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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 1,027 records · Page 57Linked to original sources

USGS1990

GLIMPCE Seismic reflection evidence of deep-crustal and upper-mantle intrusions and magmatic underplating associated with the Midcontinent Rift system of North America

Deep-crustal and Moho reflections, recorded on vertical incidence and wide angle ocean bottom Seismometer (OBS) data in the 1986 GLIMPCE (Great Lakes International Multidisciplinary Program on Crustal Evolution) experiment, provide evidence for magmatic underplating and intrusions within the lower crust and upper mantle contemporaneous with crustal extension in the Midcontinent Rift system at 1100 Ma. The rift fill consists of 20-30 km (7-10 s) of basalt flows, secondary syn-rift volcaniclastic and post-basalt sedimentary rock. Moho reflections recorded in Lake Superior over the Midcontinent Rift system have times from 14-18 s (about 46 km to as great as 58 km) in contrast to times of about 11-13 s (about 36-42 km crustal thickness) beneath the surrounding Great Lakes. The Seismically complex deep-crust to mantle transition zone (30-60 km) in north-central Lake Superior, which is 100 km wider than the rift half-graben, reflects the complicated products of tectonic and magmatic interaction of lower-crustal and mantle components during evolution or shutdown of the aborted Midcontinent Rift. In effect, mantle was changed into crust by lowering Seismic velocity (through intrusion of lower density magmatic rocks) and increasing Moho (about 8.1 km s-1 depth.

Great Lakes↗

USGS2001

Effect of depth-dependent shear modulus on tsunami generation along subduction zones

Estimates of the initial size of tsunamis generated by subduction zone earthquakes are significantly affected by the choice of shear modulus at shallow depths. Analysis of over 360 circum-Pacific subduction zone earthquakes indicates that for a given seismic moment, source duration increases significantly with decreasing depth (Bilek and Lay, 1998; 1999). Under the assumption that stress drop is constant, the increase of source duration is explained by a 5-fold reduction of shear modulus from depths of 20 km to 5 km. This much lower value of shear modulus at shallow depths in comparison to standard earth models has the effect of increasing the amount of slip estimated from seismic moment determinations, thereby increasing tsunami amplitude. The effect of using depth dependent shear modulus values is tested by modeling the tsunami from the 1992 Nicaraguan tsunami earthquake using a previously determined moment distribution (lhmle??, 1996a). We find that the tide gauge record of this tsunami is well matched by synthetics created using the depth dependent shear modulus and moment distribution. Because excitation of seismic waves also depends on elastic heterogeneity, it is important, particularly for the inversion of short period waves, that a consistent seismic/tsunami shear modulus model be used for calculating slip distributions.

Geophysical Research Letters↗

USGS1996

Shallow velocity structure and Poisson's ratio at the Tarzana, California, strong-motion accelerometer site

The 17 January 1994, Northridge, California, earthquake produced strong ground shaking at the Cedar Hills Nursery (referred to here as the Tarzana site) within the city of Tarzana, California, approximately 6 km from the epicenter of the mainshock. Although the Tarzana site is on a hill and is a rock site, accelerations of approximately 1.78 g horizontally and 1.2 g vertically at the Tarzana site are among the highest ever instrumentally recorded for an earthquake. To investigate possible site effects at the Tarzana site, we used explosive-source seismic refraction data to determine the shallow (<70 m) P -and S -wave velocity structure. Our seismic velocity models for the Tarzana site indicate that the local velocity structure may have contributed significantly to the observed shaking. P -wave velocities range from 0.9 to 1.65 km/sec, and S -wave velocities range from 0.20 and 0.6 km/sec for the upper 70 m. We also found evidence for a local S -wave low-velocity zone ( LVZ ) beneath the top of the hill. The LVZ underlies a CDMG strong-motion recording site at depths between 25 and 60 m below ground surface ( BGS ). Our velocity model is consistent with the near-surface (<30 m) P - and S -wave velocities and Poisson's ratios measured in a nearby (<30 m) borehole. High Poisson's ratios (0.477 to 0.494) and S -wave attenuation within the LVZ suggest that the LVZ may be composed of highly saturated shales of the Modelo Formation. Because the lateral dimensions of the LVZ approximately correspond to the areas of strongest shaking, we suggest that the highly saturated zone may have contributed to localized strong shaking. Rock sites are generally considered to be ideal locations for site response in urban areas; however, localized, highly saturated rock sites may be a hazard in urban areas that requires further investigation.

