A New Catalog of Explosion Source Parameters in the Utah Region with Application to ML–MC‐Based Depth Discrimination at Local Distances

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Abstract

Abstract A catalog of explosion source parameters is valuable for testing methods of source classification in seismically active regions. We develop a manually reviewed catalog of explosions in the Utah region for 1 October 2012 to 30 June 2018 and use it to assess a newly proposed, magnitude‐based depth discriminant. Within the Utah region we define 26 event clusters that are primarily associated with mine blasts but also include explosions from weapons testing and disposal. The catalog refinement process consists of confirming the explosion source labels, revising the local (ML) and coda duration (MC) magnitudes, and relocating the hypocenters. The primary features used to determine source labels are waveform characteristics such as frequency content, the proximity of the preliminary epicenter to a permitted blast region, the time of day, and prior notification from mine operators. We reviewed 2199 seismic events of which 1545 are explosions, 459 are local earthquakes, and 195 are other event types. Of the reviewed events, 127 (5.8%) were reclassified with new labels. Over 74% of the reviewed explosions have both ML and MC, a sizable improvement over the unreviewed catalog (65%). The mean ML–MC value for the new explosion catalog is −0.196±0.017 (95% confidence interval) compared with a previously determined value of 0.048±0.008 for naturally occurring earthquakes in the Utah region. The shallow depths of the explosions lead to enhanced coda production, which in turn leads to anomalously large MC values. This finding confirms that ML–MC is a useful metric for discriminating explosions from deeper tectonic earthquakes in Utah. However, there is significant variation in ML–MC among the 26 explosion source regions, suggesting that ML–MC observations should be combined with other classification metrics to achieve the best performance in distinguishing explosions from earthquakes.

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