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Filters: partyWithName: Paul A. Bedrosian (X) > Types: Citation (X)

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Within the south-western Mojave Desert, the Joshua Basin Water District is considering applying imported water into infiltration ponds in the Joshua Tree groundwater sub-basin in an attempt to artificially recharge the underlying aquifer. Scarce subsurface hydrogeological data are available near the proposed recharge site; therefore, time-domain electromagnetic (TDEM) data were collected and analysed to characterize the subsurface. TDEM soundings were acquired to estimate the depth to water on either side of the Pinto Mountain Fault, a major east-west trending strike-slip fault that transects the proposed recharge site. While TDEM is a standard technique for groundwater investigations, special care must be taken...
Categories: Publication; Types: Citation; Tags: Near Surface Geophysics
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Increasingly, groundwater management requires more accurate hydrogeologic frameworks for groundwater models. These complex issues have created the demand for innovative approaches to data collection. In complicated terrains, groundwater modelers benefit from continuous high‐resolution geologic maps and their related hydrogeologic‐parameter estimates. The USGS and its partners have collaborated to use airborne geophysical surveys for near‐continuous coverage of areas of the North Platte River valley in western Nebraska. The survey objectives were to map the aquifers and bedrock topography of the area to help improve the understanding of groundwater‐surface‐water relationships, leading to improved water management...
Categories: Publication; Types: Citation
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An estimated one-dimensional layered model of electrical resistivity beneath Florida was developed from published geological and geophysical information. The resistivity of each layer is represented by plausible upper and lower bounds as well as a geometric mean resistivity. Corresponding impedance transfer functions, Schmucker-Weidelt transfer functions, apparent resistivity, and phase responses are calculated for inducing geomagnetic frequencies ranging from 10−5 to 100 hertz. The resulting one-dimensional model and response functions can be used to make general estimates of time-varying electric fields associated with geomagnetic storms such as might represent induction hazards for electric-power grid operation....
Categories: Publication; Types: Citation; Tags: Open-File Report
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This dataset consists of 102 magnetotelluric (MT) stations collected in 2012-2014 in the Rio Grande Rift and southern Rocky Mountains. The U.S. Geological Survey acquired these data to improve regional conductivity models of the western United States. This work is in support of studies of the effect of lithospheric modification on electrical resistivity structure and tectonic evolution of the western United States.
Categories: Data; Types: Citation, Map Service, OGC WFS Layer, OGC WMS Layer, OGC WMS Service; Tags: Carson National Forest, Colfax County, Colorado, Colorado Plateau, Dona Ana County, All tags...
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Geophysical models image the 3D geometry of the mafic portion of the Bushveld Complex north of the Thabazimbi-Murchison Lineament (TML), critical for understanding the origin of the world's largest layered mafic intrusion and platinum group element deposits. The combination of the gravity and magnetic data with recent seismic, MT, borehole and rock property measurements powerfully constrains the models. The intrusion north of the TML is generally shallowly buried (generally <1500 m) with a modeled area of ∼160 km × ∼125 km. The modeled thicknesses are not well constrained but vary from ∼<1000 to >12,000 m, averaging ∼4000 m. A feeder, suggested by a large modeled thickness (>10,000 m) and funnel shape, for Lower...
Categories: Publication; Types: Citation; Tags: Precambrian Research
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Over the winter and spring of 2009, the U.S. Geological Survey conducted a general assessment of the capabilities of several geophysical tools to delineate buried paleochannel aquifers in the glacial terrain of eastern Nebraska. Mapping these paleochannels is an important objective for the Eastern Nebraska Water Resources Assessment group. Previous attempts at mapping these channels included a helicopter electromagnetic survey flown over an area near the town of Oakland, Nebraska, in March 2007. This survey had limited success in imaging the paleochannels due to the restricted depth of investigation of the system in the clay-rich till overburden. The purpose of this study was to investigate whether other airborne...
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The Elkhorn-Loup Model (ELM) was begun in 2006 to understand the effect of various groundwater-management scenarios on surface-water resources. During phase one of the ELM study, a lack of subsurface geological information was identified as a data gap. Test holes drilled to the base of the aquifer in the ELM study area are spaced as much as 25 miles apart, especially in areas of the western Sand Hills. Given the variable character of the hydrostratigraphic units that compose the High Plains aquifer system, substantial variation in aquifer thickness and characteristics can exist between test holes. To improve the hydrogeologic understanding of the ELM study area, the U.S. Geological Survey, in cooperation with the...
