Insights into Temporal Evolution of Induced Earthquakes in the Southern Delaware Basin Using Calibrated Relocations from the TXAR Catalog (2009-2016)

Abstract

The Texas Seismological Network (TexNet) has enabled real-time monitoring of induced earthquakes since 2017. Before 2017, location uncertainties and temporal gaps in seismic data obscure correlations across Texas between seismicity and saltwater disposal or hydraulic fracturing. Depth biases also complicate linking anthropogenic stress changes to faults. We relocate 73 M 1.5+ earthquakes from the TXAR catalog (2009-2016) relative to the centroid of a calibrated core cluster consisting of 116 earthquakes from the TexNet catalog post-2020, in the southern Delaware basin south of the Grisham fault zone. Hypocentroidal decomposition relocation reduces spatial uncertainties of the TXAR events to <5 km and provides updated depths. The core cluster has uncertainties less than <300 m and depth constrained from near-source stations and S-P differential times. The majority of relocated TXAR events indicate the triggering of northwest-trending faults at a mean depth of 1 km below sea level, suggesting a causal connection with shallow saltwater disposal and consistency with post-2017 seismicity. Spatiotemporal patterns of pre-2017 seismicity and saltwater disposal highlight initial triggering via pore-pressure stress perturbations from nearby low-volume injections and later from southeastward pressure diffusion along permeable anisotropic conduits and fracture zones. The comparison between pre- and post-2017 seismicity indicates shallow fault reactivation through similar triggering mechanisms since 2009.