Multi-channal analysis of surface waves of a transition zone in the near surface of the Inner Piedmont
Gallagher, Emily Daisy
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Multi-channel analysis of surface waves (MASW) was used to provide constraints on the transition zone in the Inner Piedmont. Dispersion of shear waves is used to derive models of S-wave velocity as a function of depth. Data were acquired along two profiles in Watershed 2: a 400-m, E-W profile recorded in 2007 using 30-Hz geophones, and a 170-m, NW-SE profile recorded in 2011 using 4.5-Hz geophones. Maximum depth of penetration was 12 m (former) and 15m (latter). Interpretations of S-velocities of material above bedrock were constrained by Well EPA6. Velocities of 200-250 m/s were interpreted as sandy saprolite. Velocities 250-400 m/s were interpreted as clay-rich saprolite. Velocities 400 - 550 m/s were interpreted as highly degraded bedrock. Velocities exceeding 600 m/s were interpreted as bedrock, based upon correlations with exposures of Athens gneiss. Shear-wave velocities within the transition zone (550 m/s) were higher than those within the saprolite.