By the pulse-broadening method, seismic absorption of San Francisco Holocene Bay Mud has been determined with the use of an impulsive shear-wave source at the surface, two receivers embedded in clay (Holocene Bay Mud), and digital seismic recording. The seismic anelastic quality factor is determined from 20 measurements to be 16.0 with a random error of ±0.9. Three sources of systematic error are examined. The fractional systematic error on the anelastic quality factor is estimated to be ∼ 11%. Details of experimental arrangement and error analysis are given.