If you think of earthquakes like alarm clocks, then lots of people, maybe most of us, respond by rousing briefly and then hitting the snooze bar. California experienced its largest earthquake in years just this monthit was a magnitude 6.8 shaker three weeks ago off the coast of Eureka, in the northernmost part of the state. It was felt all the way from Eugene to Reno to San Francisco. That made only a little news. But a quake that was a hundred times smaller, at magnitude 5.1, got the whole nation's attention because it struck a nerve center, in Los Angeles under the town of La Habra. Millions of people felt it.
The La Habra quake appears to have ruptured the same blind thrust fault responsible for the 1987 Whittier Narrows earthquake. That name probably means nothing to non-Angelenos, but the Whittier Narrows event (magnitude 5.9) got in the news for the same reason, and I'm sure a lot of locals remember it like yesterday. The quake didn't rupture any of the long, notorious faults in the San Andreas fault complex that are the main threats for a real Big One of magnitude 7-plus. Seismologically, it was a sideshow. Nevertheless, even small thrust faults like this one can raise a Big-Enough One. An all-star cast of earthquake scientists at the Southern California Seismic Network prepared a special page for the La Habra quake with lots of detail from the scientific side.
This earthquake didn't do a lot of damage, although I feel for the handful of people with ruined homes and those picking up broken and displaced things. It's a good teaching moment for the nation's second-largest urban area. Maybe some of them won't hit the snooze button ever again.