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

• 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

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。借助先进的海底地震仪 (OBS) 阵列、岩石采集和断层成像，这项研究将对两个 6 级地震带及其分隔区域产生多方面的了解。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、翻新和重新部署OBS，并使用自主水下航行器（AUV）勘测断层带； 3) 恢复OBS。 除了有望捕获接下来的两次 6 级主震之外，这个为期两年的数据集预计还将记录数十万次微地震。这项研究将针对 6-12 年级的学生，将来自新英格兰低收入学区的两名教师带到海上，并与这些教师合作开发可供全美国教师使用的课程。教师们将与项目科学家和新罕布什尔大学数学、科学和工程教育中心合作开发一个“课程套件”——一套基于网络的资源，其中包括基于课堂的地震调查、背景信息和定期与 Gofar 实验科学家进行课堂视频聊天。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层面的地震研究。该项目选择戈法尔断层是因为之前的工作允许规划一项精确的实验，旨在对短短几公里内断层行为的转变进行成像。该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，该项目的目的是了解为什么海洋转换断层以抗震滑移为主，具有如此可重复的地震周期，并在阻止大地震的破裂屏障中引发数十万次小地震。特别是，Gofar 之前的工作表明，破裂屏障行为不能用基本的双峰摩擦特性来解释，需要对断层带进行更复杂的流变学描述。该项目通过使用强震动阵列记录地震应力降的时间依赖性，并使用 4 个短周期 OBS 微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地震技术波束形成以确定剪切速度的时空演化。该项目将确定震前 S 速度的变化是否被限制在狭窄的断层带内，还是扩散到更广泛的损坏区域，以及它们延伸到震源深度的程度。 这项研究将比较速度异常的迁移或缺乏速度异常的情况与断层力学模型，以尝试约束破裂屏障的潜在流变性并研究剪胀性在阻止大破裂中的作用。该项目还将通过结合基于 AUV 的测深、反向散射、马赛克成像、水柱勘测以及岩石疏浚，对 RTF 进行迄今为止最全面、高分辨率的测绘。这套研究将有助于阐明剪胀性和热液蚀变在破裂带和破裂屏障区域之间产生对比地震行为中的作用。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和知识进行评估，被认为值得支持。更广泛的影响审查标准。

项目成果

Observing a Seismic Cycle at Sea

观测海上地震周期

• DOI: 10.1029/2023eo230076
• 发表时间: 2023-03
• 期刊: Eos
• 作者: Boettcher, Margaret;Roland, Emily;Warren, Jessica;Evans, Robert;Collins, John
• 通讯作者: Collins, John