Detecting Elevated Pore Pressure due to Wastewater Injection Using Ambient Noise Monitoring

The injection of large volumes of wastewater has induced earthquakes from June 2010 to July 2011 along the Guy–Greenbrier fault in Arkansas. We measure time-dependent changes in seismic velocities underneath three temporary seismic stations, using the daily autocorrelations of ambient seismic noise. We do not find any effect of the pumping rate or volume injected in the changes in velocity. However, the induced earthquakes’ ground motions are associated with an extreme reduction in seismic velocities. The magnitude of the changes surpasses ten times the values typically found in other earthquake settings. Our full-waveform investigation suggests that the changes mainly occurred around the top of the Ozark aquifer. We interpret these extreme changes as a result of dynamic shaking in the elevated pore pressure system of the Ozark aquifer.