Scientists have come up with a new forecast estimating the chances of earthquakes in California, and they say the probability of a strong magnitude-8 quake has grown. Researchers said in a study released this week the estimated risk of a magnitude-8 or larger earthquake in the next 30 years has increased to 7%, up from 4.7% in the previous assessment in 2008. Meanwhile, they said they now expect moderate-sized earthquakes of magnitudes from 6.5 to 7.5 to be somewhat less frequent than they had previously forecast. Earthquakes of magnitude 6.7 or larger — the size of the 1994 Northridge quake — are projected to strike once every 6.3 years down from once every 4.8 years.
Ned Field, a USGS geophysicist and lead author of the study, said the new forecast was created using a model that incorporates the latest research and seismological data. “What the model really does provide is where and how often earthquakes will occur throughout the state,” Field said. The findings will help update building codes and earthquake insurance policies, and will affect how engineers design skyscrapers, hospitals, bridges and schools. “This will help all those people working to make society safe,” Field said. “It will help them do a better job of that.”
David Oglesby, a seismologist at UC Riverside who wasn’t involved in preparing the forecast, said the study will also contribute to emergency preparedness. "It allows us to focus our efforts in places that can do the most good.”
Scientists have long warned that the southern part of the San Andreas is overdue for a strong earthquake — in part because the last time a big quake hit the area was around 1690. "The southern San Andreas, going through the Coachella Valley and up through the Mojave, is the most likely place in the state to host a large earthquake," Field said. "Plate tectonic stresses have really built up beyond where they do on average. And so we think that those areas are particularly high in terms of the likelihood of having a large earthquake."
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