Subsidence in the craters of nuclear tests at the Pacific Proving Grounds

The craters from high-yield nuclear tests at the Pacific Proving Ground are very broad and shallow in comparison with the bowl-shaped craters formed in continental rock at the Nevada Test Site (NTS) and elsewhere. Attempts to explain the difference in terms of device yield (which was much larger in the Pacific tests than at NTS) have been generally unsatisfactory. We have for the first time successfully modeled the Koa Event, a representative coral-atoll test. On the basis of plausible assumptions about the geology and about the constitutive relations for coral, we have shown that the size and shape of the Koa crater can be accounted for by subsidence and liquefaction phenomena. If future studies confirm these assumptions, it will mean that some scaling formulas based on data from the Pacific will have to be revised to avoid overestimating weapons effects in continental geology. 41 references, 10 figures, 1 table.