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，例如在美国西北部的级联弧中，主要城市附近的潜在自然危害是大陆壳生产的主要代理。这些系统在人类和地质时间尺度上的重要性值得对它们的运作有更多的了解。岩浆系统的管道结构和地震检测的地震成像可以照亮主动且原活跃的熔体途径和储层。但是，火山区域中的地震波场的复杂性挑战了绘制岩浆管道系统的3-D结构的努力，以及检测，定位和确定那里发生的各种地震范围的机制的努力。挑战在很大程度上反映了观察性的局限性。观测火山（例如圣海伦斯山）的典型地震仪网络由约10个长期地震仪组成。该项目将分析短期（两周）的数据，在圣海伦斯山山顶山口12公里内部署了900张地震仪。 密集的地震数据将用于识别圣海伦斯山下方微观性的精细空间和时间分布，并确定这种地震性与液体的3-D流行率以及在地壳和上层披风中的3-D流行率有关。该项目旨在解决圣海伦斯山下方的3-D岩浆管道，并以10-15公里的最高波浪成像和层析成像和断层扫描。该项目的一个主要组成部分是使用来自大量传感器的连续数据进行测试和前进的方法，用于自动检测Mirco-seismicity，每个传感器都具有潜在的高噪声水平，可防止使用单站方法检测。还将通过反射成像对下壳中深层地震中深层地震的患病率进行反射成像来研究更深的熔化和变形过程。 Moho成像将利用受控的来源和丰富的局部地震性。数据产品将公开提供，并在不久的将来推进具有密集地震仪阵列的混合动力/被动源3-D研究对地震学社区很有价值。该项目将支持研究生，本科实习生和博士后研究员的培训。