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The Burica cluster is named for the Burica Peninsula on the border between Costa Rica and Panama, where the Panama Fracture Zone intersects the Middle America Trench. The cluster contains one large event, a 6.1 Mw event on August 17, 2018 and a number of M5 events. The cluster is quite well recorded at teleseismic distances. As with most clusters at subduction zones, great care must be taken in developing the initial focal depths and locations for events because of the large open azimuth toward the sea. The cluster was restricted to events on-shore to try to ensure stable results. A number of events have teleseismic depth phase data that is compatible with the depths determined by analysis of the near- and local-distance...
The Northridge cluster is named for the city of Northridge, California, U.S.A. The cluster is based on the Northridge earthquake of January 17, 1994 (Mw 6.7) and its aftershocks but it also includes the Rosemead earthquake on October 1, 1987 (Mw 5.9) and the San Fernando earthquake on February 9, 1971 (Mw 6.6). The cluster includes a dozen or so small, recent events that were extremely well recorded by the dense modern seismograph network in the area; these events control the location calibration. These "kernel" events could be easily relocated with free depth and were used to refined the crustal velocity model. ...
The Mutata cluster is named for the city of Mutatá in Antioquia Department, northwestern Colombia. The major earthquake in the cluster is a 6.0 Mw event on September 14, 2016, but there are many events in the M5-6 range in the cluster. Because seismic stations are rather scarce in the region location calibration is only possible by extending the distance range for estimation of the hypocentroid (1.2°) into the Pg/Pn crossover range but the fit to the Pn and Sn data that are included appears to be stable. For the same reason only a bit over half the events have depth control from near- or local-distance arrival time data. Fortunately the other events in this cluster have good teleseismic depth phase reports that...
The Qinghai cluster is named for nearby Qinghai Lake in central China, on the northern edge of the Tibetan Plateau. The cluster was formed in response to the Mw 6.6 earthquake on January 7, 2022, and includes two other M6 events, on August 26, 1986 and January 20, 2016. Direct calibration of this cluster depends almost entirely on arrival time readings from provincial seismological networks collected by Sun Roumei. Station coverage at local distances is very good. All events have depth control, from near-source and local-distance stations or from teleseismic depth phases. The focal depths found for this cluster tend to be shallower than usual, ranging from zero to 15 km with many events less than 5 km depth, but...
The Page cluster is named for the city of Page in northwestern Arizona, U.S.A. The cluster is mainly north of the Grand Canyon and west of Page, with a few events in southern Nevada and southwestern Utah. According to its location the 5.7 mb earthquake near St. George, Utah, on September 2, 1992 should be in this cluster but it has very poor connectivity with the Page cluster and quite good connectivity with the nearby Caliente, Nevada, cluster so it is included in Caliente. Events prior to about 2007 are poorly recorded. The largest event in this cluster is magnitude 4.4 mb and the rest are less than M4. There are few teleseismic or far-regional readings but there is good coverage up to ~8°. Station coverage for...
For background, please see the Parent Item. The attached files below for 8 site classes each provide risk-targeted spectral accelerations (in units of g) for a grid of latitudes and longitudes and 22 spectral periods, including 0.0 seconds for peak ground acceleration (denoted SA0P0). To compare these risk-targeted spectral accelerations with uniform-hazard counterparts analogous to those in previous editions of the AASHTO Design Specifications, corresponding risk coefficients are also provided (for all of the site classes in a single ZIP file). The risk coefficients are ratios of the risk-targeted divided by uniform-hazard spectral accelerations, with the latter for a 7% probability of being exceeded in 75 years....
Categories: Data
The Rifle cluster is named for the city of Rifle in western Colorado, U.S.A. The cluster is dominated by mining explosions from longwall coal mining, especially in the Paonia region. It is known that many small seismic events in this part of the Rocky Mountains are the result of collapse of old hard-rock mines. Most events are in the magnitude 2-4 range; the largest event has magnitude 4.3. Two nuclear tests were conducted in the source region, the Rulison test on September 10, 1969 near what is now the town of Parachute and the three simultaneous shots (in a common borehole) of the Rio Blanco test near the town of Rifle on May 17, 1973. Unfortunately these events could not be included in the analysis because they...
The Conyi cluster is named for Co Nyi County (Shuanghu in Chinese) in northern Tibet. It is based on data from a long linear seismic array deployed in the area in 1998-1999 which observed 5 earthquakes in the magnitude range 3.9-4.6 at distances as close as 25 km. The azimuthal coverage is weak but is partially offset by the large number of readings to achieve a reasonable level of location accuracy. Surface elevation in this region is ~5200 meters. The trade-off between focal depth, crustal velocity model and location was carefully explored with fixed-depth relocations. Free depth relocations are unstable. Depths of 0-3 km (5-8 km below the surface) fit the local distance arrival time data best. To improve the...
