Estimating Q Factor from Multi-mode Shallow-Seismic Surface Waves

Surface waves are widely used in delineating subsurface structures. Surface-wave phase information (phase velocity) can be used for estimating near-surface S-wave velocity, and its amplitude information (attenuation coefficient) is used for characterizing near-surface quality (Q) factor. Multi-modal phenomenon of surface waves is commonly seen in shallow seismic, however, the existence of higher modes will introduce errors in the calculated surface-wave attenuation coefficients, which further reduces the accuracy of estimated Q factors. We propose to separate surface waves of different modes, and calculate surface-wave attenuation coefficients using single mode. Two synthetic cases are presented to show that errors would be introduced in the attenuation coefficients when multi-mode surface waves and body waves exist, and can be excluded if different modes of surface waves and body waves are separated beforehand. A real-world case demonstrates the feasibility of inverting surface-wave attenuation coefficients for the estimation of Q factor with our proposed method.