ultrashallow depth imaging of a channel stratigraphy with first arrival traveltime inversion and prestack depth migration a case history from bull creek oklahoma depth imaging in ultrashallow 50 m environments presents twofold challenge 1 coda available for depth migration is very limited and 2 conventional time processing with limited coda generally fails to estimate reliable velocity models for depth migration we studied the combining of first arrival traveltime inversion and prestack depth migration psdm for depth imaging of ultrashallow paleochannel stratigraphy associated with the bull creek drainage system oklahoma restricted by a limited number of geophones 24 we acquired data for inversion and migration through two coincident profiles the first profile for inversion has a wider survey aperture 115 m maximum shot receiver spacing and consequently sparse cmp spacing 2 5 m whereas the second profile for psdm has denser cmp spacing 1 m and consequently a narrower survey aperture 46 m maximum shot receiver spacing we also found that the velocity model from traveltime inversion of the wider aperture data set is more preferable for dep

the morphology and dynamics of low amplitude bedwaves upon upper stage plane beds and the preservation of planar laminae experimental studies of subcritical unidirectional flow over upper stage plane beds of medium grained sand reveal the ubiquitous presence of low amplitude bedwaves flow depth was 0 11 m mean flow velocities were 0 86 1 0 m s 1 shear velocities were 0 058 0 71 m s 1 and dimensionless shear stresses were 0 56 0 87 bedwaves are asymmetrical in profile and range from 0 75 to 11 mm in height mainly 2 6 mm from 0 7 to 1 3 m in wavelength and have mean celerities of 10 mm s 1 flow records suggest that the bedwaves are associated with accelerating flow over the bedwave crests and flow which decelerates and diverges laterally over the troughs high resolution bed profiling during aggradation of the bed combined with subsequent box coring illustrates that these bedwaves are responsible for the planar laminae characteristic of upper stage plane beds lamina preservation is dependent upon the mean aggradation rate and the sequence of bedwaves of different height crossing any point individual laminae are more readily preserved at higher aggradation rates where the possibility of reworking by later bedwaves is reduced laminae are recognized by small changes in grain size and commonly a fining upwards at the top of laminae which is generated by fine grained material infiltrating a lower lamina in the leeside of a bedwave

depth image focusing in traveltime map based wide angle migration wide aperture prestack depth migration requires application of challenging and time consuming velocity analysis and depth focusing collectively referred to here as depth focusing we present an approach to depth focusing using 1 a detailed starting velocity model obtained by a 1 d transformation of the first arrival times followed iteratively by 2 interactive analysis of the common image gathers 3 computation of coherency attributes of the wavefield in the depth domain and 4 2 d traveltime tomography to update the background velocity model we employ two interactive method of migration velocities refinement in the first method similar to the common midpoint velocity spectrum approach residual velocity updates are picked directly from the common image gathers in another method analogous to the common velocity stacks we pick the velocity updates from the areas of maximum coherency in depth sections that are migrated using rescaled traveltime maps both types of migration velocity picks

seismic imaging to help understand and manage water quality in coastal benin west africa abstractwe collected seismic data along 15 transects to characterize the geometry of a coastal aquifer in benin west africa that is being contaminated by saltwater we used standard high resolution seismic methods to image the upper 200 m using a sledgehammer source and a 120 channel recording system three transects were processed with an iterative updating flow that includes prestack depth migration residual moveout analysis and reflection tomography and the remaining 12 transects were processed with routine processing flows and poststack time migration we identified one unconfined aquifer and three confined aquifers separated by reflective confining clay layers some transects showed areas of missing reflectors which we interpreted as sand filled channels that could provide potential high permeability conduits for saltwater flow to the godomey well field

coupled conduit flow and shape in explosive volcanic eruptions volcanic conduit flow models generally utilise one of two conduit profile modes which are referred to as parallel sided typically surface choked or lithostatically pressure balanced their limitations in application to supersonically erupted basaltic and rhyolitic explosive eruptions are investigated likely changes in conduit profile over time due to catastrophic failure resulting from high wall stresses and abrasive erosion are investigated using a semi analytical model although time independent this model nonetheless reveals likely trends in shape from a simple parallel sided geometry it is found that for rhyolites early wall failure will occur in all but unusual circumstances resulting in expansion of the conduit a reduction in wall stresses and a trend towards a lithostatically pressure balanced solution at depth in both rhyolitic and basaltic eruptions abrasive erosion results in conduit flaring near the surface allowing the choking point to descent from the surface into the vent substantially changing exit conditions and resulting in a trend towards the a lithostatically pressure balanced solution at the surface although a truly lithostatically pressure balanced system can never be attained due to the effects of compressibility at supersonic velocities it is no less valid than the more commonly utilised parallel sided system for a variety of realistic eruption scenarios and can be a useful guide for potential steady states

