Raton Basin induced seismicity is hosted by networks of short basement
faults and mimics tectonic earthquake statistics
Abstract
The Raton Basin is known as an area of injection induced seismicity for
the past two decades, but the reactivated fault zone structures and
spatiotemporal response of seismicity to evolving injection have been
poorly constrained in the past due to scarce public monitoring.
Application of a machine-learning phase picker to four years of
continuous data from a local array enables the detection and location of
~38,000 earthquakes. The events between 2016-2020 are
~2.5-6 km below sea level and range from
ML<-1 to 4.2. Most earthquakes occur within
previously identified ~N-S zones of seismicity, however
our new catalog illuminates these zones are composed of many short
faults with variable orientations. The two most active zones, the
Vermejo Park and Tercio, are potentially linked by small intermediate
faults. In total, we find ~60 short (<3 km)
basement faults with strikes from WNW to slightly east of N. Faulting
mechanisms are predominantly normal but some variability, including
reverse dip-slip and oblique-slip, is observed. The Trinidad fault zone
that hosted the 2011 Mw 5.3 earthquake is quiescent
during 2016-2020, likely in response to decreased wastewater injection
after 2012 and the shut-in of two nearby wells in 2015. Unlike some
induced seismicity regions with higher injection rates, Raton Basin
frequency-magnitude and spatiotemporal statistics are not
distinguishable from tectonic seismicity. The similarity suggests that
induced earthquakes in the Raton Basin are dominantly releasing tectonic
stress.