Improved understanding of the seismic radiation generated by explosions in low coupling (damaged/fractured) media is extremely important for nuclear monitoring, as source coupling affects both detection and yield estimation. Some empirical evidence for seismic amplitude reductions have been noted for nuclear and chemical explosions detonated in fractured media (e.g., Sokolova, 2008). In order to define the physical mechanism responsible for the amplitude reduction and quantify the degree of the amplitude reduction in fractured rocks, we conducted Phase I of a multi‐phase explosion experiment in central New Hampshire. The experiment involved conducting explosions of various yields, including a 46.3‐kg explosion in the damage/fracture zone of a 231.8‐kg explosion and a 46.8‐kg shot in nearby undamaged rock.
Our analysis confirms a seismic amplitude reduction in damaged rock by a factor of 2–3. The amplitude differences are frequency dependent, with the explosion in the undamaged rock having a higher corner frequency than the explosion in the damaged zone. The overshoot parameter for the virgin/undamaged rock shots is higher than that for the damaged rock shot. We found that the corner frequency correlates with the overshoot parameter, and only weakly correlates with the yield. Additional experiments will be conducted in the near future to further quantify seismic‐wave characteristics as a function of the depth of burial, type of explosives, and other factors.
Online Material: Movies of explosions.