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USGS2021

Development of soil radiocarbon profiles in a reactive transport framework

Today, there is a greater appreciation for the importance of the physical protection of carbon (C) through interactions with mineral surfaces, isolation from microbes, and the important role of transport in shaping soil properties and controlling moisture limitations on decomposition. As our paradigm for soil organic carbon (SOC) preservation changes, so too should our representation of the underlying processes in soil models. Reactive transport models (RTMs) provide a framework capable of assessing the interactive influence of soil chemistry and transport processes on the accumulation and turnover of SOC. In this study, we present new developments in the isotopically enabled RTM “CrunchTope,” which is capable of explicitly tracking the three isotopes of carbon ( 12 C, 13 C, and 14 C) and their fractionation between multiple coexisting and interacting solid, liquid and gas phases. This modeling framework opens the door to new applications of depth-resolved RTMs models in application to SOC and deeper subsurface carbon reservoirs. Here, we demonstrate SOC accumulation and radiocarbon aging for long-timescale models of soil development in CrunchTope. Our goal is to assess advantages and limitations of such an approach and to identify the type and complexity of reaction networks that are required to adequately apply this model to SOC dynamics. We assess the behavior of this model relative to a high-resolution dataset of SOC content, stable isotope composition, and radiocarbon ages as well as physical and hydrologic data measured from a chronosequence of soils located near Santa Cruz, California. Starting from a previously published model using a simplified reaction network with a single class of carbon, we sequentially incorporate multiple C reservoirs subject to both reactivity and transport pathways. Our results indicate that multiple SOC pools with different mean ages of C do not inherently emerge as a result of including reactions which are conventionally expected to provide a diversity of transit times, i.e., sorption and complexation of SOC on mineral surfaces. Instead, transit times emerge as a result of the timescales of the reactions represented in the reaction network. For mineral associated C, the RTM framework imposes dynamic equilibrium with the fluid phase dissolved organic C, such that no distinction in radiocarbon ages is achieved between these pools. Aged C can be produced by including a solid-phase C reservoir, with a rate-limited solubilization coefficient. Aging of SOC in this way is more akin to selective preservation than to mineral protection and, while such a mechanism may be at play in many soils, mineral protection is thought to be at least as important. As such, our results indicate that additional parameterization is required to reproduce the heterogeneity of carbon transit times that result from organo-mineral interactions. These efforts show the promise of a modeling approach where the varied transit time of soil C emerges from the dynamic physical and hydrologic properties of the model rather than from the a priori assignment of operationally defined pools.

Geochimica et Cosmochimica Acta↗

USGS2020

Post-1978 tumescence at Long Valley Caldera, California: A geophysical perspective

Long Valley Caldera has been restless since at least 1978. Prominent symptoms of this unrest include earthquake swarms and tumescence (inflation) centered on the resurgent dome. Over the years, interpretations of physical processes underlying this unrest have varied considerably. Results from a collection of geophysical studies infer the presence and/or active intrusion of magma in the crust. Geologic evidence, however, does not support recent magmatic activity in the caldera, leading to an interpretation that the caldera volcanic system is moribund, and the current unrest is a result of second boiling (aqueous fluids released during crystallization of the rhyolitic magma that produced the Bishop Tuff). Here, we examine the collective constraints provided by geophysical studies over the past four decades. Although the current geophysical evidence does not conclusively discriminate between unrest driven by recent crustal magmatic intrusion versus second boiling, it does provide evidence that a large volume of partial melt persists within the mid- and lower crust. This implies that the Long Valley Caldera system as a whole is long-lived, and the magma reservoir remains at least partially molten. In the shallow crust, the possibility of small pockets of magma remains. In aggregate, the data suggest commonality with other large, long-lived silicic caldera systems, such as Yellowstone and Campi Flegrei. Although the possibility of eruption within Long Valley Caldera remains unlikely, the geophysical evidence argues that Long Valley has an active magmatic system at depth and we must retain the possibility of eruptive hazards.

