Array Science for the IRIS Community Wavefields Experiment

IRIS 社区波场实验的阵列科学

• 批准号: 1723067
• 负责人: Charles Langston
• 金额: $ 14.48万
• 依托单位: University of Memphis
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-06-01 至 2020-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1723067&HistoricalAwards=false
• 关键词: Array; Science; IRIS; Community; Wavefields

Seismic waves that move through the Earth give critical information about the earthquake sources that create them and about the physical nature of the crust and mantle that they move through. Seismic waves are generally recorded by a seismic instrument situated at a single spot on Earth's surface so that wave motion is recorded can be seen as time changes. A seismic array is a collection of seismic instruments arranged in a pattern such that waves can be imaged over space as well as time. This additional information is important to the solution of many practical problems in hydrocarbon exploration, earthquake source physics, explosion detection, earthquake hazards assessments, and scientific studies of the structure of Earth's crust and mantle. Research in this project is centered on the study of new array geometries and data analysis methods that have been made possible by the deployment of a scientific-community experiment in Northern Oklahoma by the Incorporated Research Institutions in Seismology (IRIS) consortium. Several experimental arrays were deployed over an area of active earthquake activity to collect seismic data in order to validate the new array methods. Expected results will be important in the design of future arrays and to the understanding of the relatively new Oklahoma seismic activity. In addition, the results will be incorporated into the IRIS Data Analysis and Processing short course held during the summer.The IRIS consortium deployed a community-planned experiment in northern Oklahoma in an area of presumed active induced seismicity from June 22, 2016 until the end of November 2016. Scientific goals for this experiment included: densely recording small to moderate induced earthquakes to understand their source processes, deploying experimental arrays to examine the utility of certain array geometries and methods in determining wave attributes of local and regional seismicity (e.g., horizontal phase velocity, azimuth of propagation), dense recording over two 5- and one 12-km-long profiles to probe for crustal structure, and use of local infrasound arrays in discriminating wave sources seen in the seismic signals. The present project is concerned with the PI-'s contribution to the experiment in testing two experimental array designs. These include a phased, frequency-wavenumber array in the defined by the 'Golay 3x6' spatial geometry 3x6 geometry consisting of 18 broadband stations with a 6 km aperture (3x6 geometry) and a separate 7-level, nested gradiometer consisting of 112 three-component industry nodal seismometers deployed over a square 800m on a side. Deployment of these two arrays offers an unprecedented opportunity to rigorously test the performance of a gradiometer against a phased array using the same earthquake sources that generate the wavefield. A positive result for the much smaller gradiometer would allow array deployments in areas with difficult field conditions such as inaccessibility or having poor security. Objectives for testing the performance of the "Golay 3x6' array are to examine its stability as a function of frequency and degradation of the array response due to field siting requirements. The great redundancy in sampling the wavefield will allow testing of methods to compute the spatial wave gradients and dealing with amplitude statics problems due to site, installation, and instrument response factors. In addition to evaluating the arrays, the seismic data and wave attributes will be used to study local and regional wave propagation and will serve to train young scientists on array processing techniques. The project will support a graduate student.

穿过地球的地震波提供了关于产生它们的地震源以及它们所穿过的地壳和地幔的物理性质的关键信息。 地震波通常由位于地球表面上的单个点处的地震仪器记录，使得记录的波动可以被视为时间变化。 地震台阵是以一定模式排列的地震仪器的集合，使得波可以在空间和时间上成像。 这些额外的信息对于解决油气勘探、震源物理、爆炸探测、地震危险性评估以及地壳和地幔结构的科学研究中的许多实际问题是重要的。 该项目的研究集中在新的阵列几何形状和数据分析方法的研究上，这些方法是由地震学联合研究机构（IRIS）财团在北方俄克拉荷马州部署的科学社区实验所实现的。 在一个地震活动活跃的地区部署了几个实验阵列，以收集地震数据，以验证新的阵列方法。 预期的结果将是重要的，在未来的阵列的设计和了解相对较新的俄克拉荷马州地震活动。此外，研究结果将被纳入夏季举办的IRIS数据分析和处理短期课程中。IRIS联盟在北方俄克拉荷马州的一个假定活跃诱发地震活动的地区部署了一个社区计划的实验，从2016年6月22日到2016年11月底。该实验的科学目标包括：密集记录小到中等诱发地震以了解其震源过程，部署实验阵列以检查某些阵列几何形状和方法在确定当地和区域地震活动性的波属性中的效用（例如，水平相速度、传播方位角），在两个5公里长和一个12公里长的剖面上进行密集记录，以探测地壳结构，并使用当地次声阵列来辨别地震信号中的波源。 本项目关注的是PI-的贡献，在测试两个实验阵列设计的实验。 其中包括一个由“Golay 3x 6”空间几何结构定义的相位频率波数阵列，由18个孔径为6 km的宽带台站组成（3x 6几何结构），以及一个单独的7级嵌套梯度计，由112个三分量工业节点地震仪组成，部署在一个800米的正方形上。这两个阵列的部署提供了一个前所未有的机会，严格测试性能的梯度仪对相控阵使用相同的地震源，产生波场。 小得多的梯度仪的积极结果将允许在实地条件困难的地区部署阵列，如无法进入或安全性差。 测试“Golay 3x 6”阵列性能的目的是检查其作为频率函数的稳定性以及由于现场选址要求而导致的阵列响应退化。波场采样中的大量冗余将允许测试计算空间波梯度的方法，并处理由于场地、安装和仪器响应因素而引起的振幅静校正问题。 除了对阵列进行评价外，地震数据和波属性还将用于研究当地和区域波的传播，并将用于培训年轻科学家掌握阵列处理技术。该项目将资助一名研究生。