometric synthetic aperture radar insar stacks and time series velocity maps covering an area 19 s 27 s and 66 w 69 w we combine over 750 ers and envisat interferograms from two descending and three ascending tracks these tracks cover 100 000 km 2 and span 1992 2011 our analysis extends observations at cerro blanco uturuncu and lazufre volcanic centers and uncovers two previously undocumented deformation centers cerro overo in northern chile and putana volcano in southwest bolivia cerro overo exhibits a transition from steady 0 4 cm yr deflation to 0 5 cm yr inflation over several years putana volcano underwent a short lived episode of uplift between 13 september 2009 and 31 january 2010 with a maximum uplift of 4 0 cm cerro blanco continues 1 0 cm yr deflation since 1995 uplift at lazufre began between 1997 and 2000 and has gradually accelerated to 3 5 cm yr since 2005 uturuncu volcano continues 1 0 cm yr monotonic uplift since 1992 and shows evidence for a broad moat of subsidence surrounding the uplifting region four of the nine deformation events in the cvz are not obviously associated with a particular volcanic edifice furthermore there is significant spatial and temporal variability of these deformation events within a small geographic area

teleseismic tomography of the southern puna plateau in argentina and adjacent regions abstract we performed a teleseismic p wave tomography study using seismic events at both teleseismic and regional distances recorded by a temporary seismic array in the argentine puna plateau and adjacent regions the tomographic images show the presence of a number of positive and negative anomalies in a depth range of 20 300 km beneath the array the most prominent of these anomalies corresponds to a low velocity body located in the crust most clearly seen in the center of the array 27 s 67 w between the cerro peinado volcano the cerro blanco caldera and the farallon negro in the east this anomaly southern puna magmatic body extends from the northern most part of the array and follows the line with the highest density of stations towards the south where it becomes smaller it is flanked by high velocities on the west and the east respectively on the west the high velocities might be related to the subducted nazca plate on the northeast the high velocity block coincides with the position of the hombre muerto basin in the crust and could be indicating an area of lithospheric delamination where we detected a high velocity block at 100 km depth on the eastern border of the puna plateau north of galan this block might be related to a delamination event in an area with a thick crust of paleozoic metamorphic rocks at the border between puna and eastern cordillera in the center of the array the southern puna magmatic body is also flanked by high velocities but the most prominent region is located on the east and is interpreted as part of the sierras pampeanas lithosphere with high velocities the position of the sierras pampeanas geological province is key in this area as it appears to limit the extension of the plateau towards the south

persistent uplift of the lazufre volcanic complex central andes new insights from pcaim inversion of insar time series and gps data we reanalyzed the surface displacements observed at the lazufre volcanic complex in the southern andean central volcanic zone using gps measurements made between 2006 and 2008 and a large insar data set we performed a detailed spatiotemporal analysis of the displacements using a principal component analysis inversion method pcaim the pcaim reveals a source with no significant changes in shape and dimension and with a remarkably linear strength increase over the whole period of observation i e 2003 2010 then we used a three dimensional mixed boundary element method mbem to invert the first component of surface displacement as obtained from pcaim we explored a continuum of geometries from a shallow elliptic crack to a deep massive truncated elliptical cone that could represent a sill or a large magma chamber respectively the best models indicate a large flat topped source with a roof area between 40 and 670 km2 and a depth of between 2 and 14 km below ground surface lastly on the basis of the limited data available for the thermomechanical structure of the crust in the southern andean central volcanic zone we consider some possible scenarios to explain the spatial and temporal pattern of displacements at lazufre

crustal imaging of western michoacan and the jalisco block mexico from ambient seismic noise abstract detailed crustal imaging of western michoacan and the jalisco block is obtained from ambient noise tomography results show a deep and well delineated volcanic system below the colima volcano complex rooting up to 22 km depth with a shallow magmatic chamber constrained to the first 7 km a shallow low velocity system to the south of the chapala rift and west of the michoacan guanajuato volcanic field merges underneath the colima rift with the colima volcano system at about 20 km depth honoring the geometry of the trans mexican volcanic belt for depths greater than 30 km low velocity features become parallel to the slab strike right beneath the mascota ayutla and tapalpa volcanic fields suggesting the presence of the mantle wedge above the rivera plate all mentioned low velocity bodies are spatially correlated with the superficial volcanic activity suggesting their magmatic origin so that the shallower these bodies the younger are the associated volcanic deposits along the coast different depths of the uppermost layer of the rivera and the cocos plates suggest that the latter plate subducts with an angle 9 steeper than the former

a preliminary tidal analysis of icesat laser altimetry southern ross ice shelf 1 satellite laser altimetry could soon play a key role in mapping poorly known ocean tides underneath antarctic ice shelves the amount of icesat data now collected over the southernmost part of the ross ice shelf is sufficient to warrant direct tidal analysis tides are estimated here from ten operational icesat periods totaling 363 days a response analysis helps overcome unfavorable tidal sampling especially an s2 correlation with the annual cycle comparisons of tidal estimates against independent station data show rms constituent differences around 3 cm still somewhat large but an encouraging result for such a challenging region

tides on the ross ice shelf observed with icesat 1 the ice cloud and land elevation satellite icesat provides the first opportunity for measurement of surface elevation hi over the portions of the antarctic ice shelves that are south of the european remote sensing ers satellite maximum latitude 81 5 s the dominant source of short period variability in hi is ocean tides we use crossover elevation difference hi data from the ross ice shelf ris to demonstrate icesat s ability to detect the tidal signal and to compare the accuracy of several tide models the root mean square rms value of all ris measurements of hi is 0 74 m after removing the tide using the most accurate model the rms of the residual signal in regions of optimal model performance is 0 16 0 03 m this value corresponds to an uncertainty in hi of 0 11 0 02 m we postulate that the primary sources of the residual signal are tide model errors and the inverse barometer effect

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

modeling antarctic tides in response to ice shelf thinning and retreat tides play an important role in ice sheet dynamics by modulating ice stream velocity fracturing and moving ice shelves and mixing water beneath them any changes in ice shelf extent or thickness will alter the tidal dynamics through modification of water column thickness and coastal topography but these will in turn feed back onto the overall ice shelf stability here we show that removal or reduction in extent and or thickness of the ross and ronne filchner ice shelves would have a significant impact on the tides around antarctica the ronne filchner appears particularly vulnerable with an increase in m2 amplitude of over 0 5 m beneath much of the ice shelf potentially leading to tidally induced feedbacks on ice shelf sheet dynamics these results highlight the importance of understanding tidal feedbacks on ice shelves streams due to their influence on ice sheet dynamics

mushy magma beneath yellowstone a recent prospective on the yellowstone caldera discounts its explosive potential based on inferences from tomographic studies which suggests a high degree of crystallization of the underlying magma body in this study we show that many of the first teleseismic p wave arrivals observed at seismic stations on the edge of the caldera did not travel through the magma body but have taken longer but faster paths around the edge after applying a number of waveform modeling tools we obtain much lower seismic velocities than previous studies 2 3 km sec v p and 1 1 km sec v s we estimate the physical state of the magma body by assuming a fluid saturated porous material consisting of granite and a mixture of rhyolite melt and water and co 2 at a temperature of 800 c and pressure at 5 km 0 1 gpa we found that this relatively shallow magma body has a volume of over 4 300 km 3 and is about 32 melt saturated with about 8 water plus co 2 by volume

relationship between the insar measured uplift the structural framework and the present day stress field at lazufre volcanic area central andes abstract the stress regime and structural fabric in tectonically active areas control the shape of magmatic reservoirs and the orientation of dikes hence sub volcanic structures provide potentially good indicators to assess regional geodynamic processes through time we analyse the spatiotemporal evolution of the lazufre volcanic area in the central andes where a regional scale elliptical area of surface deformation commenced in 1997 the deformation signal observed by satellite radar interferometry insar can be explained by a magmatic intrusion located at approximately 10 km depth we compare this elongated region of deformation with several nearby volcanic structures we find that a higher concentration of volcanic vents is located within the deforming area compared to the surrounding region furthermore the mean alignment of volcanic structures is nw se n129 almost perpendicular to the mean elongation of the deformation ellipticity n28 applying the borehole breakout concept we propose a unifying model that explains magmatic activity both at the short term insar and long term volcano morphometric parameters a maximum horizontal compressive stress sh oriented nw se is found to be constant in time and in space and is dominant both at the depth of the intrusion and near the surface important implications arise such as the temporal stability of the principal stress directions and the significant role of topographic loading in the stress field analysis

