A new approach to geophysical real-time measurements on a deep-sea door using decommissioned submarine cables

In order to better understand earthquake generation, tectonics at plate bou ndaries, and better image the Earth's deep structures, real-time geophysica l measurements in the ocean are required. We therefore attempted to use dec ommissioned submarine cables, TPC-1 and TPC-2. An OBS was successfully link ed to the TPC-1 on the landward slope of the Izu-Bonin Trench in 1997. The OBS detected co-seismic and gradual changes during a Mw 6.1 earthquake just below the station at 80 km depth on November 11, 1997. A pressure sensor c o-registered a change equivalent to 50 cm sea-level change. This suggests a high possibility detecting silent earthquakes or earthquake precursors if they exist. A multi-disciplinary geophysical station has been developed for deep-sea do or using TPC-2 since 1995. The station comprises eight instrument sets: bro adband seismometers, geodetic measurements, hydrophone array, deepsea digit al camera, CTD, etc. These activities are examples that decommissioned submarine cables can be g reat global resources for real-time cost-effective geophysical measurements on a deep-sea floor.