California↗

USGS2019

Two-dimensional seismic velocities and structural variations at three British Columbia Hydro and Power Authority (BC Hydro) dam sites, Vancouver Island, British Columbia, Canada

Summary In June, 2017, we acquired seismic data along five linear profiles at three British Columbia Hydro and Power Authority (BC Hydro, a Canadian provincial Crown Corporation) dam sites (John Hart, Ladore, and Strathcona Dams) on Vancouver Island, British Columbia, Canada. We also attempted to acquire linear seismic profiles at two additional BC Hydro dam sites (Ruskin Dam and Stave Falls Dam) east of the City of Vancouver, British Columbia, Canada; however, due to a seismograph programming error, little active-source data from Ruskin Dam and Stave Falls Dam were recorded. Thus, results from Ruskin Dam and Stave Falls Dam are not included in this report. At the three dam sites with successful data acquisition, we acquired both active- and passive-source data. Data acquisition details for each of the three dam sites varied in terms of seismic sources, the number of seismographs, and profile length and orientation. However, for active-source acquisition at each dam site, we acquired one or more linear seismic profiles ranging in length from about 150 to 400 meters (m), and along each profile, seismograph spacing was either 3 m or 5 m (see appendix 1). All data were recorded in three components (vertical and two horizontals). To greatly increase the resolution of the seismic velocity structure along these profiles, we co-located active sources at each seismograph.

British Columbia↗

USGS2007

Late Cenozoic Climate History of the Ross Embayment from the AND-1B Drill Hole: Culmination of Three Decades of Antarctic Margin Drilling

Because of the paucity of exposed rock, the direct physical record of Antarctic Cenozoic glacial history has become known only recently and then largely from offshore shelf basins through seismic surveys and drilling. The number of holes on the continental shelf has been small and largely confined to three areas (McMurdo Sound, Prydz Bay, and Antarctic Peninsula), but even in McMurdo Sound, where Oligocene and early Miocene strata are well cored, the late Cenozoic is poorly known and dated. The latest Antarctic geological drilling program, ANDRILL, successfully cored a 1285-m-long record of climate history spanning the last 13 m.y. from subsea-floor sediment beneath the McMurdo Ice Shelf (MIS), using drilling systems specially developed for operating through ice shelves. The cores provide the most complete Antarctic record to date of ice-sheet and climate fluctuations for this period of Earth’s history. The >60 cycles of advance and retreat of the grounded ice margin preserved in the AND-1B record the evolution of the Antarctic ice sheet since a profound global cooling step in deep-sea oxygen isotope records ~14 m.y.a. A feature of particular interest is a ~90-m-thick interval of diatomite deposited during the warm Pliocene and representing an extended period (~200,000 years) of locally open water, high phytoplankton productivity, and retreat of the glaciers on land.

Open-File Report↗

USGS2006

V P and V S structure of the Yellowstone hot spot from teleseismic tomography: Evidence for an upper mantle plume

The movement of the lithosphere over a stationary mantle magmatic source, often thought to be a mantle plume, explains key features of the 16 Ma Yellowstone–Snake River Plain volcanic system. However, the seismic signature of a Yellowstone plume has remained elusive because of the lack of adequate data. We employ new teleseismic P and S wave traveltime data to develop tomographic images of the Yellowstone hot spot upper mantle. The teleseismic data were recorded with two temporary seismograph arrays deployed in a 500 km by 600 km area centered on Yellowstone. Additional data from nearby regional seismic networks were incorporated into the data set. The V P and V S models reveal a strong low-velocity anomaly from ∼50 to 200 km directly beneath the Yellowstone caldera and eastern Snake River Plain, as has been imaged in previous studies. Peak anomalies are −2.3% for V P and −5.5% for V S . A weaker, anomaly with a velocity perturbation of up to −1.0% V P and −2.5% V S continues to at least 400 km depth. This anomaly dips 30° from vertical, west-northwest to a location beneath the northern Rocky Mountains. We interpret the low-velocity body as a plume of upwelling hot, and possibly wet rock, from the mantle transition zone that promotes small-scale convection in the upper ∼200 km of the mantle and long-lived volcanism. A high-velocity anomaly, 1.2% V P and 1.9% V S , is located at ∼100 to 250 km depth southeast of Yellowstone and may represent a downwelling of colder, denser mantle material.

Idaho, Montana, Nevada, Oregon, Utah, Wyoming↗

USGS2024

Evaluation of 2-D shear-wave velocity models and VS30at six strong-motion recording stations in southern California using multichannel analysis of surface waves and refraction tomography

To better understand the potential for amplified ground shaking at sites that house critical infrastructure, the U.S. Geological Survey (USGS) evaluated shear-wave velocities ( V S ) at six strong-motion recording stations in Southern California Edison facilities in southern California. We calculated V S30 (time-averaged shear-wave velocity in the upper 30 meters [m]), which is a parameter used in ground-motion prediction equations (GMPEs) to account for site amplification (Building Safety Seismic Council, 2003; Holtzer and others, 2005; Baltay and Boatwright, 2015). Previous site-characterization studies using multiple methods in Alameda, Napa, and Sonoma Counties, Calif., and in British Columbia (Catchings and others, 2017, 2019; Chan and others, 2018a, 2018b) show that some sites have significant lateral variability; thus, a single measurement of V S30 nearest to the strong-motion recording station may not accurately account for the actual subsurface velocity variations. In the summer of 2017, we recorded body and surface waves along linear profiles (118–174 m long) using active-source seismic methods (226-kilogram [kg] accelerated weight-drop and 3.5-kg sledgehammer impacts) near strong-motion recording stations. We used S-wave refraction tomography and a multichannel analysis of surface waves (MASW) method (using common midpoint cross-correlation; CMPCC) to evaluate two-dimensional (2-D) V S from body and surface waves, respectively. We evaluated V S from both Rayleigh- and Love-waves.

California↗

USGS2003

Old Seismic bulletins to 1920: A collective heritage from early seismologists

This chapter focuses on collective heritage from early seismologists. Scientists began systematic instrumental observation of earthquakes in the latter part of the 19 th century. Several authors describe the history of the development of an adequate instrumentation for seismology. In the 1880s, scientists in Italy, Japan, and Germany began to record more or less continuously the ground motion with their newly developed seismographs. Because of the limited ability to reproduce the original (analog) paper seismograms, seismologists had to describe their observations in words and numbers. The recording instruments were able to produce seismograms in which one could distinguish between the onsets of all three wave types (i.e., P, S, and surface waves), and a common vocabulary for the description of these records was developed. During the last half of the 19 th century, scientists in many countries began to systematically collect data of macro seismically observed earthquakes and the locations of these events, known only on the basis of such data. In some countries, scientists and/or their governments established special committees or commissions to do this work. The earthquake lists and bulletin data from the early seismic stations not only document the history of seismology but also have intrinsic scientific value. Even today, these old bulletins are needed for event relocation as our technique for earthquake location improves. They are also useful for magnitude analysis to establish a consistent magnitude scale.

