January 31, 2023

US: Magnitude 4.5 earthquake rumbles across Bay Area but no damage reported

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By Rong-Gong Lin II From LA Times

The checks were completed about 5:30 a.m. with no reports of damage, the agency tweeted.

The earthquake was centered along the Oakland-Berkeley border, just north of the Claremont Hotel. The epicenter of the earthquake is in the area of the Hayward fault, one of the most feared in the Bay Area, which could produce a magnitude 7 or greater earthquake and is directly underneath heavily populated areas.

San Francisco’s emergency managers said all city facilities and infrastructure would be inspected Thursday, though there were no initial reports of damage or injuries.

A magnitude 4.5 earthquake is not expected to cause major damage, said U.S. Geological Survey seismologist Robert Sanders. Still, “there’s always a possibility of some minor damage to older structures in the area.”

The shaking was strong enough to wake people up when the earthquake hit at 2:37 a.m. One person in San Francisco said it was strong enough to knock picture frames from the wall.

The earthquake was felt as far away as San Francisco, Marin County, Sonoma County and Silicon Valley. Some Bay Area residents reported that the earthquake woke them up.

“Only M4.5, the size we have several times a year in California,” tweeted seismologist Lucy Jones. “But when you are right on top of a quake, it feels much stronger.”

The Hayward fault courses right underneath Berkeley, Oakland, Hayward and Fremont and produces a large earthquake, on average, every 160 years, with a margin of error of about 80 years. It has been 150 years since the Hayward fault last ruptured, unleashing a huge earthquake.

The Hayward fault’s most memorable earthquake in recorded history was in 1868, and is estimated to have been a magnitude 6.8 earthquake — rupturing 20 miles of the fault’s length between San Leandro to what is now the Warm Springs neighborhood of Fremont, according to the USGS. It killed about 30 people and caused immense property damage, including the collapse of the Alameda County Courthouse’s second floor and heavy damage at the historic Mission San Jose adobe church in southern Fremont.

The Hayward fault is considered one of the nation’s most dangerous faults because it is located directly under the urban centers of the East Bay, including Memorial Stadium at UC Berkeley and a now-shuttered building that formerly housed Hayward City Hall, which is slowly being torn up by fault movement.

A USGS scenario for a 7.0 earthquake on the Hayward fault envisions it rupturing for 52 miles from San Pablo Bay to Fremont. It would cause one side of the fault to move four feet from the other. Many buildings, including apartments, still sit directly on top of the fault line, and were built before a state law passed in 1972 prohibiting new construction or substantial renovation on top of earthquake faults.

On its website, the USGS calls the Hayward fault the region’s “tectonic time bomb,” which could “cause hundreds of deaths, leave thousands homeless and devastate the region’s economy.”

In 2016, David Schwartz, a U.S. Geological Survey geologist, said in an interview that above the Hayward fault are “two million people who directly live on top of it. It sits geographically in the center of the Bay Area. There’s a tremendous amount of infrastructure built up on it — water systems, gas, electrical, BART crosses it — so a large event on that fault is like hitting the bull’s eye on a target.”

IMAGE: An earthquake with a preliminary magnitude of 4.5 centered along the Oakland-Berkeley border shook up the Bay Area Thursday morning.

For more on this story go to: http://www.latimes.com/local/lanow/la-me-ln-earthquake-bay-area-20180104-story.html

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