A magnitude 5.1 earthquake struck eastern Santa Clara County at 11:42 a.m. today, rattling cities around the San Francisco Bay Area, according to a preliminary estimate from the U.S. Geological Survey.
The largest earthquake anywhere in the Bay Area in eight years, the epicenter was in the region of Joseph D. Grant Ranch County Park, about 12 miles east of San Jose in a locked-up patch of rocks deep underground near the Calaveras Fault in a remote oak-studded landscape.
There were no immediate reports of injuries and damage. Shaking was felt as far away as Salinas and Point Reyes to Stockton.
“It was pretty strong. I’ve been in earthquakes before. It was a pretty good shake,” said one ranger at the 10,882 acre park, located in the foothills of the Diablo Range east of San Jose, who didn’t want to provide his name. “It was a rolling shake, not a jarring shake. It lasted about seven seconds. I didn’t see any damage. No broken windows, nothing off the shelves. But I’m still checking around.”
It is in an area notorious for seismic restlessness. A much larger 6.2 quake occurred in nearly the same spot in 1984, followed by a 4.1 earthquake in 2017.
The temblor was the largest earthquake in the Bay Area since the 2014 Napa quake, which was a 6.0. No one was killed in that quake but hundreds of buildings were damaged and dozens were red-tagged. Before that, a magnitude 5.4 temblor hit near Alum Rock in San Jose in 2007.
The Calaveras Fault runs roughly 76 miles from Hollister to Danville, and is linked to the Hayward Fault. The U.S. Geological Survey estimates a 7.4% likelihood of a magnitude 6.7 or greater earthquake on the Calaveras Fault in the next 30 years.
There is a 14.3% chance of a magnitude 6.7 or greater earthquake on the Hayward Fault, which runs roughly 74 miles along the western base of the densely populated East Bay Hills, and is linked to the Calaveras Fault.
The last devastating earthquake in the Bay Area was the 1989 Loma Prieta earthquake — a magnitude 6.9 quake that struck on Oct. 17, 1989, in the Santa Cruz Mountains. It killed 62 people and caused $6 billion in damages. The largest earthquake since Loma Prieta shook Napa in August 2014 with a magnitude of 6.0. No one was killed in the quake but hundreds of buildings were damaged and dozens were red-tagged. Before that, a magnitude 5.4 temblor hit near Alum Rock in San Jose in 2007.
The Bay region is located within the active boundary between the Pacific and the North American tectonic plates, where the Pacific plate slowly and continually slides northwest past the North American plate.
The same geologic process is responsible for the San Francisco Bay region’s beautiful coastlines, bays, hills, and valleys.
In 2014, a panel of experts estimated that there is a 72 percent chance that in the next 30 years the San Francisco Bay Area will experience an earthquake at least as powerful as the magnitude 6.7 Northridge earthquake that rocked Southern California in 1994. There is a far greater chance — 99 percent — that a smaller but still substantial magnitude 6.0 earthquake will strike during that time.
The scale of earthquake measurement is logarithmic: a recording of 7, for example, signifies a disturbance with ground motion 10 times as large as a recording of 6. An earthquake of magnitude 2 is the smallest size normally felt by humans. Earthquakes measuring 5 or higher are potentially damaging.
The San Francisco earthquake of 1906 has been estimated at a magnitude 8.3. The earthquake that leveled the capital of Haiti measured 7.
As with any large earthquake, there is a possibility of damaging aftershocks. If an aftershock occurs, the USGS recommends that people who are indoors stay there, taking shelter under a piece of furniture, in a hallway or against an inside wall, away from windows, fireplaces and heavy objects.
If you are outdoors, get into the open away from buildings, power lines and other things that could fall. If driving, stop carefully and move out of traffic. Avoid bridges, trees and other falling objects. Stay in your car until the shaking stops.
Check back for more on this breaking news story as it develops.
San Jose Mercury News environmental writer Paul Rogers contributed to this article.
Source: www.mercurynews.com