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San Andreas Fault primed for another big earthquake in California.


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Really, this deserves its own thread.


A new study of San Andreas Fault shows the earthquake potential of the fault’s southern, highly populated section. The fault has been stressed to a level sufficient for the next “big one” and the risk of a large earthquake in this region may be increasing faster than researchers had believed.

A new earthquake research shows that San Andreas fault in California, that has not had a big rupture since in at least 300 years, is stressed to a level sufficient for the next “big one”—an earthquake of magnitude seven or greater—and the risk of a large earthquake in this region may be increasing faster than researchers had believed. Historical records show that the San Andreas Fault experienced massive earthquakes in 1857 at its central section and in 1906 at its northern segment


Although seismologists have not been able to predict when a great earthquake will occur on the southern San Andreas, most believe such an event is inevitable. Yuri Fialko of Scripps Institution of Oceanography at the University of California, San Diego has produced the clearest evidence to date of the strain buildup that will ultimately result in a large earthquake along the southern San Andreas Fault, a 100-mile segment that cuts through Palm Springs, San Bernardino and Riverside. Such an event would be felt in the major populated areas of Los Angeles and San Diego.

“For the public the most important result of this study is that these data show definitively that the fault is a significant seismic hazard and is primed for another big earthquake,” said Fialko. One result of the study shows that the southern section of the fault is overdue in its “interseismic period,” or cycle of earthquake activity but exactly when the triggering will happen and when the earthquake will occur can not be told. It could be tomorrow or it could be 10 years or more from now,” said Fialko.

A shaded relief map of California highlights (pink lines) sections of the San Andreas fault that ruptured in great earthquakes in 1857 and 1906. The red line denotes the southern part of of the fault that has not produced a major earthquake in at least 300 years. The white box outlines the area of study for the Nature paper.

Earth’s surface is divided into several large tectonic plates separated by fault zones. The San Andreas Fault, which spans nearly 800 miles through western California from near the Salton Sea north to near Cape Mendocino, divides the slow but steady movement of the North American plate, which moves southeasterly relative to the neighboring Pacific plate. When plates slide past each other, which seismologists call “creep,” strain accumulates less than when plates “lock” and stress loads continue to escalate, increasing the prospects of an eventual fault rupture and earthquake.

Fialko found evidence that the southern San Andreas is mostly locked and continues to accumulate significant amounts of strain. He calculated the rate at which the fault is moving and estimated the “fault slip rate,” the pace of the plate movement at the fault, to be about an inch per year. According to Fialko, this means that during the last 300 dormant years the fault has accumulated approximately six to eight meters of slip “deficit,” which will be released in the future big earthquakes. If all inferred deficit is released in a single event, it would result in a magnitude eight earthquake, roughly the size of the 1906 San Francisco earthquake.

“In the earthquake business, the past is a key to understanding the present and by comparing ancient observations of the fault with what we have measured over the last 10 years, we can say with some certainty that the fault is approaching the end of its loading period,” said Fialko.

One unusual result that emerged from Fialko’s study is that the two sides of the fault are behaving vastly differently, with the North American plate showing flexibility in its movement patterns and the Pacific plate demonstrating more rigid characteristics, akin to a giant unbending block. Fialko says this new insight on fault structure may help seismologists further understand fault activity at the San Andreas and other faults. Future studies by Fialko and others will address these marked differences and their implications for earthquake risk.

Another surprising result concerned the San Jacinto Fault, a lesser known Southern California fault yet one of the most significant branches of the San Andreas system. Fialko’s analysis of the San Jacinto Fault, which winds through populated areas in San Bernardino, Riverside and Borrego Springs, found that it is moving at roughly twice the speed of previous estimates and thereby its propensity for earthquakes is greatly enhanced. While the San Andreas is at risk for an earthquake of magnitude eight or higher, the San Jacinto Fault has an even greater risk for a slightly smaller earthquake of magnitude seven, which still falls into the category of a major earthquake.

Fialko found that the San Andreas and San Jacinto faults account for so much of the North American and Pacific plate motions that the offshore faults must carry much less seismic risk than previously estimated. He says these offshore faults, including the Oceanside, Rose Canyon and Elsinore Faults, are moving much more slowly than anticipated, reducing the earthquake threats from these faults for cities such as San Diego.

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This is interesting, but part of me doesn't really pay attention to this news. It's common knowledge that at any moment a 9.0 could take various parts of California to school. But still, the fact that it is looking like we're on the verge of it is interesting nonetheless.

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Really this makes no difference to me. Before they told us "it could happen in 30 minutes or 30 years." now they're telling us "it could happen in 30 minutes or 30 years. But it might happen soon."

Whatever. If there's a giant earthquake, I'm prepared.

Hell, theoretically the whole city is, since they basically rebuilt half the buildings downtown so they wouldnt explode in an earthquake.

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Man, today is a really nice day.

It would be hot but there's a breeze coming off the ocean. All my windows and doors are open so the breeze is airing out my house.

Fuck you and your oceanside house today sucked. 90+ degrees I had all my fans on in my room and my shirt off and it was still boiling.

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I dont worry about earthquakes much since house has quake insurance. Now, an apocalyptic rise of zombies to feast on all the living is something that's more serious.

If earthquake insurance is anything like hurricane insurance (or any type of insurance, really), it's not going to help very much. The concept behind insurance is that a hundred people pay a little bit monthly to help out the three or four who get screwed over, and the company skims off the top for profit. But if 95 out of 100 people get earthquake'd, the company can't afford to pay them all, which is what you see going on in Louisiana.

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