USGS in Menlo Park releases report citing increased likelihood of large earthquake

by Contributed Content on March 11, 2015

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Every once in a while Menlo Park becomes the epicenter of earthquake news. Such is the case with a new California earthquake forecast by the U.S. Geological Survey in Menlo Park, which revises scientific estimates for the chances of having large earthquakes over the next several decades.

The Third Uniform California Earthquake Rupture Forecast, or UCERF3 ,confirms many previous findings, sheds new light on how the future earthquakes will likely be distributed across the state and estimates how big those earthquakes might be.

Compared to the previous assessment issued in 2008, UCERF2, the estimated rate of earthquakes around magnitude 6.7 — the size of the destructive 1994 Northridge earthquake — has gone down by about 30 percent. 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.

However, in the new study, the estimate for the likelihood that California will experience a magnitude 8 or larger earthquake in the next 30 years has increased from about 4.7% to about 7.0%.

“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.”

Two kinds of scientific models are used to inform decisions of how to safeguard against earthquake losses: an Earthquake Rupture Forecast, which indicates where and when the Earth might slip along the state’s many faults, and a Ground Motion Prediction model, which estimates the ground shaking given one of the fault ruptures. The UCERF3 model is of the first kind, and is the latest earthquake-rupture forecast for California. It was developed and reviewed by dozens of leading scientific experts from the fields of seismology, geology, geodesy, paleoseismology, earthquake physics and earthquake engineering.

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