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1,661 records · Page 58Linked to original sources
USGS2025

Linking permafrost to the abundance, biomass, and energy density of fish in Arctic headwater streams

Permafrost thaw alters groundwater flow, river hydrology, stream-catchment interactions, and the availability of carbon and nutrients in headwater streams. The impact of permafrost on watershed hydrology and biogeochemistry of headwater streams has been demonstrated, but there is little understanding of how permafrost influences fish in these ecosystems. We examined relations among permafrost characteristics, the resulting changes in water temperature, stream hydrology (e.g., discharge flashiness), and macroinvertebrates, with the abundance, biomass, and energy density of juvenile Dolly Varden ( Salvelinus malma ) and Arctic Grayling ( Thymallus arcticus ) across 10 headwater streams in northwestern Alaska. Macroinvertebrate density was driven by concentrations of dissolved carbon and nutrients supporting stream food webs. Dolly Varden abundance was primarily related to water temperature with fewer fish in warmer streams, whereas Dolly Varden energy density decreased with the flashiness of the headwater streams. Dolly Varden biomass was related to both temperature and bottom-up food web effects. The energy density of Arctic Grayling decreased with warmer temperatures and discharge flashiness. These relations demonstrate the importance of terrestrial–aquatic connections in permafrost landscapes and indicate the complexity of landscape effects on fish. Because permafrost thaw is one of the most impactful changes occurring as the Arctic warms, an improved understanding of how stream temperature, hydrology, and bottom-up food web processes influence fish populations can aid forecasting of future conditions across the Arctic.

Alaska↗
USGS1990

Large springs in the Valley and Ridge Province in Tennessee

Approximately 2,700 miscellaneous discharge measurements for 171 large springs in 28 counties of East Tennessee, predominantly within the Valley and Ridge physiographic province, were analyzed statistically and results tabulated to summarize data useful to the Appalachian Valleys-Piedmont Regional Aquifer System Analysis study. The number of measurements at each spring ranged from 1 to 65. Information from each spring includes station numbers, latitude, longitude, spring name and where data are sufficient, an estimate of the mean discharge and the discharge exceeded by 75%, 50%, and 25% of the miscellaneous measurements. Data are referenced to locations on a 1:1,000 ,000-scale map. The highest mean spring discharge was 32.2 cu ft/sec (14,5000 gallons/min).

Tennessee↗
USGS2025

Performance analysis of oil recovery and CO2 retention in a greenfield residual oil zone: CO2-EOR in Tall Cotton Field (Permian Basin, West Texas, USA)

Residual oil zones (ROZs) can offer significant oil resources via enhanced oil recovery (EOR) as well as subsurface carbon dioxide (CO 2 ) retention during injection. If injected CO 2 is anthropogenic, the ROZs can offer a substantial geologic storage potential. The ROZs below the oil/water contact (OWC) of main pay zones (MPZ) in conventional reservoirs or brownfields, are more commonly developed for CO 2 injection and oil production and reported in the literature. However, CO 2 -EOR in greenfield ROZs, reservoirs without a MPZ present, have rarely been developed for CO 2 -EOR operation. The Tall Cotton Field of West Texas, Permian Basin, which started production in 2015 (Phase 1) and expanded in 2017 (Phase 2) from the San Andres Limestone, is one of the first examples of greenfield ROZs developed for EOR by injecting CO 2 . This paper analyses EOR and CO 2 retention performance of Tall Cotton Field using allocated injection and production data from inverted 5-spot well patterns of Phase-1 and -2 developments. Production and injection data allocated to each of the 28 identified patterns (nine 20-acre patterns for Phase-1, three 20-acre and sixteen 10-acre patterns for Phase-2) were analyzed for historical and forecasted oil recovery using ratio-trend decline analysis, and for CO 2 retention performance of the patterns. The allocated data were further used to calculate injected reservoir pore volume and void replacement ratios (VRR) for the analysis period. Quantitative results indicated that oil recovery factors of the 5-spot patterns varied between 4–10 %, and 5–30 % between the end of injection and the forecast periods, respectively. Storage of CO 2 , on the other hand, increased to a mean value of ∼7130 MMscf per pattern in Phase-1 and to a mean storage of 3700 MMscf per pattern in Phase-2 until the end of injection, followed by a decline after the end of injection and into the forecast period. Resulting CO 2 utilization factors ∼6–50 Mscf/bbl were estimated at the end of injection. Overall, presented results suggested that developing greenfield ROZs for CO 2 -EOR can be as promising as brownfield ROZs and mature MPZs for EOR and underground storage of injected CO 2 . For Tall Cotton Field, results suggest that Phase-2 patterns generally outperformed Phase-1 for oil recovery factors, while Phase-1 performed better in CO 2 retention performance metrics. This is the first study in the literature that reports a detailed CO 2 -EOR performance analysis of a greenfield ROZ in the Permian Basin, which can potentially allow for comparison with MPZs and brownfield ROZs.

