The rate of magnitude-6.7 earthquakes expected to hit California in coming years was reduced in a new forecast released today by the U.S. Geological Survey, however, the likelihood of a magnitude-8 or larger temblor striking in the next 30 years jumped from 4.7 percent to 7 percent.
“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,” according to USGS scientist Ned Field. “This is a significant advancement in terms of representing a broader range of earthquakes throughout California’s complex fault system.”
In 2008, the USGS estimated that quakes of about magnitude-6.7 — the size of the 1994 Northridge quake — were expected to hit the state once every 4.8 years. The latest report estimates one such quake every 6.3 years.
The 2008 report found that the likelihood of a magnitude-8 or larger quake hitting in the next 30 years was 4.7 percent. The new report puts the likelihood at 7 percent.
“We are fortunate that seismic activity in California has been relatively low over the past century,” according to Tom Jordan, director of the Southern California Earthquake Center. “But we know that tectonic forces are continually tightening the springs of the San Andreas fault system, making big quakes inevitable.”
