[S-CG52] Ocean Floor Geoscience

[SCG52-P02] Array displacement estimation of seafloor crustal deformation observation by the training ship "Shioji Maru" of Tokyo University of Marine Science and Technology considering sound velocity gradient structure

*Yuu Okayama¹, Kazuo Nakahigashi¹, Motoyuki Kido², Fumiaki Tomita² (1.Tokyo University of Marine Science and Technology, 2.International Research Institute of Disaster Science, Tohoku University)

Keywords:Observation of seafloor crustal deformation

Japan is often hit by earthquakes, especially huge earthquakes, which often have epicenters in offshore areas. Although crustal deformation observations have been inferred from land-based observations, it is difficult to estimate the epicenter of an earthquake from land-based observations because the epicenter in offshore areas can be over 200 km long. The GNSS-A (GNSS-acoustic coupling) method was devised for this purpose.
In recent years, GNSS-A observations have been actively conducted by unmanned vehicles. However, it is difficult to observe off the coast of Ibaraki Prefecture, where the G20 is located, because the unmanned aircraft can only achieve a speed of about 4 knots and is swept away by the ocean currents due to the path of the Kuroshio Current. As a result, no observations have been made off the coast of Ibaraki Prefecture for several years. Therefore, TUMSAT started GNSS-A observations offshore Ibaraki Prefecture using the Shioji Maru, which was completed in 2021. In this work, we report the results of analysis of data acquired by the observation conducted in January 2022, and estimate the time series with the past array displacements. In addition, we estimate and discuss the inclined structure of the sound velocity of G20, which deviates from the actual position due to the inclination of the sound velocity change assuming a horizontal stratified structure caused by the influence of the ocean currents.