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At least 667 records · Page 37Linked to original sources

USGS1979

Deep structure under Yellowstone National Park U.S.A.: A continental "hot spot"

In order to understand the origin of long-lived loci of volcanism (sometimes called “hot spots”) and their possible role in global tectonic processes, it is essential to know their deep structure. Even though some work has been done on the crustal, upper-mantle, and deep-mantle structure under some of these “hot spots”, the picture is far from clear. In an attempt to study the structure under the Yellowstone National Park U.S.A., which is considered to be such a “hot spot”, we recorded teleseisms using 26 telemetered seismic stations and three groups of portable stations. The network was operated within a 150 km radius centered on the Yellowstone caldera, the major, Quaternary volcanic feature of the Yellowstone region. Teleseismic delays of about 1.5 sec are found inside the caldera, and the delays remain high over a 100 km wide area around the caldera. The spatial distribution and magnitude of the delays indicate the presence of a large body of low-velocity material with horizontal dimensions corresponding approximately to the caldera size (40 km × 80 km) near the surface and extending to a depth of 200–250 km under the caldera. Using ray-tracing and inversion techniques, it is estimated that the compressional velocity inside the anomalous body is lower than in the surrounding rock by about 15% in the upper crust and by 5% in the lower crust and upper mantle. It is postulated that the body is partly composed of molten rock with a high degree of partial melting at shallow depths and is responsible for the observed Yellowstone volcanism. The large size of the partially molten body, taken together with its location at the head of a 350 km zone of volcanic propagation along the axis of the Snake River Plain, indicates that the volcanism associated with Yellowstone has its origin below the lithosphere and is relatively stationary with respect to plate motion. Using our techniques, we are unable to detect any measurable velocity contrast in the mantle beneath the low-velocity body, and, hence, we are unable to determine whether the Yellowstone melting anomaly is associated with a deep heat source or with any deep phenomenon such as a convection plume, chemical plume, or gravitational anchor.

Wyoming↗

USGS2009

Constraints on deep moonquake focal mechanisms through analyses of tidal stress

[1] A relationship between deep moonquake occurrence and tidal forcing is suggested by the monthly periodicities observed in the occurrence times of events recorded by the Apollo Passive Seismic Experiment. In addition, the typically large S wave to P wave arrival amplitude ratios observed on deep moonquake seismograms are indicative of shear failure. Tidal stress, induced in the lunar interior by the gravitational influence of the Earth, may influence moonquake activity. We investigate the relationship between tidal stress and deep moonquake occurrence by searching for a linear combination of the normal and shear components of tidal stress that best approximates a constant value when evaluated at the times of moonquakes from 39 different moonquake clusters. We perform a grid search at each cluster location, computing the stresses resolved onto a suite of possible failure planes, to obtain the best fitting fault orientation at each location. We find that while linear combinations of stresses (and in some cases stress rates) can fit moonquake occurrence at many clusters quite well; for other clusters, the fit is not strongly dependent on plane orientation. This suggests that deep moonquakes may occur in response to factors other than, or in addition to, tidal stress. Several of our inferences support the hypothesis that deep moonquakes might be related to transformational faulting, in which shear failure is induced by mineral phase changes at depth. The occurrence of this process would have important implications for the lunar interior. Copyright 2009 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2011

Shallow conduit system at Kilauea Volcano, Hawaii, revealed by seismic signals associated with degassing bursts

Eruptive activity at the summit of Kilauea Volcano, Hawaii, beginning in March, 2008 and continuing to the present time is characterized by episodic explosive bursts of gas and ash from a vent within Halemaumau Pit Crater. These bursts are accompanied by seismic signals that are well recorded by a broadband network deployed in the summit caldera. We investigate in detail the dimensions and oscillation modes of the source of a representative burst in the 1−10 s band. An extended source is realized by a set of point sources distributed on a grid surrounding the source centroid, where the centroid position and source geometry are fixed from previous modeling of very-long-period (VLP) data in the 10–50 s band. The source time histories of all point sources are obtained simultaneously through waveform inversion carried out in the frequency domain. Short-scale noisy fluctuations of the source time histories between adjacent sources are suppressed with a smoothing constraint, whose strength is determined through a minimization of the Akaike Bayesian Information Criterion (ABIC). Waveform inversions carried out for homogeneous and heterogeneous velocity structures both image a dominant source component in the form of an east trending dike with dimensions of 2.9 × 2.9 km. The dike extends ∼2 km west and ∼0.9 km east of the VLP centroid and spans the depth range 0.2–3.1 km. The source model for a homogeneous velocity structure suggests the dike is hinged at the source centroid where it bends from a strike E 27°N with northern dip of 85° west of the centroid, to a strike E 7°N with northern dip of 80° east of the centroid. The oscillating behavior of the dike is dominated by simple harmonic modes with frequencies ∼0.2 Hz and ∼0.5 Hz, representing the fundamental mode ν 11 and first degenerate mode ν 12 = ν 21 of the dike. Although not strongly supported by data in the 1–10 s band, a north striking dike segment is required for enhanced compatibility with the model elaborated in the 10–50 s band. This dike provides connectivity between the east trending dike and the new vent within Halemaumau Pit Crater. Waveform inversions with a dual-dike model suggest dimensions of 0.7 × 0.7 km to 2.6 × 2.6 km for this segment. Further elaboration of the complex dike system under Halemaumau does not appear to be feasible with presently available data.

