space geodetic observations of nazca south america convergence across the central andes space geodetic data recorded rates and directions of motion across the convergent boundary zone between the oceanic nazca and continental south american plates in peru and bolivia roughly half of the overall convergence about 30 to 40 millimeters per year accumulated on the locked plate interface and can be released in future earthquakes about 10 to 15 millimeters per year of crustal shortening occurred inland at the sub andean foreland fold and thrust belt indicating that the andes are continuing to build little 5 to 10 millimeters per year along trench motion of coastal forearc slivers was observed despite the oblique convergence

distribution of slip from 11 mw 6 earthquakes in the northern chile subduction zone we use interferometric synthetic aperture radar gps and teleseismic data to constrain the relative location of coseismic slip from 11 earthquakes on the subduction interface in northern chile 23 25 s between the years 1993 and 2000 we invert body wave waveforms and geodetic data both jointly and separately for the four largest earthquakes during this time period 1993 m w 6 8 1995 m w 8 1 1996 m w 6 7 1998 m w 7 1 while the location of slip in the teleseismic only geodetic only and joint slip inversions is similar for the small earthquakes there are differences for the 1995 m w 8 1 event probably related to nonuniqueness of models that fit the teleseismic data there is a consistent mislocation of the harvard centroid moment tensor locations of many of the 6 6 earthquakes as well as three m w 7 events from the 1980s all of these earthquakes appear to rupture different portions of the fault interface and do not rerupture a limited number of asperities

block modeling with connected fault network geometries and a linear elastic coupling estimator in spherical coordinates geodetic observations of interseismic deformation provide constraints on the partitioning of fault slip across plate boundary zones the spatial distribution of both elastic and inelastic strain accumulation and the nature of the fault system evolution here we describe linear block theory which decomposes surface velocity fields into four components 1 plate rotations 2 elastic deformation from faults with kinematically consistent slip rates 3 elastic deformation from faults with spatially variable coupling and 4 homogeneous intrablock strain elastic deformation rates are computed for each fault segment in a homogeneous elastic half space using multiple optimal planar cartesian coordinate systems to minimize areal distortion and triangular dislocation elements to accurately represent complex fault system geometry block motions fault slip rates elastic coupling and internal block strain rates are determined simultaneously using a linear estimator with constraints from both geodetically determined velocity fields and geologic fault slip rate estimates we also introduce algorithms for efficiently implementing alternative fault network geometries to quantify parameter sensitivity to nonlinear perturbations in model geometry

short and long term effects of gps measured crustal deformation rates along the south central andes in this study we present the contemporary crustal deformation field along the central and southern andes 17 42 s estimated from four global positioning sys tem gps campaigns conducted in 1994 97 we find that the majority of the observed crustal deformation field is relatively homogenous roughly parallel to the plate conver gence direction with decreasing velocities away from the trench we attribute this type of deformation pattern to the inter seismic phase of an earthquake deformation cycle caused by 100 locking of the thrust interface between the subducting nazca and the overrid ing south american plates we have also detected a strong post seismic deformation sig nal in the vicinity of the 1995 mw8 0 antofagasta 22 26 s and 1960 mw9 5 chile 38 43 s earthquakes this type of deformation can be described as short term in nature compared to geological timescales the above conclusions are based on the results of the 3 d andean elastic dislocation model aedm by subtracting the aedm predicted deformation rates from the observations we obtained a residual velocity field that high lights the post seismic as well as more long term deformation eects for example we find a strong evidence for the continuing crustal shortening across the back arc reach ing its maximum 4 mm yr in the very north of our study area in addition between latitudes 29 34 s there is an indication of e w oriented extension within the fore arc in accordance with the recent geologic findings for the n s oriented normal faulting

an integrated crustal velocity field for the central andes 1 we present an integrated velocity field for the central andes derived from gps observations collected between january 1993 and march 2001 that eliminates the velocity bias between the south america nazca plate project snapp and central andes gps project cap velocity fields published by norabuena et al 1998 and bevis et al 1999 the reference frame is realized by minimizing the motion of eight continuous gps stations and one rover gps station located in the stable core of the south american plate the rms horizontal motion of these stations is just 1 1 mm yr the amplitude of these residual motions is roughly compatible with expected levels of measurement error in our new solution five of the six snapp stations located just outside the orogenic belt are effectively stationary and the velocities for adjacent cap and snapp stations now agree at a level consistent with their formal uncertainties

