In southern Chile, the Nazca plate is subducting beneath the South American plate. This region was struck by megathrust earthquakes in 1960 and 2010 and is characterized by the existence of a volcanic chain. In this region, we modeled a three-dimensional thermal structure associated with the subduction of the Nazca plate by using numerical simulations. Based on the obtained temperature distribution, we determined the updip and downdip limit temperatures for the region ruptured by these two megathrust earthquakes. In addition, the distributions of water content and dehydration gradient were calculated by using appropriate phase diagrams and compared with the location of the volcanic chain. As a result, we infer that the coseismic slip of the 2010 Mw8.8 Maule earthquake occurred only at temperatures lower than and around the 350 °C isotherm that resembles the beginning of the brittle‒ductile transition. We also deduce that the rupture of the 1960 Mw9.5 Valdivia earthquake propagated up to the 450 °C isotherm because the magnitude was considerably large and the young hot plate subducted near the Chile Ridge. In addition, the hydrous minerals in the turbidites, MORB and ultramafic rocks released fluids via dehydration reactions, and dehydrated water migrated upward almost vertically, decreasing the melting point of the mantle wedge and contributing to the formation of the volcanic chain.

中文翻译：

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智利南部俯冲带的 3D 热结构和脱水建模及其与板间地震和火山链的关系

在智利南部，纳斯卡板块正在俯冲到南美板块之下。该地区曾于 1960 年和 2010 年遭受过特大逆冲地震，其特点是存在火山链。在该区域，我们通过数值模拟模拟了与纳斯卡板块俯冲相关的三维热结构。根据获得的温度分布，我们确定了这两次特大逆冲地震破裂区域的上倾和下倾极限温度。此外，利用适当的相图计算了含水量和脱水梯度的分布，并与火山链的位置进行了比较。因此，我们推断，2010 年 Mw8.8 Maule 地震的同震滑移仅发生在低于 350 °C 等温线及其附近的温度下，这类似于脆韧转变的开始。我们还推断，1960 年 Mw9.5 瓦尔迪维亚地震的破裂传播到 450 °C 等温线，因为震级相当大，并且年轻的热板块在智利海岭附近俯冲。此外，浊积岩、MORB和超镁铁岩中的含水矿物通过脱水反应释放出流体，脱水水几乎垂直向上运移，降低了地幔楔的熔点，有助于火山链的形成。