Damage at Union Square. Photo courtesy of the Museum of the City of San Francisco.
The San Francisco earthquake occurred at 5:12 A.M. on April 18, 1906. The source was a rupture of the San Andreas Fault. The duration of severe shaking was about 40 seconds, according to Professor Alexander McAdie who experienced the earthquake firsthand.
Reference sources give magnitude estimates ranging from 7.7 to 8.25. Note that there are actually several different magnitude scales.
A "Ewing" three-component seismograph at Lick Observatory on Mt. Hamilton made a partial recording of the 1906 San Francisco earthquake. The earthquake amplitude was so severe that it exceeded the range capability of this seismograph. The Ewing seismograph was based on pendulum motion.
The earthquake damaged many buildings. The Valencia Hotel was a four-story wooden building which collapsed into its own basement.
The luxurious Palace Hotel shed its rear wall but was otherwise undamaged. It had been built in 1875 to withstand earthquakes.
Many people died in the earthquake and in the fires which followed. Death toll estimates range from 700 to 3000. For example, Bruce Bolt gives a number of 700 in Reference 1.
Fire Chief Engineer Dennis T. Sullivan was mortally wounded when a chimney of the California Theater and hotel crashed through the fire station in which he was living at 410-412 Bush St.
The fires resulted from ruptured gas lines. Water mains also ruptured, sending geysers shooting up through broken pavement. As a result, firemen had no water to fight the fires. The fires raged for three days.
Fire destroyed many buildings, including the Windsor Hotel at Fifth and Market Streets.
Fireman used dynamite to destroy some buildings in an effort to stop the fires from spreading. The fires continued to spread despite this action.
San Francisco was known as the "Paris of the West" in 1906. The earthquake, however, reduced it to a "tent city." Golden Gate Park became a refugee camp.
The area around the U.S. Mint building became a refugee village because Superintendent Frank Leach installed two pipes from the Mint's artesian well after the fire to provide fresh water to the homeless.
Damage cost estimates range from $400 million to $524 million.
The 1906 San Francisco earthquake was by far the worst U.S. earthquake in terms of death toll, even using the lower estimate of 700. The worst U.S. earthquake in terms of magnitude, however, was the 1964 Alaskan earthquake.
The San Francisco earthquake has become a benchmark by which other earthquakes are judged. For example, scientists discovered sunquakes using data from the SOHO spacecraft. Specifically, the spacecraft recorded a solar flare on July 9, 1996. This flare generated a quake that contained about 40,000 times the energy released in the 1906 San Francisco earthquake.
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1. Bruce A. Bolt Earthquakes (Earthquakes, 4th Ed) 1999.
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