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At least 19 recordsLinked to original sources
USGS2006

Chapter A6. Section 6.1. Temperature

Accurate temperature measurements are required for accurate determinations of important environmental parameters such as pH, specific electrical conductance, and dissolved oxygen, and to the determination of chemical reaction rates and equilibria, biological activity, and physical fluid properties. This section of the National Field Manual (NFM) describes U.S. Geological Survey (USGS) guidance and protocols for measurement of temperature in air, ground water, and surface water and calibration of the equipment used. Each chapter of the National Field Manual is published separately and revised periodically. Newly published and revised chapters will be announced on the USGS Home Page on the World Wide Web under 'New Publications of the U.S. Geological Survey.'

Techniques of Water-Resources Investigations↗
USGS2012

Laboratory triggering of stick-slip events by oscillatory loading in the presence of pore fluid with implications for physics of tectonic tremor

The physical mechanism by which the low-frequency earthquakes (LFEs) that make up portions of tectonic (also called non-volcanic) tremor are created is poorly understood. In many areas of the world, tectonic tremor and LFEs appear to be strongly tidally modulated, whereas ordinary earthquakes are not. Anomalous seismic wave speeds, interpreted as high pore fluid pressure, have been observed in regions that generate tremor. Here we build upon previous laboratory studies that investigated the response of stick-slip on artificial faults to oscillatory, tide-like loading. These previous experiments were carried out using room-dry samples of Westerly granite, at one effective stress. Here we augment these results with new experiments on Westerly granite, with the addition of varying effective stress using pore fluid at two pressures. We find that raising pore pressure, thereby lowering effective stress can significantly increase the degree of correlation of stick-slip to oscillatory loading. We also find other pore fluid effects that become important at higher frequencies, when the period of oscillation is comparable to the diffusion time of pore fluid into the fault. These results help constrain the conditions at depth that give rise to tidally modulated LFEs, providing confirmation of the effective pressure law for triggering and insights into why tremor is tidally modulated while earthquakes are at best only weakly modulated.

Journal of Geophysical Research B: Solid Earth↗
USGS1980

Geothermal system at 21°N, East Pacific Rise: physical limits on geothermal fluid and role of adiabatic expansion

Pressure-volume-temperature relations for water at the depth of the magma chamber at 21 ° N on the East Pacific Rise suggest that the maximum subsurface temperature of the geothermal fluid is about 420 ° C. Both the chemistry of the discharging fluid and thermal balance considerations indicate that the effective water/rock ratios in the geothermal system are between 7 and 16. Such low ratios preclude effective metal transport at temperatures below 350 ° C, but metal solubilization at 400 ° C and above is effective even at such low ratios. It is proposed that the 420 ° C fluid ascends essentially adiabatically and in the process expands, cools, and precipitates metal sulfides within the upper few hundred meters of the sea floor and on the sea floor itself.

Science↗
USGS1973

Fluid-inclusion studies of the fluorspar and gold deposits, Jamestown district, Colorado

The Jamestown district, Boulder County, Colorado, is a major producer of fluorspar; prior to 1940, gold, gold-telluride, and lead-silver ores were mined. Fluorite occurs as a primary mineral in phases of the composite sodic granite stock at Jamestown and in breccia zones, stockworks, and pipe-shaped bodies in and adjacent to the stock. Gold and telluride mineralization occurs with and without fluorite in veins peripheral to the stock. A great variety of fluid-inclusion types is present in the district, reflecting chemically and physically diverse fluids. Fluid inclusions in early-stage quartz from the fluorspar deposits have filling temperatures of 250 degrees to 375 degrees C, salinities of 20 to 30%, and boiling is indicated at many locations. Most inclusions associated with the main fluorite stage have salinities of at least 26% to more than 50% and filling temperatures in the range of 250 degrees to 350 degrees C. Probable cognate fluorite on the inclusion walls and as many as ten daughter minerals precipitated from some primary inclusions in fluorite attest to the presence of salt and CaF 2 -rich polycomponent fluorspar-depositing fluids. Carbon dioxide-rich liquids and vapors were present during and after the main period of fluorspar deposition. Gold-bearing veins contain fluid inclusions indicating that two fundamentally different types of fluids were present. Inclusions in pregold quartz and fluorite have filling temperatures which range up to 375 degrees C, and most have very high salinities comparable to those from the fluorspar deposits, suggesting that early quartz and fluorite of the gold-bearing veins was roughly contemporaneous with the main period of fluorspar deposition. Fluid inclusion and other thermometric data (Kelly and Goddard, 1969) suggest that gold and telluride deposition occurred at temperatures below 300 degrees C. Fluid inclusions most directly associated with gold deposition have filling temperatures in the range 205 degrees to 270 degrees C and have about 4% salinity. These data suggest that the gold-bearing fluids either evolved from the fluorite-bearing fluids or were later unrelated hydrothermal pulses introduced on reopened structures. Boiling occurred at many locations that were at relatively high elevations or adjacent to the sodic granite stock. From the interpretation that boiling occurred and from the heterogeneity of CO 2 contents, we deduce that fluid pressures were low and variable, commonly near 150 bars, but ranging to as much as approximately 500 bars when CO 2 pressures were high; these determinations are compatible with the depth of cover estimated from geomorphic reconstruction using the Flattop peneplain. The absence of strong thermal or salinity zonation of fluids relative to the outcropping stock suggests that fluids were emanating from a larger intrusive body at depth.

