Seismo-acoustic coupling occurs when seismic wave propagation creates air-borne acoustic signals. Research is ongoing to determine methods to distinguish between sound due to seismo-acoustic coupling and purely air-borne transmission. In a field experiment, we detonated 17 in. balloons filled with a stoichiometric oxy-acetylene mix placed both on and in the ground. We attempted to isolate ground-radiated waves by constructing a portable soundproof box to deaden air-borne sound wave. The box was constructed from mass-loaded vinyl, soundproofing composite board, liquid nails, and Green Glue. This design incorporated soundproofing through decoupling, absorption, and insulation techniques. Signals observed from a microphone placed in the box are compared with those obtained on microphones outside the box at various heights. The initial blast wave was not evident inside the box. However, the loudest sound measured in the box matches a subsequent portion of signals on microphones near the ground. Testing in a reverberation chamber is done to measure the frequency response in the transmission loss through the box. These results could suggest a viable technique for isolating ground-borne acoustic waves, which could be useful in experiments where calculating the coupling effect is impractical.
Fundamental aspects of volcano-acoustic wave propagation and source effects, such as seismo-acoustic coupling, can be explored with field-scale experiments. Buried explosives are often used for these tests but require special permission and personnel. As an alternative, we explored using an environmentally friendly source of high-amplitude noise: balloons filled with a stoichiometric oxy-acetylene mix detonated with an electric match. A field-scale experiment was conducted to test the efficacy of exploding oxy-acetylene balloons to generate infrasound and modest seismic vibrations. In prior studies with these exploding balloons, the balloons were positioned above the ground to test nonlinear propagation theory [Young et al., J. Acoust. Soc. Am. 138, EL305–EL310 (2015)] and quantify Mach Stem formation [Leete et al., J. Acoust. Soc. Am. 138, EL522–EL527 (2015)]. In the present experiment, the balloons were placed on the ground in “craters.” Specifically, 17 in. oxy-acetylene balloons were exploded in three different “crater” shapes and while sitting on the ground as a control. The explosions were recorded at 100-160 m on colocated infrasound sensors, and broadband seismometers microphones at different heights. The 17 in. oxy-acetylene balloons produce significant infrasound with peak levels at 100 m of 5-13 Pa depending on type of “crater.”
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