Hawai'i↗

USGS2026

Global primary and secondary microseism multi-decade geographic variation, secular intensification, and period lengthening

Earth's long-period background seismic wavefield is dominated by two distinct processes that couple ocean wave energy to a global microseism wavefield. We assess global microseism intensity in the secondary (4–10 s) and primary (14–20 s) bands, and across eight 2 s-wide period bands between 4 and 20 s. Robustly estimated primary and secondary secular amplitude trends are estimated at 73 globally distributed seismic station sites with continuous recording spanning at least 20 years, from as early as the late 1980s through October 2025. These trends are positive at 3⁢𝜎 significance for 61 (84%) and 46 (63%) stations with global average rates for vertical-component acceleration of 0.17 ± 0.04 and 0.11 ± 0.05%/yr, for the primary and secondary bands, respectively, with corresponding rates of energy increase of 0.27 ± 0.08 and 0.15 ± 0.09%/yr. Secular intensification is also observed within all 2 s period bands between 4 and 20 s. Amplitude histories for the longest primary microseism periods (18–20 s) correlate to near-antipodal distances, reflecting long-range teleconnections attributed to large-fetch storm systems, long-range swell and Rayleigh wave propagation, and geographically correlated El Niño Southern Oscillation and other geographically extensive atmospheric influences on storms and waves. The lower average rates of intensification for the secondary microseism suggest that crossing wave systems in remote regions are either under-observed or are intensifying more slowly than the primary microseism, possibly due to increasing swell unidirectionality. Secular intensification is greatest at the longest primary microseism periods. This is consistent with a broadening of the global ocean wave spectrum by approximately 0.01%/yr which may reflect an increasing occurrence of large storm systems.

JGR Solid Earth↗

USGS2014

Geology and neotectonism in the epicentral area of the 2011 M5.8 Mineral, Virginia, earthquake

This fi eld guide covers a two-day west-to-east transect across the epicentral region of the 2011 M5.8 Mineral, Virginia, earthquake, the largest ever recorded in the Central Virginia seismic zone. The fi eld trip highlights results of recent bedrock and surficial geologic mapping in two adjoining 7.5-min quadrangles, the Ferncliff and the Pendleton, which together encompass the epicenter and most of the 2011–2012 aftershocks. Tectonic history of the region includes early Paleozoic accretion of an island arc (Ordovician Chopawamsic Formation) to Laurentia, intrusion of a granodiorite pluton (Ordovician Ellisville pluton), and formation of a post-Chopawamsic successor basin (Ordovician Quantico Formation), all accompanied by early Paleozoic regional deformation and metamorphism. Local transpressional faulting and retrograde metamorphism occurred in the late Paleozoic, followed by diabase dike intrusion and possible local normal faulting in the early Mesozoic. The overall goal of the bedrock mapping is to determine what existing geologic structures might have been reactivated during the 2011 seismic event, and surfi cial deposits along the South Anna River are being mapped in order to determine possible neotectonic uplift. In addition to bedrock and surfi cial studies, we have excavated trenches in an area that contains two late Paleozoic faults and represents the updip projection of the causative fault for the 2011 quake. The trenches reveal faulting that has offset surfi cial deposits dated as Quaternary in age, as well as numerous other brittle structures that suggest a geologically recent history of neotectonic activity.

