SACRAMENTO, Calif. — After a magnitude 7.1 earthquake in Southern California shook parts of the Sacramento region, we wondered if "the big one" was possible here.
Daniela Pardo spoke with an expert from the Berkeley Seismology Lab to learn more. Angela Chung, a project scientist for earthquake early prediction, said nope, the big one won't hit Sacramento. But, if it happens on a nearby fault line, like the Hayward or San Andreas, it's definitely going to be felt.
Q&A WITH ANGELA CHUNG
Q: Can you break down the terms aftershock, mainshock and foreshock?
A: "Those are words that we give to describe the earthquakes that are happening. If we called them all "earthquakes" then we wouldn't know which earthquake we were talking about.
Prior to (Friday) night, we thought that the magnitude 6.4 earthquake on July 4 was the mainshock. But, now that there has been a larger earthquake, we're calling the 6.4 a foreshock. And the earthquake that happened [July 5], the magnitude 7.1, that's now what we're calling the mainshock.
It's possible that this is a foreshock to something larger, but we won't know until that larger earthquake occurs."
Q: What kind of aftershocks do you think we could see after the 7.1?
A: "Well, we know that there's going to be a lot of earthquakes, so far this earthquake sequence has been very energetic — we've seen a lot of aftershocks.
We've seen magnitude 5's, 6's, and now we have a main shock which is a magnitude 7. There's still a one in 20 chance or so that the earthquake could be followed by something even larger, but again, we won't know until that happens. But, we definitely will expect to see aftershocks for a very long time."
Q: Does this open up a floodgate for more earthquakes in different fault lines, like the one that's close to us in the Bay Area?
A: "It shouldn't trigger anything close to us. That's a little bit too far, geographically speaking. When an earthquake triggers another one [like what happened in Ridgecrest], those are occurring within a relatively close geographical area. So, it could be possible for the earthquakes that have happened to trigger something else...we know that every time an earthquake happens it makes it more likely that another earthquake is gonna happen, but I wouldn't expect to see it up into the Bay Area."
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Q: Can an earthquake happen in Sacramento?
A: "So, there's no fault that goes directly below Sacramento that I'm aware of. But, there are certainly a lot of faults in the Bay Area and looking at the USGS probability maps we see that there's more than a 60% probability that a magnitude 6.7 or greater earthquake will occur in the Bay Area at some point in the next 30 years. So, that's a pretty significant probability.
Q: What faults are we close to in Sacramento?
A: "We have a number of faults in the Bay Area. We have lots of faults in the Bay Area. The San Andreas Fault is a major one. That's the one that goes all the way from Northern California down to Southern California. There's also the Hayward Fault. That's a very significant fault, and both of those are capable of creating some pretty large earthquakes."
Q: What could happen in Sacramento if one of those faults was active?
A: "If any of these faults went off in the Bay Area we could definitely expect to see some pretty strong shaking in Sacramento. We could expect to see some damage if we had a magnitude 7.1 earthquake.
Q: So...are we closer to expecting "the big one?"
A: "We're always expecting 'the big one.' Nobody can predict earthquakes, so we don't know when the next large earthquake will occur. But, what we can do is use this as a learning experience.
This happened in a fairly remote area in California. There wasn't a lot of people in that area and there wasn't a lot of damage, relatively speaking, for such a large earthquake. If such a large earthquake happened in a major city, that's gonna cause a lot more damage.
So what we can do is, again, take that, learn from it, and say 'are we prepared for the next earthquake? Do we have our water available? Do we have our earthquake safety kit? Have we made a plan about what to do when that big earthquake happens?'"
Q: What are the next steps?
A: "Well for me personally, I'm the project scientist for earthquake early warning, so I'm very interested in how the system formed for this aftershock sequence, how it performed for the main shock and, again, how it's gonna perform in the future."