Offshore faults add to Calif. quake fears

Associated Press

LOS ANGELES — Two hidden faults capable of unleashing a magnitude-7.6 earthquake lie off the coast of heavily populated Los Angeles, Orange and San Diego counties, researchers reported toSday.

Though there’s potential for catastrophe, the chances are slim. In the worst-case scenarios detailed in the study, the biggest quakes occur once every 2,100 years on one of the faults — the Thirtymile Bank fault — and every 8,800 years on the other — the Oceanside fault.

It’s possible the faults release their energy in smaller but more frequent spurts, the researchers reported in the October edition of the journal Geology.

"Because this is new and we can’t access it easily, we don’t have the knowledge base yet to decide whether it is going to rupture in small pieces or in one single event," said study author John Shaw of Harvard University.

"The critical issue for hazard assessment is really just defining the size of these faults," he added. "The size obviously dictates the potential earthquake magnitude."

A 7.6-magnitude quake would likely cause widespread damage and injuries. The 6.7-magnitude Northridge quake in 1994 killed 72 people and caused an estimated $35 billion in damage in Los Angeles.

The Thirtymile Bank fault runs south from Santa Catalina Island, and the Oceanside fault slices south from Laguna Beach in Orange County. Both extend south to San Diego and possibly beyond the U.S.-Mexico border.

Both faults are the same type that unleashed the Northridge and 1971 Sylmar quakes. Called blind thrust faults, they are not clearly visible on the surface, whether on land or on the sea floor, and are usually detected when they produce quakes.

"This is the first concrete evidence that we have large thrust faults in the offshore region here," said Tom Henyey, director of the Southern California Earthquake Center. "It is a significant finding, if in fact it is the case."

Other offshore faults, such as the Newport-Inglewood and Rose Canyon faults are strike-slip faults, where one side slides horizontally past the other.

Thrust faults, where one side moves over the other as if on a ramp, could pose greater threats because their quakes tend to have higher vertical acceleration.

"This tends to be very destabilizing for many types of structures, including high-rise buildings and other things," Shaw said.

Copyright ©2000 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

Talk to us

More in Local News

Marysville firefighters respond to a 12-year-old boy who fell down a well Tuesday May 30, 2023 in Marysville, Washington. (Photo provided by Marysville Fire District)
Marysville firefighters save boy who fell 20 feet into well

The 12-year-old child held himself up by grabbing on to a plastic pipe while firefighters worked to save him.

Highway 9 is set to be closed in both directions for a week as construction crews build a roundabout at the intersection with Vernon Road. (Washington State Department of Transportation)
Weeklong closure coming to Highway 9 section in Lake Stevens

Travelers should expect delays or find another way from Friday to Thursday between Highway 204 and Lundeen Parkway.

Students arriving off the bus get in line to score some waffles during a free pancake and waffle breakfast at Lowell Elementary School on Friday, May 26, 2023, in Everett, Washington. (Ryan Berry / The Herald)
800 free pancakes at Everett’s Lowell Elementary feed the masses

The annual breakfast was started to connect the community and the school, as well as to get people to interact.

Marysville Mayor Jon Nehring speaks at the groundbreaking event for the I-5/SR 529 Interchange project on Tuesday, May 23, 2023 in Marysville, Washington. (Olivia Vanni / The Herald)
$123M project starting on Highway 529 interchange, I-5 HOV lane

A reader wondered why the highway had a lane closure despite not seeing work done. Crews were waiting on the weather.

Justin Bell was convicted earlier this month of first-degree assault for a December 2017 shooting outside a Value Village in Everett. (Caleb Hutton / Herald file)
Court: Snohomish County jurors’ opaque masks didn’t taint verdict

During the pandemic, Justin Bell, 32, went on trial for a shooting. Bell claims his right to an impartial jury was violated.

Gary Fontes uprights a tree that fell over in front of The Fontes Manor — a miniature handmade bed and breakfast — on Friday, May 12, 2023, at his home near Silver Lake in Everett, Washington. (Ryan Berry / The Herald)
Everett’s mini-Frank Lloyd Wright builds neighborhood of extra tiny homes

A tiny lighthouse, a spooky mansion and more: Gary Fontes’ miniature world of architectural wonders is one-twelfth the size of real life.

Will Steffener
Inslee appoints Steffener as Superior Court judge

Attorney Will Steffener will replace Snohomish County Superior Court Judge Janice Ellis, who is retiring in June.

Mountlake Terrace Library, part of the Sno-Isle Libraries, in Mountlake Terrace, Washington on Thursday, June 1, 2023. (Annie Barker / The Herald)
Sno-Isle workers cite safety, unfilled positions in union push

Workers also pointed to inconsistent policies and a lack of a say in decision-making. Leadership says they’ve been listening.

A view over the Port of Everett Marina looking toward the southern Whidbey Island fault zone in March 2021. (Olivia Vanni / The Herald)
Snohomish County agencies to simulate major disaster

The scenario will practice the response to an earthquake or tsunami. Dozens of agencies will work with pilots.s

Most Read