Virginia↗

USGS2004

Optimizing correlation techniques for improved earthquake location

Earthquake location using relative arrival time measurements can lead to dramatically reduced location errors and a view of fault-zone processes with unprecedented detail. There are two principal reasons why this approach reduces location errors. The first is that the use of differenced arrival times to solve for the vector separation of earthquakes removes from the earthquake location problem much of the error due to unmodeled velocity structure. The second reason, on which we focus in this article, is that waveform cross correlation can substantially reduce measurement error. While cross correlation has long been used to determine relative arrival times with subsample precision, we extend correlation measurements to less similar waveforms, and we introduce a general quantitative means to assess when correlation data provide an improvement over catalog phase picks. We apply the technique to local earthquake data from the Calaveras Fault in northern California. Tests for an example streak of 243 earthquakes demonstrate that relative arrival times with normalized cross correlation coefficients as low as ∼70%, interevent separation distances as large as to 2 km, and magnitudes up to 3.5 as recorded on the Northern California Seismic Network are more precise than relative arrival times determined from catalog phase data. Also discussed are improvements made to the correlation technique itself. We find that for large time offsets, our implementation of time-domain cross correlation is often more robust and that it recovers more observations than the cross spectral approach. Longer time windows give better results than shorter ones. Finally, we explain how thresholds and empirical weighting functions may be derived to optimize the location procedure for any given region of interest, taking advantage of the respective strengths of diverse correlation and catalog phase data on different length scales.

Bulletin of the Seismological Society of America↗

USGS2021

Coseismic fault slip and afterslip associated with the M5.7 March 18, 2020 Magna, Utah, earthquake

The 2020 Magna, Utah, earthquake produced observable crustal deformation over a ∼ 100 km 2 area around the southeast margin of Great Salt Lake, but it did not produce any surface rupture. To obtain a detailed picture of the fault slip, we combine strong motion seismic waveforms with GPS static oﬀsets and Interferometric Synthetic Aperture Radar (InSAR) observations to obtain kinematic and static slip models of the event. We sample the regional seismic waveﬁeld with 3-component records from 68 stations of the University of Utah Seismograph Stations network. We ﬁnd that coseismic slip and afterslip, with predominantly normal slip, distributed on a shallowly west-dipping plane, possibly augmented by afterslip on a steeply northeast-dipping plane, best ﬁts the joint dataset. The west-dipping plane locates near previously inferred sources of interseismic creep at depth. Hence the earthquake may have occurred on the downdip ex-tension of the Wasatch fault and activated further slip (afterslip) at shallow depth east of the hypocenter. This inferred afterslip may have driven the vigorous aftershock activity that was concentrated east of the hypocenter.

Utah↗

USGS2026

The Cascadia Region Earthquake Science Center (CRESCENT): Advancing understanding of Cascadia's earthquake hazards

The Cascadia Subduction Zone (CSZ) is capable of producing large megathrust earthquakes and tsunamis, posing significant risks to the Pacific Northwest. This paper examines the seismic characteristics of the CSZ, including its offshore coupling, sparse seismicity, and a complex paleoseismic record. While recent advances in geophysical methods and data collection have improved our understanding of subduction zone processes, important uncertainties remain regarding rupture dynamics, ground shaking, and tsunami impacts. The Cascadia Region Earthquake Science Center (CRESCENT) has been established to address these challenges through coordinated research, education, and community engagement. By integrating scientific studies, fostering collaboration, and leveraging new technologies, CRESCENT seeks to improve hazard assessment and resilience in the region. This paper outlines the primary challenges and opportunities in advancing subduction zone science and enhancing societal preparedness for future CSZ events.

California, Oregon, Washington↗

USGS2011

Reassessment of stable continental regions of Southeast Asia

Probabilistic seismic-hazard assessments of the central and eastern United States (CEUS) require estimates of the size of the largest possible earthquake (Mmax). In most of the CEUS, sparse historical seismicity does not provide a record of moderate and large earthquakes that is sufficient to constrain Mmax. One remedy for the insufficient catalog is to combine the catalog of moderate to large CEUS earthquakes with catalogs from other regions worldwide that are tectonically analogous to the CEUS (stable continental regions, or SCRs). After the North America SCR, the largest contribution of earthquakes to this global SCR catalog comes from a Southeast Asian SCR that extends from Indochina to southeasternmost Russia. Integration and interpretation of recently published geological and geophysical results show that most of these Southeast Asian earthquakes occurred in areas exposing abundant alkaline igneous rocks and extensional faults, both of Neogene age (last 23 million years). The implied Neogene extension precludes classification of the areas as SCR crust. The extension also reduces the number of moderate and large Southeast Asian historical earthquakes that are available to constrain CEUS Mmax by 86 percent, from 43 to six.

