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Results for “The Seismic Record”

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

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At least 1,243 records · Page 69Linked to original sources

USGS2003

Using 1-Hz GPS data to measure deformations caused by the denali fault earthquake

The 3 November 2002 moment magnitude 7.9 Denali fault earthquake generated large, permanent surface displacements in Alaska and large-amplitude surface waves throughout western North America. We find good agreement between strong ground-motion records integrated to displacement and 1-hertz Global Positioning System (GPS) position estimates collected ??? 140 kilometers from the earthquake epicenter. One-hertz GPS receivers also detected seismic surface waves 750 to 3800 kilometers from the epicenter, whereas these waves saturated many of the seismic instruments in the same region. High-frequency GPS increases the dynamic range and frequency bandwidth of ground-motion observations, providing another tool for studying earthquake processes.

Science↗

USGS2000

SMSIM--Fortran programs for simulating ground motions from earthquakes: Version 2.0.--a revision of OFR 96-80-A

A simple and powerful method for simulating ground motions is based on the assumption that the amplitude of ground motion at a site can be specified in a deterministic way, with a random phase spectrum modified such that the motion is distributed over a duration related to the earthquake magnitude and to distance from the source. This method of simulating ground motions often goes by the name "the stochastic method." It is particularly useful for simulating the higher-frequency ground motions of most interest to engineers, and it is widely used to predict ground motions for regions of the world in which recordings of motion from damaging earthquakes are not available. This simple method has been successful in matching a variety of ground-motion measures for earthquakes with seismic moments spanning more than 12 orders of magnitude. One of the essential characteristics of the method is that it distills what is known about the various factors affecting ground motions (source, path, and site) into simple functional forms that can be used to predict ground motions. SMSIM is a set of programs for simulating ground motions based on the stochastic method. This Open-File Report is a revision of an earlier report (Boore, 1996) describing a set of programs for simulating ground motions from earthquakes. The programs are based on modifications I have made to the stochastic method first introduced by Hanks and McGuire (1981). The report contains source codes, written in Fortran, and executables that can be used on a PC. Programs are included both for time-domain and for random vibration simulations. In addition, programs are included to produce Fourier amplitude spectra for the models used in the simulations and to convert shear velocity vs. depth into frequency-dependent amplification. The revision to the previous report is needed because the input and output files have changed significantly, and a number of new programs have been included in the set.

Open-File Report↗

USGS2001

Paleoliquefaction studies in continental setting; geologic and geotechnical factors in interpretations and back-analysis

Paleoliquefaction research in the last 15 years has greatly improved our ability to interpret the paleoseismic record throughout some large geographic areas, especially in regions of infrequent large earthquakes. Paleoliquefaction studies have been used extensively in the central and eastern U.S. to assess seismic hazards, and could be used elsewhere to good purpose because paleoliquefaction studies in some field settings can reveal more than other methods, such as fault studies, about the prehistoric strength of shaking and earthquake magnitude. We present guidelines for the conduct of a paleoliquefaction study in continental deposits, mainly in terms of the geologic/seismologic setting and geotechnical properties, because a successful interpretation requires factors from all these disciplines. No single discipline suffices alone. Their interactions must be appreciated in order to understand why seismically induced liquefaction features are found in some locales and not in others. The guidelines that we present also relate to three primary issues for which liquefaction features are especially useful for interpretations: Where was the tectonic source? What was the strength of shaking? And what was the magnitude? In discussing these issues we focus on the following aspects of level-ground liquefaction: (1) mechanisms that form seismic liquefaction features in the field; (2) field settings where liquefaction features should be present if strong seismic shaking has occurred; (3) field settings where an absence of liquefaction features indicates an absence of strong seismic shaking; (4) how liquefaction features should be used to interpret the tectonic source locale of a paleo-earthquake; and (5) how effects of liquefaction can be used to back-calculate the strength of shaking as well as earthquake magnitude. Several methods are available to back-calculate the strength of shaking and earthquake magnitude, and the most commonly used methods are presented and critiqued. Our critique of these methods points out the uncertainties attending each. Paleoliquefaction/paleoseismic case histories are presented to illustrate potential uncertainties in back-calculations and procedures to overcome these uncertainties. Reasonable confidence in paleoseismic interpretation generally requires using multiple methods of back-analysis, and achieving similar results from each method. An alternate approach can be used for paleo-earthquakes that were large enough to have caused liquefaction in a variety of geologic settings, in which there were differing factors affecting surface ground motions and liquefaction susceptibility. For this situation, a method such as the cyclic-stress method can be used to make back-calculations that can be cross-checked with results from other settings.