precursory inflation of shallow magma reservoirs at west sunda volcanoes detected by insar 1 we use 2006 2009 alos interferometric synthetic aperture radar data over the entire west sunda arc indonesia home of 13 of the world s active volcanoes to derive arc wide time dependent ground deformation data we present unambiguous evidence of inflation at six volcanoes three of which erupted after the observation period we show that these volcanoes have shallow magma reservoirs at 1 3 km depth below the average regional elevation a global comparison of reservoir depths at arc volcanoes suggests that volcanoes in extensional and strike slip settings west sunda can develop shallow reservoirs whereas volcanoes in compressional settings may lack them thus magma ascend through the upper crust could be influenced by intra arc tectonic settings

three dimensional resistivity image of the magmatic system beneath lastarria volcano and evidence for magmatic intrusion in the back arc northern chile lazufre volcanic center located in the central andes is recently undergoing an episode of uplift conforming one of the most extensive deforming volcanic systems worldwide but its magmatic system and its connection with the observed uplift are still poorly studied here we image the electrical resistivity structure using the magnetotelluric method in the surroundings of the lastarria volcano one of the most important features in the lazufre area to understand the nature of the magmatic plumbing the associated fumarolic activity and the large scale surface deformation results from 3 d modeling show a conductive zone at 6 km depth south of the lastarria volcano interpreted as the magmatic heat source which is connected to a shallower conductor beneath the volcano showing the pathways of volcanic gasses and heated fluid a large scale conductive area coinciding with the area of uplift points at a magma intrusion at midcrustal depth

assimilation of grace tide solutions into a numerical hydrodynamic inverse model 1 we assimilate localized mass anomalies inferred from grace ranging measurements into a hydrodynamic model to improve tidal solutions around antarctica for the m2 s2 and o1 constituents the variational approach used accounts for the spatial averaging of tidal elevations implicit in the mass anomaly parametrization used for the grace tidal analysis as well as spatial correlation of errors in the resulting estimates the inverse solution shows better agreement with independent station tide measurements around antarctica and it reduces cross over residuals for icesat laser altimeter data over the filchner ronne and ross ice shelves demonstrating that grace data can provide useful constraints for improving hydrodynamic tidal models at high latitudes

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

a large magmatic sill complex beneath the toba caldera an understanding of the formation of large magmatic reservoirs is a key issue for the evaluation of possible strong volcanic eruptions in the future we estimated the size and level of maturity of one of the largest volcanic reservoirs based on radial seismic anisotropy we used ambient noise seismic tomography below the toba caldera in northern sumatra to observe the anisotropy that we interpret as the expression of a fine scale layering caused by the presence of many partially molten sills in the crust below 7 kilometers this result demonstrates that the magmatic reservoirs of present non eroded supervolcanoes can be formed as large sill complexes and supports the concept of the long term incremental evolution of magma bodies that lead to the largest volcanic eruptions

icesat antarctic elevation data preliminary precision and accuracy assessment 1 since first light on february 20th 2003 nasa s ice cloud and land elevation satellite icesat has derived surface elevations from 86 n to 86 s latitude these unique altimetry data have been acquired in a series of observation periods in repeated track patterns using all three geoscience laser altimeter system glas lasers here we focus on antarctic ice sheet elevation data that were obtained in 2003 2004 we present preliminary precision and accuracy assessments of selected elevation data and discuss factors impacting elevation change detection we show that for low slope and clear sky conditions the precision of gla12 laser 2a release 21 data is 2 1 cm and the relative accuracy of icesat elevations is 14 cm based on crossover differences

ice shelf tidal motion derived from ers altimetry 1 ocean tides beneath floating ice shelves can affect heat and water circulations within the subshelf cavity which may influence patterns of basal melting accurate tidal predictions are essential to eliminate vertical tide motions when mapping the flow speeds and thickness changes of floating ice global ocean tide solutions are typically accurate to 2 3 cm in amplitude however their coarse resolution limits their utility in coastal regions moreover the absence of satellite and extensive gauge station data in the polar regions has resulted in significant differences between recent tide model solutions around the antarctic continent we use 9 years of high resolution european remote sensing ers satellite radar altimeter range measurements and a modified form of the orthotide method to generate tidal solutions for a series of ice shelves around the antarctic peninsula we compare our tidal solution at george vi ice shelf on the western coast of the antarctic peninsula to direct measurements from british antarctic survey tide gauge records and contrast the results with solutions from the fes99 and kantha2 0 global and the cats01 02 antarctic ocean tide models the average root mean square vector difference between the tide gauge and tide model predictions of amplitude and phase was 10 9 17 1 4 2 and 15 4 cm for the ers ice shelf kantha2 0 cats01 02 and fes99 models respectively tidal predictions derived from the ers ice shelf model are closer to the tide gauge recordings than those of the global models and the inclusion of ers altimeter data may lead to improved global model performance

