Magmatic system structure and seismicity of the Three Sisters volcanic complex

这个项目调查了俄勒冈州中部的三姐妹火山群。它将使用地震观测和方法来推进对火山危害的理解，以及产生不同类型火山和岩浆类型的基本过程。这个火山系统是活跃的，附近人口中心的存在意味着三姐妹火山被列为美国的高威胁火山系统。三姐妹火山群包括各种各样的火山结构和地质年轻的熔岩（大约2000年）。此外，大约20年的卫星数据显示，火山附近的地区由于地表下的膨胀而变形。现有的数据很少，部分原因是火山附近是一个难以进入和联邦保护的荒野。该项目将通过使用小型临时地震仪器在这些地区增加观测，这些仪器可以步行运输，不需要挖掘，以解决可达性挑战和最小化影响的需求。将新的临时地震数据与现代成像和地震探测方法相结合，研究人员将获得地下结构的系统视图。这将有助于更严格地了解以前的喷发记录和对变形的持续监测。地震数据收集和分析将吸引来自多个机构的学生和区域灾害监测机构的人员，以促进专业培训和与利益相关者的沟通。三姐妹火山复合体被美国地质调查局（U.S. geological Survey）列为高度威胁系统，有大地测量证据表明，三姐妹火山复合体的地表正在发生变形，熔岩流距今约1600年，全新世火山喷发的成分从玄武岩安山岩到流纹岩不等。然而，对于位于高喀斯喀特地堑内的多喷口火山复合体的中上部地壳岩浆储存和微地震活动的三维分布知之甚少。观测地震学受到了限制，因为它需要在广袤的联邦荒野中尽量减少影响。该项目将部署一系列低冲击节点地震检波器，首次提供三姐妹岩浆系统的局部成像。对这些数据的分析将有助于了解多喷口系统中的岩浆储层结构如何与大厦结构和喷发成分的空间变化联系在一起，火山复合体北部以玄武岩安山岩为主，而南端则以流纹岩喷发为主。新的临时网络数据的地震成像将从相对传统的环境噪声表面波层析成像开始，然后通过应用各向异性伴随层析成像来突破临时节点阵列成像的界限。利用数值三维波传播和反演方法，探讨了构造地形和径向各向异性对岩浆储层成像的影响。新数据还将用于仔细检查微地震活动，并对局部界面进行接收函数成像，这可以更好地定义构造和岩浆变形结构之间的相互作用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project investigates the Three Sisters volcanic complex in central Oregon. It will use seismic observations and methods to advance understanding of volcanic hazards and the fundamental processes that create different types of volcanoes and magma types. This volcanic system is active, and the presence of nearby population centers means the Three Sisters is classified as a Very High Threat volcanic system for the U.S. The Three Sisters volcanic complex includes a wide variety of volcanic structures and geologically young lavas (about 2,000 years old). Additionally, about two decades of satellite data show that areas near the volcanoes are deforming due to inflation under the surface. Existing data are scarce partly because the immediate vicinity of the volcanoes is a difficult to access and federally protected Wilderness. This project will add observations in these areas by using small temporary seismic instruments, that can be transported on foot and do not require digging, to address both the accessibility challenges and the need for minimal impact. Combining the new temporary seismic data with modern imaging and earthquake detection methods, the researchers will gain a systematic view of subsurface structures. This will assist in more rigorously understanding the record of prior eruptions and ongoing monitoring of deformation. The seismic data collection and analysis will engage students from multiple institutions and personnel from regional hazard monitoring agencies to promote professional training and communication to stakeholders.The Three Sisters volcanic complex is classified by a U.S. Geologic Survey report as a Very High Threat system, with geodetic evidence for ongoing surface deformation, lava flows as young as about 1,600 years, and Holocene eruptions of compositions ranging from basaltic andesite to rhyolite. Yet, there is little knowledge of the 3-D distribution of middle to upper crustal magma storage and microseismicity beneath this multi-vent volcanic complex located within the High Cascades graben. Observational seismology has been limited by the need for minimal impact in a large federal Wilderness. The project will deploy an array of low-impact nodal seismometers to provide the first local imaging of the Three Sisters magmatic system. Analysis of the data will advance understanding of how magma reservoir structure in multi-vent systems is linked to spatial variations in edifice construction and erupted compositions, with dominantly basaltic andesite in the northern part of the volcanic complex transitioning to more prevalent rhyolite eruptions at the southern end. Seismic imaging with the new temporary network data will begin with relatively conventional ambient noise surface wave tomography and then push the boundaries of temporary nodal array imaging by applying anisotropic adjoint tomography. The influences of edifice topography and radial anisotropy on magma reservoir imaging will be tested with numerical 3-D wave propagation and inversion methods. The new data will also be used to scrutinize microseismic activity and conduct receiver function imaging of localized interfaces, which could better define interactions between tectonic and magmatic deformation structures.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.