A Model Experiment on Seismic Wave Scattering in Inhomogeneous Media by Means of Laser Doppler Vibrometer

Abstract

To study seismic wave propagation in the Earth's interior, a number of laboratory physical model experiments have been conducted so far. However, most of the previous experiments could provide only qualitative results because no effective tools have been available for detecting actual elastic vibrations of solid surface. Recently, a laser Doppler vibrometer (LDV) has been used as an elastic wave transducer. The absolute particle velocity value at solid surface can be obtained directly from the Doppler shift of the He-Ne laser. LDV provides exact waveforms in a very small area with a diameter of 50 microns. Taking the advantages of LDV, we can experimentally study seismic wave propagation in random heterogeneous media by using laboratory physical models. We can reveal effects of random heterogeneity on seismic wave propagation by analyzing the waveform data obtained for model materials whose characteristics are well known. In this review, we first describe about physical model experiments by using LDV, and then present examples of elastic wave field in random heterogeneous media revealed by LDV. As one of quantitative studies of elastic waves in heterogeneous media, we present relationship between travel time fluctuations of P wave and characteristic scale lengths of heterogeneity. We further dsicuss about applications of physical model experiments in seismology and geophysical explorations.