Time-lapse passive seismic velocity tomography of longwall coal mines: A comparison of methods

Bumps in underground coal mines are violent events that result from a buildup of stress, usually in mines underlain and overlain by massive strata. Seismic velocity tomography can be implemented to infer stress distribution at mines and determine when a dangerous situation is developing. Three different methods were employed to compare time-lapse passive seismic tomograms at a longwall coal mine. The dataset is well sampled with a dense receiver array. Parameterization and results were compared using GeoTom, TomoDD, and SIMULPS. TomoDD and SIMULPS both allow for variable gridding and relocation of microseismic events while GeoTOM does not. All three methods produced consistent results for the data set showing clear high velocity zones in areas where abutment stress is expected and low velocity zones corresponding with gob. TomoDD proved to be the most suitable method for generating tomograms from mining-induced microseismic events because it resulted in the most consistent images and the calculated velocity distribution matched prior stress distribution measurements at the site.