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At least 721 records · Page 40Linked to original sources
USGS1978

On the development of strong-motion instrument networks in the United States

This report outlines a plan for the distribution of strong-motion instrumentation throughout the United States. The present "national" network of strong-motion instrumentation has evolved through the merger of several programs initiated by different agencies and organizations with objectives ranging from research to regulation. It is the result of the coordination of instrument maintenance and record archival currently provided by the Seismic Engineering Branch of the U.S. Geological Survey (formerly the Seismological Field Survey of the U.S. Coast & Geodetic Survey, or the National Ocean Survey, or the National Oceanic and Atmospheric Administration). The USGS operates the program under funding from the National Science Foundation (NSF) in cooperation with other federal, state, and local agencies. NSF supports a data management function and the operation of a network of about 200 accelerographs and 300 seismoscopes utilized for studies of ground motion and building response. The State of California is developing its own strong-motion instrumentation program (CSMIP), which includes measurements of ground motion as well as the response of representative types of structures. The CSMIP network is the largest network operated by a single agency anywhere in the world. Eventually it will contain a total of about 1000 accelerographs. The Army Corps of Engineers (COE) is developing a program for monitoring the response of earth dams, which eventually will include as many as 400 instruments on over 100 dams. Other agencies and organizations are developing networks appropriate to their missions or objectives. At present the number of instruments owned by these other agencies is less than 100 in each case, although several agencies are still expanding their networks. The present distribution of accelerographs in the United States is indicated in Figure 1 (see: USGS, 1977, also). In 1964 the cities of Los Angeles and Beverly Hills, California passed ordinances which required 3 accelerographs to be installed in all high-rise buildings. Initially, these instruments were installed and maintained as a part of the strong-motion program of the Seismological Field Survey (SFS). As the number of installations required by such codes increased, it became apparent that the maintenance of these instruments placed an inordinate burden on and created an imbalance in the SFS operated program (in 1972, 50 percent of the "national" program was concentrated in Los Angeles). With the transfer of the SFS program responsibility to the NSF and with the development of the CSMIP, the responsibility for maintenance of code required instruments has reverted to the city building officials and the building owners. As the coordinated network of strong-motion instruments has grown, the maintenance of the instruments has required a larger staff than the USGS could provide under existing personnel ceilings. This situation has been resolved by the agencies with the larger networks performing their own installation and maintenance. The USGS maintains an archive of first class copies of all records, whereas other agencies maintain archives of their own records, only. In addition, the USGS coordinates the routine processing of all of the significant records, although other agencies will process their own data if they consider it to have a higher priority than does the USGS. In response to a recent change in their legislated charter, the CSMIP is beginning to develop a capability to process the data collected under that program.

Open-File Report↗
USGS1988

Vertical seismic profiling of Oroville microearthquakes: Velocity spectra and particle motion as a function of depth

Direct evidence of site distortion of P - and S -wave microearthquake source spectra at Oroville, California, is presented. The data were gathered by placing vertical and three-component seismometers at 90 m intervals in a 500 m borehole through the Cleveland Hill normal fault, on which the 1975, M L = 5.7 Oroville earthquake took place. High-pressure, hydraulic locking mechanisms were used to firmly lock the seismometer packages against the borehole wall. Digital, event-triggering GEOS recorders were used to receive the data. Some 30 seismic events, including 12 microearthquakes, were recorded during the 4 months the seismometers were deployed. By comparing the velocity spectra of microearthquake waves at the different depths, it can be seen that scattering and attenuation in the shallow crust around the borehole dominantly affect high-frequency S waves. Above 15 Hz, the value of the apparent S -wave quality factor, Q as , for the upper 500 m of crust at this site is 9. One feature of this low Q as is a gross difference between S -wave “corner” frequencies observed at ground level and 500 m downhole. For example, the uphole and downhole S -wave corner frequencies for the M coda = 0.4 microearthquake of Julian Day 259 differ by a factor of 2 or more. Low quality factors and depth-dependent corner frequencies were also observed for P waves, but these data are less definitive due to lower signal-to-noise ratios. Based on their three-component particle motions and polarizations, the direct S waves of the microearthquakes appear to be composed of two phases, which have similar amplitudes but different apparent velocities. It is possible that the velocity differences are a result of anisotropy in the underlying rock.

