Orange County is experiencing an earthquake cluster that has lightly shaken parts of San Diego County and made some people uneasy. Such clusters aren’t unusual, and it is impossible to know whether this series will lead to a much bigger event. Scientists cannot predict quakes.

The significant shaking began at 11:23 p.m. Tuesday when a magnitude-4.4 quake broke two miles north-northeast of Yorba Linda, along the Whittier Fault system, a region that’s known for its seismic activity. That was followed by a 4.5 quake in the same area at 9:33 a.m. Wednesday. Scientists call quakes that are similar in size and which occur fairly close in time “doublets.” The region was also hit by a series of smaller quakes.

The two larger quakes jolted Orange County, but brought generally gentle rolling and shaking to such San Diego County communities as Oceanside, San Marcos, Fallbrook, Vista, Carlsbad, Bonsall, Escondido, El Cajon, La Jolla, Santee, Encinitas and San Diego. The shaking led to the same questions from the public: What’s going on? Should we be worried?

Debra Kilb, a seismologist at the Scripps Institution of Oceanography in La Jolla, said the kind of cluster now under way “typically leads to something bigger only about 5 percent of the time. We can’t say nothing will happen, but it is very unlikely.”

Kilb added that the quakes were widely felt geographically because “L.A. is like a big bowl of jelly. It shakes due to a lot of unconsolidated material.” That helps the energy to spread to more distant areas, such as San Diego.

The Whittier Fault produced a magnitude-5.9 quake on Oct. 1, 1987, which was followed by a 5.3 shaker. Collectively, those quakes caused about $350 million in damage, says the U.S. Geological Survey. The latest shaking is happening not far from where the 5.5 Chino Hills quake struck in July 2008.

Since we’re in the midst of a heat wave, it’s worth mentioning that quakes and weather are not connected.



