Multi-Channel Analysis of Surface Waves (MASW) in karst terrain
Parker, Elias Horry
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Multi-Channel Analysis of Surface Waves (MASW) has been employed in covered, karst terrain near Albany, GA to investigate potential subsidence features and fracture trends within bedrock. Surface wave data were obtained with a 24-channel recording system along seven parallel lines and two perpendicular cross-lines. Active-source (hammer) and passive-source (moving van) seismic surveys were conducted to image depth ranges of 4, 12, and 23 meters. The steep shear-wave velocity gradient at 9-10 meters is interpreted as the soil-bedrock interface, in agreement with coincident borehole data. Velocities of soil overburden range from 150-350 m/s, and velocities for fractured limestone bedrock range from 350-700 m/s. Distinct changes in apparent velocity across certain shot gathers are consistent with anomalous zones identified on the 2-D shear-wave velocity models. The low-velocity zone at the intersection of Lines A and Z is interpreted to be a potential collapse feature associated with a north-south trending fracture zone.