Open-File Report↗

USGS1986

Multichannel seismic-reflection data collected in 1980 in the eastern Chukchi Sea

The U.S. Geological Survey (USGS) collected approximately 2,652 km of 24-channel seismic-reflection data in early September, 1980, over the continental shelf in the eastern Chukchi Sea (Fig. 1). The profiles were collected on the USGS Research Vessel S.P. Lee. The seismic energy source consisted of a tuned array of five airguns with a total volume of 1213 cubic inches of air compressed to approximately 1900 psi. The recording system consisted of a 24-channel, 2400 meter long streamer with a group interval of 100 m, and a GUS (Global Universal Science) model 4200 digital recording instrument. Shots were fired every 50 meters. Navigational control for the survey was provided by a Magnavox integrated navigation system using transit satellites and doppler-sonar augmented by Loran C (Rho-Rho). A 2-millisecond sampling rate was used in the field; the data were later desampled to 4-milliseconds during the demultiplexing process. 8 seconds data length was recorded. Processing was done at the USGS Pacific Marine Geology Multichannel Processing Center in Menlo Park, California, in the sequence: editing-demultiplexing, velocity analysis, CDP stacking, deconvolution-filtering, and plotting on an electrostatic plotter. Plate 1 is a trackline chart showing shotpoint navigation.

Alaska↗

USGS2019

Geologic map of the Ferncliff and Louisa quadrangles, Louisa, Fluvanna, and Goochland Counties, Virginia

The area encompassed by the geologic map of the Ferncliff and Louisa, Va., 7.5-minute quadrangles includes the hypothetical surface projection of the Quail fault, which is the subsurface fault that was responsible for the 2011 magnitude 5.8 (M5.8) Mineral, Va., earthquake. The mapping shows that the Quail fault appears to have reactivated the Harris Creek fault, a Paleozoic fault that has been mapped and named in the study area and marks the boundary between the Ellisville pluton neck and Chopawamsic Formation. The Harris Creek fault was also reactivated in the early Mesozoic. Another result of the mapping is a well-defined, southwest to northeast, narrow zone of metagraywacke and ultramafic rocks (both part of the informal Shores complex) that marks the closure of a small ocean basin and the accretion of the 468- to 460-Ma (mega-annum) Ordovician Chopawamsic volcanic arc (part of the Carolina terrane) onto Laurentia. The accretion zone is truncated by the Ordovician-Silurian (444 Ma) Ellisville pluton; the 444-Ma age of the pluton therefore represents the minimum age of the accretion zone and indicates likely closure of the ocean basin during the Taconic orogeny. Across the map area, the metamorphic grade ranges from lower-greenschist facies in the northwest to amphibolite facies in the southeast. 40 Ar/ 39 Ar age-dating across this metamorphic gradient indicates that Taconic metamorphism was overprinted by late-Paleozoic Alleghanian metamorphism that was accompanied by refolding and faulting of Taconic structures. Quaternary terraces mapped along the South Anna River record a long history of incision and downcutting. A continuing question is how much of this downcutting was a result of neotectonic uplift in the central Virginia seismic zone. This report consists of a single geologic map sheet and an online geographic information systems database that includes bedrock geologic unit contacts and polygons, surficial geologic polygons, faults, and structural geologic information.

