Tracking induced seismicity in the Fort Worth Basin; a summary of the 2008-2018 North Texas Earthquake Study catalog

Since 2008, earthquake sequences within the Fort Worth basin (FWB), north Texas, have been linked to wastewater disposal activities related to unconventional shale-gas production. The North Texas Earthquake Study (NTXES) catalog (2008-2018), described and included herein, uses a combination of local and regional seismic networks to track significant seismic sequences in the basin. The FWB earthquakes occur along discrete faults that are relatively far apart (>30 km), allowing for more detailed study of individual sequence development. The three largest sequences (magnitude 3.6+) are monitored by local seismic networks (<15 km epicentral distances), whereas basinwide seismicity outside these three sequences is monitored using regional distance stations. A regional 1D velocity model for the FWB reflects basinwide well log, receiver function, and regional crustal structure studies and is modified for the larger individual earthquake sequences using local well-log and geology data. Here, we present an m (sub b_Lg) relationship appropriate for Texas and a basin-specific M (sub L) relationship, both calculated using attenuation curves developed with the NTXES catalog. Analysis of the catalog reveals that the earthquakes generally occur within the Precambrian basement formation along steeply dipping normal faults, and although overall seismicity rates have decreased since 2016, new faults have become active. Between 2006 and 2018, more than 2 billion barrels of fluids were injected into the Ellenburger formation within the FWB. We observe strong spatial and temporal correlations between the earthquake locations and wastewater disposal well locations and injection volumes, implying that fluid injection activities may be the main driving force of seismicity in the basin. In addition, we observe seismicity occurring at greater distances from injection wells (>10 km) over time, implying that far-field stress changes associated with fluid injection activities may be an important component to understanding the seismic hazard of induced seismicity sequences.