PLUMAS COUNTY, Calif. — A preliminary magnitude 5.5 earthquake has struck north of Chico, California, Thursday.
The U.S. Geological Survey says the quake struck around 4:20 p.m. It was centered on Lake Almanor in Plumas County.
Dr. Angie Lux, a seismologist with the Berkeley Seismology Lab, explains what happened when the earthquake hit and what people should know looking ahead.
Earthquake Q&A
What Just Happened?
Dr. Lux: We just had about a magnitude 5.5 earthquake up near Plumas County. It was a pretty shallow earthquake. I understand that there was shaking felt as far down as Sacramento.
Is it normal for that area to have earthquakes?
Dr. Lux: We've definitely seen earthquakes of about that size in that area. Before there was, I think, I'm gonna say 2013, there was about a magnitude 5.7 up in that area. So, it's not unusual for us to see earthquakes up there. They they tend to not happen quite as frequently as we see in other places. But it was a pretty good sized earthquake up there.
Why have the magnitude numbers been changing?
Dr. Lux: We have automatic programs that go in and they look at what's coming in from our waveforms and they say, well, we think it's about this big. Then we have human people who are on duty who go and adjust the program, adjust it make it look a little bit better. So, sometimes that number can change a little bit. We might update the location, the depth, and that can in turn change the magnitude estimate. But what we can say as far as right now, we know it seems to be about a magnitude 5.5.
Will there be more earthquakes and should we be concerned?
Dr. Lux: There's an always a possibility that a larger earthquake may happen after an earthquake, right? We never know. We never know if this is a foreshock until there is another earthquake, so I can't tell you whether there will or will not. But there's always a small probability that there may be another earthquake that happens after this one.
Chances are this was it. We might see some aftershocks happening in the area. It tends to be smaller earthquakes. We're pretty sure about that, but again, whether there'll be a bigger earthquake? We don't know.
The great thing about an earthquake like this is that it can serve as a reminder that we do live in earthquake country. It's great to be prepared, make sure you got your earthquake safety kit. If you haven't already, you can download MyShake. I know that a number of people got an alert from our cell phone app, MyShake, which will deliver those Earthquake Early Warning Alerts to your cell phone. So if you haven't done that already, you can get them that way as well.
How long do aftershocks last?
Dr. Lux: We see those aftershocks decaying with time. So today we probably see some aftershocks happening, especially the smaller magnitudes. That's pretty normal. And then over time, the frequency and the size of those earthquakes will decrease. This wasn't a huge earthquake again, 5.5. That's that's not really, really big. So we'll expect to see some smaller aftershocks. I would expect in that area for a little while, and it'll taper off pretty quick. I would imagine.
How big was the earthquake in context?
Dr. Lux: 5.5, I would call it a moderate earthquake. Something like we saw, again in Ridgecrest that was a 7.3 so that there was a significantly larger earthquake. We have a logarithmic scale, so every time you go up in numbers, it's actually a pretty significant increase in the amount of energy that's being released. So 5.5, we're gonna call that a moderate earthquake. People will definitely feel it if you're within 100 miles. It seems like people are definitely feeling some shaking there. But again, larger earthquakes like what we could expect to see some somewhere else -- for example, on the Hayward Fault -- we can expect to see bigger earthquakes than that. So again, I'm going to say this is a moderate earthquake. Doesn't mean that it wasn't scary, for sure. It can be startling if you're not ready for it, but again, I would say this was a moderate earthquake.
What is the MyShake App?
Dr. Lux: MyShake is an app that can deliver Earthquake Early Warning alerts. We have the west coast wide Shake Alert Earthquake Early Warning system, that's what I work on. That system will estimate where the earthquake is and how big it is. It will do it really, really fast, so fast that we can actually get that alert out to people with a general estimate of how big the earthquake is, before they feel shaking. So that's why, if you're down in Sacramento but the earthquake starts way up near - it was almost near Lassen - the amount of time that you get between when we send out that alert and when you feel shaking could have (been) up to like 30 seconds. So, it's a significant amount of time that you might get. So you can again, drop cover and hold on, get ready for that earthquake shaking to start.
Why can't we predict the next earthquake?
Dr. Lux: Unfortunately, we cannot predict when and where the next earthquake will happen. If I could I would be really rich. I'd be in very, very, very high demand, because everybody wants to know 'When's the next earthquake?' And unfortunately, it's just one of those things that as far as we know, at this point in time, there are no consistent, detectable signals or anything that we can see that will tell us when the next earthquake will happen. We may see increased seismic activity in some areas, but sometimes we don't. So again, there's nothing consistent that we can use to predict earthquakes.
Does California have to be worried about the big one?
Dr. Lux: Unfortunately, we can't tell when or where the next really big earthquake will happen. This could be a foreshock to a large earthquake, or it may not. We really cannot tell. What we do know is that again, this can serve as a reminder to be prepared for the next big earthquake.
Statistically speaking, yes, the Bay Area particularly is overdue for a large earthquake. We know that based on historical records of when earthquakes have happened in the past, and how much time has elapsed since the last big earthquake over here. But again, we don't know when the next one will happen. (It) could be tomorrow, could be 30 years from now. But we do know that we do live in earthquake country, and it's a good to be prepared for the next big one.
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