Texas↗
USGS2024

Temporal, spatial, and chemical evolution of Quaternary high-silica rhyolites in the Mineral Mountains, Utah

The Mineral Mountains in southwestern Utah are a structurally controlled core complex at the confluence of the Colorado Plateau and the Basin and Range physiographic provinces. Aside from hosting Utah’s largest batholith, the Mineral Mountains host some of the State’s youngest high-silica rhyolites, which have been linked to a magma source that is presently being utilized as an enhanced geothermal system. The high-silica rhyolites take the form of effusive lavas and domes, and explosive products are rare. Previous K-Ar dating of these Pleistocene rhyolites placed eruptions between about 790 and 500 kilo-annum (ka) with contemporaneous basalts erupting in the valley to the east of the Mineral Mountains. Large uncertainties on these ages obscured the tempo of eruptions and thus hindered attempts to constrain the timescales of the petrogenetic processes that produced the rhyolites. In this study, we build on previous studies conducted in the 1970s and 1980s by using new geochronologic and geochemical data to investigate the temporal and spatial evolution of the youngest phase of volcanism in the Mineral Mountains. We identify two major eruptive periods, from approximately 850 to 750 ka and from approximately 590 to 480 ka. The older phase is characterized by the eruption of several basaltic lavas, two obsidian flows, and a series of coalescing porphyritic rhyolite domes. The younger phase included the eruption of six evolved high-silica rhyolite domes and one pyroclastic deposit, followed by the eruption of trachyandesite in the adjacent valley to the east. Whole-rock geochemical data indicate that the rhyolites can be divided into three chemical groups, with more evolved compositions erupting through time. The youngest rhyolites along the range crest have the lowest total iron and TiO 2 concentrations and the highest incompatible element concentrations, indicative of increasing differentiation with time and elevation. Improved precision on the eruption ages indicates a recurrence interval of approximately 20 thousand years. The eruptive flux for both periods of rhyolitic volcanism is about 0.01 cubic kilometers per thousand years, which is less than the magma resurgence flux rates for syn-caldera and post-caldera eruptions of the Valles Caldera and Yellowstone Caldera volcanic systems. Collectively, these geochemical, geochronological, and volumetric data may facilitate a better understanding of heat flux and the longevity of magmatic sources related to geothermal resources in similar small-volume, silicic systems.

Utah↗
USGS2024

Radiogenic strontium- and uranium-isotope tracers of water-rock interactions and hydrothermal flow in the Upper Geyser Basin, Yellowstone Plateau Volcanic Field, USA

Natural radiogenic isotopes (primarily 87 Sr/ 86 Sr) from hot springs in the Upper Geyser Basin of the Yellowstone Plateau volcanic field and associated rocks were used to evaluate groundwater flow patterns, water-rock reactions, and the extent of mixing between various groundwater sources. Thermal waters have very low uranium concentrations and 234 U/ 238 U activity ratios near 1.0, which limit their utility as tracers in this reducing setting. Thermal waters have higher Sr concentrations (<22 ng/g) and a wide range of 87 Sr/ 86 Sr values that vary both temporally at individual discharge sites and between adjacent springs, indicating that conduits tap different subsurface reservoirs to varying degrees. Sr from local rhyolites have 87 Sr/ 86 Sr compositions that bound the range of values observed in groundwater throughout the basin. Non-boiling springs on the west flank of the basin discharge water with low 87 Sr/ 86 Sr consistent with flow through young volcanic rocks exposed at the surface. Boiling springs in the central basin have higher 87 Sr/ 86 Sr values reflecting interactions with older, more radiogenic volcanic rocks. Variability in upwelling thermal waters requires mixing with a low 87 Sr/ 86 Sr component derived from young lava or glacial sediments, or more likely, from deeper sources of hot groundwater circulating through buried Lava Creek Tuff having intermediate 87 Sr/ 86 Sr. Isotope data constrain basin-wide output of thermal water to 110–140 kg·s −1 . Results underscore the utility of radiogenic Sr isotopes as valuable tracers of hydrothermal flow patterns and improve the understanding of temperature-dependent water-rock reactions in one of the largest continental hydrothermal systems on Earth.

