Monday’s minor quake centered off the Rancho Palos Verdes coast coupled with the news that Japan had been rocked by a massive magnitude 7.6 earthquake, causing untold damage and killing dozens, once again reminds us that our chosen location to live is vulnerable to significant seismic activity.
This month also marks the 30th anniversary of the Northridge quake that devastated much of Los Angeles City on January 17, 1994. This magnitude 6.7 event produced extremely strong ground shaking, causing the greatest earthquake damage in the US since the 1906 San Francisco event and resulting in over 70 fatalities.
"There was a lot of damage to Santa Monica in the Northridge quake," says Lindsay Call, Chief Resilience Officer for the City, adding, "Both of the hospitals and St. Monica’s Catholic Church required massive rebuilding efforts."
According to a 2004 report by the California Policy Research Center, More than 1,600 housing units were damaged costing $70 million and the collapse of parts of Interstate 10 made Santa Monica hard to access for rescue workers.
The structure of the adjacent Santa Monica Mountains focused the Northridge earthquake’s seismic energy on the city like a lens, said Dr. Thomas Jordan, then Director of the Southern California Earthquake Center at USC. Santa Monica’s soft soil and older building stock may have also contributed to the devastation.
Credit: Wikipedia/Granger
In essence, the entire Pacific Ocean coastline is a horseshoe-shaped tectonic belt of active volcanoes and earthquakes about 25,000 miles long and up to about 310 miles wide. Known as the Ring of Fire, it encompasses New Zealand, Fiji, Malaysia, the Philippines, Japan, Russia’s east coast, Alaska and the entire west coast of both North and South America.
It’s not a single geological phenomenon, rather it’s the result of subduction of different tectonic plates at convergent boundaries around the Pacific Ocean. Within this zone are between 750 and 915 active or dormant volcanoes, representing about two-thirds of the world total, together with about 90% of the planet’s earthquakes.
One of the most famous fault lines in the world is the San Andreas fault, which runs almost the entire length of California. It narrowly misses the City of Los Angeles and instead runs under Palmdale and San Bernardino, but it was movement in this strike-slip fault line that caused the 1906 San Francisco disaster. But that’s not to say the Los Angeles — and indeed the City of Santa Monica — avoids any fault lines.
There are over a hundred smaller active faults in the local vicinity, including the Hollywood fault, the Newport-Inglewood fault, the San Jacinto and Elsinore faults and yes, the Santa Monica fault too. Our sunny, seaside city lies on a relatively small fault line, roughly half a mile wide that runs from the western corner of the Pacific Palisades border and ends just past Century City.
Credit: Seismological Society of America
Moreover, the Palos Verdes fault zone (PVFZ) runs close to 70 miles from the Santa Monica Bay, south down the coast, under the Palos Verdes peninsula and out into the ocean off of Dana Point and scientists believe this fault system is capable of triggering up to a 7.8 quake. It was a slip in a smaller fault line called the San Pedro Basin fault line, which branches off of the PVFZ, that caused Monday’s temblor and that was only a magnitude 4.1.
Thankfully though, the PVFZ appears to be less active than other fault zones including the San Andreas fault, which ruptures every couple hundred years. The PVFZ has a recurrence interval of between 580-610 years for single segment ruptures and 760-1110 years for the type of multi-segment ruptures that could produce a 7.8 quake.
However, the San Andreas fault is generally believed to be overdue for a sizable quake and that could still very much affect Santa Monica.
As such, the City takes earthquake preparedness very seriously. In addition to the risk of partial or complete building collapse, falling debris and ruptured pipes, much of the danger exists long after the actual tremor has subsided. Those ruptured pipes could be gas mains, clean water could quickly be in short supply and fire becomes a huge risk.
"One of the biggest things that we’ve done is implement a robust seismic retrofit program in Santa Monica. And in my opinion, that’s the most critical thing we can do to save lives and property in Santa Monica," says Call. "We’re not at 100% just yet, so work still needs to be done by local businesses, landlords and so on to implement those seismic requirements on their buildings per the requirements of the program, but we’re constantly working on it," she says.
Credit: SMDP
"After every earthquake, even the most recent one in Japan, we learn something new about how we can improve things. Japan has some of the best building codes for earthquakes in the world and there’s always an opportunity to learn and do more. Many of the things we’ve implemented in California have come from lessons learned from Japanese earthquakes," Call says.
There are also a lot of guidelines that everyone in California is advised to follow, not just residents of Santa Monica. In addition to the standard Drop, Cover and Hold On drill, there are a number of procedures that should be followed after the tremors have subsided. A detailed list can be found at earthquakecountry.org/step6/ but among the most important are shutting off the gas mains, shutting off electricity at the main breaker switch, locate a fire extinguisher and first aid kit if possible, let people know you’re OK and check on others.
Call says that after every major disaster, neighbors in the building or nextdoor have to help each other out, so maybe it’s time to make friends with that super-annoyingly noisy tenant who lives in the apartment upstairs.
"You’re more likely to be rescued by a neighbor than an actual first responder in those catastrophic incidents," she says. "So it’s important to have that connectivity in a neighborhood before a disaster event. If a community has a neighborhood watch group, have that conversation about earthquake response and ask, how could we all coordinate with one another after the shaking stops?"
Call also suggests downloading the MyShake app from the Apple App Store, ensuring your phone settings are adjusted to receive emergency alerts and even enrolling in the City of Santa Monica Community Emergency Response Team (CERT) training.
"CERT provides a three day course on disaster preparedness topics, and how individuals and households can prepare themselves for disaster events, and what they should do in the immediate aftermath of an emergency event," Call says.
The program has been on a hiatus since the pandemic, but will return to full, regular scheduling this month. Details can be found at the Santa Monica City website.
