California’s Two Recent Earthquakes Erupted on Unknown Fault Lines

My geophysicist friend tells me that the two big Ridgecrest earthquakes last week happened along fault lines we didn’t even know existed. Here’s a map of all the aftershocks from the two quakes:

The shorter set of aftershocks outlines the area of the 6.4 earthquake. The longer set outlines the 7.1 earthquake. The purple lines show all the previously mapped fault segments in the area. One of those is a potential problem:

My worry is that both of these fault segments were not mapped before, and both lie close to a long fault that ruptured historically. The Garlock Fault lies at the lower right of the figure, trending WSW-ENE, and it produced a 7.5 quake in 1952. For the last few days the folks at the USGS have probably been estimating how many bars of stress have been gained or lost on the Garlock as a result of the quakes that SoCal experienced last week. Although rock stresses are typically measured in kilobars, history tells us that 1-2 bars of additional stress can trigger the next quake. A 7.5 quake would be 0.4 Richter units larger than the Friday quake, roughly 4x larger in energy release. But also along a longer fault that crosses some major highways. I would be concerned for at least the next 12 months.

And that is your earthquake news for the day.

THE TRUTH...

is the first thing despots go after. An unwavering commitment to it is probably what draws you to Mother Jones' journalism. And as we're seeing in the US and the world around, authoritarians seek to poison the discourse and the way we relate to each other because they can't stand people coming together around a shared sense of the truth—it's a huge threat to them.

Which is also a pretty great way to describe Mother Jones' mission: People coming together around the truth to hold power accountable.

And right now, we need to raise about $400,000 from our online readers over the next two months to hit our annual goal and make good on that mission. Read more about the information war we find ourselves in and how people-powered, independent reporting can and must rise to the challenge—and please support our team's truth-telling journalism with a donation if you can right now.

payment methods

THE TRUTH...

is the first thing despots go after. An unwavering commitment to it is probably what draws you to Mother Jones' journalism. And as we're seeing in the US and the world around, authoritarians seek to poison the discourse and the way we relate to each other because they can't stand people coming together around a shared sense of the truth—it's a huge threat to them.

Which is also a pretty great way to describe Mother Jones' mission: People coming together around the truth to hold power accountable.

And right now, we need to raise about $400,000 from our online readers over the next two months to hit our annual goal and make good on that mission. Read more about the information war we find ourselves in and how people-powered, independent reporting can and must rise to the challenge—and please support our team's truth-telling journalism with a donation if you can right now.

payment methods

We Recommend

Latest

Sign up for our free newsletter

Subscribe to the Mother Jones Daily to have our top stories delivered directly to your inbox.

Get our award-winning magazine

Save big on a full year of investigations, ideas, and insights.

Subscribe

Support our journalism

Help Mother Jones' reporters dig deep with a tax-deductible donation.

Donate