time space modeling of the dynamics of santorini volcano greece during the 2011 2012 unrest the 2011 2012 unrest of santorini thera volcano aegean sea greece was associated with microseismicity confined to the kameni line kl a major tectonovolcanic lineament and has been regarded as a single magmatic episode produced by a spherical source derived from inversion of gps data however such a source is a few kilometers away from the kl and cannot explain observed microseismicity for this reason we divided the unrest episode into five periods based on the fluctuations of seismicity and deformation rates and investigated the connection between seismicity and two spherical magmatic point sources for each period based on a new inversion algorithm and consistent gps data we recognized during the volcano unrest episode an unstable pattern of intrusions correlating with both the kl and columbo line cl a second major tectonovolcanic lineament intrusions correlating with cl appear relatively persistent aseismic small and shallow which is consistent with marine geophysical evidence for arrested shallow dykes and geodetic evidence from a previous inflation episode during the two periods of intense seismicity sources close to the kl explaining seismicity were obtained this unstable pattern of intrusions explains both the well observed location and timing of seismicity as well as ground deformation and is consistent with results of an okada type inversion for a sill and a dyke the stress interactions between the two sources agree with coulomb failure stress models santorini appears to be affected by concurrent offset magma pulses and only recent activity from a magma pulse below the kl produced microseismic swarms

off line acquisition of crustal reflection and refraction data a piggy back seismic reflection survey was carried out in 1984 as part of the dekorp 2 s profile the signal from explosive sources was digitally recorded on 120 channels the objectives were a to record crustal reflections at a wide range of incidence angles 5 85 km offset b to provide 3 d control of deep crustal reflectors seen on the main profile an important consideration throughout the fieldwork was to avoid interference with the main reflection survey this experiment showed that explosive charges as small as 5 90 kg may provide sufficient energy for observations from the steep angle to the wide angle range the off line position of the receivers allowed the reconstruction of steep angle reflection profiles parallel and perpendicular to the main reflection line a strong diffraction cluster on the main line could be correlated laterally and indications about the diffractors shape could be obtained

mapping inflation at santorini volcano greece using gps and insar 1 recent studies have indicated that for the first time since 1950 intense geophysical activity is occurring at the santorini volcano here we present and discuss the surface deformation associated with this activity spanning from january 2011 to february 2012 analysis of satellite interferometry data was performed using two well established techniques namely persistent scatterer interferometry psi and small baseline subset sbas producing dense line of sight los ground deformation maps the displacement field was compared with gps observations from 10 continuous sites installed on santorini results show a clear and large inflation signal up to 150 mm yr in the los direction with a radial pattern outward from the center of the caldera we model the deformation inferred from gps and insar using a mogi source located north of the nea kameni island at a depth between 3 3 km and 6 3 km and with a volume change rate in the range of 12 million m3 to 24 million m3 per year the latest insar and gps data suggest that the intense geophysical activity has started to diminish since the end of february 2012

p and s velocity structures of the santorini coloumbo volcanic system aegean sea greece obtained by non linear inversion of travel times and its tectonic implications abstract one of the most prominent tectonic features of the eastern mediterranean region is the hellenic volcanic arc in the southern aegean sea with the santorini island being one of the most active volcanic centers recent seismic studies show that the main seismic activity of the santorini volcanic center is strongly associated with the volcanic processes as well as with the seismo tectonic regime of the broader southern aegean sea area the main cluster of local seismicity is located near the northeastern edge of the santorini island beneath the coloumbo reef which is a submarine volcanic seamount of the santorini island volcanic system the p and s wave velocity structures of the santorini coloumbo volcanic system is studied by inverting travel times of local earthquakes recorded by two independent dense seismic arrays installed in the broader area of santorini islands during the period of september 2002 september 2005 in particular 137 local earthquakes with 1600 p phases and 1521 s phases recorded by 25 seismological stations have been selected for the inversion the inversion technique applied is non linear since three dimensional ray tracing is incorporated the reliability of the final tomographic results is demonstrated through resolutions tests using synthetic seismic data the obtained results confirm the strong variations of the p and s wave velocity structures in the area of santorini coloumbo volcanic system as well as the connection between the tectonic setting of the study area with the magmatic processes taking place beneath the two volcanoes the tomographic models show that a low velocity zone extends along the northeastern edge of the santorini island parallel to the kameni coloumbo fracture zone ne sw direction which corresponds to the western termination of the major ene wsw santorini amorgos fault zone evidence is presented that this structural lineament corresponds to a tecto volcanic fracture zone which probably links the volcanic center of santorini with the submarine volcano at coloumbo reef furthermore the tomographic results show indications that the magmatic chamber beneath the coloumbo volcanic seamount is located at a depth of 6 7 km in good agreement with recent independent studies in the area though this feature is not within the resolving power of the employed data set