Wyoming↗
USGS2026

Computing flow-field distortion coefficients from well-construction and formation properties

Direct measurements of groundwater velocity made with borehole flowmeters in screened wells must be compensated for the effects of flow-field distortion (also known as borehole acceleration). A theoretical equation developed by Drost et al. (1968) and simple inputs describing hydraulic properties of well construction and geologic formation were programmed into an Excel workbook to facilitate computation by groundwater-flowmeter users. Tables describing the physical and hydraulic properties for well constructions and gravel pack media are provided with an example to facilitate use of the workbook. Groundwater flowlines converge or diverge as they pass from a geologic formation, through a gravel pack and well screen. The extent of flowline convergence or divergence and the value of the flow-field distortion coefficient is related to the relative changes in hydraulic conductivity of the well screen, gravel pack, and geologic formation. Convergence or divergence is accompanied by acceleration or deceleration of groundwater. Direct measurements of groundwater velocity at the center of the monitoring well can be adjusted to provide a more accurate estimate of velocity in the formation by applying a correction for flow-field distortion. Variables required to compute the flow-field distortion coefficient include the hydraulic conductivity of the gravel pack, well screen, and the geologic formation surrounding the well screen; the borehole radius, and the inside radius and outside radius of the well screen.

Groundwater↗
USGS2026

Streamflow, water quality, and constituent loads and yields, Scituate Reservoir drainage area, Rhode Island, water year 2023

As part of a long-term cooperative program to monitor water quality within the Scituate Reservoir drainage area, the U.S. Geological Survey, in cooperation with Providence Water (formerly the Providence Water Supply Board), collected streamflow and water-quality data in tributaries to the Scituate Reservoir, Rhode Island. Streamflow and concentrations of chloride and sodium estimated from records of specific conductance for 16 tributaries were used to calculate loads of chloride and sodium during water year 2023 (October 1, 2022, through September 30, 2023). Water-quality samples were collected by Providence Water at 38 sampling stations on tributaries to the Scituate Reservoir during water year 2023. These water-quality data are summarized by using values of central tendency and are used, in combination with measured (or estimated) streamflows, to calculate loads and yields of selected water-quality constituents for water year 2023. Annual mean streamflows for monitoring stations in this study ranged from 0.47 to 34.4 cubic feet per second during water year 2023. At the 16 continuous-record streamgages, tributaries transported about 3,000 metric tons of chloride and 1,900 metric tons of sodium to the Scituate Reservoir; annual chloride yields for the tributaries ranged from 19 to 200 metric tons per square mile, and annual sodium yields ranged from 13 to 120 metric tons per square mile. At the stations where water-quality samples were collected by Providence Water, the medians of the median daily loads were 65,000 million colony forming units per day for coliform bacteria, 870 million colony forming units per day for Escherichia coli , 200 kilograms per day for chloride, 8.2 grams per day as nitrogen for nitrite, 520 grams per day as nitrogen for nitrate, and 300 grams per day as orthophosphate for phosphate. The medians of the median yields were 25,000 million colony forming units per day per square mile for coliform bacteria, 600 million colony forming units per day per square mile for Escherichia coli , 65 kilograms per day per square mile for chloride, 4.6 grams per day per square mile as nitrogen for nitrite, 180 grams per day per square mile as nitrogen for nitrate, and 180 grams per day per square mile as orthophosphate for phosphate.

