Fine Details of Mining-Induced Seismicity at the Trail Mountain Coal Mine Using Modified Hypocentral Relocation Techniques

Abstract

Master event and double-difference techniques were used to relocate mining-induced seismicity (MIS) at the Trail Mountain Mine, a longwall coal mine in central Utah. Travel-time data were collected by Arabasz et al. (2002) using a surface seismic network with stations at elevations both above and below mine level (because of the topography) and a single in-mine station. Arabasz et al. (2002) only used surface stations above mine level to determine locations. Using this network geometry, they were only able to constrain focal depths for 321 of 1829 events. In contrast, we use all stations, creating a 3D network. Hypocentral locations are improved by implementing a master event methodology to reduce the effects of uncertainties in the velocity structure, though the resulting locations do not correspond with known structures or stratigraphy. The mismatch between the locations and geology is likely due to fracturing of the rock mass by the mining process, thereby decreasing the seismic velocity near mined-out regions. Assuming a 10% velocity decrease places the MIS in the roof of the mine. A double-difference procedure is used to mimic a timevarying velocity structure. The time-varying velocity structure results in locations that approximate the dip of the coal seam. By using all available stations and allowing for a time-varying velocity structure, we find the MIS is located immediately above the coal seam and closely follows the position of the coalface. The epicenters align with the roads along the longwall panel, where stress concentrations are expected during mining.Online Material: Animations of the progression of seismicity along the longwall panel.

Going Beyond Rate Changes as the Sole Indicator for Dynamic Triggering of Earthquakes

“…For the Utah catalog, we exclude mining induced seismicity (MIS, see Supplementary Table S4 for polygon boundaries) in central Utah. MIS is often strongly correlated with production rate 51 , and to fully understand triggering in the MIS region, one would first need a means to account for variations in rate that are the result of production efforts. In the four regional catalogs, the reported magnitudes are typically local (M L ) or duration (M d ).…”

Changes in mining‐induced seismicity before and after the 2007 Crandall Canyon Mine collapse

“…By clustering the events by waveform similarity, it is assumed that each cluster spans a short‐enough time period such that the velocity model used to locate it is not changed significantly by mining. The effects of uncertainties and changes in the assumed one‐dimensional velocity model are reduced through this preclustering process [ Boltz et al ., ].…”

“…While epicentral locations are well constrained, the depths of the detected events are more difficult to determine. This is often the case for mining‐induced seismic events [ Boltz et al ., ] and is especially true when the closest station is ~20 km away. For the double‐difference inversions performed in this study, depths are initiated at 0.6 km, very close to mine level.…”

“…The UUSS regional seismic network has been monitoring mining‐induced seismicity in Utah since 1978. Mining‐induced seismicity (MIS) is closely related in time and location to underground coal extraction and is prevalent in the active coal mines of Utah's Wasatch Plateau and Book Cliffs regions [ Arabasz et al ., ; Arabasz and Pechmann , ; Pankow et al ., ; Boltz et al ., ]. Between 2004 and 2007, UUSS located an average of 1444 mining‐induced events per year, with magnitudes ranging from M L −0.2 to M L 3.9, though mostly below M L 3.0 [ Pankow et al ., ].…”

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

“…There have been several experiments in Utah in which seismometers were temporarily deployed near active coal mines in order to obtain high-resolution MIS hypocenters. From October 2000 to April 2001, an array of 12 seismometers was installed over the Trail Mountain Mine and used to locate approximately 1900 seismic events coincident with longwall mining operations [Arabasz et al, 2005;Boltz et al, 2014]. Following the 6 August 2007 Crandall Canyon mine collapse, five seismometers were temporarily installed above and next to the mine, resulting in~1000 well-located aftershocks after application of waveform cross-correlation techniques [Kubacki et al, 2014].…”