Seismic and Underwater Responses to Sonic Boom

Abstract

Sonic booms produced by aircraft moving at supersonic speeds apply moving loads to the earth's surface.In deep water, a moving underwater pressure field is observed to accompany the hyperbolic boom trace sweeping over the surface. The pressure waveform underwater near the surface is almost identical to that of the N wave in air, but it is rapidly smoothed and attenuated with depth, typically becoming one-tenth as large at a depth less than 0.6 of the N wavelength. Overpressures may exceed background noise pressures by factors of up to 100 at moderate depths for frequencies between 2 Hz and 100 Hz, but are less than 0.16% of pressures known to harm marine life in single exposures. Adequate quantitative theories for the underwater effect have been developed, and have been verified by scale-model experiments. On land, which is generally stratified, there are two major effects: the "static" deformation field traveling with the surface load, and air-coupled Rayleigh wavetrains following each N-wave transient. The latter have frequencies and amplitudes determined by the geology and the aircraft speed. The former has always been the largest effect in over 1000 seismograms recorded in field tests. Its amplitude is proportional to the sonic-boom overpressure. The maximum ground motion recorded was about 100 times the largest natural, steady seismic noise background, but was still less than 1% of the accepted seismic damage threshold for residential structures. Movement is greater in soft ground than on hard rock, and decreases rapidly with depth. Present quantitative theories for the major seismic effects agree reasonably well with the experiments. Seismic forerunner waves, which begin at least 7 sec before arrival of the sonic boom, might be exploited for automatic warnings to lessen the startle effect. Sonic booms probably cannot trigger earthquakes, but might possibly precipitate incipient avalanches or landslides in exceptional areas which are already stressed to within a few percent of instability. I. UNDERWATER RESPONSESFor an aircraft in flight over a plane surface, such as a smooth body of water, the intersection of the Mach cone with the interface is one branch of a hyperbola, whose vertex advances over the surface with the supersonic velocity of the aircraft. At the sides of the hyper-

Point Mugu Sea Range Marine Mammal Technical Report

“…During supersonic flights over water, little of the sonic boom energy reaching the simface propagates into the water. In addition to the review in Section 3.3 of the EIS/OEIS, Cook et al (1972) and Sparrow (1995) provide more information about sonic booms as received underwater.…”

“…Cook et al (1972) summarized air-to-water propagation of sonic booms created by supersonic aircraft. Although most energy is reflected upward when it reaches the sea surface, some penetrates into the water and creates considerable acoustic pressure near the surface.…”

Environmental Statement on the Tactical Fighter Weapons Center (TFWC) Range Complex, Nellis Air Force Base

“…Several of the fish species of concern are small minnow-type fish such as the Moapa Dace, and little is known of their sensitivities. The current data (Cook et al, 1972) suggest that sonic boom pressures can be expected to exceed the ambient noise pressures, at least momentarily, by up to 50 db from the surface down to depths of a few hundred feet, between frequencies of 0.5 to a few hundred hertz. Fish in shallow streams will very likely sense levels, but the consequences cannot be determined at the present time for past, present, or future exposures.…”

“…Cook, et al, (1972) suggest that even when overpressures exceed background noise pressure by a factor of 100, it is still much less than pressures known to harm marine life in single exposures. However, overpressure data relating to fish living in shallow streams, such as those in the Pluvial White River Drainage, are needed before any effect, or lack of it, can be documented.…”

Acoustic-Seismic Detection of Ballistic-Missile Launches for Cooperative Early Warning of Nuclear Attack

“…It consists of a steep overpressure shock-wave, then about linear decrease to underpressure, followed by another steep increase to normal pressure. 62 For level flight, the duration is given by the length of the aircraft divided by its speed-with 15 m and above 330 m/s, below 50 ms. 63 Broadband noise principally similar to the one from a rocket exhaust is produced by subsonic jet aircraft. This is demonstrated for fighter-bomber overflights with about 200 m shortest distance in Figure 10; the signal duration, amplitude time course, and the absolute maximum amplitude are comparable at least with the afterburner on.…”