Secular vertical crustal deformation field in California and Nevada regions from GPS data analysis: Hydrological and anthropogenic signals

Dong, Danan; Fang, P.; Bock, Y.; Webb, F.; Kedar, S.; Lundgren P.
Jet Propulsion Laboratory, danan.dong@jpl.nasa.gov

We have reanalyzed 13.25 years of global and regional continuous GPS (CGPS) data in the period 1997.0-2010.25 with the goal of improving the precision and accuracy of the vertical component to detect tectonic signals in the California and Nevada region. The regional data set includes daily coordinate time series from 657 stations with at least 3.0 years of data. The time series are derived from a combination of independent GPS analyses at our two institutions but with a common source of station metadata. In this paper we identify locations with non-tectonic vertical signals, which are due to primarily hydrologic and anthropogenic effects such as groundwater volume undulation, compaction of the aquifer skeleton, and magma intrusion and retreat. Modeling the vertical time series indicates that the precision of our derived vertical velocities is on the order of 1 mm/yr or less. Agreement with published InSAR analyses and aquifer volume variation data indicates also that our vertical estimates provide a valid physical measurement with an accuracy of about 1 mm/yr, which is sufficiently clean of errors and artifacts to provide effective and reliable means for groundwater monitoring and management. We show that it is important to identify and consider hydrological and anthropogenic effects when searching for and interpreting underlying tectonic signals with primarily vertical expression.