Notable Earthquake of the Week

Parkfield M 6.4 Earthquake

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On March 3, 1901, an earthquake measuring M 6.4 occurred along the San Andreas fault in Central California. The quake was centered near Parkfield, then a remote farming and ranchland community, and caused chimneys to topple and windows to shatter over a wide area.

At Parkfield, three houses were twisted out of shape and one was almost wrecked. Surface fault ruptures (?) with nearly 50 cm of offset were observed.

The quake occurred in nearly the same location as two quakes prior to it (1857 and 1881), but it was not till the 1980's and after three more (1922, 1934, 1966) of similar magnitude that a pattern of every 21-22 years was discovered.

In an effort to "catch a quake", the USGS set up a sophisticated monitoring network to understand the dynamics of how and when an earthquake occurs. However, since 1966, there have been no temblors registering greater than M 5.0 (largest M 4.8, 1975).

It has been suggested that the Coalinga M 6.5 quake located 25 mi. northeast of Parkfield in 1983 may have temporarily altered the tectonic stress field in Central California, perhaps "defusing" the seismic pattern. Whatever the reason, the clock is ticking till the next Parkfield M 6.0 earthquake.

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