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San Andreas Fault Affected by Irrigation

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The San Andreas Fault, a continental transform that runs roughly 810 miles through California, is being affected by irrigation practices in the area, according to a study by Geologist Colin Amos from Western Washington University.

Readings from GPS technology have shown that water levels in the San Joaquin Valley aquifer have lowered and that the mountains nearby have simultaneously risen, which has caused the San Andreas Fault to undergo changes in pressure levels. Though, Amos points out that stress changed due to lower water levels are minuscule compared to pressure-changes seen on the fault before a major earthquake.

The San Andreas Fault forms a tectonic boundary between the Pacific Plate and the North American Plate, and a study in 2006 concluded that the fault has achieved a level of stress sufficient to facilitate the next “big one”, or an earthquake greater than magnitude 7.0. In 1906, a rupture in the San Andreas Fault caused a magnitude 7.7-8.25 earthquake in San Francisco that destroyed almost 80% of the city and killed 3,000 people. The earthquake and resulting fire are regarded as one of the worst natural disasters in the history of the United States.

Here is a small documentary on San Andreas:

Amos’ study, which was published in Nature journal on Wednesday, suggests that human-related activities can cause the San Andreas Fault to unclamp, resulting in the possibility of greater future volatility. At present, seismologists have found that the San Andreas Fault produces a magnitude 6.0 earthquake approximately once every 22 years. The last occurred in the Parkfield area in 2004.

Satellite data has shown that groundwater in and near the California Central Valley has been depleted more quickly than it can be re-filled over the past decade, and Amos’ study related the water in association to the mountains in the area as being akin to a weight sitting atop a piece of bendable wood. As the water is depleted, its weight is lifted, which in turn pushes the mountains to rise from the Earth’s crust.

Amos confirmed that seasonal fluctuations in water usage have coincided with minor earthquakes around the San Andreas Fault, and that new developments for water usage and natural groundwater retention need to be implemented.

Image via Wikimedia Commons

San Andreas Fault Affected by Irrigation
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