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Fault Connection Reveals Risk to Bay Area

Newly-discovered Fault Connection

It has been 27 years since the 6.9-magnitude Loma Prieta earthquake on the San Andreas fault rattled the San Francisco Bay Area, killing 63, injuring over 3,700, and famously interrupting that year’s World Series.  Four scientists with the United States Geological Survey have recently discovered a connection between two fault lines under the Bay that were previously believed to be unlinked, revealing a fault connection they say could lead to an even larger future earthquake.

Underwater surveys conducted in shallow portions of the northern San Francisco Bay discovered a section of the Hayward Fault that connects to the western segment of the Rodgers Creek Fault.  The Hayward Fault extends for 62 miles from San Jose to San Pablo Bay, passing directly under the densely-populated urban areas of Berkeley and Oakland.  The Rodgers Creek fracture runs north from the bay, 56 miles through the heart of wine country.

The worry is that the 188-mile connection between the two faults will make the effects of a rupture along either fault more intense and impact substantially more people.


7 million Could Be Drastically Affected

Explained in detail in a recent journal article, the study is the first evidence that the two major faults are linked. The fault connection discovery was published in the October 19th edition of the journal Science Advances. The USGS team led by Janet Watt stated that the next major earthquake to the strike the Bay Area will likely come from the (now-connected) Hayward and neighboring Rodgers Creek faults. The scientists used integrated geophysical interpretation and kinematic modeling to show that the Hayward and Rodgers Creek faults are directly connected at the surface (in San Pablo Bay), and the coinciding geometric relationship has significant implications for earthquake dynamics and seismic hazard.

They argue that the discovered link enables a simultaneous rupture along their combined 188 miles, potentially producing a quake as large as 7.4 in magnitude–five times stronger than the Loma Prieta event. According to their findings, the worst case scenario event would cause extensive damage and loss of life with global economic impact. An estimated 7 million people could be drastically affected.

 

Maps showing the Hayward and Rodgers Creek fault connection

Maps showing the Hayward and Rodgers Creek fault connection


Sources:

http://advances.sciencemag.org/content/2/10/e1601441

http://www.theverge.com/2016/10/19/13335816/earthquake-faults-san-francisco-oakland-bay-area-san-andreas-hayward

https://en.wikipedia.org/wiki/1989_Loma_Prieta_earthquake