Categories: Publication; Types: Citation; Tags: Open-File Report
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Correlating laboratory resistivity measurements with geophysical resistivity models helps constrain these models to the geology and lithology of an area. Throughout the Fort Irwin National Training Center area, 111 samples from both cored boreholes and surface outcrops were collected and processed for laboratory measurements. These samples represent various lithologic types that include plutonic and metamorphic (basement) rocks, lava flows, consolidated sedimentary rocks, and unconsolidated sedimentary deposits that formed in a series of intermountain basins. Basement rocks, lava flows, and some lithified tuffs are generally resistive (≥100 ohm-meters [Ω·m]) when saturated. Saturated unconsolidated samples are moderately...
Categories: Publication; Types: Citation; Tags: Open-File Report
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A three-dimensional lithospheric-scale resistivity model of the North American mid-continent has been estimated based upon EarthScope magnetotelluric data. Details of the resistivity model are discussed in relation to lithospheric sutures, defined primarily from aeromagnetic and geochronologic data, which record the southward growth of the Laurentian margin in the Proterozoic. The resistivity signature of the 1.1 Ga Mid-continent Rift System is examined in detail, in particular as relates to rift geometry, extent, and segmentation. An unrecognized expanse of (concealed) Proterozoic deltaic deposits in Kansas is identified and speculated to result from axial drainage along the southwest rift arm akin to the Rio Grande...
Categories: Publication; Types: Citation; Tags: Precambrian Research
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The U.S. Army Fort Irwin National Training Center (NTC), in the Mojave Desert, obtains all of its potable water supply from three groundwater basins (Irwin, Langford, and Bicycle) within the NTC boundaries (fig. 1; California Department of Water Resources, 2003). Because of increasing water demands at the NTC, the U.S. Geological Survey (USGS), in cooperation with the U.S. Army, completed several studies to evaluate water resources in the developed and undeveloped groundwater basins underlying the NTC. In all of the developed basins, groundwater withdrawals exceed natural recharge, resulting in water-level declines. However, artificial recharge of treated wastewater has had some success in offsetting water-level...
Categories: Publication; Types: Citation
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Five magnetotelluric (MT) profiles have been acquired across the Cascadia subduction system and transformed using 2-D and 3-D nonlinear inversion to yield electrical resistivity cross sections to depths of ∼200 km. Distinct changes in plate coupling, subduction fluid evolution, and modes of arc magmatism along the length of Cascadia are clearly expressed in the resistivity structure. Relatively high resistivities under the coasts of northern and southern Cascadia correlate with elevated degrees of inferred plate locking, and suggest fluid- and sediment-deficient conditions. In contrast, the north-central Oregon coastal structure is quite conductive from the plate interface to shallow depths offshore, correlating...
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Excessive groundwater seepage can be a common engineering concern with earthen dams. The application of geophysical methods, whether for characterization or for long-term monitoring, to help inform mitigation strategies is becoming a more common addition to these investigations. The U.S. Geological Survey (USGS) has completed geophysical investigations at several earthen dams in cooperation with the U.S. Army Corps of Engineers (USACE) to help characterize subsurface hydrogeologic conditions and to identify potential sources of seepage. Summaries of the investigations of Martis Creek Dam and Hidden Dam, both located in California, are presented.
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The increased application of airborne electromagnetic surveys to hydrogeological studies is driving a demand for data that can consistently be inverted for accurate subsurface resistivity structure from the near surface to depths of several hundred metres. We present an evaluation of three commercial airborne electromagnetic systems over two test blocks in western Nebraska, USA. The selected test blocks are representative of shallow and deep alluvial aquifer systems with low groundwater salinity and an electrically conductive base of aquifer. The aquifer units show significant lithologic heterogeneity and include both modern and ancient river systems. We compared the various data sets to one another and inverted...
Categories: Publication; Types: Citation; Tags: Geophysical Prospecting
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We combined aeromagnetic, induced polarization, magnetotelluric, and gravity surveys as well as drillhole geologic, alteration, magnetic susceptibility, and density data for exploration and characterization of the Cu-Au-Mo Pebble porphyry deposit. This undeveloped deposit is almost completely concealed by postmineralization sedimentary and volcanic rocks, presenting an exploration challenge. Individual geophysical methods primarily assist regional characterization. Positive chargeability and conductivity anomalies are observed over a broad region surrounding the deposit, likely representing sulfide minerals that accumulated during multiple stages of hydrothermal alteration. The mineralized area occupies only a small...
