Preliminary results of a three-year continuous observation by a deep seafloor observatory in Sagami Bay, central Japan

A comprehensive long-term deep seafloor observatory was deployed at the plate boundary between the Philippine and North American plates in Sagami Bay, central Japan in 1993 in order to investigate the relations among geophysical parameters associated with earthquake swarms and eruptions of submarine volcanoes that have occurred repeatedly from at least 0.01 Ma to the present. It is also located within the habitat range of the vesicomyid clam, Calyptogena soyoae, the presence of which suggests seepage from below. The observatory, at a depth of 1174 m off Hatsushima Island, is equipped with multi-sensors, such as a seismometer, hydrophone, heat flow temperature probes, color video cameras, a CTD and a current meter. The data and power to and from the land station at Hatsushima Island are sent in real time through an 8-km-long electro-optical cable. More than 3 years of continuous geophysical and environmental data on the deep seafloor were collected up to 1996. In this paper, we describe the system and report on significant changes in ground temperature associated with three earthquake swarms in the adjacent area. (C) 1998 Published by Elsevier Science B.V. All rights reserved.