Some Ventura County residents may have felt a little jolt on the afternoon of June 12 when a 3.6 magnitude earthquake shook off the coast near Point Mugu. While no damage was reported, residents from Ventura to Thousand Oaks could feel it, and have left some wondering if it was a sign of bigger things to come.
The 3.6 magnitude quake had a depth of 11.6 miles and coincided with two appropriately named “earthquake swarms” that occurred a week prior, one near San Clemente Island and the other east of Los Angeles. Over 1,000 earthquakes ranging in magnitude from 1.5 to 3.6 occurred over a three-week period.
William Bilodeau, PhD, professor and chair of California Lutheran University’s Department of Geology, says that earthquake swarms are not uncommon.
“These things are going to happen, we’re on a plate boundary where the tectonic plates, the Pacific and North American, are in a constant state of stress and are moving on average three inches a year,” said Bilodeau. As the plates shift, pressure is transferred to other areas along fault lines, with which Southern California is riddled, the tectonics having formed ranges such as the Santa Ynez and Santa Monica mountains. Bilodeau says that stress can be transferred from minor quakes to other parts of the fault, and in the case of the San Andreas Fault, in 100 miles in either direction.
The chances of a big earthquake, says Bilodeau, are more likely to occur relatively soon after a quake swarm.
“It’s nothing to be more worried about than anything else; if it doesn’t happen within a few weeks or even a few days in the area of the swarm then chances are it’s probably not going to happen in that area,” said Bilodeau.
Preparing for the so-called big one has been a big priority for the California Governor’s Office of Emergency Services. The California Earthquake Early Warning System is a program in collaboration with the U.S. Geological Survey. The program received approximately $15 million in funding in 2018, which is being used to complete a network of 463 sensors installed in remote areas around the state.
The ultimate goal is to expand an emergency alert text system to all residents in California. In January, the ShakeAlert app launched for residents of Los Angeles County and features alerts sent to smart phones seconds prior to an earthquake.
Patrick Maynard, emergency manager with the Ventura County Sheriff’s Office of Emergency Services, says that earthquake swarms, while not uncommon, serve as a reminder to “always be prepared.”
“The range of hazards that we’re dealing, especially in Ventura County and with fire season upon us, if anything, we want people to do what you can to prepare yourself and your family for any situation,” said Maynard. Maynard says that families should have at least three days’ worth of emergency supplies should the worst occur, from wildfire to earthquake, noting that the only disaster California doesn’t have are tornadoes.
“We do have a slim hurricane threat, though,” added Maynard.
In 2017, researchers determined that a little known fault known as Ventura-Pitas Point Fault is more dangerous than previously imagined. The fault, which runs from Santa Barbara to Ventura, is believed to be capable of producing strong quakes at the surface level. Maynard says that there are many faults that run through Ventura County and Pitas Point is just one of them.
“That is one that gained some recent notoriety because of the new information,” said Maynard. “We know, statistically speaking, that because we have not had a significant seismic event, the probability increases over time, but it’s right there with all the other hazards.”
Maynard points to Lucy Jones, seismologist and author of The Big Ones, who took to Twitter on June 20 following the earthquake swarms to reassure her followers.
“Swarms of quakes seem scary but the data says they are no more likely to trigger a big quake than just one slightly larger one in the same place,” tweeted Jones.
“When we see these small events, they serve as a reminder, and help us think of things in a broader perspective,” said Maynard.
The Ventura County Sheriff’s Office of Emergency Services, in partnership with the Federal Emergency Management Agency and the Ad Council, have a website dedicated to emergency preparedness with tips on how to prepare should the big one — or any natural disaster — occur locally, www.readyventuracounty.org.