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

continental scale salt tectonics on mars and the origin of valles marineris and associated outflow channels a synthesis of deformation patterns within and around the thaumasia plateau mars points to a new interpretation for regional deformation and the origin of valles marineris and associated outflow channels the morphology of the thaumasia plateau is typical of thin skinned deformation akin to a mega slide in which extensional deformation in syria planum and noctis labyrinthus connects via lateral zones of transtension and strike slip claritas fossae and valles marineris to a broad zone of compressional uplift and shortening defined by truncated craters and thrust faults along the coprates rise and thaumasia highlands however the low regional slope 1 results in gravitational body forces that are too small to deform the basaltic lava flows conventionally thought to compose the flanks of the tharsis volcanic province instead we conclude that geothermal heating and topographic loading of extensive buried deposits of salts and or mixtures of salts ice and basaltic debris would allow for weak detachments and large scale gravity spreading we propose that the generally linear chasmata of valles marineris reflect extension collapse and excavation along fractures radial to tharsis either forming or reactivated as part of one lateral margin of the thaumasia gravity spreading system the other dextral lateral margin is a massive splay of extensional faults forming the claritas fossae which resembles a trailing extensional imbricate fan the compressional mountain belt defined by the coprates rise and thaumasia highlands forms the toe of the mega slide topographic observations and previous structural analyses reveal evidence for a failed volcanic plume below syria planum that could have provided further thermal energy and topographic potential for initiating regional deformation either intrusively through inflation or extrusively through lava flow and or ash fall emplacement higher heat flow during noachian time or geothermal heating due to burial by tharsis derived volcanic rocks would have contributed to flow of salt deposits as well as formation of groundwater from melting ice and dewatering of hydrous salts we further propose that connection of overpressured groundwater from aquifers near the base of the detachment through the cryosphere to the martian surface created the outflow channels of echus coprates and juventae chasmata at relatively uniform source elevations along the northern margin of the mega slide where regional groundwater flow would have been directed toward the surface our hypothesis provides a unifying framework to explain perplexing relationships between the rise of the tharsis volcanic province deformation of the thaumasia plateau and the formation of valles marineris and associated outflow channels

anatomy of the chesapeake bay impact structure revealed by seismic imaging delmarva peninsula virginia usa 1 a 30 km long radial seismic reflection and refraction survey completed across the northern part of the late eocene chesapeake bay impact structure cbis on the delmarva peninsula virginia usa confirms that the cbis is a complex central peak crater we used a tomographic p wave velocity model and low fold reflection images constrained by data from two deep boreholes located on the profile to interpret the structure and composition of the upper 5 km of crust the seismic images exhibit well defined structural features including with increasing radial distance a collapsed central uplift a breccia filled moat and a collapsed transient crater margin which collectively constitute a 40 km wide collapsed transient crater and a shallowly deformed annular trough these seismic images are the first to resolve the deep structure of the crater 1 km and the boundaries between the central uplift moat and annular trough several distinct seismic signatures distinguish breccia units from each other and from more coherent crystalline rocks below the central uplift moat and annular trough within the moat breccia extends to a minimum depth of 1 5 km or a maximum of 3 5 km depending upon the interpretation of the deepest layered materials the images show 350 to 500 m of postimpact sediments above the impactites the imaged structure of the cbis indicates a complex sequence of events during the cratering process that will provide new constraints for numerical modeling

geomorphic characterization of four shelf sourced submarine canyons along the u s mid atlantic continental margin abstract shelf sourced submarine canyons are common features of continental margins and are fundamental to deep sea sedimentary systems despite their geomorphic and geologic significance relatively few passive margin shelf breaching canyons worldwide have been mapped using modern geophysical methods between 2007 and 2012 a series of geophysical surveys was conducted across four major canyons of the us mid atlantic margin wilmington baltimore washington and norfolk canyons more than 5700 km2 of high resolution multibeam bathymetry and 890 line km of sub bottom chirp profiles were collected along the outer shelf and uppermost slope depths of 80 1200 m the data allowed us to compare and contrast the fine scale morphology of each canyon system the canyons have marked differences in the morphology and orientation of canyon heads steepness and density of sidewall gullies and the character of the continental shelf surrounding canyon rims down canyon axial profiles for washington baltimore and wilmington canyons have linear shapes and each canyon thalweg exhibits morphological evidence for recent relatively small scale sediment transport for example washington canyon displays extremely steep wall gradients and contains 100 m wide 5 10 m deep v shaped incisions down the canyon axis suggesting modern or recent sediment transport in contrast the convex axial thalweg profile the absence of thalweg incision and evidence for sediment infilling at the canyon head suggest that depositional processes strongly influence norfolk canyon during the current sea level high stand the north walls of wilmington washington and norfolk canyons are steeper than the south walls due to differential erosion though the underlying cause for this asymmetry is not clear furthermore we speculate that most of the geomorphic features observed within the canyons e g terraces tributary canyons gullies and hanging valleys were formed during the pleistocene and show only subtle modification by holocene processes active during the present sea level high stand

sedimentation and tectonics of the lower and middle eocene swauk formation in eastern swauk basin central cascades central washington the swauk basin lies between the straight creek and entiat leavenworth fault systems in the central cascades of washington and is one of several early tertiary strike slip basins in the pacific northwest in this paper seven informal stratigraphic units are recognized in the lowest portion of the basin fill the lower and middle eocene swauk formation in the eastern part of the basin these units have a stratigraphic thickness of more than 4800 m and were deposited in alluvial fan braided river meandering river lacustrine deltaic and lacustrine environments rapid facies changes and reversals in paleocurrent directions indicate numerous tectonically controlled drainage reorganizations sediments were mainly derived from crystalline rocks to the east north and west and sediment accumulation rates were high about 64 cm 1000 years the leavenworth fault has a complex history and periodically formed the eastern margin of swauk basin during the final phases and shortly after deposition of th

sedimentary processes on the atlantic continental slope of the united states abstract until recently the sedimentary processes on the united states atlantic continental slope were inferred mainly from descriptive studies based on the bathymetry and on widely spaced grab samples bottom photographs and seismic reflection profiles over the past 6 years however much additional information has been collected on the bottom morphology characteristics of shallow subbottom strata velocity of bottom currents and transport of suspended and bottom sediments a review of these new data provides a much clearer understanding of the kinds and relative importance of gravitational and hydrodynamic processes that affect the surface sediments on the rugged slope between georges bank and cape lookout n c these processes include 1 small scale mass wasting within submarine canyons and peripheral gullies 2 density flows within some submarine valleys 3 sand spillover near the shelf break 4 sediment creep on the upper slope and 5 hemipelagic sedimentation on the middle and lower slope the area between georges bank and hudson canyon is further distinguished by the relative abundance of large scale slump scars and deposits on the open slope the presence of ice rafted debris and the transport of sand within the heads of some submarine canyons between cape lookout and southern florida the slope divides into two physiographic units and the topography is smooth and featureless on the florida hatteras slope offshelf sand spillover and sediment winnowing related to gulf stream flow and possibly to storm driven currents are the major processes whereas hemipelagic sedimentation is dominant over the offshore slope along the seaward edge of the blake plateau north of the blake spur slumping generally is absent south of cape lookout although one large slump scarp related to uplift over salt diapirs has been identified east of cape romain future studies concerning sedimentary processes on the atlantic slope need to resolve 1 the ages and mechanisms of mass wasting 2 the accumulation rates and thicknesses of hemipelagic sediments and 3 the causes and variability of offshelf sand spillover sediment winnowing and canyon transport

high resolution seismic velocities and shallow structure of the san andreas fault zone at middle mountain parkfield california a 5 km long high resolution seismic imaging survey across the san andreas fault saf zone and the proposed san andreas fault observatory at depth safod drill site near parkfield california shows that velocities vary both laterally and vertically velocities range from 4 0 km sec probably correspond to granitic rock of the salinian block which is exposed a few kilometers southwest of the saf the depth to the top of probable granitic rock varies laterally along the seismic profile but is about 600 m below the surface at the proposed safod site we observe a prominent lateral low velocity zone lvz beneath and southwest of the surface trace of the saf the lvz is about 1 5 km wide at 300 m depth but tapers to about 600 m wide at 750 m depth at the maximum depth of the velocity model 750 m the lvz is centered approximately 400 m southwest of the surface trace of the saf similar velocities and velocity gradients are observed at comparable depths on both sides of the lvz suggesting that the lvz is anomalous relative to rocks on either side of it velocities within the lvz are lower than those of san andreas fault gouge and the lvz is also anomalous with respect to gravity magnetic and resistivity measurements because of its proximity to the surface trace of the saf it is tempting to suggest that the lvz represents a zone of fractured crystalline rocks at depth however the lvz instead probably represents a tectonic sliver of sedimentary rock that now rests adjacent to or encompasses the saf such a sliver of sedimentary rock implies fault strands on both sides and possibly within the sliver suggesting a zone of fault strands at least 1 5 km wide at a depth of 300 m tapering to about 600 m wide at 750 m depth fluids within the sedimentary sliver are probably responsible for observed low resistivity values

