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Collaborative Research: Capturing 4D Variations in Stress, Slip, and Fault-Zone Material Properties: The 2019-2021 Gofar Transform Fault Earthquake Prediction Experiment

合作研究：捕捉应力、滑移和断层带材料特性的 4D 变化：2019-2021 年 Gofar 变换断层地震预测实验

基本信息

批准号：
2128784
负责人：
Emily Roland
金额：
$ 22.59万
依托单位：
Western Washington University
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2021
资助国家：
美国
起止时间：
2021-03-01 至 2024-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2128784&HistoricalAwards=false
关键词：
Collaborative Research Capturing 4D Variations

项目摘要

This project will determine the fault properties that control the magnitude and timing of earthquakes on Gofar Transform Fault in the equatorial Pacific Ocean. With an advanced array of ocean bottom seismometers (OBSs), rock collection, and fault imaging, this research will produce a multifaceted understanding of two magnitude 6 earthquake zones and the regions that separate them. To ensure a continuous earthquake dataset over the period that next large earthquakes are expected, this project involves three research cruises: 1) to deploy the OBSs and collect rock samples; 2) to recover, refurbish, and redeploy the OBSs and to survey the fault-zone with an autonomous underwater vehicle (AUV); and 3) to recover the OBSs. The two-year dataset is expected to record hundreds of thousands of microearthquakes in addition to hopefully capturing the next two magnitude 6 mainshocks. This research will reach 6-12th grade students, by taking two teachers from low-income school districts in New England to sea and working with these teachers to develop curricula that can be used by teachers throughout the US. The teachers will work with project scientists and the University of New Hampshire's Center for Mathematics, Science, and Engineering Education to develop a "Curriculum Kit" - a web-based set of resources that will include classroom-based earthquake investigations, background information, and periodic classroom video chats with the Gofar experiment scientists. This project will also enhance earthquake research at the university level both nationally and internationally through the support of graduate students and postdocs. Gofar fault was chosen for this project because previous work there allows for the planning of a precise experiment aimed at imaging transitions in fault behavior over just a few kilometers. This experiment will capture the temporal evolution of the fault in unprecedented detail and link these variations to the underlying geology and fault mechanics. Specifically, the aim of this project is to understand why oceanic transform faults are dominated by aseismic slip, have such repeatable seismic cycles, and nucleate hundreds of thousands of small earthquakes in the rupture barriers that stop large earthquakes. In particular, previous work at Gofar indicates that rupture barrier behavior cannot be explained by basic bimodal frictional properties and requires more sophisticated rheological descriptions of the fault zone. This project approaches these questions by recording the time dependence of earthquake stress drops with a strong-motion array and by estimating seismic velocities within the rupture barrier using 4 mini arrays of short-period OBSs that will allow us to use a seismic technique known as double beam forming to determine the space-time evolution of shear velocity. The project will determine if the pre-seismic changes in S-velocity are contained to a narrow fault-zone or spread throughout the wider damage zone and to what extent they extend to seismogenic depths. This research will compare the migration of the velocity anomalies, or lack thereof, with fault mechanics models to try to constrain the underlying rheology of the rupture barrier and investigate the role of dilatancy in stopping large ruptures. The project will also conduct the most comprehensive, high-resolution mapping of a RTF to date through a combination of AUV based bathymetry, backscatter, photomosaic imaging, and water column surveys along with rock dredging. This suite of studies will help clarify the roles of dilatancy and hydrothermal alteration in producing the contrasting seismic behavior between the rupture zones and rupture barrier regions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

该项目将确定控制赤道太平洋戈法尔转换断层地震震级和时间的断层特性。通过先进的海底地震仪（OBS）阵列，岩石收集和断层成像，这项研究将对两个6级地震带以及将它们分开的地区产生多方面的了解。为了确保在下一次大地震预计发生期间获得连续的地震数据集，该项目涉及三个研究巡航：1）部署OBS并收集岩石样本; 2）恢复，重新部署OBS并使用自主水下航行器（AUV）调查断层带; 3）恢复OBS。这个为期两年的数据集预计将记录数十万次微震，并有望捕捉到接下来的两次6级主震。这项研究将达到6- 12年级的学生，从新英格兰低收入学区的两名教师出海，并与这些教师合作，开发可供全美教师使用的课程。教师们将与项目科学家和新罕布什尔州大学数学、科学和工程教育中心合作，开发一个“课程包”--一套基于网络的资源，包括基于课堂的地震调查、背景信息，以及与Gofar实验科学家定期进行的课堂视频聊天。该项目还将通过研究生和博士后的支持，加强国内和国际大学一级的地震研究。Gofar断层被选为该项目的研究对象，因为之前的工作允许计划一个精确的实验，旨在成像断层行为在短短几公里内的转变。这项实验将以前所未有的细节捕捉断层的时间演化，并将这些变化与潜在的地质和断层力学联系起来。具体来说，这个项目的目的是了解为什么海洋转换断层主要是由地震滑动，有这样的可重复的地震周期，并在阻止大地震的破裂屏障成核的数十万个小地震。特别是，以前在Gofar的工作表明，破裂屏障的行为不能用基本的双峰摩擦性能来解释，需要更复杂的断层带的流变学描述。该项目通过记录强震阵列的地震应力降的时间依赖性和通过使用4个短周期OBSs的小型阵列估计破裂屏障内的地震速度来解决这些问题，这将使我们能够使用称为双波束形成的地震技术来确定剪切速度的时空演化。该项目将确定S速度的震前变化是否包含在狭窄的断层带中或遍布更广泛的破坏区，以及它们在多大程度上延伸到孕震深度。本研究将比较迁移的速度异常，或缺乏，与故障力学模型，试图限制潜在的流变学的破裂屏障和调查的作用，阻止大破裂的粘性。该项目还将通过结合基于AUV的水深测量、反向散射、光电成像和水柱测量沿着岩石疏浚，对RTF进行迄今为止最全面、高分辨率的测绘。这套研究将有助于澄清在破裂带和破裂屏障区域之间产生对比地震行为的过程中，水热和热液蚀变的作用。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。