The southern Mariana margin is a tectonically distinctive and rapidly deforming region with the world deepest trench and unusual deformation and magmatism. However, its related deep structure and dynamics are still poorly understood. In this study, we determine robust 3-D P and S wave velocity models down to 130 km depth beneath the southern Mariana margin by using arrival-time data of local earthquakes recorded at 12 near-field seismic stations. Our tomographic results together with local seismicity and focal mechanisms reveal that the subducted Pacific slab is rapidly rolling back with a steep dip angle and narrowly but strongly coupled with the thin forearc block, which results in the deepest trench. An inferred eastward mantle flow transports the enhanced hydrous mantle melt beneath the southwest Mariana rift to the southern Mariana Trough, causing unusual deformation, magmatism and volcanism in the new oceanic crust. In addition, seismicity in the west Mariana ridge lithosphere may indicate active foundering of the arc lower crust.

中文翻译：

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南马里亚纳边缘的结构和动力学：来自地震活动、层析成像和震源机制的约束

马里亚纳南缘是一个构造独特且变形迅速的地区，拥有世界上最深的海沟以及不寻常的变形和岩浆活动。然而，其相关的深层结构和动力学仍然知之甚少。在这项研究中，我们利用 12 个近场地震台记录的当地地震的到达时间数据，确定了马里亚纳南缘下方 130 公里深度的稳健 3-DP 和 S 波速度模型。我们的断层扫描结果以及当地的地震活动和震源机制表明，俯冲的太平洋板片正在以陡峭的倾角快速回滚，并与薄的弧前块体紧密但强烈地耦合，从而形成了最深的海沟。推测的东向地幔流将西南马里亚纳裂谷下方增强的含水地幔熔体输送到南马里亚纳海槽，在新洋壳中引起异常变形、岩浆活动和火山活动。此外，西马里亚纳海岭岩石圈的地震活动可能表明弧下地壳的活跃沉没。