Rate-and-State Friction Controls the Rate of Induced Earthquakes in the Delaware Basin, Texas

Abstract:

The number of earthquakes detected in the western region of the Permian Basin, Texas, has been increasing since ~2010, and since 2017 earthquake rates have increased even faster. In February 2020, this long-lived sequence of earthquakes culminated in an M_w 5 event, the largest event in western TX since the 1995 M_w 5.7. Wastewater disposal by deep injection is suspected to be the physical mechanism driving the majority of induced earthquakes throughout the Permian Basin. To investigate this further, we assemble all available data on wastewater disposal volumes within ~25 km of the M_w 5 mainshock and use them to relate changes in Coulomb stress applied to the inferred fault planes to changes in seismicity rate through rate-and-state friction (i.e., Dieterich, 1994). Using reasonable physical parameters, this model shows very good agreement with both the onset and evolution of the observed seismicity leading up to the M_w 5. In light of previous findings, we interpret this as compelling evidence that the rapid acceleration of earthquake nucleation in the few years prior to the M_w 5 was driven by wastewater disposal activities that increased Coulomb stresses in the region. As a consequence of the relatively low background stressing rate and the inferred frictional properties of faults in the region, this model forecasts elevated seismicity rates for many years to come; this finding is relatively insensitive to the hypothetical injection-reduction (mitigation) scenarios we tested. Finally, because our seismicity rate model cannot account for earthquake-to-earthquake interactions, further investigations are needed to understand the various factors responsible for reactivating the fault hosting the M_w 5 event.