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Results for “Near Surface Geophysics”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 199 records · Page 11Linked to original sources
USGS2002

Sediment-hosted contaminants and distribution patterns in the Mississippi and Atchafalaya River Deltas

The Mississippi and Atchafalaya Rivers transport very large amounts of bedload and suspended sediments to the deltaic and coastal environments of the northern Gulf of Mexico. Absorbed onto these sediments are contaminants that may be detrimental to the environment. To adequately assess the impact of these contaminants it is first necessary to develop an understanding of sediment distribution patterns in these deltaic systems. The distribution patterns are defined by deltaic progradational cycles. Once these patterns are identified, the natural and industrial contaminant inventories and their depositional histories can be reconstructed. Delta progradation is a function of sediment discharge, as well as channel and receiving-basin dimensions. Fluvial energy controls the sediment distribution pattern, resulting in a coarse grained or sandy framework, infilled with finer grained material occupying the overbank, interdistributary bays, wetlands and abandoned channels. It has been shown that these fine-grained sediments can carry contaminants through absorption and intern them in the sediment column or redistribute them depending on progradation or degradation of the delta deposit. Sediment distribution patterns in delta complexes can be determined through high-resolution geophysical surveys and groundtruthed with direct sampling. In the Atchafalaya and Mississippi deltas, remote sensing using High-Resolution Single-Channel Seismic Profiling (HRSP) and Sidescan Sonar was correlated to 20-ft vibracores to develop a near-surface geologic framework that identifies variability in recent sediment distribution patterns. The surveys identified bedload sand waves, abandoned-channel back-fill, prodelta and distributary mouth bars within the most recently active portions of the deltas. These depositional features respond to changes in deltaic processes and through their response may intern or transport absorbed contaminants. Characterizing these features provides insight into the fate of sediment-hosted contaminants.

Louisiana↗
USGS2020

Preparing for geophysical science on the surface of the moon enabled by Artemis

Geophysical methods have been extremely successful in identifying resources on Earth as they provide a means of characterizing and mapping the sub-surface using data gathered on and above the target structures. Geophysics on the Moon will be an important tool for identifying key targets for geological prospecting, scientific sampling, assessing hazards and risks to crew and infrastructure, and determining the near subsurface and deeper workings of the lunar interior. Artemis will require 21st century geophysics instruments to advance lunar science and exploration, similar to how Apollo gathered geophysical data that is still leading to scientific discoveries 50 years later.

Report↗
USGS1978

Results and interpretation of exploratory drilling near the Picacho Fault, south-central Arizona

Modern surface faulting along the Picacho fault, east of Picacho, Arizona, has been attributed to ground-water withdrawal. In September 1977, three exploratory test holes were drilled 5 km east of Picacho and across the Picacho fault to investigate subsurface conditions and the mechanism of the faulting. The holes were logged by conventional geophysical and geologic methods. Piezometers were set in each hole and have been monitored since September 1977. The drilling indicates that the unconsolidated alluvium beneath the surface fault is approximately 310 m thick. Drilling and piezometer data and an associated seismic refraction survey indicate that the modern faulting is coincident with a preexisting, high-angle, normal fault that offsets units within the alluvium as well as the underlying bedrock. Piezometer and neutron log data indicate that the preexisting fault behaves as a partial ground-water barrier. Monitoring of the piezometers indicates that the magnitude of the man-induced difference in water level across the preexisting fault is seasonal in nature, essentially disappearing during periods of water-level recovery. The magnitude of the seasonal difference in water level, however, appears to be sufficient to account for the modern fault offset by localized differential compaction caused by a difference in water level across the preexisting fault. In addition, repeated level surveys since September 1977 of bench marks across the surface fault and near the piezometers have indicated fault movement that corresponds to fluctuations of water level.

Open-File Report↗
USGS2022

Characterization of subsurface conditions and recharge at the irrigated four-plex baseball field, Fort Irwin National Training Center, California, 2018–20

