Seismic imaging of mid-ocean ridges and passive margins

拟议的工作重点是在地球表面发现的两个一级构造边界：大洋中脊及其侧翼和被动大陆边。洋中脊是一个不断生成新洋壳的分离板块构造边界。它们构成了世界上最广阔的山脉系统和最长的火山链。大洋中脊地壳薄，构造环境相对简单，是研究活火山岩浆管道系统的理想场所。大洋地壳如何沿着洋中脊侧翼演化，从基础科学（例如，地球固体内部和海洋之间的能量和质量交换）和俯冲地震灾害，因为它们可能受到板块水合作用的影响。被动大陆边缘位于古老的厚大陆地壳和年轻的薄洋壳之间，是地球的主要过渡带之一。它们是在大陆岩石圈裂离形成新的洋盆时形成的。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沉降过程中形成的主要沉积盆地的所在地。这些边缘盆地可能具有巨大的经济重要性，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道地震（MCS）数据。MCS数据进行分析，以形成反射图像，确定成像结构的物理属性，并通过应用浅层地震层析成像构建速度剖面。广角折射数据还将用于研究被动边缘，以独立形成深部速度模型，并与MCS数据结合，尽可能提取有关目标结构的信息。拟议计划的主要目标是：1）调查洋中脊过程中前所未有的细节，通过产生第一个三维叠前时间和深度迁移的洋中脊环境的图像; 2）表征海洋-大陆过渡的巨大变化，似乎发生在小边缘横向距离内只有一个裂谷段。

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.