Source Parameters of Microseismic Swarm Events Induced by the Explosion at the Korobkovskoe Iron Ore Deposit

Abstract

Abstract—Despite extensive research, it is still unclear, to what extent studying the parameters of weak seismicity facilitates the interpretation of the data obtained from moderate and strong earthquakes. In this paper, we analyze seismic events initiated by mine explosions at the Korobkovskoe iron ore deposit of the Kursk Magnetic Anomaly, central East European platform. The study region is distinguished by the excess of horizontal stresses over vertical stresses and is declared as a potentially rock-burst prone massif although mining-induced rock bursts have not been observed so far. In this analysis, we use the data from a seismic network of four one-component horizontal accelerometers installed in the mine. After the detection and location of weak seismic events, their source parameters were estimated based on the Brune model spectrum approximation. It was established that the sources of the recorded seismic events are densely clustered in space in the vicinity of the closest explosion room and most sources are located within a domain with a level of the explosion-induced dynamic strains higher than 10–6. The calculated moment magnitudes vary from –2.7 to –1.4. The stress drop is estimated to range from 0.002 to 0.25 MPa with the apparent stress values varying from 0.0003 to 0.017 MPa. The scaled seismic energy \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{E}_{s}}} \\mathord{\\left/ {\\vphantom {{{{E}_{s}}} {{{M}_{0}}}}} \\right. \\kern-0em} {{{M}_{0}}}}$$\\end{document} increases from 10–8 to 10–7 J/(N m) as the seismic moment changes from 1.5 × 105 to 1.5 × 106 N m. This trend is not observed in the interval of moments from 106 to 107 N m. In our opinion, this effect can probably be associated with the decrease in the shear modulus of the rock with the increase of the event size. The calculated values of the scaled energy and rupture propagation velocity indicate that the industrial explosion has probably initiated a series of microearthquakes with low radiation efficiency.