GPS OBSERVATIONS OF GROUNDWATER DRIVEN LAND SURFACE DEFORMATION IN THE CENTRAL VALLEY, CA

The extensive pumping and use of groundwater resources from the Central Valley Aquifer in California is well-known. Land subsidence has been found to occur due to changes in fluid pore pressure within the clay layers of the aquifer system. This work examines the seasonal land surface deformation observed by the SOPAC GPS network in California. The contributions of both the poroelastic response to pore pressure changes in the aquifer, as well as the crustal elastic response to the changing weight of stored terrestrial water are examined and modeled using equations for an elastic half-space presented by Tsai [2011]. Observed spatial variability of the seasonal land surface deformation in California is explained by the combination of heterogeneous poroelastic aquifer responses and elastic crustal behavior. Techniques for monitoring groundwater storage changes through observation of the land surface by GPS are explored.