The U.S. Geological Survey performed subsurface and geophysical site characterization of the irrigated four-plex baseball field in the Langford Valley–Irwin Groundwater Subbasin, as part of a research study in cooperation with the U.S. Environmental Protection Agency, the Agricultural Research Service, and the Fort Irwin National Training Center, California. To help meet future demands, the Fort Irwin National Training Center is evaluating the efficacy of gravity-fed drywells to enhance storm-water recharge into the Langford Valley–Irwin Groundwater Subbasin by bypassing fine-grained, less permeable deposits between land surface and the water table. The amount, rate, and location of recharge beneath an irrigated baseball field in the groundwater basin at the Fort Irwin National Training Center is not well understood, so data were collected using physical and geophysical techniques to characterize subsurface materials, geologic controls, and the vertical movement of water through the unsaturated zone to the water table near the drywell at the Fort Irwin National Training Center. Based on the data collected and interpreted from these techniques, several fine-grained deposits were identified. Although these deposits appear to impede the downward movement of water through the unsaturated zone locally, they are not laterally continuous, and water appears to continue to move downward when it reaches the edges of the deposits. These data will help managers evaluate recharge at the site and determine if the use of gravity-fed drywells enhances recharge from surface runoff.

California↗
USGS2018

Near-surface environmentally forced changes in the Ross Ice Shelf observed with ambient seismic noise

Continuous seismic observations across the Ross Ice Shelf reveal ubiquitous ambient res- onances at frequencies >5 Hz. These firn-trapped surface wave signals arise through wind and snow bedform interactions coupled with very low velocity structures. Progressive and long-term spectral changes are associated with surface snow redistribution by wind and with a January 2016 regional melt event. Modeling demonstrates high spectral sen- sitivity to near-surface (top several m) elastic parameters. We propose that spectral peak changes arise from surface snow redistribution in wind events, and to velocity drops re- flecting snow lattice weakening near 0◦C for the melt event. Percolation-related refrozen layers and layer thinning may also contribute to long-term spectral changes after the melt event. Single-station observations are inverted for elastic structure for multiple stations across the ice shelf. High-frequency ambient noise seismology presents opportunities for continuous assessment of near surface ice shelf or other firn environments.

Geophysical Research Letters↗
USGS2025

Advancing current understanding of Martian impact-generated hydrothermal systems through novel coupled modeling: Insights from Gale, Jezero, and other craters

Impact-generated hydrothermal systems are considered potentially habitable environments on Mars, Earth, and other planetary bodies for microbial life. However, there is an ongoing debate regarding what geological features on Mars provide definitive evidence for such systems. Although earlier studies have modeled hydrothermal processes in Martian craters, they often lacked integration with shock physics hydrocodes to constrain initial impact conditions. The importance of this two-code coupling was demonstrated by successfully replicating alteration signatures in the Earth's Haughton impact structure. In this study, we use a similar two-code approach, combining the iSALE hydrocode with the HYDROTHERM hydrothermal model to simulate the full evolution of impact-generated hydrothermal systems. We apply this method to craters the size of Jezero (∼50 km) and Gale (∼154 km) in diameter. Although Jezero's interior is largely buried, our results align with hypothesized hydrothermal vents and alteration minerals near central uplifts in similarly sized exposed craters, such as Toro and Auki. Furthermore, our models correspond to alteration patterns observed by the Curiosity in the lower layers of Mount Sharp, which may represent remnants of impact-driven hydrothermal activity. A key finding is that these systems may persist much longer than previously estimated. Our simulations suggest that a Jezero-sized system could remain habitable for thermophiles for approximately 720,000 years, whereas a Gale-sized system could persist for nearly 2 million years. Additionally, simulations under unsaturated crustal conditions reveal that air-dominated near-surface layers can suppress vertical fluid flow, enabling deep subsurface alteration without producing detectable mineral signatures at the surface.

Journal of Geophysical Research - Planets↗
USGS2023

Geophysical data provide three dimensional insights into porphyry copper systems in the Silverton caldera, Colorado, USA

The Silverton caldera in southwest Colorado, USA hosts polymetallic veins and pervasively altered rocks indicative of porphyry copper systems. Nearly a kilometer of erosion has exposed multiple levels of the hydrothermal systems from shallow lithocaps down to quartz-sericite-pyrite veins. New airborne electromagnetic and magnetic survey data are integrated with previous alteration mapping and porphyry models to show the subsurface geophysical response of shallow to deep levels of the porphyry system. Qualitative map views show lateral changes in the magnetization and resistivity of the hydrothermally altered rocks. The volcanic terrain exhibits high magnetization and high amplitude anomalies map near-surface plutonic rocks associated with porphyry systems. Magnetic susceptibility measurements on outcrops of hydrothermally altered rocks indicate magnetite content decreases upward and outward from the source intrusions where magnetic anomaly lows are observed over the lithocaps. The resistivity maps highlight hydrothermal alteration as resistivity lows with exception being rocks having propylitic alteration. Quantitative resistivity models show low resistivity zones with an apparent thickness around 50–150 m beneath quartz-sericite-pyrite veins interpreted to be the result of supergene processes that may continue today, and the calculated magnetic source depths occur near the top of this zone. The resistivity models also show rocks having propylitic, silicic, and quartz-alunite-pyrophyllite assemblages exhibit high resistivity with depth, and argillic alteration assemblages had high resistivity due to high quartz content. This integrated approach presented in a three-dimensional environment provides guidance when exploring for porphyry copper systems in less exposed terrains.

Colorado↗
USGS2014

DigitalCrust – a 4D data system of material properties for transforming research on crustal fluid flow

Fluid circulation in the Earth's crust plays an essential role in surface, near surface, and deep crustal processes. Flow pathways are driven by hydraulic gradients but controlled by material permeability, which varies over many orders of magnitude and changes over time. Although millions of measurements of crustal properties have been made, including geophysical imaging and borehole tests, this vast amount of data and information has not been integrated into a comprehensive knowledge system. A community data infrastructure is needed to improve data access, enable large-scale synthetic analyses, and support representations of the subsurface in Earth system models. Here, we describe the motivation, vision, challenges, and an action plan for a community-governed, four-dimensional data system of the Earth's crustal structure, composition, and material properties from the surface down to the brittle–ductile transition. Such a system must not only be sufficiently flexible to support inquiries in many different domains of Earth science, but it must also be focused on characterizing the physical crustal properties of permeability and porosity, which have not yet been synthesized at a large scale. The DigitalCrust is envisioned as an interactive virtual exploration laboratory where models can be calibrated with empirical data and alternative hypotheses can be tested at a range of spatial scales. It must also support a community process for compiling and harmonizing models into regional syntheses of crustal properties. Sustained peer review from multiple disciplines will allow constant refinement in the ability of the system to inform science questions and societal challenges and to function as a dynamic library of our knowledge of Earth's crust.

Geofluids↗
USGS1985

Geophysical techniques for reconnaissance investigations of soils and surficial deposits in mountainous terrain

Two techniques were assessed for their capabilities in reconnaissance studies of soil characteristics: depth to the water table and depth to bedrock beneath surficial deposits in mountainous terrain. Ground-penetrating radar had the best near-surface resolution in the upper 2 m of the profile and provided continuous interpretable imagery of soil profiles and bedrock surfaces. Where thick colluvium blankets side slopes, the GPR could not consistently define the bedrock interface. In areas with clayey or shaley sediments, the GPR is also more limited in defining depth and is less reliable. Seismic refraction proved useful in determining the elevation of the water table and depth to bedrock, regardless of thickness of overlying material, but could not distinguish soil-profile characteristics.

Soil Science Society of America Journal↗
USGS1982

A plan for hydrologic investigations of in situ, oil-shale retorting near Rock Springs, Wyoming

The recovery of shale oil by the in-situ retort process may cause hydrologic impacts, the most significant being ground-water contamination and possible transport of contaminants into surrounding areas. Although these impacts are site-specific, many of the techniques used to investigate each retort operation commonly will be the same. The U.S. Geological Survey has begun a study of hydrologic impacts in the area of an in-situ retort near Rock Springs, Wyoming, as a means of refining and demonstrating these techniques. Geological investigations include determining the areal extent and thickness of aquifers. Emphasis will be placed on determining lithologic variations from geophysical logging. Hydrologic investigations include mapping of potentiometric surfaces, determining rates of ground-water discharge, and estimating aquifer properties by analytical techniques. Water-quality investigations include monitoring solute migration from the retort site and evaluating sampling techniques by standard statistical procedures. A ground-water-flow and solute-transport model will be developed to predict future movement of the water plume away from the retort. (USGS)

Open-File Report↗
USGS2014

Spatial variability and landscape controls of near-surface permafrost within the Alaskan Yukon River Basin

The distribution of permafrost is important to understand because of permafrost's influence on high-latitude ecosystem structure and functions. Moreover, near-surface (defined here as within 1 m of the Earth's surface) permafrost is particularly susceptible to a warming climate and is generally poorly mapped at regional scales. Subsequently, our objectives were to (1) develop the first-known binary and probabilistic maps of near-surface permafrost distributions at a 30 m resolution in the Alaskan Yukon River Basin by employing decision tree models, field measurements, and remotely sensed and mapped biophysical data; (2) evaluate the relative contribution of 39 biophysical variables used in the models; and (3) assess the landscape-scale factors controlling spatial variations in permafrost extent. Areas estimated to be present and absent of near-surface permafrost occupy approximately 46% and 45% of the Alaskan Yukon River Basin, respectively; masked areas (e.g., water and developed) account for the remaining 9% of the landscape. Strong predictors of near-surface permafrost include climatic indices, land cover, topography, and Landsat 7 Enhanced Thematic Mapper Plus spectral information. Our quantitative modeling approach enabled us to generate regional near-surface permafrost maps and provide essential information for resource managers and modelers to better understand near-surface permafrost distribution and how it relates to environmental factors and conditions.

Alaska↗
USGS2015

Tidal and seasonal variations in calving flux observed with passive seismology

The seismic signatures of calving events, i.e., calving icequakes, offer an opportunity to examine calving variability with greater precision than is available with other methods. Here using observations from Yahtse Glacier, Alaska, we describe methods to detect, locate, and characterize calving icequakes. We combine these icequake records with a coincident, manually generated record of observed calving events to develop and validate a statistical model through which we can infer iceberg sizes from the properties of calving icequakes. We find that the icequake duration is the single most significant predictor of an iceberg's size. We then apply this model to 18 months of seismic recordings and find elevated iceberg calving flux during the summer and fall and a pronounced lull in calving during midwinter. Calving flux is sensitive to semidiurnal tidal stage. Large calving events are tens of percent more likely during falling and low tides than during rising and high tides, consistent with a view that deeper water has a stabilizing influence on glacier termini. Multiple factors affect the occurrence of mechanical fractures that ultimately lead to iceberg calving. At Yahtse Glacier, seismology allows us to demonstrate that variations in the rate of submarine melt are a dominant control on iceberg calving rates at seasonal timescales. On hourly to daily timescales, tidal modulation of the normal stress against the glacier terminus reveals the nonlinear glacier response to changes in the near-terminus stress field.

Alaska↗
USGS1961

Geophysical study of subsurface structure in southern Owens Valley, California

Gravity and seismic measurements in southern Owens Valley , California , have outlined a deep subsurface trough, bounded throughout the greater part of its length by steep faults. Depths to the bedrock floor along the central part of the valley range from 3,000 to 9,000 ft below the surface. The subsurface trough is divided into two parts, a narrow channel-like depression near Lone Pine bounded by northwest-trending faults, and a broad basin at Owens Lake bounded by a more complex series of border faults. The bedrock ridge that crops out to form Alabama Hills is shown to extend from Independence to the north edge of Owens Lake, nearly twice its visible extent. The main direction of faults that have formed the valley is northwest; subsidiary faults trend north, northeast, and east. A fairly sharp velocity boundary within the Cenozoic valley deposits suggests a change in the rate and character of deposition which was probably the result of renewed uplift in the nearby mountains.

California↗
USGS2019

The relationship of channel planform and point bar architecture on a reach of the Wabash River near Grayville, Illinois

The erosional and depositional characteristics of meandering rivers lead to the formation and maintenance of point bars along the inner banks of meander bends. Point bars are composed of sediment layers in patterns resulting from the rate and style of channel migration, hydrodynamics, and sediment transport and deposition within the river system (e.g. Jackson, 1976; Dietrich and Smith, 1984; Dietrich, 1987, Abad and Garcia, 2009). The distribution of the sediments preserved in the internal architecture of a river point bar provides a record of channel planform evolution. Geophysical methods are used to gain a large-scale visualization of the subsurface and aid in the interpretation of historic channel patterns (Best et al., 2003; Woodward et al., 2003; Sambrook Smith et al., 2006). Comparing known surficial extents of the point bar to features identified in the subsurface can also enhance the understanding of historic channel planform. This study investigates two point bars along bends with different styles of migration, Maier and TB3, in a well-documented reach of the Wabash River near Grayville, IL. Evidence from historic aerial photography, modern lidar, photogrammetry, and geophysical surveys were used to determine the relationship between the point bar architecture and channel planform. Airborne lidar was flown in 2011 and is used to create the 2011 point bar surface. In 2017, a terrestrial lidar and Real Time Kinematic-Global Navigation Satellite System (RTK-GNSS) topographic survey were combined to create the surface for TB3. In 2018, a photogrammetric survey collected with a small unmanned aerial system (sUAS) was used to create a structure-frommotion (SfM) derived surface for Maier bend. The 2018 survey-based point bar surfaces were differenced from the 2011 point bar surfaces to get a Digital Elevation Model (DEM) of difference (DoD) to visualize areas of erosion and deposition. In addition, geophysical surveys using ground penetrating radar (GPR) were conducted in transverse and streamwise lines across the point bars in 2018. Elevation profiles from the 2011 point bar surfaces are extracted and overlain onto the 2018 GPR images to determine how the point bar is preserving the structure of sediments previously deposited. Results from this study provide an update to current models of point bar architecture.

