HR: 0800h
AN: NS31B-0390    [Abstracts]
TI: Seismic refraction and GPR measurements of depth to bedrock: A case study from Randolph College, Virginia
AU: * Datta, A
EM: adatta@randolphcollege.edu
AF: Randolph College, 2500 Rivermont Avenue, Lynchburg, VA 24503, United States
AU: Pokharel, R
EM: rpokharel@randolphcollege.edu
AF: Randolph College, 2500 Rivermont Avenue, Lynchburg, VA 24503, United States
AU: Toteva, T
EM: ttoteva@randolphcollege.edu
AF: Randolph College, 2500 Rivermont Avenue, Lynchburg, VA 24503, United States
AB: Randolph College is located in Lynchburg, VA, in the eastern edge of the Blue Ridge Mountains. Lynchburg city lies in the James River Synclinorium and consists of metasedimentary and metaigneous rocks. As part of College's plan to expand, a new soccer field will be build. For that purpose, part of a hill has to be excavated. Information was needed on the depth to the bedrock at the site. We conducted a seismic refraction experiment as part of an eight week summer research program for undergraduate students. We used 24 vertical geophones, spaced at 1.5 m interval. Our recording device was a 12 channel Geometrics geode (ES 3000). The source was an 8 pound sledge hummer. Source positions were chosen to be at 5, 10, 15 and 20 m on both sides of the array. We collected data along a tree line (in two segments) and across a hockey field. The data collected from the hockey field had very low signal to noise ratio and clear refraction arrivals. The other two acquisition lines were much noisier and difficult to interpret. Our results are consistent with data from seven bore holes in close proximity to the field site. We interpreted depth to bedrock to be between 4 and 12 m. The bedrock velocities are consistent with weathered gneiss. To improve the interpretation of the tree line records, we conducted a GPR survey. The preliminary radar images are showing highly heterogeneous subsurface with multiple point reflectors.
DE: 0935 Seismic methods (3025, 7294)
DE: 7203 Body waves
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting