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A report that could be bad news for many Californians describes how 2 faults are, in fact, connected which might have significant consequences:
University of California, Berkeley seismologists have proven that the Hayward Fault is essentially a branch of the Calaveras Fault that runs east of San Jose, which means that both could rupture together, resulting in a significantly more destructive earthquake than previously thought. "The maximum earthquake on a fault is proportional to its length, so by having the two directly connected, we can have a rupture propagating across from one to the other, making a larger quake," said lead researcher Estelle Chaussard, a post-doctoral fellow in the Berkeley Seismological Laboratory. "People have been looking for evidence of this for a long time, but only now do we have the data to prove it."
The 70-kilometer-long Hayward Fault is already known as one of the most dangerous in the country because it runs through large population areas from its northern limit on San Pablo Bay at Richmond to its southern end south of Fremont. In an update of seismic hazards 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, and a 7.4 percent chance on the Calaveras Fault. These are based on the assumption that the two faults are independent systems, and that the maximum quake on the Hayward Fault would be between magnitudes 6.9 and 7.0. Given that the Hayward and Calaveras faults are connected, the energy released in a simultaneous rupture could be 2.5 times greater, or 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 Fault meets the San Andreas Fault," Chaussard said.
(Score: 2) by frojack on Sunday April 05 2015, @03:08AM
True, there is a huge inventory of older buildings that could present problems.
California standards do strongly recommend (and in most cases require) retrofitting older brick buildings [ca.gov]. Especially as each comes up for sale.
In fact they boast [sfgate.com]:
The impact of the improvements to building code could be seen in the 1987 Whittier Quake, 1991 Sierra Madre Quake, 1992 Landers Quake, and 1994 Northridge Quake. Los Angeles city officials say that more than 200,000 people were living in retrofitted brick buildings with the Northridge Quake hit. Not a single death or injury was reported from more than 37,000 units in 1,300 strengthened buildings. The structures that were built or strengthened under the new, stricter code experienced limited damage, while those structures that had not been retrofitted suffered greater damage.
No, you are mistaken. I've always had this sig.
(Score: 2) by kaszz on Sunday April 05 2015, @04:29PM
It's problematic because as a casual visitor it's near impossible to avoid or know which buildings that are insufficiently strengthened. Or avoiding being nearby in order to not have anything fall on your head. It may also complicate finding somewhere to live or selecting work. Buildings where you will spend a lot of time and thus their status will affect your risk significantly.
The latency from these new findings until almost all buildings are strengthened may just be longer than it takes for the next quake to happen.