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

圣海伦斯山下地震活动和散射波成像的高分辨率研究

• 批准号: 1520875
• 负责人: Brandon Schmandt
• 金额: $ 22万
• 依托单位: University of New Mexico
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-07-01 至 2018-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1520875&HistoricalAwards=false
• 关键词: resolution; studies; seismicity; scattered; wave

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.

俯冲带岩浆系统，例如美国西北部的喀斯喀特弧，是主要城市附近潜在自然灾害的根源，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人们更好地了解它们的运作方式。岩浆系统管道结构的地震成像和地震检测可以照亮活跃和以前活跃的熔体通道和储层。然而，火山地区地震波场的复杂性对绘制岩浆管道系统的 3D 结构图以及检测、定位和确定那里发生的各种地震的机制的工作提出了挑战。这些挑战很大程度上反映了观察的局限性。用于观测圣海伦斯火山等火山的典型地震仪网络由约 10 台长期地震仪组成。该项目将分析在圣海伦火山山顶火山口 12 公里范围内部署的 900 台地震仪的短期数据，为期两周。 密集的地震数据将用于识别圣海伦斯山下方微地震活动的精细尺度空间和时间分布，并确定地震活动如何与地壳和上地幔中流体和冷却侵入体的 3-D 盛行程度相关联。该项目旨在通过最上面 10-15 公里的散射波成像和断层扫描来解析圣海伦斯山下方的 3D 岩浆管道。该项目的一个主要组成部分将是测试和改进使用来自大量传感器的连续数据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，无法使用单站方法进行检测。还将通过弧下莫霍面的反射成像和下地壳深部长周期地震的发生率调查来研究更深层次的熔化和变形过程。莫霍面成像将利用受控源和丰富的当地地震活动。数据产品将公开，并且利用密集地震仪阵列推进混合主动/被动源 3D 研究可能在不久的将来对地震学界有价值。该项目将支持研究生、本科生实习生和博士后的培训。