California↗

USGS2013

Iron mineralogy and bioaccessibility of dust generated from soils as determined by reflectance spectroscopy and magnetic and chemical properties--Nellis Dunes recreational area, Nevada

Atmospheric mineral dust exerts many important effects on the Earth system, such as atmospheric temperatures, marine productivity, and melting of snow and ice. Mineral dust also can have detrimental effects on human health through respiration of very small particles and the leaching of metals in various organs. These effects can be better understood through characterization of the physical and chemical properties of dust, including certain iron oxide minerals, for their extraordinary radiative properties and possible effects on lung inflammation. Studies of dust from the Nellis Dunes recreation area near Las Vegas, Nevada, focus on characteristics of radiative properties (capacity of dust to absorb solar radiation), iron oxide mineral type and size, chemistry, and bioaccessibility of metals in fluids that simulate human gastric, lung, and phagolysosomal fluids. In samples of dust from the Nellis Dunes recreation area with median grain sizes of 2.4, 3.1, and 4.3 micrometers, the ferric oxide minerals goethite and hematite, at least some of it nanosized, were identified. In one sample, in vitro bioaccessibility experiments revealed high bioaccessibility of arsenic in all three biofluids and higher leachate concentration and bioaccessibility for copper, uranium, and vanadium in the simulated lung fluid than in the phagolysosomal fluid. The combination of methods used here to characterize mineral dust at the Nellis Dunes recreation area can be applied to global dust and broad issues of public health.

Nevada↗

USGS2006

Quantity-activity relationship of denitrifying bacteria and environmental scaling in streams of a forested watershed

The spatial variability of subreach denitrification rates in streams was evaluated with respect to controlling environmental conditions, molecular examination of denitrifying bacteria, and dimensional analysis. Denitrification activities ranged from 0 and 800 ng-N gsed-1 d-1 with large variations observed within short distances (<50 m) along stream reaches. A log-normal probability distribution described the range in denitrification activities and was used to define low (16% of the probability distributibn), medium (68%), and high (16%) denitrification potential groups. Denitrifying bacteria were quantified using a competitive polymerase chain reaction (cPCR) technique that amplified the nirK gene that encodes for nitrite reductase. Results showed a range of nirK quantities from 103 to 107 gene-copy-number gsed.-1 A nonparametric statistical test showed no significant difference in nirK quantifies among stream reaches, but revealed that samples with a high denitrification potential had significantly higher nirK quantities. Denitrification activity was positively correlated with nirK quantities with scatter in the data that can be attributed to varying environmental conditions along stream reaches. Dimensional analysis was used to evaluate denitrification activities according to environmental variables that describe fluid-flow properties, nitrate and organic material quantities, and dissolved oxygen flux. Buckingham's pi theorem was used to generate dimensionless groupings and field data were used to determine scaling parameters. The resulting expressions between dimensionless NO3- flux and dimensionless groupings of environmental variables showed consistent scaling, which indicates that the subreach variability in denitrification rates can be predicted by the controlling physical, chemical, and microbiological conditions. Copyright 2006 by the American Geophysical Union.

Journal of Geophysical Research G: Biogeosciences↗

USGS2017

Poroelastic properties of the Arbuckle Group in Oklahoma derived from well fluid level response to the 3 September 2016 M w 5.8 Pawnee and 7 November 2016 M w 5.0 Cushing earthquakes

The Arbuckle Group (Arbuckle) is a basal sedimentary unit that is the primary target for saltwater disposal in Oklahoma. Thus, the reservoir characteristics of the Arbuckle, including how the poroelastic properties change laterally and over time are of significant interest. We report observations of fluid level changes in two monitoring wells in response to the 3 September 2016 M w 5.8 Pawnee and the 7 November 2016 M w 5.0 Cushing earthquakes. We investigate the relationship between static strain resulting from these events and the fluid level changes observed in the wells. We model the fluid level response by estimating static strains from a set of earthquake source parameters and spatiotemporal poroelastic properties of the Arbuckle in the neighborhood of the monitoring wells. Results suggest that both the direction of the observed fluid level step and the amplitude can be predicted from the computed volumetric strain change and a reasonable set of poroelastic parameters. Modeling results indicate that poroelastic parameters differ at the time of the Pawnee and Cushing earthquakes, with a moderately higher Skempton’s coefficient required to fit the response to the Cushing earthquake. This may indicate that dynamic shaking resulted in physical alteration of the Arbuckle at distances up to ∼50 km from the Pawnee earthquake.