California↗
USGS2024

Utilization of stochastic ground motion simulations for scenario-based performance assessment of geo-structures

Probabilistic seismic performance assessments of engineered structures can be highly sensitive to the seismic input excitation and its variability. In the present study, the scenario-based performance assessment recommended by Federal Emergency Management Agency (FEMA) P-58 guidelines is adopted to estimate seismic fragility of concrete dams for various seismic hazard scenarios. Due to the scarcity of recorded ground motions and thereby their poor representation of uncertainties, stochastic ground motion simulation methods are utilized to obtain the required input excitations. Moreover, to understand the uncertainty in ground motion simulation models, two broadband stochastic simulation models are used to generate input excitations representing six seismic hazard scenarios defined by earthquake magnitude, source-to-site distance, and soil conditions. Optimal intensity measure parameters for each scenario are identified using a systematic procedure that considers criteria such as efficiency, practicality, proficiency, sufficiency, and hazard compatibility. Fragility curves and surfaces are derived using the cloud analysis technique, taking into account various damage measures and limit state functions. The study finds that the derived fragility curves are particularly sensitive to the selection of earthquake scenarios, the choice of records, and the methods used to calculate fragility curves, with less sensitivity observed to different engineering demand parameters. Given this sensitivity, particularly to ground motion selection, the study highlights the necessity of incorporating both model-to-model variability (epistemic uncertainty) and record-to-record variability (aleatory uncertainty), alongside the established material and modeling uncertainties, in the probabilistic seismic assessment.

Reliability Engineering and System Safety (RESS)↗
USGS2018

Local, regional, and remote seismo-acoustic observations of the April 2015 VEI 4 eruption of Calbuco volcano, Chile

The two major explosive phases of the 22-23 April 2015 eruption of Calbuco volcano, Chile produced powerful seismicity and infrasound. The eruption was recorded on seismo-acoustic stations out to 1,540 km and on 5 stations (IS02, IS08, IS09, IS27, and IS49) of the International Monitoring System (IMS) infrasound network at distances from 1,525 to 5,122 km. The remote IMS infrasound stations provide an accurate explosion chronology consistent with the regional and local seismo-acoustic data, and with previous studies of lightning and plume observations. We use the IMS network to detect and locate the eruption signals using a brute-force, grid search, cross-bearings approach. After incorporating azimuth deviation corrections from stratospheric cross-winds using 3D ray-tracing, the estimated source location is 172 km from true. This case study highlights the significant capability of the IMS infrasound network to provide automated detection, characterization, and timing estimates of global explosive volcanic activity. Augmenting the IMS with regional seismo-acoustic networks will dramatically enhance volcanic signal detection, reduce latency, and improve discrimination capability.

Calbuco volcano↗
USGS1982

Holocene sedimentation in the shallow nearshore zone off Nauset Inlet, Cape Cod, Massachusetts

