seismic tomography of the colorado rocky mountains upper mantle from crest lithosphere asthenosphere interactions and mantle support of topography abstract the crest experiment colorado rocky mountains experiment and seismic transects integrated the earthscope usarray transportable array with portable and permanent stations to provide detailed seismic imaging of crust and mantle properties beneath the highest topography region of the rocky mountains inverting approximately 14 600 p and 3600 s wave arrival times recorded at 160 stations for upper mantle v p and v s structure we find that large v p perturbations relative to ak135 of 7 and v s variations of 8 take place over very short approaching tens of kilometers lateral distances highest heterogeneity is observed in the upper 300 km of the mantle but well resolved low velocity features extend to the top of the transition zone in portions of these images the previously noted low velocity upper mantle aspen anomaly is resolved into multiple features the lowest v p and v s velocities in the region are found beneath the san juan mountains which is clearly distinguished from other low velocity features of the northern rio grande rift taos latir region aspen region and below the never summer mountains we suggest that the san juan anomaly and a similar feature below the taos latir region of northern new mexico are related to delamination and remnant heat and melt beneath these sites of extraordinarily voluminous middle cenozoic volcanism we interpret a northeast southwest grain in velocity structure that parallels the colorado mineral belt to depths near 150 km as being reflective of control by uppermost mantle proterozoic accretionary lithospheric architecture further to the north and west the wyoming province and northern colorado plateau show high velocity features indicative of thick 150 km preserved archean and proterozoic lithosphere respectively overall we interpret the highly heterogeneous uppermost mantle velocity structure beneath the southern rocky mountains as reflecting interfingered chemical proterozoic lithosphere that has been is currently being replaced and modified by upwelling asthenosphere low velocity features resolved here indicate that this process may be sourced as deeply as the top of the mantle transition zone at 410 km one driving mechanism for this is upper mantle interaction between upwelling hydration induced partial melt and destabilized downwelling lithosphere in the deeper upper mantle tomographic imaging of mantle seismic velocity and crustal thickness results and modeling from the crest experiment indicate that the highest elevations of the colorado rocky mountains are substantially supported by the mantle and strong correlations between low velocity mantle and thin crust high topography are noted across the region this along with rich upper mantle seismic heterogeneity suggests that mantle buoyancy and dynamics are central to present day topographic support and recent geomorphic evolution of the region

salinity trends in the wheatbelt of western australia results of water and salt balance studies from cuballing catchment abstract a study of water and salt balances within a first order catchment in the western australian wheatbelt has shown that the salt load in the main surface drainage comes largely from groundwater discharging upstream from the basement highs and dykes that extend across the surface drainage and conductive channels within the regolith although salt fall from rainfall is about 2 0 g m 2 year 1 cl the stream load ranges from 180 to 850 g m 2 year 1 with an out input ratio of 100 425 salt storage in the catchment varies from 900 4000 g m 2 in the top 3 m to 27 000 71 000 g m 2 in the 3 15 m depth range and 5000 21 000 g m 2 below 15 m groundwater discharge calculated using br and cl as tracers for the groundwater component fluctuates between 20 and 40 of streamflow stream salinity during the last 3 years was below the long term average this is attributed to a reduction in groundwater discharge caused by low rainfall during this period the downward displacement and leaching of salt stored in the regolith indicates that if groundwater levels continue to rise the quantity and salinity of groundwater discharge will continue to increase causing further rises in stream salinity

comparative study of methods of preparing hydraulic head surfaces and the introduction of automated hydrogeological gis techniques abstract construction of hydraulic head surface hhs maps is the most commonly used technique for groundwater evaluation a review of methods used for constructing hhs maps showed that of the manual methods the hydrogeological interpretative technique produces a better surface than the equally spaced approach geostatistical methods gave similar surfaces to the manual methods they share the problem of groundwater contours intersecting surface contours and the inability to identify groundwater discharge areas the results showed that the automated hydrogeological gis geographical information system techniques which take into account the hydrogeomorphic and topographic controls produced the most realistic surfaces groundwater contours follow the hydrogeomorphic trends do not intersect surface contours and can properly identify areas of groundwater discharge the major advantage of the hydrogeological gis technique is the ability to prepare hhs maps with a small number of data points it is also possible to use regressions from other catchments to prepare hhs maps for catchments with similar hydrogeomorphic characteristics and elevation ranges but which have no data

quantitative estimate of fracture density variations in the nordegg with azimuthal avo and curvature a case study we investigated the accuracy of surface seismic attributes in predicting fracture density variations within the nordegg formation in west central alberta we know from core drill samples well log and drilling data that the nordegg zone is fractured to some degree these fractures are of interest because the reservoir has very low permeability and therefore natural fractures may materially affect well performance 3d surface seismic techniques such as amplitude variation with azimuth or azimuthal avo avaz variation of velocity with azimuth vvaz curvature and coherence techniques are all tools that have been used to predict fractures in a qualitative fashion in this study we wanted to understand how well these attributes predicted the reservoir quality in a quantitative fashion previous quantitative studies have used image log orientation data or estimated ultimate recoveries eur in vertical wells as validation data the conclusiveness of these studies has been subject to several problems f

characterization of a fractured granitic pluton p and s waves seismic tomography and uncertainty analysis abstract a detailed characterization of the physical properties of a granitic pluton including a three dimensional reconstruction of the fractures network and its surrounding are obtained by high resolution seismic tomography of p and s waves the input p and s wave travel times were picked from three component offset and azimuth variable seismic profile ovsp acquired in a 500 m deep vertical borehole the travel time inversion resulted in two three dimensional p and s wave velocity models and the uncertainty robustness and sensitivity are estimated by performing a monte carlo type analysis and checkerboard test this study provides an indicator of the uniqueness of the determined model the 500 m deep borehole was continuously cored and extensively surveyed by geophysical techniques thus the detailed surface geological mapping fracture index logs borehole televiewer images and p and s wave velocities derived from sonic logs provide solid constraints for the interpretation of the tomographic images the three dimensional tomographic images reveal fracture zones mapped at surface that intersect the borehole at different depths and they can be identified in the core descriptions and in the borehole televiewer images the fractures identified on the cores feature relatively low values for the sonic p and s wave velocities and high values for poisson s ratio for single type lithologies the distribution of poisson s ratio differentiates fractured and altered granite from fresh unfractured domains within the rock poisson s ratios close to 0 3 correlate with fractured volumes consistent with fracture index and sonic logs otherwise poisson s ratio values close to 0 25 are related to unaltered and unfractured rock

