Revisiting the Timpson Induced Earthquake Sequence: A System of Two Parallel Faults

Abstract

The 17 May 2012 M4.8 Timpson earthquake is the largest known earthquake in eastern Texas. It is thought to have been induced by wastewater injection from two nearby, high-volume wells. Its cataloged aftershocks form a NW-SE trend, which unlike other induced earthquakes sequences is unfavorably oriented for failure in the local stress field. To understand this, we enriched the catalog using PhaseNet, a deep-learning-based picker followed by double-difference relocation with cross-correlation-based differential traveltimes. We clustered the aftershocks based on waveform similarity. Most of the seismicity falls into two clusters, which define a detailed fault structure of two parallel subfaults that are more favorably oriented than the overall trend. We inferred from waveform similarity that the sequence initiated on the northern subfault with a M3.9 foreshock and M4.8 mainshock, then extended to the southern subfault with a M4.1 aftershock, and was finally reactivated on the northern subfault with two more M4 events.