Role of warm subduction in the seismological properties of the forearc mantle: An example from southwest Japan

Abstract

A warm slab thermal structure plays an important role in controlling seismic properties of the slab and mantle wedge. Among warm subduction zones, most notably in southwest Japan, the spatial distribution of large S-wave delay times and deep nonvolcanic tremors in the forearc mantle indicate the presence of a serpentinite layer along the slab interface. However, the conditions under which such a layer is generated remains unclear. Using numerical models, we here show that a serpentinite layer begins to develop by the slab-derived fluids below the deeper end of the slab-mantle decoupling interface and grows toward the corner of the mantle wedge along the interface under warm subduction conditions only, explaining the large S-wave delay times in the forearc mantle. The serpentinite layer then allows continuous free-fluid flow toward the corner of the mantle wedge, presenting possible mechanisms for the deep nonvolcanic tremors in the forearc mantle.

Anisotropic Velocity Structure Beneath Shikoku, Japan: Insights From Receiver Function and Shear Wave Splitting Analyses

“…We found that the azimuthal anisotropic fast axes changed from a trench‐parallel to a trench‐normal direction while moving from the southern to the northern area. This change exhibited a strong correlation with the dehydration and mineral evolution resulting from the subduction of the young and hot PHS Plate (Horn et al., 2020; Ji & Yoshioka, 2017; Lee & Kim, 2021). The anisotropic strength was relatively weaker along the tectonic‐tremor‐clustered area, particularly in the northwestern part of Shikoku Island, with an average split time of 0.057 s.…”

“…(2020). The dehydration of the OC results in the serpentinite layer on the plate interface generally growing above the plate interface around the MT (Katayama et al., 2012; Lee & Kim, 2021). Furthermore, the serpentinite layer or the serpentinized MT corner can host tectonic tremors and regulate slow‐earthquake activity and plate interface coupling (e.g., Katayama et al., 2012; Tarling et al., 2019) (Figure 10).…”

Trench topography in subduction zones: A reflection of the plate decoupling depth

“…Eqs 4, 6 were numerically solved using a finite element (FE) code (COMSOL Multiphysics ® , version 5.5) within the framework of CFD. Many earlier studies have used this CFD code to deal with different geodynamic problems, such as mantle convection (He, 2014), magma upwelling (Shahraki and Schmeling, 2012), Rayleigh-Taylor instabilities (Ruffino et al, 2016), mid-ocean ridge development (Montési and Behn, 2007), wedge melting (Lee and Kim, 2021), and plate subduction (Carminati and Petricca, 2010;Rodriguez-Gonzalez et al, 2012). To track the evolving surface of model surface topography, we implemented an arbitrary Lagrangian Eulerian (ALE) scheme, the detailed mathematical formulation of which can be seen in earlier publications Mandal, 2022 andDasgupta et al,2021a).…”