seismic structure of the central us crust and shallow upper mantle uniqueness of the reelfoot rift abstract using seismic surface waves recorded with earthscope s transportable array we apply surface wave imaging to determine 3d seismic velocity in the crust and uppermost mantle our images span several proterozoic and early cambrian rift zones mid continent rift rough creek graben rome trough birmingham trough southern oklahoma aulacogen and reelfoot rift while ancient rifts are generally associated with low crustal velocity because of the presence of thick sedimentary sequences the reelfoot rift is unique in its association with low mantle seismic velocity its mantle low velocity zone lvz is exceptionally pronounced and extends down to at least 200 km depth this lvz is of variable width being relatively narrow 50 km wide within the northern reelfoot rift which hosts the new madrid seismic zone nmsz we hypothesize that this mantle volume is weaker than its surroundings and that the reelfoot rift consequently has relatively low elastic plate thickness which would tend to concentrate tectonic stress within this zone no other intraplate ancient rift zone is known to be associated with such a deep mantle low velocity anomaly which suggests that the nmsz is more susceptible to external stress perturbations than other ancient rift zones

upper mantle surprises derived from the recent virginia earthquake waveform data recent high resolution regional waveform modeling reveals that the lithosphere beneath the north american craton is subdivided into an upper nearly uniform layer and a lower layer with a high velocity gradient the boundary occurs at about a depth of 115 km and is responsible for 8 discontinuity in seismic record sections that is often observed in craton environments unexpectedly we find seismic velocities in the lower layer significantly reduced along a corridor from the new madrid rift zone to virginia this reduced velocity in the lower lithosphere may be associated with a possible historic hotspot activity we also find a well developed x discontinuity that we model as a 3 increase in p velocity starting at a depth of 290 km these anomalous features transition into a nearly 1d craton structure to the north with a strong low velocity anomaly just above the 410 discontinuity along an east west boundary the latter two features may be relics of structures formed from the descending farallon plate between late cretaceous and early tertiary

seismic vp vs tomography of texas oklahoma with a focus on the gulf coast margin abstract the northwestern gulf of mexico passive margin contains an extensive record of continental collision and rifting as well as deformation associated with orogenic events and heavy sedimentation seismic traveltime tomography that incorporates new data from 328 broadband seismic stations deployed throughout the region reveals features that correlate well with expected mantle structures as well as features that have no obvious expression at the surface among the former are a large fast anomaly that corresponds to the southern extent of the laurentia craton and a large slow anomaly associated with the southern oklahoma aulacogen among the latter are a slow layer that we interpret to be a shear zone at the base of the cratonic and transitional continental lithosphere a zone that is bounded at its top and bottom by discontinuities and high levels of seismic anisotropy identified in companion receiver function and shear wave splitting studies respectively a high velocity body underlying the gulf coastal plain may mark delaminating lower crust if this is true it could provide indirect evidence for an elevated geotherm during the rifting process that created the gulf of mexico

estimating basin thickness using a high density passive source geophone array abstract in 2010 an array of 834 single component geophones was deployed across the bighorn mountain range in northern wyoming as part of the bighorn arch seismic experiment base the goal of this deployment was to test the capabilities of these instruments as recorders of passive source observations in addition to active source observations for which they are typically used the results are quite promising having recorded 47 regional and teleseismic earthquakes over a two week deployment these events ranged from magnitude 4 1 to 7 0 m b and occurred at distances up to 10 because these instruments were deployed at ca 1000 m spacing we were able to resolve the geometries of two major basins from the residuals of several well recorded teleseisms the residuals of these arrivals converted to basinal thickness show a distinct westward thickening in the bighorn basin that agrees with industry derived basement depth information our estimates of thickness in the powder river basin do not match industry estimates in certain areas likely due to localized high velocity features that are not included in our models thus with a few cautions it is clear that high density single component passive arrays can provide valuable constraints on basinal geometries and could be especially useful where basinal geometry is poorly known

predictive modelling of management options for the control of dryland salinity in a first order catchment in the wheatbelt of western australia abstract a prototype flow model has been developed for cuballing catchment using modflow the results of the simulations showed that in a first order catchment the management strategies most likely to arrest salinity were reforestation and pumping the study confirmed that complete reforestation would arrest groundwater discharge and lead to the restoration of salinized land within the catchment it also showed that replanting the top 25 of the catchment was sufficient to reverse the salinity trend by reducing groundwater discharge to an acceptable level drainage along the main stream line was also effective in reducing groundwater levels in the unconfined aquifer and constrained the discharge in the area adjacent to the stream the simulations also showed that pumping reduced groundwater pressures in both the unconfined and confined aquifers a single windmill discharging at a rate ranging from 15 to 25 m 3 day 1 was sufficient to reduce water levels in the unconfined aquifer by more than 5 m and in the confined aquifer by more than 10 m however the pumping well must be correctly located in the catchment the preferred location is in highly transmissive areas with adequate aquifer thickness and upstream from geological structures restricting groundwater flow in western australia these areas are usually along drainage lines and within discharge areas

electrical structure of the central cascadia subduction zone the emslab lincoln line revisited abstract the emslab experiment was an ambitious onshore offshore magnetotelluric mt transect of the cascadia subduction zone when completed 1985 1988 it was the largest experiment of its kind modeling and inversion capabilities at the time were however not sufficiently sophisticated to handle a fully regularized inversion of the data including the seafloor data and bathymetric constraints with the main final model presented based on trial and error forward modeling of the responses moreover new data collected as part of the earthscope usarray program are of higher quality due to improvements in instrument technology and augment the original emslab data set presenting an opportunity to revisit the structure in this part of the subduction system we have integrated the original wide band mt data as well as several long period stations from the original emslab data set and invert these in conjunction with emslab seafloor responses and new earthscope data on land this new composite data set has been analyzed in several ways within a two dimensional geometry in which conductivity is assumed to be invariant along a strike direction roughly coincident with that of the subduction zone we have solved for fully smooth regularized models as well as solutions that allow discontinuities in conductivity along the top surface of the descending slab finally we have tested specific features in the emslab model notably a moderately shallow 30 km depth forearc conductor a feature similar to this shallow conductor is a consistent and required feature in our new inversion models but the new models highlight the connection between the slab and what is interpreted to be an accumulation of aqueous fluids in the deep crust the depth 40 km at which the conductor intersects the slab suggests that the fluids are released by the transition of hydrous basalt to eclogite at upper greenschist facies and higher metamorphic grade the nose of the mantle wedge has a conductivity consistent with a dry peridotite composition and thermal models of the system at a depth of around 80 km the mantle intersecting the slab shows a slight increase in conductivity this increase is not sufficient to require the presence of melt but a conductor indicative of melt can be inserted into the model at this depth without compromising the fit

short period surface wave phase velocities across the conterminous united states abstract surface wave phase velocity maps for the full footprint of the usarray transportable array ta across the conterminous united states are developed and tested three component long period continuous seismograms recorded on more than 1800 seismometers most of which were deployed for 18 months or longer are processed using a noise cross correlation technique to derive inter station love and rayleigh dispersion curves at periods between 5 and 40 s the phase velocity measurements are quality controlled using an automated algorithm and then used in inversions for love and rayleigh phase velocity models at discrete periods on a 0 25 by 0 25 pixel grid the robustness of the results is examined using comparisons of maps derived from subsets of the data a winter summer division of the cross correlation data results in small model differences indicating relatively minor sensitivity of the results to seasonal variations in the distribution of noise sources division of the dispersion data based on inter station azimuth does not result in geographically coherent model differences suggesting that azimuthal anisotropy at the regional scale is weak compared with variations in isotropic velocities and does not substantially influence the results for isotropic velocities the phase velocity maps and dispersion measurements are documented and made available as data products of the 10 year long usarray ta deployment