Colorado↗
USGS2026

Understanding the resource potential of natural hydrogen on Earth: Scientific gaps, uncertainties and recommendations

A comprehensive scientific research roadmap is essential to bridge knowledge gaps and deepen the understanding of key geological, geochemical, and geophysical aspects of natural hydrogen (H 2 ) as a potential new energy resource. This paper reviews major scientific uncertainties on natural H 2 , suggesting research priorities, as a guide for defining exploration strategies, techniques, and data interpretation. The uncertainties concern all phases of the natural H 2 cycle, from generation (source rocks) through migration (advection and diffusion) and accumulation (reservoir and cap rocks) to the application and interpretation of subsurface and surface geochemical and geophysical exploration techniques. Understanding H 2 sources and generation rates (the amount of H 2 generated by a given volume of rock over time) is crucial for determining whether a geological H 2 system operates as a short-term dynamic system with rapid H 2 production and release, or as a conventional gas system with long-term accumulations, analogous to petroleum reservoirs. Preliminary estimates for serpentinisation, radiolysis, and organic matter degradation suggest that H 2 generation is not inherently fast, especially for non-hydrothermal continental systems (crystalline basement of shields, ophiolites, peridotite massifs, sedimentary basins), and long-term accumulations, like those of fossil natural gas systems, represent the most likely scenario. The mechanisms of H 2 migration through geological formations require application of fundamental principles of fluid-flow physics, distinguishing advection and diffusion, as well as their forms (from gas-phase, bubble flows to aqueous solutions). Additional studies of H 2 accumulation and retention in subsurface reservoirs could improve understanding of mechanisms of H 2 migration by focusing on the rock fluid-bearing properties and the factors affecting H 2 preservation, such as the presence of cap rocks impermeable to H 2 , pressure conditions, residence times, and microbial or abiotic consumption. Advanced techniques, including reservoir modelling, flow simulations, 3D imaging (micro-CT) of H 2 -bearing rocks, and extraction and analysis of gas occluded in rocks, can provide insights into the stability and potential recoverability of H 2 accumulations. The interpretation of surface exploration techniques, including gas geochemistry, geophysics, and remote sensing, long employed in mineral and energy resource exploration, is now being adapted for natural H 2 studies, but challenges remain in the data interpretation. Distinguishing H 2 seepage due to geological degassing from H 2 produced near the surface by modern microbial processes or artificial sources, such as hammering or drilling for soil-gas sampling, drilling into aquifers, and corrosion in boreholes, is an essential step in exploration. The simple detection of H 2 in soils, even in morphological structures like sub-circular depressions or “fairy circles”, cannot be cursorily interpreted as a signal of natural H 2 seepage from a deep source. A holistic geochemical approach, including isotopic analyses of gases associated with H 2 , is recommended to distinguish among the variety of possible H 2 origins. Observations of H 2 in wells should be interrogated to rule out possible artifacts such as corrosion and drill bit metamorphism. The integration of multiple geophysical methods, including seismic, gravimetric, magnetic, and electro-magnetic surveys, is recommended to mitigate interpretation ambiguities regarding the structure of a subsurface H 2 system (source and reservoir rocks, including fluid and gas storage), due to the non-uniqueness of rock-specific physical properties.

