As if the drought couldn't get any worse, geologists now think that changes in groundwater could be destabilizing the infamous San Andreas Fault. The new research presents what one may call, as the SF Public Press put it, "a grand unified theory of California problems: drought, water use, and earthquake risk." Translation: sucks to be you, California.
The study published this week in Nature started with asking why the Sierra Nevadas and Coastal Ranges have been rising by 1 to 3 millimeters every year. The answer seems to lie with groundwater, which is being increasingly depleted by agriculture in the Central Valley. Katherine Bourzac explains in the San Francisco Public Press:
To picture how water can play a role in this, think of the Earth's surface like a flexible sheet of plywood with a weight on it. "The upper portion of the earth is elastic, and the ground water is weighing it down like a brick," [the study's author Colin] Amos said. Removing groundwater is like lifting that brick. The earth's crust literally flexes up. As it moves up, it pushes up the Sierra Nevadas and the Coastal Ranges.
If the effect of groundwater depletion is big enough to move mountains, then it's also big enough to affect the San Andreas Fault, where only friction keeps two tectonic plates from slipping. Change the balance of forces on these faults, and you could be feeling an earthquake.
Amos and his team found that seasonal fluctuations in groundwater caused seasonal patterns of tiny quakes. Long-term depletion of groundwater has led to the continued rise of the Sierra Nevadas and Coastal Ranges, and it could be further destabilizing the San Andreas fault in the long-term, too. The rise of agriculture in California's Central Valley has driven this reduction in groundwater. The current drought has made it only worse. We now have a fuller picture of earthquakes in California, and it's not a pretty picture. [Nature via San Francisco Public Press]
Top image: The cracked bed of a reservoir in California. AP Photo/Marcio Jose Sanchez