Virginia↗

USGS1969

A seismic-refraction survey of crustal structure in central Arizona

The U.S. Geological Survey conducted a seismic-refraction study of the earth's crust and upper mantle near the Tonto Forest Seismological Observatory (TFO), located 10miles south of the Mogollon Rim near Payson in central Arizona. Two recording lines 400 km long intersect in the approximate form of a cross at TFO; one line trends southeast and the other northeast. The sedimentary layer at most places southwest of the rim is less than 1 km thick, but north of the rim it is 2 to 3 km thick. The velocity in this uppermost layer ranges from 2.6 to 4.7 km/sec, with the higher limit measured near or north of the rim. Arrivals refracted in the upper crust (P g ) can be attributed to two layers for all the shot points south of the rim. The velocity in the upper layer is about 5.9 km/sec with thickness ranging from 2 to 8 km; beneath the upper layer the velocity is about 6.1 km/sec. The upper layer seems to be absent northeast of the rim, where two shot points generated P g arrivals that show only a velocity of 6.2 km/sec. A Poisson ratio of 0.22 for the upper crustal layers was measured from shear and compressional arrivals. The lower crust could not be identified from the first and later refraction arrivals; however, minimum depths to the intermediate layer were determined. An average crustal velocity of 6.2 km/sec was measured from wide-angle reflection alignments. A thin intermediate layer would explain the seismic measurements. A delay-time method was used to map the configuration of the M-discontinuity. The depth below sea level is about 36 km along the northwest-trending line. The northeast-trending line shows a shallow depth of 21 km near Gila Bend, increasing depth to about 34 km under TFO, and a flat M-discontinuity at 40 km depth under the Mogollon Mesa northeast to Sunrise Springs. There is evidence of an abrupt depth change of about 4 km on the M-discontinuity in the vicinity of TFO. The velocity in the upper mantle is 7.85 km/sec. The relation of topographic elevation to crustal thickness suggests an approach to isostatic equilibrium, which is deduced from a near-zero regional free-air gravity anomaly. However, lateral density change in the upper mantle is required to make the crustal-refraction model fit the observed gravity-anomaly values, provided that velocity and density are linearly related.

Arizona↗

USGS2026

The 2025 Puerto Rico and Virgin Islands U.S. National Seismic Hazard Model Update: Ground motion model selection and comparison

We evaluate, select, and describe the ground-motion models (GMMs) used in the 2025 update of the U.S. National Seismic Hazard Model (NSHM) for Puerto Rico and the U.S. Virgin Islands (PRVI). We identify the most appropriate models that align with GMM selection criteria for use in the PRVI region to improve the accuracy of seismic hazard assessments. The update incorporates globally applicable GMMs suited for the active crustal and subduction earthquakes in the region. We include region-specific adjustments to these GMMs derived from local site response analyses derived from ground motion records. The unadjusted and regionally-corrected GMMs are combined to create a robust model for predicting median ground motion. The model integrates epistemic uncertainty through a median ground motion logic tree that accounts for variations in magnitude and distance. This study compares the GMMs selected for the 2025 PRVI NSHM, including both as-provided and regionally adjusted NGA-West2 and NGA-Subduction models, with those used in the 2003 PRVI NSHM. We evaluate how changes in model selection, weighting, aleatory variability, and epistemic uncertainty influence seismic hazard estimates. Trends with distance, magnitude, and spectral period are analyzed to evaluate how the scaling behavior of the newer GMMs differs from that of earlier models. Relative to the GMMs used in the 2003 NSHM for this region, the 2025 models generally predict lower ground motions. Comparisons with additional GMMs indicate that the adjustments applied for PRVI are consistent with regional-specific modifications developed elsewhere globally. The increase in aleatory variability and epistemic uncertainty in the 2025 update results in a notable increase in hazard levels from these wider uncertainty bounds. These changes can result in as much as a 10%–20% variation in probabilistic ground motion at the 2% in 50 years exceedance level for hazard maps computed across the region for representative site classes and periods.

