Uplift and seismicity driven by groundwater depletion in central California.
Groundwater use in California's San Joaquin Valley exceeds replenishment of the aquifer, leading to substantial diminution of this resource and rapid subsidence of the valley floor. The volume of groundwater lost over the past century and a half also represents a substantial reduction in mass and a large-scale unburdening of the lithosphere, with significant but unexplored potential impacts on crustal deformation and seismicity. Here we use vertical global positioning system measurements to show that a broad zone of rock uplift of up to 1-3 mm per year surrounds the southern San Joaquin Valley. The observed uplift matches well with predicted flexure from a simple elastic model of current rates of water-storage loss, most of which is caused by groundwater depletion. The height of the adjacent central Coast Ranges and the Sierra Nevada is strongly seasonal and peaks during the dry late summer and autumn, out of phase with uplift of the valley floor during wetter months. Our results suggest that long-term and late-summer flexural uplift of the Coast Ranges reduce the effective normal stress resolved on the San Andreas Fault. This process brings the fault closer to failure, thereby providing a viable mechanism for observed seasonality in microseismicity at Parkfield and potentially affecting long-term seismicity rates for fault systems adjacent to the valley. We also infer that the observed contemporary uplift of the southern Sierra Nevada previously attributed to tectonic or mantle-derived forces is partly a consequence of human-caused groundwater depletion.
Geology Department, Western Washington University, Bellingham, Washington 98225-9080, USA.
Colin B
CB
Amos
Department of Earth Sciences, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada.
Pascal
P
Audet
Nevada Geodetic Laboratory, Nevada Bureau of Mines and Geology and Nevada Seismological Laboratory, University of Nevada, Reno, Nevada 89557, USA.
William C
WC
Hammond
1] Berkeley Seismological Laboratory, University of California, Berkeley, California 94720-4760, USA [2] Department of Earth and Planetary Science, University of California, Berkeley, California 97720-4767, USA.
Roland
R
Bürgmann
Berkeley Seismological Laboratory, University of California, Berkeley, California 94720-4760, USA.
Ingrid A
IA
Johanson
Nevada Geodetic Laboratory, Nevada Bureau of Mines and Geology and Nevada Seismological Laboratory, University of Nevada, Reno, Nevada 89557, USA.
Geoffrey
G
Blewitt
D000531:Altitude; D002140:California; D055866:Earthquakes / Q000706:statistics & numerical data*; D004548:Elasticity; D004784:Environmental Monitoring; D040362:Geographic Information Systems; D060587:Groundwater / Q000032:analysis*; D008962:Models, Theoretical; D012621:Seasons; D014881:Water Supply / Q000032:analysis / Q000706:statistics & numerical data*