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

behaviour and taphonomic loss in foraminiferal assemblages of mangrove swamps of french guiana abstract fifty three surface sediment samples were collected in january 1999 july 2000 and december 2000 on mud flats and in mangrove swamps of french guiana sampling stations were selected to provide information on different environmental conditions on the mud flats and in the mangrove forest thirteen samples were also collected at a depth of about 8 12 cm in the sediment additional samples were collected from three long cores in the channel of the kaw river the main parameter controlling the distribution of recent foraminiferal assemblages is the seasonally variable relative influence of coastal water of reduced salinity and low ph low ca river water areas under the influence of coastal water are dominated by calcareous species mainly ammonia tepida and cribroelphidium spp even in mangrove swamps during the dry season river water influences almost all the study area during the rainy season and leads to the dominance of agglutinated species with the nature of the assemblages depending on local environmental characteristics on the mud flats tests are typically well preserved in the 10 cm below the surface that is the most important taphonomically active zone for foraminifera however owing to intense bioturbation the taphonomic processes in the mangrove swamp may result in the total destruction of the microfauna including agglutinated tests this study shows that the preservation of thanatocoenoses in mangrove swamp environments of french guiana only occurs in exceptional circumstances when they are preserved the remaining assemblages even if modified by taphonomic processes give valuable information for paleoenvironmental reconstructions in this environment

on the strength of interplate coupling and the rate of back arc convergence in the central andes an analysis of the interseismic velocity field 1 we interpret the interseismic crustal velocity field of the central andes using a simple three plate model in which the andean mountain belt is treated as a rigid microplate located between the nazca and south american soam plates we assume that the euler vectors associated with these plates are strictly coaxial and that the surface velocity field can be decomposed into an elastic loading field driven by locking of the main plate boundary and a smaller contribution associated with back arc convergence we obtain our best fit to the geodetic velocities if the main plate boundary is fully 100 locked between depths of 10 50 km and 8 5 of nazca soam plate convergence is achieved in the back arc by underthrusting of the brazilian shield beneath the subandean zone

importance of ocean tidal load corrections for differential insar large time series of interferometric synthetic aperture radar insar measurements make it possible to detect slow tectonic motions of the earth s surface on the order of millimeters per year here we illustrate the importance of correcting insar data for the effects of ground displacements due to ocean tidal loads otl these loads can cause displacement gradients greater than 3 cm per 100 km which is larger than the accuracy of insar techniques and can be a significant percentage of the measured displacement due to slow tectonic processes we demonstrate the importance of otl with predicted displacements from selected regions of tectonic interest

atmospheric models gps and insar measurements of the tropospheric water vapour field over mount etna 1 dynamic models of atmospheric movement over the mount etna volcano are used to calculate the path delays affecting radar caused by variable water vapour in the troposphere we compare these model results with the equivalent differential radar interferogram generated by two ers 2 sar images taken 35 days apart and the water vapour delay retrievals from a network of fourteen gps stations distributed over the volcano the atmospheric model delay field agrees wellwith thelong wavelength spatial differences measured by insar and those measured by gps index terms 6924 radio science interferometry 1243 geodesy and gravity space geodetic surveys 3367 meteorology and atmospheric dynamics theoretical modeling 6964 radio science radio wave propagation 8499 volcanology general or miscellaneous citation wadge g et al atmospheric models gps and insar measurements of the tropospheric water vapour field over mount etna geophys res lett 29 19 1905 doi 10 1029 2002gl015159 2002