prestack kirchhoff depth migration of shallow seismic data prestack kirchhoff depth migration is applied successfully to shallow seismic data from a waste disposal site near arnstadt in thuringia germany the motivation behind this study was to locate an underground building buried in a waste disposal the processing sequence of the prestack migration is simplified significantly as compared to standard common cmp data processing it includes only two parts 1 velocity depth model estimation and 2 prestack depth migration in contrast to conventional cmp stacking prestack migration does not require a separation of reflections and refractions in the shot data it still provides an appropriate image our data example shows that a superior image can be achieved that would contain not just subtle improvements but a qualitative step forward in resolution and signal to noise ratio

glacial structures in northern germany revealed by a high resolution reflection seismic survey in recent years the sediments filling pleistocene glacial structures have become of increasing importance to paleoclimate research climatic changes are documented by the deposition cycles in small closed trough or bowl like structures a 2 d high resolution shallow reflection seismic survey was conducted in 1996 over such a structure near tostedt in northern germany the objective was to obtain a more accurate picture of the structure and the underlying geology designed especially for shallow surveys a newly developed impulse source provided sufficient energy to observe reflectors as deep as 400 m signals are characterized by a high frequency content with maximum energy between 80 and 180 hz the migrated section shows a distinct reflection pattern revealing local glacial dynamics reflectors at depths of 30 40 and 45 m from inside the tostedt structure correlate well with three interstadials of the weichselian period weak reflections define the bottom of the structure with a maximum depth of 70 m the structure is imbedded in a much larger previously unexpected depression of similar shape the fill of this larger depression is seismically nearly transparent high amplitude reflections delineate its lower boundary with a maximum depth of 130 m two major reflectors at depths of 170 and 270 m correlate with lower miocene and middle oligocene units they indicate that subrosion which might have been expected from the presence of a nearby salt diapir is absent this confirms the purely glacial origin of the two bowl like structures

experimental study of analogue vent erosion towards nozzle shapes abstract volcanic vent shapes evolve over the course of an explosive eruption as the high pressure ejecta erode the solid conduit walls the changing shape affects the fluid behavior of the expelled gases potentially the plume rise column collapse and the type and amount of accidental debris ejected field observations of evolving vent shape are difficult or impossible while the mechanics of this process have been studied numerically almost no laboratory studies have examined these behaviors thus a series of test samples was manufactured using 3d printing techniques which were eroded using high pressure compressed air four material combinations were considered using stainless steel and alumina powders consolidated with binder concentrations of 16 and 38 material properties were evaluated using compression testing while the erosion behavior was studied through high speed visualization and pressure measurements with identical samples at constant inflow conditions in all cases the erosion showed an initial rapid erosion of the vent exit followed by quasi steady state conditions all samples produced converging diverging nozzle shapes with exit areas increasing by 1 5 to 6 times depending on the sample properties behavior correlated strongly with binder concentration as low binder materials had significant increases in nozzle area when using high density particles these weaker samples disintegrated due to particle abrasion from higher kinetic energy impacts the nozzle shapes produced supersonic exit conditions with mach numbers from 1 48 to 2 51 for the various samples however exit pressures were not balanced suggesting that the optimum is not the isentropic pressure balanced shape previously postulated

velocity analysis by iterative profile migration in conventional seismic processing velocity analysis is performed by using the normal moveout nmo equation which is based on the assumption of flat horizontal reflectors imaging by migration either before or after stack is done normally in a subsequent step using these velocities in this paper velocity analysis and imaging are combined in one step and migration itself is used as a velocity indicator because unlike nmo migration can be formulated for any velocity function migration based velocity analysis methods are capable of handling arbitrary structures i e those with lateral velocity variations in the proposed scheme each shot gather profile is migrated with an initial depth velocity model profile migration is implemented in the x domain but the actual implementation of profile migration is not critical as long as it is not done in a spatial wavenumber domain which would preclude handling of lateral velocity variations after migration with an initial velocity model the

patterns and timing of late quaternary faulting in the great basin province and relation to some regional tectonic features large scale surface faulting events each tens of kilometers long and involving more than a meter of displacement of late quaternary age have not been uniformly distributed but have been concentrated in subprovincial and smaller belts and areas within the great basin province furthermore faulting apparently has not been uniformly distributed over time the average recurrence interval of large scale faulting events on individual faults in the province is measured in thousands or tens of thousands of years in contrast to such long recurrence intervals in the central nevada and eastern california seismic belts large scale faulting events have occurred during the last 111 years in an apparently coherent sequential belt filling pulse of activity in which events were separated by only a few years or a few decades the questions are where are other pulses of large scale faulting likely to occur and what controls the localization of such belts and areas characterized by higher rates of faulting two examples of tectonic subprovinces that may play a role in delimiting smaller zones of faulting are the black rock carson sink zone of extension and the central nevada downwarp the central nevada seismic belt lies along the dividing line between these two subprovinces and the northwest margin of the black rock carson sink zone of extension coincides with the margin of a fingerlike belt of dense faulting in northwestern nevada