Earth-Science Reviews↗
USGS1975

Fluid inclusion studies of vein, pipe, and replacement deposits, northwestern San Juan Mountains, Colorado

Base and precious metal ores valued in excess of $300 million have been mined from vein, pipe, and replacement deposits located on the northwest side of, and structurally related to, the middle Tertiary Silverton caldera. A belt of normal faults radial to the caldera contains veins which have been mined for as much as 15,000 feet (4,600 m) along strike and 3,700 feet (1,100 m) downdip. Structural relations, metal distributions, and fluid inclusion data suggest that many of the veins were open at the same general time and received the same mineralization. Fluid inclusions in quartz and sphalerite of the main ore stage of the Argentine and adjoining veins have filling temperatures ranging from 315 degrees to 249 degrees C and salinities from 7.9 to 0.1 wt percent NaCl equivalent. However, the majority of inclusions from base metal and gold stages are in a relatively narrow range near 280 degrees to 290 degrees C and salinities are unusually low (less than 2 wt %). Filling temperatures in postsulfide quartz and fluorite are as low as 153 degrees C and salinities are generally less than 0.5 wt percent. A pressure correction of about +25 degrees C should be added to the filling temperatures. Ore fluids were physically homogeneous liquids over the 3,700-foot (1,100 m) vertical and 11,200-foot (3,400 m) lateral range studied and no systematic variations in filling temperatures or salinity in this space are noted, but significant fluctuations are evident locally. Recently developed base metal replacement deposits occur in the Eocene Telluride Conglomerate adjacent to many metal-bearing veins. Calc-silicate alteration of the conglomerate host was probably by moderately saline fluids that ranged in temperature from 320 degrees to about 400 degrees C. Quartz-bearing clasts in altered zones contain secondary halitebearing inclusions with filling temperatures of about 250 degrees C and salinities about 34 wt percent; such inclusions are not known from the base metal stage and are interpreted to have been preore. Hydrothermal quartz, sphalerite, and calcite from replacement pods contain inclusions with filling temperatures ranging from 204 degrees to 309 degrees C and salinities from 11.2 to 0.2 wt percent. That the replacement zones and throughgoing veins are genetically related is suggested by the similarity of filling temperatures and compositions of base metal-stage fluid inclusions and by structural evidence. Small high-grade pipe deposits of base and precious metals occur along the ring-fault zone of the Silverton caldera. Filling temperatures for inclusions in quartz, sphalerite, and barite of the main ore stage of these deposits range from 216 degrees to 308 degrees C and salinities range from 1.6 to 0.2 wt percent NaCl. Quartz in altered wall rocks and silicified capping contains moderately saline secondary inclusions with relatively uniform liquid: vapor ratios that suggest filling temperatures of about 225 degrees to 300 degrees C. From the available samples there is no fluid inclusion evidence for boiling. Throttling, which had been hypothesized to explain the telescoped nature of the pipe ores, is neither substantiated nor discredited by the inclusion data.

Colorado↗
USGS2026

Temporal and spatial changes in seismic attenuation associated with inferred fluid migration in the 2016 central Apennines earthquake sequence

Prior work suggests that high‐frequency seismic attenuation acts as a highly sensitive proxy for crustal permeability and fluid mobility in fractured media. We test the hypothesis that the fault system responsible for the 2016–2017 Amatrice–Visso–Norcia–Capitignano sequence acted as an impermeable seal, compartmentalizing pressurized fluids until dynamic rupture triggered widespread fluid diffusion. By tracking across the sequence the spatiotemporal evolution of the S ‐wave anelastic attenuation parameter, we identify large, positive low‐frequency attenuation anomalies emerging within the hanging wall following the Amatrice mainshock and strictly preceding subsequent large ruptures. Conversely, we observe weaker, negative anomalies in the footwall, anticorrelated in time with those of the hanging wall, revealing a massive asymmetry in fluid redistribution and permeability evolution across the fault system. Furthermore, aftershock migration rates reveal distinct linear alignments in a distance‐reduced time space, allowing us to explicitly track and quantify episodes of lateral and upward fluid migration. These physically consistent patterns suggest that stress‐driven fluid diffusion directly weakens adjacent fault patches, dictating the spatiotemporal migration of seismicity. We conclude that near‐real‐time monitoring of seismic attenuation may help detect fluid redistribution in active fault systems and may provide useful information for time‐dependent seismic hazard assessment.

