Ground Truth Collection for Mining Explosions in Northern Fennoscandia and Russia

• Main Authors: Harris, D., Ringdal, F., Kremenetskaya, E., Mykkeltveit, S., Rock, D. E., Schweitzer, J., Hauk, T., Lewis, J.
• Other Authors: United States. Department of Energy.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Lawrence Livermore National Laboratory 2004
• Subjects: Mining; Underground Explosions; Wave Forms; 58 Geosciences; Ground Truth Measurements; Surface Explosions; Explosions; Khibiny; Kiruna; Kovdor; Olenegorsk; Fennoscandia; Malmberget; Northern Sweden
• Online Access: https://digital.library.unt.edu/ark:/67531/metadc1418199/

Analysis of data from our deployments and ground truth collection in northern Fennoscandia and northwestern Russia shows systematic variations in the P/S ratios of different types of explosions. The fact that this fundamental discriminant varies with firing practice is not in itself surprising - such variations probably contribute to the spread in P/S ratios normally observed for ripple-fired explosions. However, the nature of the variations is sometimes counterintuitive. Last year [Harris, 2003] we found that the P/S ratios of small compact underground explosions in mines of the Khibiny Massif are systematically lower than the P/S ratios of large ripple-fired surface explosions. We had anticipated that smaller underground shots would be more like single well-coupled explosions, thus having higher P/S ratios than large ripple-fired explosions. We now are performing a more extensive analysis of the data including compact and large ripple-fired explosions at additional mines and different types of explosions: small surface shots and large ripple-fired underground explosions. Our data are more complete as a result of an additional year of collection and allow a more complete sampling of the signals in range from the source. As of this writing we have measured Pn/Lg ratios on a larger number of explosions of three types: compact underground explosions, surface ripple-fired explosions and now underground ripple-fired explosions. We find that both types of underground explosions have systematically lower P/S ratios than surface ripple-fired shots; this effect is most pronounced in the 4-8 Hz frequency band. This result appears to be due to relatively diminished shear wave excitation by the surface explosions. We speculate that the relatively large shear phases in underground explosions may be caused by large amounts of rockfall in these events, which are designed to collapse the ceilings of tunnels. We have continued comprehensive ground truth collection at the Khibiny, Olenegorsk, Kovdor and Zapolyarnyi mines, and now have basic information on 2,052 explosions. In addition, we have more detailed information for select surface and underground ripple-fired explosions and underground compact explosions. This information ultimately may help the community understand the observed P/S ratio offsets. We also are continuing the compilation of ground truth and associated regional waveform data into a database as a prelude to further analysis. We have operated two lines of stations extending from the Khibiny Massif to the ARCES array and to the north of the ARCES array for a second year. This deployment provides the principal data for measuring the range-dependence of near-regional phase amplitudes. Data collection has been more robust in this second season of the deployment. Preparations are now underway for concluding the line deployment in late August or early September 2004 and for re-deploying the stations to the Kiruna, Malmberget and Aitik mines in northern Sweden. Like the Khibiny mines, these mines provide an interesting natural laboratory for examining questions about the phase characteristics of mining explosions since they include both underground and surface operations.