|UTC time||1957-03-22 19:44:22|
|Local date||March 22, 1957|
|Local time||11:44:22 PST |
|Magnitude||5.7 Mw |
|Depth||15 km (9.3 mi) |
|Areas affected||San Francisco Bay Area |
|Total damage||$1 million |
|Max. intensity||VII (Very strong) |
|Peak acceleration||0.18g |
|Casualties||1 dead, 40 injured |
The 1957 San Francisco earthquake (also known as the Daly City earthquake of 1957) occurred on March 22 at 11:44:22 local time with a moment magnitude of 5.7 and a maximum Mercalli Intensity of VII (Very strong). It was located just off the San Francisco Peninsula near the San Andreas Fault and was felt in a limited portion of Northern and Central California. There was a non-destructive foreshock and aftershock sequence that lasted for several months. With financial losses of around US$1 million, damage was considered minimal, with one death and forty injuries.
The San Andreas Fault is a northwest-striking transform fault that accommodates motion between the Pacific and North American Plates. The Mendocino Triple Junction is an area of high seismicity, and marks its northern extremity at the Gorda Plate, which is subducting beneath the North American Plate. Three moderate events in the San Francisco Bay Area occurred on or near the San Andreas Fault in the early nineteenth-century.
Eight foreshocks (with a maximum magnitude of 3.8) preceded the main event. The first motion method was used to determine the focal mechanism of the mainshock. It was found to be dissimilar from the 1906 earthquake, and instead showed oblique movement on a steeply-dipping thrust fault, with the eastern side of the fault rising relative to the western side. The strike-slip component was minimal; only about half as much as the thrust component.
Damage was non-structural and was limited to content within buildings and cracked plaster and was estimated at $1 million, not including loss to building content. The most significant effects were seen in the western portion of Daly City and in the Lake Merced area of San Francisco. The minimal losses were attributed to the short duration and lack of high intensity shaking.
The event was felt over an area of 12,000 square miles. Its scientific value was reinforced because it was captured on 13 strong motion instruments. A maximum (free field) peak ground acceleration of 0.13 g was recorded in Golden Gate Park and .18 g was recorded on the fourteenth floor of a building in San Francisco.
- List of earthquakes in 1957
- List of earthquakes in California
- List of earthquakes in the United States
- ISC (2015), ISC-GEM Global Instrumental Earthquake Catalogue (1900–2009), Version 2.0, International Seismological Centre
- Stover, C. W.; Coffman, J. L. (1993), Seismicity of the United States, 1568–1989 (Revised), U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, pp. 88, 150
- Cloud, W. K. (1959), "Intensity and Ground Motion of the San Francisco Earthquake of March 22, 1957", San Francisco earthquakes of March 1957, Special Report 57, California Division of Mines, pp. 51, 52
- Tocher, D. (1959), "Seismographic Results from the 1957 San Francisco Earthquakes", San Francisco earthquakes of March 1957, Special Report 57, California Division of Mines, pp. 61, 65, 70, 71
- Yeats, R. (2012), Active Faults of the World, Cambridge University Press, pp. 81, 83, ISBN 978-0521190855
- Steinbrugge, K. V.; Bush, V. R.; Zacher, E. G. (1959), "Damage to Buildings and Other Structures During the San Francisco Earthquake of March 22, 1957", San Francisco earthquakes of March 1957, Special Report 57, California Division of Mines, pp. 75, 76