Development of the off-Toyohashi seafloor cabled observatory

Abstract

The existence of fluid in seismogenic zones plays a key role in great earthquakes. Data on electrical conductivity structures obtained by electromagnetic surveys across the great earthquake zones show that the seismically locked zones correspond to low conductive zones. This low conductivity is possibly interpreted as relatively low fluid content in rock or sediment. For more discussion on the role of fluid in earthquake occurrence, we have recently started an electromagnetic and seismological monitoring project using long submarine cables off Toyohashi, in the southwest part of Japan's main island. The cables are located on the Tokai seismogenic zone, where both slow-slipping and locked zones are obvious by GPS observation. We constructed a seafloor observatory at the tip of the western cable, including a seismometer, pressure gauges, a magnetometer, voltmeters, and thermometers. These sensors measure and transfer data on the seafloor environment in real time. The data will be used for passive and active monitoring below the seafloor, including in the Tokai seismogenic zone.