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.

We've never been very good at being conservative.

And usually, that serves us well in doing the ambitious, hard-hitting journalism that you turn to Mother Jones for. But it also means we can't afford to come up short when it comes to scratching together the funds it takes to keep our team firing on all cylinders, and the truth is, we finished our budgeting cycle on June 30 about $100,000 short of our online goal.

This is no time to come up short. It's time to fight like hell, as our namesake would tell us to do, for a democracy where minority rule cannot impose an extreme agenda, where facts matter, and where accountability has a chance at the polls and in the press. If you value our reporting and you can right now, please help us dig out of the $100,000 hole we're starting our new budgeting cycle in with an always-needed and always-appreciated donation today.

payment methods

We've never been very good at being conservative.

And usually, that serves us well in doing the ambitious, hard-hitting journalism that you turn to Mother Jones for. But it also means we can't afford to come up short when it comes to scratching together the funds it takes to keep our team firing on all cylinders, and the truth is, we finished our budgeting cycle on June 30 about $100,000 short of our online goal.

This is no time to come up short. It's time to fight like hell, as our namesake would tell us to do, for a democracy where minority rule cannot impose an extreme agenda, where facts matter, and where accountability has a chance at the polls and in the press. If you value our reporting and you can right now, please help us dig out of the $100,000 hole we're starting our new budgeting cycle in with an always-needed and always-appreciated donation today.

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