Stress Variations in the Delaware Basin from Shear-Wave Splitting Analysis

The northwestern Delaware basin has experienced an increase in seismicity, including one M 5.0 earthquake in 2020, correlated to hydraulic fracturing and wastewater injec-tion activities. We conduct shear-wave splitting (SWS) analysis from local earthquakes to understand the increasing and intensifying seismicity in this area. Over 840 robust SWS parameters, the fast polarization orientation and the delay time, are obtained at five Texas Seismological Network stations by analyzing seismograms of more than 4000 events from 2019 to 2021. The fast orientations from individual events vary in a broad range for all stations, indicating a complex fracture system in the upper crust, even though the averages are consistent with the local fault strikes or the maximum horizontal stress. Fast orientations with large angles from the local stress appeared after the 2020 M 5.0 earthquake, evidencing an increase of pore pressure that facilitates slips on less favorable fracture planes by the stress field. Stress change caused by this earthquake could also contribute to the increasing diversity of SWS measurements. Future data analysis and stress modeling are needed to distinguish the different mechanisms.