Acoustic Wave Generation by Finite Surface Motions Simulated by Full 3-D Finite-Difference Method

Abstract:

Acoustic wavefields excited by ground motions are often treated by a simple point source. However, if the extent of the source is comparable with or greater than the associated acoustic wavelengths, a simple point source approximation may not be valid to represent the finite-extent ground motions. Such finite surface motions are often dealt with the Rayleigh integral method to model acoustic wave generation, but the oversimplified assumptions of a homogeneous medium and planar surface for wave propagation restrict its applicability. In practice, heterogeneous atmospheres and non-planar surface topography in the source region can have great impact on sound generation and propagation. In this study, we investigate the use of a full 3-D finite-difference method to simulate acoustic wave generation and propagation by a non-compact source. Vertical ground motions over the finite extent of epicentral area are represented by distributed point sources on non-planar surfaces, and acoustic wave propagation is simulated in realistic atmospheres with temperature, pressure, and wind profiles. This method allows for predicting how the non-spherical acoustic wavefield near the source propagates to local and regional distances in the atmosphere. We evaluated this method by the ground truth data obtained by the Source Physics Experiment (SPE). SPE consists of a series of underground chemical explosions and provides a unique dataset including direct measurements of epicentral ground motions and local acoustic pressure recording.