central Apennines↗
USGS2012

Introduction and digest to the Special Issue on Chemical Effects of Water on the Deformation and Strengths of Rocks

The important role of pore pressure in promoting such brittle processes as cataclasis, hydraulic fracturing, large‐scale faulting, and earthquakes within the crust is widely accepted in geology and geophysics [, 1957; , 1959; , 1958; ., 1963; , 1968; ., 1968; ., 1976; , 1973, 1980; , 1981]. Provided that fluid pressure is fully communicated with rock pore space, the effective normal stresses that control crack growth, macroscopic fracture, and friction are reduced by the magnitude of the fluid pressui'e. Beyond this physical effect of pore fluids, there are chemical effects of water on the strength of rocks that are also important in governing differential stresseg and flow in the continental crust. Some of these chemical effects of water on rock deformation have long been recognized.

Journal of Geophysical Research B: Solid Earth↗
USGS2003

Extraordinary phase separation and segregation in vent fluids from the southern East Pacific Rise

The discovery of Brandon vent on the southern East Pacific Rise is providing new insights into the controls on midocean ridge hydrothermal vent fluid chemistry. The physical conditions at the time ofsampling (287 bar and 405??C) place the Brandon fluids very close to the critical point of seawater (298 bar and 407??C). This permits in situ study of the effects of near criticalphenomena, which are interpreted to be the primary cause of enhanced transition metal transport in these fluids. Of the five orifices on Brandon sampled, three were venting fluids with less than seawater chlorinity, and two were venting fluids with greater than seawater chlorinity. The liquid phase orifices contain 1.6-1.9 times the chloride content of the vapors. Most other elements, excluding the gases, have this same ratio demonstrating the conservative nature of phase separation and the lack of subsequent water-rock interaction. The vapor and liquid phases vent at the same time from orifices within meters of each other on the Brandon structure. Variations in fluid compositions occur on a time scale of minutes. Our interpretation is that phase separation and segregation must be occurring 'real time' within the sulfide structure itself. Fluids from Brandon therefore provide an unique opportunity to understand in situ phase separation without the overprinting of continued water-rock interaction with the oceanic crust, as well as critical phenomena. ?? 2002 Elsevier Science B.V. All rights reserved.

Earth and Planetary Science Letters↗
USGS2011

Conference explores mechanical involvement of fluids in faulting

A growing body of evidence suggests that fluids are intimately linked to a variety of faulting processes. These include the long-term structural and compositional evolution of fault zones; fault creep; and the nucleation, propagation, arrest, and recurrence of earthquake ruptures. Besides the widely recognized physical role of fluid pressures in controlling the strength of crustal fault zones, it is also apparent that fluids can exert mechanical influence through a variety of chemical effects. To address these issues, a “Red-Book” Conference on the Mechanical Effects of Fluids in Faulting was sponsored by the U.S. Geological Survey under the auspices of the National Earthquake Hazards Reduction Program at Fish Camp, Calif., from June 6–10, 1993. The coconvenors were Steve Hickman, Rick Sibson, and Ron Bruhn.

California↗
USGS2012

The paleohydrology of unsaturated and saturated zones at Yucca Mountain, Nevada, and vicinity