a sharp cratonic lithosphere asthenosphere boundary beneath the american midwest and its relation to mantle flow abstract beneath the american midwest s to p sp converted wave imaging and multi mode surface wave tomography identify a north trending transition in seismic structure at 150 250 km depth to the east of this american midwest transition amt the lithosphere asthenosphere boundary lab is imaged as a 1 2 sp sv amplitude arrival at 200 240 km depth consistent with the depth of negative shear velocity and azimuthal anisotropy gradients imaged by surface wave tomography to the west of the amt sp conversions are much shallower at 150 190 km depth and are much weaker 0 7 or absent azimuthal anisotropy constrained by surface wave tomography also changes across the amt with stronger anisotropy to the east of the transition beneath the thicker lithospheric root we suggest that the seismic changes across the amt can be explained by considering the effects of asthenospheric flow beneath the leading edge of the thick lithospheric root the mantle flow is dominantly driven by the drift of the north america plate locally higher flow velocities are expected where the asthenosphere is forced to flow beneath the thicker root this mantle underflow could create a sharper seismic lab east of the amt via two effects first the local increase in flow velocities could steepen the thermal gradient at the base of the lithosphere and hence the isotropic velocity contrast second the increased strain rate along edge of the lithosphere could enhance the magnitude of azimuthal anisotropy our results suggest that seismically detectable lab sharpness variations could be used to constrain geographic variations in coupling between plates and mantle convection a secondary result is the image of a mid lithospheric discontinuity arrival at 80 110 km depth that is found primarily to the east of the amt this arrival is interpreted as produced by a layer of low velocity metasomatic minerals that have accumulated since the 1 8 ga creation of the lithosphere

a novel technique for modeling fracture intensity a case study from the pinedale anticline in wyoming fracture intensity indicators from well data are highly uncertain when applied or extrapolated to the whole field statistical techniques offer some useful tools for dealing with such problems in reservoir modeling the recent research and development of effort focuses strongly on the development of hybrid techniques that aim at overcoming the inherent assumptions and limitations of individual techniques and taking into consideration uncertain data for estimating error bars or confidence bounds on the calculated outputs this paper presents a recently developed hybrid technique based on soft computing methods and shows how this technique can be used to improve the workflow of fracture characterization and sweet spots identification it uses a set of rock matrix properties and a fracture related seismic attribute to simulate a three dimensional fracture intensity model at the pinedale anticline in wyoming the estimated fracture intensity results agree very well with the data at four virtual wells it also shows that use of the fracture intensity estimations together with their error bars is a valuable tool for the identification of potential sweet spots with reduced risks

correlation between p wave avoa and s wave traveltime anisotropy in a naturally fractured gas reservoir a reservoir characterization study of upper green river gas reservoirs in the bluebell altamont field in the uinta basin utah was completed in august 1995 for the u s department of energy the study included acquisition of two crossing 2 d 9 c seismic lines 9 c vsp and evaluation of the p wave and s wave seismic responses to the fractured reservoirs lynn et al tle august 1995 reported p wave amplitude variations with offset and azimuth avoa at seismic reflectors associated with fractured upper green river gas reservoirs in this field and supporting observations of shear wave birefringence in multicomponent vsps and surface reflection seismic this paper documents the proportional relationship observed between the difference in the p wave avo gradients with azimuth and the magnitude of the s wave birefringence estimated from the two multicomponent reflection seismic lines evaluated at the line intersection

basin geomorphological controls on the mechanism of recharge and discharge and its effect on salt storage and mobilization comparative study using geophysical surveys abstract downhole electromagnetic em profiles have been used to study the salt distribution in four catchments in the wheatbelt of western australia the good correlation r 2 0 7 0 9 obtained by relating the apparent conductivity profiles measured by the downhole em with salt profiles from soil cores enabled estimation of the salt storage in the uncored wells the salt distribution was compared with ground conductivity surveys using em31 and em34 instruments in three catchments and with an input aerial electromagnetic survey aem in a fourth catchment the study revealed the presence of five types of apparent electrical conductivity profiles eca which are correlated with the basin geomorphological units the conductivity profiles are 1 low eca recharge profile 2 subsurface peak discharge profile 3 two bulge profiles a single bulge accumulation weathering profile and a split aquifer development profile 4 reduced bulge leaching profile 5 high eca irregular palaeochannel profile the salt distribution showed a systematic increase in salinity from the watersheds to the valleys with salinity increasing upstream of geological structures the salt distribution was found to be controlled by the geomorphologic properties of the basins which control the hydrological and hydrogeological processes and by the recharge discharge mechanisms which influence salt mobilization and accumulation

mantle flow and lithosphere asthenosphere coupling beneath the southwestern edge of the north american craton constraints from shear wave splitting measurements abstract high quality broadband seismic data recorded by the usarray and other stations in the southwestern united states provide a unique opportunity to test different models of anisotropy forming mechanisms in the vicinity of a cratonic margin systematic spatial variations of anisotropic characteristics are revealed by 3027 pairs of splitting parameters measured at 547 broadband seismic stations the western and southern edges of the north american craton show edge parallel fast directions with larger than normal splitting times and the continental interior is characterized by smaller splitting times and spatially consistent fast directions that are mostly parallel to the absolute plate motion direction of north america at the majority of the stations no significant systematic azimuthal variations of the splitting parameters are observed suggesting that a single layer of anisotropy with a horizontal axis of symmetry can adequately explain most of the observations the spatial coherency of the splitting parameters indicates that the observed anisotropy is likely caused by shearing between the partially coupled lithosphere and asthenosphere based on previous results of seismic tomography and geodynamic modeling we propose a model involving deflecting of asthenospheric flow by the cratonic root as the cause of the observed edge parallel fast directions and large splitting times along the western and southern edges of the north american craton

distinct compositional thin layers at mid mantle depths beneath northeast china revealed by the usarray abstract we observe a clear seismic arrival at 35 45 s after the direct p wave in usarray recordings of two deep earthquakes occurring beneath northeast china velocity spectrum and beam forming analyses reveal that this arrival has a lower slowness value than the direct p wave and a back azimuth slightly different from the great circle direction the measured slowness and arrival time indicate that it is a transmitted s to p conversion from structures below the sources we employ the common conversion point ccp stacking and diffraction migration methods to determine the location and geometric features of the seismic structures the ccp stacking image indicates that the structure is a localized discontinuity at 1000 km with a dimension at 200 km by 50 km along the e w and n s directions respectively it is located at 150 km northeast to the two events the 2d migrated images on the other hand indicate that the sources structure are reflectors dipping northeastwards by 17 at a slightly shallower depths the reflectors have a length scale of 100 km ant their centers are 50 km away from the epicenters of the two earthquakes forward waveform modeling suggests that the dipping reflectors may be thin layers with a thickness of few kilometers the layers have a lower shear velocity and a higher density than that of the surrounding mantle which matches well with those predicted for mid ocean ridge basalt morb at mid mantle depths according to a recent ab initio study combined with the results from previous studies our observations here suggest that the former oceanic crust may be ubiquitously present in the lower mantle beneath subduction zones

