Numerical Modeling of P-Waves for Shallow Subsurface Cavities Associated with Old Abandoned Coal Workings

Abstract

Subsidence is a major environmental hazard associated with shallow abandoned coal workings in the Raniganj coalfield of eastern India. Most of the old abandoned coal workings are poorly documented. There is a need to detect and quantitatively infer these workings through some inexpensive geophysical techniques. High resolution reflection seismic is one such technique that suits this problem because of its sensitivity to the presence of voids through direct reflection and scattering properties of P waves. In this study, cavity identification and location remained uncertain on the basis of 2-D stacked sections in the presence of noise. To improve interpretation, a 2-D zero-offset finite-difference model was developed to characterize the seismic signature over the cavities. The model represents a rectangular cavity associated with air-filled and water-filled conditions in a multilayered interface. A seismic migration technique is also applied to the zero-offset sections to further improve the interpretation. The numerical results show the top and bottom of the cavities clearly with their shape properly delineated for air-filled cavities. The base of water-filled galleries are detected as strong positive reflections.

Estimating location of scatterers using seismic interferometry of scattered rayleigh waves

“…These scattered waves can be used for location and characterization of scatterers. Because of this, different studies have been performed that made use of scattered body and surface waves (e.g., Snieder 1987;Herman et al 2000;Leparoux et al 2000;Campman et al 2004;Gelis et al 2005;Grandjean and Leparoux 2004;Rodríguez-Castellanos et al 2006;Campman and Riyanti 2007;Kaslilar 2007;Xia et al 2007;Mohanty 2011;Chai et al 2012;Harmankaya et al 2013;Kaslilar et al 2013).…”