Cross-Hole Seismic Tomography Study in Basaltic Rock

The cross-hole seismic tomography (CST) is a semi-intrusive method for structural/geotechnical/geological investigations in between two boreholes. The seismic waves generated by the source at different positions in one borehole are received by the array of receivers in another borehole, and signal is recorded by the high-frequency seismograph. The output of the CST method is a high-resolution image of the seismic velocity distribution between the boreholes. The CST study was carried out in two boreholes in the basaltic terrain up to a depth of 90 m and located 27 m apart. The array of receivers is fixed at 1 m spacing, and source was also placed at 1 m spacing vertically in the borehole. The objective was to know the P- and S-wave velocity distribution and presence of anomalies and to determine the dynamic rock mass properties (Poisson’s ratio and Young’s modulus). P- and S-wave velocities range from 4100 to 5000 m/s and 2000 to 2900 m/s, respectively. The paper presents details of CST methodology, geotechnical interpretation of high-resolution tomogram, and dynamic properties.