tides on filchner ronne ice shelf from ers radar altimetry 1 we use harmonic analysis of 8 years of ers satellite radar altimeter ra data at orbital crossovers to retrieve complex amplitude amplitude and phase coefficients for several major tidal harmonics over the filchner ronne ice shelf fris antarctica we describe a method for estimating the accuracy of this method which ranges from 2 to 8 cm per harmonic a comparison between m2 complex amplitude from a recent ocean model and from our ers ra analyses identifies two regions of the fris where the ra data are inconsistent with the model in both regions the differences can be attributed to incorrect specification of the grounding line location in the model our study demonstrates the value of ers ra data in antarctic ice shelf tide modeling and the potential for future altimeter satellites with high polar orbits to contribute to the definition of global tide height variations

ground surface deformation patterns magma supply and magma storage at okmok volcano alaska from insar analysis 1 intereruption deformation 1997 2008 eruption magma storage had increased by 3 7 5 2 1 0 7 m 3 or 85 100 of the 1997 eruption volume we propose that the supply rate decreased in response to the diminishing pressure gradient between the shallow storage zone and a deeper magma source region eventuallytheeffectsofcontinuingmagmasupplyandvesiculationofstoredmagmacaused acriticalpressurethresholdtobeexceeded triggeringthe2008eruption asimilarpatternof initially rapid inflation followed by oscillatory but generally slowing inflation was observed prior to the 1997 eruption in both cases withdrawal of magma during the eruptions depressurized the shallow storage zone causing significant volcano wide subsidence and initiating a new intereruption deformation cycle

two scales of inflation at lastarria cordon del azufre volcanic complex central andes revealed from asar envisat interferometric data abstract asar envisat interferometric synthetic aperture radar insar data collected over the lastarria cordon del azufre complex chile argentina between march 2003 and may 2005 show the persistence of the large wavelength ground inflation revealed by pritchard and simons in 2002 from the analysis of ers insar data nature 418 2002 167 170 after reducing the tropospheric contribution in the interferograms using a combination of data network adjustment and analysis of modis images we produced an accurate interferometric time series showing a 2 yr long temporal evolution of the ground displacements patterns two distinct inflating signals are detected the main signal covers an elliptical area with a 45 km nne ssw major axis and a 37 km minor axis it is correlated with a regional topographic dome we estimated its maximum inflation rate to 2 5 cm yr 1 we inverted the insar data for a range of source geometries spherical prolate ellipsoids penny shaped cracks the inferred source parameters for 2003 2005 period are consistent with an over pressured reservoir at shallow to intermediate crustal depths 7 15 km with an average volumetric rate of inflation of about 14 106 m3 yr 1 in addition to this main signal a new feature highlighted by the asar data is short wavelength inflation 6 km wide at the location of lastarria volcano on the northern margin of the large wavelength signal we explain this short wavelength signal by a spherical over pressured source lying 1000 m below the summit of lastarria volcano we estimate the average volumetric rate of inflation during the observation period to be 35 103 m3 yr 1 it is remarkable that both volumetric variations for the large and small inflations exhibit the same evolution during the 2003 2005 period suggesting that both processes could be related on the basis of the inversion results and of arguments provided by field evidences and a morpho structural analysis of the digital elevation model of the area we propose that the deep source have a magmatic origin while the shallow source is most likely related to hydrothermal fluids in our interpretation the on going deformation processes observed at lastarria cordon del azufre volcanic complex could represent an evolving pre caldera silicic system further field geological and geophysical investigations will be required to confirm these hypotheses and refine the proposed model mostly based on satellite observations

surface elevation changes at the front of the ross ice shelf implications for basal melting 1 rapid melting beneath the ross ice shelf ris occurs near the ice front likely in response to a secondary buoyant plume with tidal mixing and is sensitive to seasonal water temperatures in front of the ice shelf the front of the ris is examined using glas icesat laser altimetry data spatial and temporal changes in surface elevations are attributed to enhanced basal melting of the ice shelf near the ice front melt rates b increase exponentially as the front is approached from approximately zero at 40 km from the front to an average of 2 8 1 0 m a 1 within the front kilometer melt estimates within the front 60 km are best fit by the relationship b 2 0 exp x 11900 m a 1 where x denotes distance from the front frontal melt totals approximately 16 km3 a 1 in the front 40 km which accounts for between 10 and 40 of current published estimates of total melt beneath the ris spatial averaging along the front reveals a different pattern of melt in regions that have recently calved as compared to regions that have not calved frontal melt is modeled as a one dimensional buoyant plume with tidal currents included these model results imply that modest increases in sea surface temperatures will lead to considerable increases in melting beneath the ice shelf front