The Kaikoura cluster is named for the town of Kaikoura on the east coast of the South Island of New Zealand. It is based on the great M7.8 earthquake of November 13, 2016, and nearly all events in the cluster are associated with that sequence. Azimuthal coverage is compromised by the large open azimuth toward the sea but the number and quality of the seismic stations in the area provides a quite stable location calibration with good depth control as well. All events have depth control from near-source or local distance arrivals, or from teleseismic depth phases. All but four events are recorded at teleseismic distances. ...
The Midland cluster is named for the city of Midland in west Texas. The cluster is based on a 5.2 Mw event on December 16, 2022. The area has been seismically active at low magnitudes since early 2019 as a result of oil and gas extraction, with a few events of magnitude 3 and 4. There is a quite dense network of seismograph stations in the area in recent years so the calibration of epicenters is very robust and many events have near-source data for depth control even though they are rather shallow (less than 10 km). The relocation is done with free depth. Most of the events are observed to at least 3° epicentral distance; only a half dozen are observed at leleseismic distances. The smaller events were retained to...
The Curití cluster is named for the town of the same name in the Santander Department of northeastern Colombia. The earthquakes are small (5.1 mb is the largest) and scattered widely. Some events were recorded only to near-regional distances were retained to improve the azimuthal coverage and statistical power of the cluster. All events have depth control, mostly from near-source and local-distance readings, but several are constrained by teleseismic depth phases. Like the epicenters, focal depths are rather uniformly distributed over a wide range from near the surface to 40 km depth. Number of...
The Salton cluster is named for the Salton Trough in southeastern California, U.S.A., a transitional region between sea-floor spreading in the Gulf of California and the San Andreas transform fault system on land. The cluster is restricted to events within the Trough, because it was found that the crustal velocity structure needed to adequately model local travel times for these earthquakes was distinctly different from what is needed for events located even a few tens of km away from the Trough. The crustal model is based on the results of a wide-angle seismic transect documented by Parson and McCarthy (Tectonics, 1996) and features thin crust (27 km) and very low velocities in the upper 5 km. Seismic activity...
Each of the downloadable files below contains spectral response accelerations at 22 periods on a grid of latitudes and longitudes that cover this geographic region. See the parent item for how Risk-Targeted Maximum Considered Earthquake (MCER) spectral response accelerations are derived from the data in these files.
The Varna cluster is named for the city of Varna on the Black Sea coast of Bulgaria. It contains two events with magnitude >5.0 in 1986 that were only 2-3 km apart: 5.5 Ms on February 21 and 5.8 Ms on December 7. All other events in the cluster are less than magnitude 5. Many are observed only to near-regional distances (at least 3.0°) but there is a substantial amount of arrival time data out to about 27° and a modest amount of teleseismic data. Station distribution for direct calibration is quite good. All events have depth control from near-source and local-distance readings. Number of events:...
The Bucharest cluster is named for Bucharest, Romania. All earthquakes are magnitude 4.0 or smaller. All events have observations to at least 3° but there are few arrival time data beyond about 6°. The calibration is very robust and all events have depth control from near-source or local-distance readings. The cluster contains several events with very shallow focal depths, which may be related to mining. There are many mining events in the catalog but they are seldom observed beyond 3° and were dropped from the cluster. Number of events: 40 Calibration type: direct calibration using data to 0.6...
Magnetotelluric (MT) method is a branch of geophysics that employs very large-scale natural sources from the solar wind and lightning. Modern-day MT uses state-of-the-art instrumentation, data processing and analysis tools to provide valuable information about deep Earth structure, complimentary to that of seismic data. These days, MT data also serve as a primary resource for estimation of geomagnetically induced currents, hazardous to modern infrastructure. However, there is a real need to modernize deeply historic MT data formats to a common standard that is fully documented, platform-independent, extensible, and accessible to the broader community of geoscientists. In the past decade, we have led just such an...
About 280 kilometers of multichannel (common-depth-point) seismic reflection profiles were obtained in the central Mississippi River Valley by Geophysical Service Inc. and Western Geophysical Company under contracts with the U.S. Geological Survey. The specific area of the profiles is southeastern Missouri, northeastern Arkansas, and northwestern Tennessee. Geologically, the area is located in the northern part of the Mississippi Embayment.
The Hawthorne cluster is named for the town of Hawthorne, Nevada, U.S.A., on the border with California. The cluster is based on two series of earthquakes, the first in December 2016 that included three events with magnitude 5 or greater, the second in May 2020 that began on May 15 with a 6.5 Mw event. Because of the high density of seismic stations in source region the calibration of the epicenters is excellent. Much of the seismicity appears to be quite shallow, less than 5 km deep. The regional elevation is ~2 km so even events that have been set at zero depth (relative to mean sealevel) for relocation have some depth. ...
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