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

大洋中脊轴附近的上洋壳及其物理特性是众所周知的，上洋壳就是在那里形成的。然而，人们对上大洋地壳的性质如何随着地壳年龄的变化知之甚少，主要是因为缺乏关于老地壳的适当数据集。一个仍然没有答案的重要问题是，当地壳远离海脊轴时，热液循环是否会继续。热流测量表明，热液循环持续存在，但它一直是不可能的澄清从现有的数据集的影响和控制这个后期阶段的循环。该项目将利用最近收集的苏门答腊和阿拉斯加俯冲带近海成熟洋壳（5000万年）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，而且独一无二，因为它们可以对海洋地壳的上部进行成像。了解老地壳中的热液循环很重要，因为我们不知道这些占地球表面约70%的广阔区域中地球与海洋之间发生的化学交换的程度。该研究支持博士的培训。研究生。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和阿拉斯加俯冲带近海成熟洋壳（5千万年）上采集的二维海洋地震数据。 这些数据是在2011年在R/V Marcus Langseth上和2009年在M/V Geowave Champion上在TIDES计划（IPG-巴黎）期间获得的。 本研究的主要目的是提供新的见解的地震不均匀性的最上层地壳和主导过程，控制上洋壳的老化。长拖缆MCS数据将提供上地壳的地震成像，包括在大偏移距处看到的临界后反射。MCS成像还将使人们能够确定沉积物厚度、上地壳地形以及沉积物和上地壳内断层活动丰富程度的变化特征。 对拖缆数据进行向下延拓和旅行时间建模，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波速度和衰减的进一步信息。这两个数据集将使人们能够比较以不同扩张速度形成的、年龄略有不同的洋壳剖面。

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.