Book chapter↗

USGS2008

Observations and interpretation of fundamental mode Rayleigh wavefields recorded by the Transportable Array (USArray)

Broadband recordings of the dense Transportable Array (TA) in the western United States provide unparalleled detailed images of long-period seismic surface wavefields. With 400 stations spanning most of the western United States, wavefronts of fundamental mode Rayleigh waves may be visualized coherently across the array at periods ???40 s. In order to constrain the Rayleigh wave phase velocity structure in the western United States, I assemble a data set of vertical component seismograms from 53 teleseismic events recorded by the TA from April 2006 to October 2007. Complex amplitude spectra from these recordings at peni ods 27-100 s are interpreted using the multiplane wave tomographic method of Friederich and Wielandt (1995) and Pollitz (1999). This analysis yields detailed surface wave phase velocity and three-dimensional shear wave velocity patterns across the North American plate boundary zone, elucidating the active processes in the highly heterogeneous western U.S. upper mantle.

Journal of Geophysical Research B: Solid Earth↗

USGS1998

Postimpact deformation associated with the late Eocene Chesapeake Bay impact structure in southeastern Virginia

Upper Cenozoic strata covering the Chesapeake Bay impact structure in southeastern Virginia record intermittent differential movement around its buried rim. Miocene strata in a graben detected by seismic surveys on the York River exhibit variable thickness and are deformed above the crater rim. Fan-like interformational and intraformational angular unconformities within Pliocene–Pleistocene strata, which strike parallel to the crater rim and dip 2°–3° away from the crater center, indicate that deformation and deposition were synchronous. Concentric, large-scale crossbedded, bioclastic sand bodies of Pliocene age within ∼20 km of the buried crater rim formed on offshore shoals, presumably as subsiding listric slump blocks rotated near the crater rim.

Geology↗

USGS2024

Comparing subduction ground-motion models to observations for Cascadia

We evaluate Cascadia subduction ground-motion models (GMMs), considered for the 2023 US National Seismic Hazard Model (NSHM) update, by comparing observations to model predictions. The observations comprise regional recordings from intraslab earthquakes, including contributions from 2021 and 2022 events in southern Cascadia and global records from interface earthquakes. Since the 2018 NSHM update, new GMMs for Cascadia have been published by the Next Generation Attenuation (NGA)-Subduction Project that require independent evaluation. In the regional intraslab comparisons, we highlight a characteristic frequency dependence for Cascadia data, with short periods having lower ground motions and longer periods being comparable to other subduction zones. We evaluate differences in northern and southern Cascadia and find that the NGA-Subduction GMMs developed using southern Cascadia data perform better in this region than the model that did not consider these data. We compare ground-motion variability in Cascadia with the NGA-Subduction model predictions and find differences at short periods ( T = 0.1 s) due to the use of global versus regional data in the development of these models. Moreover, the within-event component of aleatory variability from the GMMs overpredicts the standard deviation of Cascadia recordings at very short periods ( T < 0.05 s). Using global interface earthquakes as a proxy to evaluate the Cascadia GMMs, we find long-period overprediction from a simulation-based GMM and some of the empirical GMMs. When comparing recent observations, we find a similar misfit to GMMs and the 2010 and 2022 Ferndale earthquakes. Finally, we observe different basin amplification factors arising in different subsets of the data, which indicate that differences in basin factors between empirical GMMs could arise from the data selection choices by the developers. As part of evaluating the regional basin terms, we apply basin amplification factors from the magnitude 9 Cascadia earthquake simulations to the empirical GMMs for interface earthquakes. The comparisons presented in this study indicate that the NGA-Subduction GMMs for Cascadia perform well relative to observations and older subduction GMMs.

British Columbia, California, Oregon, Washington↗

USGS2006

Introduction to the special issue on the 2004 Parkfield earthquake and the Parkfield earthquake prediction experiment

The 28 September 2004 M 6.0 Parkfield earthquake, a long-anticipated event on the San Andreas fault, is the world's best recorded earthquake to date, with state-of-the-art data obtained from geologic, geodetic, seismic, magnetic, and electrical field networks. This has allowed the preearthquake and postearthquake states of the San Andreas fault in this region to be analyzed in detail. Analyses of these data provide views into the San Andreas fault that show a complex geologic history, fault geometry, rheology, and response of the nearby region to the earthquake-induced ground movement. Although aspects of San Andreas fault zone behavior in the Parkfield region can be modeled simply over geological time frames, the Parkfield Earthquake Prediction Experiment and the 2004 Parkfield earthquake indicate that predicting the fine details of future earthquakes is still a challenge. Instead of a deterministic approach, forecasting future damaging behavior, such as that caused by strong ground motions, will likely continue to require probabilistic methods. However, the Parkfield Earthquake Prediction Experiment and the 2004 Parkfield earthquake have provided ample data to understand most of what did occur in 2004, culminating in significant scientific advances.

