SURVEY LIBRARY VELOCITY OF SOUND IN SEDIMENTS CORED FROM SOUTHERN LAKE MICHIGAN

Measurements of the velocity of sound were made on lake bottom samples obtained by gravity coring in south-ern Lake Michigan during July 1971. Measurements were made at several stations with a specially designed device that measures the travel time of acoustic waves while the sediment is fresh from the lake floor, still enclosed in a plastic liner. The measurements were necessary for the calibra-tion of high-resolution seismic reflection profiles of a va-riety of sediment types whose bed thicknesses could not be accurately measured without specific velocity measure-ments. The velocity of sound in the lake bottom water was determined to be near 1428 meters per second. The veloc-ity of sound in the sediments ranges from 1348 to 1550 me-ters per second, slower and faster than the velocity in wa-ter. The velocity clearly corresponds to sediment type. Velocities in the soft silts and clays of the Lake Michigan Formation range from 1348 to 1488 meters per second. In the relatively dense glacial-lacustrine clay of the Equality Formation the velocities range from 1360 to 1529 meters per second. The highest velocity, about 1550 meters per second, was noted in an unnamed compact glacial till unit