source model for the mw 6 7 23 october 2002 nenana mountain earthquake alaska from insar 1 the 23 october 2002 nenana mountain earthquake mw 6 7 occurred on the denali fault alaska to the west of the mw 7 9 denali earthquake that ruptured the same fault 11 days later we used 6 interferograms constructed using radar images from the canadian radarsat 1 and european ers 2 satellites to determine the coseismic surface deformation and a source model data were acquired on ascending and descending satellite passes with incidence angles between 23 and 45 degrees and time intervals of 72 days or less modeling the event as dislocations in an elastic half space suggests that there was nearly 0 9 m of right lateral strike slip motion at depth on a near vertical fault and that the maximum slip in the top 4 km of crust was less than 0 2 m the nenana mountain earthquake increased the coulomb stress at the future hypocenter of the 3 november 2002 denali earthquake by 30 60 kpa

earthquake cycle dominates contemporary crustal deformation in central and southern andes with the advent of global positioning system gps technology and its applications to high precision geodesy earth scientists have gained an unprecedented opportunity to study the kinematics and dynamics of present day deformation processes along plate boundary zones however until now our knowledge of the deformation processes associated with the andean subduction along the western coast of south america has been limited here we present first estimates of present day crustal deformation rates in the central and southern sections of the andes between latitudes 22 s and 42 s we find that the deformation in the central section of our study area is dominated by the interseismic phase of an earthquake deformation cycle caused by 100 coupling of the thrust interface between the subducting nazca and the overriding south america plates the estimated depth of coupling is not uniform along strike north of 30 s it is v33 km deep while south of 35 s it reaches 50 km depth in addition we observed postseismic relaxation effects in the northern part of our network in the area of the 1995 mw8 0 antofagasta earthquake south of 38 s we detected a similar deformation pattern as in the antofagasta area which we attribute to postseismic relaxation effects of the 1960 mw9 5 valdivia earthquake fl 2001 elsevier science b v all rights reserved

interferometric synthetic aperture radar atmospheric correction gps topography dependent turbulence model 1 over the last two decades repeat pass interferometric synthetic aperture radar insar has been widely used as a geodetic technique for measuring the earth s surface including topography and deformation like other astronomical and space geodetic techniques repeat pass insar is limited by the variable spatial and temporal distribution of atmospheric water vapor in this paper a topography dependent turbulence model gttm for short has been developed using gps data only to produce zenith path delay difference maps for insar atmospheric correction application of the gttm model to ers tandem data over the los angeles southern california integrated gps network area has shown that use of the gttm can reduce water vapor effects on interferograms from 10 mm down to 5 mm which is of great interest to a wide community of geophysicists the principal finding of this paper is that interpolation methods should be applied to zenith total delay ztd differences from different times instead of ztd values themselves for the purpose of insar atmospheric correction this is crucial to reduce if not completely remove topographic effects on ztd values

testing mechanisms of subduction zone segmentation and seismogenesis with slip distributions from recent andean earthquakes abstract a long standing goal of subduction zone earthquake studies is to determine whether or not there are physical processes that control seismogenesis and the along strike segmentation of the megathrust studies of individual earthquakes and global compilations of earthquakes find favorable comparison between coseismic interplate slip distributions and several different long lived forearc characteristics such as bathymetry coastline morphology crustal structure and interplate frictional properties but no single explanation seems to govern the location and slip distribution of all earthquakes one possible reason for the lack of a unifying explanation is that the inferred earthquake parameters most importantly the slip distribution calculated in some areas were inaccurate blurring correlation between earthquake and physical parameters in this paper we seek to test this possibility by comparing accurate slip distributions constrained by multiple datasets along several segments of a single subduction zone with the various physical properties that have been proposed to control or correlate with seismogenesis we examine the rupture area and slip distribution of 6 recent and historical large mw 7 earthquakes on the peru northern chile subduction zone this analysis includes a new slip distribution of the 14 november 2007 mw 7 7 earthquake offshore tocopilla chile constrained by teleseismic body wave and insar data in studying the 6 events we find that no single mechanism can explain the location or extent of rupture of all earthquakes but analysis of the forearc gravity field and its gradients shows correlation with many of the observed slip patterns as suggested by previous studies additionally large scale morphological features including the nazca ridge arica bend mejillones peninsula and transverse crustal fault systems serve as boundaries between distinct earthquake segments

