CGPS detected hydrological and anthropogenic signals in California and Nevada from NASA REASoN project

The continuous GPS (CGPS) network data products of the NASA REASoN (Research, Education and Applications Solution Network) project combine loosely constrained daily coordinate solutions from SOPAC and JPL analysis centers to generate daily a single solution under a unified reference frame (ITRF2005) for stations in Western North America. These new solutions exhibit consistent good quality and can be used to detect subtle tectonic signals, which were buried in the noise of earlier solutions. In particular, the CGPS vertical solutions reveal mixed signals of strong hydrological and anthropogenic variations and moderate tectonic variations. Separating the vertical hydrological signals from the tectonic signals becomes a critical procedure for both tectonic and hydrological applications. The new solutions also improve the reliability of the vertical terrestrial reference frame and the error model assessment of the geodetic solutions. We discuss the vertical crustal velocity field in California and Nevada from 11.5 years (1997.0-2008.58) of daily CGPS coordinate time series. After regional filtering, the vertical velocity field displays moderate (< 3 mm/yr) background deformation and isolated strong (> 3 mm/yr, up to 15 mm/yr) deformation 'spots'. For this presentation, we study the nature of the abnormal vertical motion spots. We find that most of these strong motion spots display good agreement with the published InSAR results and with studies involving aquifer volume variations. The nature of these spots is identified as hydrological and anthropogenic signals, such as groundwater volume undulation, compaction of aquifer skeleton, magma intrusion and retreat. Thus, the GPS-derived vertical station coordinate solutions provide effective and reliable input for groundwater monitoring and management. Furthermore, the vertically detected hydrological and anthropogenic signals can be used to correct non-tectonic biases in horizontal velocity solutions.