Ask LAist: Why does it seem like earthquakes happen more when we’re asleep?

Our newsroom is dedicated to answering the questions that keep you up at night.

Usually, we mean that metaphorically. But this time, we mean it literally.

Sabrina Skacan grew up in San Pedro, so earthquakes aren’t exactly new to her. In fact, she used to sleep through a lot of them. But lately, she has started to notice them more, mostly at night.

And when a series of 4 a.m. quakes woke up much of Southern California — myself included — back in April 2021 she sent me this email:

I took Skacan’s questions to Susan Hough with the U.S. Geological Survey.

First, Hough told me that nobody's been able to find a correlation between earthquakes and time.

But if that's true, then why does it seem like they tend to strike at night?

I had expected her to show me a bunch of data to answer this, as scientists often do. Instead, she told me a story about March 10, 1933.

Yes, That Albert Einstein

Albert Einstein — yes, that Albert Einstein — had befriended a seismologist named Beno Gutenberg. It was late in the afternoon, and they had just gotten out of a physics lecture at Caltech. They were walking across campus together when — right before 6 p.m. — an earthquake struck Long Beach.

It wasn’t The Big One, but it was pretty big: 6.4.

“It’s one of the events that generated some of the strongest shaking that’s been experienced in this area,” Hough says.

Many buildings suffered severe damage during the March 10, 1933 Long Beach earthquake.

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Security Pacific National Bank Collection/Los Angeles Public Library

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Even up in Pasadena, where Einstein and Gutenberg were walking at the time, Hough said it still should have caused enough shaking to knock things off of shelves, maybe even break some windows.

But here’s the thing: When Gutenberg got to his seismic lab (remember, he was a prominent seismologist), he didn’t know why everybody was abuzz.

“Neither he nor Albert Einstein had noticed this earthquake that had just struck,” Hough said.

To be completely honest with you, this sounded unbelievable to me. So with the help of the kind people at the Caltech Archives, I listened to an oral history interview with Gutenberg’s wife Hertha — and she confirmed it. In fact, she said the men were literally talking about earthquakes at the time.

“People sort of chuckle at the story, but the point remains that you can miss fairly strong shaking if you’re outside or if you’re walking around,” Hough said. “It’s kind of surprising what people may not notice.”

As it turns out, there are a lot of factors that determine whether you’ll feel an earthquake.

Some are obvious, like whether it’s a big one or not. How close you are to the epicenter matters, too.

And what you’re doing at the time factors in as well.

If you’re in a car, the combination of moving, being outside, and the car’s own suspension system may make it hard to feel a quake, Hough said. Similarly, if you’re outside — like Einstein and Gutenberg were — you might not be able to notice shaking as easily as if you were inside watching things fall off shelves.

So don’t feel bad if you don’t notice the smaller quakes here and there. You’re in good company.

“We don’t feel all that many earthquakes in California,” Hough said, even though they're relatively common.

I used the USGS Earthquake Catalog to graph all the earthquakes magnitude 4 and up in the KPCC/LAist coverage area over the past 100 years. And, as you can see below, they’re pretty evenly distributed throughout all hours of the day. There is, admittedly, a bit of a bump at 6 a.m., though Hough said that isn’t too surprising. Aftershocks could play a part, and the data set might just be a bit too small.

“You might see a cluster just by random chance,” she said.

But if you look at the big picture, at more earthquakes, the way seismologists do, you shouldn’t see significant patterns, Hough said. Earthquakes seem to happen at any hour of the day.

So to answer Sabrina Skacan’s question: Are there more earthquakes happening at night?

Probably not, though if it seems that way, it could be because you’re not driving, reading LAist, or talking to Albert Einstein — like you are during the day. That's why you might be more likely to notice the shaking at night.