Brawley Seismic Zone
The Brawley Seismic Zone (BSZ), also known as the Brawley fault zone, is a predominantly
Geology
The Brawley Seismic Zone represents the northernmost extension of the spreading center axis associated with the
The
Earthquake swarms
On August 26, 2012 near Brawley, a swarm of more than 300 small to moderate earthquakes occurred with the largest two reaching a maximum of 5.3 and 5.5. Some light cosmetic damage was found on some older buildings in downtown Brawley. Earthquake swarms are not unusual for the area. In 2005, also near Brawley, there was a swarm with a peak magnitude of 5.1, while in 1981 a swarm included one quake which was measured at 5.8. The swarm activity is not understood completely, but the new restlessness could generate data that will help scientists to gain a better understanding of the region.[3] According to a geologist at the United States Geological Survey (USGS), such swarms are typical for the Brawley zone: "The area sees lots of events at once, with many close to the largest magnitude, rather than one main shock with several much smaller aftershocks."[4]
Other activity
The Imperial Valley of southern California experiences high rates of seismicity with a pronounced portion of the activity occurring within the Brawley Seismic Zone that separates the San Andreas fault to the north and the Imperial fault to the south. The Imperial fault was the source of the 1940 El Centro earthquake and the 1979 Imperial Valley earthquake. There was more than 30 km (19 mi) of surface rupture associated with the 1979 event along the northwest trending Imperial fault from just north of the Mexico–United States border to an area south of Brawley and the BSZ was found to have ruptured, with surface cracks, for a length of 13 km (8.1 mi).[5] The 1940 and 1979 mainshocks were of similar size and both were followed by damaging aftershocks near Brawley.[6]
References
- ^ a b Fuis, Gary S.; Mooney, Walter D. (1990), "Lithospheric structure and tectonics from seismic-refraction and other data", The San Andreas Fault System, California, Geological Survey Professional Paper 1515, United States Geological Survey, pp. 207–236
- ^ David L. Alles (2011). "Geology of the Salton Trough" (PDF). Western Washington University. Retrieved September 30, 2012.
- ^ Sewell, Abby (August 26, 2012). ""Earthquake storm" continues to rattle Imperial County, surrounding areas". Los Angeles Times. Retrieved August 26, 2012.
- ^ Associated Press (August 26, 2012). "Series of earthquakes rattle Southern California" The Oklahoman
- hdl:2060/19900012177.
- ISBN 978-0716775485
Sources
- Hauksson, E.; Stock, J.; Bilham, R.; Boese, M.; Chen, X.; Fielding, E. J.; Galetzka, J.; Hudnut, K. W.;
- Meltzner, A J.; Rockwell, T. K.; Owen, L. A. (2006), "Recent and long-term behavior of the Brawley Fault Zone, Imperial Valley, California: An escalation of slip rate?" (PDF), Bulletin of the Seismological Society of America, 96 (6),
External links
- Fault History and Architecture of the Southernmost San Andreas Fault and Brawley Seismic Zone: New Constraints from CHIRP Data Acquired in the Salton Sea – American Geophysical Union, Fall Meeting 2006
- List of all events for Brawley Swarm – Southern California Seismic Network
- August 2012 Brawley, California Earthquake Swarm – United States Geological Survey