fractal geometries of vein systems and the variation of scalingrelationships with mechanism abstract investigation of vein geometries has identified empirical relationships which allow extrapolation of outcrop scale observation to larger scales measurements of vein shapes and aspect ratios in a number of different environments demonstrate that veins follow similar empirical scaling laws to those of faults geometries of veins are easier to characterise accurately than faults because their thickness is related to the variation in displacement from zero at their tips to a maximum at their thickest point vein sizes obey the empirical relationship l kta where l length in mm t thickness in mm 20 1 this suggests that veins amplify initially by inflation and subsequently by elongation

the effects of topography on magma chamber deformation models application to mt etna and radar interferometry we have used a three dimensional elastic finite element model to examine the effects of topography on the surface deformation predicted by models of magma chamber deflation we used the topography of mt etna to control the geometry of our model and compared the finite element results to those predicted by an analytical solution for a pressurized sphere in an elastic half space topography has a significant effect on the predicted surface deformation for both displacement profiles and synthetic interferograms not only are the predicted displacement magnitudes significantly different but also the map view patterns of displacement it is possible to match the predicted displacement magnitudes fairly well by adjusting the elevation of a reference surface however the horizontal pattern of deformation is still significantly different thus inversions based on constant elevation reference surfaces may not properly estimate the horizontal position of a magma chamber we have investigated an approach where the elevation of the reference surface varies for each computation point corresponding to topography for vertical displacements and tilts this method provides a good fit to the finite element results and thus may form the basis for an inversion scheme for radial displacements a constant reference elevation provides a better fit to the numerical results

gravity interpretation of the southern wind river mountains wyoming the wind river range is the largest laramide uplift in wyoming and is cored by precambrian rocks thrust over sedimentary rocks of the green river basin to the southwest the origin of these uplifts is in dispute it has been ascribed to horizontal compression along thrusts or vertical movement along high angle reverse faults therefore the attitude of the bounding fault is critical to understanding the mechanics of deformation a gravity study based on 1800 stations has been carried out to attack this question and to complement a cocorp deep crustal reflection study smoothed free air gravity anomalies are highly positive over the wind river range and near zero over the adjacent margins bouguer gravity anomalies range from 252 and 225 mgal in the green river basin and wind river basin respectively to 150 mgal in the basement core of the wind river range the bulk density of sedimentary rocks in the adjacent basins is the critical parameter for gravity interpretation of the deep structure and ranges

two dimensional synthetic seismogram modeling of wide angle seismic data from the wichita uplift oklahoma abstract in conjunction with the 1979 cocorp wichita uplift survey wide angle reflection refraction data were recorded on a fixed array the object of the present study is to model and interpret these wide angle data to add independent constraints on the deep structure of the wichita uplift three common receiver profiles were extracted from the data recording apertures were 3 2 to 23 4 km to the north of the array 4 2 to 14 9 km to the east and 4 2 to 12 6 km to the west these profiles are modeled by iterative fitting of high frequency synthetic seismograms computed by asymptotic ray theory the model derived contains low velocity 2 0 to 2 16 km sec surficial sediments that vary in thickness these account for strong local travel time variations of 0 05 sec and for a small but persistent ghost arrival that follows all the main branches with a delay of 0 2 sec the basement granites rhyolites and gabbros are very near the surface throughout the study area both granite and gabbro outcrops are seen basement p wave velocities are therefore relatively high representative velocities are 4 7 km sec at 0 8 km depth 6 2 at 1 8 6 4 at 2 8 and 6 5 at 4 0 local velocities as high as 7 4 km sec may be present the basement is fairly transparent beneath the wichita uplift with only a few local reflectors present this is consistent with the cocorp results

low velocity zone reflections observed in geometrical shadows of refraction profiles summary a low velocity zone lvz shadow on a refraction profile may contain coherent energy if the lvz contains reflectors the corresponding pre critical reflection branches will lie within the geometrical shadow such energy is observed in data and can via inversion or synthetic seismogram modelling potentially provide information on the location and character of the main structural features those with significant reflectivity within the lvz