some thoughts on the use of insar data to constrain models of surface deformation noise structure and data downsampling repeat pass interferometric synthetic aperture radar insar provides spatially dense maps of surface deformation with potentially tens of millions of data points here we estimate the actual covariance structure of noise in insar data we compare the results for several independent interferograms with a large ensemble of gps observations of tropospheric delay and discuss how the common approaches used during processing of insar data affects the inferred covariance structure motivated by computational concerns associated with numerical modeling of deformation sources we then combine the data covariance information with the inherent resolution of an assumed source model to develop an efficient algorithm for spatially variable data resampling or averaging we illustrate these technical developments with two earthquake scenarios at different ends of the earthquake magnitude spectrum for the larger events our goal is to invert for the coseismic fault slip distribution for smaller events we infer the hypocenter location and moment we compare the results of inversions using several different resampling algorithms and we assess the importance of using the full noise covariance matrix

a multiscale approach to estimating topographically correlated propagation delays in radar interferograms when targeting small amplitude surface deformation using repeat orbit interferometric synthetic aperture radar insar observations can be plagued by propagation delays some of which correlate with topographic variations these topographically correlated delays result from temporal variations in vertical stratification of the troposphere an approximate model assuming a linear relationship between topography and interferometric phase has been used to correct observations with success in a few studies here we present a robust approach to estimating the transfer function k between topography and phase that is relatively insensitive to confounding processes earthquake deformation phase ramps from orbital errors tidal loading etc our approach takes advantage of a multiscale perspective by using a band pass decomposition of both topography and observed phase this decomposition into several spatial scales allows us to determine the bands wherein correlation between topography and phase is significant and stable when possible our approach also takes advantage of any inherent redundancy provided by multiple interferograms constructed with common scenes we define a unique set of component time intervals for a given suite of interferometric pairs we estimate an internally consistent transfer function for each component time interval which can then be recombined to correct any arbitrary interferometric pair we demonstrate our approach on a synthetic example and on data from two locations long valley caldera california which experienced prolonged periods of surface deformation from pressurization of a deep magma chamber and one coseismic interferogram from the 2007 mw 7 8 tocapilla earthquake in northern chile in both examples the corrected interferograms show improvements in regions of high relief independent of whether or not we pre correct the data for a source model we believe that most of the remaining signals are predominately due to heterogeneous water vapor distribution that requires more sophisticated correction methods than those described here

crustal deformation and fault slip during the seismic cycle in the north chile subduction zone from gps and insar observations summary the different phases of the earthquake cycle can produce measurable deformation of the earth s surface this work is aimed at describing the evolution of that deformation in space and time as well as the distribution of causal slip on the fault at depth we have applied gps and synthetic aperture radar sar interferometry insar techniques to northern chile where fast plate convergence rates are associated with large subduction earthquakes and extensive crustal deformation the region of northern chile between 18 s and 23 s is one of the most important seismic gaps in the world with no rupture having occurred since 1877 in 1995 the mw 8 1 antofagasta earthquake ruptured the subduction interface over a length of 180 km in the region immediately to the south of this 450 km long gap the coseismic deformation associated with this event has been documented previously here we use gps position time series for 40 benchmarks measured between 1996 and 2000 and ers sar interferograms for the interval between 1995 and 1999 to map both the post seismic deformation following the 1995 event and the ongoing interseismic deformation in the adjacent gap region in the seismic gap the interseismic velocities of 20 30 mm yr 1 to the east with respect to south america are mapped both the gps and the insar measurements can be modelled with 100 per cent coupling of the thrust interface of the subduction to a depth of 35 km with a transition zone extending down to 55 km depth the slip rate in that zone increases linearly from zero to the plate convergence rate south of the gap the interferometric map shows interseismic deformation superimposed with deformation following the 1995 earthquake and covering the same area as the coseismic deformation some 40 per cent of this deformation is related to seismic activity in the 3 3 yr following the 1995 event in particular slip during a mw 7 1 earthquake in 1998 however most of the signal 60 per cent corresponds to post seismic deformation resulting from widespread aseismic slip in the subduction interface the afterslip appears to have occurred down dip in the transition zone at 35 55 km depth and to have propagated laterally northwards at 25 45 km depth under the mejillones peninsula which is a prominent geomorphological feature at the boundary between the 1877 and 1995 rupture zones we propose a simple slip model for the seismic cycle associated with the antofagasta earthquake where the transition zone alternates between aseismic shear and seismic slip