Surface, unsaturated-zone, and saturated-zone hydrologic conditions at Yucca Mountain responded to past climate variations and are at least partly preserved by sediment, fossil, and mineral records. Characterizing past hydrologic conditions in surface and subsurface environments helps to constrain hydrologic responses expected under future climate conditions and improve predictions of repository performance. Furthermore, these records provide a better understanding of hydrologic processes that operate at time scales not readily measured by other means. Pleistocene climates in southern Nevada were predominantly wetter and colder than the current interglacial period. Cyclic episodes of aggradation and incision in Fortymile Wash, which drains the eastern slope of Yucca Mountain, are closely linked to Pleistocene climate cycles. Formation of pedogenic cement is favored under wetter Pleistocene climates, consistent with increased soil moisture and vegetation, higher chemical solubility, and greater evapotranspiration relative to Holocene soil conditions. The distribution and geochemistry of secondary minerals in subsurface fractures and cavities reflect unsaturated-zone hydrologic conditions and the response of the hydrogeologic system to changes in temperature and percolation flux over the last 12.8 m.y. Physical and fluid-inclusion evidence indicates that secondary calcite and opal formed in air-filled cavities from fluids percolating downward through connected fracture pathways in the unsaturated zone. Oxygen, strontium, and carbon isotope data from calcite are consistent with a descending meteoric water source but also indicate that water compositions and temperatures evolved through time. Geochronological data indicate that secondary mineral growth rates are less than 1–5 mm/m.y., and have remained approximately uniform over the last 10 m.y. or longer. These data are interpreted as evidence for hydrological stability despite large differences in surface moisture caused by climate shifts between the Miocene and Pleistocene and between Pleistocene glacial-interglacial cycles. Secondary mineral distribution and δ18O profiles indicate that evaporation in the shallower welded tuffs reduces infiltration fluxes. Several near-surface and subsurface processes likely are responsible for diverting or dampening infiltration and percolation, resulting in buffering of percolation fluxes to the deeper unsaturated zone. Cooler and wetter Pleistocene climates resulted in increased recharge in upland areas and higher water tables at Yucca Mountain and throughout the region. Discharge deposits in the Amargosa Desert were active during glacial periods, but only in areas where the modern water table is within 7–30 m of the surface. Published groundwater models simulate water-table rises beneath Yucca Mountain of as much as 150 m during glacial climates. However, most evidence from Fortymile Canyon up gradient from Yucca Mountain limits water-table rises to 30 m or less, which is consistent with evidence from discharge sites in the Amargosa Desert. The isotopic compositions of uranium in tuffs spanning the water table in two Yucca Mountain boreholes indicate that Pleistocene water-table rises likely were restricted to 25–50 m above modern positions and are in approximate agreement with water-table rises estimated from zeolitic-to-vitric transitions in the Yucca Mountain tuffs (less than 60 m in the last 11.6 m.y.).

Nevada↗
USGS2003

Volcano seismology

A fundamental goal of volcano seismology is to understand active magmatic systems, to characterize the configuration of such systems, and to determine the extent and evolution of source regions of magmatic energy. Such understanding is critical to our assessment of eruptive behavior and its hazardous impacts. With the emergence of portable broadband seismic instrumentation, availability of digital networks with wide dynamic range, and development of new powerful analysis techniques, rapid progress is being made toward a synthesis of high-quality seismic data to develop a coherent model of eruption mechanics. Examples of recent advances are: (1) high-resolution tomography to image subsurface volcanic structures at scales of a few hundred meters; (2) use of small-aperture seismic antennas to map the spatio-temporal properties of long-period (LP) seismicity; (3) moment tensor inversions of very-long-period (VLP) data to derive the source geometry and mass-transport budget of magmatic fluids; (4) spectral analyses of LP events to determine the acoustic properties of magmatic and associated hydrothermal fluids; and (5) experimental modeling of the source dynamics of volcanic tremor. These promising advances provide new insights into the mechanical properties of volcanic fluids and subvolcanic mass-transport dynamics. As new seismic methods refine our understanding of seismic sources, and geochemical methods better constrain mass balance and magma behavior, we face new challenges in elucidating the physico-chemical processes that cause volcanic unrest and its seismic and gas-discharge manifestations. Much work remains to be done toward a synthesis of seismological, geochemical, and petrological observations into an integrated model of volcanic behavior. Future important goals must include: (1) interpreting the key types of magma movement, degassing and boiling events that produce characteristic seismic phenomena; (2) characterizing multiphase fluids in subvolcanic regimes and determining their physical and chemical properties; and (3) quantitatively understanding multiphase fluid flow behavior under dynamic volcanic conditions. To realize these goals, not only must we learn how to translate seismic observations into quantitative information about fluid dynamics, but we also must determine the underlying physics that governs vesiculation, fragmentation, and the collapse of bubble-rich suspensions to form separate melt and vapor. Refined understanding of such processes—essential for quantitative short-term eruption forecasts—will require multidisciplinary research involving detailed field measurements, laboratory experiments, and numerical modeling.

