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.

阿拉斯加的阿留申弧由数十座活火山组成。火山爆发危及当地社区以及国内和国际空中交通。这种弧也具有科学意义，因为它们是新大陆地壳形成的地质背景。我们对火山地下管道的了解最近有所发展。从一个单一岩浆房的简单图像，一个复杂的系统的图像在地壳的各个层面相互连接的房间已经出现。详细调查这些深层结构对于更好地了解火山及其相关危害至关重要。然而，由于技术限制，这种调查一直具有挑战性。在这里，研究人员使用了一种新方法。他们与阿拉斯加火山观测站合作，利用发生在地球仪周围的地震记录。通过分析记录波形的整体形状-而不仅仅是到达时间-他们对火山下方的3D岩浆结构进行了成像。它们揭示了重要的特征，例如，凝固岩浆中晶体的取向和邻近岩石中熔体填充的裂缝的取向。新的观测结果显示，在地壳的所有深度水平上都可以检测到复杂的地下结构，这些结构似乎与火山同心。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险评估。 它促进了对K-12科学教师的宣传，并通过乌纳拉斯卡的阿留申群岛博物馆向公众宣传，特别是通过当地电视广播。它还通过面向地球科学中代表性不足的群体的方案促进对本科生的培训。岛弧作为大陆地壳生产的场所在构造学中很有意义。阿留申群岛和阿拉斯加的火山提供了弧火山作用类型的极好的横截面。该项目利用了最近对阿拉斯加火山现有监测网络的更新。它测试了一种新的方法，被动源成像的岩浆系统下弧火山通过所有地壳深度。拟议的工作是开发一种新的基于波形的方法，用于深入地壳的火山结构的详细成像和表征。 它使用稀疏数量的宽带站，补充更昂贵的有源实验和密集部署。该方法还使用了大量的到来，从附近的弧火山，主要是由一个周期性的backazimuthal组件（极性反转与方位角的发病率）的oceanic接收器功能。极性反转的位置落在与火山建筑物同心的方位角上。所观察到的到来意味着倾斜的各向同性层和/或各向异性织物之间的对比集中在火山至少地壳中部的深度。最近，阿拉斯加火山观测站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多。 模拟工作将有助于区分几个端元模型的穿壳岩浆结构，已提出解释结果从其他方法，如岩石学，层析成像，大地测量，大地电磁学，地震活动性搬迁。这些端元模型包括高或低速地壳体的倾斜界面，岩浆房上方的倾斜断层，以及岩脉和岩床复合体的倾斜。所提出的方法提供的额外的限制将允许更高的分辨率岩浆结构在整个地壳比目前possible.This奖项反映了NSF的法定使命，并已被认为是值得的支持，通过使用基金会的智力价值和更广泛的影响审查标准进行评估。