Earthquake overdue in San Francisco Bay area

Downtown San Francisco from Alamo Square Park. A 2009 report by the San Francisco Planning & Urban Research Association concluded that the city's infrastructure and buildings were unpreapred for a major earthquake.

Four sections of California's San Andreas fault in the San Francisco Bay area have built up so much strain, they could produce a major earthquake at any time, scientists warn.

They have been studying fault creep – the slip and slow release of strain in the upper layers of the Earth's crust that helps protect against large, damaging quakes. When fault creep does not take place, a fault is considered locked and stress keeps building until it is released in an earthquake.

The San Francisco State University Creep project has been monitoring creep on faults in the Bay area and examining details of past ruptures, unearthed in paleoseismic studies. The results have been published in the Bulletin of the Seismological Society of America.

The research found that three sections of the 2012 km-long fault – Rodgers Creek, northern Calaveras and southern Green Valley – have accumulated enough strain to produce an earthquake of at least magnitude 6.7. A fourth, the Hayward fault which produced a 6.8 magnitude earthquake in 1868, is also overdue to rupture.

"The extent of creep on some fault sections is not yet well determined, making our first priority to study the urban sections of the San Andreas, which is directly beneath millions of Bay Area residents," said James Lienkamper, co-author of the study and research geophysicist at the US Geological Survey.

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