Magnitude-5.4 Earthquake in Greater Los Angeles

David Hebert: Hello, everyone, and welcome to this episode of the USGS CoreCast. I'm David Hebert.

As many of you probably know, there was a magnitude 5.4 earthquake in the greater Los Angeles area today. So I'm here with Mike Blanpied. He is the Associate Coordinator of the USGS Earthquake Hazards program and he's going to fill us in on what went on.

Thanks for giving us some of your time, Mike.

Mike Blanpied: Glad to be with you.

David Hebert: So where exactly did this earthquake occur and what were the consequences?

Mike Blanpied: This earthquake occurred in the Chino Hills area of L.A. which is east, maybe 30 miles east of L.A. proper. This is an earthquake of 5.4, as you said, which is enough to cause quite intense shaking in the upper central area and be widely felt, but it would be expected to do rather little damage, and I think the early news reports that we're seeing are in concert with that.

David Hebert: Well, that's good news. How widely was it felt?

Mike Blanpied: It was felt quite widely. We have a website called Did You Feel It, in which citizens who feel the earthquake can fill out a brief web form and contribute to a map that shows the extent of shaking, and we have reports as far away as San Diego, which is a couple of hours drive. So it's quite widely felt in the area.

David Hebert: Right. And so this site actually allows people to sort of log there experiences?

Mike Blanpied: That's right. Off of our website, earthquake.usgs.gov, there is a link to Did You Feel It, and it's a brief web form and you indicate your location by zip code and what you experienced in the earthquake and you contribute to the map, which illustrates the extent of shaking, how strong it was, and how widespread.

David Hebert: Do we know what fault this earthquake occurred on?

Mike Blanpied: So far we're not sure what fault. The Chino Hills area is laced with thrust faults under the ground, and any one of those could have been responsible for the earthquake. Geologists and seismologists were examining data, such as the locations of aftershocks right now and hopefully, within fairly short order though, we'll make a determination of which fault likely hosted the earthquake.

David Hebert: And we've had quite a few aftershocks so far? 

Mike Blanpied: The last time I looked we had about 40 aftershocks in the first hour and a half since the earthquake, and we'll expect to have more. Most of those are quite small but many of them were felt. The largest so far has been a magnitude 3.8, which is large enough to be fairly widely felt but not to do any damage.

David Hebert: Okay, and what about the possibility of this earthquake being a precursor to a larger event?

Mike Blanpied: It's possible that any earthquake is going to be followed by one that's larger, that likelihood is modest for any earthquake, and it's become more modest with time. So the longer we go without a larger earthquake, the better off we are.

David Hebert: Okay. What was the last earthquake of this magnitude in the Los Angeles area?

Mike Blanpied: Los Angeles area has actually been fairly quiet for the last number of years. Back in 1994, of course, there was the magnitude 6.7 Northridge earthquake, which did quite a serious amount of damage. The earthquake that was closest to this particular place was the Whittier Narrows earthquake of 1987. Whittier Narrows was a magnitude 5.9 compared to 5.4, and half a magnitude unit is actually a fairly large amount. Whittier Narrows did a severe amount of damage in the upper central area.

David Hebert: So this November, the USGS and several partners will take part in the Great Shakeout, which will be the largest earthquake preparedness drill in the U.S. history and will take place, appropriately, in Southern California.

Could you talk a little bit how today's earthquake underscores the importance of a drill like the Shakeout?

Mike Blanpied: Well, everybody in the Los Angeles knows that they live in earthquake country, but as years go by, people either forget or other priorities take precedence and people may not be thinking day to day on what steps they can be taking to make themselves and their families safe in the event of earthquakes.

The Shakeout is going to be a tremendous exercise—as you say it's the largest ever. Millions of people will be participating, and this earthquake, if anything is going to alert people to and remind them that they live with earthquake danger around them, and hopefully, increase the number of people who will participate and learn something from the exercises.  

David Hebert: So how do people get involved and where do they go to do that?

Mike Blanpied: There's a terrific web site for the Shakeout, and it's shakeout.org, appropriately enough, and that web site contains information about the event, about the . . . all the host of events that are surrounding the exercise.

It's an emergency preparedness exercise, but there are innumerable other organizations and groups that are also testing their emergency preparedness as part of it. There is a link on shakeout.org for registering your interest, and almost two million people have already filled out their form there to indicate their commitment to take an advantage of this opportunity to make themselves more aware and more safe.

David Hebert: Great. Mike, I know you're really busy when these kinds of things happen, so we appreciate your time and once again, if people want to learn more that's shakeout.org and earthquake.usgs.gov. Is that right?

Mike Blanpied: Absolutely.

David Hebert: Great. Thank you so much.

Mike Blanpied: Thank you.

David Hebert: And thank you for listening to this episode of the USGS CoreCast. CoreCast is a product of the U.S. Geological Survey, Department of Interior. Until next time, I'm David Hebert. Have a great day. 

Resources related to this episode:

• earthquake.usgs.gov
  • info on this earthquake, including Did You Feel It?
  • press release about this earthquake
• www.shakeout.org
  • Great ShakeOut press release