Present conditions and sedimentary evolution of the shallow offshore region near Nauset Inlet on Cape Cod, Massachusetts were clarified using high-resolution seismic-reflection profiles, sidescan-sonar records, surface grab samples and current meter measurements. The study area contains three provinces: (1) a nearshore province (shallower than 18 m) with a relatively steep slope (0.6°) and a cover of medium sand; (2) a northern offshore province covered with coarse sand, gravel, and boulders, interpreted to be glacial drift; and (3) a southern offshore province with a gentle seaward-dipping slope (0.3°) and a surface sediment of coarse sand. The glacial drift exposed in the northern offshore province can be traced southward under the coarse sand province. The overlying fill is comprised of either outwash sediment derived from the Pleistocene South Channel ice lobe to the east or Holocene-aged marine sediments eroded from seacliffs to the north. Latest Holocene sediment appears to be limited to the zone shoreward of 18 m where the medium sand occurs. Near-bottom mean flows (measured over two winter months in 10 m water depth) average 6 cm sec −1 to the south. Mean flows exceeded 20 cm sec −1 approx. 23% of the time. Ninety percent of the flows exceeding 20 cm sec −1 were directed to the south, reflecting the dominant atmospheric forcing during these winter months. Waves had an average variance of 650 cm 2 with variance exceeding 5000 cm 2 , 3% of the time, indicating moderate wave activity. Present processes are actively reshaping the nearshore province, which is characterized by many east to northeast-trending shore-oblique channels that do not extend seaward of the 18-m contour. Coarse sand in the floors of these channels suggests they may be erosional features, and the presence of megaripples oriented perpendicular to the channel axes indicates active transport in these channels. Megaripple orientation and the current and wave regime of the study area support a rip-current origin for these channels.

Massachussetts↗
USGS2023

Quantifying site effects and their influence on earthquake source parameter estimations using a dense array in Oklahoma

We investigate the effects of site response on source parameter estimates using earthquakes recorded by the LArge-n Seismic Survey in Oklahoma (LASSO). While it is well known that near-surface unconsolidated sediments can cause an apparent breakdown of earthquake self-similarity, the influence of laterally varying site conditions remains unclear. We analyze site conditions across the 1825-station array on a river plain within an area of 40 km by 23 km using vertical ground motions from 14 regional earthquakes. While the source radiation pattern controls P-wave ground motions below 8 Hz, the surface geology correlates with P-wave ground motions above 8 Hz and S-wave ground motions at 2–21 Hz. Stations installed in alluvial sediments have vertical ground motions that can exceed three times the array median. We use the variation of ground motion of regional earthquakes across the array as a proxy for site effects. The corner frequencies and stress drops of local earthquakes ( M L = 0.01–3) estimated using a standard single-spectra approach show negative correlations with the site-effect proxy, while the seismic moments show positive correlations. In contrast, the spectral-ratio approach effectively shows no correlation. The overall bias is small as expected for this relatively homogeneous structure; accurate estimation of site-related biases requires at least 30 stations. Correcting for site-related biases reduces the standard deviations of the source parameters by less than 13% of the total variations. Remaining variations are partially associated with source directivity and model misfits— as small earthquakes can have complex ruptures.

Oklahoma↗
USGS2025

Timescales of surface faulting preservation in low-strain intraplate regions from landscape evolution modeling and the geomorphic and historical record

Large surface-rupturing intraplate earthquakes in stable continental regions (SCRs) are uncommon globally and have recurrence intervals of thousands to hundreds of thousands of years based on the paleoseismic and geomorphic record, challenging accurate active fault identification in these regions. To constrain the timescales of preservation for scarps created by surface ruptures from dip-slip earthquakes, we use a two-dimensional scarp diffusion model for typical intraplate settings and explore which parameters influence fault scarp preservation. These parameters include the coseismic vertical surface offset, the recurrence interval of similar magnitude earthquakes, diffusivity (as a proxy for mean annual precipitation rate), and the erodibility of the surficial material. We constrain parameter ranges from a compilation of historical surface ruptures in intraplate settings in a variety of climates, including the Central and Eastern United States, Australia, Europe, Central Asia (Mongolia, China), India, and West Africa. The timescales of scarp preservation from landscape evolution modeling agree well with observations of scarp preservation in low-strain SCR and intraplate tectonic settings, with some notable exceptions for Australian scarps. We find that the erodibility of the surficial material and earthquake recurrence interval have a stronger effect on the timescales of scarp preservation than diffusivity or coseismic vertical surface offset. Our model results may aid in identifying and characterizing subtle, slow-moving active faults in low-strain SCR and intraplate tectonic settings for different tectonic, geomorphic, and climatic characteristics. Accurate fault locations and characterization from the landscape record has implications for both probabilistic seismic and fault displacement hazard analyses.