Seismological Research Letters↗

USGS2024

Late-Quaternary surface displacements on accretionary wedge splay faults in the Cascadia Subduction Zone: Implications for megathrust rupture

Because splay faults branch at a steep dip angle from the plate-boundary décollement in an accretionary wedge, their coseismic displacement can potentially result in larger tsunamis with distinct characteristics compared to megathrust-only fault ruptures, posing an enhanced hazard to coastal communities. Elsewhere, there is evidence of coseismic slip on splay faults during many of the largest subduction zone earthquakes, but our understanding of potentially active splay faults and their hazards at the Cascadia subduction zone remains limited. To identify the most recently active splay faults at Cascadia, we conduct stratigraphic and structural interpretations of near-surface deformation in the outer accretionary wedge for the ~400 km along-strike length of the landward vergence zone. We analyze recently acquired high-frequency sparker seismic data and crustal-scale multi-channel seismic data to examine the record of deformation in shallow slope basins and the upper ~1 km of the surrounding accreted sediments and to investigate linkages to deeper décollement structure. We present a new fault map for widest, most completely locked portion of Cascadia from 45 to 48°N latitude, which documents the distribution of faults that show clear evidence of recent late Quaternary activity. We find widespread evidence for active splay faulting up to 30 km landward of the deformation front, in what we define as the active domain, and diminished fault activity landward outside of this zone. The abundance of surface-deforming splay faults in the active outer wedge domain suggests Cascadia megathrust events may commonly host distributed shallow rupture on multiple splay faults located within 30 km of the deformation front.

British Columbia, California, Oregon, Washington↗

USGS1970

LASA anomalies and their relations to crust and upper-mantle structure

Body-wave data from nine teleseisms recorded at the Large Aperture Seismic Array (LASA), Montana, have been analyzed. The events were at different azimuths and distances from LASA. Apparent-velocity measurements using arrival-time data at the subarrays differed by about 30 percent for events in the northwest and southeast directions.Apparent velocities were high near the center of the array for events in the northwest and low for events in the southeast. For events in the other azimuths, the patterns were more complex, but anomalous values were found near the center. Apparent-velocity measurements at subarrays were made using a cross-spectral technique. The resulting values showed patterns similar to those obtained using arrival-time data near the center. Anomalous high and low values were found near the center and also at the E and F subarrays.

Open-File Report↗

USGS1979

Preliminary report on an exploratory drill hole: New Madrid test well-1-X in Southeast Missouri

As part of the U.S. Geological Survey's investigation of earthquake hazards in the upper Mississippi embayment, a test well (NMTW-l-X) was drilled in the "bootheel" of Missouri, 21 km south-southwest of the town of New Madrid. The primary purpose of the well was to obtain in situ stress measurements from zones within subsurface Paleozoic rocks using the hydraulic fracturing (hydrofracture) technique. Such measurements determine the character and magnitude of the active tectonic stress field in an area and are helpful in evaluating the potential for faulting (Zoback and others, 1978). The new data about the active tectonic stress field can then be used to evaluate the various theories that have been proposed to explain the genesis and characteristics of the upper Mississippi embayment earthquakes. A second goal of the test well was to extensively study the post-Paleozoic stratigraphy in the area. Detailed stratigraphic information would provide a better understanding of the structural framework of the upper Mississippi embayment. Accurate knowledge of the stratigraphy would also help to identify the reflecting horizons that were recorded in a series of seismic reflection profiles that the U.S. Geological Survey had previously run throughout the upper Mississippi embayment. To strengthen the correlation between reflecting horizons and stratigraphic units, one of the reflection profiles was run within 10 m of the well. The stratigraphy and structure of the New Madrid, Mo., area are, at present, poorly understood. Only a handful of deep wells and test holes, some with only generalized driller's logs and few with accompanying geophysical logs, are available to aid in interpreting the subsurface geology of the upper Mississippi embayment. Extensive paleontologic and palynologic studies are planned to assist in identifying formal stratigraphic units and to help define the depositional history of the sediments. For the Tertiary and Cretaceous sequences, these investigations will also yield valuable biostratigraphic data by defining the biofacies changes that occur between the well-studied marine facies in the southern part and the time-equivalent, continental and nearshore-deltaic facies in the northern part of the embayment. This report was prepared to release preliminary data obtained during the drilling phase of the test well. It includes a short text describing mechanical operations and history of the drilling, some initial stratigraphic interpretations of the test-well data, and a brief discussion of studies generated by the project which are now in progress. Attached appendices contain a field driller's log and geophysical logs. In order to maintain consistency with standard drilling usage, measurements related to drilling operations are cited in English units.

