Frequency Dependence of Elastic Wave Attenuation in Rock Samples during Fracture

Abstract

The frequency dependence of elastic wave attenuation during progressing rock fracturing is examined in laboratory experiments with ultrasonic monitoring of sandstone and granite samples. The attenuation is calculated from spectral ratios, which allows quantitative assessment of the attenuation dynamics during the experiments. Dedicated experiments are conducted to quantify the influence of sensor–sample coupling on the sounding signal. The effects of porosity, microfracturing, and fluid saturation on attenuation are investigated across a range of frequencies. Experimental results demonstrate that attenuation is sensitive to changes in both the stress state of the rock material during mechanical testing and changes in material properties induced by fracture development. The closure of pores and microfractures at early stages of mechanical loading reduces the attenuation, whereas intense fracture formation upon reaching a critical load causes attenuation to increase sharply, particularly at high frequencies. The applicability of power-law approximation for describing frequency dependence of attenuation in porous rocks is confirmed. The systematic variation of the approximation parameters at different stages of loading and fracture of the material highlights the potential of frequency dependence of attenuation as a diagnostic tool for monitoring processes leading to rock failure.