improving antarctic tide models by assimilation of icesat laser altimetry over ice shelves 1 assimilation of laser altimeter data from the ice cloud and land elevation satellite icesat significantly improves the accuracy of ocean tide models for the ross ice shelf ris for the most energetic tidal harmonic k1 assimilation reduces the root mean square error rmse between the model and a set of 16 independent tide records on and near the ris from 6 0 to 2 8 cm and the combined rmse for the six most energetic tidal harmonics from 7 7 to 5 4 cm when only the six most recent and highest quality tide records are considered the combined rmse is 4 8 cm this value is close to the uncertainty expected from tidal analyses of the short 1 2 month validation records indicating that assessing further improvements in tide model accuracy will require development of a higher quality validation data set

tide deflection of campbell glacier tongue antarctica analyzed by double differential sar interferometry and finite element method abstract a glacier tongue the terminus of a glacier projecting out from the coastline and floating over the ocean experiences vertical deflection due to the fluctuation of ocean tide accurate analysis of the tidal deflection of a glacier tongue is necessary to understand the elastic properties and dynamics of glacial ice we extracted the tidal deflection of campbell glacier tongue cgt one of the fast flowing glacier tongues in east antarctica by using 120 double differential interferometric sar ddinsar images from the 16 cosmo skymed one day tandem interferometric sar image pairs obtained during 2010 and 2011 a map of tide deflection ratio map defined as the ratio of the tidal deflection over tide height was generated by pixel based linear regression between the ddinsar derived tidal deflection and the tidal variation predicted by various tide models such as tpxo7 1 fes2004 cats2008a and ross inv after the inverse barometer effect correction we also generated the maps of r 2 root mean square error rmse and intercept of the linear regression model we confirmed that the horizontal flow of the campbell glacier is steady over the whole data acquisition period due to the fact that values were close to zero over the grounded part of the glacier ross inv provided the most reliable map with the highest r 2 0 97 and the smallest rmse 0 3 cm beyond the hinge zone than other tide models the spatial variation of the tidal response of the whole cgt was clearly defined from the map the grounding line retreated by 0 3 1 5 km in comparison with that in 1996 defined by rignot et al 2011a the ice thickness of cgt was estimated to be 397 71 m from icesat surface elevation data the young s modulus of cgt was found to be 0 5 1 3 gpa 0 8 gpa at an ice thickness of 397 m by simulating the in the hinge zone using a 2 dimensional finite element method

strain pattern and deformational history in the eastern part of the cauvery shear zone southern india abstract regional structural mapping guided by remote sensing interpretation in the eastern part of the cauvery shear zone csz southern granulite terrain reveals a structural framework of two major boundary shear zones interlinked by a set of sigmoidal shear belts the strain pattern and deformational history are manifest in terms of two major episodes d1 and d2 while d1 structures are well preserved in low strain areas the d2 fabrics are well reflected in high strain belts enveloping the low strain domains our multiscale structural observations can be modelled in terms of a plan view duplex showing a cross sectional flower structure related to regional transpression resulting from late neoproterozoic collisional processes in the eastern gondwana

hydrothermal and magmatic reservoirs at lazufre volcanic area revealed by a high resolution seismic noise tomography we determine here for the first time the geometry and location of the hydrothermal and magmatic reservoirs in the lazufre volcanic area this furthers the understanding of the origin of one of the largest worldwide volcanic uplift regions both in space and amplitude the exact locations and shapes of the sources generating a double wide uplift region in the lazufre found by past deformation data insar and gps and generating hydrothermal and magmatic fluids found by geochemical gas analysis have not been well delimited in this study we use seismological data to perform a 3 d high resolution s wave velocity model which allows defining better the locations and shapes of the sources of the deformations and the hydrothermal and magmatic reservoirs we find three anomalies two of them with s wave velocity of about 1 2 1 8 km s are located below the lastarria volcano the shallow one 1 km below the volcano base has a funnel like shape the deeper one is located between a depth of 3 and 6 km below the volcano base both are strongly elliptical in an ew direction and separated by a 2 3 km thick zone with vs of 1 5 2 km s as far as these anomalies are located under the hydrothermal activity of lastarria volcano they are interpreted as a double hydrothermal the shallow part and magmatic source the deeper part the latter can feed the former this double hydrothermal and magmatic source is in agreement with previous geochemical deformation gps and insar and magneto telluric studies in particular it explains the double origin of the gases hydrothermal and magmatic the third low velocity zone with s wave velocity of about 2 3 km s located at 5 km depth and deeper is centered beneath an area of surface uplift as determined by insar data we compare the seismic tomography and insar results to propose that this low velocity zone is at the top of a large reservoir hosting hydrothermal fluids and possibly also magma