motion on upper plate faults during subduction zone earthquakes case of the atacama fault system northern chile 1 motion on the atacama fault system afs in northern chile is driven by andean subduction zone processes we use two approaches observational and theoretical to evaluate how the afs and other forearc faults responded to coseismic stress induced by one well studied megathrust earthquake the 1995 mw 8 1 antofagasta event we use synthetic aperture radar interferometry insar to search for small scale coseismic and postseismic deformation on individual faults the insar data are ambiguous some images show offset consistent with coseismic faulting on the paposo segment of the afs and others lack such signal the fact that we do not observe the fault like displacement in all coseismic interferograms suggests that atmospheric contamination not tectonic deformation is responsible for the signal to explore the capacity of the earthquake to trigger motion on upper plate faults we use seven published slip maps constrained by geodetic and or seismic data to calculate static and dynamic coulomb stress change csc on faults in the antofagasta region the static csc field varies between models and depends on the distribution of coseismic interplate slip on the basis of the csc distribution predicted by our preferred model constrained by all available data we suggest it was unlikely that the antofagasta earthquake directly triggered normal motion on the afs and the insar data are consistent with this null result field reports of normal faulting related to the earthquake may reflect recent but not coseismic motion or highly localized behavior not representative of the regional coseismic stress field

crustal motion in the southern andes 26 36 s do the andes behave like a microplate 1 a new global positioning system gps derived velocity field for the andes mountains 26 36 s allows analysis of instantaneous partitioning between elastic and anelastic deformation at the orogen s opposing sides adding an andes microplate to the traditional description of nazca south america plate convergence provides the kinematic framework for nearly complete explanation of the observed velocity field the results suggest the oceanic nazca boundary is fully locked while the continental backarc boundary creeps continuously at 4 5 mm yr the excellent fit of model to data 1 7 mm yr rms velocity misfit and the relative aseismicity of the upper crust in the interior andean region in comparison with its boundaries supports the notion that the mountains are not currently accruing significant permanent strains additionally the model implies permanent deformation is not accumulating throughout the backarc contractional wedge but rather that the deformation is accommodated only within a narrow deformational zone in the backarc

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

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

an insar based survey of volcanic deformation in the central andes we extend an earlier interferometric synthetic aperture radar insar survey covering about 900 remote volcanos of the central andes 14 27 s between the years 1992 and 2002 our survey reveals broad 10s of km roughly axisymmetric deformation at 4 volcanic centers two stratovolcanoes are inflating uturuncu bolivia and hualca hualca peru another source of inflation on the border between chile and argentina is not obviously associated with a volcanic edifice here called lazufre and a caldera cerro blanco also called robledo in northwest argentina is subsiding we explore the range of source depths and volumes allowed by our observations using spherical ellipsoidal and crack like source geometries we further examine the effects of local topography upon the deformation field and invert for a spherical point source in both elastic half space and layered space crustal models we use a global search algorithm with gradient search methods used to further constrain best fitting models inferred source depths are model dependent with differences in the assumed source geometry generating a larger range of accepted depths than variations in elastic structure source depths relative to sea level are 8 18 km at hualca hualca 12 25 km for uturuncu 5 13 km for lazufre and 5 10 km at cerro blanco deformation at all four volcanoes seems to be time dependent and only uturuncu and cerro blanco were deforming during the entire time period of observation inflation at hualca hualca stopped in 1997 perhaps related to a large eruption of nearby sabancaya volcano in may 1997 although there is no obvious relation between the rate of deformation and the eruptions of sabancaya we do not observe any deformation associated with eruptions of lascar chile at 16 other volcanoes that had recent small eruptions or fumarolic activity or associated with a short lived thermal anomaly at chiliques volcano we posit a hydrothermal system at cerro blanco to explain the rate of subsidence there for the last decade we calculate the ratio of the volume of magma intruded to extruded is between 1 10 and that the combined rate of intrusion and extrusion is within an order of magnitude of the inferred geologic rate

