Some called it an "earthquake cluster," others a "swarm." Seismologists used the term "earthquake sequence."
Whatever the name, a series of more than 30 small to moderate temblors jolted Southern California on Tuesday night and Wednesday morning, rattling nerves but causing no significant damage.
The cluster of earthquakes that struck near Yorba Linda was centered near the Whittier fault, but preliminary data suggested that fault was not responsible for the temblor, said Doug Given, a geophysicist with theU.S. Geological Survey.
"There are lots and lots of little faults all over that area," Given said of the northern Orange County region where the quakes were centered. "It's a known active area."
The shaking began with a magnitude 4.5 earthquake near Yorba Linda about 11:30 p.m. Tuesday, bookended by another 4.5 quake about 9:30 a.m. Wednesday, but with many smaller ones in between.
At a news conference Wednesday morning, Kate Hutton of theU.S. Geological Surveysaid that of all the quakes, only three were probably felt by residents. The two 4.5 temblors were felt across a wide swath of Southern California, with people reporting shaking as far away as Thousand Oaks, the Santa Clarita Valley, the Westside and northern San Diego County, according to the USGS's "Did You Feel It?" website.
"This is all part of the same earthquake sequence; they're all in the same area," Hutton told reporters.
"It shook us pretty good. We've felt earthquakes before, so it came as no surprise," said Chris Nordyke, director of marketing at the Richard Nixon Library and Birthplace in Yorba Linda. "It shook open the door, but nothing fell off the shelves."
Given said the excitement offers a lesson for the region. "We live in earthquake country. Earthquakes are normal here, and people should be prepared," he said.
Times staff writers Richard Winton and David Zahniser contributed to this report.