<i>Q_s</i> estimation for unconsolidated sediments using first‐arrival <i>SH</i> wave critical refractions

Abstract

On the basis of the assumptions of multilayered and homogenous media with constant velocities and Q values, and plane seismic waves, the seismic pulse‐broadening equation, τ = τ 0 + Ct / Q ( C = 0.5), is used to estimate the shear wave quality factor ( Q s ) of unconsolidated sediments from SH wave critical refractions in the upper Mississippi embayment. The principal advantage of using the SH wave pulse‐broadening technique instead of other methods for deriving Q s is that only one‐fourth to one‐half wavelength of signal is needed. Results from the study show (1) Q s varies from 10 to 60 in the unconsolidated sediments studied, (2) Q s is independent of frequency in the range of 10 to 70 Hz, and equivalent to the constant( Q 0 ) of power law attenuation ( Q = Q 0 ƒ γ , 0 &lt; γ &lt; 1.0), and (3) Q s , to the first approximation, is related to the shear wave velocities ( V s ) of the unconsolidated sediments by the relationship Q s = 0.08 V s + 6.99 ± 12.10.