seismicity faulting and structure of the koyna warna seismic region western india from local earthquake tomography and hypocenter locations although seismicity near koyna reservoir india has persisted for 50 years and includes the largest induced earthquake m 6 3 reported worldwide the seismotectonic framework of the area is not well understood we recorded 1800 earthquakes from 6 january 2010 to 28 may 2010 and located a subset of 343 of the highest quality earthquakes using the tomodd code of zhang and thurber 2003 to better understand the framework we also inverted first arrivals for 3 d vp vs and vp vs and poisson s ratio tomography models of the upper 12 km of the crust epicenters for the recorded earthquakes are located south of the koyna river including a high density cluster that coincides with a shallow depth 1 5 km zone of relatively high vp and low vs also high vp vs and poisson s ratios near warna reservoir this anomalous zone which extends near vertically to at least 8 km depth and laterally northward at least 15 km is likely a water saturated zone of faults under high pore pressures because many of the earthquakes occur on the periphery of the fault zone rather than near its center the observed seismicity velocity correlations are consistent with the concept that many of the earthquakes nucleate in fractures adjacent to the main fault zone due to high pore pressure we interpret our velocity images as showing a series of northwest trending faults locally near the central part of warna reservoir and a major northward trending fault zone north of warna reservoir

radar and photoclinometric studies of wrinkle ridges on mars earth based radar altimetry and image derived photoclinometric profiles were analyzed to examine both the long and short wavelength topography associated with wrinkle ridges on mars photoclinometrically derived elevation data across wrinkle ridges were evaluated to determine the sensitivity of profiles to two empirical photoclinometric parameters the horizontal digital number hdn and the scattered light value slv the photoclinometric profiles are extremely sensitive to small variations in hdn the sense of slope of a profile can be completely reversed over a range in hdn of as little as 1 comparably small variations in the slv have relatively minor effects on the photoclinometrically derived elevations the existence of elevation offsets from one side of the ridge to the other reported in previous photoclinometric studies of martian wrinkles were not confirmed through photoclinometry in addition no evidence of elevation offsets were found in earth based radar altimetry profiles across wrinkle ridges in order to more accurately model wrinkle ridge topography we controlled photoclinometrically derived elevations with long wavelength topography obtained from the radar altimetry the results of this study do not support kinematic models for the origin of planetary wrinkle ridges that involve deeply rooted thrust faults which separate crustal blocks at different elevations a kinematic model involving buckling of shallow crustal layers into concentric folds that close leading to the development of thrust faults is consistent with wrinkle ridge morphology and terrestrial analogs recent geophysical studies of terrestrial analogs and the influence of shallow subsurface structures particularly buried craters on the localization of many wrinkle ridges on mars suggest that thrust faults associated with the ridges are confined to the ridged plains material and do not extend into the lithosphere

reply to comment on faulting apparently related to the 1994 northridge california earthquake and possible co seismic origin of surface cracks in potrero canyon los angeles county california by r d catchings m r goldman w h k lee m j rymer and d j ponti by brian j swanson allan e seward perry l ehlig and james e slosson swanson et al 2002 herein referred to as the comment authors take issue with numerous aspects of our 1998 article catchings et al 1998 on potrero canyon los angeles county california the comment authors take considerable liberty in paraphrasing our conclusions and discounting our interpretations principally because they believe that our seismic images do not represent the geologic structure beneath potrero canyon in particular the comment authors contend that our subsurface images are inconsistent with surface geologic mapping the comment authors attempt to support their objections by suggesting a combination of reflection artifacts and errors in our velocity model result in an inaccurate seismic profile in response to their contentions we show a published map two published cross sections and two sets of published borehole data that are consistent with our seismic image and the known geologic structure of the potrero canyon area we present velocity measurements from a borehole along our seismic profile that are consistent with our velocity model and inconsistent with the comment authors assumed velocities furthermore we show that the comment authors assumptions about our acquisition and processing techniques are based on inadequate research and lack of familiarity with seismological techniques below we address 16 objections by the comment authors on a topical basis comment catchings et al the authors stated that potrero canyon is believed to be within or overlie a broad syncline that is faulted along its axis they interpreted this syncline to be present in their seismic profiles based on the shallow dipping 0 20 reflectors shown in their figures 5 and 6 but they did not provide a geologic cross section at the seismic line to verify this in contrast to the author s statements and seismic profile however winterer and durham 1962 did not show a syncline below potrero canyon

imaging beneath an opaque basaltic layer using densely sampled wide angle obs data a combined reflection refraction wide angle seismic survey was conducted on the continental shelf north west of britain using a conventional streamer with an air gun source and static ocean bottom seismometers obs to record wide angle energy the shallow structure down to a basaltic layer was reasonably well imaged on the stacked reflection section the basalts however proved to be opaque to the conventional reflection method and prevented the imaging of deeper horizons where an important velocity inversion was anticipated this paper reports on the processing modeling and interpretation of the densely sampled wide angle obs data that were coincident with the reflection profile eleven obs instruments were deployed along a 75 km line and recorded signal from a powerful 149 liter 9100 in sup 3 air gun array fired every 50 m data processing was performed using a standard industrial reflection seismic software package prior to first arrival picking processing steps included geometry definition trace summation and display of the data using various scaling algorithms an initial model was constructed from 1d velocity time profiles digitized every 4 km along the stacked section first arrival travel time modeling rapidly converged to a detailed model of the structure of the top 5 km of the crust modeling revealedmore the existence of a buried low velocity mesozoic sedimentary basin of a prominent basement horst and of a normal fault penetrating to the basement less

evolution of veatch washington and norfolk submarine canyons inferences from strata and morphology abstract investigations of veatch washington and norfolk submarine canyons on the eastern continental margin of the united states resulted in a detailed assessment of their past and present geologic processes norfolk and washington canyons share such characteristics as similar levee geometry stratigraphy and mineralogy veatch canyon differs from norfolk and washington canyons in these respects seismic reflection profiles of all three submarine canyon heads indicate an erosional origin seismic profiles of veatch canyon s lower continental slope indicate a formation by depositional processes in contrast the continental slope profiles of washington and norfolk canyons reveal a history of alternating episodes of deposition and erosion cored sediments from washington and norfolk canyons disclose recent intermittent down canyon transport of sand to the continental rise bathymetric and seismic profiles suggest veatch washington and norfolk canyons have all been subjected to a minimum of two periods of development similar axial trends of washington and norfolk canyons imply a common structural influence

integrating high resolution refraction data into near surface seismic reflection data processing and interpretation shallow seismic reflection surveys commonly suffer from poor data quality in the upper 100 to 150 ms of the stacked seismic record because of shot associated noise surface waves and direct arrivals that obscure the reflected energy nevertheless insight into lateral changes in shallow structure and stratigraphy can still be obtained from these data by using first arrival picks in a refraction analysis to derive a near surface velocity model we have used turning ray tomography to model near surface velocities from seismic reflection profiles recorded in the hueco bolson of west texas and southern new mexico the results of this analysis are interval velocity models for the upper 150 to 300 m of the seismic profiles which delineate geologic features that were not interpretable from the stacked records alone in addition the interval velocity models lead to improved time to depth conversion when converted to stacking velocities they may provide a better estimate of stacking velocities at early travelt

faulting apparently related to the 1994 northridge california earthquake and possible co seismic origin of surface cracks in potrero canyon los angeles county california apparent southward dipping reverse fault zones are imaged to depths of about 1 5 km beneath potrero canyon los angeles county california based on their orientation and projection to the surface we suggest that the imaged fault zones are extensions of the oak ridge fault geologic mapping by others and correlations with seismicity studies suggest that the oak ridge fault is the causative fault of the 17 january 1994 northridge earthquake northridge fault our seismically imaged faults may be among several faults that collectively comprise the northridge thrust fault system unusually strong shaking in potrero canyon during the northridge earthquake may have resulted from focusing of seismic energy or co seismic move ment along existing related shallow depth faults the strong shaking produced ground surface cracks and sand blows distributed along the length of the canyon seismic reflection and refraction images show that shallow depth faults may underlie some of the observed surface cracks the relationship between observed surface cracks and imaged faults indicates that some of the surface cracks may have devel oped from nontectonic alluvial movement but others may be fault related imme diately beneath the surface cracks p wave velocities are unusually low 400 m sec and there are velocity anomalies consistent with a seismic reflection image of shallow faulting to depths of at least 100 m on the basis of velocity data we suggest that unconsolidated soils 800 rrdsec extend to depths of about 15 to 20 m beneath our datum 25 m below ground surface the underlying rocks range in velocity from about 1000 to 5000 m sec in the upper 100 m this study illustrates the utility of high resolution seismic imaging in assessing local and regional seismic hazards

