Induced seismicity in the Raton Basin from 2016–2020

Abstract:

For almost the past two decades, increased wastewater injection from coal-bed methane production has coincided with increased seismicity in the Raton Basin located in northeastern New Mexico and southeastern Colorado. We investigate the last four years of seismicity using an ongoing 8-station broadband array with an average station spacing of ~30 km and a 96-node short period array recording for one month (Summer 2018) with <3 km station spacing. Two earthquake catalogs were generated. The first one contains >5000 earthquakes identified with a traditional short-term average to long-term average detector with an event association step and hand-picked phase arrival times. The second catalog includes >32,000 earthquakes detected using a machine-learning based phase picker (PhaseNet) and an automated method for event association and preliminary hypocenter estimation (REAL). For both catalogs, earthquakes were relocated using hierarchical clustering based on waveform similarity and differential travel times from cross-correlation (GrowClust). Previous seismic studies of the Raton Basin using significantly less dense arrays (>70 km station spacing) revealed three dominant N-S striking faults extending ~10–25 km in length located in the central part of the basin. Our integrated catalog locations and full moment tensor inversions for earthquakes M_w>2.5 collectively reveal dozens of short (<3 km) fault segments with a range of strikes from ~NE-SW to NW-SE. The majority of earthquakes occur within basement rock with depths between 2–6 km below sea level. We find two of the three previously identified regions of seismicity are composed of multiple short dense earthquake clusters some of which have rotated strikes with respect to the orientation of the composite cluster. Limited seismicity occurs in the final previously identified region which hosted the largest recent earthquake (M_w 5.3 in 2011). Several newly identified earthquake clusters occur near the northeastern edge of the basin (>30 km from the previously identified composite clusters). This northeastern group exhibits increasing seismic activity since 2016 and suggests that the footprint of seismicity induced by wastewater injection in the Raton Basin may be expanding.