Oklahoma↗

USGS2011

Detecting aseismic strain transients from seismicity data

Aseismic deformation transients such as fluid flow, magma migration, and slow slip can trigger changes in seismicity rate. We present a method that can detect these seismicity rate variations and utilize these anomalies to constrain the underlying variations in stressing rate. Because ordinary aftershock sequences often obscure changes in the background seismicity caused by aseismic processes, we combine the stochastic Epidemic Type Aftershock Sequence model that describes aftershock sequences well and the physically based rate‐ and state‐dependent friction seismicity model into a single seismicity rate model that models both aftershock activity and changes in background seismicity rate. We implement this model into a data assimilation algorithm that inverts seismicity catalogs to estimate space‐time variations in stressing rate. We evaluate the method using a synthetic catalog, and then apply it to a catalog of M ≥ 1.5 events that occurred in the Salton Trough from 1990 to 2009. We validate our stressing rate estimates by comparing them to estimates from a geodetically derived slip model for a large creep event on the Obsidian Buttes fault. The results demonstrate that our approach can identify large aseismic deformation transients in a multidecade long earthquake catalog and roughly constrain the absolute magnitude of the stressing rate transients. Our method can therefore provide a way to detect aseismic transients in regions where geodetic resolution in space or time is poor.

Journal of Geophysical Research B: Solid Earth↗

USGS2022

Science mission requirements for a globally ranging, riserless drilling vessel for U.S. Scientific Ocean Drilling

