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<p>Various seismological methods are used to determine crustal stress fields, but most only provide stress changes, not absolute amounts of stress. In this study, we used Global Navigation Satellite System data to determine the spatiotemporal slip distribution of four slow slip events (SSEs) in the Bungo Channel between Shikoku and Kyushu Islands, Japan. Based on the obtained relationship between shear stress change and slip velocity, we plotted slip trajectories that were similar to theoretically stable trajectories for a spring-slider system subject to velocity weakening following a rate- and state-dependent friction law. Accordingly, we estimated the absolute values of the effective normal stress during SSE slip acceleration to have been 18–45&#xa0;MPa at depths of 16.5–21.5&#xa0;km. These values are very small compared to the lithostatic pressure at the depths investigated, suggesting the existence of very high pore fluid pressures at the plate boundary in the SSE source area. Our results and previous results obtained for SSEs off the Boso Peninsula, Japan, outline a positive correlation between the effective normal stress and total slip. Therefore, pore fluid pressure values at plate boundary interfaces may be an indicator of the amount of slip during SSEs.</p> Graphical Abstract <p></p>

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Estimating absolute values of effective normal stress during slow slip events in the Bungo Channel from slip velocities and shear stress variations

  • 期刊论文

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  • 发表日期：

    2026年4月18日

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  • Yojiro Sasagawa,
  • Toshinori Sato,
  • Takuma Kobayashi

摘要

Various seismological methods are used to determine crustal stress fields, but most only provide stress changes, not absolute amounts of stress. In this study, we used Global Navigation Satellite System data to determine the spatiotemporal slip distribution of four slow slip events (SSEs) in the Bungo Channel between Shikoku and Kyushu Islands, Japan. Based on the obtained relationship between shear stress change and slip velocity, we plotted slip trajectories that were similar to theoretically stable trajectories for a spring-slider system subject to velocity weakening following a rate- and state-dependent friction law. Accordingly, we estimated the absolute values of the effective normal stress during SSE slip acceleration to have been 18–45 MPa at depths of 16.5–21.5 km. These values are very small compared to the lithostatic pressure at the depths investigated, suggesting the existence of very high pore fluid pressures at the plate boundary in the SSE source area. Our results and previous results obtained for SSEs off the Boso Peninsula, Japan, outline a positive correlation between the effective normal stress and total slip. Therefore, pore fluid pressure values at plate boundary interfaces may be an indicator of the amount of slip during SSEs.

Graphical Abstract