Volcanic transcrustal magmatic systems imaged with teleseismic converted phases

阿拉斯加的阿留申火山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。这类弧线也具有科学价值，因为它们是形成新的大陆地壳的地质背景。我们对火山地下管道的理解最近有所发展。从单一岩浆室的简单图像中，出现了地壳各级相互连接的洞室的复杂系统的图像。详细研究这些深部结构对于更好地了解火山及其相关危险至关重要。然而，由于技术限制，这样的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，利用全球发生的地震记录。通过分析记录的波形的整个形状--而不仅仅是到达时间--他们描绘了火山下面的3D岩浆结构。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。新的观测显示了复杂的地下结构，这些结构看起来像是围绕火山的同心圆，在地壳的所有深度都可以检测到。该项目有助于改善对当地社区、基础设施和空中交通路线的危险评估。它促进了与K-12科学教师的接触，并通过乌纳拉斯加州的阿留申博物馆，特别是通过当地电视广播向公众宣传。它还通过面向在地球科学中代表性不足的群体的计划，促进对本科生的培训。岛弧作为大陆地壳产生的地点，对构造学感兴趣。阿留申群岛和阿拉斯加的火山提供了极好的弧形火山活动类型的横截面。该项目利用了最近对阿拉斯加火山现有监测网络的更新。它测试了一种新的被动震源成像方法，可以在整个地壳深度对弧形火山下的岩浆系统进行被动震源成像。拟议的工作是开发一种新的基于波形的方法，用于详细成像和描述地壳深处的火山结构。它使用数量稀少的宽带站，以补充更昂贵的有源源实验和密集部署。该方法还利用弧形火山附近的远震接收功能中的大到达，这些弧形火山由周期性的后方向分量(极性与入射方位角反转)主导。极性反转的位置落在与火山建筑物同心的方位上。观测到的到达意味着各向同性地层和/或以火山为中心的各向异性组构之间的倾斜对比，至少达到地壳中部深度。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多。建模工作将有助于区分跨地壳岩浆结构的几个端元模型，这些模型已被提出用来解释其他方法的结果，如岩石学、层析成像、大地测量学、大地电磁和地震活动重新定位。这些端元模型包括与高或低速地壳的倾角界面，岩浆室上方的倾角断层，以及岩脉和岩床杂岩中的倾角。提议的方法提供的额外限制将允许整个地壳中比目前可能的更高分辨率的岩浆结构。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.