fluvial responses to the weichselian ice sheet advances and retreats implications for understanding river paleohydrology and pattern changes in central poland the evolution of the fluvial systems during the weichselian pleniglacial in the torun basin central poland was investigated through sedimentological investigation and paleohydraulic analysis within the basin three fluvial cycles deposited after successive phases of the ice advance which took place 50 28 and 20 ka ago successions of four fluvial lithotypes characterize each fluvial formation that are related to the paleoenvironmental changes e g climate instability and changes in the river regime which affected the channel hydraulics and morphology the successions comprise river style metamorphosis between high energy sand bed meandering rivers lithotype m1 high energy sand bed braided rivers lithotype b1 and medium energy sand bed braided rivers with either unit bars lithotype b2 or compound bars lithotype b3 reflects the maturity stage of sand bed braided river evolution in the basin the assessment of the fluvial sedimentary environments enabled the construction of a quantitative model of the changes in the river channel pattern in relation to the climate oscillation both the paleohydrological controls and their sedimentary consequences are discussed in the article lithotypes m1 and b1 represent riverbed modeled under supercritical flow condition deposition of lithotype b2 corresponded to the river channel pattern transformation and was manifested by decreasing flow velocity energy losses associated with bedform roughness and with the transportation of coarser particles the flow velocity was generally greater in rivers of lithotype b3 and energy of sedimentary environment was more stable than during the deposition of lithotype b2

imaging a shallow aquifer in temperate glacial sediments using seismic reflection profiling with dmo processing we acquired a seismic reflection profile to image a shallow 100 m aquifer system on a small island in puget sound north of seattle washington the aquifer system is comprised of temperate glacial sedimentary strata with the primary aquifer lying approximately 45 m below the surface we chose the site because there are water well boring descriptions available and a sea cliff parallels the profile location providing stratigraphic control a 20 lb 9 kg weight drop was used as an energy source to acquire a 30 fold common midpoint cmp reflection profile along a 400 m line analysis of the recorded wavefield was not straightforward because of complex stratigraphy and the presence of a laterally variable thin bed 5 15 m of high impedance lodgement till within a few meters of the surface we used finite difference modeling to determine that conventional cmp processing would provide a reasonable approximation for imaging strata in the primary target zone roughly 20 m below the high velocity till fo

depth characterization of shallow aquifers with seismic reflection part ii prestack depth migration and field examples it is common in shallow seismic studies for the compressional wave velocity in unconsolidated sediments to increase by a factor of four or more at the transition from dry or partial water saturation to full saturation under these conditions conventional nmo velocity analysis fails and leads to large depth and layer thickness estimates if the dix equation is assumed valid prestack depth migration psdm is a means of improving image accuracy a comparison of psdm with conventional nmo processing for three field examples from differing hydrogeologic environments illustrates that psdm can significantly improve image quality and accuracy

shear wave seismic reflection studies of unconsolidated sediments in the near surface we have successfully applied of sh wave seismic reflection methods to two different near surface problems targeting unconsolidated sediments at the former fort ord where the water table is approximately 30 m deep we imaged aeolian and marine aquifer and aquitard stratigraphy to a depth of approximately 80 m we identified reflections from sand clay and sand silt interfaces and we mapped these interfaces along our transects at an aggregate study site in indiana where the water table is at a depth of 1 to 2 m we imaged stratigraphy in alluvial sand and gravel and observe a strong reflection from the 32 m deep bedrock surface in both cases we exploited the high resolution potential of sh waves their insensitivity to water content and the possibility of reducing love wave contamination by working along a roadway we accomplished our results using only sledgehammer sources and simple data processing flows

ultrashallow seismic imaging of the causative fault of the 1980 m6 9 southern italy earthquake by pre stack depth migration of dense wide aperture data 1 a two step imaging procedure including pre stack depth migration psdm and non linear multiscale refraction tomography was applied to dense wide aperture data with the aim of imaging the causative fault of the 1980 m6 9 irpinia normal faulting earthquake in a very complex geologic environment psdm is often ineffective for ultrashallow imaging 100 m of depth and less of laterally heterogeneous media because of the difficulty in estimating a correct velocity model for migration dense wide aperture profiling allowed us to build accurate velocity models across the fault zone by multiscale tomography and to record wide angle reflections from steep reflectors psdm provided better imaging with respect to conventional post stack depth migration and improved definition of fault geometry and apparent cumulative displacement results indicate that this imaging strategy can be very effective for near surface fault detection and characterization fault location and geometry are in agreement with paleoseismic data from two nearby trenches the estimated vertical fault throw is only 29 38 m this value combined with the vertical slip rate determined by trench data suggests a young age 97 127 kyr of fault inception

