In November 1980, a high-resolution seismic survey was conducted at the Hanna underground coal gasification area. The objectives of the survey were to locate and characterize the burn cavity at the Hanna II, phases 2 and 3 gasification site, and to locate shallow geologic faults. Seismic data acquisition and processing parameters were specifically designed to emphasize reflections at the shallow, 200 to 500 ft (60 to 160 m) depths. A three-dimensional grid of data was obtained over the burn zone. Processing included time-varying filters, deconvolution, trace compositing, and two-dimensional, areal stacking of the data in order to identify anomalies. An anomaly was clearly discernible resulting from the rubble-collapse void in the burn zone. The anomaly was studied in deta l and compared to synthetic models. The fault system was found to be a graben complex with antithetic faults. The fault system contains folded beds. A series of anomalies was discovered on the northeast end of one of the seismic lines. These reflections have been identified as underground mine adits from the old Hanna No. 1 coal mine.

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