Rhode Island↗
USGS2025

Hydrogeology, water budget, and simulated groundwater availability in the Salt Fork Arkansas River and Chikaskia River alluvial aquifers, northern Oklahoma, 1980–2020

The 1973 Oklahoma Groundwater Law (Oklahoma Statute §82–1020.5) requires that the Oklahoma Water Resources Board conduct hydrologic investigations of the State’s aquifers to determine the maximum annual yield for each groundwater basin. The U.S. Geological Survey, in cooperation with the Oklahoma Water Resources Board, conducted an updated hydrologic investigation of the Salt Fork Arkansas River and Chikaskia River alluvial aquifers in northern Oklahoma for the study period spanning 1980–2020 and evaluated the simulated effects of potential groundwater withdrawals on groundwater flow and availability in the Salt Fork Arkansas River alluvial aquifer. A hydrogeologic framework and conceptual model were developed to guide the development of a numerical model. Three groundwater-availability scenarios were evaluated by using the calibrated numerical model, which was focused on the Salt Fork Arkansas River alluvial aquifer. These scenarios were used to (1) estimate equal-proportionate-share groundwater withdrawal rates, (2) quantify the potential effects of projected well withdrawals on groundwater storage over a 50-year period, and (3) simulate the potential effects of a hypothetical 10-year drought. The 20-, 40-, and 50-year equal-proportionate-share groundwater withdrawal rates for the Salt Fork Arkansas River alluvial aquifer under normal recharge conditions were about 0.63, 0.58, and 0.57 acre-foot per acre per year, respectively. Projected 50-year groundwater withdrawal scenarios were used to simulate the effects of modified well withdrawal rates. Because well withdrawals were less than 2 percent of the calibrated numerical-model water budget, changes to the well groundwater withdrawal rates had little effect on simulated Salt Fork Arkansas River base flows and groundwater storage in the Salt Fork Arkansas River alluvial aquifer. A hypothetical 10-year drought scenario was used to simulate the potential effects of a prolonged period of reduced recharge on groundwater storage. Groundwater storage at the end of the hypothetical drought period was 14.5 percent less than the groundwater storage of the calibrated numerical model without the simulated drought.

Oklahoma↗
USGS2010

Divisions of geologic time—Major chronostratigraphic and geochronologic units

Effective communication in the geosciences requires consistent uses of stratigraphic nomenclature, especially divisions of geologic time. A geologic time scale is composed of standard stratigraphic divisions based on rock sequences and is calibrated in years. Over the years, the development of new dating methods and the refinement of previous methods have stimulated revisions to geologic time scales. Advances in stratigraphy and geochronology require that any time scale be periodically updated. Therefore, Divisions of Geologic Time, which shows the major chronostratigraphic (position) and geochronologic (time) units, is intended to be a dynamic resource that will be modified to include accepted changes of unit names and boundary age estimates. This fact sheet is a modification of USGS Fact Sheet 2007-3015 by the U.S. Geological Survey Geologic Names Committee.

Fact Sheet↗
USGS2008

Geology and geochemistry of Jurassic plutonic rocks, Baboquivari Mountains, south-central Arizona

Among the plutons of the Jurassic magmatic arc segment in southern Arizona, northern Sonora, and southern California, two distinctive rock types dominate, occurring together in numerous mountain ranges: porphyritic, titanite-bearing hornblende-biotite granodiorite; and biotite leucogranite. These characteristic rocks are particularly well preserved and well exposed around Kitt Peak, in the Baboquivari Mountains, southern Arizona. The Middle to early Late Jurassic Kitt Peak Plutonic Suite (KPPS) comprises three units: Aguirre Peak Quartz Diorite (APQD;<170 Ma, >=165 Ma, U-Pb), chiefly hornblende mesodiorite; Kitt Peak Granodiorite (KPGD; 165 Ma), hornblende-biotite granodiorite and monzogranite; and Pavo Kug Granite (PKG; 159 Ma), equigranular biotite leucogranite. This range also hosts a fourth, regionally unusual, Jurassic plutonic unit: the Baboquivari Peak Perthite Granite, related to post-arc, Late Jurassic crustal extension. Binary variation diagrams, incompatible element patterns, and REE spectra indicate APQD and KPGD are consanguineous. APQD basaltic mesodiorite evidently approximates the parental magma for the APQD–KPGD series. More evolved rocks of this series evidently formed by combinations of fractional crystallization and mixing with or assimilation of crustal material. PKG is less directly related to APQD and KPGD than these two are to one another.