tracing surface features to great depths a powerful means for exploring the deep crust abstract seismic reflection profiling of the continental basement provides a means for tracing known features from the surface to great depths and hence for exploring and identifying deep and inaccessible subsurface geology some examples based on cocorp data illustrate the power and potential of this method which has not commonly been applied on a crustal scale

squeesar and gps ground deformation monitoring of santorini volcano 1992 2012 tectonic implications abstract the santorini volcanic complex svc has been in a dormant state for the last 60 years until january 2011 when upward influx of magma reawakened the volcano with intense radial ground deformation and inter caldera seismicity that lasted until january 2012 but declined afterwards this paper aims to study the ground deformation and the inferred tectonic implications of the svc for the period 1992 2012 mainly based on the squeesar technique and dgps campaign results of our local network which incorporates available data on internet from several continuous gps stations established on the island the spatial deformation of the svc during the quiet period 1992 2010 was deduced by joint analysis of ers1 and 2 and envisat it was found that the intra caldera palaea kammeni shield volcano was being uplifted 2 3 mm yr with increasing rate whilst the adjacent nea kammeni shield volcano was being subsided up to 6 mm yr with increasing rate the rest of the svc showed a velocity field varying from 1 to 2 mm yr indicating a rather linear deformation during that period the results from the gps network are in full agreement with the squeesar results based on the results of squeesar analysis of 12 envisat images and dgps cgps data to end 2012 the deformation for the unrest period 2011 2012 was non linear being characterized by strong radial deformation in the northern part of the caldera 50 120 mm yr and accelerating values 130 mm yr 2 combined gps squeesar mogi modeling indicated a source located north of nea kammeni at a shallow depth however a progressively decreasing rate in deformation was noted at most gps cgps station components after january 2012 indicating magma settlement consistent with the constantly decreasing rate of the inter caldera seismicity the faulting features seem to have a key role in the evolution of the deformation which continues up the end 2012 but at a very low level

caldera formation on santorini and the physiography of the islands in the late bronze age the caldera of santorini is a composite structure with a subsidence history extending over 100 ka or more geomorphological mapping shows that the present day caldera wall is a complex assemblage of cliff surfaces of different ages and that collapse at santorini has repeatedly exhumed earlier caldera cliffs and unconformities cliffs bounding the southern southeastern and northwestern rims of the caldera are morphologically fresh and probably formed during or soon after the minoan eruption in the late bronze age the well scalloped shape of these cliffs is attributed to large scale rotational landslip around the margins of the minoan caldera the deposit from one landslip is preserved subaerially minoan landslips in southeast santorini detached along the basement unconformity exposing a cliff of the prevolcanic island the caldera wall in the north northeast and east preserves evidence for three generations of cliff those of minoan age and two earlier generations of caldera wall the two early calderas can be dated relative to a well established statigraphy of lavas and tuffs the presence of in situ minoan tephra plastered onto the present day caldera wall provides evidence that these ancient caldera cliffs had already been exhumed prior to the minoan eruption field relationships permit reconstruction of the physiography of bronze age santorini immediately before the minoan eruption the reconstruction differs from some previously published versions and is believed to be the most accurate to date bronze age sa ntorini had a large flooded caldera formed 21 ka ago this caldera must have acted as an excellent harbour for the bronze age inhabitants of the island the 3 6 ka minoan eruption deepened and widened the extant caldera the volume of minoan collapse 25 km3 is in good agreement with published estimates for the volume of discharged magma if between 5 and 8 km3 of minoan ignimbrite ponded as intracaldera tuff

a new algorithm for modelling simple and double mogi magma sources in active volcanoes accuracy sensitivity limitations and implications a new algorithm for modelling one or two mogi magma sources in actively deforming volcanoes is proposed using santorini thera greece volcano as a test site this algorithm is based on a quasi deterministic grid scan search followed by a topological inversion in rn space it avoids point solutions and local minima and is primarily designed for gps observations it can be extended to other types of magma sources defined by closed functions and to other types of data a validation of the method used an accuracy oriented approach a comparison between true or reference and inverse modelled magma sources which revealed bias free precise magma source solutions a validation of the algorithm for false alarms i e for identification of non existent sources produced by computation artefacts was also made computed solutions correspond to point sources affecting idealized media homogeneous elastic half spaces and hence ignore errors induced by magma source and lithology complexities which should be superimposed to obtain the total error budget still the solutions allow modelling of the propagation of measurement errors because of the mathematical model adopted this problem has previously been ignored a sensitivity analysis of results obtained using this method permit us to predict and quantify expected bias and uncertainties in modelled magma sources as a function of their depth and of the observation networks increased bias and noise in solutions for specific observations networks and types of data are inferred and this may explain reported discrepancies in various magma source models some implications for the santorini volcano which had an unrest episode in 2011 2012 are that the algorithm can lead to less noisy solutions of the mogi sources that the surface deformation may be recognized as resulting from inflation of two spherical sources and that differences in magma source models using different types of data may only indicate predictable uncertainties in the solutions