Missouri↗

USGS1996

Rupture directivity and slip distribution of the M 4.3 foreshock to the 1992 Joshua Tree earthquake, Southern California

Details of the M 4.3 foreshock to the Joshua Tree earthquake were studied using P waves recorded on the Southern California Seismic Network and the Anza network. Deconvolution, using an M 2.4 event as an empirical Green's function, corrected for complicated path and site effects in the seismograms and produced simple far-field displacement pulses that were inverted for a slip distribution. Both possible fault planes, north-south and east-west, for the focal mechanism were tested by a least-squares inversion procedure with a range of rupture velocities. The results showed that the foreshock ruptured the north-south plane, similar to the mainshock. The foreshock initiated a few hundred meters south of the mainshock and ruptured to the north, toward the mainshock hypocenter. The mainshock (M 6.1) initiated near the northern edge of the foreshock rupture 2 hr later. The foreshock had a high stress drop (320 to 800 bars) and broke a small portion of the fault adjacent to the mainshock but was not able to immediately initiate the mainshock rupture.

Bulletin of the Seismological Society of America↗

USGS1980

Tremors from earthquakes and blasting in the Powder River basin of Wyoming and Montana

Coal in the Powder River Basin of Wyoming and Montana (fig. 1) is greatly in demand. It can be economically mined from the surface, and the land is much easier to reclaim than land above underground mines that has been damaged by subsidence or by underground fires. Exploitation of the vast coals resources in the basin has caused a rapid influx of population into the area and an associated increase in building construction. The activity has also generated concern about possible regulation of development. With these facts in mind, the U.S Geological Survey has been investigating the geologic implications of development in the Powder River Basin. One area of study has been the effect of earth tremors caused by blasting in the large coal surface mines or by naturally occurring earthquakes. The basin proper was classified by Algermissen and Perkins (1976) as belonging to a region of low seismic risk. Naturally occurring earthquakes are, therefore, mainly of scientific interest, unless of course there was an isolated event that occurred near a populated area or a surface mine. We are not aware of any damage to people or to property caused by blasting in the coal surface mines even though thousands of tons of explosives are detonated each year in the basin. The maximum weight of an individual explosive charge and the time interval between blasts are regulated so that any nearby structures will not be damaged or the residents disturbed. Blasting, nevertheless, does produce seismic tremors that can be recorded over 200 kilometers away. In addition, at one mine, some very low order aftershocks were recorded relatively close to the source within 2 hours after blasting.

Montana; Wyoming↗

USGS2012

Archive of digital boomer subbottom data collected during USGS cruise 05FGS01 offshore east-central Florida, July 17-29, 2005

In July of 2005, the U.S. Geological Survey (USGS), in cooperation with the Florida Geological Survey (FGS), conducted a geophysical survey of the Atlantic Ocean offshore of Florida's east coast from Flagler Beach to Daytona Beach. This report serves as an archive of unprocessed digital boomer 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. Filtered and gained (showing a relative increase in signal amplitude) digital images of the seismic profiles are also provided. Refer to the Acronyms page for expansions of acronyms and abbreviations used in this report. The USGS Saint Petersburg Coastal and Marine Science Center (SPCMSC) assigns a unique identifier to each cruise or field activity. For example, 05FGS01 tells us the data were collected in 2005 for cooperative work with the FGS and the data were collected during the first field activity for that project in that calendar year. Refer to http://walrus.wr.usgs.gov/infobank/programs/html/definition/activity.html for a detailed description of the method used to assign the field activity ID. The boomer subbottom processing system consists of an acoustic energy source that is made up of capacitors charged to a high voltage and discharged through a transducer in the water. The transducer is towed on a sled floating on the water surface and when discharged emits a short acoustic pulse, or shot, which propagates through the water column and shallow stratrigraphy below. The acoustic energy is reflected at density boundaries (such as the seafloor or sediment layers beneath the seafloor), detected by the receiver (a hydrophone streamer), and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (for example, 0.5 s) and recorded for specific intervals of time (for example, 100 ms). In this way, a two-dimensional (2-D) vertical image of the shallow geologic structure beneath the ship track is produced. Figure 1 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 Society of Exploration Geophysicists (SEG) SEG Y format (Barry and others, 1975), except an ASCII format is used for the first 3,200 bytes of the card image header instead of the standard EBCDIC format. For a detailed description about the recorded trace headers, refer to the SEG Y Format page. The SEG Y files may be downloaded and processed with commercial or public domain software such as Seismic Unix (Cohen and Stockwell, 2005). See the How To Download SEG Y Data page for download instructions. The printable profiles provided here are GIF images that were processed and gained using SU software; refer to the Software page for links to example SU processing scripts. The processed SEG Y data were also exported to Chesapeake Technology, Inc. (CTI) SonarWeb software to produce a geospatially interactive version of the profile that allows the user to obtain a geographic location and depth from the profile for a given cursor position; this information is displayed in the status bar of the browser. Please note that clicking on the profile image switches it to "Expanded View" (a compressed image of the entire line) and cursor tracking is not available in this mode.