Arizona, Sonora↗
USGS2024

Recent advances in characterizing the crustal stress field and future applications of stress data: Perspectives from North America

The stress field controls patterns of crustal deformation, including which faults are likeliest to cause earthquakes or transmit fluids. Since the 1950s, maps of maximum horizontal stress ( S Hmax ) orientations have advanced dramatically, and the style of faulting (relative principal stress magnitudes) has recently been mapped in some regions as well. This perspectives paper summarizes developments in characterizing stress orientations and (relative) magnitudes, including new seismic and borehole methods, as well as progress in identifying the causes of stress variations. Despite these advances, adding far more spatiotemporal detail would allow geoscientists to address many of today's key challenges regarding natural hazards, energy development, and geodynamics. In particular, it is critically important to characterize stress heterogeneity at multiple scales while also recognizing the coherent variability of the stress field. The second part of the paper considers how more detailed stress datasets could prove essential to addressing some of the grand questions in geoscience, including deciphering the poorly understood feedbacks between crustal dynamics and surface processes, improving earthquake and eruption forecasts, and determining the origins and shared properties of plate boundaries.

Geological Society, London, Special Publications↗
USGS2025

Chemostratigraphy of the Cretaceous Hue Shale in Arctic Alaska: Exploring paleoceanographic controls on trace element enrichment, organic matter accumulation, and source-rock evolution

We document chemostratigraphy in an outcrop of late Albian to early Campanian (∼103–82 Ma) marine source rocks to better understand paleoenvironmental controls on trace element (TE) enrichment and organic matter accumulation in the distal Colville foreland basin of Arctic Alaska and how those drivers are linked to arc volcanism and successions of Cretaceous oceanographic and climatic biogeochemical events. This unique, 113-m-thick section of Cretaceous Hue Shale deposited during a series of previously undocumented Arctic Cretaceous oceanic anoxic events (Lease et al., 2024) is the only known exposure of thermally immature (0.48–0.52% R o , random vitrinite reflectance) Hue Shale in Arctic Alaska. Strata comprise mainly clay-rich mudstone with elevated total organic carbon (TOC) and hydrogen index values reaching 26.3 wt% (mean = 7.5 wt%) and 689 mg hydrocarbon (HC)/g TOC (mean = 385 mg HC/g TOC), respectively. Maceral composition consists predominantly of fluorescent amorphous organic matter, with abundant brightly fluorescent alginite, including Tasmanites , acritarchs, and Leiosphaeridia . Discrete layers of volcanic ash (preserved as bentonite) are present throughout the section and provide quantitative age control based on U–Pb dates. Chemostratigraphic trends are investigated to advance our understanding of local oceanographic conditions and controls on stratigraphic and temporal heterogeneity of Brookian source rocks. Concurrent sedimentary enrichment in Mo, U, V, Pb, and Cu across the Albian–Cenomanian boundary of the exposed basal gamma-ray zone, may reflect anoxic to euxinic benthic redox conditions favoring organic matter accumulation and preservation. Fluctuating degrees of anoxia-euxinia are inferred throughout the overlying Hue Shale succession, reflected by varying patterns of TE enrichment and TE–TOC covariation. Elevated C org /P molar ratios (>250) across most of the section, with several values exceeding 690, signify that enhanced biological productivity is sustained throughout deposition. Enhanced productivity, recorded by both C org /P and excess Ba, also parallels increases in source rock richness (elevated TOC and S 2 values) during the late Albian–early Cenomanian and late Cenomanian – Turonian. Enhanced productivity and variations in oceanic circulation/stratification likely both drove changes in benthic redox conditions that favored organic carbon accumulation and preservation. Increased continental arc volcanism (e.g., Okhotsk–Chukotka volcanic belt) and High Arctic Large Igneous Province magmatic eruptions throughout the Cretaceous, inferred to have influenced nutrient cycling and local aqueous nutrient availability, also have been invoked as potential drivers of organic carbon burial and source-rock development across the sedimentary sequence. Results presented here document the organic-rich and oil-prone source-rock quality of the Hue Shale in the distal part of the Colville foreland basin and bolster the potential for a Cretaceous petroleum system beneath the eastern North Slope.

