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News

L.A. Is Sinking Thanks To The San Andreas Fault

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Scientists have studied the San Andreas Fault line extensively, but a new study published this week in Nature's Geoscience journal reveals, for the first time, a dramatically vertical portrait of the fissure. As the L.A. Times reports, the study found that much of coastal Southern California is sinking a few millimeters each year as pressure builds along the fault line, while other portions along the Central Coast and inland are sinking at a similar rate.

Vertical torquing of the land as pressure builds is absolutely expected, but this study is the first to actually map out precisely just how much the land's elevation changes yearly. Land that is colored blue in the above map is losing elevation yearly. The land that sits beneath most of the built-up L.A. area is losing elevation at a rate of 2 to 3 millimeters annually. Red areas, especially up north, are gaining elevation at a similar rate.

Research scientists used GPS data collected over a period of years to develop the data. The data was then assembled and examined, while the researchers weaned out GPS signal variances that could have been caused by something other than tectonic motion. This filtering component was the scientific breakthrough.

While the data can't really be used to help predict when the San Andreas Fault will next rupture, the information can help scientists better model the subtle complexities of the fault line itself. Inevitably, the data will be worked into future models of how the fault could rupture.

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The image just above gives a bit of perspective on what's actually going on in the fault itself. Technically titled a "Strike-Slip" fault, the San Andreas is formed by the juncture between the Pacific and North American tectonic plates. While the plates are supposed to slide past each other, and are miles below the surface, some of the land at the very surface gets stuck. Pressure builds along the points that are stuck, and causes the land to warp. This warping is what leads to the elevation changes described earlier.

We get earthquakes when the pressure releases, as the land that was previously stuck springs forward to catch up with the land miles beneath it that had been sliding past without catch.

As for the San Andreas, we're roughly due for a large earthquake sometime in the next 30 years. Earlier this year, a scientist described the San Andreas as "locked, loaded, and ready to roll."

A section of the San Andreas roughly between Indio and San Luis Obisbo hasn't ruptured in 159 years, since 1857. Extensive geologic study has found that that area of the fault line has, historically, ruptured roughly every 150 years.

Of course, 'the big one' doesn't necessarily have to occur on the San Andreas. The L.A. area is crisscrossed with dozens of fault lines that could all potentially hold devastating power. Earthquakes like the 1987 Whittier Narrows, 1994 Northridge, 1971 Sylmar and 1933 Long Beach events all occurred on faults other than the San Andreas.

Anyway, here's a lovely song about earthquakes. Just make sure you've got food and water stored up. Let Ben Gibbard's voice soothe you this Wednesday: