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兹弧形岩浆系统，在主要城市附近潜伏着潜在的自然灾害，被认为是大陆地壳产生的主要因素。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发挥作用的。岩浆系统管道结构的地震成像和地震的探测可以阐明活动的和以前活动的熔融路径和储集层。然而，火山地区地震波场的复杂性对绘制岩浆管道系统的三维结构图以及探测、定位和确定发生在那里的各种地震的机制提出了挑战。这些挑战在很大程度上反映了观测的局限性。用于观测火山等火山的典型地震仪网络。圣海伦斯由约10台长期地震仪组成。该项目将分析在山顶火山口12公里范围内部署900台地震仪的短期、为期两周的数据。圣海伦斯。高密度的地震资料将被用来识别山下微震活动的细尺度时空分布。并确定地震活动如何与地壳和地幔最上部的流体和冷却侵入的3D流行联系在一起。该项目旨在解决山下的三维岩浆管道问题。圣海伦斯用散射波成像和层析成像，最高处10-15公里。该项目的一个主要组成部分将是使用来自大量传感器的连续数据来测试和推进自动检测微震活动的方法，每个传感器都具有潜在的高噪声水平，使单站方法无法进行检测。还将通过弧下莫霍面的反射成像和调查下地壳深部长周期地震的盛行情况来研究更深层次的熔融和变形过程。莫霍面成像将同时利用受控震源和丰富的局部地震活动。数据产品将公之于众，利用密集的地震仪阵列推进主动/被动混合震源三维研究可能在不久的将来对地震学界有价值。该项目将支持培养一名研究生、一名本科实习生和一名博士后研究员。

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.