High-resolution studies of seismicity and scattered wave imaging beneath Mt. St. Helens

俯冲带岩浆系统，如美国西北部的喀斯喀特弧，是主要城市附近潜在的自然灾害的基础，被认为是大陆地壳形成的主要因素。这些系统在人类和地质时间尺度上的重要性值得我们更好地了解它们是如何运作的。岩浆系统管道构造的地震成像和地震探测可以阐明活跃的和曾经活跃的熔体路径和储层。然而，火山地区地震波场的复杂性给绘制岩浆管道系统的三维结构以及探测、定位和确定发生在那里的各种地震的机制带来了挑战。这些挑战在很大程度上反映了观测的局限性。典型的观测火山（如圣海伦火山）的地震仪网由~10台长期地震仪组成。该项目将在圣海伦火山山顶火山口12公里范围内部署900台地震仪，在两周内分析短期数据。密集的地震数据将用于确定圣海伦斯山下微地震活动的精细尺度时空分布，并确定地震活动如何与地壳和上地幔中流体和冷却侵入物的三维流行相关联。该项目旨在通过最上层10-15公里的散射波成像和断层扫描，解决圣海伦斯山下的三维岩浆管道问题。该项目的一个主要组成部分将是测试和改进微震活动自动检测方法，该方法使用来自大量传感器的连续数据，每个传感器都可能具有高噪声水平，无法使用单站方法进行检测。还将通过弧下莫霍反射成像和下地壳深长周期地震流行率的调查来研究更深层次的融化和变形过程。莫霍成像将利用可控震源和丰富的当地地震活动性。数据产品将向公众开放，在不久的将来，利用密集地震仪阵列推进混合有源/被动源3-D研究可能对地震学界有价值。该项目将支持培养1名研究生、1名本科生实习生和1名博士后。

Subduction zone magmatic systems, such as in the Cascades Arc of the northwestern U.S., underlie potential natural hazards near major cities and are considered the primary agents of continental crust production. The significance of these systems on both human and geological time scales merits a greater understanding of how they function. Seismic imaging of the plumbing structure of magmatic systems and detection of earthquakes can illuminate active and formerly active melt pathways and reservoirs. However, the complexity of seismic wave fields in volcanic regions challenges efforts to map the 3-D structure of magma plumbing systems as well as efforts to detect, locate, and determine the mechanisms of the diverse range of earthquakes that occur there. The challenges largely reflect observational limitations. Typical seismograph networks for observing volcanoes such as Mt. St. Helens are composed of ~10 long-term seismographs. This project will analyze data from a short-term, two week, deployment of 900 seismographs within 12 km of the summit crater of Mt. St. Helens. The dense seismic data will be used to identify the fine scale spatial and temporal distribution of micro-seismicity beneath Mt. St. Helens and determine how that seismicity is linked to the 3-D prevalence of fluids and cooled intrusions in the crust and uppermost mantle. The project aims to resolve the 3-D magma plumbing beneath Mt. St. Helens with scattered wave imaging and tomography of the uppermost 10-15 km. A major component of the project will be testing and advancing methods for automated detection of mirco-seismicity using continuous data from large numbers of sensors, each with potentially high noise levels that prevent detection with single-station methods. Deeper melting and deformation processes will also be investigated through reflection imaging of the sub-arc Moho and investigation of the prevalence of deep long period earthquakes in the lower crust. Moho imaging will exploit both controlled sources and abundant local seismicity. Data products will be made publicly available, and advancing hybrid active/passive source 3-D studies with dense seismograph arrays is likely to be valuable for the seismology community in the near future. The project will support the training of a graduate student, an undergraduate intern, and a postdoctoral fellow.