Mapping Small-scale Mantle Heterogeneities Using USArray

使用 USArray 绘制小尺度地幔异质性图

• 批准号: 1610612
• 负责人: Jun Korenaga
• 金额: $ 25.99万
• 依托单位: Yale University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-06-01 至 2019-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1610612&HistoricalAwards=false
• 关键词: Mapping; Small; scale; Mantle; Heterogeneities

Mapping small-scale mantle heterogeneities using USArrayDeep currents within the rocky portion of the Earth?s interior are called mantle convection, and this is the engine for almost all kinds of geological processes on the Earth, not only generating earthquakes, volcanoes, and continental drift, but also modulating the evolution of the geomagnetic field and even the atmospheric composition. At the same time, understanding how this mantle convection is actually operating is difficult and subject to large uncertainty, because it is mostly hidden from our eyes, except for its surface manifestation known as plate tectonics. One of the fundamental questions regarding mantle convection is how efficiently it can mix things up, and the efficiency of convective mixing has a number of important bearings on how mantle convection has shaped the history of the Earth and its surface environment. In this project, we will apply a state-of-the-art seismic imaging technique to the USArray data, to detect small-scale heterogeneities in the mantle surrounding the North American continent. The distribution of small-scale heterogeneities, when interpreted in the context of the tectonic history of a relevant mantle section, has a potential to elucidate the long-term mixing efficiency of mantle convection. In the last few years, the PI has been developing new data processing tools to overcome various difficulties associated with the detection of small-scale mantle heterogeneities, including a powerful signal detection technique called dual bootstrap stacking (DBS) and a teleseismic migration method based on DBS. Seismic migration is an imaging technique in which seismic energy recorded at surface receivers is projected back to its origin in the subsurface. As it directly uses the entire waveform of seismic data, migration has a potential to achieve the highest spatial resolution allowed by the given data. The Transportable Array of USArray finished its eastward migration in 2013, and the time is ripe to explore the vast wealth of USArray data by DBS-based teleseismic migration in a systematic manner. Given a large number of possible source-receiver combinations and a variety of scattering mechanisms to be exploited, this project focuses on the following two objectives as the top priorities: (1) parallelization of DBS-based migration, and (2) searching for small-scale heterogeneities in the mantle around the North American continent with P-to-P scattering. The DBS-based migration is a very time-consuming processing, but with the planned code parallelization, it will become possible to process a large volume of data. The P-coda part of seismograms, bounded by the direct P arrival and the PP phase, is suitable to be searched for potential scattered phases generated by S-to-P and P-to-P scattering. Because of travel times involved, S-to-P scattering can illuminate only the vicinity of earthquakes, but P-to-P scattering can probe all along the ray path of the direct P. The use of differential travel times with respect to the direct P limits the source-receiver distance to be shorter than ∼100°, but a number of good seismic sources (i.e., deeper than 100 km and Mw ≥5.0) around the Pacific will allow us to image scatterers in the mantle beneath the Northern Pacific, Central America, and possibly the Northern Atlantic.

使用Usarraydeep电流在地球内部的岩石部分中使用UsArraydeep电流绘制小型地幔异质性，这是地球上几乎各种地质过程的发动机，不仅会产生地震，火山和连续的漂移，还可以调整地质势头和杂物杂物的进化。同时，了解这种地幔结构的实际运行方式非常困难且遭受巨大的不确定性，因为它主要隐藏在我们的眼中，除了其表面表现称为板块构造。关于地幔结构的基本问题之一是，它可以使事物融合的效率如何，而对流混合的效率具有许多重要的轴承，这些轴承对地幔结构如何塑造了地球及其表面环境的历史。在这个项目中，我们将对USArray数据应用最先进的地震成像技术，以检测北美大陆周围地幔的小规模异质性。当在相关地幔部分的构造历史上解释时，小规模异质性的分布有可能阐明地幔连接的长期混合效率。在过去的几年中，PI一直在开发新的数据处理工具，以克服与检测小规模套层异质性相关的各种困难，包括一种强大的信号检测技术，称为Dual Bootstrap堆叠（DBS）和基于DBS的远距离迁移方法。地震迁移是一种成像技术，其中在地面接收器中记录的地震能将其起源于地下。由于它直接使用了地震数据的整个波形，因此迁移具有实现给定数据允许的最高空间分辨率的潜力。 USArray的可运输阵列在2013年完成了向东的移民，现在是时候以系统的方式探索基于DBS的远程宣传迁移的大量USArray数据。考虑到大量可能的源接收器组合和要探索的各种散射机制，该项目集中在以下两个对象上，作为首要优先级：（1）基于DBS的迁移的并行化，以及（2）在北美大陆周围的小规模异质性与p-tos-p散射。基于DBS的迁移是非常耗时的处理，但是借助计划的代码并行化，可以处理大量数据。地震图的p-CODA部分，受直接P到达和PP相界的界定，适合搜索由S-to-P-p-t-p-p散射产生的潜在散射相。由于涉及旅行时间，S-P散射只能照亮地震的附近，但是p-to-p散射可以沿着直接的射线路径探测。直接使用差分旅行时间，限制了源源距离的距离，限制了源代码距离的距离，比＆＃8764; 100°要短，但比良好的seisis sisismic sources（i.eisis couse）（i.ep ye 5 km y。太平洋将使我们能够在北太平洋，中美洲以及可能的北大西洋下面的地幔中进行散射。