High-Frequency Shallow Seismic Reflection Characterization of Overburden at an Abandon Pb-Zn Mine Beneath U.S. Highway 69 in Treece, Kansas Using Seismic Imaging and Vp/Vs Ratio

摘要

Overburden at an abandoned Pb-Zn mine beneath U.S. Highway 69 in Kansas was evaluated using P- and S-wave seismic reflection methods to estimate Vp/Vs ratio. Drilling reports indicate the mine works have lateral spans of unsupported roof rock as large as ∼180 m vertically filled with up to ∼30 m of water. Past borings encountered roof rock at depths ranging between 58 -- 88 m beneath the highway right away. Historical records suggest the mined ore and the highly-fractured chert overburden at this location are part of the Mississippian Boone Fm. KDOT routinely investigates for indications of roof rock failure using elevation surveys and cross-hole seismic surveys. The project described in this thesis focuses on characterizing the fitness of the mine overburden. Two seismic reflection surveys were conducted within a 2.4 km segment of U.S. Highway 69 in extreme SE Kansas. The high-resolution P-wave allowed for interpretation of the the mine location and subsurface structure. Extensive preprocessing and data conditioning was required to accurately image the subsurface. A useful CMP stack was produced after combining detailed velocity analysis with surface consistent statics. A S-wave survey spanning the southernmost 1.6 km portion of the survey area intended to characterize the strength of the overburden and search for areas of elevated stress. Delineating reflections in both data sets allowed interpretation of the mine location. Lithology extracted from well data were roughly correlated to the seismic data to confirm the mine's signature and time depth for the data. Calculated Vp/Vs ratio were used to infer if lateral changes in rock velocities were sufficient to imply zones of elevated stress, or reduced strain. These data and analysis in this appraisal provide an excellent baseline study comparison point for future time-lapse studies designed to detect change in physical properties and seismic velocities, to determine if precautionary measures are necessary to minimize transportation hazards and public safety.