![\"isoseismal](\"CA_Apr_1906.gif\")
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Official Magnitude and Location updated 05-Feb-2018
\nLocation Reference:
\nLomax, A., (2005) A Reanalysis of the Hypocentral Location and Related Observations for the Great 1906 California Earthquake, Bull. Seism. Soc. Am., 95, 861-877.
\nMagnitude Reference:
\nSong, Beroza, and Segall (2008) A Unified Source Model for the 1906 San Francisco Earthquake, Bull. Seis. Soc. Am., 98, 823-831.\n
\nThis earthquake is one of the most devastating in the\nhistory of California. The earthquake and resulting\nfires caused an estimated 3,000 deaths and $524\nmillion in property loss. Damage in San Francisco\nresulting only from the earthquake was estimated at\n$20 million; outside the city, it was estimated at $4\nmillion. The sensible duration of the shaking in San\nFrancisco was about 1 minute.\n
\n\nThe earthquake damaged buildings and structures\nin all parts of the city and county of San Francisco,\nalthough over much of the area, the damage was\nmoderate in amount and character. Most chimneys\ntoppled or were badly broken. In the business\ndistrict, which was built on ground made by filling in\nthe cove of Yerba Buena, pavements were buckled,\narched, and fissured; brick and frame houses of ordinary\nconstruction were damaged extensively or\ndestroyed; sewers and water mains were broken; and\nstreetcar tracks were bent into wavelike forms.\n
\n\nOn or near the San Andreas fault, buildings were\ndestroyed (one was torn apart), and trees were\nknocked to the ground. The surface of the ground\nwas torn and heaved into furrow-like ridges. Roads\ncrossing the faultline were impassable, and pipelines\nwere broken. One pipeline that carried water from\nSan Andreas Lake to San Francisco was broken,\nshutting off the water supply to the city. The fires\nthat ignited soon after the onset of the earthquake\nquickly raged through the city because of the lack of\nwater to control them. They destroyed a large part of\nSan Francisco and intensified the loss at Fort Bragg\nand Santa Rosa.\n
\n\nThis earthquake caused the most lengthy rupture\nof a fault that has been observed in the contiguous\nUnited States. The displacement of the San Andreas\nFault was observed over a distance of 300 kilometers from\nSan Juan Bautista to Point Arena, where it passes\nout to sea. Additional displacement was observed\nfarther north at Shelter Cove in Humboldt County, and,\nassuming the rupture was continuous, the total\nlength of rupture would extend 430 kilometers. The\nlargest horizontal displacement - 6.4 meters - occurred\nnear Point Reyes Station in Marin County.\n
\n\nIn areas where dislocation of fences and roads indicated\nthe amount of ground movement, motions of\n3 to 4.5 meters were common. Near Point Arena, in Mendocino \nCounty, a fence and a row of trees were displaced\nalmost 5 meters. At Wright's Station, in Santa\nClara County, a lateral displacement of 1.4 meters was\nobserved. Vertical displacement of as much as 0.9 meters\nwas observed near Fort Ross in Sonoma County.\nVertical displacement was not detected toward the south\nend of the fault.\n
\n\nAlthough Santa Rosa lies about 30 kilometers from\nthe San Andreas fault, damage to property was severe,\nand 50 people were killed. The earthquake also was\nsevere in the Los Banos area of the western San\nJoaquin Valley, where the MM intensity more than\n48 kilometers from the fault zone was IX. Santa Rosa lies\ndirectly inland from the region of greatest motion on\nthe San Andreas fault.\n
\n\nTrees swayed violently, and some were broken off\nabove the ground or thrown down. The water in\nsprings and artesian wells either increased or\ndecreased its flow. A few sand craterlets formed in\nareas where water was ejected through cracks or\nfissures.\n
\n\nThe region of destructive intensity extended over a\ndistance of 600 kilometers. The total felt area included\nmost of California and parts of western Nevada and\nsouthern Oregon. The maximum intensity\nof XI was based on geologic effects, but the highest\nintensity based on damage was IX. Several\nforeshocks probably occurred, and many aftershocks\nwere reported, some of which were severe. (Ref. 38, 56, 378, 381, 517, 533, 567, 571, 572, 573.)\n
\nMaximum observed Modified Mercalli Intensity (MMI) XI\n
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\n\nAbridged from Seismicity of the United States, 1568-1989 (Revised),\nby Carl W. Stover and Jerry L. Coffman,\nU.S. Geological Survey Professional Paper 1527,\nUnited States Government Printing Office, Washington: 1993.\n
\n\nA small, but geophysically significant, tsunami was recorded on the Presidio tide gauge in San Francisco. There was a 10-cm lowering of sea level with a period of about 16 minutes beginning about 7.5-10 minutes after the earthquake (blurring of the record by the earthquake caused uncertainty about the absolute time). Then a “series of two to three oscillations with an apparent period of 40 to 45 minutes and a maximum amplitude of 5 cm were recorded approximately a half-hour after the initial solitary depression.”\n
\n\nAbridged from Examination of the Tsunami Generated by the 1906 San Francisco Mw =7.8 Earthquake, Using New Interpretations of the Offshore San Andreas Fault, by Eric L. Geist and Mary Lou Zoback, in Crustal Structure of the Coastal and Marine San Francisco Bay Region, California, Tom Parsons, Editor, U.S. Geological Survey Professional Paper 1658, United States Government Printing Office: 2002.\n
\n\nAccording to the Report of the State Earthquake Investigation Commission (1908), 135 aftershocks were felt on April 18, and 22 were felt on April 19. That publication lists many aftershocks between April 18, 1906 and June 10, 1907.\n
\n\nAbridged from Descriptive Catalog of Earthquakes of the Pacific Coast of the United States, 1769-1928, by Sidney D. Townley and Maxwell W. Allen (1939), Bulletin of the Seismological Society of America, 29(1), p. 1-297. [Stover and Coffman Ref. 56.]\n
\nAdditional Reference: The California Earthquake of April 18, 1906: Report of the State Earthquake Investigation Commission, Andrew C. Lawson, chairman (1908, reprinted 1968), Carnegie Institution of Washington Publication 87, 2 vols.\n
\nAs of July 2026 this is the largest and most destructive earthquake located within the State of California. The other Mw 7.9 event is the 1857 Fort Tejon Earthquake, but that event caused less damage and had a lower maximum intensity. The Mw 9.0 Cascadia Earthquake in January 1700 is presumed to have included Northern California in its rupture zone but is off the coast of the State and there are no reports of damage from that event within what is now California.
\nThis is one of the World’s Most Deadly Earthquakes (>=1,000 people killed) and is one of the Largest Earthquakes in the United States (M>=7.0).
\nThe USGS has designated this as an event for “This Date in Earthquake History” and for “This Date in U.S. Earthquake History” for April 18.\n