migration of wide angle seismic reflection data from the grenville front in lake huron under the auspices of the great lakes international multidisciplinary program on crustal evolution glimpce coincident steep and wide angle seismic reflection data sets were acquired in lake huron the wide angle data were recorded at stationary onshore receivers during the shooting and recording of the conventional marine steep angle survey to extract information from the wide angle data a variety of processing techniques including automatic trace editing amplitude balancing f k filtering static corrections and predictive deconvolution were applied to the wide aperture common receiver gather before migration the application of a slowness weighted depth migration algorithm which was first tested on synthetic data and which included a slowness filter resulted in an image of the grenville front tectonic zone gftz remarkably similar to that observed in the multichannel steep angle section the migrated wide angle data suggest that prominent bands of east dipping seismic reflections observed across the gftz extend unattenuated to depths of at least 45 km

uplift unbuckling and collapse flexural history and isostasy of the wind river range and granite mountains wyoming two dimensional gravity and flexural models constrain the structure and isostatic compensation of the wind river range and granite mountains wyoming these ranges are asymmetric basement cored laramide uplifts their large positive isostatic gravity anomalies imply that the topography of the uplifts is not locally compensated for the wind river range gravity data are consistent with thrusting along a listric fault which flattens and soles out at 30 km depth with no detectable offset on the moho we model the large bouguer gravity high over the range with high density lower crustal rocks emplaced over lower density middle crustal rocks along the wind river thrust the high positive gravity anomaly over the granite mountains can be modeled as an extension of the south pass greenstone belt from the southern wind river range eastward beneath the emigrant trail thrust a crustal root as required in local airy compensation for either range requires unreasonably high density material in the upper crust to obtain the observed anomaly combined gravity and flexural models show that a flexural rigidity at least 2 55 1022 n m maximum deflection of 2 km of the moho is required to satisfy the gravity data our results are consistent with models of uplift due to horizontal compression and support of the resulting topography by lithospheric strength an otherwise puzzling episode of oligocene uplift of the wind river range can be explained as unbuckling decrease of deflection of lithosphere accompanying release of laramide compressional stresses flexurally supported uplifts will collapse if the lithosphere is weakened a number of laramide uplifts have collapsed primarily east west trending structures such as the granite mountains the southern end of the wind river range and the uinta mountains we propose that collapse has occurred along zones of established weakness in the crust in response to north south extension

recent geodetic unrest at santorini caldera greece 1 after approximately 60 years of seismic quiescence within santorini caldera in january 2011 the volcano reawakened with a significant seismic swarm and rapidly expanding radial deformation the deformation is imaged by a dense network of 19 survey and 5 continuous gps stations showing that as of 21 january 2012 the volcano has extended laterally from a point inside the northern segment of the caldera by about 140 mm and is expanding at 180 mm yr a series of spherical source models show the source is not migrating significantly but remains about 4 km depth and has expanded by 14 million m3since inflation began a distributed sill model is also tested which shows a possible n s elongation of the volumetric source while observations of the current deformation sequence are unprecedented at santorini it is not certain that an eruption is imminent as other similar calderas have experienced comparable activity without eruption

geodetic observations and modeling of time varying deformation at taal volcano philippines abstract we investigate active crustal deformation patterns associated with magmatic activity at taal volcano an active tholeiitic volcano located in southwestern luzon philippines we present comparisons of elastic and combined elastic viscoelastic modeling results with deformation observed by continuous gps measurements on and near the volcano continuous dual frequency and single frequency l1 gps data between 1998 and 2005 provide evidence for smoothly transitioning periods of inflation and deflation centered under the volcano within deformation phases that typically last 3 9 months with rates exceeding 200 mm yr 1 prominent inflationary phases were observed in february november 2000 and june 2004 march 2005 the 2000 period of inflation was characterized by up to 145 mm yr 1 surface extension and 220 mm yr 1 of uplift of the center of volcano island relative to the northern caldera rim while the 2005 inflation was characterized by as much as 116 mm yr 1 horizontal extension of the volcanic edifice and 180 mm yr 1 uplift inversions of observed surface deformation to determine the source location points to a relatively stable spherical source situated under volcano island s central crater at depths of 5 km based on the preferred mogi model using this source geometry we develop axisymmetric finite element models with annuli of concentric shells around the magma reservoir embedded within a multi layered elastic lithosphere using simply varying pressure histories as input a variety of forward models are fit to the time history of continuously observed deformation for gps stations located on volcano island though the inferred source geometry volume and near source rheological properties are non unique they represent more physically appropriate material properties than those assumed in simple elastic half space models the sources inferred using viscoelastic shell models suggest simpler pressure histories and reduced overall pressure changes relative to equivalent elastic half space models

