Seismic imaging of mid-ocean ridges and passive margins

这项工作的重点是在地球表面发现的两个一级构造边界：洋中脊及其侧翼，以及被动大陆边缘。洋中脊是一个发散的板块构造边界，在这里不断产生新的洋壳。它们构成了世界上最广阔的山系和最长的火山链。洋中脊的薄地壳和相对简单的构造环境使它们成为研究活火山岩浆管道系统的理想环境。从基础科学（例如，地球固体内部与海洋之间的能量和质量交换）和俯冲地震危险（因为它们可能受到板块水化过程的影响）的角度来看，海洋地壳如何沿着洋中脊侧翼演化是很重要的。被动大陆边缘位于古老的厚大陆地壳和年轻的薄海洋地壳之间，是地球的主要转变之一。它们是在大陆岩石圈分裂形成新的海洋盆地时形成的。大陆-海洋边界也是在变薄的大陆地壳和新形成的海洋地壳下沉过程中形成的主要沉积盆地的位置。这些边缘盆地具有潜在的巨大经济价值，因为它们可以容纳大型油气藏。这里提出的所有调查都依赖于使用多通道地震（MCS）数据。对MCS数据进行分析，形成反射图像，确定成像结构的物理性质，并通过浅层地震层析成像构建速度剖面。广角折射数据也将用于被动边缘的研究，以独立形成深部速度模型，并与MCS数据相结合，以提取目标结构的最大可能信息。该计划的主要目标是：1)通过生成海洋中脊环境的第一个三维叠前时间和深度偏移图像，以前所未有的细节研究海洋中脊过程；2)描述仅在一个裂谷段内的小边缘横向距离上出现的海洋-大陆过渡的大变化。

The proposed work is focused on two of the first order tectonic boundaries found on the Earth's surface: Mid-ocean ridges and their flanks, and passive continental margins. The mid-ocean ridges are a divergent plate tectonic boundary where new oceanic crust is being continuously generated. They make up the most extensive mountain system and the longest chain of volcanoes in the world. The thin crust and relatively simple tectonic setting of mid-ocean ridges make them ideal settings to investigate the magma plumbing system of an active volcano. How oceanic crust evolves along the mid-ocean ridge flanks is important from the perspectives of both basic science (e.g., energy and mass exchange between the Earth's solid interior and the oceans) and subduction earthquake hazards as they may be influenced by the plate hydration processes. Passive continental margins located at the boundary between old, thick continental crust and young, thin oceanic crust are one of the Earth's major transitions. They are formed when continental lithosphere is rifted apart to form new ocean basins. The continent-ocean boundary is also the site of major sedimentary basins created during subsidence of the thinned continental crust and the newly formed oceanic crust. These marginal basins are potentially of great economic importance because they can host large hydrocarbon reservoirs. All of the investigations proposed here rely on using multichannel seismic (MCS) data. MCS data are analyzed to form reflection images, determine physical properties of the imaged structures, and construct velocity profiles by applying shallow seismic tomography. Wide-angle refraction data will also be used for the study of passive margins to independently form deep velocity models, and in combination with the MCS data to extract maximum possible information about the targeted structures. The key goals of the proposed program are to: 1) Investigate mid-ocean ridge processes at unprecedented detail by producing the first 3D prestack time and depth migrated images of a mid-ocean ridge environment; 2) Characterize large variations in the ocean-continent transitions that appear to occur over small margin-lateral distances within just one rift segment.