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At least 217 records · Page 12Linked to original sources
USGS2018

Geothermal potential of the Umatilla Indian Reservation, Oregon: Evidence from detailed geophysical investigations

Recent geologic and geophysical investigations were undertaken in northeastern Oregon to better assess earthquake hazards in the region and determine relative favorability for geothermal energy development on lands of the Confederated Tribes of the Umatilla Indian Reservation (CTUIR). This work was funded in part by a Bureau of Indian Affairs grant awarded to the CTUIR to identify areas most suitable for further exploration of geothermal resources. Results from this work were utilized as inputs to a geothermal favorability modeling process that led to the identification of target sites for further geothermal investigation. Beyond the geothermal aspect of this project, the region is of great tectonic significance as it marks the intersection of two major physiographic and geophysical features, the Klamath-Blue Mountain lineament (KBL) and Olympic-Wallowa lineament (OWL), inferred to represent major basement boundaries. The Thorn Hollow and Hite faults, which appear to be major linkages between the KBL and OWL, run through the study area. New aeromagnetic, gravity and magnetotelluric (MT) surveying, along with fault analyses, were conducted as part of this effort. Detailed geophysical exploration resulted in the collection of 1,380 new gravity stations, 34,524-line kilometers of aeromagnetic data (covering 12,524 km2) and measurements from 36 MT stations. Two-dimensional (2D) forward-modeling was executed along several profiles using gravity and aeromagnetic data, combined with existing geologic mapping and rock property constraints measured from hand samples and outcrops. These models are used to define lithologic contacts in the subsurface in the absence of well logs or borehole data to determine possible geothermal fluid reservoirs, as well as identify major structures that may act as conduits for the upward migration of geothermal fluids.

Oregon↗
USGS2018

A geophysical characterization of the structural framework of the Camas Prairie Geothermal System, southcentral Idaho

Play Fairway Analysis methods, utilizing existing geologic, thermal, geochemical, and geophysical data were employed in an initial assessment of geothermal resources in the Snake River Plain. These efforts identified the Camas Prairie in southcentral Idaho as a region with elevated resource potential. Subsequent efforts included structural and geophysical data collection to identify the most favorable structural settings for exploiting resources in the valley. The present work involved high-resolution gravity, magnetic, magnetotellurics (MT), field mapping, and seismic surveys to further characterize the system and target sites for exploration drilling around Barron’s Hot Springs (BHS) in the southwest part of the valley. Geophysical mapping and modeling reveal that the BHS coincides with a complex intersection of two major fault systems: a prominent NW-trending system that includes the Pothole fault, and EW-trending basin-bounding faults that control NS-extension. This complex zone includes a dense network of EW-oriented faults and a right stepover in the Pothole fault which, given the dominant dextral-normal to normal slip inferred for this fault, would promote extension in the immediate vicinity of the BHS. Surface faulting in this region indicate Pleistocene or younger slip, and seismic imaging documents offsets of shallow strata that suggest ongoing activity on these structures. MT modeling results show that this zone also coincides with a prominent conductive anomaly, characteristic of the presence of hydrothermal alteration or hydrothermal fluids. These results point to the importance of these structures in maintaining current and long-lived shallow hydrothermal activity around the BHS. The detailed structural mapping and conceptual framework developed from this study provide critical constraints for siting a drill hole aimed at documenting reservoir characteristics and informing potential future development of these geothermal resources.

Idaho↗
USGS2025

Airborne geophysics for geologic mapping of critical mineral systems in the United States southern midcontinent

