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Large sections of southern California are slowly rising or sinking, a groundbreaking …
Earthquake research detects movement on both sides of San Andreas fault
Land on both sides of the San Andreas fault is moving vertically by a few millimeters each year.
(David McNew/Getty Images)Researchers have observed for the first time that, along portions of the San Andreas fault, land on both sides is moving vertically by a few millimeters each year. Such motion had been theorized but never proven.
Vertical movement of tectonic plates is difficult to track compared with horizontal movement, which is much easier to predict and the cause of most earthquakes in California. GPS sensors helped the scientists study large, southern areas of the state that included the Los Angeles Basin, San Diego County and Santa Barbara, Calif.
“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,” Samuel Howell, lead author of the study, said in a statement.
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Previously, vertical movement had been difficult to detect because of groundwater levels, Howell told the Los Angeles Times. As California's large agriculture industry flushes out groundwater for irrigation, parts of the state sink.
A new study showed that large sections of southern California are slowly rising or sinking.
(Kevin Schafer/Getty Images/Minden Pictures RM)Howell said quakes along the southern San Andreas happen once every 150 years on average. The last major earthquake along the southern San Andreas fault occurred in 1857 — a 7.9 magnitude quake, according to the study.
The San Andreas fault forms the boundary between the tectonic plates for most of North America and the Pacific Ocean and sits on the infamous “Ring of Fire,” where a large number of earthquakes and volcanic eruptions occur. It is also classified as a “strike-slip” fault, meaning the plates move alongside each other horizontally.
Vertical movement is more common in “subduction zones,” where tectonic plates instead press against each other and one side is forced into the Earth's mantle over time. The Cascadia fault, which sits just north of the San Andreas and stretches into Canada, is a known active subduction zone.
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