The Unique Source Mechanism of an Explosively Induced Mine Collapse

Mining explosions and collapses, in addition to earthquakes, may trigger the future Comprehensive Test Ban Treaty (CTBT) monitoring system. Most naturally occurring mine collapses have source mechanisms similar to a closing void which might provide a physical basis to discriminate them from explosions. In this study, an explosively induced mine collapse is investigated. The collapse occurred immediately after the support pillars of an underground mine opening were destroyed by explosives. We estimated the time-dependent source moment tensor of the collapse by inverting the surface ground motion data ({lt}1200 m). The results indicate that the source mechanism of the collapse can be represented by a horizontal crack. A unique source characteristic of the induced collapse is that, unlike natural collapses, the induced collapse initiated as a tensile crack. Because of the initial expansion source mechanism, induced mine collapses may pose some difficulties to the seismic discrimination problem. On the other hand, the collapse has a more band limited source spectrum than a typical underground explosion