Seismic study aimed at smuggler's tunnels

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ALBUQUERQUE, Dec. 10 (UPI) -- An effort to use seismic waves to detect tunnels dug by smugglers of drugs, weapons or people is proving difficult with mixed success, U.S. researchers say.

Scientists at the Sandia National Laboratories in New Mexico have nearly completed a 2-year study with the goal of better understanding the nature of ground around tunnels and why seismic data can reveal some tunnels but misses others, a laboratory release reported.

Nedra Bonal of Sandia's geophysics and atmospheric sciences group says the aim is to develop a seismic detection process for the U.S.-Mexico border and other areas where tunnels create a security threat.

"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.

The new study began when it was discovered that standard seismic refraction and reflection techniques utilized by Sandia were unable successfully detect some tunnels.

One problem, the researchers suspected, was a so-called halo effect around a tunnel caused by fracturing and other geological anomalies that can create diffuse boundaries and hide a tunnel.

The halo effect problem is complex, they said.

"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."

But improvements have come from the new study and its efforts to sharpen seismic results, she said.

"I think there are still plenty of questions we have that need to be answered but I am very excited about the progress made so far. I have been able to detect a tunnel that I previously had not seen by other analyses."