insight into ground deformations at lascar volcano chile from sar interferometry photogrammetry and gps data implications on volcano dynamics and future space monitoring abstract we present a detailed study of lascar volcano chile based on the combination of satellite aerial and ground based data in order i to better characterize the deformation style of andean explosive volcanoes and ii to provide new insights on the potential of space techniques to monitor active volcanic deformations on such edifices lascar is one of the most active volcanoes in central andes characterized by a recent cyclic activity additionally it is located in favourable conditions for radar imaging lascar thus offers very good conditions for studying large to small scale ground deformations associated with volcano dynamics the analysis of insar synthetic aperture radar interferometry time series data from the european and japanese satellites ers jers acquired between 1993 and 2000 encompassing three eruptive events confirmed the absence of broad far field deformation signal thus during the recent activity of lascar we discard significant magmatic input at depth the following approaches were used to improve the insar signal noise ratio in order to detect possible local deformation we carried out a quantitative evaluation of the potential tropospheric contribution in insar interferograms for the salar de atacama lascar area using radar asar envisat and spectrometer modis data we also used an accurate aerial photogrammetric and gps constrained dem in our insar data reprocessing we find a co eruptive ground deformation confined into the summit crater for the 1995 eruption this deformation has spatial dimension of 500 by 400 m and relates to a subsidence of crater floor up to 17 mm we interpret it as pressure or volume decrease at subsurface levels below the active crater our study made it possible to image a new near field volcanic deformation confined within the summit crater of the lascar volcano it also demonstrates that the combination of precise photogrammetry dem and insar data can significantly improve our ability to remotely sense subtle surface deformation on these explosive volcanoes this methodology might contribute to better understand volcano dynamics and to complement their monitoring in remote areas

accounting for atmospheric delays in insar data in a search for long wavelength deformation in south america insar has been successfully used to observe the deformation of the earth s surface from many processes but mostly dealing with relatively large signals 1 cm over short wavelengths 100 km we use interferometric synthetic aperture radar insar data from two orbital tracks in northern chile to study the feasibility of imaging the broad interseismic ground deformation signal from the nazca plate subduction in order to measure 1 5 cm year of ground motion across 1000 km of satellite track length due to interseismic loading of the subduction interface the atmospheric contribution cannot be ignored we attempt to remove the atmospheric signal using global weather models and by estimating atmospheric parameters directly from the insar data due to the poor temporal and spatial resolutions of the weather model this method fails to produce reliable results the empirical model reduces the phase variance in the interferograms but leaves a residual signal that continues to mask the interseismic signal which demonstrates the importance of carefully applying corrections to the data as they can significantly affect any interpretation that is based on the corrected observations although the methods presented here are not suited for removing all atmospheric path delays this paper does provide suggestions about improvements that can be made to corrective techniques methods that should be further developed are the following 1 corrections with independent and direct observations of atmospheric properties e g continuous gps or satellite observations e g the meris sensor 2 improvements using empirical corrections either in conjunction with a deformation model or constrained by real atmospheric structures and 3 further work with high resolution and improved weather models

formation and growth of extensional fracture sets naturally occurring extension fractures including some joints and veins form sets consisting of numerous subparallel fractures each with well defined ends in order to correctly interpret these fractures in the field it is necessary to determine which factors control the geometries of fracture sets this requires consideration of the conditions leading to both the initiation and the cessation of fracture propagation a fracture begins to propagate when the crack extension force reaches a critical value which is a property of the rock and of environmental conditions after propagation initiates the crack extension force varies owing to 1 increase in crack length 2 change in remote strain 3 elastic interaction with nearby cracks 4 change in internal fluid pressure and 5 stress relaxation due to growth of cracks in the surrounding rock each fracture continues to propagate as long as its crack extension force exceeds the critical value and terminates when this condition is no longer met neglecting fluid effects the final geometry of the fracture set is a function of the remote strain history and the initial crack geometry which can be characterized by the initial crack density for low initial densities large increases in crack length occur with little or no increase in remote strain however for large initial densities crack lengths increase only if the applied strain increases this analysis is used to estimate the variation in remote strain during formation of a fracture set in granitic rock from observations of the final fracture geometry