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    • Progress in Earth and Planetary Science
    Progress in Earth and Planetary Science

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    Solid earth sciences


    Relationship between strain accumulation and release associated with recent slow slip events on the Japanese Islands

    Hiroki Kawabata, Shoichi Yoshioka, Francisco Ortega-Culaciati

    GNSS, Slow slip event, Strain accumulation and release, Tokai region, Boso-Oki, Shikoku region, Subduction zone

    Spatial distributions of displacement and each strain for the 2013–2016 Tokai L-SSE. a–d represent before the L-SSE, and e–h represent during the L-SSE. The orange circle denotes the approximate location of the L-SSE. a, e Spatial distributions of displacements. The black arrows represent the displacements during the analysis period with respect to the reference station. The ellipse at the tip of each black arrow represents the error of 1σ. b, f Spatial distributions of dilatation. The blue and red areas represent contraction and expansion, respectively. The thick grey line represents the plate boundary at the earth’s surface (Bird 2003). c, g Spatial distributions of maximum shear strain. The green areas and red areas represent compressional regions and extensional regions, respectively. The grey lines indicate the same information as (b). d, h Spatial distributions of principal strain expressed by double-headed arrows. The black outwards arrows and black inwards arrows represent extension and compression, respectively. The grey lines represent the same information as (b).

    In this study, we investigated the relationship between the strain accumulation before a slow slip event (SSE) and the strain release during the SSE for three recent SSEs along the Suruga Trough, Sagami Trough, and Nankai Trough, which are subduction zones in central to southwest Japan. The three analysed SSEs were the 2013–2016 Tokai long-term SSE (L-SSE), the 2018 Boso-Oki short-term SSE (S-SSE), and the 2019–2021 Central Shikoku L-SSE. We applied exponential and logarithmic functions to remove the postseismic deformations caused by the Mw 9.0 2011 Tohoku-Oki earthquake. We discovered a strong negative correlation between strain accumulation and strain release in the dilatation of all three SSEs and in the maximum shear strain of the 2018 Boso-Oki S-SSE. A comparison of the amount of strain accumulation with that of strain release revealed that approximately 30% of the strain was released in the 2013–2016 Tokai L-SSE, that 40% of the strain was released in the 2019–2021 Central Shikoku L-SSE, and that approximately 60% of the strain was released in the 2018 Boso-Oki S-SSE. This finding suggests that all of the accumulated strains are not necessarily released by the SSEs.