extension of godavari gondwana sediments underneath trap covered region of satpura basin as evidenced from seismic studies in deccan syneclise india abstract we present a shallow p wave velocity structure of the eastern part of deccan syneclise central india from the refraction and wide angle reflection data recorded along two 100 km long seismic refraction profiles in east west e w and north south n s directions using travel time inversion method in addition to the p wave velocity model we have derived s wave velocity model and estimated vp vs and poisson s ratios along the east west profile travel time analysis and inversion of the data revealed three layers above the basement the first layer with a p wave velocity of 1 4 1 5 km s 1 represents alluvium and the thickness of this layer is varying between 100 400 m in the e w and 30 100 m in the n s profile the deccan trap thickness is observed to be varying between 850 and 1250 m constitutes the second layer p wave velocity of the deccan traps is 4 8 5 2 km s 1 amplitude decay and travel time skips in the first arrival refraction data in some of the record sections indicate the presence of a velocity inversion i e low velocity zone lvz beneath the traps wide angle reflection phases from top and bottom of the lvz top of basement together with basement refraction phase are identified and modeled to derive lvz thickness the lvz has been interpreted to be the gondwana sediments sandwiched between deccan traps and basement these sediments are about 200 450 m thick with a p wave velocity of 3 6 km s 1 the basement lies at about 1 60 km depth near khandala in the west and rajola in the north shows an upward trend towards south east the p wave velocity of the basement is about 6 0 6 2 km s 1 the inferred subtrappean sediments could be the possible extension of gondwana sediments of the godavari graben towards the satpura basin

elastic wave velocities within oceanic layer 2 from sonic full waveform logs in deep sea drilling project holes 395a 418a and 504b multichannel full waveform acoustic logs were recorded in deep sea drilling project dsdp hole 418a during ocean drilling program odp leg 102 dsdp hole 395a during odp leg 109 and dsdp hole 504b during odp leg 111 to provide nearly continuous measurements of elastic wave velocities as a function of depth within oceanic layer 2 for different spreading rates and crustal ages the velocities depend primarily on the morphology of the basalt massive units have vp above 5 km s vs above 2 8 km s and vp vs below 1 9 their velocities increase with depth as expected from crack closure due to confining stress and are lower where fractures are present vp and vs within pillows are quite variable but in general are lower than in massive units and vp vs is higher velocities within breccias are similar to or lower than those of pillows within a given morphology the elastic properties do not depend on spreading rate within pillows velocity variations depend primarily on the degree of alteration infilling and the mineralogy of the infilling material and secondarily on conditions at emplacement coherent shear arrivals are sometimes not found within shallow pillows and in extreme cases the compressional arrival is also incoherent because of scattering resulting from the similarity between the sonic wavelength and the pillow size this sampling bias in the sonic log is the most likely cause of somewhat higher average sonic than seismic velocities measured within extrusive basalts at shallow depths other causes include the fact that laterally finite massive units may be oversampled by borehole measurements and that voids between pillows and fractures whose size is within an order of magnitude of the sonic wavelength have less effect on sonic than on seismic velocities the crustal section can be separated only roughly into seismic layers on the basis of the sonic velocities changes in velocity with depth within the extrusive section at a single site giving rise to previously defined seismic layers 2a and 2b are due to a change with depth in the properties of the pillows associated with differences in the amount and type of infilling materials rather than to a change with depth in the relative proportion of pillows and massive units because alteration occurs early and its history is different at different depths depth dependent variations in pillow properties are 1 established at young age and 2 persist even in old crust within the intrusive section of dsdp hole 504b velocities are similar to or higher than those measured in saturated minicores at atmospheric pressure and seismic and sonic velocities are approximately equal suggesting that little large scale porosity is present

a method and example of seismically imaging near surface fault zones in geologically complex areas using vp vs and their ratios abstract the determination of near surface vadose zone and slightly below fault locations and geometries is important because assessment of ground rupture strong shaking geologic slip rates and rupture histories occurs at shallow depths however seismic imaging of fault zones at shallow depths can be difficult due to near surface complexities such as weathering groundwater saturation massive nonlayered rocks and vertically layered strata combined p and s wave seismic refraction tomography data can overcome many of the near surface fault zone seismic imaging problems because of differences in the responses of elastic bulk and shear moduli of p and s waves to shallow depth fault zone properties we show that high resolution refraction tomography images of p to s wave velocity ratios v p v s can reliably identify near surface faults we demonstrate this method using tomography images of the san andreas fault saf surface rupture zone associated with the 18 april 1906 m 7 9 san francisco earthquake on the san francisco peninsula in california there the saf cuts through franciscan melange which consists of an incoherent assemblage of greywacke chert greenstone and serpentinite a near vertical zone 75 northeast dip of high p wave velocities up to 3000 m s low s wave velocities 150 600 m s high v p v s ratios 4 8 8 and high poisson s ratios 0 44 0 49 characterizes the main surface rupture zone to a depth of about 20 m and is consistent with nearby trench observations we suggest that the combined v p v s imaging approach can reliably identify most near surface fault zones in locations where many other seismic methods cannot be applied

compressional velocity structure and poisson s ratio in marine sediments with gas hydrate and free gas by inversion of reflected and refracted seismic data south shetland islands antarctica abstract a bottom simulating reflector bsr on the south shetland margin antarctic peninsula was surveyed within the progetto nazionale di ricerche in antartide pnra high resolution multichannel mcs reflection profiles were acquired and a three component ocean bottom seismograph obs was deployed where the bsr was particularly strong the compressional velocity field associated to the bsr was determined by the inversion of travel times of reflected mcs data and refracted obs data events information on shear wave velocities was extracted from the horizontal components of the obs records the analysis indicates the presence of velocity anomalies both above and below the bsr that are not related to the lithologic characteristics of the sedimentary column but can be associated to gas hydrate and free gas presence in pore space amplitude versus offset avo analysis was performed on common depth point gathers which correspond to the obs position the study determined reflection coefficient trends that provided qualitative information about gas hydrate and free gas abundance a theoretical model for elastic porous media was applied to quantify amounts of gas hydrate and free gas the resulting theoretical velocity curves were compared to interval velocity obtained by seismic inversion a quantitative estimation of free gas and gas hydrates trapped in the sediment pore spaces was made by interpreting velocity anomalies with respect to reference velocity curves normally consolidated marine terrigenous sediments the comparison of the results obtained by these independent methods seismic inversion avo analysis and theoretical model gives consistent values of poisson s ratio and gas hydrate and free gas estimation

reply to comment on near surface location geometry and velocities of the santa monica fault zone los angeles california by r d catchings g gandhok m r goldman d okaya m j rymer and g w bawden by t l pratt and j f dolan in a comment on our 2008 paper catchings gandhok et al 2008 on the santa monica fault in los angeles california pratt and dolan 2010 herein referred to as p d cite numerous objections to our work inferring that our study is flawed however as shown in our reply their objections contradict their own published works published works of others and proven seismic methodologies rather than responding to each repeated invalid objection we address their objections by topic in the subsequent sections in catchings gandhok et al 2008 we presented high resolution seismic reflection images that showed two near surface faults in the upper 50 m beneath the grounds of the wadsworth veterans administration hospital wvah although p d suggest we effectively duplicated their seismic acquisition our survey was not a duplication of their efforts rather we conducted a seismic imaging survey over a similar profile as pratt et al 1998 but used a different data acquisition system and different data processing methods to evaluate methods of seismically imaging blind faults in the wake of the 17 january 1994 m 6 7 northridge earthquake we used an acquisition method that provides both tomographic seismic velocities and reflection images our combined data approach allowed for shallower imaging 2 5 m minimum than the 20 m minimum of pratt et al 1998 clearer images of the fault zone and more accurate depth determinations rather than time images in processing the reflection images we used prestack depth migration which is generally accepted as the only proper imaging method for imaging subsurface structures with strong lateral velocity variations versteeg 1993 a condition shown to exist at the wvah site we correlated our reflection images with refraction tomography images borehole lithology and velocity data interferometric synthetic aperture radar images and changes in groundwater depths except for some minor differences our seismic reflection images coincide with previously published seismic reflection

electromagnetic mapping of electrical conductivity beneath the columbia basalts sedimentary rocks beneath the columbia river basalt group are recognized as having potential for oil and gas production but the overlying layered basalts effectively mask seismic reflections from the underlying sediments four electromagnetic em methods have been applied on profiles crossing boylston ridge a typical east west trending anticline of the yakima fold belt in an attempt to map the resistivity interface between the basalts and the sediments and to map variations in structure and resistivity within the sediments the em surveys detected strong variations in resistivity within the basalts and in particular the continuous magnetotelluric array profiling emap revealed resistivity lows beneath the surface anticlines these low resistivity zones probably coincide with fracturing in the core of the anticlines and they appear to correlate well with similar zones of low seismic velocity observed on a nearby seismic profile the controlled source em surveys in loop transient long offset transient and variable offset frequency domain were designed in anticipation of relatively uniform high resistivity basalts and were found to have been seriously distorted by the intrabasalt conductors discovered in the field in particular the resistivity sections derived from 1d inversions were found to be inconsistent and misleading the emap survey provided the most information about themore subsurface resistivity distribution and was certainly the most cost effective however both controlled source and emap surveys call for accurate 2d or 3d inversion to accommodate the geological objectives of this project references 18 less

