Lithologic controls on microfracturing from legacy underground nuclear explosions

Detection and verification of underground nuclear explosions (UNEs) can be improved with a better understanding the nature extent explosion-induced damage in rock effect this on radionuclide migration. Much previous work area has focused centimeter- to meter-scale manifestations damage, but predict permeability for migration, observations at smaller scales are needed determine deformation mechanisms. Based studies tectonic tuff, we expected that heterogeneous tuff layers would manifest differently, welded tuffs showing more fractures nonwelded bands. In comparing post-UNE samples lithologically matched pre-UNE equivalents, observed multiple lithologies through quantitative microfracture densities. We find texture (e.g., from deposition, welding, alteration, etc.) affects fracture densities, stronger units fracturing than weaker units. While see no evidence bands tuffs, do observe, as expected, much larger densities close range (<50 m) explosive source. also observe subtle increase samples, relative all depths. The interpreted UNE-induced primarily transgranular grain-boundary microfractures, intragranular being largely similar those samples. This implications models how may affect flow pathways subsurface.