No, there is *not* a 99.9% chance of an LA earthquake

sylmar-quake-bridge-usgs.jpgUSGS image from 1971 Sylmar quake.

It seemed pretty dicey when, for the first time, a scientist here in Southern California confidently predicted a substantial earthquake was 99.9 percent likely within three years. But the scientist was from JPL and the claim was made in a scientific paper, so the media bit and a new quake meme was born this week. Well, now the U.S. Geological Survey has disputed the claim, saying it's own evidence pegs the chance of a quake in or around La Habra at about 85 percent over the next three years.

From USGS on Facebook:

While the earthquake forecast presented in this paper has been published in the online journal Earth and Space Sciences, it has not yet been examined by the long-established committees that evaluate earthquake forecasts and predictions made by scientists. These committees, the California Earthquake Prediction Evaluation Council, which advises the California Office of Emergency Services, and the National Earthquake Prediction Evaluation Council, which advises the U.S. Geological Survey, were established to provide expert, independent assessment of earthquake predictions.

The earthquake rate implied by the 99.9% probability is significantly higher than observed at any time previously in Southern California, and the lack of details on the method of analysis makes a critical assessment of this approach very difficult. Therefore, the USGS does not consider the analysis presented in this paper a reason to change our assessment of the hazard.

Or, put another way, in the LA Times story:

“I have serious doubts that the conclusions of the paper are supported by the analysis that's presented there,” Robert Graves, a USGS seismologist and Southern California coordinator for earthquake hazards, said in an interview Wednesday. The study lists Graves as a consultant who helped with calculations for the study, but Graves says he has deep concerns about the study.


“It does not seem like a reasonable number,” Graves said. “There’s no information from that paper that that number can be substantiated.

“The 99.9% number -- I don’t know the method that was used to derive that. But basically, that's saying that’s going to happen. And that level of certainty, to my knowledge, is just not attainable. We can never be that certain.”

The lead author of the study that appeared in the journal Earth and Space Science, JPL research scientist Andrea Donnellan, said the 99.9% figure was part of a test. “As scientists, we were not putting out an official forecast. We were putting out something in a paper to test,” Donnellan told the Times. “We never said in this paper we were predicting an earthquake. And we said that's the probability of an event. There is still a 0.1% chance it won't happen. So we need to test it."

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