Claremont is overdue for ‘The Big One.’ Should you be concerned?

A cartoon depiction of Pomona's Bridges Auditorium tilted at a 45-degree angle on cracked, fissuring ground. Boulders and rocks are distributed around the image.
Graphic by Anaga Srinivas

This past July, two strong earthquakes centered in Ridgecrest, California shook the ground in Claremont. With a 46 percent chance of a 7.5-magnitude earthquake hitting California in the next 19 years, TSL news writers Anushe Engineer SC ’22 and Maggie Lind SC ’22 sat down with Pomona College Geology Professor Nicole Moore to discuss the likelihood of an earthquake in the Claremont area and what students should know to prepare themselves.

Moore said it’s impossible to predict an earthquake, but the 5Cs would likely be hit hard if the infamous “Big One” strikes. She said students should be prepared — but not worried.

TSL: After the latest earthquakes this summer, the Big One has become a common topic of conversation. Can you give us some background on this concern?

NM: The idea of the Big One is centered around the fact that we have the San Andreas Fault to the North, just on the other side of the San Gabriel Mountains. This … segment [of the fault]  hasn’t ruptured in a long time, and it tends to rupture on that large scale of a 7.8- or 7.9-magnitude about every 150 years. 

Earthquakes cannot be predicted — it depends on how much pressure and stress has built up over time. But since it tends to rupture, we expect that we’re due, or overdue, at this point, for a very large earthquake of that segment.

TSL: What kind of damage would we expect to see in Claremont?

NM: It would be pretty devastating. The relative magnitude is less important than how close you are to that earthquake. So, if we’re really close to a big magnitude earthquake, we’re going to experience very strong and very sustained shaking here. 

Earthquakes cannot be predicted — it depends on how much pressure and stress has built up over time. But since it tends to rupture, we expect that we’re due, or overdue, at this point, for a very large earthquake of that segment. – Pomona Geology Professor Nicole Moore 

That kind of shaking can definitely damage buildings. It could completely disrupt the roads and cellphone service. Power lines would come down. 

Secondary effects of that would be starting fires, especially in this area where we have really dry conditions. Water mains and gas lines could break. All of that leads to the fact that if our roads are impassable, we’re not going to be able to get food and supplies in. 

If our water mains break, then we can’t put out the fires because of that. As far as buildings are concerned, most in this area have been built under earthquake codes that would make them withstand shaking to the point where they’re not going to collapse on us. But we certainly might see the ceiling panels fall or maybe even the lights.

TSL: You talked a little bit about how the Big One would affect our access to resources. Can you talk specifically about how our access to water could be affected? 

NM: Most of the water in the LA basin in our region gets pumped in from the Sierra Nevada through the Owens Valley. So, yeah, that could certainly be cut off. That’s why it’s recommended that when you live in ‘earthquake country,’ as part of your ‘Earthquake Kit’ to have at least 72 hours of water supply — that’s the minimum suggestion. 

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Water is one thing you can’t live without. You can go several days without food and be fine, but you can’t go several days without water and be fine. The importance of keeping water backup supply is heightened here since the opportunity for cutting off that supply is so great.

TSL: Are the 5Cs affected by any fault lines other than the San Andreas Fault?

NM: Absolutely, there are quite a few in fact. The San Andreas curves, just north of the San Gabriel Mountains, and then bends back up towards San Francisco. The bend causes compression in either direction, and so to shorten that space, you create faults in the rocks. 

That’s what’s happening in the front part of [the San Gabriel Mountains], where we have a whole series of faults where rocks are getting shoved on top of one another to make the mountains move up and shorten that space. 

But, most of those faults are shorter, and the length of the fault dictates how much energy could be released. Those faults don’t have the probability of making as big of earthquakes. 

There’s one called the Indian Hill Fault just north of Foothill [Boulevard]. You can stand on Foothill [Boulevard] and see the expression of the fault — it’s a little hill. And then there’s one just to our south here that runs through town called the San Jose Fault. 

TSL: Is the San Jose Fault on the Metrolink?

NM: Well, right where the train tracks are there’s a hump, and it looks like the expression of a fault there. That fault doesn’t continue directly East-West all along the Metrolink. 

It’s just expressing itself right there by that part of the train tracks, and then continues off sort of in a southeast direction off of the train tracks. It’s not like the whole time you’re riding the Metrolink you’re riding along a fault. 

[An earthquake] could completely disrupt the roads and cellphone service. Power lines would come down.  Secondary effects of that would be starting fires, especially in this area where we have really dry conditions. Water mains and gas lines could break. All of that leads to the fact that if our roads are impassable, we’re not going to be able to get food and supplies in.  – Moore

TSL: Do you think that the earthquake safety measures that the colleges are putting in place are sufficient? What should students do to prepare individually?

NM: Education, to me, is the key thing here. The colleges do what they need to in terms of having the backup supplies ready in case of an emergency, so having your own emergency kit is not something you really need to worry about, although that wouldn’t be a bad idea. 

As soon as you feel an earthquake, know that you need to drop, cover and hold. The dropping is essential, because if it’s a strong enough earthquake and you try to walk somewhere, you’re going to get knocked off your feet. 

Get down on your hands and knees, and crawl to something that can cover your head like a desk or a table. The thing that I don’t feel like the Great ShakeOut is great at practicing, and I’m not sure how well this is communicated to you guys, is that there are things called muster stations where you go once an earthquake has happened. 

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Each building has a set location that you’re supposed to congregate and be accounted for so that we can know if there are people trapped in the buildings somewhere. There’ll be further instructions from there in the event of a major earthquake.

TSL: Do you think students should be worried, and, if so, about what?

NM: No, don’t be worried, just prepare yourself and know what to do if the situation arises. Worry is the result of the unknown and if you know what you’re going to do in that scenario, then that’s going to alleviate the concern. 

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