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

application of two dimensional synthetic seismogram modeling to interpretation of wide angle seismic data from wind river wyoming in conjunction with the 1977 cocorp wind river project wide angle reflection refraction data were recorded on a fixed array the goals of the present study were to model these wide angle data to provide independent constraints on the wind river structure a common receiver profile extracted from these data forms a pseudo split spread with maximum offsets of 13 3 km toward the southwest and 19 1 km toward the northeast the first 10 s of these data are modeled by iterative fitting of synthetic seismograms computed by asymptotic ray theory the result is a two dimensional velocity model that extends from the center of the wind river mountains into the wind river basin and from the earth s surface to a depth of 25 km the major features of the model are 1 surficial sediments that thicken toward the center of the wind river basin 2 precambrian basement that underlies the sediments and outcrops in the wind river mountains 3 an intrabasement reflector at 5 km depth 4 a low velocity region from 6 to 15 km depth 5 a local high reflectivity laminar zone possibly an intrusive feature at 15 km depth 6 a second low velocity region from 17 to 23 km depth and 7 a laminar transition zone between 23 and 25 km depth that separates the middle crust average velocity 6 km s from the lower crust average velocity 7 km s this study clearly reveals the major crustal structures the most interesting result is tentative evidence that they may be secondary local intrusion of high velocity material as well as the primary horizontal thrusting in the wind river uplift

intrusion triggering of the 2010 eyjafjallajokull explosive eruption the ash cloud that brought chaos to european air traffic in april this year was the result of emissions from an icelandic volcano that had been intermittently active for about 18 years a combination of detailed space based geodetic measurements and seismic monitoring of the eyjafjallajkull volcano in the run up to the ash producing explosive summit eruption reveals an unusual deformation pattern that may be attributed to its off rift setting with relatively cool subsurface structure and limited magma at shallow depth as to the predictability of such a dramatic reawakening the immediate precursors to the initial eruption of the volcano in 2010 were subtle and difficult to detect but the clear signs of volcanic unrest during the weeks months and years preceding it may provide better clues to the catastrophic explosion

geodetic evidence and modeling of a slow small scale inflation episode in the thera santorini volcano caldera aegean sea abstract analysis of a radial geodetic monitoring record indicated small scale inflation of the nw part of the thera santorini caldera up to 10 cm baseline length increase between 1994 and 2000 corresponding to up to 2 10 5 strain and subsequent stabilization especially after 2006 as gps data indicate the southern part of the caldera on the contrary remained practically stable this partial caldera inflation was assigned to slow magma intrusion which was not associated with changes in the seismicity using a stochastic approach based on numerical analysis and the theory of graphs and sets the mogi source of this magmatic activity was identified between the nea kammeni and the therasia islets along a major tectonovolcanic lineament at a depth of around 1 km or possibly 5 5 km it remained stable during the whole small scale inflation period and was associated with small scale pressure changes slow deformation events have been observed in other volcanoes as well but they were associated with abrupt seismicity changes

problems and interpretation of cocorp deep seismic reflection data wind river range wyoming before the consortium for continental reflection profiling cocorp deep crustal reflection profile across the wind river range wyoming can be understood problems involving velocity multiple reflections and structural style associated with thrusting must be resolved measurements from boreholes to maximum depths of 7 8 km show that a strong velocity inversion is associated with overpressured zones primarily in cretaceous shales one dimensional 1 d synthetic seismograms generated using the detailed velocity distribution closely duplicate the seismic trace on line 1 and produce multiple reflections of significant amplitude to record times of l0 sec other data including auto correlograms demonstrate presence of abundant multiple reflection energy to times of 10 to 12 sec on lines 1 and 2 and suggest that most of the deep events on these lines are multiple reflections because this area has not been known as a problem area for multiples in shallow industry reflection surveys we conclude that mult