Through the collection and analysis of shallow and deep subseafloor sediments, rocks, fluids, and life, scientific ocean drilling has enriched our understanding of the complex Earth system. Among other achievements, scientific ocean drilling has documented the history of Earth’s climate, the waxing and waning of polar ice sheets, the past changes in ocean and atmospheric circulation, the existence and function of microbial life in the subseafloor, the compositional variations in Earth’s crust and underlying mantle, and the physical and chemical processes acting at subduction zones, including those associated with tsunamigenic earthquakes. Over the decades, more than 12,000 articles that depend on analyses of scientific ocean drilling samples and geophysical data have been published, many detailing breakthrough contributions to global knowledge about the Earth system. Approximately 45% of these publications were led by U.S.-affiliated authors (International Ocean Discovery Program Publication Services, 2021). Since the mid-1980s, the workhorse of this multidisciplinary, international research effort has been the riserless D/V JOIDES Resolution, operated by Texas A&M University with funding from the U.S. National Science Foundation (NSF). D/V JOIDES Resolution has conducted the vast majority of scientific ocean drilling expeditions and collected most of the scientific cores over that period, including 82% of the expeditions and 93% of the cores in the last decade alone, despite being one of three platforms that is operated within the International Ocean Discovery Program. However, D/V JOIDES Resolution is approaching the end of its useful life. With a strong commitment to continue scientific ocean drilling beyond the end of the current phase, the community developed a document outlining the research frontiers that should be pursued. Exploring Earth by Scientific Ocean Drilling: 2050 Science Framework (Koppers and Coggon, 2020) describes seven scientific strategic objectives that focus on understanding interconnections within the Earth system and five flagship initiatives that integrate these objectives into long-term research efforts that address issues facing society. Additional elements in the 2050 Science Framework, including STEM education, workforce development, technology development, and innovative applications of data analytics, will advance the goals of scientific ocean drilling. Addressing the 2050 Science Framework also requires building partnerships with allied U.S. and international science programs and strengthening existing ones. To implement a significant portion of the 2050 Science Framework, the U.S. scientific community seeks to lease or acquire a newly built, globally ranging, state-of-the art, riserless drilling vessel. The many and varied technical and human resources requirements for successful accomplishment of scientific and educational goals summarized in this document and described in detail in the 2050 Science Framework require broad community input and careful consideration. Following receipt of NSF’s formal Request for Assistance to the United States Science Support Program (USSSP), the U.S. scientific ocean drilling community conducted a one-year exercise to identify its national scientific needs and priorities in order to determine the Science Mission Requirements (SMRs) presented here. This community effort included: (1) a U.S. community-wide survey to identify the specific operational and technical capabilities critical to addressing science in the 2050 Science Framework; (2) a series of online workshops focusing on critical capabilities identified by the survey; and (3) a large in-person workshop to synthesize the results of the survey and the virtual workshops (Appendix 1). The approach was designed to reach as many participants as possible. Overall, 278 survey responses were received from U.S. community members, representing 104 unique institutions from 39 states and the District of Columbia, and 137 unique individuals participated in the workshops (Appendix 2). The results of this effort comprise two classes of SMRs: Foundational Science Mission Requirements and Primary Science Mission Requirements. Foundational SMRs define minimum criteria for a new riserless drilling vessel that can address significant portions of the 2050 Science Framework. Primary SMRs build upon the Foundational SMRs and will create more robust science opportunities and data collection capabilities, will increase progress in addressing the 2050 Science Framework objectives, and will provide more real-time ship-to-shore interaction to improve science productivity, engagement, and outreach. Modern safety and environmental standards, including meeting standards to access protected waters such as exclusive economic zones, extended continental shelves, or high latitudes, while being cognizant of the vessel’s environmental footprint. Safe and efficient operations in global locations and in water depths from 70 m to 6000+ m, with total drill string length of at least 7000 m. High-quality core and data collection from a range of key subseafloor environments. Advanced heave compensation, dynamic positioning, and drill pipe stability. Modern mud and cement/casing systems. Critical onboard measurements for safety, operational decision-making, documentation of ephemeral properties, mission-specific science, and long-term science goals that extend beyond a single expedition. Designated and appropriate space for sample and data preservation. Highly skilled onboard personnel, including technical staff for curation and core handling; support for safety, time-sensitive, and critical shipboard measurements; computer support; equipment and instrument repair; application support; and data assurance. Primary Science Mission Requirements include: Flexible shipboard space for laboratories and on deck to ensure safe, successful implementation of diverse science objectives and operations. Minimizing contamination of recovered samples. Over-the-side capabilities for science-supporting technology (e.g., remotely operated vehicles, water- column sampling, sediment-water interface sampling). Downhole logging and measurements. Expanded borehole observatory capabilities. Reliable and consistent ship-to-shore communications. NSF’s investment in a new globally ranging, riserless drilling vessel will have a powerful economic multiplier effect, including the infusion of additional science support funds in the United States for training and research, the development of new technologies and tools, and the associated scientific and technical workforce development. The skills and knowledge gained through scientific ocean drilling are translatable to careers in fields such as sustainable energy development (e.g., geothermal and offshore wind), carbon sequestration, data management and cyberinfrastructure, biotechnology, communications, science education, policy, hazard mitigation, and environmental management. The United States is a leader in a well-established and internationally collaborative scientific ocean drilling community. A modern, globally ranging, riserless drilling vessel will allow the United States to expand its leadership position, address broad scientific questions that current capabilities preclude, and cultivate equitable international, multidisciplinary collaborations that will ensure scientific ocean drilling’s future success.