Puerto Rico, Virgin Islands↗

USGS2012

Extension of the spatial autocorrelation (SPAC) method to mixed-component correlations of surface waves

Using ambient seismic noise for imaging subsurface structure dates back to the development of the spatial autocorrelation (SPAC) method in the 1950s. We present a theoretical analysis of the SPAC method for multicomponent recordings of surface waves to determine the complete 3 × 3 matrix of correlations between all pairs of three-component motions, called the correlation matrix. In the case of isotropic incidence, when either Rayleigh or Love waves arrive from all directions with equal power, the only non-zero off-diagonal terms in the matrix are the vertical–radial (ZR) and radial–vertical (RZ) correlations in the presence of Rayleigh waves. Such combinations were not considered in the development of the SPAC method. The method originally addressed the vertical–vertical (ZZ), RR and TT correlations, hence the name spatial autocorrelation. The theoretical expressions we derive for the ZR and RZ correlations offer additional ways to measure Rayleigh wave dispersion within the SPAC framework. Expanding on the results for isotropic incidence, we derive the complete correlation matrix in the case of generally anisotropic incidence. We show that the ZR and RZ correlations have advantageous properties in the presence of an out-of-plane directional wavefield compared to ZZ and RR correlations. We apply the results for mixed-component correlations to a data set from Akutan Volcano, Alaska and find consistent estimates of Rayleigh wave phase velocity from ZR compared to ZZ correlations. This work together with the recently discovered connections between the SPAC method and time-domain correlations of ambient noise provide further insights into the retrieval of surface wave Green’s functions from seismic noise.

Geophysical Journal International↗

USGS1992

Acoustic waveform logging: Advances in theory and application

Full-waveform acoustic logging has made significant advances in both theory and application in recent years, and these advances have greatly increased the capability of log analysts to measure the physical properties of formations. Advances in theory provide the analytical tools required to understand the properties of measured seismic waves, and to relate those properties to such quantities as shear and compressional velocity and attenuation, and primary and fracture porosity and permeability of potential reservoir rocks. The theory demonstrates that all parts of recorded waveforms are related to various modes of propagation, even in the case of dipole and quadrupole source logging. However, the theory also indicates that these mode properties can be used to design velocity and attenuation picking schemes, and shows how source frequency spectra can be selected to optimize results in specific applications. Synthetic microseismogram computations are an effective tool in waveform interpretation theory; they demonstrate how shear arrival picks and mode attenuation can be used to compute shear velocity and intrinsic attenuation, and formation permeability for monopole, dipole and quadrupole sources. Array processing of multi-receiver data offers the opportunity to apply even more sophisticated analysis techniques. Synthetic microseismogram data is used to illustrate the application of the maximum-likelihood method, semblance cross-correlation, and Prony's method analysis techniques to determine seismic velocities and attenuations. The interpretation of acoustic waveform logs is illustrated by reviews of various practical applications, including synthetic seismogram generation, lithology determination, estimation of geomechanical properties in situ, permeability estimation, and design of hydraulic fracture operations.

Log Analyst↗

USGS2019

Azimuthal seismic anisotropy of 70 Ma Pacific‐plate upper mantle

Plate formation and evolution processes are predicted to generate upper mantle seismic anisotropy and negative vertical velocity gradients in oceanic lithosphere. However, predictions for upper mantle seismic velocity structure do not fully agree with the results of seismic experiments. The strength of anisotropy observed in the upper mantle varies widely. Further, many refraction studies observe a fast direction of anisotropy rotated several degrees with respect to the paleospreading direction, suggesting that upper mantle anisotropy records processes other than 2D corner flow and plate‐driven shear near mid‐ocean ridges. We measure 6.0 ± 0.3% anisotropy at the Moho in 70 Ma lithosphere in the central Pacific with a fast direction parallel to paleospreading, consistent with mineral alignment by 2D mantle flow near a mid‐ocean ridge. We also find an increase in the strength of anisotropy with depth, with vertical velocity gradients estimated at 0.02 km/s/km in the fast direction and 0 km/s/km in the slow direction. The increase in anisotropy with depth can be explained by mechanisms for producing anisotropy other than intrinsic effects from mineral fabric, such as aligned cracks or other structures. This measurement of seismic anisotropy and gradients reflects the effects of both plate formation and evolution processes on seismic velocity structure in mature oceanic lithosphere, and can serve as a reference for future studies to investigate the processes involved in lithospheric formation and evolution.