Journal of Geophysical Research Solid Earth↗
USGS1975

Anomalous delays of teleseismic P waves in Yellowstone National Park

TELESEISMIC P waves recorded by a short-period seismic network, comprising 12 stations, in Yellowstone National Park, show anomalous delays of 1–2 s in their travel times in the central region of the park relative to the surrounding area. To explain this phenomenon, I propose that a substantial body of low velocity material is present beneath the park, with horizontal dimensions of several tens of kilometres; it may be the magma chamber associated with the volcanism of Yellowstone (ref. 1, and G. P. Eaton et al. , unpublished).

Wyoming↗
USGS2001

P-wave velocity structure of the uppermost mantle beneath Hawaii from traveltime tomography

We examine the P-wave velocity structure beneath the island of Hawaii using P-wave residuals from teleseismic earthquakes recorded by the Hawaiian Volcano Observatory seismic network. The station geometry and distribution of events makes it possible to image the velocity structure between ~ 40 and 100 km depth with a lateral resolution of ~ 15 km and a vertical resolution of ~ 30 km. For depths between 40 and 80 km, P-wave velocities are up to 5 per cent slower in a broad elongated region trending SE-NW that underlies the island between the two lines defined by the volcanic loci. No direct correlation between the magnitude of the lithospheric anomaly and the current level of volcanic activity is apparent, but the slow region is broadened at ~ 19.8??N and narrow beneath Kilauea. In the case of the occanic lithosphere beneath Hawaii, slow seismic velocities are likely to be related to magma transport from the top of the melting zone at the base of the lithosphere to the surface. Thermal modelling shows that the broad elongated low-velocity zone cannot be explained in terms of conductive heating by one primary conduit per volcano but that more complicated melt pathways must exist.

Geophysical Journal International↗
USGS2026

3D broadband ground motion simulations of Cascadia megathrust earthquakes: Full-margin scenarios incorporating variable magnitudes and frontal thrust splay faulting

Great megathrust earthquakes (∼ M w 8–9) that rupture along the Cascadia Subduction Zone pose significant shaking and tsunami hazards to the U.S. Pacific Northwest. Although these large earthquakes are documented in the geologic record, none have been recorded with modern instrumentation, complicating regional seismic hazard assessments. To improve constraints on seismic hazard estimates for future earthquakes, we develop 3D broadband (0–10 Hz) ground‐motion simulations for 36 full‐margin megathrust earthquake scenarios through the Cascadia Coastlines and Peoples Hazards Research Hub. These simulations expand on the M9 Project ( Frankel et al. , 2018 ; Wirth, Frankel, et al. , 2018 ) by incorporating a broader range of rupture parameters—variable magnitudes, splay faulting, and geodetically informed slip distributions. Benchmarking these simulations against the Next Generation Attenuation Subduction (NGA‐Sub) ground‐motion models shows reasonable fits for non‐basin sites, although simulations predict stronger shaking at short (0–2 s) and long (6–10 s) periods. NGA‐Sub basin terms improve fits to synthetic shaking within the Seattle Basin but underpredict amplitudes by a factor of 2 at periods of 2–5 s. We also evaluate how rupture characteristics influence regional inland shaking variability and basin response in the Puget Lowlands. Larger magnitude scenarios generally cause stronger inland shaking due to farther inland extents of slip and larger strong‐motion‐generating fault patches but show little difference in basin amplification within the Puget Lowlands compared to smaller magnitude events. Along‐dip hypocenter location strongly influences overall inland shaking, with offshore (updip) hypocenters generating on average ∼45% higher shaking at long periods (>6 s) compared to onshore (downdip) hypocenters due to rupture directivity effects. Offshore splay faults minimally affect inland shaking but alter offshore deformation important for coupled ground‐shaking and tsunami scenarios. Finally, we show that rupture directivity increases amplification within the Seattle Basin through the generation and interaction of higher order mode surface waves, an effect of 3D basin geometry that cannot be captured using 1D approximations.

