Magnitude 4.3 Earthquake Shakes Northern California, Reveals New Fault

April 2, 2009

A magnitude 4.3 earthquake struck near Santa Clara Valley Calif., this week near Mt. Hamilton, revealing a fault scientists did not know existed, according to the U.S. Geological Survey in Menlo Park, Calif.

According to its summary of the event, the quake occurred on a north-south oriented fault about 3 km to the east of the of the Calaveras fault as defined by the past 40 years of earthquake epicenters. “The fault has no name and is not mapped at the surface of the earth.”

USGS said the fault is similar in orientation and tectonics to the fault that was ruptured by the Mt. Lewis sequence in 1986 (M5.7). However, the Mt. Lewis sequence lasted for 491 days and contained 1930 aftershocks. In contrast, as of Mar 30, there were only 4 located aftershocks with the largest having a magnitude of 1.2. “Although this quake is on a similar structure, it is not exhibiting the similar behavior,” USGS said. The group said it was unlikely that this recent earthquake will trigger a significant earthquake on this section of the Calaveras fault.

Source: USGS

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