Detecting clandestine tunnels by using near-surface seismic techniques

Geophysical detection of clandestine tunnels is a complex problem that has been met with limited success. Multiple methods have been applied spanning several decades, but a reliable solution has yet to be found. This report presents shallow seismic data collected at a tunnel test site representative of geologic settings found along the southwestern U.S. border. Results demonstrate the capability of using compressional wave diffraction and surface-wave backscatter techniques to detect a purpose-built subterranean tunnel. Near-surface seismic data were also collected at multiple sites in Afghanistan to detect and locate subsurface anomalies (e.g., data collected over an escape tunnel discovered in 2011 at the Sarposa Prison in Kandahar, Afghanistan, which allowed more than 480 prisoners to escape, and data from another shallow tunnel recently discovered at an undisclosed location). The final example from Afghanistan is the first time surface-based seismic methods have detected a tunnel whose presence and location were not previously known. Seismic results directly led to the discovery of the tunnel. Interpreted tunnel locations for all examples were less than 2 m of the actual location. Seismic surface wave backscatter and body-wave diffraction methods show promise for efficient data acquisition and processing for locating purposefully hidden tunnels within unconsolidated sediments.