Earlier this week, the U.S. Geological Survey released a new study, which concluded that California faces a bigger chance of experiencing a powerful earthquake in the next 30 years than previous studies had predicted.
Non-seismologists who just glanced at the news headlines about the study -- including ours -- may have been left worrying that the risk of "The Big One" is now greater, due to some alarming change in Earthquake faults.
But the explanation is actually more complicated, though not necessarily more comforting. The upside is that recent discoveries about the nature of earthquakes and how they spread, coupled with advances in supercomputer software and monitoring technology, now enable scientists to make more accurate predictions about future quakes.
The Third Uniform California Earthquake Rupture Forecast, also known as UCERF3, used those conceptual and technological advances to predict that the chances of an 8.0 or greater event -- roughly, the equivalent of the San Francisco earthquake of 1906 -- rocking the state in the next 30 years has increased from 4.7 percent to 7.0 percent. Meanwhile, the chances of significant but less-than-catastrophic quakes in the 6.5 to 7.0 range actually has gone down slightly in the new forecast.
The big reason for the difference from previous forecasts is that scientists have figured out how to solve a longstanding limitation in earthquake prediction models, according to Tom Jordan, a University of Southern California professor of earth sciences and one of the study's authors.
On the simplest level, an earthquakes can occur when a portion of a single fault ruptures. But scientists have known since the early 1900s that earthquakes also have the capability to jump from one fault to other nearby ones and become more powerful, almost the way that a single burning house can ignite nearby houses as well. This phenomenon was illustrated by the June 1992 Landers earthquake, a 7.3 event which actually resulted in ruptures of five different faults, and involvement of numerous smaller ones as well.