the decompression of volcanic jets in a crater during explosive volcanic eruptions during explosive volcanic eruptions fragmented silicic magma and volatiles exit the vent with pressures typically in the range 10 100 atm and at the speed of sound of the mixture we show that for magmatic volatile contents no in the range 0 03 no 0 06 this has the approximate value 0 95 0 05 nort 12 where r is the gas constant and t is the eruption temperature this speed is nearly independent of the vent pressure and vent radius by assuming there is negligible mixing with the air we have modelled the decompression of such jets following eruption from the vent for free decompression into the atmosphere the velocity of the decompressed jet has the approximate value 1 85 0 05 nort 12 this is nearly independent of the eruption rate for decompression into a crater the process is more complex at low eruption rates with low vent pressure the material becomes underpressured as it rises in the crater a shock then forms in the crater this recompresses the magma volatile mixture which then issues from the crater as a relatively slow subsonic jet at atmospheric pressure as the eruption rate increases such shocks move towards the top of the crater and ultimately cannot form in the crater instead the material issues from the crater as a high speed supersonic jet the upward thrust provided by the crater walls on this high pressure jet then increases the upward velocity above that of a freely decompressing jet the presence of a crater may therfore cause collapse in relatively small eruptions whereas it may promote formation of buoyant eruption columns at higher eruption rates if a crater grows through erosion during an eruption column collapse will typically ensue even if the mass flux remains steady

seismic reflection imaging of a geothermal aquifer in an urban setting a seismic reflection survey that was conducted in downtown boise idaho to help city planners site a new well for injection of spent geothermal water illustrates some methods to safely and successfully employ a seismic reflection survey in an urban setting the objective of the seismic survey was to estimate the depth and continuity of a basalt and rhyolite volcanic sequence well siting was based on geothermal aquifer depth location of interpreted faults projected thermal impact of injection on existing wells surface pipe extension costs and public land availability seismic acquisition tests and careful processing were used to ensure high quality data while minimizing the potential for damage along city streets a video camera placed in a sewer and a blast vibration monitor were used to confirm that energy from the seismic source a 75 in3 land air gun did not damage nearby buildings street surfaces or buried utilities along the survey lines walkaway seismic tests were also used to compare sign

tertiary structural development of selected valleys based on seismic data basin and range province northeastern nevada reflexion seismic data in railroad diamond mary s river and goshute valleys provide information on their structural development that cannot be deduced solely from outcrop and well data these valleys contain tertiary sediments that in dip section define an asymmetrical basin bounded along the eastern flank by a major listric normal fault with about 3 0 4 5 km of displacement the west flank is defined by a gentle east dipping ramp seismically the trace of the listric fault is interpreted to dip westward and sole into the palaeozoic section exploiting regionally recognized mesozoic decollement surfaces the tertiary depocentre adjacent to this fault shifted from west to east with continued slippage through time the greatest movement occurring in the miocene and post miocene in the strike direction the valleys are separated into at least two subbasins by an east west structurally high axis the axis is postulated to be the result of a tear fault associated with movement along the listric normal fault tertiary stratigraphy varies between valleys and between sub basins in a given valley all the valleys contain miocene and younger rocks however not all sub basins contain the pre miocene section suggesting a complex scheme of structural development

incremental subglacial meltwater sediment deposition and deformation associated with repeated ice bed decoupling a case study from the island of funen denmark abstract on the island of funen denmark sediments that are 4 7 m below the land surface consist of a 2 4 m thick sequence of stacked and folded glaciofluvial sediments overlain by a 2 3 m thick basal till the glaciofluvial sediments consist of tabular beds of planar stratified massive and cross stratified sand and gravel with localized channel fills of open framework gravel sand and gravel beds exhibit curvilinear sheath folding often leading to eye folds this folding is attributed to repeated glacier bed decoupling and recoupling with subglacial deposition of sand and gravel by meltwater occurring during the decoupling phase and deformation occurring during recoupling sand and gravel beds are typically separated by silty clay beds and laminations recording slackwater deposition within subglacial cavities folds frequently display attenuated upper limbs reflecting shearing associated with overlying ice movement on lower fold limbs only localized thrusting is observed suggesting water saturation of sands and gravels during deformation and relatively low strain rates folds are frequently truncated by overlying sand and gravel beds no evidence of shearing is found along these contacts which are interpreted as erosional surfaces thus we propose that the glaciofluvial sediment sequence records incremental step wise subglacial deposition and deformation rather than wholesale deformation following emplacement of the entire glaciofluvial sequence specifically we envisage that individual beds were deposited and folded subglacially with ice bed decoupling occurring during sediment deposition followed by recoupling and shearing of the upper bed surface by the ice base to produce folds with attenuated upper limbs incremental deformation and folding were facilitated by elevated porewater pressure within the sediments silty clay beds helped to maintain elevated porewater pressure by acting as local aquitards a general absence of till from the glaciofluvial sequence save for localized cm scale blocks suggests either non deposition or reworking into the glaciofluvial sediments deposition of tabular sand and gravel beds and open framework gravel filling scours within single beds suggest broad sheet like subglacial flows 10 100 m wide that become increasingly channelized we propose that the sedimentary sequence records a highly dynamic glaciohydraulic system characterized by repeated localized subglacial cavity development and storage and release of meltwater leading to glacier decoupling that may have facilitated fast flow of the baltic ice stream

