The Unique Source Mechanism of an Explosively Induced Mine Collapse
The source characteristics of an explosively induced mine collapse were investigated with source moment tensor inversion. The results indicate that the collapse is similar to a horizontal crack. The time histories of the moment tensor estimates illustrate an initial expansion at the beginning of the source. This phenomenon and the observation that the first motions of the observed data are compressional everywhere are in conflict with the implosional nature of traditional collapse models. To explain this , we propose an induced collapse source model which includes an opening crack at the beginning of the source. Because of the initial expansion and volumetric source characteristics of the explosively induced collapses, this kind of sources may pose some difficulties to the seismic discrimination of underground nuclear explosions. On the other hand, the peaked nature of the isotropic moment rate spectrum could be a diagnostic signature of collapses. Further study on another explosively induced collapse reveals that even though the source configurations are similar, there are still variations in the source processes from collapse to collapse. Nevertheless, the initial expansive source signature is observed.
Craig Pearson, C.L. Edwards, Diane Baker, Roy Boyd, Hans Hartse, Keith Kihara and Keithe Dalrymple at Los Alamos National Laboratory participated in the data collection. Daniel St. Don and Steve Brooks at the White Pine Mine are appreciated for their cooperation. We would like to thank Diane Baker for preparing the data; Craig Pearson, Steve Taylor and Howard Patton for helpful discussions on the problem. The Seismology Group of Lawrence Livermore National Laboratory is thanked for the natural collapse data.
Experiment and Data |
Analysis Results |
Interpretation and Discussion |