active geologic processes in barrow canyon northeast chukchi sea abstract circulation patterns on the shelf and at the shelf break appear to dominate the barrow canyon system the canyon s shelf portion underlies and is maintained by the alaska coastal current a c c which flows northeastward along the coast toward the northeast corner of the broad chukchi sea offshelf and onshelf advective processes are indicated by oceanographic measurements of other workers these advective processes may play an important role in the production of bedforms that are found near the canyon head as well as in processes of erosion or non deposition in the deeper canyon itself coarse sediments recovered from the canyon axis at 400 to 570 m indicate that there is presently significant flow along the canyon the canyon hooks left at a point north of point barrow where the a c c loses its coastal constriction the left hook as well as preferential west wall erosion continues down to the abyssal plain of the canada basin at 3800 m a possible explanation for the preferential west wall erosion along the canyon at least for the upper few hundred meters is that the occasional upwelling events which cause nutrient rich water to flow along the west wall would in turn cause larger populations of burrowing organisms to live there than on the east wall and that these organisms cause high rates of bioerosion this hypothesis assumes that the dominant factor in the canyon s erosion is biological activity not current velocity sedimentary bedforms consisting of waves and furrows are formed in soft mud in a region on the shelf west of the canyon head their presence there perhaps reflects a the supply of fine suspended sediments delivered by the a c c from sources to the south probably the yukon and other rivers draining northwestern alaska and b the westward transport of these suspended sediments by the prevailing beaufort gyre which flows along the outer shelf

imaging of subvolcanic mesozoics in the saurashtra peninsula of india using traveltime inversion of wide angle seismic data low velocity mesozoic sediments exposed in the northeastern part of the saurashtra peninsula of western india are assumed to be below the high velocity volcanic rock cover conventional seismic refraction and reflection profiling experiments often fail to map hidden low velocity formations caused by inherent limitations of these methods however wide angle seismics involving both refractions and reflections is an effective tool for imaging in such a geological setting inversion of wide angle seismic traveltime data from a 45 km long profile reveals a three layered velocity structure above the basement with mesozoic sediments sandwiched between exposed volcanic rock and an underlying basalt flow the derived velocity model closely matches the lithology of the nearby deep lodhika well demonstrating the potential of wide angle seismics in mapping formations hidden below volcanic rock cover the volcanic rock cover is almost flat 1 4 km thick with an average velocity of 5 1 km s 1 the mesozoic sediments have a velocity of 4 3 km s 1 and thickness variations from 0 9 to 1 6 km the underlying basalt flow has a velocity of 5 15 km s 1 and varies in thickness from 1 to 2 km the basement with a velocity of 5 80 5 95 km s 1 is at an average depth of 3 9 km shear wave analysis yielded velocities varying between 2 65 2 75 and 3 30 3 40 km s 1 for the exposed volcanic rock and the subsurface basement respectively corresponding to poisson ratios of 0 31 and 0 26 the high poisson ratio in the volcanic rock cover is a result of rock fracturing as indicated by the fast decay of seismic energy with offset

bathymetry and sediment dispersal dynamics along the yallahs fan delta front jamaica abstract the shallow offshore yallahs fan delta serves as a model for the interaction of littoral processes and bathymetry and how they influence sedimentation on steep submarine slopes and in deep marine basins in tectonically active areas bottom reflection profiles show that the yallahs delta front is characterized by two bathymetric zones a narrow island shelf and a steep slope dissected by the heads of at least three submarine canyons the refraction and diffraction of waves across these canyons and shelf control sediment distribution and the alternation of erosional and depositional beaches a dominantly westward longshore drift transports coarse grained sediments until they are trapped in the heads of the submarine canyons or temporarily stored on steep unstable slopes between the canyons mass gravity processes presumably move these sediments downslope where they are deposited as turbidites in the yallahs basin and out onto the colombian abyssal plain

phase relations to 3 kbar in the systems edenite h2o and edenite excess quartz h2o abstract amphiboles approached edenite naca 2 mg 5 si 7 alo 22 oh 2 richterite na 2 camg 5 si 8 o 22 oh 2 tremolite ca 2 mg 5 si 8 o 22 oh 2 solid solutions were studied by conventional hydrothermal techniques employing the bulk compositions edenite and edenite additional quartz all with excess h 2 o for the stoichiometric edenite bulk composition excess h 2 o the equilibrium phase assemblage is diopside na phlogopite forsterite fluid at and just above the amphibole high temperature limit at 850 5 c 500 bar and 880 5 c 1000 bar the breakdown temperature of sodic phlogopite is 855 3 c at 500 bar and 890 5 c at 700 bar producing nepheline plagioclase or melt additional forsterite and fluid diopside and na phlogopite solid solution coexist over a broad p fluid t region even within the amphibole field where they are associated with an edenite richterite tremolite solid solution of approximate composition ed 35 rc 50 tr 15 in the system edenite 4 quartz excess h 2 o nearly pure tremolite and albite coexist stably between 670 and 830 c at 1000 bar and give way to the possibly metastable assemblage diopside talc albite below 670 c in the presence of albite tremolite reacts to produce diopside quartz enstatite fluid above 830 c at 1000 bar for the investigated silica rich bulk composition amphibole p fluid t stability is divided by the albite melting curve into a tremolite albite field and a tremolite aqueous melt field substantial equilibrium solid solution of tremolite towards edenite or richterite was not observed for silica excess bulk compositions metastable edenite rich amphiboles initially synthesized change to tremolite with increasing run length in the presence of free sio 2 edenitic amphibole is stable only over a very limited temperature range in silica undersaturated environments thus accounting for its rarity in nature na phlogopite solid solutions are also disfavored by high a sio 2 even for nepheline normative lithologies a hypothesized rapid low temperature conversion to vermiculite or smectite could partly explain the scarcity of sodic phlogopite in rocks

basement configuration of the jhagadia rajpipla profile in the western part of deccan syneclise india from travel time inversion of seismic refraction and wide angle reflection data abstract 2 d velocity structure up to the basement is derived by travel time inversion of the first arrival seismic refraction and wide angle reflection data along the sw ne trending jhagadia rajpipla profile located on the western part of deccan syneclise in the narmada tapti region the study region is mostly covered by alluvium inversion of refraction and wide angle reflection data reveals four layered velocity structure above the basement the first two layers with p wave velocities of 1 95 2 3 km s 1 and 2 7 3 05 km s 1 represent the recent and quaternary sediments respectively the thickness of these sediments varies from 0 15 km to 3 4 km the third layer with a p wave velocity of 4 8 5 1 km s 1 corresponds to the deccan volcanics whose thickness varies from 0 5 km to 1 0 km presence of a low velocity zone lvz below the high velocity volcanic rocks in the study area is inferred from the travel time skip and amplitude decay of the first arrival refraction data and the wide angle reflection from top of the lvz present immediately after the first arrival refraction from deccan trap layer the thickness of the low velocity mesozoic sediments varies from 0 3 km to 1 7 km the basement with a p wave velocity of 5 9 6 15 km s 1 lies at a depth of 4 9 km near jhagadia and shallows to 1 2 km towards northeast near rajpipla the results indicate presence of low velocity mesozoic sediments hidden below the deccan trap layer in the western part of the deccan syneclise

stability and composition relations of calcic amphiboles in ultramafic rocks calcic amphiboles are observed in ultramafic rocks that have equilibrated under a broad span of geological conditions and might prove to be good indicators of metamorphic grade if their stabilities could be determined as a function of their compositions experiments were performed on the stability of tremolite plus forsterite in the system h2o cao mgo sio2 from 5 to 20 kbar a univariant curve was fitted to the experimental brackets using volume water fugacity and heat capacity data the results indicate that the maximum stability of tremolite in the presence of forsterite is about 825 c at 5 kbar addition of al2o3 to this system increases the stability of tremolitic amphibole by only 20 40 c and induces solubility of 5 7 wt al2o3 in the amphibole as determined from quantitative sem analyses of individual amphibole crystals thus substitution of the tschermakite component ca2 mg3al2 si6al2 o22 oh 2 alone cannot lead to the greatly enhanced al2o3 contents or thermal stability of natural calcic amphiboles