The increased demand for clean energy technology and a significant reliance on foreign supply chains have given impetus to understanding critical mineral systems and locating potential resources within the United States. At least thirteen critical mineral-bearing systems have been identified throughout the U.S. southern Midcontinent (Hofstra and Kreiner, 2020) but much of the region’s geologic framework is concealed by vegetation and sedimentary cover that hinder traditional geologic mapping efforts. Airborne geophysical data provide an effective way to overcome these obstacles and to provide additional insight into the deeper structures that underlie shallow mineralization. However, legacy airborne magnetic and radiometric data were collected using now-outdated instruments and methods, inconsistent survey parameters, and large flight-line spacings resulting in low-resolution data that present challenges to regional-scale study and interpretation. Over the last decade, the U.S. Geological Survey Earth Mapping Resources Initiative (EMRI) and National Cooperative Geologic Mapping Program have conducted a series of high-resolution airborne magnetic and radiometric surveys across the southern Midcontinent (Fig. 1) as part of an effort to improve understanding of the geophysical framework and natural resource potential in the region. These surveys are designed using modern survey methods and instruments with consistent parameters for flight-line spacing and flight height relative to magnetic sources. The EMRI airborne surveys are planned in collaboration with State geological surveys based on focus areas (Dicken et al., 2022) according to the presence of or potential for critical mineral deposits. High-resolution airborne magnetic and radiometric data cover focus areas such as the southeast Missouri iron metallogenic province and South-Central iron-oxide-apatite (IOA) – iron-oxide-copper-gold (IOCG) province, the Magnet Cove alkaline-carbonatite complex, the Midwest Permian ultramafic dike district, the Illinois-Kentucky fluorspar district, and several Mississippi Valley-type lead-zinc deposits and districts (Fig. 1). These focus areas represent known deposits or prospective host systems of critical minerals including rare earth elements (REEs), platinum-group elements (PGEs), cobalt, lithium, fluorspar, niobium, titanium, vanadium, lead, zinc, gallium, germanium, and many more. Other significant geologic and geophysical features covered include the Reelfoot rift, the New Madrid seismic zone, the Illinois basin, the Arkoma basin, the South-Central magnetic lineament, and the Kentucky-Tennessee magnetic anomaly (Fig. 1). This presentation focuses on new airborne magnetic and radiometric data with continuous coverage across parts of six states, preliminary interpretations, examples of geologic mapping applications, and discussion of newly discovered magnetic anomalies and follow-up investigations.

Conference Paper↗
USGS2025

Multi-scale geophysical mapping of the brine and bedrock surfaces along the Dolores River, Paradox Valley, Colorado, December 2023

Total dissolved solids derived from salt dome–sourced brine in the underlying alluvial aquifer substantially increase with distance in the reach of the Dolores River that passes through Paradox Valley in southwestern Colorado. The area has been the site of salinity control operations since the 1990s to reduce salt loading to the downstream Colorado River. Previous airborne and ground/water-based electromagnetic (EM) geophysical data have successfully mapped the top of the brine surface, albeit with relatively coarse near-surface resolution and limited spatial coverage. This present December 2023 study used ground-based high-resolution EM and passive seismic (horizontal-to-vertical spectral ratio, HVSR) tools to map in detail the depth and thickness of the brine zone in the alluvial aquifer (top of the brine down to bedrock contact) in areas immediately surrounding the Dolores River where previous airborne EM (AEM) results indicated brine within 10 m of land surface. Results indicate the deepest bedrock is generally associated with the shallowest brine and local depressions in the collapse breccia (caprock to the Paradox Formation salt) may facilitate vertical migration of brine into the alluvial aquifer. Additionally, the ground-based EM mapping corroborated general patterns in depth to brine that were observed in previous AEM results while also revealing additional detail, including suspected focused brine discharge zones to the Dolores River. A river-based survey wherein EM data, channel depth and river water–specific conductance information were collected augmented these findings and indicated specific areas on both the western and eastern sides of the river where focused brine discharge may occur. This study comprises a large-scale, ground- and water-based geophysical mapping effort, including hundreds of HVSR soundings and 100s of kilometres of EM data, which were successfully translated into digital brine and bedrock surfaces that could be incorporated into groundwater modelling efforts, future well siting or other decision-making.

