The San Andreas fault in California, perhaps the best-known geological fault in the country, is slipping quickly, according to new measurements. Could a long-anticipated major quake in The Golden State be coming soon?

The EarthScope Plate Boundary Observatory's GPS array was utilized to record the positions of rock formations around the feature, revealing that portions of the San Andreas had moved in recent years, where such travel had never before been recorded. Researchers recorded lobes of earth stretching 125 miles from side to side, sinking and rising relative to neighboring regions.

Computer models of the region have predicted movement like that seen by the GPS network, but this is the first time scientists have actually recorded the phenomenon. Statistical modeling was used to reveal the crustal movement, which can become hidden in the large amount of noise recorded by these systems.

"While the San Andreas GPS data has been publicly available for more than a decade, the vertical component of the measurements had largely been ignored in tectonic investigations because of difficulties in interpreting the noisy data. Using this technique, we were able to break down the noisy signals to isolate a simple vertical motion pattern that curiously straddled the San Andreas fault," said Samuel Howell from the University of Hawaii at Manoa.

Although this movement has never before been measured, the total shift is minute — just around 1/8 inch each year. Small changes in the height of land can occur from changes in the concentration of groundwater as well as geological motions taking place far underground.

A large network of GPS-equipped monitors and detectors are placed along the San Andreas fault in an effort to record movement of the land on a continuous basis. Geologists hope that by recording small-scale slips between rock formations, they will be able to successfully predict when a large quake is ready to strike, potentially saving lives.

On April 18, 1906, an earthquake of magnitude 7.8 struck San Francisco, taking the lives of more than 3,000 people and destroying 28,000 buildings.

This new finding is unlikely to be a precursor to the next big earthquake in California but could help researchers predict when such a catastrophic event is likely to occur. Using data collected in this study, geologists will better understand background movements in the fault, which could otherwise be confused with more significant slippage.

Detection and analysis of vertical movement of the San Andreas fault was published in the journal Nature Geoscience.

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