Journal of Geophysical Research B: Solid Earth↗

USGS2014

Volcanic tremor masks its seismogenic source: Results from a study of noneruptive tremor recorded at Mount St. Helens, Washington

On 2 October 2004, a significant noneruptive tremor episode occurred during the buildup to the 2004–2008 eruption of Mount St. Helens (Washington). This episode was remarkable both because no explosion followed, and because seismicity abruptly stopped following the episode. This sequence motivated us to consider a model for volcanic tremor that does not involve energetic gas release from magma but does involve movement of conduit magma through extension on its way toward the surface. We found that the tremor signal was composed entirely of Love and Rayleigh waves and that its spectral bandwidth increased and decreased with signal amplitude, with broader bandwidth signals containing both higher and lower frequencies. Our modeling results demonstrate that the forces giving rise to this tremor were largely normal to conduit walls, generating hybrid head waves along conduit walls that are coupled to internally reflected waves. Together these form a crucial part of conduit resonance, giving tremor wavefields that are largely a function of waveguide geometry and velocity. We find that the mechanism of tremor generation fundamentally masks the nature of the seismogenic source giving rise to resonance. Thus multiple models can be invoked to explain volcanic tremor, requiring that information from other sources (such as visual observations, geodesy, geology, and gas geochemistry) be used to constrain source models. With concurrent GPS and field data supporting rapid rise of magma, we infer that tremor resulted from drag of nearly solid magma along rough conduit walls as magma was forced toward the surface.

Washington↗

USGS2003

Paleolimnology of Lake Tanganyika, East Africa, over the past 100 k yr

New sediment core data from a unique slow-sedimentation rate site in Lake Tanganyika contain a much longer and continuous record of limnological response to climate change than have been previously observed in equatorial regions of central Africa. The new core site was first located through an extensive seismic reflection survey over the Kavala Island Ridge (KIR), a sedimented basement high that separates the Kigoma and Kalemie Basins in Lake Tanganyika. Proxy analyses of paleoclimate response carried out on core T97-52V include paleomagnetic and index properties, TOC and isotopic analyses of organic carbon, and diatom and biogenic silica analyses. A robust age model based on 11 radiocarbon (AMS) dates indicates a linear, continuous sedimentation rate nearly an order of magnitude slower here compared to other core sites around the lake. This age model indicates continuous sedimentation over the past 79 k yr, and a basal age in excess of 100 k yr. The results of the proxy analyses for the past ??? 20 k yr are comparable to previous studies focused on that interval in Lake Tanganyika, and show that the lake was about 350 m lower than present at the Last Glacial Maximum (LGM). Repetitive peaks in TOC and corresponding drops in ??13C over the past 79 k yr indicate periods of high productivity and mixing above the T97-52V core site, probably due to cooler and perhaps windier conditions. From ??? 80 through ??? 58 k yr the ??13C values are relatively negative (-26 to -28???) suggesting predominance of algal contributions to bottom sediments at this site during this time. Following this interval there is a shift to higher values of ??13C, indicating a possible shift to C-4 pathway-dominated grassland-type vegetation in the catchment, and indicating cooler, dryer conditions from ??? 55 k yr through the LGM. Two seismic sequence boundaries are observed at shallow stratigraphic levels in the seismic reflection data, and the upper boundary correlates to a major discontinuity near the base of T97-52V. We interpret these discontinuities to reflect major, prolonged drops in lake level below the core site (393 m), with the lower boundary correlating to marine oxygen isotope Stage 6. This suggests that the previous glacial period was considerably cooler and more arid in the equatorial tropics than was the last glacial period.