Alaska↗
USGS2026

Ground-motion characterization for the 2025 U.S. National Seismic Hazard Model for Puerto Rico and the U.S. Virgin Islands

We develop the ground-motion characterization (GMC) for the 2025 U.S. National Seismic Hazard Model for Puerto Rico and the U.S. Virgin Islands (NSHM-PRVI) for earthquakes in active crustal, subduction interface, and subduction intraslab regimes. Using ground-motion models (GMMs) from the Next-Generation Attenuation (NGA)-West2 and NGA-Subduction projects, the GMC is parameterized by scaled-backbone models for median ground motions and by independent logic trees of aleatory variability. We introduce several novel GMC features into the U.S. NSHM: (1) use of regional ground-motion data for modeling median ground motions; (2) development of scaled-backbone models for median ground motions; and (3) development of independent logic trees of aleatory variability from variance components of GMMs and computed from multiple ground-motion datasets, and incorporating regional ground-motion data effects on variability. We compute probabilistic seismic hazard curves and maps to evaluate the contributions from the GMC components and for comparison with the 2003 GMC. Contributions of the GMC to epistemic uncertainty in seismic hazard are evaluated through spatial variations in epistemic uncertainty in hazard maps, comparisons between mean hazard curves and fractiles, as well as investigations of the contributions of logic-tree branches to hazard maps and curves. Comparisons between seismic hazard from the 2025 and 2003 GMCs allow examination of the changes in hazard curves and mapped values with 2% and 10% probabilities of exceedance in 50 years. The 2025 GMC exhibits modest changes in median predictions, relative to the 2003 GMC; overall, values of aleatory variability are higher, except at long periods ( ), resulting in changes to probabilistic ground motions at low probabilities of exceedance (<10% probability of exceedance in 50 years). Changes in hazard at 2% and 10% probabilities of exceedance in 50 years are also relatively modest (within 20%) at most sites, with the impacts from the 2025 GMC exhibiting minor reductions and increases at 0.2 and 1.0 s periods, respectively, relative to the 2003 GMC.

Puerto Rico, U.S. Virgin Islands↗
USGS2025

Observing northern high-latitude river systems to understand changes in a warming Arctic

Purpose of Review Streams and rivers are undergoing rapid change as the Arctic warms and thaws. We review recent observations in Arctic stream systems to identify ubiquitous changes and the most useful tools for observing change and exploring the underlying processes. Recent Findings Recent literature indicates increasingly significant trends in river hydrology and chemistry due to persistent warming in the Arctic and longer observational records for analysis. However, regional differences in the magnitude and direction of these trends persist. We also observe thresholds in ground thaw and surface–groundwater interactions that can impact river hydrology and chemistry. Summary Warming and thaw are occurring rapidly at high latitudes, resulting in increasing, yet variable responses in stream systems across regions and scales. These differences highlight the need for long-term records and an interdisciplinary approach to explain trends and predict future states. Stream systems respond to multiple landscape changes related to hydrology (changing precipitation and subsurface flow), geology (ground thaw dynamics), and ecology (vegetation change).

Current Climate Change Reports↗
USGS1995

Evaluation of ground-water flow and hydrologic budget for Lake Five-O, a seepage lake in northwestern Florida

Temporal and spatial distributions of ground-water inflow to, and leakage from Lake Five-O, a softwater, seepage lake in northwestern Florida, were evaluated using hydrologic data and simulation models of the shallow ground-water system adjacent to the lake. The simulation models indicate that ground-water inflow to the lake and leakage from the lake to the ground-water system are the dominant components in the total inflow (precipitation plus ground-water inflow) and total outflow (evaporation plus leakage) budgets of Lake Five-O. Simlulated ground-water inflow and leakage were approximately 4 and 5 times larger than precipitation inputs and evaporative losses, respectively, during calendar years 1989-90. Exchanges of water between Lake Five-O and the ground-water system were consistently larger than atmospheric-lake exchanges. A consistent pattern of shallow ground-water inflow and deep leakage was also evident throughout the study period. The mean time of travel from ground-water that discharges at Lake Five-O (time from recharge at the water table to discharge at the lake) was estimated to be within a range of 3 to 6 years. Flow-path evaluations indicated that the intermediate confining unit probably has a negligible influence on the geochemistry of ground-water inflow to Lake Five-O. The hydrologic budgets and flow-path evaluations provide critical information for developing geochemical budgets for Lake Five-O and for improving the understanding of the relative importance of various processes that regulate the acid-neutralizing capacity of softwater seepage lakes in Florida.

