An Experimental Multi-disciplinary observatory (VENUS) at the Ryukyu Trench using the Guam-Okinawa Geophysical Submarine Cable

A MultiDisciplinary Ocean Bottom Observatory (MDOBO) was installed on VENUS (Versatile Eco-monitor- ing Network by Undersea-cable System) at a depth of 2170 m on the slope of the Ryukyu Trench. In this con- text, «Eco-»refers to both economic (e.g., earthquake hazard mitigation) and ecological motivation. The first step in this instillation was to insert a telemetry/power system into the submarine coaxial cable; this system could then service the MDOBO, which consists of seven major bottom sensor packages. During August-Sep- tember 1999, using a deep-towed unit and both manned and unmanned submersibles coupled with precise ship navigation, the MDOBO system and its attendant cables were deployed over a range of distances from 80 m to 1 km from the telemetry system, with several meters allowance for navigational uncertainty in positioning. The unmanned submersible then extended the multi-conductor extension cables from the instrument units toward the telemetry system and connected them to undersea mateable connectors on a junction box installed on the submarine cable. The MDOBO collected one and half months of continuous records. Several kinds of useful data were collected after installation, including an aftershock (Ms= 6.1) of the 1999 Chi-Chi earthquake (Ms= 7.7) in Taiwan.