Illinois↗
USGS2021

Integrated geophysical imaging of rare-earth-element-bearing iron oxide-apatite deposits in the eastern Adirondack Highlands, New York

The eastern Adirondack Highlands of northern New York host dozens of iron oxide-apatite (IOA) deposits containing magnetite and rare earth element (REE)-bearing apatite. We use new aeromagnetic, aeroradiometric, ground gravity, and sample petrophysical and geochemical data to image and understand these deposits and their geologic framework. Aeromagnetic total field data reflect highly magnetic leucogranite host rock and major structures that likely served as fluid conduits for the hydrothermal system. Bandpass filtering of the aeromagnetic data reveals individual deposits that were verified in the field or from historical records. A three-dimensional inversion for magnetic susceptibility images these deposits at depth, allowing inference of plunge directions and relative size. Radiometric data highlight variations in the surface geology and several large tailings piles that contain REE-bearing apatite. Within the host rock, eTh (equivalent Th), K and the eTh/K ratio are variable with high eTh/K near several of the IOA deposits. Areas with elevated K or low eTh/K representing potassic alteration appear to be rare; instead elevated eTh/K ratios likely reflect widespread sodic alteration overprinting potassic alteration. Bouguer gravity anomalies show limited correspondence to the surface geology, radiometric data, or magnetic data, but do exhibit ~10-km wide highs in areas where deposits are observed. Two-dimensional forward models of the gravity and magnetic data show that deeper dense material beneath the leucogranite is quantitatively feasible. If these dense rocks represent intrusions that were emplaced or still cooling at the time of mineralization, they may have served as a heat source that helped to drive the hydrothermal system. Combining datasets, we find that deposits occur towards the distal ends of major structures within the host leucogranite and mostly above gravity highs. The geophysical modeling thus suggests that IOA deposits formed in structural, thermal, and chemical traps near the distal ends of the hydrothermal system.

New York↗
USGS1978

Friction of rocks

Experimental results in the published literature show that at low normal stress the shear stress required to slide one rock over another varies widely between experiments. This is because at low stress rock friction is strongly dependent on surface roughness. At high normal stress that effect is diminished and the friction is nearly independent of rock type. If the sliding surfaces are separated by gouge composed of Montmorillonite or vermiculite the friction can be very low. ?? 1978 Birkha??user Verlag.

Pure and Applied Geophysics PAGEOPH↗
USGS2008

HiRISE observations of fractured mounds: Possible Martian pingos

Early images from the High Resolution Imaging Science Experiment (HiRISE) camera have revealed small fractured mounds in the Martian mid‐latitudes. HiRISE resolves fractures on the mound surfaces, indicating uplift, and shows that the mound surface material resembles that of the surrounding landscape. Analysis of Mars Orbiter Camera (MOC) images shows that in Utopia Planitia the mounds lie almost exclusively between 35–45°N. This range coincides with the peak‐abundance latitudes of several landforms attributed to ground water or ice, including gullies, and suggests a ground ice‐related origin. The best terrestrial analogues for the observed mound morphology are pingos, although some differences are noted. The presence of uncollapsed pingos would indicate the presence of near‐surface ground ice in the Martian mid‐latitudes, at depths greater than the ∼1 meter sampled by orbital spectrometers. Pingo formation may require near‐surface liquid water, which is consistent with a shallow groundwater model for the origin of gullies.

Geophysical Research Letters↗
USGS2014

Magnetic anomalies at high altitudes

To investigate the effect of anomalies in the Earth's magnetic field at high altitudes , aeromagnetic maps of two representative areas showing isanomalic curves for total intensity are projected to levels of 10 and 20 miles above the surface of a plane Earth. The projections are accomplished by numerical computations and by use of a magnetic ‐field projecting machine at the Naval Ordnance Laboratory. It is found that anomalies of 500 gammas near the surface of the Earth, in merging into neighboring anomalies , may produce effects of 100 gammas or more at an altitude of 20 miles.

Eos, Transactions, American Geophysical Union↗