Seismo-acoustic ground coupling: Wave types, transfer efficiency, and near-surface structure
<p>Pressure perturbations such as e.g. impulsive acoustic waves can couple into solid earth through the long-known phenomenom of seismo-acoustic coupling. Yet, the associated mechanisms are not always clear. Most studies investigate seismo-acoustic through low-frequency and high amplitude signals generated by e.g. natural or man-made explosions.</p><p>We conducted a small-scale field experiment with firecrackers as acoustic sources and hundred 3-component nodal geophones as receivers in a 20m diameter ring layout, some of them co-located with seismically decoupled Hyperion IFS-5111 infrasound sensors. This allowed us to investigate seismo-acousting coupling for higher frequencies and very small (meter scale) offsets.</p><p>The large receiver density enabled us to observe and distinguish different wave types induced by acoustic sources, including direct air waves, air-coupled Rayleigh waves, and possibly slow Biot waves. Having co-located seismic and pressure sensors additionally allowed us to investigate the coupling efficiency, which is in the order of 10<sup>-7</sup> and thus similar to many of the low-frequency and large-offset studies. Furthermore, we can deduct soil properties such as rigidity, bulk modulus, and density from the co-located sensors, and efficiently infer near-surface (soil) properties using cheap acoustic sources.</p>