A magnitude 5.1 earthquake shook the San Francisco Bay Area, including San Jose and its Silicon Valley, on Tuesday, triggering alerts on tens of thousands of cellphones.
Despite widespread shaking reported in a region home to nearly 5 million people, there were no immediate reports of injuries or major damage.
Lucy Jones, a retired US Geological Survey seismologist, said he was the largest earthquake in the Bay Area in 15 years. She said NBC Bay Area it was followed by aftershocks that measured 3.1 and 2.2.
The 11:42 a.m. quake hit the foothills 12 miles (20 km) east of San Jose, the Bay Area’s largest city, the USGS reported. Its depth has been measured at about 4 miles.
About 95,000 people who signed up for an earthquake alert system received a ShakeAlert message, with most receiving it on their cellphones seconds before the ground shook, California Office officials said. of Emergency Management and the USGS.
The number represents wireless service providers that have reported alert numbers of their users so far on Tuesday, officials said. The figure is likely to increase significantly as more vendors step in, said USGS ShakeAlert outreach coordinator Robert de Groot.
“People had several seconds of warning time before the shaking started in some places,” he said.
In San Francisco, about 80 miles north, some cellphone users had 18 seconds between the alert and the jolt, according to Cal OES.
Warning time depends on distance, with people closest to an earthquake receiving little or no warning and those living furthest away receiving alerts that can exceed the wave of an earthquake by as much. that two minutes.
Because the earthquake exceeded a 5.0 magnitude threshold, alerts were sent through the federally operated wireless emergency alert system.
The ShakeAlert system is fully operational in California, Oregon and Washington and can reach more than 50 million people, De Groot said.
Californians as far away as Sacramento and Fresno said they felt the tremor on Tuesday.
Cal OES officials were coordinating with Bay Area first responders to assess injuries and damage, the office said. The San Jose Fire Department said it did not receive any emergency calls for help or shaker-related service.
“In accordance with SJFD’s #Earthquake policy, firefighters are vetting personnel, monitoring their immediate response area, and inspecting stations and devices to ensure they are ready to respond to any emergency,” the department said. . tweeted.
The Valley Transportation Authority serving Santa Clara County, where the earthquake occurred, said railcar and track inspections caused a brief 5-minute delay in rail service. No injuries or damage were reported and service was restored on schedule, he added.
Bay Area Rapid Transit, serving San Francisco, East Bay and other communities, implemented its own 5-minute shift to facilitate inspections, but warned that “significant delays” were also possible.
Jones said Tuesday’s tremor likely took place along the Calaveras Fault, which was the scene of the last major quake in the region on Oct. 30. the 2007 Alum Rock earthquake, which measured 5.4 and caused a 3 mile surface break.
The Calaveras Fault is part of a conflicting plate system ruled by the state’s most feared geological feature, the San Andreas Fault, which runs parallel to the coast along most of California. and is estimated at capable of producing a magnitude 8.2 stirrer.
Jones said, however, that the Calaveras Fault is best known for producing moderate earthquakes like Tuesday’s.
“The Calaveras Fault is the one that tends to have smaller earthquakes,” said Caltech’s visiting associate professor. “It’s something that pops up with 5s more often than the other faults. It doesn’t accumulate a lot of slip [energy]but he has the capacity for greater.”
The Associated Press contributed.