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Abstract

In the southern Chile subduction zone, the Nazca plate is subducting beneath the South American plate. This region was recently struck by great megathrust earthquakes and is characterized by the existence of a volcanic chain. In this study, we calculated the three-dimensional thermal structure in the southern Chile subduction zone associated with the subduction of the Nazca plate by using numerical simulations. Based on the obtained temperature distribution, we determined the temperature ranges for the coseismic slips of the two megathrust earthquakes and temperatures at the hypocentres of the interplate earthquakes. In addition, the distributions of the water content and dehydration gradient were calculated by using the phase diagrams and were compared with the location of the volcanic chain. As a result, we found that coseismic slips occurred only at temperatures lower than the 350 °C isotherm. This finding occurs because the effective friction coefficient increases as the slip velocity increases at the plate boundary where the temperature is higher than 350 °C. In addition, the hydrous minerals in and above the slab release fluids through dehydration reactions, which decrease the melting point of the mantle wedge, contributing to the formation of the volcanic chain.