California quake project aimed to ID future hotspots

Half a dozen teams decided to give it a shot. They developed sophisticated computer models, submitted their best guesses and waited. As part of the ground rules, they could not change their forecasts, which were checked against actual quakes that hit during the study period.

The goal was to see whether there was a reliable way to flag a seismic hotspot before the ground shakes.

The exercise, which began in 2006 and wrapped up last December, was not aimed at predicting quakes, which remains elusive. Instead, researchers were asked to pinpoint regions where quakes were more likely to occur based on past seismic history, activity on fault lines or other factors. The state was divided into 7,700 sections and teams had to give probabilities of quakes of varying magnitudes occurring in each one.

During the test period, 31 quakes larger than magnitude-4.9 rattled the state, including the greater Los Angeles region, San Francisco Bay area and off the Northern California coast. The largest was the 2010 Easter earthquake centered in Baja California that produced sizable aftershocks along the U.S.-Mexico border.

So how did scientists do?

"No single model takes home all the gold," said seismologist John Vidale of the University of Washington who was not part of any team.

U.S. Geological Survey seismologist Sue Hough agreed. The experiment shows just "how difficult it is to even evaluate rigorously the success of prediction methods," she said.

By one measure, three groups that took into account all past quakes regardless if they were big or small fared better than the rest. One of them analyzed the performance and published results online Monday in the Proceedings of the National Academy of Sciences.

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