Deep Sea Bottom Methane Hydrate Investigations Aboard Fisheries Training Ship III - Comparison of Methane Plume Occurrence after Major Earthquakes with Past Data -

Abstract

In May 2022, June 2023 and 2024, the methane hydrate plume generated from the seafloor at a depth of about 560 to 570 meters in the Joetsu Basin was investigated on the training cruise of Nagasaki University's fishery training vessel "Nagasaki-Maru". These observations have mainly been made with “the quantitative echo sounder”, also with “the multi-beam echo sounder”, “the sub-bottom profilers” and “conductivity, temperature and depth profiler”, which equipped at “Nagasaki-maru”. From these, we were able to confirm some plumes at a specific area that continued for over 10 years, and we were also able to estimate the surrounding seafloor shape, the subseafloor structure, which could estimate the presence of methane hydrate solid, and the water structure, which could prove the deflection and melting properties of the plumes. And, these observations were conducted approximately six months after the Noto Peninsula earthquake that occurred on January 1, 2024. Therefore, we attempted to compare these with past observation data.