The Washington PostDemocracy Dies in Darkness

Opinion A San Andreas earthquake is unlikely now. But we should still plan to prevent catastrophe.

(Richard Vogel/AP)
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Lucy Jones, a seismologist at the California Institute of Technology, is the author of “The Big Ones: How Natural Disasters Have Shaped Us (and What We Can Do About Them) and host of the podcast “Getting Through It.”

On Monday, the U.S. Geological Survey issued an earthquake advisory stating that there was a 1-in-100 chance of a very damaging 7+ magnitude earthquake on the southern San Andreas fault this week. But the announcement is the quantification of the truism “When you have a lot of earthquakes, you tend to have a lot of earthquakes,” and it’s probably the closest scientists will ever get to earthquake prediction.

We all want the one correct forecast, to pinpoint the time of the Big One. But instead of focusing on when a particular catastrophe will occur, we would be better off thinking about what will happen when it does — and preparing ourselves accordingly. Would you rather have a two-hour warning that a building will fall, or a building that doesn’t fall down in the first place?

Human beings face danger by looking for patterns, and we will create them even when they don’t exist. Our ancestors survived to pass on their genes by recognizing patterns and using them to avoid danger. Today, science is all about finding the sequences that will let us predict the future. And we will tend to believe in these patterns, even when a situation is in fact completely random.

But the only pattern we have ever found in the timing of earthquakes is that one earthquake can trigger another nearby. Mostly, the triggered earthquakes are smaller, and we call them “aftershocks.” About 5 percent of the time, the triggered earthquake is bigger than the first one, and then we call the first one a “foreshock.” Beyond this, earthquakes are random. We can estimate how many earthquakes will happen in an area over the next 100,000 years, but the timing of any one event remains unknown.

Still, when a formal advisory is issued by the U.S. Geological Survey, it does represent a consensus of the scientific community — a sign that the latest earthquake pattern has passed the necessary statistical tests. What should we do in those cases?

First, recognize that the risk of a major event is often still quite small.

A warning means a particular risk is enough higher than the normal background risk to be worth noting — but 99 percent of the time, it will lead to nothing. This week’s advisory was issued because an earthquake sequence is currently occurring close enough to the San Andreas fault that it could trigger a major earthquake along the fault line itself. But the sequence is small enough (the largest earthquake was 4.6 in magnitude) and far enough away from the fault (about eight miles) that the probability that it will trigger a major earthquake is still minimal.

Yes, the risk of a major earthquake along the fault is up substantially this week, from 1 in 10,000 to 1 in 100. But in absolute terms, that is still quite low.

Second, know that the risk of a major seismic event dies off quickly with time. Although the risk is given as one number for a week (say, 1 in 100), that chance dies off quickly — and now, a few days after the first event, most of the additional risk is gone.

Third, look for the scientific information about earthquakes that is readily available and put it to use.

Where earthquakes occur, how large they may be and their potential future impacts are well understood and published in the form of the National Seismic Hazard Maps. The newly developed earthquake early-warning system uses U.S. Geological Survey data to determine when an earthquake is underway and sends those in the affected area that information, potentially before the shaking get to their location. The maps should be used to build more resilient infrastructure. The warning system could also enable protective action, from a dentist removing the drill from a patient’s mouth to residents sheltering for safety under a table.

Finally, all of us should begin asking ourselves why we are so focused on when a particular event will happen, whether it’s an earthquake or another “once in a lifetime” natural disaster. What would you do differently? Is it something you should have done anyway?

As a society, we need to accept that floods along the Mississippi, tornadoes in the Midwest, hurricanes in the South and East and earthquakes in the West are absolutely inevitable — and we should plan accordingly. We don’t know which cities will be hit by this year’s hurricanes or when the Big One will strike along the San Andreas or the Cascadia subduction zone, but we know that these things are absolutely part of our future. How do we create a resilient society that can take them in stride?

It is hard to imagine any earthquake that could kill as many Americans or destroy as many jobs as the 2020 pandemic. But for both earthquakes and pandemics, all we really have is the scientific knowledge that tells us these events are inevitable eventually. Instead of guessing at the exact time, we should use that information to better prepare and effectively respond.

Read more:

Leana S. Wen: Four concepts to assess your personal risk as the U.S. reopens

Irwin Redlener: Disaster season is upon us. The pandemic changes everything.

Rebecca R. Rubin and Sam Bleicher: Climate change, like the coronavirus, requires hard choices and leadership

Steven Bingler and Martin C. Pedersen: Planners talk about resilience in the face of climate change. We need to start using a different R word.

Susan Hough: Five myths about earthquakes