A prototype soundproof box for isolating ground-air seismo-acoustic signals

Wave conversion and transmission at the interface between solid earth and fluid atmosphere result in air-ground and ground-air seismic and acoustic (seismo-acoustic) coupling. Seismo-acoustics is particularly relevant in observational geophysics; networks of seismic instrumentation are increasingly collocated with infrasonic pressure sensors and used in the study of a wide array of natural and anthropogenic sources. Two field experiments were carried out to isolate the ground-air converted signal from subaerial explosions. One experiment used 17” balloons filled with a stoichiometric oxy-acetylene mix placed on the ground, and another used Pentex configured at depths of 30 and 60 cm. Ground-radiated signals were isolated with a portable soundproof box constructed of mass-loaded vinyl, soundproofing composite board, liquid nails and wood glue to dampen air-borne sound waves. Random incidence insertion loss of the box was estimated and applied to signals measured outside the box. These filtered signals are compared with the signals observed from a microphone placed inside the box. Preliminary analysis shows evidence of ground radiated signals detected in the Pentex experiment, but not in the balloon experiment. These observations need confirmation with additional seismic and infrasonic signal processing methods. However, preliminary results suggest a viable technique for isolating ground-borne acoustic waves.