Seismic Surveys at Alabama Electric Cooperative’s
Damascus, Alabama Site

Richard D. Miller Jianghai Xia

Shallow seismic reflection and surface wave imaging techniques were used to delineate subsidence-prone areas at Alabama Electric Cooperative’s proposed power generation plant site near Damascus, Alabama (Figure 1). Discussions in this report will be limited to the seven seismic reflection profiles (lines 1, 2, 3, 6, 8, 9, and 10) and the thirteen shear wave velocity field cross-sections (lines 1-13) (Figure 2). A feasibility survey (Miller and Xia, 1999; Appendix C) conducted during mid-December 1998 provided conclusive evidence that shallow seismic reflection surveying had the potential at this site to delineate dissolution features tens of feet in diameter. The shear wave velocity field was shown to provide valuable information in areas that might be subsidence risks. Areas studied with “young” sinkholes directly tied to karst features consistently produced velocity inversions in proximity to large velocity gradients (generally forming a closure on contoured cross-sections). These characteristic anomalous areas were interpreted to indicate high stress associated with either roof rock loading over rubble zones or void areas or loading over roof support structures or pillars. Shot gathers and shear wave profiles from the feasibility study and stacked reflection sections and shear wave cross-sections possessed several unique features that are likely related to dissolution and subsidence. A complete preliminary discussion of the techniques, limitations, and resolution potential is included in the preliminary report (Miller and Xia, 1999).

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