Seismic Modeling and Imaging for Detection of Clandestine Tunnels

Covert subterranean tunnels have especially been used for drug smuggling and illegal trading across country boarders such as the United States – Mexico, Egypt – Israel and so on over the years. Conventional border security measures and intel activities of border security agencies remain insufficient in stopping these illegal underground passageways. During the 2016 U.S. presidential election, arguments were particularly focused on constructing a wall that contains sensors to locate possible existing and future clandestine tunnels between the U.S. and Mexico. The reliability of a specific scientific method that can detect tunnel locations accurately has not been established yet. Among many proposed methods, seismic method is a promising technique for imaging those tunnels, despite its many potential drawbacks, such as low signal-to-noise ratio (S/N), scattering, absorption, and heterogeneity of complex subsurface structures. Instead, by assigning proper parameters into numerical modeling and projecting, the modeled results derived from these forward numerical model examples may allow us to investigate the seismic detection capability under optimal conditions and various data acquisition geometries. The experience acquired from the numerical modeling and imaging may lead us to locate the clandestine tunnels under realistic conditions. In our modeling, we use the elastic full-wave finite-element method to simulate seismic wave interaction with subsurface tunnels. We test different frequencies and observational geometries including surface and borehole sources and receivers. We then used the modeled seismic data to implement the Kirchhoff migration. We have investigated various types of soils and boundary conditions. The modeling and imaging can help us define the optimal seismic data acquisition scheme for detecting subsurface voids and tunnels.