Report↗

USGS1959

Lithologic log and drilling information for the Marble exploration hole 3, U15 area, Nevada Test Site, Nye County, Nevada

The Marble exploration hole 3 is in the northern part of the Tippipah Spring NE 7-1/2 minute quadrangle at the north end of Yucca Valley (fig.1). The collar elevation of the hole is about 5,316 feet and has the approximate Nevada State coordinates of N. 903,093 and E. 674,870. The hole was drilled to determine the physical and chemical properties of the marble within a radius of 200 feet of a point 950 feet below the surface. The exploration hole is 978 feet deep and was drilled from June 12 to July 8, 1959, by Minerals Engineering Co. of Grand Junction, Colorado, using conventional NX coring equiipment and a Portadrill 2,500 drill rig. Water-base bentonitic mud was used as the drilling fluid in the upper part of the hole. Clear water was used after circulation became unrestorable below 200 feet. The hole was cased from surface to 20 feet. The drilling rate during coring ranged from 2.0 to 19.3 minutes per foot and averaged 4.6 minutes per foot (table 1). The core recovered was excellent in quality and quantity. The average core recovery is 92.7 percent (table 2).

Nevada↗

USGS2024

Relatively stable pressure effects and time-increasing thermal contraction control Heber geothermal field deformation

Due to geological complexities and observational gaps, it is challenging to identify the governing physical processes of geothermal field deformation including ground subsidence and earthquakes. In the west and east regions of the Heber Geothermal Field (HGF), decade-long subsidence was occurring despite injection of heat-depleted brines, along with transient reversals between uplift and subsidence. These observed phenomena contradict current knowledge that injection leads to surface uplift. Here we show that high-yield production wells at the HGF center siphon fluid from surrounding regions, which can cause subsidence at low-rate injection locations. Moreover, the thermal contraction effect by cooling increases with time and eventually overwhelms the pressure effects of pressure fluctuation and poroelastic responses, which keep relatively stable during geothermal operations. The observed subsidence anomalies result from the siphoning effect and thermal contraction. We further demonstrate that thermal contraction dominates long-term trends of surface displacement and seismicity growth, while pressure effects drive near-instantaneous changes.

California↗

USGS1988

Facies composition calculated from the sonic, neutron, and density log suite, upper part of the Minnelusa Formation, Powder River basin, Wyoming

Sandstones and dolomites of the Permian upper part of the Minnelusa Formation are treated here as four-component systems consisting of fluid-filled pore space, quartz, dolomite, and anhydrite. Response equations of sonic, neutron, and density logs form a system of four simultaneous equations. With four equations and four unknowns, the composition of upper Minnelusa facies is defined by the three-log suite and can be calculated by solving a 4 ?? 4 matrix. Such calculations of facies composition help in establishing subsurface correlations and yield information on the diagenesis and physical character of upper Minnelusa sandstones and dolomites. Applications of composition calculations are illustrated by examples drawn from the area of the West Mellott field (T52N, R68W), where the upper Minnelusa is at depths of about 7000 ft (2100m). -from Authors

Mountain Geologist↗

USGS2023

Simulation of regional groundwater flow and advective transport of per- and polyfluoroalkyl substances, Joint Base McGuire-Dix-Lakehurst and vicinity, New Jersey, 2018

