Descr: Laboratory studies have demonstrated that frozen rock is significantly stronger than unfrozen rock. It has been hypothesized that this increased strength can significantly alter seismically estimated yield. Using rock property data from these laboratory studies, we computed synthetic seismograms and our results demonstrate clear support for the hypothesis that seismic yield estimates in frozen rock could be significantly overestimated by nearly a factor of two (2). In order to verify these results, Weston Geophysical Corporation, the Geophysical Institute at the University of Alaska, and New England Research, Inc. propose to conduct an extensive series of field experiments in Alaska. The experiments will take place at the Ft. Knox Gold Mine, located approximately 40 km north of Fairbanks, consisting of small, repeated explosions ranging from 2 to 1000 lbs of explosives. Alternate sites, such as the Red Dog mine in northwest Alaska may also be considered. The explosions ! will be detonated in granite above and below the permafrost at this mine, and will be recorded on a near-source network of 10 accelerometers and broadband velocity instruments. The mine is located near several stations of the Alaska Earthquake Information Center network and is within 100 km of AFTAC’s ILAR seismic array, thus the explosions will be recorded by an extensive regional network. The near-source data collected from the experiments will be analyzed and source functions will be modeled to fit the data. Additionally, coupling variations, in terms of different steady-state values, overshoot, roll-off, and corner frequency, for the explosions in frozen and unfrozen media will be quantified. The local and regional data will also be analyzed and the phases (e.g., Pg, Lg and Rg) will be contrasted for similar yield explosions in frozen and unfrozen rock, as well as an analysis of energy partitioning among phases. The information derived from the proposed research wi! ll provide a thorough test of the hypothesis. It will also provide im portant results for application in regions where explosions have been detonated in permafrost conditions, such as Novaya Zemlya.
