On the basis of the assumptions of multilayered and homogeneous media with constant velocities and Q values, and plane seismic waves, the seismic pulse-broadening equation, &tgr;=&tgr;0+Ct/Q (C=0.5), is used to estimate the shear wave quality factor (Qs) 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 Qs is that only one-fourth to one-half wavelength of signal is needed. Results from the study show (1) Qs varies from 10 to 60 in the unconsolidated sediments studied, (2) Qs is independent of frequency in the range of 10 to 70 Hz, and equivalent to the constant(Q0) of power law attenuation (Q=Q0f&ggr;, 0<&ggr;<1.0), and (3) Qs, to the first approximation, is related to the shear wave velocities (Vs) of the unconsolidated sediments by the relationship Qs=0.08 Vs+6.99¿12.10. ¿ American Geophysical Union 1994