British Columbia, California, Oregon, Washington↗
USGS2001

Reprocessing of multi-channel seismic-reflection data collected in the Chukchi Sea

Contained on this set of two CD-ROMs are stacked and migrated multi-channel seismic-reflection data for 44 lines recorded in the Chukchi Sea, northern Alaska, by the United States Geological Survey in 1977, 1978, and 1980. All data were reprocessed by the USGS in 2000 using updated methods. The resulting final data have both increased temporal and spatial resolution thus providing improved interpretability. An added benefit of these CD-ROMs is that they are a more stable, long-term archival medium for the data.

Open-File Report↗
USGS1979

Preliminary catalog of aftershocks of the Guatemala earthquake of February 4, 1976, from the area between Guatemala City and Lake Atitlan

A six-station seismic network, about 140 km in diameter, has been operated just west of Guatemala City since March 1975, as part of a cooperative project between the U.S. Geological Survey and the Institute Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia (INSIVUMEH), of Guatemala. The purpose of this project was to monitor the seismicity near the active volcanoes Pacaya and Fuego bait the seismic stations were well situated to record several thousand aftershocks from the magnitude 7.5 (Ms) Guatemalan earthquake of February 4, 1976. This catalog contains hypocentral data on 1560 of these events from selected time frames between February 5 and June 30, 1976.

area between Guatemala City and Lake Atitlan↗
USGS1981

Seismic-reflection and sidescan-sonar data collected off eastern Cape Cod, Massachusetts, during April 1979

The U.S. Geological Survey collected 98 line kilometers of single-channel seismic-reflection profiles and sidescan sonar records on the inner shelf of eastern Cape Cod, Massachusetts, during April 1979. The data were obtained during cruise NE-1-79 of the R/V NEECHO. The purposes of the survey were: (1) to study the development of barrier islands; (2) to document the frequency and rate of migration of inlets that breach barrier islands; and (3) to define the characteristics of shoreface ridges on a barrier island. he survey uti I ized two acoustic systems. Information about the bottom was obtained by using an EDO Western model 606 sidescan-sonar system (100 kHz). Profiles of the subbottom were collected by an EG&G Uni boom transducer (400-4,000 Hz) and a Del Norte streamer. Positional control for al I track! ines was provided by a shore-based Miniranger system and by LORAN-C. The quality of the records generally is very good. However, subbottom penetration did vary somewhat from place to place during the survey due to the nature of the bottom sediments and to the presence or absence of buried channels. The original records may be examined at the U.S. Geological Survey, Woods Hole, MA 02543. Microfilm copies of the data are avai I able for purchase from the National Geophysical pnd Solar-Terrestrial Data Center, NOAA/EDIS/NGSDC, Code D621, 325 Broadway, Boulder, CO 80303 (303-497-6338).

Open-File Report↗
USGS2021

Local explosion detection and infrasound localization by reverse time migration using 3-D finite-difference wave propagation

Infrasound data are routinely used to detect and locate volcanic and other explosions, using both arrays and single sensor networks. However, at local distances (<15 km) topography often complicates acoustic propagation, resulting in inaccurate acoustic travel times leading to biased source locations when assuming straight-line propagation. Here we present a new method, termed Reverse Time Migration-Finite-Difference Time Domain (RTM-FDTD), that integrates numerical modeling into the standard RTM back-projection process. Travel time information is computed across the entire potential source grid via FDTD modeling to incorporate the effects of topography. The waveforms are then back-projected and stacked at each grid point, with the stack maximum corresponding to the likely source. We apply our method to three volcanoes with different network configurations, source-receiver distances, and topography. At Yasur Volcano, Vanuatu, RTM-FDTD locates explosions within ∼20 m of the source and differentiates between multiple vents. RTM-FDTD produces a more accurate location for the two Yasur subcraters than standard RTM and doubles the number of detected events. At Sakurajima Volcano, Japan, RTM-FDTD locates the source within 50 m of the active vent despite notable topographic blocking. The RTM-FDTD location is similar to that from the Time Reversal Mirror method, but is more computationally efficient. Lastly, at Shishaldin Volcano, Alaska, RTM and RTM-FDTD both produce realistic source locations (<50 m) for ground-coupled airwaves recorded on a four-station seismic network. We show that RTM is an effective method to detect and locate infrasonic sources across a variety of scenarios, and by integrating numerical modeling, RTM-FDTD produces more accurate source locations and increases the detection capability.