A three-dimensional numerical model of groundwater flow was developed and calibrated for the unconsolidated New Jersey Coastal Plain aquifers underlying Joint Base McGuire-Dix-Lakehurst (JBMDL) and vicinity, New Jersey, to evaluate groundwater flow pathways of per- and polyfluoroalkyl substances (PFAS) contamination associated with use of aqueous film forming foam (AFFF) at the base. The regional subsurface flow model spans an area of approximately 518 square miles around JBMDL and is based on a previously developed hydrogeologic framework of the area. Steady-state flow in the unconsolidated aquifers was simulated using the MODFLOW 6 groundwater flow model, which is able to account for hydrostratigraphic pinchouts and discontinuities in the Coastal Plain aquifers underlying JBMDL. To account for local patterns of fluid flow driving advective subsurface migration of PFAS, the grid was refined using quadtree meshes spanning 21 areas where historical AFFF use was identified, five off-site reconnaissance areas identified by AFCEC as areas in which the occurrence of PFAS is most likely to pose a potential danger to local drinking water supplies, and along streams that behave as drains in the base-flow-dominated Coastal Plain. Following grid refinement, four physical processes known to govern subsurface flow were introduced to the model. These included effective precipitation recharge, discharge to streams and stream-connected wetlands, regional inflows and outflows along the model bottom, and withdrawals from wells, each of which were incorporated into the model as either external or internal boundary conditions. To account for effective precipitation recharge, a specified-flow boundary was assigned along the top of the model. Similarly, regional flows predicted using the modified U.S Geological Survey’s New Jersey Coastal Plain Regional Aquifer System Analysis model were treated as specified-flow boundary conditions along the bottom of the model. Base-flow losses were treated as drains along streams delineated using a 10-foot LiDAR dataset. Drains were also assigned to cells falling within stream-connected National Hydrologic Database wetlands. Finally, well-pumpage data mined from the New Jersey Water Transfer database were added to the model to account for extraction of groundwater through pumping from industrial-supply and drinking-water-supply wells. Along model edges established at groundwater divides, where the net flux of water across the boundary is equal to zero, natural no-flow boundary conditions were imposed. The refined flow model was calibrated using the parameter-estimation (PEST) program, which adjusts model parameters by performing a gradient search over the sum-of-squared-error objective function until the parameter set that produces simulated water levels and base flows most closely matches 544 water levels and 20 estimated base flows and closely adheres to initial parameter estimates. Based on the analysis of calibration residuals, the model did not appear to be affected by significant model structural error. The MODPATH particle-tracking algorithm was used to estimate advective transport paths of PFAS in the vicinity of JBMDL. Forward tracking was used to determine paths of PFAS away from AFFF source areas to streams, wetlands, pumping wells, and geographic areas that PFAS may contaminate. Additionally, reverse tracking was used to determine particle pathlines away from off-site PFAS reconnaissance areas, or areas within which all sources of PFAS might be advectively transported into subsurface drinking-water supplies, to locations at land surface that may indicate a source of PFAS. The coupled and calibrated groundwater flow and particle-tracking transport model provide valuable tools for predicting the relative extent of PFAS contamination from onsite legacy source areas. The calibrated model also provides measures of water-level and base-flow observation influence that can help guide future data-collection efforts related to groundwater and surface water sampling for PFAS.

New Jersey↗

USGS2003

Modeling radium and radon transport through soil and vegetation

A one-dimensional flow and transport model was developed to describe the movement of two fluid phases, gas and water, within a porous medium and the transport of 226Ra and 222Rn within and between these two phases. Included in this model is the vegetative uptake of water and aqueous 226Ra and 222Rn that can be extracted from the soil via the transpiration stream. The mathematical model is formulated through a set of phase balance equations and a set of species balance equations. Mass exchange, sink terms and the dependence of physical properties upon phase composition couple the two sets of equations. Numerical solution of each set, with iteration between the sets, is carried out leading to a set-iterative compositional model. The Petrov-Galerkin finite element approach is used to allow for upstream weighting if required for a given simulation. Mass lumping improves solution convergence and stability behavior. The resulting numerical model was applied to four problems and was found to produce accurate, mass conservative solutions when compared to published experimental and numerical results and theoretical column experiments. Preliminary results suggest that the model can be used as an investigative tool to determine the feasibility of phytoremediating radium and radon-contaminated soil. ?? 2003 Elsevier Science B.V. All rights reserved.

Journal of Contaminant Hydrology↗

USGS2012

Isotropic, anisotropic, and borehole washout analyses in Gulf of Mexico Gas Hydrate Joint Industry Project Leg II, Alaminos Canyon well 21-A

