Hammond and Blewitt Paper in Nature

Water in Southern California’s Great Valley flows along the California Aqueduct. Credit: Bill Hammond

Bill Hammond and Geoff Blewitt (both of Nevada Bureau of Mines and Geology/Nevada Geodetic Laboratory and Nevada Seismological Laboratory in the College of Science at UNR) are co-authors on this paper released online May 14, 2014 in the journal Nature.

Uplift and seismicity driven by groundwater depletion in central California
 By Colin B. Amos, Pascal Audet, William C. Hammond, Roland Bürgmann, Ingrid A. Johanson, and Geoffrey Blewitt

Nature (2014) doi: 10.1038/nature13275

Abstract: “Groundwater use in California’s San Joaquin Valley exceeds replenishment of the aquifer, leading to substantial diminution of this resource [references 1-4] and rapid subsidence of the valley floor [reference 5]. 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 [reference 3]. 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 [reference 6] 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 [references 7-10] is partly a consequence of human-caused groundwater depletion.”

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