Alaska↗
USGS2016

Archive of Digital Chirp Subbottom Profile Data Collected During USGS Cruise 14BIM05 Offshore of Breton Island, Louisiana, August 2014

From August 11 to 31, 2014, the U.S. Geological Survey ( USGS ), in cooperation with the U.S. Fish and Wildlife Service ( USFWS ), conducted a geophysical survey to investigate the geologic controls on barrier island framework and long-term sediment transport offshore of Breton Island, Louisiana as part of a broader USGS study on Barrier Island Mapping ( BIM ). Additional details related to this activity can be found by searching the USGS's Coastal and Marine Geoscience Data System (CMGDS), for field activity 2014-317-FA (also known as 14BIM05). These surveys were funded through the USGS Coastal and Marine Geology Program ( CMGP ) and the Louisiana Outer Coast Early Restoration Project. This report serves as an archive of unprocessed digital chirp subbottom data, trackline maps, navigation files, Geographic Information System ( GIS ) files, Field Activity Collection System ( FACS ) logs, and formal Federal Geographic Data Committee ( FGDC ) metadata. Gained digital images of the seismic profiles are also provided. Refer to the Abbreviations page for explanations of acronyms and abbreviations used in this report. All chirp systems use an acoustic signal of continuously varying frequency; the EdgeTech 512i system used during this survey produced high-resolution, shallow-penetration (typically less than 50 milliseconds [ ms] ) profile images of sub-seafloor stratigraphy. The towfish contains a transducer that transmits and receives acoustic energy and typically is towed 1&ndash;2 meters ( m ) below the sea surface. As transmitted acoustic energy intersects density boundaries, such as the seafloor or sub-surface sediment layers, some energy is reflected back toward the transducer, received, and recorded by a Personal Computer ( PC) -based seismic acquisition system. This process is repeated at regular intervals (for example, 0.125 seconds ( s) ) and returned energy is recorded for a specific duration (for example, 50 ms ). In this way, a two-dimensional ( 2-D ) vertical image of the shallow geologic structure beneath the ship's track is produced. Figure 2 displays the acquisition geometry. Refer to table 1 for a summary of acquisition parameters and table 2 for trackline statistics. The archived trace data are in standard SEG Y rev. 0 format (Barry and others, 1975); the first 3,200 bytes of the card image header are in American Standard Code for Information Interchange ( ASCII ) format instead of Extended Binary Coded Decimal Interchange Code ( EBCDIC ) format. The SEG Y files are available on the DVD version of this report or online, downloadable via the USGS Coastal and Marine Geoscience Data System ( http://cmgds.marine.usgs.gov ). The data are also available for viewing using GeoMapApp ( http://www.geomapapp.org ) and Virtual Ocean ( http://www.virtualocean.org ) multi-platform open source software. The Web version of this archive does not contain the SEG Y trace files. To obtain the complete DVD archive, contact USGS Information Services at 1-888-ASK-USGS or infoservices@usgs.gov. The SEG Y files may be downloaded and processed with commercial or public domain software such as Seismic Unix ( SU ) (Cohen and Stockwell, 2010). See the How To Download SEG Y Data page for download instructions. The printable profiles are provided as Graphics Interchange Format ( GIF ) images processed and gained using SU software and can be viewed from the Profiles page or by using the links located on the trackline maps; refer to the Software page for links to example SU processing scripts.

Louisana↗