Groundwater depletion leading to more earthquakes along San Andreas fault

A GPS station in the Sierra Nevada.

UNAVCO

Poets and songwriters sometimes pledge to move mountains for their beloved to prove their devotion. If any of them also farmed California’s San Joaquin Valley, they may have actually followed through on their promise. What’s more, they may have helped affect earthquakes along the San Andreas Fault while they were at it.

The dry but agriculturally productive San Joaquin Valley is a poster child for groundwater depletion. As groundwater levels have dropped, so has the ground surface. Groundwater between grains of sediment actually provides pressure that counteracts some of the overlying weight. Remove the water, and the sediment will compact, lowering the elevation of the surface. Between 1926 and 1970, the land surface in the valley subsided by as much as 30 feet.

But that’s not the only impact of drawing down groundwater levels. A new study led by Western Washington University’s Colin Amos focuses on the solid rock beneath all that sediment to see how it is responding to being relieved of the burden of that huge weight of water.