The likelihood of a giant earthquake in California at a magnitude of 8.0 or more within the next 20 years has increased, according to the U.S. Geological Survey.
A study by the Third Uniform California Rupture Forecast, or UCERF3, sheds new light on where earthquakes will likely hit in California over the next couple of decades and how big they’re expected to be.
“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,” said lead author and USGS scientist Ned Field. “This is a significant advancement in terms of representing a broader range of earthquakes throughout California’s complex fault system.”
Compared to the 2008 assessment, earthquakes around magnitude 6.7, the size of the destructive 1994 Northridge quake, has gone down by 30 percent with a frequency from an average of one per 4.8 years to about one per 6.3 years.
The study also says the likelihood that California will experience a magnitude 8 or larger earthquake in the next 30 years has gone up from about 4.7 percent to about 7 percent.
One particularly ready fault is the Southern San Andreas, which geologists have long believed will be most likely to host a large earthquake.
There’s a lower chance for for the Northern San Andreas near San Francisco partly because of the relatively recent 1906 earthquake on that fault. Probabilities on two other Bay Area faults, the Hayward–Rodgers Creek and the Calaveras, actually rival or exceed those on the Northern San Andreas, mostly because they are both relatively ready.
The UCERF3 model is the first of its kind to indicate where and when the Earth might slip along the state’s many faults.
“The UCERF3 model provides our leaders and the public with improved information about what to expect, so that we can better,” said Tom Jordan, Director of the Southern California Earthquake Center and a co-author of the study.