On October 12, 2016, the U.S. Department of Energy’s National Nuclear Security Administration (NNSA) detonated an underground conventional explosive at its Nevada National Security Site (NNSS) as part of its on-going Source Physics Experiment (SPE) research efforts. This explosion was the sixth in a series of SPE experiments (SPE-6) designed to improve the Nation’s capability to detect and characterize underground nuclear explosions and to help develop an advanced capability for the United States to monitor low-yield nuclear testing.

“The Source Physics Experiment series and NNSA’s ongoing research and development at our National Laboratories are key to strengthening our national security. These efforts advance technical solutions for treaty monitoring by the United States and its partner nations,” said Anne Harrington, NNSA Deputy Administrator for Defense Nuclear Nonproliferation.

By conducting the experiments near the location of previous underground nuclear tests, researchers are able to better compare data from conventional and nuclear explosions. This helps to improve the U.S. capability to differentiate low-yield nuclear test explosions from other seismic activity, such as mining operations and small earthquakes.

SPE-6 included chemical explosives equivalent to 2,200 kilograms of TNT detonated 31 meters underground. Researchers will collect and analyze seismic, infrasound, optical, acoustic, geospatial, and magnetic data with technologies such as high-resolution accelerometers, high-speed video, drone- and ground-based photogrammetry, as well as light detection and ranging (LIDAR) and synthetic aperture radar (SAR). Seismic data from the SPE series are shared on the Incorporated Research Institutions for Seismology website at http://www.iris.edu/hq/ for researchers around the world to analyze. 

SPE-6 marks the end of Phase I of the SPE series. These six experiments were conducted in granite or “hard” rock at different depths and explosive weights. Phase II of SPE will focus on explosions in softer, less structured rock called alluvium. These different SPE phases allow researchers to determine the generic role that geology plays in affecting seismic waves generated by underground nuclear explosions. The five explosions planned for Phase II will be conducted over the next two years. 

The SPE team is composed of researchers from the NNSS, Lawrence Livermore National Laboratory, Los Alamos National Laboratory, Sandia National Laboratories, the University of Nevada-Reno, Air Resources Laboratory, and the Desert Research Institute.


Established by Congress in 2000, NNSA is a semi-autonomous agency within the U.S. Department of Energy responsible for enhancing national security through the military application of nuclear science. NNSA maintains and enhances the safety, security, and effectiveness of the U.S. nuclear weapons stockpile without nuclear explosive testing; works to reduce global danger from weapons of mass destruction; provides the U.S. Navy with safe and effective nuclear propulsion; and responds to nuclear and radiological emergencies in the U.S. and abroad. Visit nnsa.energy.gov for more information.

Workers at the NNSS prepare to insert a canister holding explosives and diagnostic equipment into a 31-meter deep hole in preparation for the SPE-6 experiment.