Unraveling the diversity of Arc volcanism and deep low-frequency tremors in Southwest Japan from numerical modeling.

Differences in slab dehydration and fluid transport influence the distribution of magmatism and deep low-frequency tremors in subduction zones. Southwest Japan, particularly Kyushu and Shikoku/Chugoku, exhibits significant along-arc variation in the spatial distribution of Quaternary arc volcanoes and adakites as well as deep low-frequency tremors beneath the forearc. Using two-dimensional numerical modeling, we quantitatively evaluate melting and fluid transport via a weak hydrous layer on the slab interface since the subduction initiation to clarify the observed key differences. In Kyushu, our model shows that dehydration of the colder subducting slab is mostly completed at sub-arc depths of 80-120 km, triggering intense flux melting in the mantle wedge and an absence of sub-forearc fluid percolation for the tremors. Adakitic signature in Kyushu could be diluted by the basaltic magma in the mantle wedge which the adakitic magma traverses. Whereas the model for Shikoku/Chugoku shows shallower sub-forearc dehydration of the warmer slab (< 80 km), allowing less flux melting, slab melting for adakite, and sub-forearc fluid percolation for the tremors.