Florida↗
USGS2025

High frequency and region-scale simulations of large (Mw7+) earthquakes on the southern Whidbey Island fault, Washington, USA

We simulate ground shaking in western Washington State from hypothetical M w 7.0–7.5 earthquakes on the southern Whidbey Island fault (SWIF). Ground motions are modeled considering kinematic source distributions on a complex fault plane, a 3D seismic velocity model, and region‐specific soil velocity models. We run simulations with varying model resolutions, including regional‐scale simulations with a maximum‐modeled frequency of ∼1 Hz and local‐scale simulations with a maximum‐modeled frequency of ∼2.5 Hz. Additional local‐scale simulations are run considering high‐resolution surface topography. We explore how source parameters (i.e., magnitude, hypocenter location, and dip direction) and 3D velocity structure impact peak shaking intensity and its variability. In particular, we find that earthquakes on the SWIF would likely produce strong shaking throughout the populated Puget Lowland, including in the cities of Everett, Seattle, Bellevue, and Tacoma, Washington. Simulated short‐period ( T ≤ 2 s) spectral accelerations are strong throughout the Puget Lowland, and long‐period shaking ( T ≥ 5 s) is strong in the deep regional sedimentary basins, especially the Everett and Seattle basins. Source parameters strongly influence intra‐ and interevent variability in response, primarily through changes in source and site geometry, as well as rupture directivity. We also note a potential coupling between rupture directivity and basin effects, wherein directivity pulses are seemingly guided through the region’s deep, interconnected sedimentary basins. Overall, this work highlights the impacts of 3D source, path, and site effects on seismic hazard in the U.S. Pacific Northwest and substantially expands the catalog of simulated ground motions for Puget Sound area crustal faults.

Washington↗
USGS2025

Summary of results from monitoring the Geysers with continuous passive seismic and repeat magnetotelluric measurements (2021-2023)

Understanding temporal variations in a geothermal field can support operators in decision making that pertains to optimizing production and mitigating hazards. Between 2021 and 2023, The Geysers geothermal field in northern California was monitored with an array of continuous passive seismic sensors and annual repeat magnetotelluric (MT) measurements. Each of these data sets were analyzed and modelled separately to understand the data, sensitivity, and any observable changes. Then, the data were inverted jointly using a crossgradient method to further constrain temporal changes in geophysical properties within the geothermal field. Multiple permutations of annual datasets were used as inputs to the joint inversion. Results demonstrate seismic data constrain smooth inversion of the MT data, and the MT data provide supplementary information about the location of temporal fluid changes. Estimating relative changes in steam saturation for various time intervals of the joint models shows compartmentalized changes in the field, and good spatial correlation with the location of injection wells. These results demonstrate that collecting both passive seismic and MT measurements then modeling them jointly provide complementary information and a relatively inexpensive method for monitoring temporal changes in an active geothermal field that provides results to support operators.

California↗
USGS2025

The impact of burial diagenesis on soil-formed minerals in paleosols using stable isotopes of phyllosilicates and carbonate clumped isotopes

To understand the effects of burial diagenesis on the stable isotope geochemistry of soil-formed clay and carbonate minerals in paleosols, samples were collected from seven cores, spanning middle- to upper-Pennsylvanian strata of the Illinois Basin, with varied maximum burial depths of 1–3 km. Mixed-layer illite-smectite and kaolinite mixtures give δ 2 H and δ 18 O values of −83 ‰ to −36 ‰ and 11.9 ‰ to 21.1 ‰ (VSMOW), respectively. After carbonates were screened petrographically for diagenetic textures using transmitted light and cathodoluminescence, measured clumped isotope Δ 47 values range from 0.504 to 0.563 ‰ (I-CDES). Resulting mineral formation temperatures for phyllosilicate mineral mixtures are 28 to 66 °C (mean = 47 °C), whereas T(Δ 47 ) estimates for calcites are 36 to 61 °C (mean = 45 °C). Calculated δ 18 O water values from which phyllosilicate minerals and calcites precipitated under isotopic equilibrium ranges from −7.1 to −1.2 ‰ and − 1.4 to +4.9 ‰, respectively. Closed and open-system phyllosilicate-fluid exchange modeling indicates that phyllosilicate alteration occurred in the presence of a low temperature brine or meteoric water and is interpreted to occur in a layer-by-layer illitization transformation. Due to the lack of diagenetic textures and positively correlated T(Δ 47 ) and δ 18 O water , calcites are interpreted to have undergone solid-state bond reordering. Despite low to moderate temperatures (<125 °C) and varying depths of shallow burial (1–3 km), solid-state transformation of phyllosilicates and calcites indicates paleosols had prolonged exposure to burial conditions which has implications for the use of paleosol minerals for paleoenvironmental reconstructions.

Illinois, Indiana, Kentucky↗