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Monogr. Environ. Earth Planets, Vol. 5 (No. 1), pp. 1-34, 2017 doi:10.5047/meep.2017.00501.0001 ISSN: 2186-4853

Role of H2O in Generating Subduction Zone Earthquakes

Akira Hasegawa

Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan

(Received January 7, 2016; Revised June 13, 2016; Accepted July 3, 2016; Online published March 22, 2017)

Citation: Hasegawa, A. (2017), Role of H2O in generating subduction zone earthquakes, Monogr. Environ. Earth Planets, 5, 1–34, doi:10.5047/meep.2017.00501.0001.

Abstract: A dense nationwide seismic network and high seismic activity in Japan have provided a large volume of high-quality data, enabling high-resolution imaging of the seismic structures defining the Japanese subduction zones. Here, the role of H2O in generating earthquakes in subduction zones is discussed based mainly on recent seismic studies in Japan using these high-quality data. Locations of intermediate-depth intraslab earthquakes and seismic velocity and attenuation structures within the subducted slab provide evidence that strongly supports intermediate-depth intraslab earthquakes, although the details leading to the earthquake rupture are still poorly understood. Coseismic rotations of the principal stress axes observed after great megathrust earthquakes demonstrate that the plate interface is very weak, which is probably caused by overpressured fluids. Detailed tomographic imaging of the seismic velocity structure in and around plate boundary zones suggests that interplate coupling is affected by local fluid overpressure. Seismic tomography studies also show the presence of inclined sheet-like seismic low-velocity, high-attenuation zones in the mantle wedge. These may correspond to the upwelling flow portion of subduction-induced secondary convection in the mantle wedge. The upwelling flows reach the arc Moho directly beneath the volcanic areas, suggesting a direct relationship. H2O originally liberated from the subducted slab is transported by this upwelling flow to the arc crust. The H2O that reaches the crust is overpressured above hydrostatic values, weakening the surrounding crustal rocks and decreasing the shear strength of faults, thereby inducing shallow inland earthquakes. These observations suggest that H2O expelled from the subducting slab plays an important role in generating subduction zone earthquakes both within the subduction zone itself and within the magmatic arc occupying its hanging wall.

Keywords: H2O, Fluid overpressure, Weak fault, Subduction zone, Earthquake generation mechanism, Fluid-related embrittlement, Mantle upwelling flow.


Corresponding author e-mail: akira.hasegawa.d8@tohoku.ac.jp


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