1892 Vacaville–Winters earthquakes

Damaging earthquake doublet in northern California 1892 Vacaville–Winters earthquakes USA California California 40.58 -122.37 Redding 100 right Green pog.svg California 39.31 -119.65 Virginia City 100 right Green pog.svg California 36.68 -121.66 Salinas 100 left Green pog.svg California 36.75 -119.77 Fresno 100 Green pog.svg California 36.14 -120.36 Coalinga 100 bottom Green pog.svg California 38.4 -122 Bullseye1.png 40 yes 250 right yes yes doublet ushis302 ushis303 1892-04-19 1892-04-21 A: 1892 04 19B: April 21, 1892 6.4 M y 6.2 M 38.4 -122 region:US_type:event inline,title Unknown $225,000–250,000 9 1 dead The 1892 Vacaville–Winters earthquakes occurred in northern California as a large doublet on April 19 and April 21. Measured on a seismic scale that is based on an isoseismal map or the event's felt area, the 6.4 M y and 6.2 M events were assigned a maximum Mercalli intensity of IX (Violent), and affected the North Bay and Central Valley areas. The total damage was estimated to be between $225,000 and 250,000 and one person was killed. No evidence of fault movement on the surface of the ground was observed as a result of either of the strong shocks. Both occurred in the domain of the San Andreas strike-slip system of faults, but their focal mechanism is uncertain. Tectonic setting The primary tectonic feature of the region is the strike-slip San Andreas system of faults (that move laterally alongside one another). From west to east, the Hayward–Rogers Creek Fault Zone and the Concord–Green Valley Faults are the closest to Vacaville and Winters. A 1999 forecast stated that the Hayward and Rogers Creek Faults have been given a 32% chance of a M6.7 or greater shock before 2030, and the Concord and Green Valley Faults have been assigned a lower probability of 6% each.Active Faults of the World https://books.google.com/books?id=aQUgAwAAQBAJ Yeats R. 2012 Cambridge University Press 978-0521190855 80, 89–94 Vacaville and Winters both lie to the east of these faults along the low foothills. Numerous geoscientists have remarked on the potential for blind thrust earthquakes in this area. These professionals specifically labelled it the Coast Range–Sierran Block Boundary Zone in a sequence of published articles from the 1980s and 1990s and stated that the 1983 Coalinga earthquake (a blind thrust event) occurred within the zone.Source Characterization and Ground-Motion Modeling of the 1892 Vacaville–Winters Earthquake Sequence, California http://bssa.geoscienceworld.org/content/91/6/1471.abstract R. H. O'Connell J. R. Unruh L. V. Block 2001 Bulletin of the Seismological Society of America 91 6 10.1785/0120000267 1471, 1473, 1495 2001BuSSA..91.1471O subscription Earthquakes Seismic wave Each large shock in the doublet, one on April 19 and the other two days later on April 21, had a high intensity and was felt over roughly the same geographical area. The area over which the initial shock was felt with an intensity of VIII (Severe) was about 1,100 km2 and the area for the second shock was about 890 km2. The furthest extent that they were felt was from Redding in the north to Salinas and Fresno in the south and to Virginia City, Nevada in the east. Investigators completed a study of the area that included a three dimensional crustal velocity model. Proprietary seismic reflection data were also inspected in an attempt to establish a source for the sequence. Observations of the range front and modelling of strong ground motions led to the presentation of a 17 km on rupture on the west-dipping Gordon Valley blind thrust fault that could have produced the felt intensities that were specific to the April 19 event. Damage The shocks affected Solano and Yolo Counties along the border of the Sacramento Valley. In the north, the communities of Esparto and Capay both experienced Mercalli intensities of VIII (Severe)—which is associated with damage—and in the south, Vacaville and Fairfield both experienced the same. Work by seismologist Toussan Toppozada, that was published in a 1981 report, further clarified that Vacaville was at the center of the destruction. Damage also occurred at Dixon as well as the area of the highest reported intensity of IX (Violent), midway between Winters and Vacaville, at Allendale. There, some buildings were damaged, some collapsed, and 1 mi km flip on long ground fissures were observed.Vacaville–Winters earthquakes . . . 1892: Solano and Yolo counties https://www.conservation.ca.gov/cgs/Documents/Publications/California-Geology-Magazine/CG_1987-04A.pdf J. H. Bennett 1987 California Geology 40 4 75–82Harry O. Wood Harry O. Wood Frank Neumann 1931 Modified Mercalli Intensity Scale of 1931 Bulletin of the Seismological Society of America 21 4 277–283 10.1785/BSSA0210040277 1931BuSSA..21..277W https://pangea.stanford.edu/scits/sites/default/files/277.full_.pdf These widespread and north-trending cracks were very narrow, from 1 - 3 in cm flip us in width. Despite these surface cracks and other offset drainages and other lineaments, no surface faulting occurred. This was confirmed by trench excavations where these features were found. Other ground effects occurred though. Reports of rockslides and dislodged boulders were written about in the newspapers, but the most common type of damage were the many chimneys that were damaged or destroyed. Total damage was estimated between $225,000 and $250,000, and one person was reported dead. Intensity An isoseismal map for the April 19 event shows an asymmetrical and slightly elongated pattern of isoseismal lines (of equal intensity) on the north–south axis. There are high intensities east of the Napa–Solano county border. No locations in Napa county reached any higher than intensity VI (Strong), indicating that the shock originated east of the Vaca Mountains. The April 21 event differed slightly, in that the strongest effects were shifted slightly to the northwest. See also List of earthquakes in California List of earthquakes in the United States List of historical earthquakes References Preparation of isoseismal maps and summaries of reported effects for pre-1900 California earthquakes https://pubs.er.usgs.gov/publication/ofr81262 T. R. Toppozada C. R. Real Open-File Report 1981 Open-File Report 81-262 United States Geological Survey 107, 108, 164 10.3133/ofr81262 free Significant Earthquake Information https://www.ngdc.noaa.gov/hazel/view/hazards/earthquake/event-more-info/2418 National Geophysical Data Center / World Data Service (NGDC/WDS) NCEI/WDS Global Significant Earthquake Database National Geophysical Data Center, NOAA 10.7289/V5TD9V7K 1972 Data Set August 2, 2022 C. W. Stover J. L. Coffman Seismicity of the United States, 1568–1989 (Revised) https://books.google.com/books?id=eeKGtQEACAAJ&pg=PA110 U.S. Geological Survey professional paper 1527 1993 United States Government Printing Office 74, 110, 111 1892 Category:1892 earthquakes Category:1892 in California Earthquakes Earthquakes Category:History of Solano County, California Category:History of Yolo County, California Category:April 1892 in the United States Category:Buried rupture earthquakes