A Study on the propagation characteristics of surface waves in a granite based on ultrasonic measurement

Kimoto, Kazushi*; Okano, Aoi*; Saito, Takayasu*; Sato, Tadanobu*; Matsui, Hiroya 

This study investigates the propagation characteristics of high frequency surface wave in a granite block by ultrasonic measurements. To this end, a surface wave field excited by a line-focus transducer is scanned finely over a rectangular aperture with a laser Doppler vibrometer. From the measured waveforms, the spatial distribution of Fourier phase is reconstructed, and the structure of the wave front system is investigated. Due to the heterogeneity of the granite, the wave fronts fluctuate spatially at a rate dependent on the ultrasonic frequency. The intensity of the fluctuation is then quantified as a local wavenumber vector. It was found as a result that the granite sample can be characterized by a random wave number whose probability density is frequency dependent, asymmetric and non-Gaussian having a finite support.