Analysis Using Surface Wave Methods to Detect Shallow Manmade Tunnels

摘要

Multi-channel Rayleigh wave data were acquired across a 1 meter diameter spillway tunnel along three parallel traverses with surface to tunnel separations of 0.90 meters, 2.15 meters and 3.13 meters depth, respectively. These surface wave data were acquired by placing a 24- channel geophone array perpendicular to the center-line of the spillway tunnel and incrementally moving the array across the tunnel. The near source-receiver offset was 6 meters; the 4.5 Hz geophones were spaced at 0.5 meters. The tunnel locations were identified visually on velocity-filtered common-shot gathered field records. Tunnel locations were also identified by analyzing common shot- gathered records using two newly-developed automated interpretation programs: Spiking Filter Analysis and Attenuation Analysis of Rayleigh Waves (AARW). Electrical resistivity data was acquired along each traverse for comparison purposes. The engineering geophysics community has recently focused on the use of Rayleigh (surface) wave methods, such as Multichannel Analysis of Surface Waves (MASW) and Refraction Micrometer (ReMi), to detect manmade tunnels in the earth's shallow subsurface. Successful tunnel-detection applications of these methods have been reported. However, further experimental and analytical investigations are required to comprehend all significant aspects of the observed surface wave data. This case study reports on three alternate surface wave methods that were used to locate a 1 meter diameter tunnel: visually- identified diffracted/reflected surface-wave energy; the Attenuation Analysis of Rayleigh Wave (AARW); and Spiking Filter Analysis.