Installation of high precision seismometer unit at the Ryukyu Trench using Guam-Okinawa geophysical submarine cable (GOGC: FOMER TPC-2 cable)

Abstract

An ocean bottom broadband seismometer (OBBS) was installed 2170 m deep on the slope of the Ryukyu Trench with other sensors through the VENUS project. Prior to the installation of the OBBS unit, the bottom telemetry system, which supplies electrical power to the instruments, telemetry system and cable was installed on the ocean bottom by a method similar to cable repair works. Since broadband seismometers are extremely fragile, it was handled with special care. The installation of the seismometer was done by use of a deep-tow system and the ROV Kaiko-10 K. In September 1999, the OBBS unit was deployed at the target position, at 80-meter from the bottom telemetry system, with several meters allowances using a deep-tow system. To install the instrument at the exact location, the mother ship of the deep-tow system was precisely navigated. The connecting cable and eight weights were also dropped from the deep-tow system. The ROV Kaiko-10 K extended the 100 m-long connecting cable from the seismometer to the junction box and connected it to the junction box. The OBBS unit collected one and half month records. Several significant earthquakes near Japan, in Taiwan and San Francisco have been observed since the installation.