Source parameters and ML-Mw scaling relations for micro-earthquakes in a coal mine

Seismicity related to industrial mining activities poses a man-made (induced) seismic hazard that needs to be understood and quantified in order to ensure safe mining operations. While recording and location mining induced earthquakes and rock-burst is common practice, detailed source studies of such events are still lacking. Moreover, it is of great scientific interest if such events follow the common models and theories of earthquake sources, or if they obey different rupture physics. Therefore, we analyze earthquake sequences recorded in Lao Hutai coal mine to determine their source properties. Firstly, we simply analyze the spatial and temporal evolution of micro-earthquakes in this mine. Then we compute the source parameters (source radius R, corner frequency f0, seismic attenuation Q, energy E, stress drop △σ and apparent stress σa) and other related parameters, and analyze the relationship between them. Finally, we further compute and analyze the relationship between moment magnitude (Mw) and local magnitude(ML). The results show that the number of micro-earthquakes and the intensity of mining are positive correlation. In this particular mine, the frequency of seismic activity is more intense during the maintenance time than active mining; The ω2 model is well suited to estimate source parameters of micro-earthquakes in this coal mine; The source parameters of f0, R and E basically show a linear increase with the increase of M0, but the △σ did not show a clear increase and the σa fluctuated almost at a certain value, and the values of the f0 and △σ are obviously smaller than that of tectonic earthquake under the same magnitude; The cumulated source parameters is proportional to the number of recorded events. All events occurring in relatively close proximity to the working slope, but there is also no clear relation between the related parameters (Mw, E, △σ and σ ) and distance from the working slope to source; The ML calculated by two also methods are both linear relationship with Mw. ML1(0.03-2.00)-Mw(0.25-2.08): ML1=1.04Mw-0.17; ML2(0.45-2.23)-Mw(0.25-2.08): ML2=0.93Mw+0.28. The results help us to better understand causes and consequences of mine microseismicity.