Bulletin of the Seismological Society of America↗

USGS2016

Earthquake source properties from pseudotachylite

The motions radiated from an earthquake contain information that can be interpreted as displacements within the source and therefore related to stress drop. Except in a few notable cases, the source displacements can neither be easily related to the absolute stress level or fault strength, nor attributed to a particular physical mechanism. In contrast paleo-earthquakes recorded by exhumed pseudotachylite have a known dynamic mechanism whose properties constrain the co-seismic fault strength. Pseudotachylite can also be used to directly address a longstanding discrepancy between seismologically measured static stress drops, which are typically a few MPa, and much larger dynamic stress drops expected from thermal weakening during localized slip at seismic speeds in crystalline rock [Sibson, 1973; McKenzie and Brune, 1969; Lachenbruch, 1980; Mase and Smith, 1986; Rice, 2006] as have been observed recently in laboratory experiments at high slip rates [Di Toro et al., 2006a]. This note places pseudotachylite-derived estimates of fault strength and inferred stress levels within the context and broader bounds of naturally observed earthquake source parameters: apparent stress, stress drop, and overshoot, including consideration of roughness of the fault surface, off-fault damage, fracture energy, and the 'strength excess'. The analysis, which assumes stress drop is related to corner frequency by the Madariaga [1976] source model, is restricted to the intermediate sized earthquakes of the Gole Larghe fault zone in the Italian Alps where the dynamic shear strength is well-constrained by field and laboratory measurements. We find that radiated energy exceeds the shear-generated heat and that the maximum strength excess is ~16 MPa. More generally these events have inferred earthquake source parameters that are rate, for instance a few percent of the global earthquake population has stress drops as large, unless: fracture energy is routinely greater than existing models allow, pseudotachylite is not representative of the shear strength during the earthquake that generated it, or unless the strength excess is larger than we have allowed.

Gole Larghe fault zone↗

USGS2019

Using component ratios to detect metadata and instrument problems of seismic stations: Examples from 18 years of GEOSCOPE data

Replacement or deterioration of seismic instruments and the evolution of the installation conditions and sites can alter the seismic signal in very subtle ways, so it is notoriously difficult to monitor the signal quality of permanent seismic stations. We present a simple tool, energy ratios between each pair of the three recorded components, aimed at characterizing and monitoring signal quality, as a complement to existing methods. To calculate stable daily energy ratios over a large frequency range (0.01 Hz – 5 Hz), we use the daily median energy ratio over all 5-minute windows within the day. The method is applied to all GEOSCOPE stations, for continuous BH channel data collected since 2001. We show applications to identify past gain problems (stations ROCAM and CRZF), to provide feedback after field interventions at remote sites (Antarctic station DRV), and to shed light on complex instrument problems (stations ECH and KIP). Our results show that component energy ratios have excellent time resolution and that they are visually simple for identification of problems. They can be used both for ongoing continuous monitoring of the signal quality, or as a tool to identify past problems. The associated python codes are available on GitHub.

