News Release

In California, large-scale water cycles impact quakes a little

Peer-Reviewed Publication

American Association for the Advancement of Science (AAAS)

In California, Large-scale Water Cycles Impact Quakes A Little

image: Water storage estimated from the regional GPS network throughout central and northern California shown as average water-layer thickness on a 25 km grid. The summer months experience a loss of water in the Sierra Nevada and Central Valley that is replenished in the mountains during the wet winter months as reservoirs fill and snow accumulates. In the Central Valley, water storage has been continuously decreasing due to large scale agriculture. The seasonal change in mass deforms the crust and the associated stress changes modulate regional seismicity. This material relates to a paper that appeared in the 16 June 2017, issue of <i>Science</i>, published by AAAS. The paper, by C.W. Johnson at University of California, Berkeley in Berkeley, CA, and colleagues was titled, "Seasonal water storage, stress modulation, and California seismicity." view more 

Credit: Image produced by Christopher Johnson, Berkeley Seismological Laboratory

In California, seasonal changes in large-scale water cycles modestly influence small-scale quake activity, a new study reports. The results reveal how snow, rain, snowmelt and runoff - as well as water changes related to agriculture - alter stress on regional faults, with seismic consequence, in some cases. Stress changes on or near fault lines can drive seismic activity. Such changes may be caused by myriad phenomena, including variations in fluid pore pressure. Here, Christopher Johnson and colleagues wanted to further explore a role for alternating wet and dry cycles in altering ground stress, and ultimately, in driving tremors. They compared seasonal changes in ground stress estimated from GPS data from 2006 to 2014 to California earthquake rates between these years, finding that slight changes in stress to the ground associated with water and snow accumulation, snow melt, runoff, or irrigation for agriculture did influence earthquake likelihood. In the San Andreas fault system, for example, conditions for quakes were more favorable for faulting during the dryer summer months, the authors say. Along the Eastern California Shear Zone faults to the east of the Sierra Nevada, meanwhile, quakes were more likely during the wet winter months.

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