neogene synvolcanic and syntectonic sedimentation in central washington neogene drainage evolution and sedimentation in central washington were controlled by extrusion of flood basalts aggradation of volcanism induced sedimentary sequences and fold belt deformation most columbia river basalt group lavas accumulated between 17 0 and 13 5 ma and repositioned streams to the margin of the columbia plateau lava dammed lakes were not major contributors to the stratigraphic record fluvial sedimentation in response to lowered gradients produced broad flood plain dominated alluvial sequences distribution of basalts and the thickness and facies trends in intercalated sediments record growth of the yakima fold belt throughout the middle miocene to pliocene adequate topographic relief to generate widespread basaltic gravel however lagged behind initial deformation by at least 10 m y because of burial of the slowly developing folds by high frequency eruptions of large volume basalt flows neogene uplift and incision of the cascade range are recorded by derivation of successively younger epiclastics from lower levels of the cascade stratigraphic sequence episodes of dacitic volcanism in the cascades produced widespread monomictic sediments with abundant pyroclastic material in proximal to medial positions this detritus was deposited primarily by floods and debris flows

a quantitative study on the use of converted waves for sub basalt imaging the idea of imaging beneath a high velocity layer using converted waves has been popular since 1990 because these wave types have their maximum amplitudes at mid to far offsets the search for pure p waves at the highly multiple contaminated near offsets can be avoided for the atlantic margin with buried thin layered basalts our quantitative study shows that the initial single layered approach is not viable even in an unrealistic ideal geological setting the amplitude of the symmetrical psp mode is far too weak to be recognized on towed streamer data furthermore in the far offset window where locally converted waves have their strongest amplitudes there is a multitude of other reflections refractions and interbedded multiples which have similar moveouts and often higher amplitudes without the removal of these events a reliable image of the subsurface cannot be produced we show that even if this problem were solved it would be far easier to use the p wave reflection from beneath the basalt at near offsets our study shows that this wave type is by far the strongest response a borehole derived model using a thin layered basalt sequence reveals that the strongest locally converted wave has an asymmetrical path and is 10 times weaker all our results indicate that the pure p modes provide the best chance of imaging sub basalt sedimentary interfaces

delineation of subtrappean mesozoic sediments in deccan syneclise india using travel time inversion of seismic refraction and wide angle reflection data 2 d shallow velocity structure is derived by travel time inversion of the first arrival seismic refraction and wide angle reflection data along the e w trending narayanpur nandurbar and n s kothar sakri profiles located in the narmada tapti region of the deccan syneclise deccan volcanic trap rocks are exposed along the two profiles inversion of seismic data reveals two layered velocity structures above the basement along the two profiles the first layer with a p wave velocity of 5 15 5 25 km s 1 and thickness varying from 0 7 1 5 km represents the deccan trap formation along the narayanpur nandurbar profile the trap layer velocity ranges from 4 5 to 5 20 km s 1 and the thickness varies from 0 95 to 1 5 km along the kothar sakri profile the second layer represents the low velocity mesozoic sediments with a p wave velocity of 3 5 km s 1 and thickness ranging from about 0 70 to 1 6 km and 0 55 to 1 1 km along the e w and n s profiles respectively presence of a low velocity zone lvz below the volcanic rocks in the study area is inferred from the travel time skip and amplitude decay of the first arrival refraction data together with the prominent wide angle reflection phase immediately after the first arrivals from the deccan trap formation the basement with a p wave velocity of 5 8 6 05 km s 1 lies at a depth ranging from 1 5 to 2 45 km along the profiles the velocity models of the profiles are similar to each other at the intersection point the results indicate the existence of a mesozoic basin in the narmada tapti region of the deccan syneclise

dispersion of bauxitic red mud in the gulf of corinth greece abstract bauxitic red mud slurry discharged by an aluminium processing factory on the shelf of the gulf of corinth greece is used as a tracer to examine sediment transport and dispersion processes in a tectonically active deep basin the gulf of corinth is a silled elongate basin with a maximum depth of 860 m it is characterised by high seismicity the red mud is discharged through a pipeline at a depth of 100 m where it forms an extensive deposit grab sampling has shown that the red mud extends over the slope and the abyssal plain up to a distance of 17 km from the mouth of the pipeline it forms small scattered sheet like deposits of up to 3 cm in thickness the structures observed in the scattered patches of the red mud which in some places are overlain by a thin veneer of grey olive green natural sediments suggest that the red mud is transported from the shelf to the abyssal plain by gravitative sediment flows the flows are triggered by earthquakes granulometric and geochemical analyses of the red mud samples show that the red mud during its transport from the shelf to the abyssal plain is subjected to mixing with the surrounding sediments a different mixing ratio is determined however by reference to the various trace metals fe ni co pb

inversion for crustal structure using reflections from the passcal ouachita experiment an interface inversion has been tested and applied to wide angle reflection data from the 1986 passcal ouachita experiment an interface corrugation with a relief of 10 km and a width of 30 km was successfully imaged in a test of the interface inversion velocity depth curves derived for shot points 14 19 using the tail sum method are similar to an average one dimensional velocity model from forward modeling using travel time correlations from southern profiles 14 19 the similarity of these velocity depth curves positioned over the southern half of the passcal experiment suggests that crustal structure in this region is approximately laterally homogeneous lower crustal velocities are not well resolved due to the recording on most profiles of only small segments of the travel time triplications a two dimensional velocity structure was derived by using the average one dimensional velocities for the deeper crustal layers and formally inverting for depth to interfaces the final inversion model is found to be consistent with previous refraction interpretations south of the ouachita orogenic trend and concurrent interpretations of the passcal data set inversion results for the central and southern portion of the passcal profile indicate a depth of 10 12 km for a midcrustal layer which thins southward from approximately 10 km to about 4 km a lower crustal layer with an average thickness of 12 km and a moho depth of approximately 29 5 km are also determined interface depths are in agreement with a normal moveout stack of the passcal data set in particular the shallowing of the moho to a depth of 30 km over the northern 50 km of the profile matches previous interpretations of the data set and has been interpreted here and in previous studies as the location of the paleozoic continental margin geophysical studies of the modern atlantic continental passive margin provide the simplest comparison to the crustal structure derived here the lower crustal layer found south of the shallowing of the moho to 30 km beneath the passcal profile is analogous in thickness and position to rift stage lower crust however other tectonic interpretations are possible given the uncertainties in velocity and lithology relationships

sediment transport processes on an active submarine fault escarpment gulf of corinth greece abstract sediment transport processes on the escarpment of a listric fault in the tectonically active and terrigenous sediment dominated corinth graben in greece are studied using 3 5 khz and airgun profiles and sidescan sonar images the whole of the slope area is affected by gravitational mass movements slumps debris mud flows and liquified and turbidity flows in canyon fan systems large volumes of sediment are transported through slumping debris mud and turbidity flows into the basin here they build coalescing fans which consist of intercalations of debris flow deposits and turbidites in delta front slope fan apron systems sediments are transported radially downslope through slumping debris mud flows liquified flows and high density turbidity flows into the basin where they build coalescing fan aprons these consist of massive homogenized deposits fluxoturbidites in shelf slope systems retrogressive rotational slumping is the dominant instability feature however due to the sharp increase in the slope gradient caused by the slumping debris and turbidity flows are triggered the major factors responsible for triggering gravitational mass movements in the region are earthquakes high sedimentation rates off the river mouths and heavy rainfalls and high seas these mass movements appear to occur at least once every 2 yrs as indicated by the failure of submarine cables

wonesite a new rock forming silicate from the post pond volcanics vermont a new na rich trioctahedral layer silicate with the composition caoo naorroko or orr mg nofeo 77smno o cro oortb oroal ro r4 alr 534sl 466 8 0oooro oh f a has been discovered in the post pond volcanics vermont the mineral is similar in optical chemical and physical properties to phlogopite the major differences being the high na k and smaller d 9 574 monoclinic unit cell dimensions are a 5 312 3 b 9 163 5 c 9 825 6 a f 103 18 6 and y 465 6 5 a3 the mineral coexists with phlogopite talc chlorite cordierite gedrite anthophyllite qvartz and plagioclase an o ro and is thought to be a stable equilibrium phase under metamorphic conditions the mineral has been given the name wonesite in honor of david r wones

the seismicity geomorphology and structural evolution of the corinth area of greece in the eastern gulf of corinth geological structure is closely reflected in the topography in the 1981 corinth earthquakes ground deformation accentuated existing geomorphological patterns we explore the relationship between seismicity and landforms in space and time the area examined extends beyond the epicentral region of the 1981 events and its evolution is traced over the last 40000 years to understand the relation between deep and superficial structures we discuss processes that occurred in the 1981 earthquakes and go on to propose that surface faulting appears only above linear faults at depth that move in earthquakes with magnitudes m s greater than six where faults at depth intersect or bend the faulting becomes distributed and prim ary faulting does not reach the surface here the surface manifestation of faulting at depth is surface folding and secondary faulting such regions are identified in maps of the eastern gulf of corinth evidence for the evolution of the fault systems is provided by eyewitness accounts of shoreline changes following the recent earthquakes historical and archaeological data pertaining to old sea levels and 14 c dates for molluscs collected from fossil shorelines the results of these studies broadly confirm an earlier view of j a jackson et al earth planet sci lett 57 377 397 1982 that motion has shifted from faulting south of the city of corinth to faulting in the perachora peninsula but the transfer is not complete areas lying between the two fault systems have moved up and down in historical and archaeological times indicating that both systems are still active the evidence for activity of the northern system points to a repeat time of 300 years for earthquakes com parable with those of 1981 the work discussed in this paper suggests that some of the features previously described as m arine terraces are fault controlled continental surfaces furtherm ore beach deposits at a num ber of different levels long regarded as successive shorelines are in fact contemporaneous the critical ages were obtained by radiocarbon dating of shell carbonate a technique which yields dependable results if applied to samples which have been carefully selected and pretreated palaeontological dating of the terraces in contrast is found to be misleading because the faunas are environm entally controlled and consequently diachronous

