Vibration of natural rock arches and towers excited by helicopter-sourced infrasound

[摘要] Helicopters emit high-power infrasound in a frequency range thatcan coincide with the natural frequencies of rock landforms. While a singleprevious study demonstrated that close-proximity helicopter flight was ableto excite potentially damaging vibration of rock pinnacles, the effects on abroader range of landforms remain unknown. We performed a series ofcontrolled flights at seven sandstone arches and towers in Utah, USA,recording their vibration response to helicopter-sourced infrasound. Wefound that landform vibration velocities increased by a factor of up to 1000during close-proximity helicopter flight as compared to ambient conditionsimmediately prior and that precise spectral alignment between infrasoundand landform natural frequencies is required to excite resonance. We defineadmittance as the ratio of vibration velocity to infrasound pressure andrecorded values of up to 0.11 mm s −1  Pa −1 . While our resultsdemonstrate a strong vibration response, the measured velocities are lowerthan likely instantaneously damaging values. Our results serve as a basisfor predicting unfavorable degradation of culturally significant rocklandforms due to regular helicopter overflights.

[学科分类] 土壤学