An aerial shot of the San Andreas Fault. (Courtesy photo/USGS)

With Sunday’s 4.7-magnitude earthquake in Los Angeles, which was felt as far south as San Diego, and last month’s earthquakes in Italy and Mexico ^[1], many in San Diego may be wondering, “could we be next?”

Well, to be quite frank, yeah. We could be.  Such is the nature of living in “quake country.”

But it’s nothing new. If you are like the majority of San Diego County residents, you’ve experienced earthquakes before. You may have even felt, or at least heard about, the swarm of small quakes that happened in late March in Bombay Beach near the Salton Sea (about 90 miles east of San Diego). During that swarm, dozens of sub-3.0-magnitude quakes shook the region, but did no significant damage.

What is significant is Bombay Beach’s close proximity to the southern edge of the San Andreas Fault. Dozens of small earthquakes near one of the largest fault lines in the world? That can’t be good. Right?

But fear not. It’s nothing out of the ordinary.

“This is an area of Southern California that is prone to these swarms,” said UCSD geophysics professor Jean Bernard Minster. “Earthquakes do tend to happen in very large numbers, without any particular one being the main shock. It’s not surprising because we see that a lot in volcanic areas, along the Pacific Fire Belt.”

Author and geologist Pat Abbott said that not only are earthquake clusters common, they are actually beneficial.

“The beauty of earthquake swarms is that you get dozens, hundreds, even thousands of these little earthquakes that release a large amount of energy in big number of small events,” Abbott said. “They are going on all the time but are too small to do any damage.”

He said that the concern is when that energy is stored up, and what that might mean.

“In the state of California, the number one thing on everybody’s list, the one with the highest probability for a significant earthquake is the southern edge of the San Andreas fault, where all this is happening,” Abbott said.

Minster and Abbott both acknowledged that the potential of “the big one,” a magnitude 7.5 or higher earthquake, is a very real possibility for the area, given the lack of a significant incident on that region of the fault for almost 400 years.

“From Bombay Beach to San Bernardino to Wrightwood has not broken in a very long time,” said Minster. “Historically, we’re used to seeing breaking every 220 years or so. I wouldn’t say this part of the fault is overdue, but the potential is there for a very big earthquake somewhere in Southern California, with a high probability in the next 30 years.”

Abbott agreed, and said that geologists expect something somewhere in the 7.5-7.9 range on the Richter scale. Even 80-90 miles away, an event of that magnitude is such that everyone in San Diego will feel it.

This assumption was put into practice last November, when more than 5.5 million people participated in “The Great California Shakeout,” ^[3] a statewide preparedness event. The purpose of the Shakeout was a series of exercises to help train people what to do in the event of a high-magnitude earthquake along the San Andreas Fault. The Shakeout involved students in schools, fire and rescue and other service personnel, hospital workers, and regular civilians. In a sense, it was a form of muscle memory, helping individuals and groups better understand what steps should be taken in the event of “the big one.”

The event was a success as a preparedness teaching tool, and another Shakeout is scheduled for Oct. 15.

Abbott said that though the San Andreas is the biggest and most likely fault capable of producing a large quake, it is not the only one that could be potentially damaging, citing the parallel faults that run along the coast of San Diego and those miles out into the Pacific.

“The offshore faults aren’t really talked about,” said Abbott. “But a significant fault movement there could generate a tsunami. And if that’s the case, literally in minutes, something like Mission Beach or the Silver Strand could be overrun by a sizeable tsunami wave.”

He said it’s not an event that is going to happen frequently, but has happened in the past and will more than likely happen in the future.

Abbott admits that though earthquakes aren’t as destructive as wildfires, especially in the San Diego region, there is a stigma attached to quakes that creates a certain amount of fear.

“Earthquakes are outside of our natural understanding,” he said. “There’s just something about ‘terra firma’ - solid earth. We expect that the ground is going to be solid beneath our feet. And when that starts shaking violently, it doesn’t compute well in our brains. It’s strange and unfamiliar not part of our normal experience.”

Still, he said that if people are properly prepared, even a devastating quake can have relatively low casualty rates. He recommended these preparation tips:

—- Mental preparation. Abbott said that this is something that often gets overlooked. People know they live in earthquake country, they should know these things are going to happen. He said the main thing is to remain calm. If you’ve thought about it in advance, you’re not taken off guard.

—- Get to a safe spot. The biggest danger is heavy or breakable items falling on you, so if you’re in your house, get under a table or in a door jamb, etc.  Abbott said you should know how long you’re going have to be there (usually anywhere from 30-90 seconds.) Emotionally, it might feel like longer, but it is suggested that you “Drop, Cover, and Hold On” until the shaking stops.

—- Be prepared to help. After the quake is over, Abbott said you should come out and be ready to shut off natural gas supply, and go throughout the neighbors and see if anyone needs help or is hurt. He added “the goal is to come out of it being ready to be a caregiver, not someone who is going to be hysterical or is requiring aid.”

—- Prepare for infrastructure failure. One of the big ways that earthquakes hit us is through damage to infrastructure.  “We rely on electricity brought in over power lines, water and natural gas brought in by pipes, sewage taken away by pipes, etc. You probably should have in your plans that none of those things will work and we’ll be cut off from all your urban lifelines,” Abbott said.

—- Plan for three days. Make sure you have enough canned food, bottled water, candles, flashlights and batteries, to be able to sustain you and your family for about 72 hours.

Minster said that it’s pointless to create a sense of panic in people when talking about earthquakes, but it’s equally as pointless to not be informed and prepared. And Abbott said that things will go a lot smoother if people treat earthquakes as every day events, even if it is “The Big One.”

“When thunderstorms come, you have to stay inside. If you get the flu or a cold, your activities are going to be restricted for a number of days,” Abbott said. “Earthquakes need to be looked at the same way. It’s going to happen once in awhile.”