An Experiment in Seismic Tomography: The Three-Dimensional Structure of the East Pacific Rise

了解在大洋中脊形成新海底的过程是海洋地质和地球物理研究的一个重要方面。尽管现在人们普遍认为，海底扩张在过去大约2亿年里创造了现在的洋壳，但新的火山物质产生和侵位在海脊的细节仍然没有解决。一个重要的未知数是地下岩浆室的分布和寿命，其中部分熔融的地幔物质在喷发到海底之前被储存在其中。最近从东太平洋隆起获得的深穿透地震反射数据揭示了沿着隆起顶部似乎有一个相当连续的岩浆室的顶部。本项目的目标是使用地震折射技术对岩浆室进行比从地震反射数据中获得的更详细的检查。具体地说，该项目将在隆起顶部部署一系列海底地震仪/水听器，然后使用爆炸和声能源来记录能量通过地壳的水平传输。这些数据将通过最近开发的断层扫描技术进行分析，这种技术允许使用整个数据集进行三维成像。需要解决的具体问题包括地下岩浆室的宽度、深度和速度结构。这是伍兹霍尔海洋研究所和麻省理工学院的科学家合作的项目。该项目的资金水平如下：伍兹霍尔--87财年=30000美元，88财年=297000美元，89财年=87000美元，麻省理工学院-87财年=30000美元，88财年=163000美元，89财年=133000美元

Understanding the processes that create new seafloor at mid- ocean ridges is a critical aspect of marine geological and geophysical research. Although it is now well accepted that seafloor spreading has created the present ocean crust during approximately the last 200 million years, the details by which new volcanic material is generated and emplaced at the ridges remains unresolved. An important unknown is the distribution and longevity of subsurface magma chambers in which partially melted mantle material is stored before being erupted to the seafloor. Recently acquired deep penetration seismic reflection data from the East Pacific Rise has revealed what appears to be the top of a fairly continuous magma chamber along the Rise crest. The objective of the present project is to use seismic refraction techniques to examine the magma chamber in more detail than can be obtained from the seismic reflection data. Specifically, the project will deploy a series of ocean bottom seismometer/hydrophones across the Rise crest and then use explosive and acoustic energy sources to record the horizontal transmission of energy through the crust. These data will be analyzed by recently developed tomographic techniques which allow three dimensional imaging using the entire data set. Specific questions to be addressed include the width, depth, and velocity structure of the subsurface magma chamber. This is a cooperative project between scientists at Woods Hole Oceanographic Institution and the Massachusetts Institute of Technology. The project will be funded at the following levels: Woods Hole -FY87=$30000, FY88=$297000, FY89=$87000 MIT -FY87=$30000, FY88=$163000, FY89=$133000