Pure and Applied Geophysics↗
USGS1968

On the maintenance of anomalous fluid pressures: I. thick sedimentary sequences

Various physical and chemical processes may be envisioned which will cause anomalous pressures on an underground fluid. In order to consider the maintenance of anomalous pressure, it is necessary to consider the problem as one of nonsteady fluid flow. The time rate of pressure change and maintenance depends upon the hydrodynamics of flow through porous media and the particular boundary conditions. This paper presents a series of general solutions to hydrodynamic models which are germane to the problem of creating and maintaining excess-fluid pressures in a thick sedimentary sequence. The creation and maintenance of fluid pressures approaching lithostatic pressure through a process of continuous sedimentation was evaluated. Our results indicate that a sedimentation rate of 500 m/10 6 yr (reasonable for the Gulf Coast) will create fluid pressures approaching lithostatic in a sedimentary column that has a hydraulic conductivity of 10 -8 cm sec -1 , or lower. It is apparent that the creation of anomalous pressure and its maintenance depends, to a large degree, upon the hydraulic conductivity and, to a lesser extent, upon the specific storage of clay layers within the system. © 1968, The Geological Society of America, Inc.

Geological Society of America Bulletin↗
USGS1973

Geochemical studies in the Park City district; I, ore fluids in the Mayflower mine

Ore bodies in the Mayflower mine, Park City district, Utah, are localized along a normal fault zone which cuts Mississippian sedimentary and Tertiary intrusive rocks. Fissure filling and replacement Pb-Zn-Cu-Ag-Au mineralization occurs in both sedimentary and intrusive host rocks over a known vertical distance of 3,000 feet. The paragenesis of three major recognized veins in the mine is nearly the same, consisting of early quartz, anhydrite, hematite, and pyrite + or - chalcopyrite, followed by sphalerite and galena, grading into pyrite + chalcopyrite + hematite, in turn followed by quartz + carbonate and minor anhydrite, followed by sphalerite and chalcopyrite. Deep, early veins outside of the Mayflower ore zone are characterized by quartz, K-feldspar, biotite, pyrite, and anhydrite, and some also contain magnetite, amphibole or chalcopyrite; these veins contain halite-bearing and gas-rich inclusions which are not known from the ore zone. The deep, early fluids had 34 to 44% salinity, homogenization temperatures of 315 degrees to 430 degrees C, and at times were boiling. Fluid inclusions in samples from the three ore-bearing veins, which contain only simple two-phase inclusions with consistent phase proportions, indicate a marked change in the fluids prior to ore deposition. Homogenization temperatures range from 220 degrees to 300 degrees C, and probably require a pressure correction of approximately + 10 degrees C. Freezing tests indicate salinities in the range 0.3 to 11 wt %NaCl equivalent; no CO 2 -bearing phases were detected at reduced temperatures. Near-surface veins, presumably contemporaneous with the Mayflower ore zone, show evidence for boiling and suggest that there was approximately 90 bars pressure at the present Mayflower vein outcrop. The distribution of fluid densities, temperatures, boiling, and key minerals in time and space indicates a dramatic change from very hot dense post-magmatic fluids to cooler, relatively low salinity fluids at the onset of economic basemetal deposition, probably concurrent with normal faulting. The changes in the physical properties of the hydrothermal fluids are believed to reflect the structural and magmatic evolution of the area.

Utah↗
USGS2003

Constitutive relations associated with the Mott-Smith distribution function

It is shown that the distribution function assumed by Mott-Smith determines a unique relation between heat flux, stress, and fluid velocity given by q = (3/2) τ u, i.e., it provides a constitutive relation for heat flux, and it also determines a simple expression for this ratio of third-order central moments Q = (C 3 x) / C x C 2 . These expressions allow the equation of transfer for c x2 to be cast in a form that yields a nonlinear constitutive relation for stress. The results obtained from the Mott-Smith ansatz are compared with the theory of Baganoff and Nathenson and results from a numerical solution of the Boltzmann equation for shock-wave structure obtained by Hicks and Yen.