Colorado↗
USGS1993

Using borehole geophysics and cross-borehole flow testing to define hydraulic connections between fracture zones in bedrock aquifers

Nearly a decade of intensive geophysical logging at fractured rock hydrology research sites indicates that geophysical logs can be used to identify and characterize fractures intersecting boreholes. However, borehole-to-borehole flow tests indicate that only a few of the apparently open fractures found to intersect boreholes conduct flow under test conditions. This paper presents a systematic approach to fracture characterization designed to define the distribution of fractures along boreholes, relate the measured fracture distribution to structure and lithology of the rock mass, and define the nature of fracture flow paths across borehole arrays. Conventional electrical resistivity, gamma, and caliper logs are used to define lithology and large-scale structure. Borehole wall image logs obtained with the borehole televiewer are used to give the depth, orientation, and relative size of fractures in situ. High-resolution flowmeter measurements are used to identify fractures conducting flow in the rock mass adjacent to the boreholes. Changes in the flow field over time are used to characterize the hydraulic properties of fracture intersections between boreholes. Application of this approach to an array of 13 boreholes at the Mirror Lake, New Hamsphire site demonstrates that the transient flow analysis can be used to distinguish between fractures communicating with each other between observation boreholes, and those that are hydraulically isolated from each other in the surrounding rock mass. The Mirror Lake results also demonstrate that the method is sensitive to the effects of boreholes on the hydraulic properties of the fractured-rock aquifer. Experiments conducted before and after the drilling of additional boreholes in the array and before and after installation of packers in existing boreholes demonstrate that the presence of new boreholes or the inflation of packers in existing boreholes has a large effect on the measured hydraulic properties of the rock mass surrounding the borehole array.

Journal of Applied Geophysics↗
USGS2011

Geophysical Research Letters: New policies improve top-cited geosciences journal

Geophysical Research Letters (GRL) is the American Geophysical Union's premier journal of fast, groundbreaking communication. It rapidly publishes high- impact,letter-length articles, and it is the top-cited multidisciplinary geosciences journal over the past 10 years, with an impact factor that increased again in 2009, to 3.204. For manuscripts submitted to GRL, the median time to first and final decision is 23 and 27 days, respectively—a 35% improvement since 2007—and the median time from submission to publication is 13 weeks for 90% of GRL papers—a 25% improvement since 2007. Among high-impact publications in the geosciences, GRL has the fastest turnaround.

Eos, Transactions, American Geophysical Union↗
USGS2020

Seasonal subsurface thaw dynamics of an aufeis feature inferred from geophysical methods

Aufeis are sheets of ice unique to cold regions that originate from repeated flooding and freezing events during the winter. They have hydrological importance associated with summer flows and possibly winter insulation, but little is known about the seasonal dynamics of the unfrozen sediment layer beneath them. This layer may support perennial groundwater flow in regions with otherwise continuous permafrost. For this study, ground penetrating radar (GPR) were collected in September 2016 (maximum thaw) and April 2017 (maximum frozen) at the Kuparuk aufeis field on the North Slope of Alaska. Supporting surface nuclear magnetic resonance (NMR) data were collected during the maximum frozen campaign. These point-in-time geophysical data sets were augmented by continuous subsurface temperature data and periodic Structure-from-Motion digital elevation models (DEM) collected seasonally. GPR and difference DEM data showed maximum ice thicknesses of up to 6 m over the sediment surface. Below the ice, GPR and NMR identified regions of permafrost and regions of seasonally frozen sediment (i.e., the active layer) underlain by a substantial perennially unfrozen zone or “lateral talik” that ranged from 0 m to over 13 m thick. The seasonally frozen cobble layer above the talik was typically 3 to 5 m thick, with freezing apparently enabled by relatively high thermal diffusivity of the overlying ice and rock cobbles. The large talik beneath the aufeis and active layer suggests that year-round groundwater flow and coupled heat transport occurs beneath much of the feature. Highly permeable alluvial material and discrete zones of apparent groundwater upwelling indicated by geophysical and ground temperature data allows direct connection between the aufeis and the talik below.

Alaska↗
USGS2022

Achievements and prospects of global broadband seismographic networks after 30 years of continuous geophysical observations

Global seismographic networks (GSNs) emerged during the late nineteenth and early twentieth centuries, facilitated by seminal international developments in theory, technology, instrumentation, and data exchange. The mid- to late-twentieth century saw the creation of the World-Wide Standardized Seismographic Network (1961) and International Deployment of Accelerometers (1976), which advanced global geographic coverage as seismometer bandwidth increased greatly allowing for the recording of the Earth's principal seismic spectrum. The modern era of global observations and rapid data access began during the 1980s, and notably included the inception of the GEOSCOPE initiative (1982) and GSN (1988). Through continual improvements, GEOSCOPE and the GSN have realized near-real time recording of ground motion with state-of-art data quality, dynamic range, and timing precision to encompass 180 seismic stations, many in very remote locations. Data from GSNs are increasingly integrated with other geophysical data (e.g., space geodesy, infrasound and Interferometric Synthetic Aperture Radar). Globally distributed seismic data are critical to resolving crust, mantle, and core structure; illuminating features of the plate tectonic and mantle convection system; rapid characterization of earthquakes; identification of potential tsunamis; global nuclear test verification; and provide sensitive proxies for environmental changes. As the global geosciences community continues to advance our understanding of Earth structure and processes controlling elastic wave propagation, GSN infrastructure offers a springboard to realize increasingly multi-instrument geophysical observatories. Here, we review the historical, scientific, and monitoring heritage of GSNs, summarize key discoveries, and discuss future associated opportunities for Earth Science.

Reviews of Geophysics↗
USGS2014

Preliminary report on the North Atlantic deep‐sea cores taken by the Geophysical Laboratory, Carnegie Institution

A series, of 11 cores from the North Atlantic sea‐bottom between the Newfoundland Banks and the banks off the Irish Coast have been studied by a group of geologists of the United States Geological Survey. These cores were taken by Dr. C. S. Piggot of the Carnegie Institution's Geophysical Laboratory from the cable ship Lord Kelvin with the explosive type of sounding‐apparatus, which he designed (C. S. Piggot, Apparatus to secure core‐samples from the oceanbottom, Bull. Geol. Soc. Amer., v. 47, pp. 675–684, 1936). This preliminary report is based largely on the results obtained by M. N. Bramlette, who studied the lithology, and Jos. A. Cushman, who studied the forarainifera. The geographic position, the depth of water at each station, and the length of core obtained are given in Table 1. ©1937. American Geophysical Union. All Rights Reserved.

Newfoundland and Labrador↗
USGS2014

Part I—History and activities of the section of geophysics of the United States Geological Survey

From the beginning of time, all ingenuity of mankind has been concentrated upon the methods of finding gold and unusual deposits in the earth. An illustration (Fig. 1) from the old treatise by Agricola, “De Re Metallica,” published in 1580, will serve to show the implicit faith of that generation in divining methods. However, it was not until 1920 that real progress was made in prospecting by using the latest advances of the physical sciences. The public interest was stimulated by the successes of these methods on the part of commercial operators, and governmental agencies received many requests for information concerning their reliability. There were also, in the late 1920's, high‐pressure mine‐promotion schemes which used geophysical methods in a very questionable manner, symbolized in Figure 2 as of 1928 by an electrified forked stick. Authoritative information concerning such practices for public protection was needed to curb such notorious undertakings. Dr. Scott Turner, then Director of the United States Bureau of Mines, thoroughly understood the situation and was first in the governmental departments to recognize the possible value of a study of modern prospecting methods. The Bureau of Mines began this investigation by employing Drs. A. S. Eve and D. A. Keys of McGill University for short periods in the summer in 1927. Their first publication [see 1 of “References” at end of paper] served to illustrate the fundamental scientific principles which underlie geophysical prospecting. This was followed by a second publication [2] giving the results of field‐tests. In the light of the rapid improvements during the intervening ten years, these two papers take a historical position.

Eos, Transactions, American Geophysical Union↗
USGS2014

Part II—Geophysical investigations in the Hawaiian Islands

During 1938 and 1939, an extensive series of geophysical surveys, employing both resistivity and magnetic methods, have been carried on in the Hawaiian Islands by the Section of Geophysics of the United States Geological Survey in cooperation with the Division of Ground‐Water of the Survey and the Division of Hydrography of the Territorial Government (see Fig. 1). During this time, surveys have been conducted on the islands of Oahu, Molokai, and Maul. Two distinct types of ground‐water occurrence are being investigated: (1) The basal fresh‐water lens floating on underlying salt water in obedience to the Ghyben‐Herzberg principle (Fig. 2); and (2) perched ground‐water (Fig. 3) .

Hawaii↗
USGS2014

Part III—Fundamental research in geophysics relating to prospecting

In addition to projects such as those reported in parts I and II above, the Section of Geophysics of the Federal Government has undertaken a considerable amount of fundamental research. Two such field‐projects may be mentioned, one a magnetometric study in the Comstock District of Nevada, and the other a resistivity‐study of snow and ice. In addition to the field‐problems, there have been two classes of research of a mathematical type. One of these has been the preparation of tables, scales, and charts for the important geophysical functions already known; the other has been the extension of the relations involved in the resistivity‐problem.

Eos, Transactions, American Geophysical Union↗
USGS2007

A three-dimensional geophysical model of the crust in the Barents Sea region: Model construction and basement characterization

BARENTS50, a new 3-D geophysical model of the crust in the Barents Sea Region has been developed by the University of Oslo, NORSAR and the U.S. Geological Survey. The target region comprises northern Norway and Finland, parts of the Kola Peninsula and the East European lowlands. Novaya Zemlya, the Kara Sea and Franz-Josef Land terminate the region to the east, while the Norwegian-Greenland Sea marks the western boundary. In total, 680 1-D seismic velocity profiles were compiled, mostly by sampling 2-D seismic velocity transects, from seismic refraction profiles. Seismic reflection data in the western Barents Sea were further used for density modelling and subsequent density-to-velocity conversion. Velocities from these profiles were binned into two sedimentary and three crystalline crustal layers. The first step of the compilation comprised the layer-wise interpolation of the velocities and thicknesses. Within the different geological provinces of the study region, linear relationships between the thickness of the sedimentary rocks and the thickness of the remaining crystalline crust are observed. We therefore, used the separately compiled (area-wide) sediment thickness data to adjust the total crystalline crustal thickness according to the total sedimentary thickness where no constraints from 1-D velocity profiles existed. The BARENTS50 model is based on an equidistant hexagonal grid with a node spacing of 50 km. The P -wave velocity model was used for gravity modelling to obtain 3-D density structure. A better fit to the observed gravity was achieved using a grid search algorithm which focussed on the density contrast of the sediment-basement interface. An improvement compared to older geophysical models is the high resolution of 50 km. Velocity transects through the 3-D model illustrate geological features of the European Arctic. The possible petrology of the crystalline basement in western and eastern Barents Sea is discussed on the basis of the observed seismic velocity structure. The BARENTS50 model is available at http://www.norsar.no/seismology/barents3d/ .

Geophysical Journal International↗
USGS1956

Geophysical studies in the intermontane basins in southern California

Geophysical surveys were made by the U. S. Geological Survey in Searles Lake basin and in the Mojave Desert near Barstow, California to test the application of geophysical exploration to the study of the geologic problems associated with the intermontane basins of southern California. In Searles Lake basin a coordinated gravity and seismic reflection and refraction survey indicated that the fill in the basin is about 3,300 feet thick with the greatest thickness occurring east of the center of the basin. The regional gravity data from the area near Barstow can be used to estimate the thickness and extent of the Tertiary and Quaternary deposits.

California↗
USGS1987

Role of geophysics in identifying and characterizing sites for high-level nuclear waste repositories.