Florida↗

USGS2004

Archive of Digital Boomer Seismic Reflection Data Collected During USGS Field Activities 93LCA01 and 94LCA01 in Kingsley, Orange, and Lowry Lakes, Northeast Florida, 1993 and 1994

In August and September of 1993 and January of 1994, the U.S. Geological Survey, under a cooperative agreement with the St. Johns River Water Management District (SJRWMD), conducted geophysical surveys of Kingsley Lake, Orange Lake, and Lowry Lake in northeast Florida. This report serves as an archive of unprocessed digital boomer seismic reflection data, trackline maps, navigation files, GIS information, observer's logbook, Field Activity Collection System (FACS) logs, and formal FGDC metadata. A filtered and gained GIF image of each seismic profile is also provided. Refer to the Acronyms page for expansion of acronyms and abbreviations used in this report. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU). Examples of SU processing scripts and in-house (USGS) software for viewing SEG-Y files (Zihlman, 1992) are also provided. The data archived here were collected under a cooperative agreement with the St. Johns River Water Management District as part of the USGS Lakes and Coastal Aquifers (LCA) Project. For further information about this study, refer to http://coastal.er.usgs.gov/stjohns, Kindinger and others (1994), and Kindinger and others (2000). The USGS Florida Integrated Science Center (FISC) - Coastal and Watershed Studies in St. Petersburg, Florida, assigns a unique identifier to each cruise or field activity. For example, 93LCA01 tells us the data were collected in 1993 for the Lakes and Coastal Aquifers (LCA) Project and the data were collected during the first field activity for that project in that calendar year. For a detailed description of the method used to assign the field activity ID, see http://walrus.wr.usgs.gov/infobank/programs/html/definition/activity.html. The boomer is an acoustic energy source that consists of capacitors charged to a high voltage and discharged through a transducer in the water. The transducer is towed on a sled at the sea surface and when discharged emits a short acoustic pulse, or shot, that propagates through the water and sediment column. The acoustic energy is reflected at density boundaries (such as the seafloor or sediment layers beneath the seafloor), detected by the receiver, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (e.g., 0.5 s) and recorded for specific intervals of time (e.g., 100 ms). In this way, a two-dimensional vertical image of the shallow geologic structure beneath the ship track is produced. Acquisition geometery for 94LCA01 is recorded in the operations logbook. No logbook exists for 93LCA01. Table 1 displays acquisition parameters for both field activities. For more information about the acquisition equipment used, refer to the FACS equipment logs. The unprocessed seismic data are stored in SEG-Y format (Barry and others, 1975). For a detailed description of the data format, refer to the SEG-Y Format page. See the How To Download SEG-Y Data page for more information about these files. Processed profiles can be viewed as GIF images from the Profiles page. Refer to the Software page for details about the processing and examples of the processing scripts. Detailed information about the navigation systems used for each field activity can be found in Table 1 and the FACS equipment logs. To view the trackline maps and navigation files, and for more information about these items, see the Navigation page. The original trace files were recorded in nonstandard ELICS format and later converted to standard SEG-Y format. The original trace files for 94LCA01 lines ORJ127_1, ORJ127_3, and ORJ131_1 were divided into two or more trace files (e.g., ORJ127_1 became ORJ127_1a and ORJ127_1b) because the original total number of traces exceeded the maximum allowed by the processing system. Digital data were not recoverable for 93LCA

