SPEED OF SOUND IN UNCONSOLIDATED SEDIMENTS OF BOSTON HARBOR, MASSACHUSETTS
MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF GEOLOGY AND GEOPHYSICS
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In situ measurements of the speed of sound in surficial marine sediments of Boston Harbor have been made at approximately 100 stations. A simple spark discharge of charged capacitors created the sound pulse which was received by a conventional hydrophone-amplifier-oscilloscope system. Photographs were taken of the trigger pulse as displayed on the oscilloscope screen. Detailed time records were obtained using a delay time base. First arrivals transmitted by the hydrophone appeared in the frequency range of 10 to 30 kilocyclessecond while the sound source likely emitted a broad spectrum of frequencies. Sediment samples at all stations have been obtained either by gravity coring aided by hammar blows or bucket grabs. Laboratory analyses of grain size distribution and water content have been made. Porosity was calculated assuming complete water saturation. The author attempted to correlate these various physical properties with in situ sound speed measurements and has compared his work to studies of similar sediments by other investigators. The presence of methane and hydrogen disulfide gases in the sediment limited the degree of simple correlation between sound transmission and other physical properties.