infrasound detection of the chelyabinsk meteor at the usarray abstract on february 15 2013 a small asteroid entered earth s atmosphere near chelyabinsk russia this extremely rare event was recorded by the 400 station usarray deployed in the continental united states and alaska these stations recorded infrasound signals from the event at distances from 6000 to 10 000 km across a sector spanning 55 that encompassed the north pole this dense extensive network permitted a detailed study of long range infrasound propagation and source characteristics we observe long wavetrains at all stations ranging to over 100 min but clear variations in the character of the wavetrains across the network ray tracing through a spatially and temporally varying atmospheric model indicates the source excited resonance in the thermospheric duct to all stations resonance was also excited in a persistent stratospheric duct between the source and stations in alaska and along the west coast of the united states due to favorable winds at those azimuths leading to higher group velocities and frequency content at these stations than those to the east an attenuation formula derived from parabolic equation simulations is used to estimate infrasound transmission losses at all stations using simplified models of the effective sound speed along each source receiver path observed variations in signal energies from higher than expected at stations in the thermospheric duct in the eastern united states to lower than expected in alaska at azimuths nearly orthogonal to the asteroid s mach cone lead us to conclude that 1 the source was dominantly isotropic and 2 the model overestimates attenuation in the thermospheric duct

detection of gravity waves across the usarray a case study abstract barometers deployed as part of the usarray transportable array ta recorded large 300 pa peak to peak gravity waves or gust fronts that originated near a severe tornadic storm system in the southern united states on april 27 2011 we present a new method in which the ta is divided into a large number of elemental sub arrays each 3 element sub array triad is sufficiently closely spaced so that the long period gravity wave signal is coherent but large enough to provide a robust estimate of the signal s direction and speed the results from each triad are combined to follow the progress of gravity waves as they propagate across the ta over 2 days in late april 2011 we observe a large high amplitude gravity wave spanning a region over 200 000 km2 progressing to the nnw away from the tornadic storm region we also observe gravity waves with lower amplitudes and smaller spatial extent along the gulf coast propagating southward away from the storm region this study demonstrates the functionality of the usarray pressure sensors for analyzing gravity wave dynamics over periods greater than 40 min and across a wide region in principle the method could be applied to study other long period wave phenomena recorded by any dense large scale network and is not limited to gravity waves

sp receiver function imaging of a passive margin transect across texas s gulf coastal plain abstract the gulf coast of texas has been the subject of intensive geological and geophysical investigation in pursuit of hydrocarbons but studies that penetrate beyond the upper crust are limited to a few refraction profiles and regional surface wave investigations the passing of earthscope s transportable array has facilitated regional investigations of the lithosphere but its 70 km station spacing does not allow many important tectonic features to be imaged a broadband seismic transect across the texas gulf coastal plain was therefore performed in order to image deep structure beneath this passive margin and the transition to the neighboring craton a 2d sp receiver function common conversion point ccp stacked image produced for this transect reveals several discontinuities in the sub crustal lithosphere the region nearest the shoreline is underlain by an anomalous 18 km thick low velocity layer that produces a strong negative pulse in the sp receiver functions the drop in velocity is too large to be due to any reasonable change in fe or mg content but could be produced by partial melt or mantle hydration it is unlikely that partial melt would still be found in a 160 180 year old passive margin such as the gulf coast but hydration possibly introduced by a through going balcones fault system and resulting serpentinization could produce the observed anomaly an event with negative polarity appears at a depth of 110 km which we interpret to be the lithosphere asthenosphere boundary lab thermal variations alone would not produce a sufficiently sharp discontinuity to be imaged by sp converted phases recent shear wave splitting studies revealed unusually large delay times in this region along with fast polarization directions that differ from measurements on the laurentian craton large delay times may imply significant flow which could also produce frictional heating due to shearing and partial melt which would steepen the velocity gradients an additional layer is bounded by discontinuities at 145 165 km depth with negative polarity and 185 205 km depth with positive polarity the appearance of these discontinuities suggests that the mantle beneath the lab is more complicated here than elsewhere and that the transition from lithosphere to asthenosphere occurs over a broad 85 100 km thick depth interval

observed and predicted north american teleseismic delay times abstract using a newly developed cross correlation based computer tool we measured absolute delay times of teleseismic p and s waves recorded by about 2000 broadband seismic stations from earthscope s usarray previous passcal arrays and additional permanent networks in north america we estimate contributions to the delays from crustal structure using various prior crustal models and from event side heterogeneity using the delay time distribution itself we then subtract these contributions from our measurements and map the average delay at each station location we analyze these average delay times to investigate the structure of the north american mantle and formation of the north american continent mantle s delay times from stations west of the rocky mountains are 4 2 s larger than delay times from stations within the us portion of stable north america locally s delays at yellowstone are another 4 s larger than those west of rocky mountains decreasingly sharp delay time contrasts occur across the rocky mountains the appalachian mountains and on the southern edge of the north american craton respectively these delay time gradients of various steepness broadly coincide with surface geological boundaries but are offset to either side of these boundaries predictions of teleseismic s delays from twelve three dimensional tomographic mantle s velocity models agree generally with observed delay time patterns but underestimate the delays and advances to varying degrees tomographic models derived from different data than teleseismic arrival times predict similarly valid delays as models derived from teleseismic arrivals while overestimating the smoothness of delay time patterns to varying degrees we further utilize these tomographic models to predict and study the size and distribution of delay contributions from modeled heterogeneity in different depth ranges this study shows that the 80 240 km depth range is the dominant contributor to delay time contrasts and variance this depth range generally corresponds to asthenosphere in the western us and lithosphere in the central and eastern us the average depth to which the observed delays require the central us lithosphere to extend is likely shallower than 240 km and consistent with the seismic bottom of lithosphere imaged in seismic velocity models not derived from teleseismic delay times

