Long-period water-wave measurements for the MILROW and CANNIKIN nuclear explosions

Abstract

Three types of high-resolution, ocean-bottom instruments were installed to monitor predicted low-amplitude, long-period water-wave activity associated with the MILROW and CANNIKIN underground nuclear explosions at Amchitka Island, Alaska. These instruments provided data on: (a) permanent vertical oceanfloor displacements in the expected generation region up to 15 km from surface zero, (b) wave propagation in deep water at ranges beyond 15 km, and (c) shoaling and nearshore effects at Amchitka and several other islands in the Aleutian chain. For MILROW, permanent undersea displacements and propagating waves were unobservable above the natural long-period background level of ∼ 1 cm (rms). For CANNIKIN, areas of ocean-floor uplift were observed in both the Bering Sea and in the Pacific Ocean within 6 km of ground zero. Vertical displacements averaged several centimeters, with a more localized region showing 56 cm of uplift; these values seem to be consistent with results of land surveys on the island. Resonant oscillations having amplitudes up to 10 cm were induced in two bays on the Bering Sea coastline. The absence of observable tsunami-like waves at deep water instruments and at more distant islands suggests that much of the waterwave energy generated near CANNIKIN was constrained in edge-wave modes along the shallow offshore slope along the Bering Sea coastline of Amchitka, and was dissipated there.