9314695 Webb Funds are provided to modify and upgrade a suite of general purpose oceanographic instruments that are used in long-term deployments on the sea floor. The Marine Physical Laboratory at Scripps Institu- tion of Oceanography maintains a number of adaptable, instruments to record seafloor seismic and other signals for intervals of many months at high data rates. Modifications will involve the development of three component, broad band sensors for obtaining long-period surface wave records from the seafloor. The short period geophones in the existing ocean bottom seismometers (OBS) are useless for surface wave studies because of poor sensitivity and high self-noise at periods longer than 10s. This limitation may be overcome by installing displacement sensors on the OBS geophones. A modified sensor is planned that is more than 50 dB quieter than the standard sensors and will be adequate to readily detect Love and Rayleigh waves. Studies of the propagation of Rayleigh and Love wave using arrays of seafloor instruments will provide important information on the structure of the oceanic mantle. The new displacement sensors will be installed in ten existing OBS's. Once upgraded, this suite of instruments will be capable of long-term deployments required of experiments such as those proposed in the Global Change RIDGE program and other individual research projects. ***