coupled fluid and solid evolution in analogue volcanic vents volcanic eruptions emit rock particulates and gases at high speed and pressure which change the shape of the surrounding rock simplified analytical solutions field studies and numerical models suggest that this process plays an important role in the behavior and hazards associated with explosive volcanic eruptions here we present results from a newly developed laboratory scale apparatus designed to study this coupled process the experiments used compressed air jets expanding into the laboratory through fabricated rock analogue material which evolves through time during the experiment the compressed air was injected at approximately 2 5 times atmospheric pressure we fabricated rock analogues from sand and steel powder samples with a three dimensional printing process we studied the fluid development using phase locked particle image velocimetry while simultaneously observing the solid development via a video camera we found that the fluid response was much more rapid than that of the solid permitting a quasi steady approximation in most cases the solid vent flared out rapidly increasing its diameter by 20 to 100 after the initial expansion the vent and flow field achieved a near steady condition for a long duration the new expanded vent shapes permitted lower vent exit pressures and larger jet radii in one experiment after an initial vent shape development and establishment of steady flow behavior rock failure occurred a second time resulting in a new exit diameter and new steady state this second failure was not precipitated by changes in the nozzle flow condition and it radically changed the downstream flow dynamics this experiment suggests that the brittle nature of volcanic host rock enables sudden vent expansion in the middle of an eruption without requiring a change in the conduit flow

the plinian eruptions of 1912 at novarupta katmai national park alaska the three day eruption at novarupta in 1912 consisted of three discrete episodes episode i began with plinian dispersal of rhyolitic fallout layer a and contemporaneous emplacement of rhyolitic ignimbrites and associated proximal veneers the plinian column was sustained throughout most of the interval of ash flow generation in spite of progressive increases in the proportions of dacitic and andesitic ejecta at the expense of rhyolite accordingly plinian layer b which fell in unbroken continuity with purely rhyolitic layer a is zoned from 99 to 15 rhyolite and accumulated synchronously with emplacement of the correspondingly zoned ash flow sequence in mageik creek and the valley of ten thousand smokes vtts only the andesiterichest flow units that cap the flow sequence lack a widespread fallout equivalent indicating that ignimbrite emplacement barely outlasted the plinian phase on near vent ridges the passing ash flows left proximal ignimbrite veneers that share the compositional zonation of their valley filling equivalents but exhibit evidence for turbulent deposition and recurrent scour episode ii began after a break of a few hours and was dominated by plinian dispersal of dacitic layers c and d punctuated by minor proximal intraplinian flows and surges after another break dacitic layers f and g resulted from a third plinian episode iii intercalated with these proximally are thin intraplinian ignimbrites and several andesite rich fall flow layers both cd and fg were ejected from an inner vent 400 m wide nested within that of episode i into which the rhyolitic lava dome novarupta was still later extruded two finer grained ash layers settled from composite regional dust clouds layer e which accumulated during the d f hiatus includes a contribution from small contemporaneous ash flows and layer h settled after the main eruption was over both are distinct layers in and near the vtts but distally they merge with cd and fg respectively they are largely dacitic but include rhyolitic shards that erupted during episode i and were kept aloft by atmospheric turbulence published models yield column heights of 23 26 km for a 22 25 km for cd and 17 23 km for fg and peak mass eruption rates of 0 7 1x108 0 6 2x108 and 0 2 0 4x108 kg s 1 respectively fallout volumes adjusted to reflect calculated redistribution of rhyolitic glass shards are 8 8 km3 4 8 km3 and 3 4 km3 for episodes i ii and iii microprobe analyses of glass show that as much as 0 4 km3 of rhyolitic glass shards from eruptive episode i fell with cde and 1 1 km3 with fgh most of the rhyolitic ash in the dacitic fallout layers fell far downwind se of the vent near the rhyolite dominated ignimbrite however nearly all of layers e and h are dacitic showing that the downwind rhyolitic ash is of co plinian rather than co ignimbrite origin

gravity isotope and geochemical study of the alvord valley geothermal area oregon summary the alvord valley in southeast oregon has considerable geothermalpower potential groh 1966 godwin and others 1971 white and williams 1975 muffler 1979 the mickey springs system is estimated to have an electrical potential of 160 megawatts for a life of 30 yr and alvord springs and borax lake to the south are estimated to have 49 and 91 megawatts respectively muffler 1979 by comparison the geysers in california have a potential of 1 610 megawatts for 30 yr

dynamic routing of flow resistance and alluvial bed form changes from the lower to the upper regime on the basis of a strouhal number and the definition of the control factor m a new routing to calculate the energy slope in the lower and upper alluvial regimes is proposed the control factor m representing the interactions in alluvial rivers is reckoned as a bed form index while the flow evolves through transition the control factor m decreases from m 2 associated with two dimensional fully developed dunes to m 1 associated primarily with in phase waves the way to predict the value of the control factor m is drawn from a previously published criterion for delineating the upper regime and is calibrated with experimental data on several data from flumes and rivers the routing is tested and compared with other methods from the literature it appears that the new routing is the most robust because it allows researchers to obtain low averages of the discrepancy ratio for a wide range of ratios between the water depth and the median sediment diameter on a selection of contrasted freshet events the new routing allows for the capture of the primary dynamic of the flow resistance decrease

shallow subsurface structure of the wasatch fault provo segment utah from integrated compressional and shear wave seismic reflection profiles with implications for fault structure and development integrated vibroseis compressional and experimental hammer source shear wave seismic reflection profiles across the provo segment of the wasatch fault zone in utah reveal near surface and shallow bedrock structures caused by geologically recent deformation combining information from the seismic surveys geologic mapping terrain analysis and previous seismic first arrival modeling provides a well constrained cross section of the upper 500 m of the subsurface faults are mapped from the surface through shallow poorly consolidated deltaic sediments and cutting through a rigid bedrock surface the new seismic data are used to test hypotheses on changing fault orientation with depth the number of subsidiary faults within the fault zone and the width of the fault zone and the utility of integrating separate elastic methods to provide information on a complex structural zone although previous surface mapping has indicated only a few faults the seismic section shows a wider and more complex deformation zone with both synthetic and antithetic normal faults our study demonstrates the usefulness of a combined shallow and deeper penetrating geophysical survey integrated with detailed geologic mapping to constrain subsurface fault structure due to the complexity of the fault zone accurate seismic velocity information is essential and was obtained from a first break tomography model the new constraints on fault geometry can be used to refine estimates of vertical versus lateral tectonic movements and to improve seismic hazard assessment along the wasatch fault through an urban area we suggest that earthquake hazard assessments made without seismic reflection imaging may be biased by the previous mapping of too few faults

unusually low rates of slip on the santa rosa range fault zone northern nevada the santa rosa range fault zone srrfz is one of the most topographically prominent normal fault systems in the northern basin and range province of the western united states it has been assigned high rates of vertical slip by others and has been identified as a possible site of the future extension of the central nevada seismic belt cnsb we use detailed trench mapping and luminescence dating to estimate displacements and timing of the last several large magnitude paleoearthquakes on the southern part of the srrfz at a trench site near orovada nevada coseismic vertical displacements ranged from 1 to 2 8 m for each of the last four events luminescence ages provide time limits for the last three events of 125 155 ka 90 108 ka and 11 16 ka these data yield recurrence intervals of 17 65 k y and 74 97 k y and an elapsed time of 11 16 k y since the youngest event slip rate determinations at the orovada site are complicated by multiple fault strands but rates calculated from a variety of data are surprisingly low 0 01 0 16 mm yr given the topographic prominence of the santa rosa range a lack of compelling patterns in a comparison of paleoseismic parameters indicate that the srrfz is no more likely a location for a large magnitude earthquake than previously identified seismic gaps or along faults that lie directly north of the cnsb

satellite observations and interpretation of the 1991 mount pinatubo eruption plumes we demonstrate the use of hourly geostationary meteorological satellite gms and noaa polar orbiting advanced very high resolution radiometer avhrr satellite images of the june 1991 mount pinatubo volcanic eruption plumes in providing details of the timing changing eruptive style and umbrella plume movement and dynamics a chronology of explosive events which culminated in a 9 hour long climactic phase on june 15 has been determined from satellite data and favorably compared to ground based and other ancillary information maximum eruption column altitudes of 40 km and column top undercooling in excess of 55 c below the ambient atmosphere occurred during the climactic phase phases dominated by plinian versus coignimbrite eruptive plumes can be distinguished on the images analysis of the spreading umbrella plume during the climactic phase suggests that over the first 4 5 hours the plume spread laterally as a gravitational intrusion before becoming advected in the ambient winds we compare the rate of plume growth to a model of a radially symmetric continuously fed intrusion to describe the motion the rate of plume growth shows good agreement with this simple model for the first 4 5 hours from column top heights we determine eruption rates and obtain an independent estimate of the total volume of magma erupted from june 12 16 of 5 5 km3 dense rock equivalent dre in good agreement with an independent estimate of the total eruptive volume made from deposits on land and submarine ash fall of up to 5 3 km3 dre we also show that secondary explosions in the pinatubo ignimbrite deposits produced ash plumes reaching altitudes as high as 19 km in september 1991 this study indicates that realistic interpretation and monitoring of major eruption plumes can be accomplished by analysis of high temporal resolution satellite data

