Array Science for the IRIS Community Wavefields Experiment

在地球上传播的地震波提供了有关产生地震波的震源以及地震波通过的地壳和地幔的物理性质的关键信息。地震波通常是由位于地球表面某一地点的地震仪记录的，因此记录的波动可以随着时间的变化而被看到。地震阵列是以某种模式排列的地震仪器的集合，以便可以在空间和时间上对波进行成像。这一补充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科学研究中的许多实际问题很重要。该项目的研究集中在研究新的阵列几何和数据分析方法，这些新的阵列几何和数据分析方法是通过地震研究所(IRIS)联盟在俄克拉荷马州北部部署的科学社区实验而成为可能的。在地震活跃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。预期结果将对未来阵列的设计和对相对较新的俄克拉荷马州地震活动的了解具有重要意义。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。IRIS联盟在俄克拉荷马州北部一个假定活跃的诱发地震地区部署了一项社区计划的实验，从2016年6月22日到2016年11月底。这次实验的科学目标包括：密集记录中小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的波属性(如水平相速度、传播方位)方面的效用，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，以及利用当地次声阵列区分地震信号中看到的波源。本项目涉及Pi-‘S对测试两个实验阵列设计的实验的贡献，其中包括一个由18个宽带站组成、口径为6公里(3x6几何)的相控式频率波数阵列和一个独立的7级嵌套梯度计，该梯度计由112个三分量工业节点地震仪组成，分布在一侧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，可以使用产生波场的相同震源，严格测试梯度计与相控阵的性能。小得多的梯度计的积极结果将允许在野外条件困难的地区部署阵列，例如无法进入或安全性较差的地区。测试“Golay 3x6”阵列的性能的目的是检查其稳定性随频率的变化以及由于现场选址要求而引起的阵列响应的退化。对波场采样的巨大冗余度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引起的幅度静校正问题。除了评估阵列外，地震数据和波属性将用于研究本地和区域波的传播，并将用于培训年轻的科学家阵列处理技术。该项目将支持一名研究生。

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.