Categories: Publication; Types: Citation; Tags: Geophysics
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In reaching across traditional disciplinary boundaries, solid-Earth geophysicists and space physicists are forging new collaborations to map magnetic-storm hazards for electric-power grids. Future progress in evaluation storm time geoelectric hazards will come primarily through monitoring, surveys, and modeling of related data.
Categories: Publication; Types: Citation; Tags: Space Weather
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Airborne geophysical surveys of selected areas of the North and South Platte River valleys of Nebraska, including Lodgepole Creek valley, collected data to map aquifers and bedrock topography and thus improve the understanding of groundwater - surface-water relationships to be used in water-management decisions. Frequency-domain helicopter electromagnetic surveys, using a unique survey flight-line design, collected resistivity data that can be related to lithologic information for refinement of groundwater model inputs. To make the geophysical data useful to multidimensional groundwater models, numerical inversion converted measured data into a depth-dependent subsurface resistivity model. The inverted resistivity...
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In support of a multiagency project for assessing induction hazards, we present maps of extreme-value geoelectric amplitudes over about half of the continental United States. These maps are constructed using a parameterization of induction: estimates of Earth surface impedance, obtained at discrete geographic sites from magnetotelluric survey data, are convolved with latitude-dependent statistical maps of extreme-value geomagnetic activity, obtained from decades of magnetic observatory data. Geoelectric amplitudes are estimated for geomagnetic waveforms having 240 s sinusoidal period and amplitudes over 10 min that exceed a once-per-century threshold. As a result of the combination of geographic differences in geomagnetic...
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Advancements in aeromagnetic acquisition technology over the past few decades have led to greater resolution of shallow geologic sources with low magnetization, such as intrasedimentary faults and paleochannels. Detection and mapping of intrasedimentary faults in particular can be important for understanding the overall structural setting of an area, even if exploration targets are much deeper. Aeromagnetic methods are especially useful for mapping structures in mountain-piedmont areas at the margins of structural basins, where mineral exploration and seismic-hazard studies may be focused, and where logistical or data-quality issues encumber seismic methods. Understanding if the sources of aeromagnetic anomalies...
Categories: Publication; Types: Citation; Tags: The Leading Edge
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Maps of geoelectric amplitude covering about half the continental United States are presented that will be exceeded, on average, once per century in response to an extreme-intensity geomagnetic disturbance. These maps are constructed using an empirical parameterization of induction: convolving latitude-dependent statistical maps of extreme-value geomagnetic disturbances, obtained from decades of 1-minute magnetic observatory data, with local estimates of Earth-surface impedance obtained at discrete geographic sites from magnetotelluric surveys. Geoelectric amplitudes are estimated for geomagnetic waveforms having a 240-s (and 1200-s) sinusoidal period and amplitudes over 10 min (1 h) that exceed a once-per-century...
Categories: Publication; Types: Citation
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The magnetotelluric component of the EarthScope USArray program has covered over 35% of the continental United States. Resistivity tomography models derived from these data image lithospheric structure and provide constraints on the distribution of fluids and melt within the lithosphere. We present a three-dimensional resistivity model of the northwestern United States which provides new insight into the tectonic assembly of western North America from the Archean to present. Comparison with seismic tomography models reveals regions of correlated and anti-correlated resistivity and velocity that help identify thermal and compositional variations within the lithosphere. Recent (Neogene) tectonic features reflected...


map background search result map search result map Hydrostratigraphic interpretation of test-hole and surface geophysical data, Elkhorn and Loup River Basins, Nebraska, 2008 to 2011 Integrated geophysical imaging of a concealed mineral deposit: a case study of the world-class Pebble porphyry deposit in southwestern Alaska Regional scale magnetotelluric data from the Rio Grande Rift and southern Rocky Mountains Integrated geophysical imaging of a concealed mineral deposit: a case study of the world-class Pebble porphyry deposit in southwestern Alaska Hydrostratigraphic interpretation of test-hole and surface geophysical data, Elkhorn and Loup River Basins, Nebraska, 2008 to 2011 Regional scale magnetotelluric data from the Rio Grande Rift and southern Rocky Mountains