17:15 〜 19:15
[SCG45-P29] 熊野灘における海底圧変動と流体ダイナミクスの再考
キーワード：海底地殻変動、間隙流体圧、海洋との相互作用
The Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) (Kawaguchi et al., 2015; Kaneda et al., 2015) has provided seafloor observations above the source region of the 1944 Tonankai earthquake, revealing that crustal deformation is driven by slow slip events (SSEs) in the shallower extension of megathrust earthquakes (Araki et al., 2017; Ariyoshi et al., 2021). However, the detected SSEs have been limited to the vicinity of the D-node. One exceptional case was reported by Suzuki et al. (2016), which suggested that an SSE was detected from seafloor pressure data near the B-node of DONET-1. However, neither low-frequency tremors nor very low-frequency earthquakes have been detected in this region.
This limitation is primarily due to the spatial distribution of observation points. The three boreholes monitoring crustal deformation via pore pressure measurements are aligned along the dip direction from the C-node to the D-node. Furthermore, the geometry between the B-node and D-node is asymmetrical. Around the B-node, recent studies have pointed out that a seamount has subducted beneath the continental plate (Sun et al., 2020), and pore water has migrated upward (Tsuji et al., 2014) along a normal fault (Toh et al., 2015).
In this study, we explore an alternative source model for the local seafloor pressure change event observed near the B-node in 2013. Our results suggest that this local event can be explained by localized dilation and compression in fluid reservoirs with radii of 1–2 km at depths of 2–3 km beneath the outer ridge, where a temporary connection between two reservoirs was induced by oceanic perturbations. This finding highlights the importance of monitoring oceanic phenomena and conducting detailed investigations of seafloor geometry to robustly identify the sources of static seafloor pressure changes.
This limitation is primarily due to the spatial distribution of observation points. The three boreholes monitoring crustal deformation via pore pressure measurements are aligned along the dip direction from the C-node to the D-node. Furthermore, the geometry between the B-node and D-node is asymmetrical. Around the B-node, recent studies have pointed out that a seamount has subducted beneath the continental plate (Sun et al., 2020), and pore water has migrated upward (Tsuji et al., 2014) along a normal fault (Toh et al., 2015).
In this study, we explore an alternative source model for the local seafloor pressure change event observed near the B-node in 2013. Our results suggest that this local event can be explained by localized dilation and compression in fluid reservoirs with radii of 1–2 km at depths of 2–3 km beneath the outer ridge, where a temporary connection between two reservoirs was induced by oceanic perturbations. This finding highlights the importance of monitoring oceanic phenomena and conducting detailed investigations of seafloor geometry to robustly identify the sources of static seafloor pressure changes.