Physics of Fluids↗
USGS2017

A 15-year catalog of more than 1 million low-frequency earthquakes: Tracking tremor and slip along the deep San Andreas Fault

Low-frequency earthquakes (LFEs) are small, rapidly recurring slip events that occur on the deep extensions of some major faults. Their collective activation is often observed as a semi-continuous signal known as tectonic (or non-volcanic) tremor. This manuscript presents a catalog of more than 1 million LFEs detected along the central San Andreas Fault from 2001-2016. These events have been detected via a multi-channel matched-filter search, cross-correlating waveform templates representing 88 different LFE families with continuous seismic data. Together, these source locations span nearly 150 km along the central San Andreas Fault, ranging in depth from ~16-30 km. This accumulating catalog has been the source of numerous studies examining the behavior of these LFE sources and the inferred slip behavior of the deep fault. The relatively high temporal and spatial resolution of the catalog has provided new insights into properties such as tremor migration, recurrence, and triggering by static and dynamic stress perturbations. Collectively, these characteristics are inferred to reflect a very weak fault likely under near-lithostatic fluid pressure, yet the physical processes controlling the stuttering rupture observed as tremor and LFE signals remain poorly understood. This paper aims to document the LFE catalog assembly process and associated caveats, while also updating earlier observations and inferred physical constraints. The catalog itself accompanies this manuscript as part of the electronic supplement, with the goal of providing a useful resource for continued future investigations.

California↗
USGS2023

Two-dimensional inverse energy cascade in a laboratory surf zone for varying wave directional spread

Surfzone eddies enhance the dispersion and transport of contaminants, bacteria, and larvae across the nearshore, altering coastal water quality and ecosystem health. During directionally spread wave conditions, vertical vortices (horizontal eddies) are injected near the ends of breaking crests. Energy associated with these eddies may be transferred to larger-scale, low-frequency rotational motions through an inverse energy cascade, consistent with two-dimensional turbulence. However, our understanding of the relationships between the wave conditions and the dynamics and energetics of low-frequency surfzone eddies are largely based on numerical modeling. Here, we test these relationships with remotely sensed and in situ observations from large-scale directional wave basin experiments with varying wave conditions over alongshore-uniform barred bathymetry. Surface velocities derived with particle image velocimetry were employed to assess the spatial scales of low-frequency surfzone eddies and compute structure functions with alongshore velocities. Second-order structure functions for directionally spread waves ( ⁠

Physics of Fluids↗
USGS2012

Migration rates and formation injectivity to determine containment time scales of sequestered carbon dioxide

Supercritical carbon dioxide exhibits highly variable behavior over a range of reservoir pressure and temperature conditions. Because geologic sequestration of supercritical carbon dioxide is targeted for subsurface injection and containment at depths ranging from approximately 3,000 to 13,000 feet, the investigation into the physical properties of this fluid can be restricted to the pressure and temperature conditions likely encountered in the sedimentary strata within this depth interval. A petrophysical based approach was developed to study the widest range of formation properties potentially encountered in sedimentary strata. Fractional porosities were varied from 5 to 95 percent, in 5-percent increments, and permeability values were varied over thirteen orders of magnitude, from 10.0 darcys down to 1.0 picodarcy. Fluid-flow modeling incorporated two constitutive equations from fluid dynamics: hydraulic diffusivity for near-surface applications, and Darcy's Law for deeper formations exhibiting higher pressure gradients. Based on the flow modeling results, first-order approximations of carbon dioxide lateral migration rates were determined. These first-order approximations enable the establishment of a permeability classification system for dividing the subsurface into flow units that provide short, moderate, and long-term containment of carbon dioxide. These results enable a probabilistic determination of how fluids will enter and be contained in a subsurface storage formation, which is a vital step in the calculation of the carbon dioxide storage capacity of a reservoir. Additionally, this research establishes a methodology to calculate the injectivity of a target formation. Because injectivity describes the pressure increase due to the introduction of fluids into a formation, the relevant application of injectivity is to determine the pressure increase, due to an injection volume and flow rate, that will induce fractures in the reservoir rocks. This quantity is defined mathematically as the maximum pressure differential between the hydrostatic gradient and the fracture gradient of the target formation. Injectivity is mathematically related to the maximum pressure differential of the formation, and can be used to determine the upper limit for the pressure increase that an injection target can withstand before fracturing.

Open-File Report↗