The earthquake advisory warning that was issued on September 26 by the California Office of Emergency Services and notes increased likelihood of an earthquake of magnitude 7 or above being triggered in Southern California, remains in effect till Tuesday, though the probability has decreased each day.
More than 140 swarm earthquakes were recorded under the Salton Sea last Monday when the warning was issued, ranging from magnitudes 1.4 to 4.3 on the Richter scale and occurring at depths between 2.5 to 5.5 miles, according to seismologists at the United States Geological Survey (USGS).
Swarm earthquakes refer to a series of earthquakes striking an area in a short period of time. No single earthquake in the series acts as the main earthquake, which differentiates it from aftershocks.
This swarm was recorded under the Salton Sea, which lies south of the San Andreas Fault. The San Andreas Fault is one of the most seismically complex areas in California and the southernmost stretch has not experienced a rupture since 1680, according to a Los Angeles Times report. On average, an earthquake happens in this region every 150 to 200 years.
According to USGS, the probability of a major earthquake striking from this swarm has been anywhere between 1 in 100 to 1 in 3000. The average probability of such an earthquake happening without the swarms is 1 in 6000.
Here's a map of all the recorded earthquakes of magnitude 2.5 to 4.3 in California
USC uses an earthquake early warning system developed by USGS called ShakeAlert that allows DPS to send out a TrojansAlert once they are notified of the possibility of an earthquake through ShakeAlert. However, the amount of warning time depends on the distance of campus from the earthquake epicenter, meaning that if the epicenter lies close to campus, there will be no warnings given out, as there will not be enough time.
USC also has an emergency protocol document that outlines things to do during and after an earthquake. Jason Ballmann, Communications Specialist at the Southern California Earthquake Center emphasized on the importance of Shakeout earthquake drills that will be organized on the third Thursday of October.
"Shakeout is a chance for everyone to practice drop cover and hold on for one minute. We need a time for people to come together, practice this together and act as a whole community because that's what it takes to recover and survive from a damaging earthquake," he said.
He also referred to the advisory and said that it is important to put numbers in context. "The chance of a large earthquake occurring here in the San Andreas Fault is about 7 percent over the next 30 years. That's for the southern San Andreas Fault. And this advisory that came out this past week didn't do much but to essentially raise that percentage by a minuscule amount, from 7 percent to 7.0003 percent," Ballman said.
Some students on USC campus said that they did not feel too prepared for an earthquake, while others did not know anything about it. "My roommate has his bag, in case of an earthquake. Like there's water, there's a flashlight, batteries. But not for me, I'm not prepared," said MK Cho, an Accounting major.
"I was unaware of it. I never thought about [earthquakes] a lot until last year when there were a couple of earthquakes. I'm a senior so I guess after this year I won't be in the earthquake district anymore," Willa Zhal, a Computer Science and Business major.
For those wanting to be prepared in case an emergency strikes, Ballmann suggested reading up on tips for safety on the Earthquake Country Alliances website.