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.