Earthquake Lessons: Be Prepared for the Big One

The 5.4 magnitude earthquake that struck near Los Angeles yesterday just before noon was felt as far east as Las Vegas and as far south as San Diego. Since the quake, whose epicenter was about 28 miles southeast of Los Angeles near the affluent suburb of Chino Hills and 8.5 miles beneath the Earth's surface, there have been nearly 50 aftershocks, most of them small, according to the U.S. Geological Survey.

Although the quake was one of the strongest to hit urban southern California since the deadly 6.7 magnitude Northridge quake in 1994, it didn't cause any severe damage or major injury. So southern California residents are exhaling with relief—that for now, they've eluded The Big One.

But seismologists, who've concluded that this jolt was not tied directly to any of southern California's major fault lines, insist it could have been much more destructive and that it was just a reminder that the big one is indeed still looming. Graham Kent, a seismologist and geophysicist at the Scripps Institution of Oceanography in La Jolla, Calif., studies the complex series of fault lines that run beneath California's surface. NEWSWEEK'S Jamie Reno spoke with Kent about this quake and the threat that possible future quakes pose to southern California. Excerpts:

NEWSWEEK: First of all, can you tell us which fault produced this particular earthquake?
Graham Kent:
Geographically, it's located in a messy area, near the Elsinore Fault near downtown Los Angeles, but not truly on that fault. Elsinore is relatively major fault line, and runs into the larger faults such as San Andreas. The smaller faults die out and meld into a whole melange of what we call thrust faults. This is an area under a lot of compression, and so in some ways the thrust faults have more of a pop, that's why we felt this quake so widely. The L.A. basin is riddled with thrust faults.

Have there been other earthquakes in this particular area? Did this quake take seismologists by surprise?
The Whitter Narrows quake in 1987 was relatively close, and it was a little bit bigger. But it was the same type of quake, a thrust fault. If you looked at the image of faults of the L.A. basin, you'd be amazed, there are a lot. We tend to think about San Andres and San Jacinto, the larger faults, but there are any number of thrust faults from large to small that can rupture in the Los Angeles area. This one is in the middle as far as size. It's significant but a thrust fault can be up into the sevens. The San Fernando Valley earthquake was in the high sixes, the Northridge was in the high sixes. That was a thrust event as well, the same type of thing.

We've seen about 50 aftershocks already, the largest of which so far has been a 3.8 magnitude quake. Is that typical?
Yes, that's not a surprise for any earthquake. If there weren't dozens and dozens of aftershocks by now, that would be the bigger story.

Does this quake give us any clues about future southern California quakes in terms of when or where?
We tell people it's a very low probability that an earthquake like this might be a foreshock, but I think the more responsible way of looking at it is that this quake is a reminder. The L.A. Basin is fraught with potential hazards, the thrusting event as well as the large strike event, and we've been lucky. The San Andreas Fault on average ruptures every 150 to 200 years over the last several thousand years, and it has not ruptured for about 340 years. So every morning we wake up we set a new record between large ruptures.

Would you say Los Angeles dodged a bullet with this event?
Yes, thrust faults than can be a seven-ish event, this one got up to 5.4. But the point is they are there and people need to be prepared. The way I look at events like this, other than making our afternoon crazy, is that this is really just a strong reminder to people that earthquakes can and will occur in this region that are 100 times larger in energy; some day the big one will in fact occur. These are reminders to people to be prepared with food and water. Have your wall units bolted. Do your kids know where to go? People throughout southern California should have all of this already planned. Unfortunately, people don't ask us about this stuff when we don't have an earthquake, so during times like these we use you [the media] to answer the public's questions and remind them that we need to be prepared.

Can any of the things people do, from construction to detonation (or blasting), influence earthquake behavior?
Not really. In general, earthquakes will happen on their own erratic time calendar. But again, it's been a long time since we've had a large one. That's why the Dare to Prepare program is so important. It's a program whose motto is Shift Happens. They have a Web site: www.daretoprepare.org.

What are some of the things we'll be seeing from this program?
We'll be running both northern and southern California earthquake scenarios to see how well we are really prepared.  In southern California we'll create a San Andreas rupture scenario, and in northern California we'll have a Lake Tahoe large-earthquake scenario, with a tsunami.

Is a tsunami actually possible in Lake Tahoe as a result of an earthquake?
Yes, it is. In November we will assess where we are in terms of preparation. The universities, USGS, emergency services, the State of California, a lot of people and organizations will be involved in this because when the big one does hit, we won't be talking about a 5.4. It will be something like a 7.8.

Wasn't that the size of the San Francisco quake in 1906?
Yes, and that's what San Andreas can get to. San Jacinto is midrange seven, Elsinore is up to seven, then there are the possibilities of another big thrust earthquake in L.A., and they can get up to the sevens, as well. The whole idea behind Dare to Prepare is to get everyone in southern as well as northern California to realize that the big one is going to happen. This earthquake was a warning. If it increases awareness and preparedness, those are good things.

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