Chance of earthquake 8.0-magnitude or greater increases in California

A new earthquake forecast released Tuesday has upped the likelihood that California will experience an earthquake 8.0-magnitude or greater within the next 30 years, from 4.7 percent to 7 percent.

The Third Uniform California Earthquake Rupture Forecast, a new earthquake forecast model for California, highlights the possibilities of earthquakes in the state by using new data and lessons learned from recent earthquakes.

“We are fortunate that seismic activity in California has been relatively low over the past century. But we know that tectonic forces are continually tightening the springs of the San Andreas fault system, making big quakes inevitable,” Tom Jordan, director of the Southern California Earthquake Center and a co-author of the study, said in a statement.

But the information does not point to an increased chance of earthquakes overall.

The study shows that the estimated rate of earthquakes around magnitude-6.7, the size of the 1994 Northridge earthquake and slightly larger than the 6.0-magnitude temblor that rattled Napa and much of the Bay Area in August, has decreased by about 30 percent compared to the previous forecast issued in 2008.

Additionally, the expected frequency of such events statewide has dropped from an average of one per 4.8 years to about one per 6.3 years, according to the study.

Experts credit a variety of factors with altering California's expected earthquake frequency.

“The new likelihoods are due to the inclusion of possible multi-fault ruptures, where earthquakes are no longer confined to separate, individual faults, but can occasionally rupture multiple faults simultaneously,” lead author and USGS scientist Ned Field said in a statement.

Bay Area NewsEarthquakeU.S. Geological Survey

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