What Makes California's Quake Warning System So Timely?

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The collapsed Cypress Viaduct was the site of the first earthquake early-warning system, in 1989. USGS photo by Howard Wilshire
The collapsed Cypress Viaduct in Oakland was the site of the first earthquake early-warning system, in 1989. USGS photo by Howard Wilshire

Earlier this week, State Senator Alex Padilla went before the cameras with a group of earthquake scientists to kick-start California into building the world's best earthquake early-warning system. Does such a thing really work? And why should we start now?

Early-warning systems are not a scientific boondoggle; they really work. First things first, though: these do not predict earthquakes. Instead, they're automatic systems that detect quakes right at the epicenter, and measure their size almost instantly. With that information, they signal faraway users that strong shaking is on its way RIGHT NOW. You could call that a prediction if you like, an instant shaking prediction. But quake researchers are extremely allergic to the word "prediction," so please call these warning systems. They're like the tsunami warning systems we're familiar with by now, only a lot faster.

The Bay Area had the world's first example back in 1989, in the aftermath of the Loma Prieta earthquake. It detected aftershocks. It consisted of a handful of seismographs around the epicenter in the Santa Cruz Mountains, a computer and a microwave radio network. When the computer got enough simultaneous signals from the seismographs, it considered that the detection of a large aftershock and sent out an alarm on the radio network. Crews who were taking down the wreckage of the Cypress Structure, 100 kilometers away, got about 20 seconds of warning to back off and get out. You can imagine how useful that system was to those workers, crude as it was.

Today much larger and better systems are at work around the world. Japan's is the most advanced—not so much scientifically, because every system's software uses the latest science, but in terms of being integrated into people's lives. If you saw it in action during the 2011 Tohoku earthquake, you can imagine one like it in California.

Senator Padilla's bill was triggered after one of his regular visits to Caltech. (He's an astronomy geek, it turns out.) While he was there, the earthquake people got hold of him and demonstrated the early-warning tools on the California Integrated Seismic Network (CISN), like the experimental ElarmS project. The CISN people told him, as they've been telling anyone who will listen for ten years now, that they're ready to roll whenever the money can be found. Right now their research relies on a lean stream of funds from government projects and the Gordon and Betty Moore Foundation.


Padilla's bill (Senate Bill 135) is mostly preamble with one new sentence for the Government Code that commits the Office of Emergency Services to work with the CISN partners to "develop a comprehensive statewide earthquake early warning system in California." In the preamble is one unusual item: a reference to a dry scientific paper in Nature last month. The paper is also prominently featured in Padilla's news release about SB-135, which linked to a Caltech press-office piece on the paper.

Peggy Hellweg, the CISN point person at Cal Berkeley's Seismological Lab, explained where the paper fits in the larger story. Ever since the 1992 Landers quake in Southern California, she told me, a major weak point in our understanding of earthquake faults is how ruptures can expand beyond the limits we thought they had. At Landers, five separately mapped faults gave way at once in a single rupture. On the larger scale, both the giant 2004 Sumatra and 2011 Tohoku quakes ruptured fault segments that no one expected to fail. As for our own San Andreas fault system, we've always taken it as a given that the so-called creeping section, which runs between San Juan Bautista and Parkfield, separates northern and southern California. We don't expect a rupture on either the north or south end of the fault to rip through the creeping section, because its degree of creep—steady motion without earthquakes—would seem to preclude the more wrenching motion of a proper earthquake. It shouldn't have enough strain energy on it.

The Nature paper combined simulations of faulting with lab tests of actual material drill-sampled from the fault zone that ruptured in the large 1999 Chi Chi earthquake in Taiwan. Its authors described scenarios in which ruptures advancing into a creeping fault, if they hit it just right, would set it off. In fact, that supposedly low-strain creeping section could release quite a lot of energy.

The authors suggested that creeping might be a temporary state between the relaxed state right after a quake (no energy) and the "stuck" state that most earthquake faults are in (lots of energy). "Temporary" in this case means centuries. If their work holds up and can be generalized, then it's plausible that the San Andreas fault could all go at once. An article in Science News quotes some of the cautionary comments, which make the same points I would.

It strikes me as unusual that such a scientific article would be used as a "news hook" to promote something as fundamental as a new statewide quake-warning system. Normally, in California, we would cite the latest awful earthquake, because that seems to focus people's attention better. But as Senator Padilla said, better to get a system in place before rather than after the next Big One. I absolutely support SB-135 anyway, regardless of this one paper.