Acoustically induced seismic waves

Abstract

When an airborne acoustic wave is incident at the ground surface, energy is coupled into the ground as seismic motion. In a previous publication [Sabatier et al., J. Acoust. Soc. Am. 78, 1345–1352 (1986)] the ground surface was modeled as an air-filled poroelastic layer overlying a semi-infinite, nonporous elastic substrate. In this work, the model is extended to include calculations of the normal seismic transfer function (ratio of the normal soil particle velocity at a depth d to the acoustic pressure at the surface). Measurements of the seismic transfer function for three sites are considered and compared to the predicted values. Generally good agreement between theory and experiment is achieved by best fits assuming the soil or seismic attenuation. This is accomplished by specifying the ratio of the imaginary to real part of the measured seismic p- and s-wave speeds. The seismic transfer functions quite typically exhibit minima and maxima which are associated with the seismic layering of the ground surface. Typical layer depths are 1–2 m. An analytical expression predicting the location of these maxima is offered based on hard substrate and the experimental and theoretical comparisons are reasonable.