SHEAR‐WAVE REFLECTION PROFILING FOR NEAR‐SURFACE LIGNITE EXPLORATION*

Abstract

ABSTRACTWe present the results of a shear‐wave reflection experiment and in situ measurements in opencast lignite exploration. Near‐surface coal seams have lower shear‐wave velocities (∼ 200 m/s) and lower densities than sand and clay layers. Due to strong reflection coefficients, a shear‐wave reflection survey provides a powerful tool in lignite prospecting. Due to shorter seismic wavelengths shear waves will yield a higher resolution of shallow subsurface structure than compressional waves. Low shear‐wave velocities and strong lateral velocity variations, however, require a dense data acquisition in the field. The variation of stacking velocities can exceed ± 15% within a profile length of 300 m. The different steps in processing and interpretation of results are described with actual records. The final CMP‐stack shows steep‐angle fault zones with maximum dislocations of 20 m within a coal seam.