orogenic bending around a rigid proterozoic magmatic rift beneath the central appalachian mountains abstract the transition zone between the modern northern and southern appalachian mountains is located in pennsylvania where the structural orientation of the fold and thrust belt changes from north south to east west and the orogeny narrows significantly vintage studies of wide angle reflection and temporary broadband seismic data suggest that the crust beneath the 8 km of foreland basin sequences was thickened and heavily intruded around the margins of and beneath a failed neoproterozoic rift we use receiver function analysis of broadband seismic data recorded by additional and permanent stations along with forward and inverse modeling of bouguer gravity data to constrain the geometry and depth extent of mafic intrusion and underplating in the rift as well as the role of this proterozoic heterogeneity on the location and geometry of the curvature of the appalachian orogen the receiver function analyses suggest that the crust is 47 49 km thick beneath the ancient rift about 5 7 km thicker than the surrounding area inverse models of gravity data indicate that the 300 km long zone of thickened high density crust is bounded on both the nw and se sides by steep contacts its shorter ne and sw margins are also steep contacts interpreted as crustal scale faults forward modeling of the gravity data constrained by the receiver function crustal thickness estimates sparse seismic reflection data and euler deconvolution solutions implies that the proterozoic rift has been heavily intruded as well as thickened by a 7 10 km mafic underplate its margins appear to have been sheared along ne striking fault zones that parallel appalachian thrust sheet transport directions these combined results suggest that the mid and lower crust of the proterozoic rift was enriched with pyroxene which strengthened the crust locally and localized compressional strain along its margins during the north american african collision compressional strain in the pre appalachian crystalline crust to the southwest and northeast of the proterozoic rift may have been more distributed leading to the formation of oblique slip faults orthogonal to the axes of folds and leading to the curvature in the pennsylvania salient additionally the thrust sheets are stacked most thickly in front of the rift suggesting that the rift served as a backstop during collision

a statistical assessment of seismic models of the u s continental crust using bayesian inversion of ambient noise surface wave dispersion data we present a new approach for evaluating existing crustal models using ambient noise datasets and its associated uncertainties we use a transdimensional hierarchical bayesian inversion thbi approach to invert ambient noise surface wave phase dispersion maps for love and rayleigh waves using measurements obtained from ekstrom 2014 spatiospectral analysis show that our results are comparable to a linear least squares inverse approach except at higher harmonic degrees but the procedure has additional advantages 1 it yields an auto adaptive parameterization that follows earth structure without making restricting assumptions on model resolution regularization or damping and data errors 2 it can recover non gaussian phase velocity probability distributions while quantifying and separating the sources of uncertainties in the data measurements and modeling procedure and 3 it enables statistical assessments of different crustal models e g crust1 0 litho1 0 and nacr14 using variable resolution residual and standard deviation maps estimated from the ensemble these assessments show that in the stable old crust of the archean the misfits are statistically negligible requiring no significant update to crustal models from the ambient noise dataset in other regions of the us significant updates to regionalization and crustal structure are expected especially in the shallow sedimentary basins and the tectonically active regions where the differences between model predictions and data are statistically significant

quantifying and predicting naturally fractured reservoir behavior with continuous fracture models this article describes the workflow used in continuous fracture modeling cfm and its successful application to several projects our cfm workflow consists of four basic steps 1 interpreting key seismic horizons and generating prestack and poststack seismic attributes 2 using these attributes along with log and core data to build seismically constrained geocellular models of lithology porosity water saturation etc 3 combining the derived geocellular models with prestack and poststack seismic attributes and additional geomechanical models to derive high resolution three dimensional 3 d fracture models and 4 validating the 3 d fracture models in a dynamic reservoir simulator by testing their ability to match well performance our cfm workflow uses a neural network approach to integrate all of the available static and dynamic data this results in a model that is better able to identify fractured areas and quantify their impact on well and reservoir flow behavior this technique has been successfully applied in numerous sandstone and carbonate reservoirs to both understand reservoir behavior and determine where to drill additional wells three field case studies are used to illustrate the capabilities of the cfm approach

lithospheric expression of geological units in central and eastern north america from full waveform tomography abstract the earthscope ta deployment has provided dense array coverage throughout the continental us and with it the opportunity for high resolution 3d seismic velocity imaging of both lithosphere and asthenosphere in the continent building upon our previous long period waveform tomographic modeling in north america we present a higher resolution 3d isotropic and radially anisotropic shear wave velocity model of the north american lithospheric mantle constructed tomographically using the spectral element method for wavefield computations and waveform data down to 40 s period the new model exhibits pronounced spatial correlation between lateral variations in seismic velocity and anisotropy and major tectonic units as defined from surface geology in the center of the continent the north american craton exhibits uniformly thick lithosphere down to 200 250 km while major tectonic sutures of proterozoic age visible in the surface geology extend down to 100 150 km as relatively narrow zones of distinct radial anisotropy with vsv vsh notably the upper mantle low velocity zone is present everywhere under the craton between 200 and 300 km depth east of the continental rift margin the lithosphere is broken up into a series of large somewhat thinner 150 km high velocity blocks which extend laterally 200 300 km offshore into the atlantic ocean between the craton and these deep rooted blocks we find a prominent narrow band of low velocities that roughly follows the southern and eastern laurentia rift margin and extends into new england we suggest that the lithosphere along this band of low velocities may be thinned due to the combined effects of repeated rifting processes and northward extension of the hotspot related bermuda low velocity channel across the new england region we propose that the deep rooted high velocity blocks east of the laurentia margin represent the proterozoic gondwanian terranes of pan african affinity which were captured during the rodinia formation but left behind after the opening of the atlantic ocean our results suggest that recurring episodes of tectonic events that are well exposed at the surface also leave persistent scars in the continental lithosphere mantle marked by isotropic and radially anisotropic velocity anomalies that reach as deep as 100 150 km

a comparative study of low frequency earthquake templates in northern cascadia abstract using network correlation methods we generate low frequency earthquake templates for a set of 4 composite arrays on vancouver island and washington state that employ data from earthscope transportable and flexible arrays plate boundary observatory polaris and permanent network canadian national seismograph network pacific northwest seismic network sources on the basis of empirical and semi analytical arguments the templates can be viewed as green s function sections corresponding to moment tensor point sources with step function time dependence in displacement low frequency earthquake hypocentres follow the general epicentral distribution of tremor and occur along tightly defined surfaces in depth with washington locations averaging slightly deeper than those on vancouver island we invert template waveforms for moment tensor mechanisms and find that data are well modelled by double couple sources for southern vancouver island with the highest quality templates the majority of mechanisms are consistent with shallow thrusting in the direction of plate motion the three other data sets with lower signal to noise levels show predominantly thrust mechanisms with more variable orientations taken together with other constraints our observations support the hypothesis that low frequency earthquakes manifest shear slip on a relatively thin plate boundary