Conference Paper↗

USGS1997

Stratigraphic evolution of the inner continental shelf in response to late Quaternary relative sea-level change, northwestern Gulf of Maine

Accumulations of deltaic and littoral sediments on the inner continental shelf of Maine, Gulf of Maine, preserve a record of postglacial sea-level changes and shoreline migrations. The depositional response of coastal environments to a cycle of regression, lowstand, and transgression was examined with seismic-reflection profiles, vibracores, and radiocarbon dates collected from sediments at the mouths of the Kennebec and Penobscot Rivers. Sequence-stratigraphic analysis of these data reveals two distinctly different successions of late Quaternary deposits that represent end members in an evolutionary model for this glaciated coast. Seaward of the Kennebec River, coarse-grained shorelines with foreset beds occur at depths of 20–60 m and outline the lobate margin of the Kennebec River paleodelta, a complex, rock-framed accumulation of glaciomarine and deltaic sediments capped by estuarine and marine deposits. Sand derived from this system today supports large barrier spits and extensive salt marshes. In contrast, the mouth of the Penobscot River is characterized by thick deposits of glaciomarine mud overlain by marine mud of Holocene age, including gas-charged zones that have locally evolved into fields of pockmarks. The distinct lack of sand and gravel seaward of the Penobscot River and its abundance seaward of the Kennebec River probably reflect differences in sediment sources and the physiography of the two watersheds. The contrasting stratigraphic framework of these systems demonstrates the importance of understanding local and regional differences in sediment supply, sea-level change, bedrock structure, and exposure to waves and tides in order to model river-mouth deposition on glaciated coasts.

Gulf of Maine↗

USGS1978

Notes on acquisition of high-resolution seismic profiles in southern Puget Sound, Washington

Approximately 275 km of high-resolution seismic reflection profiles were obtained in Puget Sound, Washington from the U.S. Geological Survey's research vessel DON J. MILLER from January 13 through 19, 1976. These data, recorded on microfilm, were obtained to provide information on the thickness and distribution of Quaternary deposits, to identify folds and faults that deform them, and to provide a basis for assessing geological environmental hazards.

Open-File Report↗

USGS2003

Simulation of ground motion using the stochastic method

A simple and powerful method for simulating ground motions is to combine parametric or functional descriptions of the ground motion's amplitude spectrum with a random phase spectrum modified such that the motion is distributed over a duration related to the earthquake magnitude and to the distance from the source. This method of simulating ground motions often goes by the name "the stochastic method." It is particularly useful for simulating the higher-frequency ground motions of most interest to engineers (generally, f>0.1 Hz), and it is widely used to predict ground motions for regions of the world in which recordings of motion from potentially damaging earthquakes are not available. This simple method has been successful in matching a variety of ground-motion measures for earthquakes with seismic moments spanning more than 12 orders of magnitude and in diverse tectonic environments. One of the essential characteristics of the method is that it distills what is known about the various factors affecting ground motions (source, path, and site) into simple functional forms. This provides a means by which the results of the rigorous studies reported in other papers in this volume can be incorporated into practical predictions of ground motion.

Pure and Applied Geophysics↗

USGS2021

Yellowstone Volcano Observatory 2020 annual report

The Yellowstone Volcano Observatory (YVO) monitors volcanic and hydrothermal activity associated with the Yellowstone magmatic system, conducts research into magmatic processes occurring beneath Yellowstone Caldera, and issues timely warnings and guidance related to potential future geologic hazards. This report summarizes the activities and findings of YVO during the year 2020, focusing on the Yellowstone volcanic system. Highlights of YVO research and related activities during 2020 include an active-source seismic experiment to image the top of Yellowstone’s magma reservoir; semipermanent Global Positioning System array deployment, including a new site near Mary Mountain; studies of hydrothermal activity in the southwest portion of Yellowstone National Park; numerous geological studies, including characterization of hydrothermal explosion craters, updating existing maps, and refining the ages of Yellowstone volcanic units; investigation of a dormant period at Old Faithful Geyser that may be related to regional drought 800–650 years ago, and development of a publicly available online map interface. Steamboat Geyser, in Norris Geyser Basin, continued the pattern of frequent eruptions that began in 2018 with 48 water eruptions in 2020, matching the record for a calendar year that was set in 2019. Giantess Geyser, in the Upper Geyser Basin, erupted for the first time in 6 years in August 2020 and experienced a second eruption in September. Patterns of both seismicity and deformation in 2020 were similar to those in 2019. Deformation patterns during 2020 showed trends that were similar to previous years. Overall subsidence of the caldera floor, ongoing since late 2015 or early 2016, continued at rates of a few centimeters (1–2 inches) per year, and minor subsidence of Norris Geyser Basin that began in 2018 slowed during 2020 and stopped by the end of the year. Throughout 2020, the aviation color code for Yellowstone Caldera remained at “green” and the volcano alert level remained at “normal.”