migration moveout analysis and depth focusing prestack depth migration still suffers from the problems associated with building appropriate velocity models the two main after migration before stack velocity analysis techniques currently used depth focusing and residual moveout correction have found good use in many applications but have also shown their limitations in the case of very complex structures to address this issue we have extended the residual moveout analysis technique to the general case of heterogeneous velocity fields and steep dips while keeping the algorithm robust enough to be of practical use on real data our method is not based on analytic expressions for the moveouts and requires no a priori knowledge of the model but instead uses geometrical ray tracing in heterogeneous media layer stripping migration and local wavefront analysis to compute residual velocity corrections these corrections are back projected into the velocity model along raypaths in a way that is similar to tomographic reconstruction while this approa

thin eolianites interbedded within a fluvial and marine succession early proterozoic whitworth formation mount isa inlier australia abstract the early proterozoic whitworth formation in the mount isa inlier australia contains the oldest known thinly bedded eolian dune and amalgamated interdune deposits and records the complex interplay of eolian fluvial and marginal marine depositional processes the whitworth formation accumulated during the waning phases of rifting in a north south trending trough that began between 1808 and 1790 ma and ended before 1740 ma three eolian facies are recognized 1 cosets of cross strata 2 sets of horizontal to low angle strata and 3 isolated sets of cross strata facies el records preservation of dunes with low angles of climb without intervening interdune deposits sets of facies e2 are interpreted as either sand sheet preserved dune plinths or amalgamated interdune deposits facies e3 is encased in facies e2 and consists of lenses of cross strata with irregular tops this association of facies is comparable to recent gypsum dune and interdune deposits at white sands new mexico facies e3 reflects limited dune preservation during migration and accumulation at or near the groundwater table vertical change from amalgamated interdune deposits to dune without interdune deposits records dunefield initiation or lateral migration from a peripheral to a more centralized position within the dunefield increased sedimentation rates promoted preservation of dune deposits represented by facies e1 decreased sedimentation rate and possible limited sediment bypassing resulted in amalgamation of interdune deposits on the dunefield periphery eolian facies e1 and e2 are interbedded with ephemeral river deposits three ephemeral river facies are recognized 1 cosets of horizontal strata 2 cosets of horizontal strata and overlying trough cross beds and 3 cosets of medium scale trough cross beds ephemeral river facies f3 often are preserved in channels incised into eolian facies e3 associated marginal marine facies consist of 1 thin bedded arenites of intertidal to supratidal origin and 2 trough and tabular planar cross bed sets and cosets that resulted from migration of subaqueous dunes within a tide dominated subtidal setting interbedded fluvial and eolian deposits reflect either autogenic processes such as reworking of fluvial sands by eolian processes or incursion of a fluvial system into a dunefield related to allogenic processes such as climatic change dune deposits in the whitworth formation probably developed under arid to semi arid conditions as indicated by extensive ephemeral river deposits presence of evaporite pseudomorphs and absence of wet interdune deposits interbedded eolian fluvial and marginal marine deposits resulted from relative sea level fluctuations related to a combination of eustasy and intrabasinal tectonics

interaction between tectonic and erosion processes on the morphogenesis of an alpine valley geological and geophysical investigations in the lower romanche valley belledonne massif western alps in the belledonne massif the steep paleozoic belledonne middle fault bmf separates micaschists displaying numerous landslides from amphibolites the massif is incised by the lower romanche river valley when crossing the bmf the valley widens into a lozenge shaped basin recently interpreted as an active pull apart type structure associated with a major n110 striking quaternary fault multidisciplinary investigations were carried out in the basin to check if this model has implications on the seismic and landslide hazard assessment this study demonstrated the existence of a n80 sinistral strike slip sechilienne fault zone sfz this fault zone is suspected to offset the bmf by 375 m across the basin geophysical experiments revealed that the bedrock depth increases strongly in the basin up to 350 m our study invalidates the active pull apart origin of the basin and suggests it results from quaternary glacial and fluvial erosion processes magnified by the intersection of two inherited structures the bmf and the sfz

high resolution densely spaced wide aperture seismic profiling as a tool to aid seismic hazard assessment of fault bounded intramontane basins application to vallo di diano southern italy abstract seismic hazards in extensional regions are mostly posed by high angle normal faults and deep hanging wall basins that can promote significant ground motion amplifications characterized by strong lateral velocity variations these structures represent challenging targets for seismic exploration in this paper we show that prestack depth migration of high resolution seismic reflection data collected with nonconventional dense wide aperture arrays can effectively assist deterministic seismic hazard assessment of fault bounded basins our high resolution 3 2 km long seismic profile was acquired along vallo di diano the largest fault bounded intramontane basin in the southern apennines seismic belt italy the imaging strategy combines prestack depth migration with an iterative velocity building technique that utilizes results of multiscale refraction tomography in particular migration of steeply dipping reflections is essential in imaging the complex morphology of the basement rocks beneath the basin by combining seismic reflection and v p tomography results we were able to evaluate 1 the structure of the vallo di diano basin along a representative transect from near surface to basement depths 2 the shallow depth geometry of the vallo di diano fault system which bounds the basin to the east 3 the structure of the sediment basement interface and 4 the velocity structure of basement and sediments within the basin these findings are valuable both for understanding the tectonic evolution of the vallo di diano and for developing earthquake shaking scenario studies

