Super-deep-sea ocean bottom seismometers using ceramic spheres

Abstract

We developed a new ocean bottom seismometer (OBS) that can be deployed to the ocean floor to 9,000 m depth. We conducted the first observations using the device. Conducting seismic observations in waters deeper than 6,000 m had been difficult because the maximum applicable depth of conventional ocean bottom seismometers is 6,000 m. The Japan Trench, where the Great East Japan Earthquake occurred, is included in those areas which are difficult to observe. To increase the applicable depth, we used newly developed ceramic pressure-tight spheres for the housing in place of 17-inch glass spheres. Although the rated maximum depth is 11,000 m, its size and the weight are almost equal to those of 17-inch glass spheres. We have also refurbished acoustic transponders, radio beacons, and flashers for application to 9,000 m water depth. We have deployed six Super-deep-sea OBS (SDOBS) in the Japan Trench deeper than 6,000 m, and have succeeded in observations. Herein, we present an outline of the SDOBS.