The 17 May 2012 M4.8 Timpson earthquake is the largest known earthquake
in eastern Texas. It is suspected 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 complex 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.