seismic structure of basalt flows from surface seismic data borehole measurements and synthetic seismogram modeling we use the wide angle wavefield to constrain estimates of the seismic velocity and thickness of basalt flows overlying sediments wide angle means the seismic wavefield recorded at offsets beyond the emergence of the direct wave this wide angle wavefield contains arrivals that are returned from within and below the basalt flows including the diving wave through the basalts as the first arrival and p wave reflections from the base of the basalts and from subbasalt structures the velocity structure of basalt flows can be determined to first order from traveltime information by ray tracing the basalt turning rays and the wide angle base basalt reflection this can be refined by using the amplitude variation with offset avo of the basalt diving wave synthetic seismogram models with varying flow thicknesses and velocity gradients demonstrate the sensitivity to the velocity structure of the basalt diving wave and of reflections from the base of the basalt layer and below the diving wave amplitudes of the

continuity of the west napa franklin fault zone inferred from guided waves generated by earthquakes following the 24 august 2014 mw 6 0 south napa earthquake we measure peak ground velocities from fault zone guided waves fzgws generated by on fault earthquakes associated with the 24 august 2014 m w 6 0 south napa earthquake the data were recorded on three arrays deployed across north and south of the 2014 surface rupture the observed fzgws indicate that the west napa fault zone wnfz and the franklin fault ff are continuous in the subsurface for at least 75 km previously published potential field data indicate that the wnfz extends northward to the maacama fault mf and previous geologic mapping indicates that the ff extends southward to the calaveras fault cf this suggests a total length of at least 110 km for the wnfz ff because the wnfz ff appears contiguous with the mf and cf these faults apparently form a continuous calaveras franklin wnfz maacama cfwm fault that is second only in length 300 km to the san andreas fault in the san francisco bay area the long distances over which we observe fzgws coupled with their high amplitudes 2 10 times the s waves suggest that strong shaking from large earthquakes on any part of the cfwm fault may cause far field amplified fault zone shaking we interpret guided waves and seismicity cross sections to indicate multiple upper crustal splays of the wnfz ff including a northward extension of the southhampton fault which may cause strong shaking in the napa valley and the vallejo area based on travel times from each earthquake to each recording array we estimate average p s and guided wave velocities within the wnfz ff 4 8 5 7 2 2 3 2 and 1 1 2 8 km s respectively with fzgw velocities ranging from 58 to 93 of the average s wave velocities

use of traveltime skips in refraction analysis to delineate velocity inversion1 first arrival refraction data does not normally provide any indication of the velocity inversion problem however under certain favorable circumstances when the low velocity layer lvl is considerably thicker than the overlying higher velocity layer hvl the velocity inversion can be seen in the form of a traveltime skip model studies show that in such cases the length of the hvl traveltime branch can be used to determine the thickness of the hvl and the magnitude of the traveltime skip in order to determine the thickness of the lvl this is also applicable in the case of field data

large explosive source wide recording aperture seismic profiling on the columbia plateau washington clear subsurface seismic images have been obtained at low cost on the columbia plateau washington the columbia plateau is perhaps the most notorious of all bad data areas because large impedance contrasts in surface flood basalts severely degrade the seismic wavefield this degradation was mitigated in this study via a large explosive source wide recording aperture shooting method the shooting method emphasizes the wide angle portion of the wavefield where fermat s principle guarantees reverberation will not interfere with the seismic manifestations of crucial geologic interfaces the basalt diving wave normally discarded in standard common midpoint cmp seismic profiling can be used to image basalt velocity structure via traveltime inversion maximum depth penetration of the diving wave tightly constrains basalt sediment interface depth an arrival observed only at shot receiver offsets greater than 15 km can be used to determine the velocity and geometry of basement via simultaneous inversion

hammadah al hamra 193 the first amphibole bearing winonaite the hammadah al hamra 193 winonaite was found in the libyan desert in 1996 unlike most winonaites with fine to medium grained equigranular textures it consists predominantly of very large up to 5 mm optically continuous orthopyroxene grains enclosing smaller grains of olivine and plagioclase it also contains large up to 2 mm poikilitic grains of amphibole enclosing clinopyroxene plagioclase olivine and occasionally orthopyroxene which occur interstitial to the large orthopyroxene grains the amphibole is identified as fluoro edenite and textures indicate that it replaces clinopyroxene via a reaction in which diopside olivine and plagioclase form fluoro edenite trace element data are consistent with the formation of fluoro edenite from clinopyroxene and plagioclase fluoro edenite has a ree pattern similar to that of clinopyroxene but has elevated abundances of na k and ba elements typically enriched in plagioclase the source of the f is uncertain but may be apatite which is fluor apatite in this meteorite the presence of fluoro edenite in hah 193 a meteorite that experienced extensive thermal metamorphism indicates a significant stability field for this rare mineral

mechanisms of sediment transport and dispersion in a tectonically active submarine valley canyon system zakynthos straits nw hellenic trench abstract physical oceanographic and geophysical data sets are used to examine sediment transport processes currents were directed generally along the axis of the valley canyon system and in an area of low tidal range are attributed to regional weather patterns near bed and near surface currents are opposed both in terms of instantaneous observations and net lagrangian drift near bed down canyon water movement provides a mechanism for the offshore movement of fine grained sediment slope failures have been identified in the geophysical records and are considered to be controlled by earthquakes and salt diapirism in a tectonically active area these failures as mass displacement or slow down slope creep result in debris infill and the generation of turbidity currents fine grained sediments resuspended by the turbidity currents would be transported down canyon by the slowly moving near bed residual water movement hence the dominant transport mechanisms in the valley canyon system are 1 frequent mass sediment failure and 2 nearly continuous down channel fine grained suspended sediment movement

interpretation of a vertical seismic profile conducted in the columbia plateau basalts seismic reflection data are often of poor quality when recorded in areas where volcanic rocks are present at or near the surface in order to investigate this phenomenon a vertical seismic profiling vsp experiment was conducted in the columbia plateau basalts so that the behavior of seismic energy in subsurface volcanic rocks could be observed directly thus giving insight into data acquisition in volcanic terrains the lithologic section at the vsp site consists of low velocity 400 m s to 900 m s alluvium in the uppermost 50 m beneath which are layers of high velocity about 5800 m s high density basalts interbedded with clay layers with much lower velocities about 1700 m s and densities these large velocity and density contrasts dramatically influence wave generation and propagation in spite of the small source borehole offset 61 m large amplitude s waves are generated by the downgoing p waves when they reach a shallow 250 m clay basalt boundary these s waves in turn generate strong

sub basalt imaging of hydrocarbon bearing mesozoic sediments using ray trace inversion of first arrival seismic data and elastic finite difference full wave modeling along sinor valod profile of deccan syneclise india imaging below the basalt for hydrocarbon exploration is a global problem because of poor penetration and significant loss of seismic energy due to scattering attenuation absorption and mode conversion when the seismic waves encounter a highly heterogeneous and rugose basalt layer the conventional short offset seismic data acquisition processing and modeling techniques adopted by the oil industry generally fails to image hydrocarbon bearing sub trappean mesozoic sediments hidden below the basalt and is considered as a serious problem for hydrocarbon exploration in the world to overcome this difficulty of sub basalt imaging we have generated dense synthetic seismic data with the help of elastic finite difference full wave modeling using staggered grid scheme for the model derived from ray trace inversion using sparse wide angle seismic data acquired along sinor valod profile in the deccan volcanic province of india the full wave synthetic seismic data generated have been processed and imaged using conventional seismic data processing technique with kirchhoff pre stack time and depth migrations the seismic image obtained correlates with all the structural features of the model obtained through ray trace inversion of wide angle seismic data validating the effectiveness of robust elastic finite difference full wave modeling approach for imaging below thick basalts using the full wave modeling also allows us to decipher small scale heterogeneities imposed in the model as a measure of the rugose basalt interfaces which could not be dealt with ray trace inversion furthermore we were able to accurately image thin low velocity hydrocarbon bearing mesozoic sediments sandwiched between and hidden below two thick sequences of high velocity basalt layers lying above the basement

