Uplift and seismicity driven by groundwater depletion in central California

• Published in: Nature (London) 2014-05, Vol.509 (7501), p.483-486
• Main Authors: Amos, Colin B., Audet, Pascal, Hammond, William C., Bürgmann, Roland, Johanson, Ingrid A., Blewitt, Geoffrey
• Format: Article
• Language: English
• Subjects: 704/2151/2809; 704/2151/508; 704/2151/562; Altitude; Aquatic resources; California; Earthquakes; Earthquakes - statistics & numerical data; Elasticity; Environment; Environmental aspects; Environmental Monitoring; Geographic Information Systems; Global positioning systems; GPS; Groundwater; Groundwater - analysis; Groundwater depletion; Humanities and Social Sciences; letter; Lithosphere; Load; Models, Theoretical; multidisciplinary; Observations; Science; Seasonal variations; Seasons; Summer; Tectonics (Geology); Time series; Uplift (Geology); Water Supply - analysis; Water Supply - statistics & numerical data; Water, Underground
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature13275

Human-caused groundwater depletion in California’s San Joaquin Valley contributes to uplift of the surrounding mountains and may affect the stability of the San Andreas Fault. Groundwater depletion driving central California uplift Through a combination of pumping, irrigation and evapotranspiration across the past 150 years, California's Central Valley has lost close to 160 km 3 of groundwater. Colin Amos and co-authors use GPS measurements of vertical ground deformation to show that a broad zone of rock uplift surrounds the San Joaquin Valley, on the southern part of the Central Valley basin. The observed uplift closely matches the flexure predicted by a simple elastic model driven by current rates of water-storage loss within the valley. The authors suggest that such seasonal uplift of the Coast Ranges reduces the effective normal stress resolved on the adjacent San Andreas Fault, which may explain some of the annual modulation of seismicity observed in this area. They also infer that observed contemporary uplift of the southern Sierra Nevada, previously attributed to tectonic and/or mantle-derived forces, is partly a consequence of human-induced groundwater depletion. Groundwater use in California’s San Joaquin Valley exceeds replenishment of the aquifer, leading to substantial diminution of this resource 1 , 2 , 3 , 4 and rapid subsidence of the valley floor 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 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 6 and p