Through the use of three-dimensional seismic amplitude mapping, several gas hydrate prospects were identified in the Alaminos Canyon area of the Gulf of Mexico. Two of the prospects were drilled as part of the Gulf of Mexico Gas Hydrate Joint Industry Program Leg II in May 2009, and a suite of logging-while-drilling logs was acquired at each well site. Logging-while-drilling logs at the Alaminos Canyon 21–A site indicate that resistivities of approximately 2 ohm-meter and P-wave velocities of approximately 1.9 kilometers per second were measured in a possible gas-hydrate-bearing target sand interval between 540 and 632 feet below the sea floor. These values are slightly elevated relative to those measured in the hydrate-free sediment surrounding the sands. The initial well log analysis is inconclusive in determining the presence of gas hydrate in the logged sand interval, mainly because large washouts in the target interval degraded well log measurements. To assess gas-hydrate saturations, a method of compensating for the effect of washouts on the resistivity and acoustic velocities is required. To meet this need, a method is presented that models the washed-out portion of the borehole as a vertical layer filled with seawater (drilling fluid). Owing to the anisotropic nature of this geometry, the apparent anisotropic resistivities and velocities caused by the vertical layer are used to correct measured log values. By incorporating the conventional marine seismic data into the well log analysis of the washout-corrected well logs, the gas-hydrate saturation at well site AC21–A was estimated to be in the range of 13 percent. Because gas hydrates in the vertical fractures were observed, anisotropic rock physics models were also applied to estimate gas-hydrate saturations.

Scientific Investigations Report↗

USGS2021

Correlation of porosity variations and rheological transitions on the southern Cascadia megathrust

The unknown onshore extent of megathrust earthquake rupture in the Cascadia subduction zone represents a key uncertainty in earthquake hazard for the Pacific Northwest that is governed by the physical state and mechanical properties of the plate interface. The Cascadia plate interface is segmented into an interseismically locked zone located primarily offshore that is expected to rupture in large earthquakes, a region of aseismic slow slip at greater depth, and an intervening transition zone of uncertain rupture potential. Here we image the evolution of the ratio of seismic compressional to shear wave velocities from the locked zone to the transition zone, which is related to changes in fluid content of the plate boundary zone, using a dense onshore–offshore seismic dataset from southernmost Cascadia. The locked zone shows evidence of high fluid content implying a high porosity, yet the downdip transition zone shows an order of magnitude lower porosity. This strong variation is consistent with models that contain a ductile region between the earthquake rupture and slow slip zones that would inhibit onshore propagation of future large earthquake ruptures and hence reduce seismic hazard.

California↗

USGS2004

Estimating tectonic history through basin simulation-enhanced seismic inversion: Geoinformatics for sedimentary basins

A data assimilation approach is demonstrated whereby seismic inversion is both automated and enhanced using a comprehensive numerical sedimentary basin simulator to study the physics and chemistry of sedimentary basin processes in response to geothermal gradient in much greater detail than previously attempted. The approach not only reduces costs by integrating the basin analysis and seismic inversion activities to understand the sedimentary basin evolution with respect to geodynamic parameters-but the technique also has the potential for serving as a geoinfomatics platform for understanding various physical and chemical processes operating at different scales within a sedimentary basin. Tectonic history has a first-order effect on the physical and chemical processes that govern the evolution of sedimentary basins. We demonstrate how such tectonic parameters may be estimated by minimizing the difference between observed seismic reflection data and synthetic ones constructed from the output of a reaction, transport, mechanical (RTM) basin model. We demonstrate the method by reconstructing the geothermal gradient. As thermal history strongly affects the rate of RTM processes operating in a sedimentary basin, variations in geothermal gradient history alter the present-day fluid pressure, effective stress, porosity, fracture statistics and hydrocarbon distribution. All these properties, in turn, affect the mechanical wave velocity and sediment density profiles for a sedimentary basin. The present-day state of the sedimentary basin is imaged by reflection seismology data to a high degree of resolution, but it does not give any indication of the processes that contributed to the evolution of the basin or causes for heterogeneities within the basin that are being imaged. Using texture and fluid properties predicted by our Basin RTM simulator, we generate synthetic seismograms. Linear correlation using power spectra as an error measure and an efficient quadratic optimization technique are found to be most effective in determining the optimal value of the tectonic parameters. Preliminary 1-D studies indicate that one can determine the geothermal gradient even in the presence of observation and numerical uncertainties. The algorithm succeeds even when the synthetic data has detailed information only in a limited depth interval and has a different dominant frequency in the synthetic and observed seismograms. The methodology presented here even works when the basin input data contains only 75 per cent of the stratigraphic layering information compared with the actual basin in a limited depth interval.

