Volcanic transcrustal magmatic systems imaged with teleseismic converted phases

使用远震转换相位成像的火山穿地壳岩浆系统

• 批准号: 2051243
• 负责人: Vera Schulte-Pelkum
• 金额: $ 12.15万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2051243&HistoricalAwards=false
• 关键词: Volcanic; transcrustal; magmatic; systems; imaged

The Aleutian arc in Alaska consists of dozens of active volcanoes. Their eruptions imperil local communities as well as domestic and international air traffic. Such arcs are also of scientific interest because they are the geological setting in which new continental crust forms. Our understanding of the subterranean plumbing of volcanoes has recently evolved. From the simple picture of a single magma chamber, the image of a complex system of interconnected chambers at all levels in the Earth’s crust has emerged. Investigating these deep structures in detail is critical to better understand volcanoes and their associated hazards. However, such investigation has been challenging because of technical limitations. Here the researchers use a new method. In collaboration with the Alaska Volcano Observatory, they use seismic records of earthquakes occurring around the globe. By analyzing the whole shape of recorded waveforms – instead of just the arrival times - they image the 3D magmatic structure underneath volcanoes. They reveal important features, e.g., the orientation of crystals in solidified magma and of melt-filled cracks in the adjacent rocks. New observations show complex subterranean structures that appear concentric around volcanoes, detected at all depth levels of the crust. The project helps improving hazard assessment for local communities, infrastructures as well as air traffic routes. It fosters outreach to K-12 science teachers, and to the public through the Museum of the Aleutians in Unalaska with, notably, a local television broadcast. It also promotes training for undergraduate students via programs geared towards groups underrepresented in Earth Sciences.Island arcs are of interest in tectonics as sites of continental crust production. Volcanoes in the Aleutians and Alaska offer an excellent cross section of types of arc volcanism. This project leverages recent updates to existing monitoring networks at Alaskan volcanoes. It tests a new approach for passive source imaging of magmatic systems under arc volcanoes through all crustal depths. The proposed work is to develop a new waveform-based method for detailed imaging and characterization of volcanic structures into the deep crust. It uses sparse numbers of broadband stations, complementing more expensive active source experiments and dense deployments. The approach also uses large arrivals in teleseismic receiver functions from the vicinity of arc volcanoes that are dominated by a periodic backazimuthal component (polarity reversals with azimuth of incidence). The positions of the polarity reversals fall on azimuths that are concentric to the volcanic edifice. The observed arrivals imply dipping contrasts between isotropic layers and/or anisotropic fabric centered on the volcano to at least midcrustal depths. Recent station upgrades to monitoring networks by the Alaska Volcano Observatory more than double the number of volcanoes available for study. A modeling effort will help distinguish between several endmember models of transcrustal magmatic structure that have been proposed to explain results from other methods such as petrology, tomography, geodesy, magnetotellurics, and seismicity relocations. These endmember models include dipping interfaces to high- or low-velocity crustal bodies, dipping faults above magma chambers, and dip in dike and sill complexes. The added constraints offered by the proposed method will allow higher resolution magmatic structures throughout the crust than currently possible.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

阿拉斯加的阿留申岛弧由数十座活火山组成，它们的喷发危及当地社区以及国内和国际空中交通，因为它们是我们对新大陆地壳形成的地质环境。火山的地下管道最近从单一岩浆室的简单图像发展而来，地壳中各个层面相互连接的岩浆室的复杂系统的图像已经出现，详细研究这些深层结构至关重要。然而，由于技术限制，研究人员使用了一种新方法，利用全球各地发生的地震记录进行研究。记录波形的整体形状（而不仅仅是到达时间）对火山下方的 3D 岩浆结构进行成像，揭示了重要的特征，例如凝固岩浆中晶体的方向以及邻近熔体填充的裂缝的方向。新的观测结果显示，在地壳的各个深度都检测到了以火山为中心的复杂地下结构，该项目有助于改善对当地社区、基础设施以及空中交通路线的危害评估。 ，并通过乌纳拉斯加的阿留申群岛博物馆向公众公开，特别是通过当地电视广播。它还通过面向地球科学领域代表性不足的群体的项目来促进对本科生的培训。阿留申群岛和阿拉斯加的火山提供了弧火山活动类型的绝佳剖面，该项目利用了阿拉斯加火山现有监测网络的最新更新，测试了一种岩浆系统被动源成像的新方法。拟议的工作是开发一种新的基于波形的方法，用于对地壳深处的火山结构进行详细成像和表征，它使用稀疏数量的宽带站。该方法还使用来自弧火山附近的大量到达的远震接收器功能，这些接收器功能由周期性反向方位角分量（随入射方位角的极性反转）而下降。在与火山大厦同心的方位角上，观测到的到达意味着以火山为中心的各向同性层和/或各向异性结构之间的对比。阿拉斯加火山观测站最近对监测网络进行了升级，使可供研究的火山数量增加了一倍以上，建模工作将有助于区分几种穿地壳岩浆结构的端元模型，这些模型已被提出来解释其他方法的结果。例如岩石学、层析成像、大地测量学、大地电磁学和地震活动重定位这些端元模型包括高速或低速地壳体的倾斜界面、倾斜。所提出的方法提供的额外约束将允许比目前更高分辨率的整个地壳岩浆结构。该奖项反映了 NSF 的法定使命，并通过使用评估被认为值得支持。基金会的智力价值和更广泛的影响审查标准。