Living in California means living in earthquake country. Thousands of quakes occur every year – most of which are too small for residents to feel.
But with the February earthquakes in Turkey and Syria that have killed over 47,000 in the region, questions around what California fault might be next for a “big one” earthquake have started to resurface.
To understand what faults might be overdue for a major earthquake, experts say that it’s important to understand what the “big one” could be.
When people think of a “big one,” a magnitude 8.0 earthquake on the Richter Scale might come to mind.
But, as Dr. Pat Abbott, professor of geology emeritus at San Diego State University, said that threshold for what a “big one” in California could look like might not be as simple.
The last “big one”-level movements in California’s recorded earthquake history are the 1857 earthquake in the central third of the San Andreas and the 1906 earthquake in the northern third. Both were under the 8.0-magnitude threshold.
While there hasn’t been many over 7.5 earthquakes in recent history, that’s not to say there haven’t been major earthquakes since then.
The 1989 San Francisco-area earthquake and the 1994 Northridge earthquakes, for instance, were both devastating and destructive shocks, causing widespread damage to infrastructure and considerable loss of life. But both of those earthquakes were both under 7.0 in magnitude.
“Now, technically that’s not the ‘big one,’ but when you go back and look at what happened, each of those earthquakes, they were horrendous,” Abbott said.
The impact that a large earthquake has, whether it’s a 6.5 or an 8.0, largely depends on the proximity to urbanized areas.
“In some respects, the ‘big one’ in terms of damages and deaths would be ones running through town rather than one that’s a long distance away,” he continued. “There’s the size of the earthquake, and then also where you are situated compared to where the fault’s moving.”
The southern San Andreas is particularly of concern for experts when looking at places that are overdue for an earthquake above a 7.5, impacting areas like San Bernardino, Palm Springs and Imperial County.
That portion of the 700 mile-long fault has not had an earthquake around that size in magnitude since about 1690, Abbott said.
A 2008 projection behind the Great California ShakeOut estimated that a potential 7.8 earthquake in the southern section of the fault could have a death toll as high was 1,800.
But scientists are also especially worried about a smaller fault that’s overdue for a major earthquake: the Hayward fault, which runs directly under cities in the Bay Area.
“Part of the worry there is not just the magnitude, but the whole East Bay area is full of old cities that have a lot of old buildings,” Abbott said. “You could have a horrendous loss of life from a magnitude 6.5 earthquake.”
With these two areas of concern for seismologists, there are a number of potential scenarios that could play out in the earth’s crust – some of which could look a lot like the catastrophic, magnitude 7.8 earthquake in Turkey and Syria due to similarities in the way those faults are set up compared to California.
“We are challenged by these earthquakes happening so rarely,” said Alice Gabriel, associate professor of seismology with the Scripps Institute of Geophysics and Planetary Physics. “It’s just a very long timescale. Now, we have the Turkey events, which were very devastating but also have important lessons for us.”
One such lesson is the potential for a “doublet” earthquake, or additional earthquakes triggered along nearby faults to one that has a “big one.”
“Something that we saw in Turkey that is really difficult to predict, is that there wasn’t only one earthquake,” Gabriel said. “A magnitude 7.8 (was) the first event, but it triggered nine hours and a few minutes later, a second event that was almost as large.”
The Hayward fault would be a candidate for a secondary earthquake that is dynamically set off if an earthquake, like a 7.4, were to hit in Southern California, she said, considering how much stress has already built up between the plates – mirroring what was seen in Turkey.
Despite what can be learned from events like Turkey’s quake, it’s still impossible to determine exactly where a “big one” might happen, when it might be or what it will look like – though experts say California likely wouldn’t see as much destruction and loss of life as Turkey due to the concerted state efforts toward earthquake safety.
“No one can really tell you whether one fault is going to rupture over another fault,” Jose Lara, chief of the California Governor’s Office of Emergency Services Seismic Hazards Branch said. “We know both are overdue.”
“(But,) California is in a much more resilient position to withstand an earthquake because of our many decades old mitigation efforts that have occurred,” he continued.
These endeavors include the regular updating and enforcement of building codes in the state and dedicated work towards developing catastrophic plans that would guide the government’s response, from the deployment of personnel to emergency supply chains.
Regardless of how the next large-scale earthquake ends up happening, Lara stressed that people need to be prepared for the eventuality that a major earthquake occurs near where they live.
Lara and the other experts said that the best way people can do that is by:
- Identifying and securing things in one’s home or work that could fall during a major quake, like china cabinets or ceiling fans
- Making a household preparedness plan
- Securing an emergency kit that has items – like flashlights, cash or food – in case damage to critical infrastructure occurs
- Download the MyShake app for California earthquake warnings
“Even though Californians improve the building standards after every earthquake and things get safer, it’s not the same thing as saying, ‘is everything safe?’” Abbott said. “California gets safer all the time, (but) there’s still a lot of danger.”
This story originally reported by KTLA sister station KSWB.