near surface cavities mapping using integrated geophysical techniques: case study of gadwalian dam, north pakistan

Integrated geophysical techniques have always been useful in identifying subsurface features. in the present study, three integratedgeophysical methods of ground-penetrating radar (gpr), resistivity and multi-channel analysis (masw) of surface waves have beenutilized for near surface studies and identification of subsurface cavities near the gadwalian dam. acquisition of four inline andcrossline profiles through gpr (100 mhz shielded antenna), two resistivity profiles through imaging system and six seismic refractionprofiles (masw) have been made on the selected site having potential subsurface cavities. the processing and interpretation of gprdata through different software’s exhibit variations in amplitude/diffraction patterns and several cavities have been identified in thegpr profiles. sweetness attributes applied on the gpr data set also validate the cavities and unsaturated/saturated fractures. slate bedsand cavities have also been identified on pseudosections obtained through resistivity imaging. further studies on 2d shear velocity(vs30) profiles using masw analysis for interpretation suggested that the absence of low velocity layer in shallow surface and velocityincrease with respect to depth.