Idaho, Montana, Wyoming↗

USGS2024

Infrasound for volcano monitoring

Introduction Volcanic eruptions produce acoustic waves when volcanic gases and hot material rapidly expand in the atmosphere. Volcanic activity can produce acoustic signals with a wide range of frequencies, from very long period (>10 seconds) to audible (>20 hertz [Hz]), but the most energetic band is typically in the infrasound from 0.5 to 20 Hz. Studies of volcanic infrasound and the deployment of infrasound for volcano monitoring have increased rapidly in the past two decades as sensors have improved and as analytical tools have become more widely available. Improved sensors and tools have led to a growing diversity of eruptive activity being recorded and characterized, from Hawaiian to Plinian eruption styles at scales from local to global (Johnson and Ripepe, 2011; Fee and Matoza, 2013). Infrasound sensors on volcanoes are most commonly deployed locally with seismic stations, and the combination of co-located seismic and infrasound is more useful for characterizing unrest and detecting changes in activity than either data stream alone (for example, Lyons and others, 2016; Fee and others, 2017a; Matoza and others, 2018). At local (<15 kilometers [km]) to regional (15–250 km) distances from volcanoes, arrays of infrasound sensors are commonly deployed to detect coherent signals, constrain the direction to the source, and provide information on eruption dynamics; thus, infrasound is well suited to regional monitoring of volcanoes when local sensor networks are not feasible. A common usage of infrasound data in an observatory is to provide rapid confirmation that an explosion has occurred (for example, Coombs and others, 2018), although near-real-time eruption intensity quantification is also possible (Fee and others, 2010a; Ripepe and others, 2018; fig. C1). Infrasound is well suited to this task because it is not affected by clouds or precipitation and can propagate long distances with little attenuation. However, wind and ocean noise also produce infrasound, and spatiotemporal variability in the atmosphere can affect the propagation of infrasound, so care must be taken when deploying, analyzing, and interpreting the data. In addition to detecting and monitoring explosive activity, investigations of infrasound records from eruptions help constrain source processes, which in turn enhance syneruptive forecasting capabilities (for example, Fee and others, 2017b; Lyons and others, 2019). The following is a description of the capabilities recommended for real-time monitoring of eruptive phenomena with infrasound. Infrasound is also beginning to be used for tracking hazardous surface flows that occur on volcanoes, including pyroclastic density currents (Ripepe and others, 2010), lahars (Johnson and Palma, 2015), debris flows (Marchetti and others, 2019), snow avalanches (Havens and others, 2014), and lava flows (Patrick and others, 2019). Please refer to the chapter on lahars (this volume; Thelen and others, 2024a) for more information on this application.

Scientific Investigations Report↗

USGS2025

Evidence for fluid pressurization of fault zones and persistent sensitivity to injection rate beneath the Raton Basin

Subsurface wastewater injection has increased the seismicity rate within the Raton Basin over more than two decades, with the basin-wide injection rate peaked between 2009-2015. To understand the evolution of injection-induced earthquakes, we systematically analyzed 2016-2024 broadband recordings with a machine-learning-based phase picker and constructed a catalog with 95,993 earthquakes (-1≤ M L ≤4.3). We then inverted for full centroid moment tensors (CMT) for 90 M L ≥ 2 events, with a special interest in constraining the non-double-couple components via probabilistic metrics. Both relocations and CMT solutions support basement-rooted normal faults, including graben and half-graben structures. Furthermore, we observe the non-double-couple components that imply elevated pore pressure in the fault zones. An earthquake cluster emerged in the north-central basin in 2023, preceded by ~1-yr of increased injection volume from wells within 15km. Despite a basin-wide decrease in the injection volume, we highlights the persistence of seismicity that remains to sensitive to injection rates within the Raton Basin.

Colorado, New Mexico↗