[M-GI31] Drilling Earth Science

[MGI31-P10] Current status of pore pressure observation in a borehole off the Kii Channel: Toward high-precision extraction of crustal deformation components on the seafloor

*Keisuke Ariyoshi¹, Eiichiro Araki¹, Hiroyuki Matsumoto¹, Yuya Machida¹, Shuhei Tsuji¹, Takashi Yokobiki¹, Shuhei Nishida¹, Shuichiro Yada¹, Tomokazu Saruhashi¹, Kan Aoike¹, Yasuyuki Nakamura¹, Gou Fujie¹, Takeshi Iinuma¹, Takane Hori¹, Nobuhisa Eguchi¹, Shuichi Kodaira¹ (1.Japan Agency for Marine-Earth Science and Technology)

Keywords:Pore pressure, Seafloor crustal deformation, Nankai Trough

In November 2023, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) installed pore pressure and fiber-optic strain gauges as a new borehole observatory about 500 m below the seafloor off Kii Channel using the deep-sea scientific drilling vessel "Chikyu". Subsequently, from December 2023 to January 2024, during the voyage of the research vessel "Shinsei Maru," an unmanned research vehicle (ROV) "Hyper Dolphin" was used to lay submarine cables and connect the borehole observatory and DONET2. As a result, real-time observation of "slow slip" has been continued for the first time in the assumed epicenter of the Nankai earthquake.
The pore pressure data in the borehole includes non-crustal deformation components such as oceanic disturbances. Therefore, using a seafloor hydraulic pressure at the borehole mouth, we extract the seafloor crustal deformation component by applying appropriate coefficients and time differences and taking differences (Ariyoshi et al., 2021). We have implemented this algorithm in a real-time processing and monitoring regime.
In this presentation, we will introduce the acquired data and discuss the influence of ocean disturbance as a noise factor and problems with the analysis processing method, aiming to improve the quality of the extraction of seafloor crustal deformation components with high accuracy.