1981 Westmorland earthquake

1981 earthquake in southern California, United States 1981 Westmorland earthquake USA California 1981-04-26 12:09:31 628772 ci514869 1981 04 26 5:09 a.m. PDT 5.9 w ISC y 10 km on 33.02 N 115.68 W region:US-CA_type:event inline, title Strike-slip Imperial Valley Southern California United States US$1–3 million 7 The 1981 Westmorland earthquake occurred at 05:09 Pacific Daylight Time (12:09 UTC) on April 26. The moderate strike-slip shock took place in the Imperial Valley of Southern California, just north of the Mexico–United States border. No injuries or deaths occurred, but damage was estimated at $1–3 million. With a Mercalli intensity of VII (Very strong), this was one of fifteen intensity VII or greater shocks in the Imperial Valley that were observed in the 20th century up until April 1981. The region experiences large stand-alone events and earthquake swarms due to its position in an area of complex conditions where faulting transitions from strike-slip movement to the north and divergence to the south. Preface Remotely triggered earthquakes The Imperial Valley of Southern California is very active seismically and has been subject to numerous destructive earthquakes since communities began to form in this desert area in the late 19th and early 20th centuries. Records of events prior to this period do not exist due to a lack of settlers in the area. Fifteen shocks of intensity VII or higher were recorded prior to April 1981 and beginning with the intensity VIII shock of April 18, 1906, which was a triggered event following the 1906 San Francisco earthquake.Barnhard Thenhaus Algermissen 1982 1, 1A, 1BAftershocks and Triggered Events of the Great 1906 California Earthquake A. J. Meltzner D. J. Wald 2003 Bulletin of the Seismological Society of America 93 5 2,160, 2,164, 2,166, 2,169, 2,170 10.1785/0120020033 2003BuSSA..93.2160M 128704816 https://authors.library.caltech.edu/47920/ Tectonic setting Brawley Seismic Zone Cerro Prieto Geothermal Power Station East Pacific Rise Imperial Fault Zone The Gulf of California Rift Zone underlies the Gulf of California from the mouth of the Colorado River in Baja California and stretching to the southeast. It contains numerous right-lateral transform faults and rift zones that make up the Pacific–North American plate boundary. The southern portion has matured into seafloor spreading, and at the northern end of the province is the Salton Trough, which is considered to be an onshore spreading center. The rift zone is covered by thick layers of sediment from the Colorado River drainage basin.Continental rupture and the creation of new crust in the Salton Trough rift, Southern California and northern Mexico: Results from the Salton Seismic Imaging Project 2016 10.1002/2016JB013139 7471, 7472 Han Liang Hole John A. Stock Joann M. Joann Stock Fuis Gary S. Kell Annie Driscoll Neal W. Kent Graham M. Harding Alistair J. Rymer Michael J. González-Fernández Antonio Lázaro-Mancilla Octavio Journal of Geophysical Research: Solid Earth 121 10 2016JGRB..121.7469H free The region experiences large stand-alone events and earthquake swarms due to its position in an area of complex faulting where it transitions from the strike-slip movement of the San Andreas Fault system to that of the divergent Gulf of California Rift Zone, which is an area of active seafloor spreading. Earthquake Strike-slip tectonics The Global Centroid Moment Tensor Database shows a NNW strike on a nearly vertical fault, with a rake angle that is within 45 degrees of being pure strike-slip. Intensity Calipatria and Westmorland both experienced intensity VII shaking (Very strong), which was the maximum observed intensity for the event. At these locations, roads and house foundations were cracked, interior and exterior walls experienced partial collapse, chimneys fell, windows were broken, and underground water pipes burst. The shock was felt over an area of 73,500 km2, and the communities of Encino and Cedar Glen in California, and Bouse in Arizona were at the outermost extremity of the felt area in the United States.10.3133/ofr84981 United States earthquakes, 1981 Open-File Report 1984 Stover C.W. 21–26 free See also California List of earthquakes in California List of earthquakes in the United States References ISC-GEM Global Instrumental Earthquake Catalogue (1900–2009) http://www.isc.ac.uk/iscgem/index.php ISC 2015 International Seismological Centre Version 4.0 PAGER-CAT Earthquake Catalog https://earthquake.usgs.gov/static/lfs/data/pager/catalogs/ https://web.archive.org/web/20200313112456/ftp://hazards.cr.usgs.gov/web/data/pager/catalogs/ dead 2020-03-13 September 4, 2009 United States Geological Survey Version 2008_06.1 Stover C.W. Coffman J.L. Seismicity of the United States, 1568–1989 (Revised) https://books.google.com/books?id=bY0KAQAAIAAJ&pg=PA166 U.S. Geological Survey professional paper 1527 1993 United States Government Printing Office 96, 168 Sources Distribution of intensity for the Westmorland, California, earthquake of April 26, 1981 https://pubs.er.usgs.gov/publication/ofr82485 L.M. Barnhard P.C. Thenhaus S.T. Algermissen Open-File Report 1982 Open-File Report 82-485 United States Geological Survey 10.3133/ofr82485 free Further reading Dorsey Rebecca J. Sedimentation and crustal recycling along an active oblique-rift margin: Salton Trough and northern Gulf of California https://pages.uoregon.edu/rdorsey/Downloads/Dorsey_2010.pdf Geology Geological Society of America 38 5 2010 1943-2682 10.1130/g30698.1 443–446 2010Geo....38..443D Lohman, R. B., and McGuire, J. J. (2007), Earthquake swarms driven by aseismic creep in the Salton Trough, California, J. Geophys. Res., 112, B04405, 10.1029/2006JB004596. 10.3133/ofr811149 Strong-motion data from the Westmorland, California, earthquake of April 26, 1981 Open-File Report 1981 Maley R.P. Etheredge E.C. free Category:Earthquakes in California Category:1981 earthquakes Category:Imperial Valley Category:1981 in California Category:History of Imperial County, California Category:Geology of Imperial County, California