１. Key points

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Using an autonomous sea surface vehicle with automatic navigation, data were successfully recorded by patrolling 14 seafloor crustal movement observation points along the Japan Trench over a period of approximately 40 days.

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The use of autonomous surface vehicles can significantly reduce the cost of GNSS-acoustic positioning coupled with observations of submarine crustal movements, which have thus far necessitated the use of ships.

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It is now realistic to increase the frequency of observations, and the detection of changes in interplate locking and slipping over time along shallow plate boundaries (i.e., near trench axes) can be expected.

2. Overview

A team led by Dr. Takeshi Iinuma, at the Japan Agency of Marine–Earth Science and Technology (JAMSTEC) Research Institute for Marine Geodynamics, along with Prof. Ryota Hino of the Tohoku University Graduate School of Science and Prof. Motoyuki Kido of the Tohoku University International Research Institute for Disaster Science (IRIDeS), developed a system to perform Global Navigation Satellite System (GNSS*)-acoustic positioning coupled with observations of submarine crustal movement (Fig. 1; hereinafter “GNSS-A observations”) using an autonomous sea surface vehicle, “Wave Glider” (Fig. 2). By having the Wave Glider patrol multiple observation points, the team succeeded in automatically acquiring observation data at many points in just over a month (Fig. 3).

In the past, GNSS-A observations have necessitated the use of research vessels or moored buoys, such that high operating costs have limited the enhancement of observation systems. However, with the realization of observations via Wave Glider, it is now possible to reduce the cost per observation to 1/10^th or less of that required using traditional techniques. In the future, increasing the frequency of seafloor crustal movement observations by utilizing autonomous surface vehicles may allow the processes by which the strain accumulated along marine–continental plate boundaries is released to be clarified, especially where large subduction zone earthquakes have repeatedly occurred. Such observations are expected to greatly improve the reliability of probabilistic estimates of large earthquakes and thus help to mitigate their impacts on marine infrastructure and coastal communities.

This research was partially funded by the Japan Society of the Promotion of Science (JSPS) [grant no. JP19H05596].