Magnitude-based discrimination of man-made seismic events from naturally occurring earthquakes in Utah, USA

We investigate using the difference between local (M-L) and coda/duration (M-C) magnitude to discriminate man-made seismic events from naturally occurring tectonic earthquakes in and around Utah. For 6846 well-located earthquakes in the Utah region, we find that M-L-M-C is on average 0.44 magnitude units smaller for mining-induced seismicity (MIS) than for tectonic seismicity (TS). Our interpretation of this observation is that MIS occurs within near-surface low-velocity layers that act as a waveguide and preferentially increase coda duration relative to peak amplitude, while the vast majority of TS occurs beneath the near-surface waveguide. A second data set of 3723 confirmed or probable explosions in the Utah region also has significantly lower M-L-M-C values than TS, likely for the same reason as the MIS. These observations suggest that M-L-M-C is useful as a depth indicator and could discriminate small explosions and mining-induced earthquakes from deeper, naturally occurring earthquakes at local-to-regional distances.