Last Tuesday, after a magnitude 7.9 quake occurred in the Gulf of Alaska, tsunami warnings for Alaska, as well as the West Coast from Canada to California, were issued for four hours before being cancelled. The next day, it was reported that a newly discovered earthquake fault that runs through Rodeo Drive in Beverly Hills is capable of producing a magnitude 7.0 earthquake. The following morning, a magnitude 4.0 earthquake centered in the Santa Ana Mountains could be felt from northern L.A. County to San Diego.
It turned out last week was the perfect time for Malibu Public Safety Manager Susan Dueñas to have scheduled a town hall meeting on earthquake preparedness.
The city presentation, given by Dueñas and consulting geologist Chris Dean, reminded everyone that it’s not just the shaking from the earthquake itself that causes damage and injuries—collateral damage includes tsunamis, ruptured water lines, landslides and ruptured gas lines that can start wildfires.
Fault lines and slide areas
Dean said the major earthquake fault line in Southern California is, of course, the San Andreas Fault out near Palm Springs.
“On average, it ruptures every 160 years, and the last big one was in 1867—a magnitude 7.9 with a rupture zone of 225 miles.” That means it’s due for another big one around 2027.
The Malibu area has its own network of fault zones, with the longest being the Malibu Coast Fault that extends the entire length of the city. There are also several active faults offshore.
The city has three active landslide areas that could be triggered by an earthquake, according to Dean—Big Rock Mesa, La Costa and the western portion of Malibu Road—which are monitored annually. The Civic Center area is a liquefaction zone, meaning the land there could turn quicksand-like in the event of a quake.
Tsunamis
Dueñas said the risk of a tsunami caused by an earthquake is relatively low in Malibu compared to other areas of the world. Even when it does happen, most estimates show little more than a few inches of water coming over the shore areas.
There are four levels of tsunami alerts—a tsunami watch is for an expected wall of water that’s just a few inches high, a tsunami advisory is for water up to three feet high, and a tsunami warning is for over three feet.
Fifteen tsunamis have been recorded in this area since 1855, with the latest one in 2011 originating from an earthquake in Japan. It resulted in some minor damage to boats and docks in LA County.
Impact on Malibu
An earthquake’s impact on Malibu will depend on where it originates. If the earthquake comes from a more distant source, like the San Andreas Fault, then structures here would have “minor to moderate damage,” according to Dueñas. However, she pointed out that the city’s water comes from the California Aqueduct, and if it were severely damaged by an earthquake in the desert, Malibu could be without water for months. “That’s the biggest thing we have to plan for,” she said.
In addition, if the epicenter of a large earthquake is more distant, then the state’s resources and first responders will go to that immediate area first, and Malibu, even if it suffers damage, cannot expect to get a lot of help right away.
How Malibu is preparing for earthquakes
The city adopted a set of geotechnical guidelines in 2013 for all new structures, which is more restrictive than the state’s building codes. They require an investigation for any new structure within 500 feet of a fault, and are also trying to identify vulnerable existing buildings.
Preparations also include public education, Community Emergency Response Team (CERT) training programs, stashes of emergency supplies throughout the city, training city staff as emergency service workers, and this year’s Earthquake Resiliency Initiative.
For tips on how to prepare for earthquakes, click here.