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中Gofar变换断层的地震的大小和时机的断层特性。借助高级海洋底部地震仪（观察），岩石收集和故障成像，这项研究将产生对两个6级地震区及其分开的区域的多方面理解。为了确保在预期下一次大地震期间进行连续的地震数据集，该项目涉及三个研究巡游：1）部署观察器并收集岩石样品； 2）恢复，翻新和重新部署观察器，并使用自动水下车辆（AUV）调查断层区； 3）恢复obss。除了希望捕获接下来的两个级主震外，预计两年的数据集将记录成千上万的微观。这项研究将吸引6至12年级的学生，通过将两名来自新英格兰低收入学区的老师带到海上，并与这些老师合作开发课程，这些课程可以被美国各地的老师使用。教师将与项目科学家和新罕布什尔大学的数学，科学和工程教育中心合作，以开发一个“课程套件”，这是一组基于网络的资源，其中包括基于课堂的地震调查，背景信息以及与Gofar实验科学家的定期课堂视频聊天。该项目还将在研究生和博士后的支持下，在国内和国际上在大学层面增强地震研究。选择了该项目的Gofar故障，因为那里的先前工作允许计划进行精确的实验，该实验旨在仅在几公里的时间内进行故障行为的过渡。该实验将以前所未有的细节捕获断层的时间演变，并将这些变化与潜在的地质和断层力学联系起来。具体而言，该项目的目的是了解为什么海洋变换断层由Aseismic滑动主导，具有可重复的地震循环，并在破裂的破裂屏障中构成了数十万个小地震，以阻止大地震。特别是，Gofar的先前工作表明，破裂的屏障行为不能用基本的双峰摩擦特性来解释，并且需要对断层区的更复杂的流变描述。该项目通过使用强度运动阵列记录地震应力下降的时间依赖性，并使用4个短期的小型阵列估算破裂屏障内的地震速度，从而解决这些问题，从而使我们能够使用地震技术使用称为双光束形成的地震技术来确定剪切速度的剪切速度速度的剪切速度进化。该项目将确定S速度的地震前变化是否包含在狭窄的断层区域中或在整个更广泛的损伤区域中分布在何种程度上，并在多大程度上扩展到地震深度。这项研究将比较速度异常的迁移或缺乏故障力学模型，以试图限制破裂屏障的潜在流变学，并研究膨胀性在停止大型破裂中的作用。该项目还将通过基于AUV的测深，反向散射，光摩西成像和水柱调查以及岩石挖泥的结合，对RTF进行最全面的高分辨率映射。这套研究将有助于阐明膨胀和水热改变在破裂区和破裂障碍区域之间产生对比的地震行为方面的作用。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的智力和更广泛影响的评估来通过评估来获得支持的。