A magnitude 4.2 earthquake gave the Los Angeles region a wake-up call early in the morning, but no significant damage has been reported
LOS ANGELES – A magnitude 4.2 earthquake gave the Los Angeles region a wake-up call before dawn Thursday, prompting local alerts for the state’s new earthquake warning system, but not leading to reports of significant damage .
The 4:29 am shake centered in the northern San Fernando Valley and occurred at a depth of 5.5 miles (8.9 kilometers), the US Geological Survey said. Dozens of aftershocks followed.
The Los Angeles Fire Department found no damage or injury in a survey by ground and air units, a standard procedure after earthquakes in the second largest city in the country.
The Police Department also reported no problems.
Good morning to Los Angeles. Yes, we are sorry too, “Los Angeles police tweeted, noting that 911 and other systems were unaffected.
The earthquake was felt primarily in the Los Angeles metropolitan area, according to thousands of contributions to the USGS citizen complaint system. Some reports came from more distant places.
The ShakeAlert earthquake early warning system at one point estimated a magnitude greater than 4.5, the threshold for alerts, and between 3.6 seconds and 12.8 seconds after detection, sent messages to areas where shocks were predicted to reach at least a certain intensity level.
Alerts reaching the public through apps are meant to give people time to protect themselves or allow systems like manufacturing operations and rail lines to shut down before damaging shakes arrive.
More than 10,000 alerts were sent Thursday in the Southern California region through two of the apps, said Robert de Groot, ShakeAlert coordinator for the USGS.
“Really good results from this particular event,” he said at an online news conference hosted by the California Institute of Technology.
The USGS research seismologist Susan Hough said that while the earthquake was not large enough to cause damage, the tremor was stronger than average for a 4.2 magnitude earthquake and will need to be analyzed.
The earthquake occurred in the vicinity of destructive and deadly earthquakes that focused on the San Fernando Valley in 1971 and 1994.
“We cannot say if today’s event is related to them, but it is not surprising that we have seismic activity in this area,” said Jen Andrews, a seismologist at the Caltech Seismology Laboratory. “We have several fault zones nearby.”
Hough said the USGS generally does not issue a replication forecast for magnitude 5 earthquakes, but will do so for Thursday’s earthquake because it affected a populated area.
The initial post-earthquake aftershock forecast was an earthquake 1 in 10 probability of an earthquake equal to or greater than magnitude 4.2 over the next month, Hough said.
Thursday’s earthquakes were “garden variety,” according to former USGS seismologist Lucy Jones, who now runs a center focused on making communities resilient to disasters.
“What does that mean? It means you live in California,” he tweeted.
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