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Yorba Linda earthquake comes amid a 'cluster' of temblors

August 29, 2012 |  2:07 pm

“Did you feel it?” map.
The magnitude 4.1 Yorba Linda earthquake that jolted residents around Southern California on Wednesday afternoon came amid a earthquake swarm in Imperial County.

But it remains unclear whether the two events are connected. Seismologists have said there was no evidence the Imperial swarm would cause bigger quakes closer to L.A.

Yorba Linda has experienced several moderate quakes this month.

Seismologists referred to this earlier Yorba Linda quakes as a "cluster." They struck near the Whittier fault, but preliminary data suggested that that fault was not responsible for the cluster. The strongest was a magnitude 4.5. The cluster seemed to end Aug. 9.

More than 400 earthquakes greater than magnitude 1.0 have been recorded in Imperial County since Saturday evening. The largest were a 5.3 and a 5.5 about midday Sunday.

For all the ground movement, experts said there was no evidence the earthquake swarms were a precursor of much larger quakes on longer, more dangerous faults. And scientists don't see any immediate signs of added pressure to the San Andreas fault, which is not far from the location of the earthquake swarm.

That makes this weekend's swarm different from the one that occurred after the 2010 Easter Sunday quake that shook up the California-Mexico border. The 7.2 quake appeared to have directed tectonic stress northward, toward populated areas in Southern California. Three months after the Mexicali quake, a 5.4 quake that centered south of Palm Springs rattled the region.

Scientists said the Easter Sunday quake and its aftershocks triggered movement on at least six faults, including the Elsinore and San Jacinto faults, which run close to heavily populated areas in eastern Los Angeles County and the Inland Empire.

As on Monday, officials said there is no evidence that this weekend's swarm will trigger quakes elsewhere.


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Image: “Did you feel it?” map. Credit: U.S. Geological Survey