Tunnel detectionDetecting tunnels -- used to smuggle drugs, weapons, or people – is not easy
It seems reasonable to assume that it would be easy to use seismic waves to find tunnels dug by smugglers of drugs, weapons, or people, but this assumption is wrong; scientists are trying to get a better look at the ground around tunnels to learn why seismic data finds some tunnels but not others – and come up with a seismic detection process for the border and other areas where tunnels pose a security threat
It seems reasonable to assume that it would be easy to use seismic waves to find tunnels dug by smugglers of drugs, weapons, or people. This assumption is wrong.
Nedra Bonal of Sandia Lab’s geophysics and atmospheric sciences organization is nearing the end of a 2-year study, “Improving Shallow Tunnel Detection From Surface Seismic Methods,” aimed at getting a better look at the ground around tunnels and learning why seismic data finds some tunnels but not others.
A Sandia Lab release reports that her goal is to come up with a seismic detection process for the border and other areas where tunnels pose a security threat. Bonal’s project is funded by Sandia’s Early Career Laboratory Directed Research and Development program.
Most tunnels are found by tips from people rather than by scientific methods, Bonal said. “It would be great if we could use this to do a better job with tunnel detection, so you could scan an area and know if there is or is not a tunnel and find it and stop it,” she said.
If researchers discover what it takes to pinpoint tunnels, the next step would be to develop streamlined seismic methods that would be more practical for the Border Patrol and military.
The study arose from earlier work at Sandia detecting shallow tunnels. Bonal said she was surprised when standard refraction and reflection processing techniques Sandia used could not successfully pinpoint some tunnels.
Researchers speculate the difficulty might be what’s called a halo effect around a tunnel, in which fracturing and other geological anomalies create diffuse boundaries and hide the tunnel. The earlier, broader research produced several successes in tunnel detection, but was not focused specifically on what happens in the area where tunnel and earth meet, which might help explain why tunnels can be detected in some cases but not others.
The release notes that Bonal is looking at whether seismic waves are strongly impacted by fracturing or saturation of pores in rock or soil, as well as varying pressures at different depths. Physical processes change from shallow depths to deeper depths, but it isn’t clear just where that change occurs, she said.
In addition, the halo effect is both asymmetrical and complex.
“It depends on the geology or the soil as well as the seasonal variation, rain events and the relation to the water table,” Bonal said. “So it’s a pretty complex regime just from the hydrology standpoint.”
More research is needed, but asymmetry
