2004-05-28_GENERAL DOCUMENTS - M1999002

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3.1.2 Defining Velocity Model The seismic records were dominated by waves traveling along the steel pipes (velocity 16,700 ft/s) and the tube waves in water (velocity 4750 ft/s), as shown in figures A6 and A7. No seismic velocity numbers measured in the ground were available for the site. Therefore, the average velocity values for the mine zone were derived from Young's modulus = 1,402,000 psi, and Poisson's ratio = 0.41, which were provided by the Agapito and Associates. The resulting velocity numbers of 10,500 ft/s for P-waves and 4,100 ft/s for S-waves were used to generate two average velocity models within the orthogonal block selected for seismic data processing. The square base of the block was 400 by 400 feet, and the vertical dimension was set in the depth range from 2,190 to 1,240 feet. The block was centered with respect to We1128-21. 3.2 Data Processing Seismic data for each set of sources and receivers were processed separately, once for S- wave reflections using an S-wave velocity model, and once for P-wave reflections using a P-wave velocity model. The results for all three sets and for both wave modes were normalized and merged together to produce the final image of the surveyed site. Section 4.0 Data Interpretation Figure A8 shows the tomographic slice through the merged image and the contour anomalies in the parallel projection. Figure A9 shows the contour images alone. The blue colors typically delineate weaker/fractured zones or open caverns. The depths of blue anomalies in the two images appear to correspond well with the nahcolite deposits in the geological profile shown in figure A1. This correlation adds to the credibility of the imaged horizontal extent of possible solution caverns. In particular, a significantly larger extent of the lowest anomaly is in accord with the horizontal extent of extraction expected to be inversely proportional to the brine condensation that increases with the flow upward. The blue `profile' marked with dashed line around the anomalies could be indicative of a possible shear failure above some of the caverns. Section 5.0 Conclusions 1. The TRT test survey provided images of the underground features within the solution mining zone that are in accord with geological data. 2. The configuration and horizontal dimensions of imaged reflective anomalies are in accord with the most likely development and horizontal extent of solution- mining-related caverns and structural changes. 3. The horizontal dimensions of imaged anomalies represent the average values as the array of sources and receivers placed in a single vertical well lacks the directional resolution in horizontal planes.