SURFACE UPLIFT AND TIME-DEPENDENT SEISMIC HAZARD DUE TO FLUID-INJECTION: CASE STUDIES FROM TEXAS AND KANSAS (Invited Presentation)

Increasing seismicity in the central USA since 2009 coincides in space and time with wastewater injection. However, observations of the surface deformation and physical models to constrain the extent to which fluid migrates and to unequivocally link the seismicity and wastewater injection are scarce. Here we present examples from Texas and Kansas and show that wastewater injection causes uplift at a few mm/year, detectable using radar interferometric data. Then the evolution of crustal strain and pore pressure is constrained using the measured uplift and reported injection data through a poroelastic model. We infer that > 1 MPa increase in pore pressure in rocks with low compressibility triggers earthquakes including the M_w4.8, 17 May 2012 event, the largest earthquake recorded in east Texas. Observations that only deeper wells are associated with earthquakes, whereas large pressure change in more shallow aquifers are not, highlights the importance of hydrogeology. The frequency and magnitude of earthquakes increased, even while the injection rates declined, owing to diffusion of pore pressure from earlier periods with higher injection rates. We show that surface deformation data are useful to evaluate the evolution of pore pressure and earthquake potential in the vicinity of injection sites.