Did you feel that magnitude 3.5 earthquake on Sunday?

By this fall, we might know where Santa Monica’s fault lines are located.

The California Geological Survey (CGS) is in the process of drawing up fault zones for the beachside city.

The Alquist-Priolo Earthquake Fault Zones allow the state to regulate development built near faults. Santa Monica does not yet have one of these zones but it likely will by the end of the year.

The current fault map is on a statewide scale so the difference of three millimeters on the map is about one kilometer on the ground, a state geologist told the Daily Press last year.

The new map will establish a zone around the traces of the fault. If a developer wants to build in that zone, they’ll have to pay for a thorough examination of the site. If the planned placement for the project is on top of a trace, they can’t proceed.

“We have one guy who’s working on the Santa Monica fault and the western extent of the Hollywood fault,” said Tim McCrink, who heads CGS’s Alquist-Priolo program.

It’s largely a one-person job and most of it happens at a desk.

“They reach out to the consulting community and they reach out to the city and county geologists and building officials and get their hands on existing reports,” McCrink said. “And that’s even more critical in the urban and suburban areas around L.A. than it would be in a more remote area. There’s just not much left at the ground surface for them to look at: Certainly there’s some sizable scars that you can go out and look at but somebody’s put a flower bed on there or cut a driveway into it so the fieldwork is kind of less important than getting information on the subsurface.”

Occasionally, he said, a consultant might open a fault investigation trench and send a crew to check out the site.

“They can get LIDAR-based images that can point out some subtle geomorphic features,” he said, “but it’s old air photos, it’s boring logs, trench excavation logs, things like that, so a lot of office work.”

Typically, McCrink said, they don’t excavate standing buildings or their foundations.

Last year, The Los Angeles Times, through an independent investigation, identified four Santa Monica buildings that may sit on top of a fault. City officials responded, saying they are confident that the buildings are located near, not on, the fault.

If a building were found to have been built on a fault trace, McCrink said, it would not be required to be demolished. It’s left up to local governments and landowners to decide what to do with that information. Sometimes landowners do decide to rebuild and sometimes they don’t.

For Santa Monica, the question of whether or not buildings lie on faults is months from being answered.

“It’s still too early,” McCrink said. “We’re still accumulating information. They’ve got to work through some pretty voluminous reports. It’s kind of a good news-bad news: You have all this information but the bad news is you have to read it.”
dave@smdp.com

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