Automated seismographs reported a series of six quakes, most in the 1-2 magnitude, starting at 7:45 a.m.
The largest quakes were magnitude 2.7 at 7:52 and magnitude 3.1 at 7:54, according to preliminary automated reports that have not been reviewed by humans.
A magnitude 2.0 temblor hit the mountain at 10:14 a.m.As a precaution, Los Angeles city fire trucks were rolled out of station houses, where garage doors can jam or stall if a major quake occurs.
Seismologists routinely give a 10 percent chance of a major shaker following what turns out to be a foreshock.
Firefighters also scanned bridges and buildings near their station houses, which is the standard drill following a quake. No damage was found.
Persons reported to the USGS that they felt weak shaking in the northern half of the San Fernando Valley, and in across Santa Clarita, and as far away as Westlake Village, Glendale and the Antelope Valley.
Oat Mountain is the highest point in the mountain range north of the San Fernando Valley, and was the epicenter of the 6.7 magnitude Northridge Earthquake of 1994, which killed 57 people.
That quake reportedly raised the elevation of the mountain by 20 inches above sea level.
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