Characterizing tectonic and fluid production deformation signals in GPS and InSAR time-series

Bawden, Gerald W. and Sneed, Michelle
US Geological Survey, Sacramento; gbawden@usgs.gov

Large ground-surface deformations associated with anthropogenic fluid withdrawal and injection represent unique challenges for resolving the subtle surface deformation associated with slip at depth on faults and the migration of magmatic fluids. At the same time, these large signals offer new opportunities to better understand managed groundwater, hydrocarbon, and geothermal systems such that they can be characterized and modeled, and then their effects can be filtered out of tectonic/volcanic time-series measurements. Fluid production can have several influences on a geodetic time series: 1) pumping of unconfined aquifers may produce little, if any, measurable surface deformation outside of gravity changes but may have longer-term loading/unloading effects if the net fluid production is unbalanced; 2) elastic deformation, where fluid recharge/extraction is in balance, will typically result in seasonal uplift/subsidence with accompanying horizontal surface deformation orthogonal to the deformation gradient, but with little to no net permanent deformation; and 3) inelastic deformation, where the net fluid flux is out of balance, will produce permanent horizontal and vertical deformation signals in GPS and InSAR time series data. The timing of the geodetic measurements with respect to the fluid production is also a key factor in initially identifying time-series trends. This is especially true where there is quasi-steady state fluid pumping/injection that can mimic or mask tectonic/magmatic signal in GPS time series, however, the fluid-production effects can be isolated and characterized with InSAR imagery.