Seismological Research Letters↗

USGS2023

Uncertainties in intensity-based earthquake magnitude estimates

Estimating the magnitude of historical earthquakes is crucial for assessing seismic hazard. Magnitudes of early‐instrumental earthquakes can be inferred using a combination of instrumental records, field observations, and the observed distribution of shaking intensity determined from macroseismic observations. For earthquakes before 1900, shaking intensity distributions often provide the only information to constrain earthquake magnitude. Considerable effort has been made to develop methods to estimate the magnitude of moderate‐to‐large historical earthquakes using shaking intensities derived from macroseismic data. In this study, we consider earthquakes in California with known instrumental magnitudes to explore uncertainties in estimating the magnitude of historical earthquakes from intensity information alone. We use three California‐specific intensity prediction equations (IPEs) and an IPE based on a global ground‐motion model (GMM) to determine optimum intensity‐based magnitudes for 33 moderate‐to‐large California earthquakes between 1979 and 2021. Intensity‐based magnitudes are close to instrumental magnitudes on average. However, intensity‐based magnitudes for individual events differ by as much as 2.2 magnitude units from instrumental magnitudes. This result reflects the weak dependence of ground motions and shaking intensities on moment magnitude and their strong dependence on stress drop. Considering the intensity distributions of the 1906 San Francisco and 1989 Loma Prieta earthquakes, we show that information that could constrain rupture length is discarded when considering only the 2D decay of intensity with distance. We also show that ground‐motion intensity conversion equations used in a GMM‐based approach may cause a systematic overestimation of large historical earthquake magnitudes. This study underscores both the reducible and potentially irreducible uncertainties associated with using intensity data to estimate magnitudes of historical earthquakes using IPEs and highlights the value of using additional information to constrain rupture dimensions. Using intensity observations alone, moment magnitude uncertainties are typically on the order of a full unit.

California↗

USGS2006

Earthquakes in Virginia and vicinity 1774 - 2004

This map summarizes two and a third centuries of earthquake activity. The seismic history consists of letters, journals, diaries, and newspaper and scholarly articles that supplement seismograph recordings (seismograms) dating from the early twentieth century to the present. All of the pre-instrumental (historical) earthquakes were large enough to be felt by people or to cause shaking damage to buildings and their contents. Later, widespread use of seismographs meant that tremors too small or distant to be felt could be detected and accurately located. Earthquakes are a legitimate concern in Virginia and parts of adjacent States. Moderate earthquakes cause slight local damage somewhere in the map area about twice a decade on the average. Additionally, many buildings in the map area were constructed before earthquake protection was added to local building codes. The large map shows all historical and instrumentally located earthquakes from 1774 through 2004.

Virginia↗

USGS2009

High-Resolution Geologic Mapping of the Inner Continental Shelf: Cape Ann to Salisbury Beach, Massachusetts

The geologic framework of the Massachusetts inner continental shelf between Cape Ann and Salisbury Beach has been shaped by a complicated history of glaciation, deglaciation, and changes in relative sea level. New geophysical data (swath bathymetry, sidescan sonar and seismic-reflection profiling), sediment samples, and seafloor photography provide insight into the geomorphic and stratigraphic record generated by these processes. High-resolution spatial data and geologic maps in this report support coastal research and efforts to understand the type, distribution, and quality of subtidal marine habitats in the Massachusetts coastal ocean.

Open-File Report↗

USGS2008

Earthquakes in Ohio and Vicinity 1776-2007

This map summarizes two and a third centuries of earthquake activity. The seismic history consists of letters, journals, diaries, and newspaper and scholarly articles that supplement seismograph recordings (seismograms) dating from the early twentieth century to the present. All of the pre-instrumental (historical) earthquakes were large enough to be felt by people or to cause shaking damage to buildings and their contents. Later, widespread use of seismographs meant that tremors too small or distant to be felt could be detected and accurately located. Earthquakes are a legitimate concern in Ohio and parts of adjacent States. Ohio has experienced more than 160 felt earthquakes since 1776. Most of these events caused no damage or injuries. However, 15 Ohio earthquakes resulted in property damage and some minor injuries. The largest historic earthquake in the state occurred in 1937. This event had an estimated magnitude of 5.4 and caused considerable damage in the town of Anna and in several other western Ohio communities. The large map shows all historical and instrumentally located earthquakes from 1776 through 2007.

Open-File Report↗