physical modelling studies of 3 d p wave seismic for fracture detection summary we have carried out two seismic physical experiments to acquire wide azimuth p wave 3d seismic data with a scaled down model 1 10 000 and scaled up frequencies 10 000 1 our aims are to verify the physical basis of using p wave attributes for fracture detection to understand the usage of these attributes and their merits and to investigate the effects of acquisition geometry and structural variations on these attributes the base model consists of a fractured layer sandwiched between two isotropic layers epoxylite inside the fractured layer there is a dome and a fault block for investigating the effects of structural variations the two experiments were carried out using different acquisition geometries the first experiment was conducted to maximize the data quality with an offset depth ratio of only 0 68 to the bottom of the fracture layer for comparison the second experiment was carried out to maximize the anisotropy effects with the offset depth ratio to the bottom of the fracture layer raised to 1 34 for each experiment about 20 km 2 of wide azimuth 3 d data were acquired with a p wave source the physical modelling confirms that the p wave attributes traveltime amplitude and velocity exhibit azimuthal variations diagnostic of fracture induced anisotropy for the first experiment with noise free data the amplitude from the top of the fracture layer yields the best results that agree with the physical model parameters and free of the acquisition footprint the results from other attributes traveltime velocity avo gradient are either contaminated by the structural imprint or by the acquisition footprint due to the lack of offset coverage for the second experiment despite the interferences from multiples and other coherent noise the traveltime attributes yield the best results both the acquisition footprint and the structural imprint are reduced due to the increased offset coverage however the results from the amplitudes are affected by the noise and are less reliable analysis of the two experiments reveals that the offset depth ratio to the target is a key parameter for the success of the p wave techniques smaller offset depth coverage may only be applicable to amplitude attributes with high quality data whilst large offset coverage makes it possible to use traveltime attributes a reliable estimation from traveltime attributes requires an offset depth ratio of 1 0 or more

two year survey of earthquakes and injection production wells in the eagle ford shale texas prior to the mw4 8 20 october 2011 earthquake abstract between november 2009 and september 2011 the earthscope usarray program deployed 25 temporary seismograph stations on a 70 km grid in south central texas between 27 n 31 n and 96 w 101 w this area includes the eagle ford shale for decades this geographic region has produced gas and oil from other strata using conventional methods but recent developments in hydrofracturing technology has allowed extensive development of natural gas resources from within the eagle ford our study surveys small magnitude seismic events and evaluates their correlation with fluid extraction and injection in the eagle ford identifying and locating 62 probable earthquakes including 58 not reported by the u s geological survey the 62 probable earthquakes occur singly or in clusters at 14 foci of these foci two were situated near wells injecting recently increased volumes of water eight were situated near wells extracting recently increased volumes of oil and or water and four were not situated near wells reporting significant injection extraction increases thus in this region while the majority of small earthquakes may be triggered induced by human activity they are more often associated with fluid extraction than with injection we also investigated the m w 4 8 20 october 2011 fashing earthquake the largest historically reported earthquake in south central texas that occurred two weeks after the removal of the temporary usarray stations a field study indicated that the highest intensity mmi vi region was about 10 km south of 2010 2011 foreshock activity and that there were no high volume injection wells within 20 km of the mmi v vi region or the foreshocks however the 20 october 2011 earthquake did coincide with a significant increase in oil water extraction volumes at wells within the mmi v vi region and this was also true for previous earthquakes felt at fashing in 1973 and 1983 in contrast our study found significant increases in injection prior to an mblg3 6 20 july 1991 earthquake near falls city texas thus the eagle ford geographic region with seismic activity associated both with extraction and injection appears to be more complex than the barnett shale of northeast texas where a similar survey found possible correlations only with fluid injection

local amplification of rayleigh waves in the continental united states observed on the usarray abstract we develop a method based on ratios of amplitudes measured at adjacent stations to determine local amplification of surface waves across an array of seismic stations we isolate the effects of local structure from those of the earthquake and propagation by systematic averaging of ratios corresponding to many sources we apply the method to data recorded on the usarray for the years 2006 2011 and determine amplification factors at each station of the array for rayleigh waves at periods between 35 s and 125 s local amplification factors are spatially coherent and display variations of 10 at a period of 125 s and greater variations at shorter periods maps of local amplification exhibit spatial correlation with topography and geologic structures in the western and central united states at long periods the observed amplification factors correlate well with predictions from a regional crust and mantle model of north america at short periods correlations are weaker suggesting that the local amplification factors can be useful for constraining shallow structure better

reprint of two year survey of earthquakes and injection production wells in the eagle ford shale texas prior to the mw4 8 20 october 2011 earthquake abstract between november 2009 and september 2011 the earthscope usarray program deployed 25 temporary seismograph stations on a 70 km grid in south central texas between 27 n 31 n and 96 w 101 w this area includes the eagle ford shale for decades this geographic region has produced gas and oil from other strata using conventional methods but recent developments in hydrofracturing technology has allowed extensive development of natural gas resources from within the eagle ford our study surveys small magnitude seismic events and evaluates their correlation with fluid extraction and injection in the eagle ford identifying and locating 62 probable earthquakes including 58 not reported by the u s geological survey the 62 probable earthquakes occur singly or in clusters at 14 foci of these foci two were situated near wells injecting recently increased volumes of water eight were situated near wells extracting recently increased volumes of oil and or water and four were not situated near wells reporting significant injection extraction increases thus in this region while the majority of small earthquakes may be triggered induced by human activity they are more often associated with fluid extraction than with injection we also investigated the m w 4 8 20 october 2011 fashing earthquake the largest historically reported earthquake in south central texas that occurred two weeks after the removal of the temporary usarray stations a field study indicated that the highest intensity mmi vi region was about 10 km south of 2010 2011 foreshock activity and that there were no high volume injection wells within 20 km of the mmi v vi region or the foreshocks however the 20 october 2011 earthquake did coincide with a significant increase in oil water extraction volumes at wells within the mmi v vi region and this was also true for previous earthquakes felt at fashing in 1973 and 1983 in contrast our study found significant increases in injection prior to an m blg 3 6 20 july 1991 earthquake near falls city texas thus the eagle ford geographic region with seismic activity associated both with extraction and injection appears to be more complex than the barnett shale of northeast texas where a similar survey found possible correlations only with fluid injection

3 d structure of the rio grande rift from 1 d constrained joint inversion of receiver functions and surface wave dispersion the southern terminus of the rio grande rift region has been poorly defined in the geologic record with few seismic studies that provide information on the deeper rift structure in consequence important questions related to tectonic and lithospheric activity of the rio grande rift remain unresolved to address some of these geological questions we collect and analyze seismic data from 147 earthscope transportable array usarray and other seismic stations in the region to develop a 3 d crust and upper mantle velocity model we apply a constrained optimization approach for joint inversion of surface wave and receiver functions using seismic s wave velocities as a model parameter in particular we compute receiver functions stacks based on ray parameter and invert them jointly with collected surface wave group velocity dispersion observations the inversions estimate 1 d seismic s wave velocity profiles to 300 km depth which are then interpolated to a 3 d velocity model using a bayesian kriging scheme our 3 d models show a thin lower velocity crust anomaly along the southeastern rio grande rift a persistent low velocity anomaly underneath the colorado plateau and basin and range province and another one at depth beneath the jemez lineament and the southern rgr

