The next big earthquake: When is the Bay Area due?
But a few, like the 1906 San Francisco earthquake, are massive, capable of widespread destruction. The last significant damaging earthquake in the Bay Area was the 6.0 South Napa Quake on Aug. 24, 2014, which killed 1 person, injured 300 and caused $1 billion in damage in Napa and Vallejo. Before that, it was the 6.9 magnitude Loma Prieta Earthquake on Oct. 17, 1989, which disrupted the World Series, and wrecked the Bay Bridge, Oakland's Cypress Freeway, downtown Santa Cruz, and parts of San Francisco, killing 63 people.
The Bay Area has had a quiet few decades. Is it due for another major quake any time soon? Sarah Minson is a research geophysicist with the U.S. Geological Survey's Earthquake Science Center at Moffett Field.
This conversation has been condensed and edited for clarity and length.
Question: What's the current risk of a major quake occurring in the Bay Area?
Answer: There is about a 72% probability of one or more magnitude 6.7 or larger earthquakes within 30 years in the San Francisco Bay Area.
Q: That sounds pretty high. How aware of that risk do you think Bay Area residents are?
A: Relative to other parts of the country, or possibly even other parts of California, people in the Bay Area do tend to be very well aware because of events like Loma Prieta and the Napa earthquake.
They happened in living memory. And even if there is always a new group of arrivals in the Bay Area or young kids who haven't lived through them, it is within a human lifespan, so there is a lot more lived experience - stories from your close friends and family - than in other places where earthquakes happen only once every 100 years or 1,000 years.
Q: What would the impact be of a 6.7 to a 7.0 quake in the Bay Area today?
A: I like the fact that you're asking about 6.7-to-7.0 magnitude earthquakes because it turns out that most of our earthquake risk is from magnitude 6-ish earthquakes, rather than a magnitude 8 big one, like the 1906 earthquake. That's just because they happen so much more often.
A good rule of thumb is that every magnitude decrease is an increase by a factor of 10 in how frequently earthquakes happen. So, for every magnitude 8, like the 1906 San Francisco earthquake, there are 10 Loma Prieta-sized earthquakes, and 100 Napa-sized earthquakes, and 1,000 magnitude 5 earthquakes.
Even though each of those smaller earthquakes impacts a smaller area and they are less likely to cause damage, they happen so much more frequently that overall the risk from them is higher.
Q: Why is that?
A: A colleague of mine likes to say that the comparison between big and small earthquakes is like the difference between sharks and cows. Think of big earthquakes like sharks and little earthquakes like cows. Sharks are scary. Cows are not. But you almost never come face to snout with a shark, right? Whereas you meet cows all the time. And if you look at the statistics, it turns out that sharks kill on average about five people a year and cows kill on average about 22 people a year.
So even though the 2014 Napa earthquake didn't impact all of Northern California like the 1906 San Francisco earthquake did, the shaking locally in Napa was probably higher there than it was during the 1906 earthquake.
These earthquakes that we experience year after year and decade after decade are actually where most of our hazard comes from. When you're thinking about preparing for an earthquake, these are really the kinds of earthquakes you want to be preparing for.
The cataclysmic earthquakes happen so infrequently. They are the sharks. But the cows are what's going to get you.
Q: Which faults in the Bay Area are of most concern?
A: In general, the Hayward Fault seems to have the highest rate of earthquakes. Not in our lifetime. But if you look in the 1800s, there were a number of earthquakes and so overall that seems to be the highest rate long term, followed by the San Andreas Fault.
Q: The Hayward Fault seems to be the one we hear people most worried about. Is that fair?
A: Everyone is concerned about the faults to go through the urban core. But it's important to know that your hazard isn't necessarily governed by your proximity to the fault.
It's not the earthquake itself that causes damage. It's the shaking from the earthquake or potentially liquefaction or landslides. In fact, one of the highest hazard places in the Bay Area would be the Santa Clara Valley, because it's right in between the Hayward Fault and the San Andreas Fault, so it's going to feel shaking if there's an earthquake on either of them.
On top of that, it's a valley full of soft sediment, and soft sediment can amplify shaking.
Q: What should you do if you feel an earthquake?
A: You have bookcases in buildings that can tip over or books that can just fall out of a bookcase. You might have a chandelier over your head. That's why if you feel shaking, you should drop, cover and hold on to protect yourself.
Don't go anywhere. Don't run outside. A huge number of the injuries that occur in earthquakes are people stepping on broken glass or trying to run during the shaking and falling down.
Q: How should we prepare?
A:The sort of things you need to do are the things you need in any other disaster, like large winter storms and wildfires. You want to have a plan to be in contact with your family in case normal communication or transportation is interrupted.
You want water, food, those sorts of things. Think of your pets. You can go to ready.gov for more information.
Q: What's the takeaway message?
A: Earthquakes are something that you don't want to be fatalistic about. We have a tendency to focus on apocalyptic stories of magnitude 8 earthquakes on the San Andreas Fault or magnitude 9 on the Cascadia Subduction Zone that bring destruction to a huge swath of the state. If you're an emergency manager or someone like that you should be prepared for these possibilities. But for you as a human, with a human life span, the thing much more likely to impact you is not even something like Loma Prieta but something like the Napa earthquake.
These earthquakes are very survivable. They don't even necessarily have to interrupt your life all that much with some very simple preparedness.
Five interesting things about Sarah Minson
-Raised in Mendocino County, California
-Earned her bachelor's degree in geophysics at the University of California, Berkeley in 2003.
-Earned her master's and doctorate degrees in geophysics at the California Institute of Technology in 2005 and 2010, with a doctoral thesis on "A Bayesian Approach to Earthquake Source Studies."
-Expert in rupture models, earthquake early warning systems, earthquake source mechanisms, crustal deformation, and public outreach of seismic issues
-Awards include 2020 USGS Superior Service Award; 2018 Kavli Fellow (National Academy of Sciences and The Kavli Foundation); 2021, 2021, 2019, 2016 U.S. Geological Survey STAR Award; 2014 Presidential Early Career Award for Scientists and Engineers.
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Instead, even those fault segments ruptured in the big March earthquake. So what gives? A possible explanation is the Sagaing fault's extraordinary smoothness. 'And people have observed that when the fault is very smooth, the rupture ... tends to propagate at a velocity' so fast that it results in an 'extremely elongated rupture,' Avouac said. The study also published the results of a computer model simulation looking at how earthquakes might rupture along sections of the entire 750-mile long Sagaing fault. The code, developed by study coauthor Kyungjae Im of Caltech, suggests that over a hypothetical 1,400-year period, there would be no repeatable patterns. In other words, earthquakes didn't seem to re-occur like clockwork, rupturing the same stretch of fault in a repeatable, predictable pattern. 'There is complexity here. And this is because each time you have an earthquake, it redistributes the stress on the fault, which is going to influence the next earthquake,' Avouac said. 'There's a self-induced complexity in the process, and that leads to a bit of randomness.' There is one certainty, which is bound to disappoint anyone who shares the hope that a 'Big One' simply won't ever strike California again. 'There will be an earthquake at some point,' Antoine said. 'If there is stress building up on the fault, the fault won't hold forever.' Further research and observations are essential to refine models of future possible earthquakes, including from the Sentinel satellites, which are operated by the European Space Agency, the authors said. The other coauthors of the study are Rajani Shrestha and Chris Milliner of Caltech; Chris Rollins of Earth Sciences New Zealand; Kang Wang of the Washington-based EarthScope Consortium; and Kejie Chen of the Southern University of Science and Technology in Shenzhen, China.
