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Intermediate period surface waves (2-20 s) are generated by long-source-duration mining explosions. Data from a PASSCAL broadband network in China and a similar deployment in Wyoming are used in a comparative study to understand sources and shallow crustal structure in the two regions.
Typical broadband regional seismograms from long-time-duration mining explosions are illustrated in the panel below. Group velocities of fundamental mode Rayleigh waves were estimated using the Multiple Filter Analysis technique and refined with Phase Matched Filtering. These data were then used to assess the path effects in China and Wyoming. The crustal structure inverted from the fundamental mode Rayleigh wave for China is reproduced below. The paths in this example reflect the importance of the Yanshan uplift to all the paths except BJT.
The velocity models developed from intermediate period surface wave dispersion allow surface wave magnitude estimates to be made from intermediate period surface waves. Such estimates allow the investigation of mb/Ms ratios as an earthquake-explosion discriminate for smaller industrial explosions. mb and Ms values for the US and China large mining explosions (red x-marks) are superimposed on explosion measures published by Stevens and Day (1985, black dots) and Bonner et al. (2003, purple rectangles). This comparison suggests that large, long-delay mining explosions that are normally detonated may fall away from the earthquake populations. One event occurred on Aug. 1, 1996, plots in the explosion population. In-mine observations of this event indicate that it did not detonate as planned. A large portion of the blast accidentally detonated simultaneously.
This work was supported by Defense Threat Reduction Agency contract DSWA01-98-C-0176, the Air Force Research Laboratory under contract DTRA01-02-C-0003, and DOE/NNSA under cooperative agreement DF-FC52-03NA99510/A000.
Date Taken: January 29, 2009 Photographer / Contributor: Rong-Mao Zhou, Brian W. Stump, Chris T. Hayward • Southern Methodist University; Yun-Tai Chen, Zhi-Xian Yang • Institute of Geophysics, China Earthquake Administration