applying reflection tomography in the postmigration domain to multifold ground penetrating radar data acquisition and processing of multifold ground penetrating radar gpr data enable detailed measurements of lateral velocity variability the velocities constrain interpretation of subsurface materials and lead to significant improvement in image accuracy when coupled with prestack depth migration psdm reflection tomography in the postmigration domain was introduced in the early 1990s for velocity estimation in seismic reflection this robust accurate method is directly applicable in multifold gpr imaging at a contaminated waste facility within the u s department of energy s hanford site in washington the method is used to identify significant lateral and vertical velocity heterogeneity associated with infilled waste pits using both the psdm images and velocity models in interpretation a paleochannel system that underlies the site and likely forms contaminant migration pathways is identified

seismic reflection evidence for two phase development of tertiary basins from east central nevada two east west seismic reflection profiles crossing antelope valley smokey valley railroad valley and big sand springs valley in east central nevada demonstrate the evolution of tertiary basin extension in the basin and range province from broad sags to narrow fault bounded basins reprocessing of a 480 channel 60 fold dynamite source experiment enabled good imaging of basin stratigraphy these data suggest two distinct phases of basin development occurred separated by a regional unconformity the early phase is characterized by development of a broad symmetric basin riddled with many small offset normal faults the later phase shows a narrowing of the basin and subsidence along one dominant structure an apparent planar normal fault the unconformity separating the two phases of extension marks a transition from broad subsidence to local asymmetric tilting that took place over a short period of time relative to sedimentation rates antelope valley smokey valley and railroad valley clearly show evidence for two phase development big sand springs valley represents only the later phase of extension the absence of dating of stratigraphic units within the basins precludes us from determining if the abrupt tectonic transition within the basins resulted from differences in local strain rates or amounts or was due to changes in regional stress fields

insights into volcanic conduit flow from an open source numerical model 1 numerical models that calculate the fluid dynamics of explosive volcanic eruptions have been used with increasing frequency to understand volcanic processes and evaluate volcanic hazards yet those who develop such models rarely make them publicly available so that they can be verified used and possibly improved by other scientists in this paper i present a visual interactive open source numerical model that calculates steady state flow of magma and gas in vertical eruptive conduits and contains user friendly utilities for quickly determining physical thermodynamic and transport properties of silicate melts h2o gases and melt gas crystal mixtures the model represents an advance over previously published conduit models by incorporating a non arrhenian viscosity relation for hydrous silicate melts a relation between viscosity and volume fraction of gas that depends on capillary number and adiabatic temperature changes in the mixture using established thermodynamic relations for melts and h2o gas respectively volcanologists who have not had access to conduit models have frequently approximated conduit flow using an analytical equation for incompressible laminar newtonian pipe flow which predicts that the mass flux is proportional to the fourth power of conduit radius and inversely proportional to mixture viscosity the model presented here which is not much more difficult to use than a back of the envelope calculation shows that the pipe flow approximation significantly overestimates the sensitivity of mass flux to both conduit radius and mixture viscosity results from the model also show that viscous heating in the lower conduit which is not considered in most other models may increase the mass flux of large silicic eruptions by several percent and decrease the viscosity of the mixture at the fragmentation depth by a few tens of percent

imaging complex structure in shallow seismic reflection data using prestack depth migration prestack depth migration psdm analysis has the potential to significantly improve the accuracy of both shallow seismicreflectionimagesandthemeasuredvelocitydistributions inastudydesignedtoimagefaultsinthealvordbasin oregon at depths from 25 1000 m psdm produced a detailed reflection image over the full target depth range in contrast poststack time migration produced significant migration artifacts in the upper 100 m that obscured reflection events and limited the structural interpretation in the shallow section additionally an abrupt increase from 2500 to 3000 m s in the psdm velocity model constrained the interpretation of the transition from sedimentary basin fill to basementvolcanicrocks psdmanalysisrevealedacomplex extensional history with at least two distinct phases of basin growthandamidbasinbasementhighthatformsthedivision betweentwomajorbasincompartments

effects of the near field on shallow seismic studies seismic studies in the near surface typically involve path lengths that are on the order of a wavelength however most investigators extrapolate seismic imaging and parameter extraction techniques to the near surface without incorporating the near field in their processing approach for such short path lengths we find that the near field is strongly present in the recorded waveforms which consequently biases seismic parameter estimation such as q measurement to suppress the near field effects we examined the challenges of near field removal and the issues involving the accurate modeling of the near field using the mathematical expression for a source monopole which describes an elastic impact source typically used in shallow seismic studies we modeled the near and far field terms of the waveform with distance in a homogeneous elastic medium for thiscase we found that the near field can be suppressed through frequen cy domain or polarization filtering however in heterogeneous media the near