estimation of groundwater recharge in sandy till with two different methods using groundwater level fluctuations abstract two methods for estimation of groundwater recharge both based on groundwater level fluctuations were applied in a moraine area in southeastern sweden the first method utilized a onedimensional soil water model which was tested against observed groundwater levels the boundary conditions were defined by using standard meteorological data and submodels for precipitation snow dynamics interception evapotranspiration and horizontal groundwater outflow the second method directly transformed groundwater level fluctuations to equivalent amounts of water from a constructed recession curve and the specific yield concept conceptually the two methods could be characterized as inflow and response methods respectively a good fit between observed and simulated groundwater levels was obtained by the soil water modelling the results were however shown to be rather insensitive to displacement in the water balance between evapotranspiration and groundwater outflow giving a good fit for a simulated net groundwater recharge ranging between 134 and 197 mm the results from the attempts to use groundwater level fluctuations directly were discouraging compared to the soil water simulations the results were unstable and quite different for different years it was impossible to use a constant specific yield or even different specific yields depending on depth the conclusion was that the possibilities to use groundwater level data for quantitative water balance studies are limited under the studied climatical and hydrogeological conditions the modelling effort clearly demonstrated the need for a better quantitative knowledge on soil properties if water balance information is to be deduced the soil water model though could be a valuable tool studying variations within and between different years as well as processes and single events

love and rayleigh phase velocity maps 5 40 s of the western and central usa from usarray data abstract continuous data recorded on more than 1600 usarray seismic stations operating in the western and central us between 2006 and 2012 are used to map phase velocities of love and rayleigh waves at short periods 5 40 s using a noise correlation technique vertical and transverse records for all station pairs separated by less than 600 km are cross correlated in 4 h long segments and the resulting spectra are stacked for the time period of station operation dispersion curves are determined from the locations of zeros in the real component of the correlation spectra using a method based on that of aki 1957 phase velocity maps expanded on a 0 25 by 0 25 pixel grid are estimated by inversion of the phase velocity measurements comparison with predicted phase velocity maps based on the crustal model crust2 0 combined with the mantle model nd08 shows good agreement at the longer periods strong slow anomalies 25 in the short period maps are geographically correlated with basins and regions of thick sedimentary cover the strength of these anomalies is not well predicted by existing crustal velocity models

lg attenuation in the central and eastern united states as revealed by the earthscope transportable array abstract lg waveforms recorded by earthscope s transportable array ta are used to estimate lg q 0 in the central and eastern united states ceus attenuation is calculated based on lg spectral amplitudes filtered at a narrow band from 0 5 to 1 5 hz two station and reverse two station techniques are used to calculate q 0 values 39 events occurring from 2010 to 2012 and ranging from magnitude 3 to magnitude 6 are used in this study 39 258 and 4 627 interstation q 0 values are determined using the two station and reverse two station techniques respectively the results show northeast trending high q 0 regions low attenuation ranging from eastern new mexico to wisconsin regions of low q 0 high attenuation are seen along the minnesota wisconsin border the gulf coastal plain gcp along the south dakota nebraska border and along the oklahoma texas border a positive correlation between heat flow sediment thickness recent tectonic activity fluids and low q 0 was observed areas with low heat flow thin sediment cover no recent tectonic activity and a lack of fluids were observed to have consistently high q 0 these new models use a greater amount of data attain more coverage than previous studies and better constrain attenuation this increase in detail can improve high frequency ground motion predictions of future large earthquakes for more accurate far field hazard assessment and improve the overall understanding of the structure and assemblage of the ceus

spatial orientation and distribution of reservoir fractures from scattered seismic energy wepresentthedetailsofanewmethodfordeterminingthereflection and scattering characteristics of seismic energy from subsurface fractured formations the method is based upon observations we have made from 3d finite difference modeling of the reflected and scattered seismic energy over discrete systems of vertical fractures regularly spaced discrete vertical fracture corridors impart a coda signature which is a ringing tail of scatteredenergy toanyseismicwaveswhicharetransmittedthrough or reflected off of them this signature varies in amplitude and coherence as a function of several parameters including 1 the difference in angle between the orientation of the fractures and the acquisition direction 2 the fracture spacing 3 the wavelength of the illuminating seismic energy and 4 the compliance or stiffness of the fractures this coda energy is most coherent when the acquisition direction is parallel to the strike of thefractures ithasthelargestamplitudewhentheseismicwavelengths are tuned to the fracture spacing and when the fractures have low stiffness our method uses surface seismic reflection tracestoderiveatransferfunctionthatquantifiesthechangeinan apparent source wavelet before and after propagating through a fracturedinterval thetransferfunctionforanintervalwithnoor low amounts of scattering will be more spikelike and temporally compact the transfer function for an interval with high scattering will ring and be less temporally compact when a 3d survey is acquired with a full range of azimuths the variation in the derived transfer functions allows us to identify subsurface areas with high fracturing and to determine the strike of those fractures wecalibratedthemethodwithmodeldataandthenapplied ittotheemiliofieldwithafracturedreservoir themethodyielded results which agree with known field measurements and previously published fracture orientations derived from ps anisotropy

shear velocity structure and mineralogy of the transition zone beneath the east pacific rise abstract models of seismic velocity as a function of depth through the upper mantle provide some of the strongest constraints on the mineralogy and composition of the mantle although receiver function studies have provided new information on the depths of upper mantle discontinuities they do not provide as much information on seismic gradients between discontinuities and absolute velocities within the upper mantle the waveforms and travel times of upper mantle turning waves provide the strongest constraints on vertical variations in upper mantle velocity although in the past they suffered from the lack of dense profiles of data sampling a single part of the upper mantle that would minimize effects of 3d variations in velocity here we model three dense profiles of triplicated upper mantle broadband s and ss waves recorded by usarray canadian and nars baja stations located in western north america earthquakes along the east pacific rise were recorded along profiles within 5 back azimuth windows and with stations at a maximum of 0 5 separation the distance range covered is from 35 to 60 and thus the waves sample the mantle from the shallow upper mantle to depths near 1000 km the data were inverted using a conjugate gradient algorithm that utilizes the reflectivity synthetic technique the results show a much smaller gradient within the transition zone than the prem model with larger jumps in velocity across the 410 km and 660 km depth discontinuities these results are consistent with velocities predicted for a pyrolite composition mantle transition zone compositional models with lower olivine content such as piclogite are not consistent with our seismic model

an introduction to the special issue of earth and planetary science letters on usarray science abstract the usarray observatory a component of the earthscope science initiative has provided a geophysical dataset that densely samples the continental us with unprecedented scale and resolution the major scientific target of the multidisciplinary earthscope project is an understanding of the structure dynamics and evolution of the north american continent with emphasis on imaging the continental crust and lithosphere as well as illuminating dynamic processes in the deep earth this special issue of earth and planetary science letters presents a collection of papers that leverage data from the usarray observatory to provide fundamental insights into earth s structure and dynamics here we present an overview of the papers in this issue on a range of topics including the nature of crustal and mantle heterogeneity across north america the dynamics of the subcontinental mantle the assembly and preservation of continental interiors and the physics of earthquakes and faulting