Data Series↗

USGS2021

The proliferation of induced seismicity in the Permian Basin, Texas

The Permian Basin has a long history of induced earthquakes, but the seismicity rates have increased dramatically over the past two decades and included a M W 5.0 likely induced by wastewater disposal (WD) in March 2020. A detailed characterization of the proliferation of seismicity in the Permian Basin throughout this time period is needed for improving the scientific understanding of the mechanisms responsible and for mitigating future seismic hazard. Due to a sparse regional seismic network before the advent of Texas Seismological Network in 2017, we characterize seismicity using the 10-station TXAR array that is 100s of km away from most of the seismicity, with the objective of improving upon the substantial contributions from previous work. By exploiting the nature of waveform similarity, we detect events with template matching, performing a quantitative analysis of spatially varying detection capabilities throughout the study area. From an initial catalog of 10,753 events, we identify 45,009 earthquakes and 10,208 quarry blasts. Using our catalog of earthquakes, we improve epicentral locations, compare relative magnitude techniques, and associate earthquakes to WD or hydraulic stimulations. We further use our earthquake catalog to investigate the relationship between seismicity and human activities near the city of Pecos, Texas. Through a comparison of our earthquake catalog with industrial records, we determine that the vast majority seismicity near Pecos, Texas, since 2000 is likely induced by an increase of WD at wells injecting at depths greater than 1.5 km.

Texas↗

USGS2009

Archive of digital boomer seismic reflection data collected offshore east-central Florida during USGS cruise 00FGS01, July 14-22, 2000

In July of 2000, the U.S. Geological Survey (USGS), in cooperation with the Florida Geological Survey (FGS), conducted a geophysical survey of the Atlantic Ocean offshore Florida's east coast from Brevard County to northern Martin County. This report serves as an archive of unprocessed digital boomer seismic reflection data, trackline maps, navigation files, Geographic Information System (GIS) information, digital and handwritten Field Activity Collection System (FACS) logs, and Federal Geographic Data Committee (FGDC) metadata. A filtered and gained (a relative increase in signal amplitude) digital image of each seismic profile is also provided. Refer to the Acronyms page for expansions of all acronyms and abbreviations used in this report. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU) (Cohen and Stockwell, 2005). Example SU processing scripts and USGS Software for viewing the SEG-Y files (Zihlman, 1992) are also provided. The USGS St. Petersburg Coastal and Marine Science Center assigns a unique identifier to each cruise or field activity. For example, 00FGS01 tells us the data were collected in 2000 for cooperative work with the Florida Geological Survey (FGS) and the data were collected during the first field activity for that study in that calendar year. Refer to http://walrus.wr.usgs.gov/infobank/programs/html/definition/activity.html for a detailed description of the method used to assign the field activity ID. The boomer plate is an acoustic energy source that consists of capacitors charged to a high voltage and discharged through a transducer in the water. The transducer is towed on a sled floating on the water surface and when discharged, emits a short acoustic pulse, or shot, which propagates through the water, sediment column, or rock beneath. The acoustic energy is reflected at density boundaries (such as the seafloor, sediment, or rock layers beneath the seafloor), detected by the receiver, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (for example, 0.5 s) and recorded for specific intervals of time (for example, 100 ms). In this way, a two-dimensional (2D) vertical profile of the shallow geologic structure beneath the ship track is produced. Figure 1 displays the acquisition geometry. Refer to table 1 for a summary of acquisition parameters. The unprocessed seismic data are stored in SEG-Y format (Barry and others, 1975). For a detailed description of the data format, refer to the SEG-Y Format page. See the How To Download SEG-Y Data page for download instructions. The printable profiles provided are GIF images that were filtered and gained using Seismic Unix software. Refer to the Software page for details about the processing and examples of the processing scripts. The printable profiles can be viewed from the Profiles page or from links located on the trackline maps. To view the trackline maps and navigation files, and for more information about these items, see the Navigation page. Detailed information about the navigation system used can be found in table 1. Of a total record length of 200 ms, only the upper 100 ms of each profile are displayed because no useful information was observed deeper in the sections. A 10 ms deep water delay appears on lines b57-b63 and sl2-sl28. No digital data were collected for line sl6. However, line sl6r is a second attempt to collect digital data for this line. Digital data and 500-shot-interval location navigation are not available for the last 1,161 shots of line sl26 due to an equipment malfunction.

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