Scientists have documented the rise and fall of part of California along the San Andreas fault.
In the new study published in the science journal Nature Geoscience, researchers reveal how their instruments detected 200-kilometre wide “lobes” of uplift and subsidence (downward motion) that move a few millimetres a year.
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“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,” said Samuel Howell, lead author of the study. “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.”
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The findings are significant as it was long believed that parts of California were rising and sinking, but it hadn’t been documented. The new research will now help scientists better monitor and map the fault line as it continues to move.
The San Andreas fault is a boundary between the Pacific Plate and the North American Plate. As these plates move against one another, they can trigger earthquakes. This fault — which stretches for 1,300 km through California and is about 20 million years old — is of particular interest to scientists as it is capable of producing a large, damaging earthquake. Seismologists anticipate another large earthquake is overdue.
The research was conducted by the University of Hawai’i at Manoa, University of Washington and the Scripps Institution of Oceanography. The research team used GPS instruments placed along part of the fault that detect both large- and small-scale movement.
According the the U.S. Geological Survey, California is second to Alaska in the number of annual earthquakes.