As part of a large discrimination study in the western United States (Taylor et al., 1989), one earthquake was consistently classified as an explosion. The magnitude (M) 3.5 disturbance occurred on 14 May 1981 and was conspicuous in its lack of Love waves, relative lack of high frequency energy, low Lg/Pg ratio, and high moment tensor. Additionally, a moment-tensor solution by Patton and Zandt (1991) indicated that the event had a large implosional component. The event occurred in the Gentry Mountain coal mining region in the eastern Wasatch Plateau, Utah. Previous microearthquake studies in the region have demonstrated the existence of numerous small implosional events associated with the mining activities. The event is more comparable in appearance [at the broadband station at Kanab, Utah (KNB)] to the ATRISCO collapse at the Nevada Test Site (NTS) than to another double-couple event near the mining region. Using a simple source representation, we modeled the event as a tabular excavation collapse that occurred as a result of normal mining activities. This study raises the importance of having a good catalog of seismic data and information about mining activities from potential proliferant nations. This information will be critical in resolving potential false alarms that may be generated from natural mine seismicity.

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