geodetic evidence for tectonic activity on the strymon fault system northeast greece abstract the current kinematic patterns of northeast greece remain largely unknown this is mainly because this region is characterised by low seismicity rates and is poorly covered by gps stations here we analyse new homogeneous gps data collected over a period of 5 5 years from the first permanent network in northeast greece hepos to shed light in the kinematics of this region we find that gps displacement vectors that derive from either side of the natural depression of the strymon valley differ significantly in orientation and magnitude specifically we find that across a distance of ca 30 km the gps displacement vectors change orientation by 130 from nnw to ssw producing a mean horizontal strain rate of 3 3 0 3 mm yr we attribute this kinematic translation to result from movement along the strymon fault system sfs a 200 km long structure that strikes nw se and extends from sw bulgaria to north aegean where possibly abuts against the north anatolian fault up to date the sfs was considered to be a major alpine and neogene geotectonic boundary of unclear holocene activity if the interseismic strain stored currently across the fault system is released seismically large earthquakes m 7 and associated coseismic lateral displacements should be expected in the area these results call for a better assessment of the earthquake risk in northeast greece which is currently evaluated as a low seismic hazard region

effects of topography on the interpretation of the deformation field of prominent volcanoes application to etna we have investigated the effects of topography on the surface deformation field of volcanoes our study provides limits to the use of classical half space models considering axisymmetrical volcanoes we show that interpreting ground surface displacements with half space models can lead to erroneous estimations of the shape of the deformation source when the average slope of the flanks of a volcano exceeds 20 tilting in the summit area is reversed to that expected for a flat surface thus neglecting topography may lead to misinterpreting an inflation of the source as a deflation comparisons of mogi s model with a three dimensional model shows that ignoring topography may lead to an overestimate of the source volume change by as much as 50 for a slope of 30 this comparison also shows that the depths calculated by using mogi s solution for prominent volcanoes should be considered as depths from the summit of the edifices finally we illustrate these topographic effects by analyzing the deformation field measured by radar interferometry at mount etna during its 1991 1993 eruption a three dimensional modeling calculation shows that the flattening of the deflation field near the volcano s summit is probably a topographic effect

depth migration and interpretation of the cocorp wind river wyoming seismic reflection data to better understand laramide deformation deep seismic reflection data have been depth migrated focused or imaged in order to more clearly reveal structural features associated with the wind river thrust wyoming major structural features displayed in the migrated data are the wind river fault zone and the pacific creek anticline the wind river fault zone is seen to a depth of at least 25 km and interpretively to 32 km it is a complex zone that includes numerous splays flattening with depth the wind river range was tilted along these arcuate splays as it was compressionally thrust up the pacific creek anticline is asymmetric and thrust cored with the top of basement offset 600 m the pacific creek thrust is viewed as an embryonic wind river thrust

near vertical and intermediate offset seismic reflection data from west of the whipple mountains se california during a seismic reflection survey conducted by the california consortium for crustal studies in the basin and range province west of the whipple mountains se california a piggyback experiment was carried out to collect intermediate offset data 12 31 km these data were obtained by recording the vibroseis energy with a second passive recording array deployed twice at fixed positions at opposite ends of the reflection lines the reflection midpoints fall into a 3 km wide and 15 km long region in vidal valley roughly parallel to a segment of one of the near vertical reflection profiles this data set makes three unique contributions to the geophysical study of this region 1 from forward modeling of the observed travel times using ray tracing techniques a shallow layer with velocities ranging from 6 0 to 6 5 km s was found this layer dips to the south from 2 km depth near the whipple mountains to a depth of 5 km in rice valley these depths correspond closely to the westward projection of the whipple detachment fault which is exposed 1 km east of the near vertical profiles in the whipple mountains 2 on the near vertical profile the reflections from the mylonitically deformed lower plate at upper crustal and mid crustal depths are seen to cease underneath a sedimentary basin in vidal valley however the piggyback data which undershoot this basin show that these reflections are continuous beneath the basin thus near surface energy transmission problems were responsible for the apparent lateral termination of the reflections on the near vertical reflection profile 3 the areal distribution of the midpoints allows us to construct a quasi three dimensional image on perpendicular profiles at the cross points we determined the true strike and dip of reflecting horizons this analysis shows that the reflections from the mylonitically deformed lower plate dip to the southwest westward of the whipple mountains and dip to the south southward of the turtle mountains the results of this study support the interpretation of crustal reflectivity in the near vertical reflection profiles to be related to the mid tertiary episode of extension which produced the whipple metamorphic core complex this association geometrically suggests a more regionally distributed mechanism for crustal thinning as compared with single detachment fault models