eocene and neogene volcanic rocks in the southeastern nechako basin british columbia interpretation of the canadian hunter seismic reflection surveys using first arrival tomography geological investigation of the near surface in the southeastern nechako basin is difficult shallow seismic reflection imaging is poor due in part to an extensive cover of eocene and neogene volcanic rocks outcrops of these volcanic rocks and the primarily cretaceous bedrock are commonly obscured by quaternary deposits and vegetation estimates of near surface p wave velocity are derived from the tomographic inversion of seismic first arrivals an effective tool when seismic imaging is poor tomographic model velocities are in agreement with sonic logs and laboratory samples except for those from the neogene chilcotin group cretaceous sedimentary rocks have velocities of 2800 4200 ms 1 the eocene endako and ootsa lake groups which have velocities of 3000 4200 ms 1 are not distinguishable based on velocity the velocity the character density focus and penetration depth of rays and ties with well and surface geology constrain the subsurface extent of the endako group adjacent to well b 82 c

paleogeographic evolution of the united states pacific northwest during paleogene time paleogeographic reconstructions for oregon and washington during paleogene time illustrate a major transition from a dominantly compressional prior to middle eocene time to an extensional tectonic regime this transition resulted in the development of three phases of paleogene basin evolution in the united states pacific northwest during the initial phase basins formed along the continental margin during collision of oceanic islands sediments in these basins were derived from nearby orogenic highlands the second phase of basin development began in middle eocene time and consisted of rapid subsidence of individual basins that formed within a broad forearc region nonmarine basins that formed during this phase were caused by extension possibly associated with transcurrent faulting rapid sedimentation in both marine and nonmarine basins during this time consisted dominantly of sandstone derived from cretaceous plutonic sources far to the east the final stage of basin development was the modification

amphibole plagioclase equilibria an empirical model for the relation albite tremolite edenite 4 quartz equilibria between plagioclase calcic amphibole and quartz can be described in part by the relation among mineral components naalsi3o8 ca2mg5si8o22 oh 2 naca2mg5alsi7o22 oh 2 4sio2 this relation governs the partitioning of na between plagioclase and the a site of coexisting amphibole data from natural amphibolites reveal that this partitioning is systematic and sensitive to metamorphic grade the ideal portion of the equilibrium constant kid xna a x a xab derived from natural samples is sensitive to bulk composition inasmuch as both plagioclase and amphibole are highly non ideal samples from a single outcrop have values ranging from 0 5 xab 0 74 to 4 1 xab 0 10 the continuous reaction naalsi3o8 ca2mg5si8o22 oh 2 naca2mg5alsi7o22 oh 2 4sio2 proceeds to the right with increasing grade of metamorphism and for a given bulk composition kid increases with increasing temperature two related discontinuous reactions actinolite albite hornblende oligoclase quartz and actinolite oligoclase hornblende anorthite quartz also proceed to the right with increasing metamorphic grade and result in changes in the topology of a phase diagram that describes the partitioning of na between plagioclase and amphibole a site a schreinemakers net is presented that is consistent with natural occurrences the results of this study should aid in the delineation of metamorphic facies within amphibolites

structures textures and cooling histories of columbia river basalt flows flood basalt flows of the columbia river basalt group commonly exhibit well developed colonnade and entablature structures formed during cooling of individual flows the colonnade refers to the well defined columnar structure of many flows which appears in the lowermost 10 to 30 and in places the uppermost 10 to 20 entablature refers to those parts of a flow that have smaller column diameters and more irregular pattern fractures than those of colonnade entablature commonly occupies the central 60 to 70 of a flow in some cases however the entablature is interrupted by colonnade in such cases the entablature and colonnade may be repeated once or twice within a single flow in other cases flows may lack an entablature entirely petrographic examination reveals a pronounced correlation between structural and textural features thin sections of colonnade basalt have relatively coarse cruciform or octahedral fe ti oxide crystals and 20 glassy mesostasis the central entablature basalt in contrast has much more mesostasis as much as 60 and has textural features such as feathery fe ti oxide crystals indicative of more rapid cooling these features are the reverse of what might be expected for normal conductive cooling because cooling rates at the flow margins should be greater than those in the flow interior we reconciled the observed basalt textures with thermal models by taking into account rainfall and deranged drainage during crystallization of the flow downward migration of water through cracks would cause convective cooling of underlying unsolidified lava this effect and its consequences have been modeled numerically in order to clarify the physical constraints on the mechanism by which the central part of the lava can be quenched we have found that a water infiltration front can explain the presence of a thick quenched flow interior provided that the infiltration front moves downward just behind the lava solidification front despite heavy rainfall on hawaii for example 250 cm yr at kilauea iki exposed prehistoric lava flows on that island exhibit only colonnades we deduce from this that heavy rainfall alone is inadequate to quench flow interiors extensive flooding by deranged drainage or perhaps extremely heavy rainfall 250 cm yr is apparently required to produce entablatures the model also can be used to explain the occurrence of repeated entablature and colonnade by considering the effects of intermittent inundation the imposition of boundary conditions that mimic the removal and reoccurrence of flooding yields cooling histories that are consistent with the development of multiple colonnades and entablatures

the tectonic architecture of wrinkle ridges on mars abstract the geodynamic history of mars is written largely in the form of its tectonic structures a global population of compressional structures records a history of interior cooling and contraction in combination with volcanic loading and flexure of the lithosphere the most common of these structures are wrinkle ridges interpreted as having formed by folding of near surface layered volcanic materials above blind thrust faults topographic profiles of wrinkle ridges are found to dominantly fall into three classes symmetric ridges arch style ridges characterized by broad convex upward backlimbs and double ridges characterized by a broad arch and narrow ridge a monte carlo boundary element model was used to constrain the underlying geometry of faults associated with the different ridge types symmetric ridges are pop up structures formed between quasi symmetric thrust and backthrust faults in some cases above a horizontal decollement or low angle fault at depth arch style ridges formed above a dominant primary thrust fault of near constant dip with a secondary backthrust playing a lesser role in generating subtle inflections in the backlimb double ridges require two backthrust faults to localize strain within the narrow ridge at the ridge crest and to generate the secondary antiform on the backlimb in these ridges both the upper primary thrust and backthrust are contained within the layered volcanic materials while the lower portions of the primary thrust can extend deep into the crust or upper mantle a shallower depth of fault penetration in areas of thicker crust is consistent with the depth of faulting being limited by the brittle ductile transition dips vary widely but are typically steep in the upper faults and quite gentle in the lower faults thus while wrinkle ridges do provide important records of tectonic and geodynamic processes on mars as well as other bodies the associated tectonic structures are more complex and varied than previously considered

metamorphic evolution of the eiksunddal eclogite complex western norway and some tectonic implications the metamorphic evolution of the western gneiss region of norway wgr can be evaluated from examination of eclogites formed as an integral part of the gneiss terrain ie in situ petrologic data from one of the larger country rock eclogites within the northwestern part of wgr have been used to construct a p t t path for this crustal volume textural relations as well as mineral composition and zonation suggest an early period of amphibolite facies conditions followed by movement along a very steep positive p t gradient towards very high pressure p 25 kb and moderate temperature t 600 c orthopyroxene coexisting with garnet at such conditions was poor in al 0 5 wt al2o3 and is preserved in the cores of orthopyroxene grains in garnet websterites the increasing al content of orthopyroxene towards garnet and increasing edenite substitution rimwards in zoned amphiboles suggest a period of decompression accompanied by heating towards the metamorphic maximum at t 750 c p 20kb garnet zoning reflects a general prograde history but the reactions that control the zoning are insensitive to pressure changes jadeitic pyroxenes may have formed in the gneisses at p max but would revert to plagioclase subsequent to the metamorphic maximum giving rise to the observed mineralogy further decompression and cooling continued towards high rank amphibolite facies conditions this p t t path reflects crustal thickening to 80 90 km during caledonian time the uplift path is qualitatively similar to theoretically derived paths in which uplift is assumed to be controlled by erosion however uplift following the metamorphic maximum may have been accelerated by a period of suture progradation

electromagnetic sounding in the columbia basin yakima washington a controlled source electromagnetic csem survey was conducted near yakima washington to map the thickness and resistivity of a thick volcanic sequence overlying a sedimentary section and to infer structure in the sediments the survey was conducted with a frequency domain system employing loop transmitters 400 500 m on a side and three component squid magnetometer receivers separated from the loop by 1 to 5 km data collected along a 30 km profile orthogonal to regional strike were interpreted initially with 1 d layered models which were then pieced together to make a geoelectric section induction logs in a 5000 m exploration hole at one end of the profile agree very well with the csem soundings made around the hole the geoelectric section reveals a smoothly varying thickness of volcanics with a pronounced anticlinal structure approximately concordant with a surface topographic ridge to assess the validity of inferring lateral structure from 1 d interpretations we made scale models of an anticlinal structure and of a surface inhomogeneity and conducted csem measurements over the scale models layered model inversions of these data show that the anticlinal structure and its location are very well determined by 1 d inversion but its height and width are not accurately determined csem sounding over the surface inhomogeneity model shows that this feature does not significantly degrade the interpretation of a deep target layer in this setting a geoelectric section made up from 1 d interpretations provides good qualitative measures of subsurface structure and also provides excellent starting models for detailed 2 d or 3 d modeling

