caution
Transcript: February 9, 1971 -A 6.6M quake with an epicenter in the San Fernando-Sylmar region. The earthquake caused over $500 million in damage, injured more than 2,000 people, and took 65 lives. Fort Tejon; January 9, 1857 Magnitude 7.9 Owens Valley; March 26, 1872 Magnitude 7.4 Imperial Valley; February 24, 1892 Magnitude 7.8 San Francisco; April 18, 1906 Magnitude 7.8 West of Eureka; January 31, 1922 Magnitude 7.3 Kern County; July 21, 1952 Magnitude 7.3 Landers; June 28, 1992 Magnitude 7.3 The westward- moving North American Plate began to override the spreading ridge between the Farallon Plate and the Pacific Plate. This action divided the Farallon Plate into two smaller plates, the northern Juan de Fuca Plate (JdFP) and the southern Cocos Plate (CP). By 20 million years ago, two triple junctions began to migrate north and south along the western margin of the West Coast. (Triple junctions are intersections between three tectonic plates; shown as red triangles in the diagrams.) The change in plate configuration as the North American Plate began to encounter the Pacific Plate resulted in the formation of the San Andreas Fault. Location: California Length: Approximately 800 miles 28 millions years old A fault is a planar crack in a rock along which slippage has taken place. Most faults are small - even microscopic - and are not important. Some faults are many miles long. Faults can be classified according to which of the three directions of space the rocks on either side move. When the motion is predominantly vertical, they are called dip slip faults. Dip slip faults with dips less than 45 degrees are called thrust faults. As they break and scrape by one another, they produce seismic waves that travel through the ground and shake the surface. We know this shaking as earthquakes. All states and all continents have faults but California has more than most. What makes the SAF so important is that it is a plate boundary and that it is on land. Most plate boundaries are in the ocean and so they are hard to study. The earliest reported earthquake in California was felt in 1769 July 28, 1769 Portola Expedition in the Los Angeles basin he estimated 6.0M quake was followed by at least a dozen aftershocks through August 3rd, with three violent shocks reported after. December 8, 1812 -Originally believed to have an epicenter close to San Juan Capistrano, where the mission church collapsed killing 40 native Americans attending mass. Based on scientific evidence, it is believed that the epicenter was actually along the Mojave segment of the San Andreas Fault at Wrightwood with an estimated 7.5M. December 21, 1812 -Potentially triggered by the Wrightwood quake two weeks earlier, this was believed to be two quakes-one at 10am; the other at 10:15am-both with an estimated 7.0M and a probable epicenter located offshore, possibly in the Santa Barbara Channel. Damage to the church at Mission Santa Barbara. September 24, 1827 -Felt in the Los Angeles region, an estimated 5.5M quake with an epicenter in the Santa Monica Bay. January 9, 1857 -With an approximate epicenter of about 72km NE of San Luis Obispo on the San Andreas Fault, and an estimated magnitude of 7.9Mw, it is considered one of the greatest recorded earthquakes in U.S. history. The SAF was born when the Pacific Plate first touched the North American Plate. The San Andreas Fault received its name from Andrew Lawson after the 1906 earthquake. He named it for San Andreas Lake, a (now) man-modified sag pond in San Mateo county through which the fault passes. The lake was named by Gaspar de Portola in 1769 who camped near the (then) small body of water. The earliest documented record of an earthquake comes from China, in 1831 BC from the Shandong province. The most complete historical records also come from China, starting in 780 BC during the Zhou Dynasty in China. Alejandra Aguiar Professor Beaman Geology May 11 2016 Other Devastating Earthquakes SAN ANDREAS FAULT Evolution of San Andreas Fault Earthquake stress is built up in rocks when two plates that are trying to move push against one another. Because of friction between the plates at the fault, they cannot slide freely. Instead, they deform (strain) and build up energy, like compressing a spring. When the stress exceeds the friction or the breaking strength of the rocks, the rocks break or slide and in a short period of time - seconds - the energy stored in the deformed rock is released in the form of heat and seismic waves. The process is called elastic rebound. History CAUTION Quick Facts Haiti 2010 7.0M Chile 2010 8.8M Japan 2011 9.0M Historic Earthquakes in California
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