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Thursday, April 18, 2013

106th anniversary of The Great Quake - 1906 San Francisco earthquake

The death toll from the earthquake and resulting fire is the greatest loss of life from a natural disaster in California's history.

The San Francisco earthquake of 1906 was a major earthquake that struck San Francisco and the coast of Northern California at 5:12 a.m. on Wednesday, April 18, 1906.[3] Devastating fires broke out in the city and lasted for several days. As a result of the quake and fires, about 3,000 people died[4] and over 80% of San Francisco was destroyed.
The earthquake and resulting fire are remembered as one of the worst natural disasters in the history of the United States[5] alongside the Galveston Hurricane of 1900 and Hurricane Katrina in 2005.[6]The death toll from the earthquake and resulting fire is the greatest loss of life from a natural disaster in California's history.

At the time, 375 deaths were reported.[7] That figure was fabricated by government officials who felt that reporting the true death toll would hurt real estate prices and efforts to rebuild the city.[citation needed] Hundreds of casualties in Chinatown went ignored and unrecorded; that number is still uncertain today, and is estimated to be roughly 3,000 at minimum.[8] Most of the deaths occurred in San Francisco itself, but 189 were reported elsewhere in the Bay Area;[3] nearby cities, such as Santa Rosa and San Jose also suffered severe damage. In Monterey County, the earthquake permanently shifted the course of the Salinas River near its mouth. Where previously the river emptied into Monterey Bay between Moss Landing and Watsonville, it was diverted 6 miles south to a new outlet just north of Marina.
Between 227,000 and 300,000 people were left homeless out of a population of about 410,000; half of the people who evacuated fled across the bay to Oakland and Berkeley. Newspapers at the time described Golden Gate Park, the Presidiothe Panhandle and the beaches between Ingleside and North Beach as being covered with makeshift tents. More than two years later, many of these refugee camps were still in full operation.[9]

Magnitude and geology

The most widely accepted estimate for the magnitude of the earthquake is a moment magnitude (Mw) of 7.9;[1] however, other values have been proposed, from 7.7 to as high as 8.25.[14] The main shock epicenter occurred offshore about 2 miles (3.2 km) from the city, near Mussel Rock. Shaking was felt fromOregon to Los Angeles, and inland as far as central Nevada.[15]
The earthquake was caused by a rupture on the San Andreas Fault, a continental transform fault that forms part of the boundary between the Pacific Plate and theNorth American Plate. It ruptured along the fault both northward and southward for a total of 296 miles (476 km).[16] This fault runs the length of California from theSalton Sea in the south to Cape Mendocino to the north, a distance of about 810 miles (1,300 km). The earthquake ruptured the northern third of the fault for a distance of 296 miles (476 km). The maximum observed surface displacement was about 20 feet (6 m); however, geodetic measurements show displacements of up to 28 feet (8.5 m).[17]
A strong foreshock preceded the mainshock by about 20 to 25 seconds. The strong shaking of the main shock lasted about 42 seconds. The shaking intensity as described on the Modified Mercalli intensity scale reached VIII in San Francisco and up to IX in areas to the north like Santa Rosa where destruction was devastating. There were decades of minor earthquakes – more than at any other time in the historical record for northern California – before the 1906 quake. Widely interpreted previously as precursory activity to the 1906 earthquake, they have been found to have a strong seasonal pattern and have been postulated to be due to large seasonal sediment loads in coastal bays that overlie faults as a result of the erosion caused by hydraulic mining in the later years of the California Gold Rush.[18]

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****REMINDER**** Every fire has the ability to be catastrophic. The wildland fire management environment has profoundly changed. Growing numbers of communities, across the nation, are experiencing longer fire seasons; more frequent, bigger, and more severe, fires are a real threat. Be careful with all campfires and equipment.
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