seismic imaging of upper crustal structure using travel times from the passcal ouachita experiment a first arrival travel time inversion applied to the 1986 passcal ouachita experiment has been used to image upper crustal structure twenty one shot points every 10 km were recorded along two 100 km long segments with 400 seismographs on each segment a splined velocity model parameterization allowed for the inversion of laterally inhomogeneous models but not velocity discontinuities over 800 travel times were used in the inversion with a variable data covariance weighting the multiple source nature of the experiment design allowed the use of reciprocity relationships among 21 shot points to enhance data correlation a succession of models with velocities specified at 30 90 171 and 221 nodes were inverted for whose horizontal node spacing decreased from 100 to 12 5 km in the final 221 node model vertical node spacings of 3 0 and 1 5 km were used the results of the inversions indicate changes in depth of isovelocity lines which are interpreted as triassic fault structure based on nearby well data the final rms travel time residual is 0 045 s resolution using first arrivals deteriorates rapidly below 9 km depth three distinct velocity gradients can be correlated with geologic units surface exposed cretaceous and jurassic sediments with velocities from 3 0 tomore 3 5 km s extend to 1 5 km depth triassic rift fill sediments which do not outcrop have inverted velocities ranging from 3 5 to 4 75 km s between depths of 1 5 3 0 km paleozoic sediments are imaged by a decreased velocity gradient below a depth of 3 0 km lack of resolution at depths greater than 9 km necessitates detailed modeling of wide angle reflected phases to further constrain deeper crustal structure less

elastic dislocation modeling of wrinkle ridges on mars wrinkle ridges are one of the most common landforms on mars although it is generally agreed that they are compressional tectonic features formed by folding and thrust faulting there is no consensus on the number of faults involved the geometry of the faults or the maximum fault depth the topography of martian wrinkle ridges in solis planum and lunae planum has been studied using mola data as determined in previous studies the topography shows that most wrinkle ridges are a composite of two landforms a broad low relief arch and a superimposed ridge constrained by mola topographic profiles the geometry and parameters of the faults associated with wrinkle ridges have been modeled the best fits are obtained with a blind listric thrust fault that flattens into a decollement the listric fault geometry is approximated by a series of linear connecting segments with varying dips the major morphologic elements of wrinkle ridges can be matched by varying the displacement on the different fault segments modeling of large scale wrinkle ridges indicates that the maximum depth of faulting or depth to the decollement is about 4 5 km this may correspond to the depth of the contact between the ridged plains volcanic sequence and the underlying megabreccia the results suggest that wrinkle ridge thrust faults are shallow rooted and reflect thin skinned deformation

the saddle mountains the evolution of an anticline in the yakima fold belt the saddle mountains uplift is an asymmetrical north vergent anticline with a length of about 110 km it varies from an open to tight fold and is divided into six segments based upon differences in geometry flows of the columbia river basalt group intercalated sedimentary deposits of the ellensburg formation and suprabasalt sediments thin over the uplift and thicken into the synclines variations in thickness are used to determine the timing of deformation and age of major and minor structures the close correlation of growth rate of the folds with rate of magma supply of the columbia river basalt group suggests that the yakima fold belt resulted from the same tectonic processes that produced eruption of the columbia river basalt modified journal abstract

are large explosive sources applicable to resource exploration seismologists from government and academia are finding that large chemical explosions are an excellent seismic source not only for profiling the deep crust but also for imaging the shallower geologic targets of interest to the oil and gas industry for the purposes of this article we define a large explosion as one that utilizes at least 100 kg about 220 lbs of ammonium nitrate or equivalent explosive in general shot sizes ranging from this minimum up to 2700 kg about 3 tons are used in deep crustal seismic profiling programs

exploration in the shetland faeroe basin using densely spaced arrays of ocean bottom seismometers recent exploration activity in the peripheral regions of the shetland faeroe basin offshore northwest scotland has led to the discovery of some of the largest oil reserves on the united kingdom uk continental shelf we present results from two ocean bottom seismometer profiles acquired by mobil north sea ltd across the center of the shetland faeroe basin these data provide a powerful tool for delineating long wavelength velocity variations and thus have potential for reducing the nonuniqueness associated with conventional seismic exploration methods analysis of the first arrival traveltime data using both forward and inverse ray based techniques produces a well constrained velocity depth model of the basin fill we estimate that the uncertainty in the velocity structure is 5 from a series of trial and error perturbations applied to the final models the velocity structure of the faeroe basin has three principal layers 1 a near surface layer with velocities in the range 1 6 to 2 2 km s 2 a 3

seismic signature of sub trappean gondwana basin in central india abstract the digitized and trace normalized record sections of original analog deep seismic sounding dss data collected along the multai pulgaon profile have been re interpreted to find basement and intra basement structure in the area between the satpura basin and the pranhita godavari gondwana graben in central india it is found that the data are best satisfied by a model with a low velocity zone in between the deccan traps and the basement the study delineates a basement fault that could be associated with the known gavaligarh salbardi lineament low velocity sediments vp 3 7 km s delineated from the present study could be gondwana sediments which have been reported in surrounding areas this finding indicates the possible extension of gondwana formations of the pranhita godavari graben to the satputra basin through the wardha valley

tomographic imaging of sub basalt mesozoic sediments and shallow basement geometry for hydrocarbon potential below the deccan volcanic province dvp of india summary a shallow 2d tomographic p wave velocity image is obtained in the deccan volcanic province dvp of india using first arrival seismic data along a 90 km long n s trending profile in the deccan syneclise region the tomographic image depicts smooth velocity variations of quaternary 2 0 2 5 km s sediments basalt 5 0 5 5 km s and sub basalt mesozoic sediments 4 0 4 5 km s as well as basement 5 8 6 0 km s configuration down to a maximum depth of 5 0 km due to late cretaceous volcanism with outpouring of basaltic lava flows this region is affected by numerous dyke intrusions and thick basaltic trap forming sills with the presence of horst and graben structures due to deep basinal faults although imaging below the basalt is a major challenge for the oil industry with the help of tomographic imaging technique of long offset seismic refraction data we are able to image sporadic sub and intra trappean mesozoic sediments 0 75 km deposited below thick columns 0 3 km of basalt flows above the basement the imaged mesozoic sediments are expected to contain hydrocarbon due to their wide extension and suitable trapping mechanism of basaltic sills the robustness of the velocity image is assessed through numerous tests like velocity perturbations 2 estimates rms residuals of traveltime fit resolution and uncertainty estimates through computation of ray density or hits

mapping the sub trappean mesozoic sediments in the western part of narmada tapti region of deccan volcanic province india abstract deccan traps spread over large parts of south west and central india possibly hiding underneath sediments with hydrocarbon potential here we present the results of seismic refraction and wide angle reflection experiments along three profiles and analyze them together the results from all other refraction profiles executed earlier in the western part of narmada tapti region of the deccan volcanic province dvp we employ travel time modelling to derive the granitic basement configuration including the overlying trap and sub trappean sediment thickness if any travel time skips and amplitude decay in the first arrival refraction data are indicative of the presence of low velocity sediments mesozoic which are the low velocity zones lvz underneath the traps reflection data from the top of lvz and basement along with the basement refraction data have been used to derive the mesozoic sediment thickness in the middle and eastern parts of the study region between narmada and tapti the mesozoic sediment thickness varies between 0 5 and 2 0 km and reaches more than 2 5 km south of sendhwa between narmada and tapti rivers thick mesozoic sediments in the eastern parts are also accompanied by thick traps the mesozoic sediments along the present three profiles may not be much prospective in terms of its thickness except inside the cambay basin where the subtrappean sediment thickness is about 1000 1500 m in the eastern part of the study area the deepest section 4 km has thick 2 km mesozoic sediments but with almost equally thick deccan trap cover results of the present study provide important inputs for future planning for hydrocarbon exploration in this region

coal seismic surveying over near surface basalts experience from central queensland australia abstractseismic reflection surveying in basalt covered areas often fails to image underlying reflectors to gain insights into the nature of the problem and obtain potential solutions we have conducted experimental 2d seismic reflection and offset vsp surveys at two coal mines in the bowen basin of australia at the first mine the basalt is relatively deep 114 m and relatively thin 20 m conventional seismic acquisition and processing of a 2d seismic line provide poor results however upgoing reflections from layers below the basalt are clearly evident in the vsp survey and prestack depth migration is able to improve the continuity of the reflectors beneath the basalt at the second mine the 360 m wide basalt is at a depth of 40 m and has a thickness of about 40 m it is fresh and unweathered and consists of multiple flows which are interlayered with unconsolidated sediments long offset data acquisition combined with prestack depth migration was expected to produce satisfactory results but this i