As we ring in Disaster Anniversary week here in the Bay Area, some bad news comes via a new study published in the journal Science Advances. As KRON 4 reports, a team from the U.S. Geological Survey has found a previously unknown strand of the Hayward Fault that connects up to the Rodgers Creek Fault in Napa and Sonoma Counties, and the connection point means that a severe break on the Hayward Fault that caused a subsequent break along the second fault could mean severe shaking along a 188-mile stretch all the way the Healdsburg and the potential for a 7.4 magnitude quake.
To put that in perspective, that would mean that five times the energy of the Loma Prieta quake (6.9M) would be released, and that would occur much closer to the urban areas of San Francisco and the East Bay, since the earlier big quake was centered so far south of the city.
Per the study:
The ability of an earthquake on the Hayward fault to continue onto its northern extension along the Rodgers Creek fault (or vice versa) greatly depends on the geometrical relationship between these faults beneath San Pablo Bay.
And that relationship is what scientists have been examining, concluding that "data strongly suggest that the offshore Hayward fault connects to the western strand of the Rodgers Creek fault through a releasing (extensional) bend in northern San Pablo Bay."
Things get pretty technical from there, but the intent of the study is to anticipate the intensity and direction of potential shaking under various dual-fault scenarios the idea of a dual rupture of both faults is not a new one, however, and the USGS published this scenario of a 7.2M quake along both faults much earlier.
As CBS 5 explains, the new study simply confirms what many scientists already suspected about the faults' connection, and clarifies that beneath San Pablo Bay this occurs as the Hayward Fault bends ten degrees to meet up with the Rodgers Creek Fault.
FYI: There hasn't been a major rupture along the Hayward Fault since 1868, and it tends to rupture every 100-150 years. I'll let you do the math.
P.S. Get your earthquake kit together.