Vibration of natural rock arches and towers excited by helicopter-sourced infrasound
<p>Helicopters emit high-power infrasound in a frequency range that can coincide with the natural frequencies of rock landforms. While a single previous study demonstrated that close-proximity helicopter flight was able to excite potentially damaging vibration of rock pinnacles, the effects on...
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| Autores principales: | , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
Copernicus Publications
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/c22e1ac3a95a4d60b3666eb5bdb31344 |
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| Sumario: | <p>Helicopters emit high-power infrasound in a frequency range that
can coincide with the natural frequencies of rock landforms. While a single
previous study demonstrated that close-proximity helicopter flight was able
to excite potentially damaging vibration of rock pinnacles, the effects on a
broader range of landforms remain unknown. We performed a series of
controlled flights at seven sandstone arches and towers in Utah, USA,
recording their vibration response to helicopter-sourced infrasound. We
found that landform vibration velocities increased by a factor of up to 1000
during close-proximity helicopter flight as compared to ambient conditions
immediately prior and that precise spectral alignment between infrasound
and landform natural frequencies is required to excite resonance. We define
admittance as the ratio of vibration velocity to infrasound pressure and
recorded values of up to 0.11 mm s<span class="inline-formula"><sup>−1</sup></span> Pa<span class="inline-formula"><sup>−1</sup></span>. While our results
demonstrate a strong vibration response, the measured velocities are lower
than likely instantaneously damaging values. Our results serve as a basis
for predicting unfavorable degradation of culturally significant rock
landforms due to regular helicopter overflights.</p> |
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