Formation and evolution of upper oceanic crust from seismic data acquired over mature oceanic crust near the Sumatra and Alaska subduction zones

大洋上部地壳及其物理性质在大洋中脊轴线附近是众所周知的，地壳就是在那里形成的。然而，人们对大洋上层地壳的性质如何随着地壳的老化而变化知之甚少，这主要是因为缺乏关于较老地壳的适当数据集。一个仍未得到解答的重要问题是，随着地壳从山脊轴线向外扩散，热液循环是否会继续。热流测量表明，热液循环仍然存在，但不可能从现有的数据集中澄清对这种后期循环的影响和控制。该项目将使用最近在苏门答腊岛和阿拉斯加俯冲带附近的成熟洋壳(50Myr)上收集的海洋地震数据来解决这些问题。这两个数据集的质量非常高，而且非常独特，因为它们允许对大洋地壳上部进行成像。了解古老地壳中的热液循环很重要，因为我们不知道在这些占地球表面约70%的广阔地区发生的地球和海洋之间的化学交换的程度。这项研究支持博士研究生的培养。该项目还涉及与法国同事的国际合作。该项目将检查在苏门答腊岛和阿拉斯加俯冲带附近的成熟洋壳(50英里)上获得的二维海洋地震数据。这些数据是2011年在R/V Marcus Langseth上和2009年在潮汐期间M/V Geowave冠军计划(IPG-Paris)上获得的。这项研究的主要目的是对上地壳的地震非均质性和控制上洋壳老化的主导过程提供新的见解。长流光MCS数据将提供上地壳的地震成像，包括在大偏移量处看到的临界点后反射。MCS成像还将能够表征沉积物厚度、上地壳地形以及沉积物和上地壳内断层丰富程度的变化。向下延拓，然后对流光数据进行走时模拟，将提供构成上地壳的两层的厚度和P波速度。综合计算将产生关于S的进一步信息--波速和衰减。这两个数据集结合在一起，将允许比较以不同扩张速度形成的洋壳部分和略有不同的年龄。

The upper oceanic crust and its physical properties are well known near the mid-ocean ridge axis where the crust is formed. However, little is known about how the properties of the upper oceanic crust change as the crust ages, primarily because of the lack of the appropriate datasets over older crust. An important question that remains unanswered is whether or not hydrothermal circulation continues as the crust spreads away from the ridge axis. Heat flow measurements suggest that hydrothermal circulation persists, but it has been impossible to clarify from existing datasets the effects and the controls on this late stage circulation. This project will use recently collected marine seismic data over mature oceanic crust (50 Myr) offshore the Sumatra and Alaska subduction zones to address these problems. These two datasets are very high quality and unique in that they allow imaging of the upper part of the oceanic crust. Understanding hydrothermal circulation in older crust is important because we do not know the extent of the chemical exchanges that occur between the earth and oceans in these vast regions that represent about 70% of the surface of the earth. The study supports the training of a Ph.D. graduate student. The project also involves an international collaboration with French colleagues.This project will examine 2-D marine seismic data acquired over mature oceanic crust (50 Myr) offshore the Sumatra and Alaska subduction zones. These data were acquired in 2011 on the R/V Marcus Langseth and in 2009 on the M/V Geowave Champion during the TIDES Program (IPG-Paris). The main objective of this study is to provide new insights on the seismic heterogeneity of the uppermost crust and the dominant processes that control the aging of upper oceanic crust. The long-streamer MCS data will provide seismic imaging of the upper crust including post-critical reflections seen at large offsets. The MCS imaging will also allow the characterization of variations in the sediment thickness, topography of the upper crust, and abundance of faulting within the sediments and upper crust. The downward continuation followed by travel time modeling of the streamer data will provide the thickness and P-wave velocity of the two layers that constitute the upper crust. Synthetic computation will generate further information on S-wave velocities and attenuation. Together the two datasets will allow the comparison between sections of oceanic crust formed at different spreading rates and of slightly different ages.