Geophysical Journal International↗

USGS1971

Sulfur isotope study of the "B" limestone and Galena fissure ore deposits of the U.S. mine, Bingham mining district, Utah

The delta S 34 values for 261 sulfide concentrates from the "B" limestone replacement and Galena fissure deposits of the U. S. mine range from +3.8 to --8.0 permil; the mean is +0.56 permil. The data indicate that (1) sulfides of the "B" limestone ore deposits are depleted in S 34 by 0.4 to 0.7 permil relative to those of the Galena fissure ore deposits; (2) sulfides of both deposits exhibit a primary fractionation trend characterized by increasing S 34 depletion in the sequence pyrite, sphalerite, tetrahedrite, and galena; (3) delta values for coexisting sulfide pairs of the "B" limestone deposit increase with increasing altitude; (4) sulfides of both deposits are increasingly depleted in S 34 with increasing altitude; (5) the paragenetic order of sulfide deposition is accompanied by an apparent depletion of S 34 that is independent of mineral species; and (6) pyrite disseminated in wall rocks is depleted in S 34 relative to pyrite from adjacent ore deposits. The similarity of delta S 34 values and isotopic trends to those of the central porphyry-type deposit at Bingham (Field, 1966) suggests that the hydrothermal deposits of the district were formed by fluids that originated from a common source during one episode of sequential mineralization. Gross isotopic differences between the deposits, consistent differences between coexisting sulfides, and systematic variations of delta values are attributed to temperature effects imposed upon sulfide exchange equilibria; isotopic temperatures suggest a lateral gradient between the "B" limestone and adjacent Galena fissure deposits and a possible vertical gradient within the "B" limestone deposit. The vertical zonation of delta S 34 values and trends related to pyrite physical occurrence and sulfide paragenesis are provisionally attributed to a pH-Eh control. Although the apparent trends are imperfectly resolved because of textural complexities, the marked depletion of S 34 in pyrite disseminated in country rocks warrants additional study as a potential exploration method.

Utah↗

USGS2016

Dynamics of permeability evolution in stimulated geothermal reservoirs

Spatially and temporally evolving permeability fields are fundamentally associated with the operation of enhanced geothermal systems. This chapter explores the resulting magnitude and patterns of permeability alteration as well as the coupled physical processes that control the evolution of permeability during shear stimulation and long-term evolution of a geothermal reservoir. It also explores mechanisms involved in the enhancement of fracture permeability, targeting injection pressures that encourage self-propping shear stimulation alongside elastic pressure and thermal dilatation of fracture sets. Simulation of a short-term, high-injection-rate enhanced geothermal system stimulation explored the importance of hydraulic versus thermal effects and the impact of a temperature differential between fluid in the fractures and the adjoining rock matrix. The effects of variations in fracture spacing on the evolution of permeability is at least as important as the magnitude of initial permeability, and quantifying the driving mechanisms is critical to understanding reservoir response.

Book chapter↗

USGS1975

Flows of impact melt at lunar crater

Lavalike materials that were emplaced in a fluid state occur in and around lunar impact craters whose diameters range from 3 km to more than 200 km and whose ages span a time interval of at least 3.5 b.y. Evidence of fluid emplacement includes flow lobes and leveed channels, a veneer mantling rough crater topography, level-surfaced pools, and complex contraction fissuring. The distribution of the lavalike deposits conforms to asymmetries of other ejecta from the same craters, and the material is concentrated downrange to distances as great as a crater radius. The character and distribution of the lavalike materials support the idea that they formed by impact melting rather than by volcanism. Returned samples indicate that materials with appropriate physical characteristics are generated by partial melting of feldspathic rocks by impact. The geologic evidence at lunar craters suggests that there is more melt rock in and near the craters than is predicted by experiment and theory.

Journal of Research of the U.S. Geological Survey↗