Ocean Bottom Gravity Meter

An ocean bottom gravity meter was designed and built to measure gravity at the ocean floor in order to detect up-and-down motions of the sea bottom and density changes in the oceanic crust corresponding to changes preceding a strong earthquake. The gravity sensor is a vibrating-string gravimeter based on the TSSG surface ship gravity meter. The gravity meter was consisted of an underwater part, a land station and an underwater cable. Measured data was transmitted continuously from the sea bottom to the land by means of an optical fiber cable which contains six optical fibers embedded in a grooved aluminum line. The test of the gravity meter was carried out on the bottom in the shallow water at a depth of about 30 meters. The gravity meter had operated in a good condition and measured gravity changes for more than two months.