Collaborative Research: Imaging small-scale convection and structure of the mantle in the south Pacific: a US contribution to an international PacificArray

地球表面的所有变形，包括导致地震的断层，都是由构造板块的运动产生的。 人们普遍认为地幔中的热对流驱动了板块运动，但对流的细节以及它如何确切地移动板块却知之甚少。 海洋板块占地球表面的70%，为地幔对流提供了重要的窗口，但由于缺乏来自海洋盆地的地震数据，它们在很大程度上未被探索。 关于大洋板块的热结构、大洋板块中部火山活动的意义以及板块下方的对流地幔如何控制板块运动，存在着大量的问题。重力场中的波动和无法解释的海底变浅暗示着海洋板块下方的小规模对流。该项目有助于国际社会努力在太平洋盆地战略性地放置记录地震能量的临时仪器阵列。最近在海底地震仪方面取得的社区进展将用于在目前覆盖范围存在巨大差距的地点记录独特的数据集。这些数据将使我们能够推断与小尺度对流有关的地幔温度的变形和变化。 作为国际合作的一部分，所有数据都将向世界各地的科学家开放。该项目支持培训研究生和本科生，将在中部和南部太平洋的两个30个台站阵列中收集12-15个月的宽带海底地震仪数据。这些阵列部署在两个不同的板块年龄（~30 Ma和~120 Ma），将解决有关海洋软流圈动力学的具体关键问题，包括其基本状态（温度、熔体、水或其他挥发物的存在以及变形机制）。这些阵列的设计目的是对小规模对流的各向异性速度特征进行成像，这被用来解释古老海洋板块年龄与深度曲线的扁平化、140-200公里波长的重力线理以及在各种尺度上观察到的无处不在的离轴非羽状火山活动。各向异性表面波和体波层析成像模型将补充剪切波分裂和衰减测量，以获得多方面的了解软流圈和基地的板块。最后，数量级的增加，在路径覆盖的表面和体波在太平洋中南部将使新的进展，全球层析成像。

All deformation on the surface of Earth, including faulting responsible for earthquakes, is produced by the motion of tectonic plates. It is widely accepted that thermal convection in the mantle drives plate motion, but details of that convection and how exactly it moves the plates are poorly understood. Oceanic plates make up 70% of the Earth's surface and offer important windows into mantle convection, yet they are largely unexplored due to the lack of seismic data from the ocean basins. Questions abound regarding the thermal structure of oceanic plates, the significance of volcanism in the middle of oceanic plates, and how the convecting mantle beneath the plates controls their movements. Waves in the gravity field and un-explained shallowing of the ocean floors hint at small-scale convection beneath the oceanic plates. This project contributes to an international effort to strategically place temporary arrays of instruments across the Pacific Ocean basin that record the energy from earthquakes. Recent community advances in ocean bottom seismographs will be used to record unique datasets in locations where large gaps in coverage exist today. These data will allow us to infer deformation and variations in mantle temperature related to small-scale convection. As part of the international collaboration, all data will be openly available to scientists worldwide. The project supports the training of graduate and undergraduate students.This project will collect 12-15 months of broadband ocean bottom seismograph (OBS) data in two 30-station arrays in the central and southern Pacific. These arrays, deployed at two distinct plate ages (~30 Ma and ~120 Ma), will address specific critical questions on the dynamics of the oceanic asthenosphere, including its underlying state (temperature, presence of melt, water or other volatiles, and deformation mechanism). The arrays are designed to image the anisotropic velocity signature of small-scale convection, which has been invoked to explain the flattening of the age versus depth curve in old ocean plates, 140-200 km wavelength gravity lineations, and ubiquitous off-axis, non-plume volcanism observed at a variety of scales. Anisotropic surface wave and body wave tomographic models will be supplemented by shear wave splitting and attenuation measurements to obtain a multi-faceted understanding of the asthenosphere and base of the plates. Finally, the order-of-magnitude increases in path coverage for surface and body waves in the south-central Pacific will enable new advances in global tomography.