PRELIMINARY-RESULTS OF A 3-YEAR CONTINUOUS OBSERVATION BY A DEEP SEA-FLOOR OBSERVATORY IN SAGAMI-BAY, CENTRAL JAPAN

A comprehensive long-term deep seafloor observatory was deployed at th e plate boundary between the Philippine and North American plates in S agami Bay, central Japan in 1993 in order to investigate the relations among geophysical parameters associated with earthquake swarms and er uptions of submarine volcanoes that have occurred repeatedly from at l east 0.01 Ma to the present. It is also located within the habitat ran ge of the vesicomyid clam, Calyptogena soyoae, the presence of which s uggests seepage from below. The observatory, at a depth of 1174 m off Hatsushima Island, is equipped with multi-sensors, such as a seismomet er, hydrophone, heat flow temperature probes, color video cameras, a C TD and a current meter. The data and power to and from the land statio n at Hatsushima Island are sent in real time through an 8-km-long elec tro-optical cable. More than 3 years of continuous geophysical and env ironmental data on the deep seafloor were collected up to 1996. In thi s paper, we describe the system and report on significant changes in g round temperature associated with three earthquake swarms in the adjac ent area. (C) 1998 Published by Elsevier Science B.V. All rights reser ved.