arrival angle anomalies across the usarray transportable array abstract we construct composite maps of surface wave arrival angle anomalies using clustered earthquakes and an array method for measuring wave front geometry this results in observations of arrival angles covering the entire footprint of the usarray transportable array during 2006 2010 bands of arrival angle deviations in the propagation direction indicate the presence of heterogeneous velocity structure both inside and outside of the array we compare the observed patterns to arrival angles predicted using two global tomographic models the mantle model s362ani and the surface wave dispersion model gdm52 we use both ray theory based prediction methods and measurements on synthetic data calculated using a spectral element method both models and all prediction methods produce similar mean arrival angles and long wavelength patterns of anomalies which are similar to the observations predicted short wavelength features generally do not agree with the observations the spectral element method produces some complexity that is not obtained using the ray theory based methods this predicted complexity is similar in character to the observed patterns but does not match them

imaging mantle discontinuities using multiply reflected p to s conversions abstract improving the reliability and accuracy in the determination of the depth to velocity discontinuities in the earth s mantle is essential for a better understanding of mantle dynamics as well as for addressing such fundamental questions as the origin of mantle plumes and fate of subducted slabs most existing techniques that utilize receiver function stacking which is perhaps the most commonly used method to image mantle discontinuities suffer from strong trade offs between the depth and velocity anomalies above the discontinuities here we propose and test a procedure that utilizes both the p to s converted phase pds and the multiply reflected and converted phase ppds at the discontinuities to simultaneously determine the depth of mantle discontinuities and velocity anomalies in the overlying layer the procedure includes masking the strong pp arrivals prior to computing receiver functions computing non plane wave travel times for pds and ppds for accurate moveout corrections and utilizing the discrepancies in the apparent discontinuity depths from pds and ppds to simultaneously estimate velocity anomalies and discontinuity depths that are independent of velocity anomalies application of the procedure to data recorded by stations in seven radius 1 5 circles along a 780 km n s profile centered at the yellowstone hotspot reveals lower than normal upper mantle and mtz velocities beneath yellowstone a positive temperature anomaly of 40 190 c in the vicinity of the 410 km discontinuity d410 and a lower than normal temperature in the vicinity of the 660 km discontinuity d660 the perceived hotspot is not associated with a localized depression of the d410 or an uplift of the d660 suggesting that the proposed mantle plume does not traverse the mtz beneath the profile

contrasting lithospheric signatures across the western united states revealed by sp receiver functions abstract to explore how lithospheric structure varies between tectonic and magmatic terranes of the western united states we use observations of shear to compressional wave conversions across lithospheric velocity interfaces with a newly developed automatic method designed to take advantage of the earthscope transportable array and other broadband seismic arrays deployed across the region and an optimized deconvolution technique based on the extended time multi taper method we map variations in the depth to the seismic moho lithosphere asthenosphere boundary lab and mid lithospheric discontinuities mlds beneath areas that have undergone substantial extension in the neogene including the eastern great basin the southern basin and range and the southern rio grande rift we detect strong sp conversions across a relatively shallow 60 80 km seismically defined lab we detect sp conversions across an 80 90 km depth discontinuity beneath the high rockies which we interpret as the seismically defined lab beneath areas that have remained relatively undeformed including the wyoming craton and the great plains craton we detect sp conversions in the 90 140 km depth range that are substantially weaker and more distributed in depth than those beneath less stable regions beneath the colorado plateau sp ccp stacks show that lithospheric thinning has accompanied magmatic encroachment and the lab beneath the margins of the plateau is indistinguishable from the lab of the surrounding extensional provinces in contrast beneath central and northern colorado plateau weaker sp conversions are observed in the 90 140 km depth range the observed variations in lithospheric structure across structural blocks with different magmatic and deformational histories imply that 1 both mechanical thinning and magmatic and thermal erosion have likely contributed to the thin lithosphere observed in the basin and range and southern rio grande rift 2 at the margins of the colorado plateau and beneath the high rockies where extension has been relatively minor strong and shallow seismic labs indicate magmatic alteration of the lithosphere 3 mlds seen in comparatively thick stable lithosphere produce weaker sp conversions and are often more distributed in depth than seismically observed labs in regions of thin lithosphere 4 mlds and weak deep phases consistent with a seismic lab are sometimes observed together

static and dynamic support of western united states topography article history accepted 7 october 2013 available online 31 october 2013 editor p shearer isostatic and dynamic models of earth s surface topography can provide important insights into the driving processes of tectonic deformation we analyze these two estimates for the tectonically active western united states using refined structural models derived from earthscope usarray for the crust use of recent moho depth measurements and crustal density anomalies inferred from passive source seismology improve isostatic models however seismically determined lithospheric thickness variations from lithosphere asthenosphere boundary lab maps and lithospheric and mantle density anomalies derived from heat flow or uppermost mantle tomography do not improve isostatic models substantially perhaps this is a consequence of compositional heterogeneity a mismatch between thermal and seismological lab and structural complexity caused by smaller scale dynamics the remaining non isostatic dynamic component of topography is large topography anomalies include negative residuals likely due to active subduction of the juan de fuca plate and perhaps remnants of formerly active convergence further south along the margin our finding of broad scale positive residual topography in the basin and range substantiates previous results implying the presence of anomalous buoyancy there which we cannot fully explain the colorado plateau does not appear dynamically anomalous at present except at its edges many of the residual topography features are consistent with predictions from mantle flow computations this suggests a convective origin and important interactions between vigorous upper mantle convection and intraplate deformation

effects of forest clearing on groundwater abstract groundwater systems were studied in five catchments 0 8 3 5 km2 over ten years at the end of the third year forest vegetation was totally or partially cleared in three catchments the cleared areas were sown to pasture or crop in accord with conventional agricultural practice for the region permanent aquifers were encountered within a deeply 30 m weathered regolith derived from igneous basement rocks in the higher rainfall catchment pair aquifer boundaries corresponded reasonably well with the surface divide but permanent aquifers were encountered mainly in lower parts of the three catchments in the medium rainfall areas slug test measurements of hydraulic conductivity k varied by more than a factor 100 within a catchment but there was no significant difference between the geometric mean of k in each catchment which varied between 1 4 and 7 6 mm d 1 in the higher rainfall catchments the potentiometric surface under forest normally responded by 1 4 m after each winter wet season this indicates significant seasonal recharge on the basis of the number of piezometers exhibiting this behaviour seasonal recharge was widespread in this area by contrast the seasonal response of the potentiometric surface was rarely more than 1 m under forest in the medium rainfall catchments and at many sites there was no apparent recharge in several years of this study in areas fully cleared for agriculture the potentiometric surface moved upward at more than 2 6 m yr 1 averaged over several years this was equivalent to increased recharge estimated as 6 12 of rainfall depending on the specific yield used for the aquifer the potentiometric surface was observed to rise less rapidly 0 9 m yr 1 in areas subjected to partial clearing groundwater chloride concentrations exhibit no obvious spatial pattern in the catchments probability density functions of the chloride data have similar shapes in the higher and medium rainfall catchment areas with median values of 460 and 1000 mg 1 1 respectively chloride concentrations were essentially constant with time in some piezometers while in others concentrations varied with or without trend recorded changes in time and space are not consistent with the transport equation for solute in an aquifer leading to the conclusion that local variability of solution velocity may be important this is in accord with the observed variability of hydraulic conductivity in these aquifers