accuracy assessment of ocean tide models around antarctica 1 accurate ocean tide models for the circum antarctic seas are required to remove unwanted signals from floating ice elevation and space borne time variable gravity measurements e g grace we present accuracy assessments for several global csr4 fes2004 fes99 got00 2 nao 99b tpxo6 2 and antarctic cada00 10 and cats02 01 ocean tide models using coastal and pelagic tide gauges gravimetric data and gps records of ice shelf surface elevation the accuracies of csr4 and nao 99b are poor in the ice shelf regions the optimum model for the entire circum antarctic seas is tpxo6 2 with a root mean square deviation of 5 7 cm 40 lower than the next best model fes2004 the main exception is the filchner ronne ice shelf where cada00 10 and cats02 01 most accurately represent observations from two sites near the rutford ice stream grounding line

ocean tides in the weddell sea new observations on the filchner ronne and larsen c ice shelves and model validation 1 ocean tides under the large weddell sea ice shelves are among the least well observed on earth here we present new spatially extensive observations of the vertical tidal motion of the filchner ronne and larsen c ice shelves using global positioning system gps data spanning a few weeks to years we pay particular attention to the major tidal constituents m2 s2 o1 k1 as well as important grace aliasing periods k2 and s1 we compare the estimated constituents with recent global and regional tide models and find that no single model is the most accurate across all constituents or ice shelves the root sum square errors are 7 8 cm cats2008a and tpxo7 2 and 11 12 cm got4 7 and fes2004 with the energetic m2 rmse 4 8 cm and s2 4 5 cm generally dominating these statistics the fes2004 k1 is particularly inaccurate near the larsen c ice shelf with errors approaching 20 cm meaning that grace release 4 estimates of mass change in the northern antarctic peninsula will be biased we find tidal energy at 3 4 5 6 and weakly at 7 cycles per day at all of our sites the largest amplitudes within these bands are at m4 mo3 and sp3 and approach 30 mm although significant spatial variations exist we show that they generally do not appear to originate in areas of reduced water column in ice shelf grounding zones comparing model estimates with our m4 ms4 and mn4 values shows that models do not accurately represent these terms

shallow seismicity triggered seismicity and ambient noise tomography at the long dormant uturuncu volcano bolivia using a network of 15 seismometers around the inflating uturuncu volcano from april 2009 to 2010 we find an average rate of about three local volcano tectonic earthquakes per day and swarms of 5 60 events a few times per month with local magnitudes ranging from 1 2 to 3 7 the earthquake depths are near sea level more than 10 km above the geodetically inferred inflation source and the altiplano puna magma body the mw 8 8 maule earthquake on 27 february 2010 triggered hundreds of earthquakes at uturuncu with the onset of the love and rayleigh waves and again with the passage of the x2 x3 overtone phases of rayleigh waves this is one of the first incidences in which triggering has been observed from multiple surface wave trains the earthquakes are oriented nw se similar to the regional faults and lineaments the b value of the catalog is 0 49 consistent with a tectonic origin of the earthquakes we perform ambient noise tomography using love wave cross correlations to image a low velocity zone at 1 9 to 3 9 km depth below the surface centered slightly north of the summit the low velocities are perhaps related to the hydrothermal system and the low velocity zone is spatially correlated with earthquake locations the earthquake rate appears to vary with time a seismic deployment from 1996 to 1997 reveals 1 5 earthquakes per day whereas 60 events day were seen during 5 days using one seismometer in 2003 however differences in analysis methods and magnitudes of completeness do not allow direct comparison of these seismicity rates the rate of seismic activity at uturuncu is higher than at other well monitored inflating volcanoes during periods of repose the frequent swarms and triggered earthquakes suggest the hydrothermal system is metastable