BERKELEY (KCBS) – New research from seismologists at University of California, Berkeley shows the Hayward Fault is actually a branch of the Calaveras Fault, meaning the faults have a much greater destructive potential in the case of a simultaneous rupture, potentially triggering a tremor stronger than the 1989 disaster.

“Now that we have direct connection between the two faults, it means that they could both rupture simultaneously in an earthquake. So instead of having a 6.9, we could have a magnitude 7+ on these two faults,” said Estelle Chaussard, a postdoctoral fellow with the Berkeley Seismological Laboratory and lead researcher for the study.

And there’s more.

The Calaveras Fault is connected all the way through to the San Andreas Fault.  An earthquake across the entire length of that system could lead to even higher magnitudes, above 7.3.

Last month, the U.S. Geological Survey estimated a 14.3 percent likelihood of a magnitude 6.7 or greater earthquake on the Hayward Fault in the next 30 years. It was 7.4 percent on the Calaveras Fault.

Those estimates are based on the assumption that the faults are independent systems. With the discovery that the faults are connected, the group of seismologists found that a simultaneous rupture could lead to a magnitude 7.3 quake.

“A rupture from Richmond to Gilroy would produce about a 7.3 magnitude quake, but it would be even greater if the rupture extended south to Hollister, where the Calaveras meets the San Andreas,” Chaussard said.

Although Chaussard could not estimate the likelihood of a simultaneous rupture on the two faults, she said a rupture could propagate across the faults, making for a larger earthquake.

“The magnitude scale is dependent on the length of the fault. So the longer the fault, the larger the magnitude and the larger the intensity of the earthquake,” said Chaussard.

The study compared 19 years of creep data, and satellite photos, showing the movement of land over nearly two decades of seismic movement and quakes.

COMPLETE STUDY:  UC Berkeley Research

The Hayward Fault, which stretches from San Pablo Bay in Richmond to south of Fremont, is already known as one of the most dangerous in the country, because it runs through largely populated areas.

Chaussard said researchers are now investigating whether the Hayward Fault might also be linked to the Rodgers Creek Fault, that cuts through the heart of Sonoma County.

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