Is 4.4 jolt an end to Los Angeles’ ‘earthquake drought’?

LA Times – by Ari Bloomekatz, Rong-Gong Lin II and Matt Stevens

Seismologists say Monday’s magnitude 4.4 temblor near Westwood could mark the beginning of the end for L.A.’s years-long “earthquake drought.”

Typically, they would expect a 4.4-sized earthquake about once a year in the Los Angeles Basin, but that hasn’t happened for years.  

“We don’t know if this is the end of the earthquake drought we’ve had over the last few years, and we won’t know for many months,” said Caltech seismologist Egill Hauksson.

The magnitude 4.4 earthquake that struck near Westwood at 6:25 a.m. is the most significant shake in Southern California since a 5.5 earthquake hit Chino Hills in 2008.

Significant earthquakes were far more common in the Los Angeles Basin the 1980s and the 1990s, in which the 1987 Whittier Narrows earthquake, the 1991 Sierra Madre earthquake and the 1994 Northridge earthquake occurred.

Monday’s earthquake was followed up by seven smaller temblors, with two registering as magnitude 2.5 or greater, according to the U.S. Geological Survey.

The seven quakes all occurred about five to six miles northwest of Westwood, with a magnitude 2.5 temblor hitting at 10:07 a.m. Most of the aftershocks were magnitude 1.3 or smaller, according to the USGS.

Monday’s quake struck the northern edge of the Santa Monica Mountains, an area that has not seen much recent seismological activity.

“The location is somewhat surprising. It’s within the Santa Monica Mountains. We have not seen seismicity in it in recent times,” Hauksson said. “It has been dormant for quite some time.”

In contrast, there are well-known faults to the south of the Santa Monica Mountains: the Santa Monica and Hollywood faults roughly along Santa Monica and Hollywood boulevards.

The largest and most dangerous earthquake fault closest to Monday’s quake is the Santa Monica fault, which could produce a magnitude 7.0 earthquake underneath Santa Monica Boulevard. The chance of Monday’s quake causing such a massive shaker on the Santa Monica fault, however, is a small one. There was a 5% chance just after the 6:25 a.m. earthquake, but that risk will fall to 1% by Tuesday morning, said U.S. Geological Survey seismologist Lucy Jones.

Also close by is the Hollywood fault, which is near Hollywood Boulevard.

The quake was felt over a large swath of Southern California but especially on the Westside and in the San Fernando Valley.

Aaron Green, 28, a post-doctorate student in chemistry, was asleep at his apartment on Landfair Avenue when he felt a shake: boom-boom, boom-boom.

“I just figured the neighbors upstairs we’re gettin’ to it,” he said. “But it was a little more vigorous than normal. Pretty surprising, and a little scary too.”

Christina Toth, 26 and Andresa Maia, 25, were among the few that were not shaken awake by the earthquake at UCLA. The two master’s students were making a model for their architecture final so they were up all night.

Still, Toth said the shaking “kind of freaked us out.” UCLA’s architecture building is old, the students said, a fact they realized after they had fled the scene. “We looked at each other,” Maia said, “and we just sort of ran outside.”

Quake another win for early-warning system (8:54 a.m.)The earthquake demonstrated the success of an early earthquake warning system being tested by scientists at the U.S. Geological Survey. The center’s offices in Pasadena received some seconds of early warning. The farther an earthquake epicenter is away, the more seconds of warning the system can provide.

“It certainly worked in terms of notifying ahead of time, before the shaking arrived,” Graves said.

http://www.latimes.com/local/lanow/earthquake-47-quake-strikes-near-westwood-california-yxdnr8,0,4535905.story#ixzz2wFcAeanC