Characterization of the 2015 Dallas-Irving Earthquake Sequence

Abstract:

In January 2015, a pair of M3.6 earthquakes and numerous M3+ occurred along the border of Irving and Dallas, Texas, in a heavily populated portion of the Dallas-Fort Worth metropolitan area. The Irving-Dallas swarm occurs at the eastern edge of the Fort Worth (Barnett Shale) Basin, an active shale gas production area associated with induced earthquakes. However, the nearest injection well is over 10 km to the northwest and the only nearby production well shutdown in 2012. The cause of the current swarm remains unknown. A temporary seismic network was deployed in early January 2015 to acquire data to improve earthquake location estimates and better characterize the earthquake sequence. Twenty-four stations were deployed, including 13 short-term Texans and 2 USGS NetQuakes instruments. Here, we present high-resolution relative earthquake locations derived using waveform cross-correlation and double difference techniques using both P and S-waves. Waveform data shows a high degree of similarity for both phases throughout the sequence. The P-wave data exhibit power at frequencies ranging from 10 to 40 Hz, while the S-wave data typically exhibit power in the range of 2 to 10 Hz. Initial catalog locations (January-July, 2015) reveal a spatially concentrated sequence of over 480 events, ranging from M0.0 to M3.6, migrating along a NE-SW striking fault. The sequence migrated from southwest to northeast over 4 km in January, but has since migrated back to the southwest. Events occur between 4-8 km in depth, consistent with faulting in the Precambrian basement. Fault plane solutions and event locations suggest a ~70° SE dipping normal fault. Event locations within or near the granitic basement, a series of M3.3+ events, a fault area of ~16 km², and a NE-SW trending normal fault are consistent with the characteristics of previous North Texas earthquake sequences.