INDUCED EARTHQUAKES FROM THE 2013 BINGHAM CANYON LANDSLIDES

On 11 April 2013 two massive rock avalanches, separated in time by 1.5 hours, occurred at the Bingham Canyon mine (BCM) southwest of Salt Lake City, UT. Seismic and infrasound data from the landslides were well recorded by the Utah Regional Seismic Network (URSN). Following the slides, four small (M_L ≤ 2.5) earthquakes were detected and located in the mine area using routine URSN procedures. Initial waveform cross-correlation analysis using continuous data for the month of April 2013 identified 12 additional seismic events, beginning just after the first slide and decreasing in frequency over 10 days. To better assess seismic activity near the mine both the URSN catalog and continuous data from seven nearby (< 20 km) seismic stations were analyzed. From the catalog analysis, using time of day to discriminate between earthquakes and blasts, ~20-30 earthquakes were located near the BCM since January 1981. Using waveform cross-correlation between the four earthquakes detected immediately following the landslides and 690 events in the URSN catalog located near BCM between 1 October 2012 and 8 November 2013, we found only one event on 22 January 2013 that had similar waveforms, suggesting a similar location and mechanism to the original four earthquakes. Again using the four originally detected earthquakes, plus the January 2013 event as templates, waveforms were cross-correlated against one year of continuous data beginning 1 January 2013. This analysis identified 21 (including 12 from the initial analysis) earthquakes (-0.8 < M_L < 0.5), all occurring after the landslides. Earthquakes identified by the cross-correlation analysis were located using station delays determined from ground-truth events and relative relocation. For the largest earthquake (M_L 2.5), a first-motion focal mechanism is consistent with reverse faulting on a shallowly dipping plane. This focal mechanism, as well as the timing of the majority of the earthquakes following the landslides, suggest that the earthquakes were triggered by mass unloading associated with the landslides.