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Abstract

Multi-channel analysis of surface waves (MASW) was used to map bedrock topography, detect anomalies in the soil overburden, and differentiate between competent and weathered limestone in covered, karst terrain near Albany, Georgia. Surface-wave data were acquired along seven parallel lines and two perpendicular cross-lines. Two surveys using a hammer and moving van-source were conducted to image depth ranges of 4, 12, and 23 meters to address the trade-off between lateral resolution and depth penetration. A steep S-velocity gradient marked by the 350 m/s contour at depths of 9-12 meters is interpreted as the bedrock surface, in agreement with coincident borehole data. the observed range in shear-wave velocities for limestone (S-velocity: 350-700 m/s) below 10 meters is likely due to variations in fracture density, weathering, and open or in-filled dissolution features. Standard penetration tests at two locations 45 meters apart confirm variations in limestone rigidity suggested by the velocity models. At one location, a dissolution feature within highly weathered, saturated limestone (N-values: 12 and 19) at a depth of 11-13 meters correlates with low S-velocities (<350 m/s) extending to 13 meters. Borehole data from the second location shows rigid limestone (N-values: 25 and 34) at a depth of 9 meters that correlates with S-velocities between 350-400 m/s at a depth of 8-10 meters. A zone of weathered rock at depths of 12-20 meters imaged along a suspected fracture zone is consistent with borehole data and sinkhole formation at the ground surface. An anomaly associated with a burn pit at the intersection of two perpendicular profiles was resolved with MASW at two different scales. S-velocity models and distinct changes in apparent velocity across shot gathers constrain both the lateral and vertical extent of the anomaly, and borehole data verify changes in soil composition and depth (5m) to the base of the anomaly.

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/content/papers/10.3997/2214-4609-pdb.247.43
2011-04-10
2023-02-01
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http://instance.metastore.ingenta.com/content/papers/10.3997/2214-4609-pdb.247.43
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