Evaluation of potential high-level nuclear waste repository sites is an area where geophysical capabilities and limitations may significantly impact a major governmental program. Since there is concern that extensive exploratory drilling might degrade most potential disposal sites, geophysical methods become crucial as the only nondestructive means to examine large volumes of rock in three dimensions. Characterization of potential sites requires geophysicists to alter their usual mode of thinking: no longer are anomalies being sought, as in mineral exploration, but rather their absence. Thus the size of features that might go undetected by a particular method take on new significance. Legal and regulatory considerations that stem from this different outlook, most notably the requirements of quality assurance (necessary for any data used in support of a repository license application), are forcing changes in the manner in which geophysicists collect and document their data. -Authors

Journal of Geophysical Research↗
USGS1990

Geophysical investigations in Jordan

A number of geophysical investigations have been undertaken in the Hashemite Kingdom of Jordan to provide data for understanding the tectonic framework, the pattern of seismicity, earthquake hazards and geothermal resources of the country. Both the historical seismic record and the observed recent seismicity point to the dominance of the Dead Sea Rift as the main locus of seismic activity but significant branching trends and gaps in the seismicity pattern are also seen. A wide variety of focal plane solutions are observed emphasizing the complex pattern of fault activity in the vicinity of the rift zone. Geophysical investigations directed towards the geothermal assessment of the prominent thermal springs of Zerga Ma'in and Zara are not supportive of the presence of a crustal magmatic source.

Tectonophysics↗
USGS1968

The relationship of geophysical measurements to engineering and construction parameters in the Straight Creek Tunnel pilot bore, Colorado

Seismic-refraction and electrical-resistivity measurements made along the walls of the Straight Creek Tunnel pilot bore indicate that both a low-velocity and a high-resistivity layer exist in the disturbed rock surrounding the excavation. Seismic measurements were analyzed to obtain the thickness and seismic velocity of rock in the low-velocity layer, the velocity of rock behind the layer and the amplitude of seismic energy received at the detectors. Electrical-resistivity measurements were analyzed to obtain the thickness and electrical resistivity of the high-resistivity layer and the resistivity of rock behind the layer. The electrical resistivity and the seismic velocity of rock at depth, the thickness of rock in the low-velocity layer, and the relative amplitude of seismic energy were correlated against the following parameters, all of which are important in tunnel construction: height of the tension arch, stable vertical rock load, rock quality, rate of construction and cost per foot, percentage of lagging and blocking, set spacing, and type and amount of steel support required, The correlations were statistically meaningful, having correlation coefficients ranging in absolute value from about 0·7 to nearly 1·0. This finding suggests the possibility of predicting parameters of interest in tunnel construction from geophysical measurements made in feeler holes drilled ahead of a working face. Predictions might be based on correlations established either during the early stages of construction or from geophysical surveys in other tunnels of similar design in similar geologic environments.

Colorado↗
USGS2005

Hydrologic properties of coal beds in the Powder River Basin, Montana I. Geophysical log analysis

As part of a multidisciplinary investigation designed to assess the implications of coal-bed methane development on water resources for the Powder River Basin of southeastern Montana, six wells were drilled through Paleocene-age coal bedsalong a 31-km east–west transect within the Tongue River drainage basin. Analysis of geophysical logs obtained in these wells provides insight into the hydrostratigraphic characteristics of the coal and interbedded siliciclastic rocks and their possible interaction with the local stress field. Natural gamma and electrical resistivity logs were effective in distinguishing individual coal beds. Full-waveform sonic logs were used to determine elastic properties of the coal and an attendant estimate of aquifer storage is in reasonable agreement with that computed from a pumping test. Inspection of magnetically oriented images of the borehole walls generated from both acoustic and optical televiewers and comparison with coal cores infer a face cleat orientation of approximately N33°E, in close agreement with regional lineament patterns and the northeast trend of the nearby Tongue River. The local tectonic stress field in this physiographic province as inferred from a nearby 1984 earthquake denotes an oblique strike-slip faulting regime with dominant east–west compression and north–south extension. These stress directions are coincident with those of the primary fracture sets identified from the televiewer logs and also with the principle axes of the drawdown ellipse produced from a complementary aquifer test, but oblique to apparent cleat orientation. Consequently, examination of these geophysical logs within the context of local hydrologic characteristics indicates that transverse transmissivity anisotropy in these coals is predominantly controlled by bedding configuration and perhaps a mechanical response to the contemporary stress field rather than solely by cleat structure.

Montana↗