CAREER: Stress, deformation and seismicity in continental interiors: Testing the "weak zone" hypothesis

职业：大陆内部的应力、变形和地震活动：检验“薄弱区”假说

• 批准号: 1944998
• 负责人: Maximiliano Bezada
• 金额: $ 47.44万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-07-01 至 2025-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1944998&HistoricalAwards=false
• 关键词: CAREER; Stress; deformation; seismicity; continental

Most earthquakes happen around the edges of tectonic plates. Yet, large and damaging earthquakes occasionally happen in the continental interiors. The reasons why earthquakes occur away from tectonic plate boundaries is not well understood. Several possible explanations have been proposed and they have been debated for decades. Here, the researchers test one of the leading explanations: "weak zones" in the continental interior may lead to the buildup of stress, resulting in earthquakes. To explore this possibility, they use records of seismic waves produced by distant earthquakes. These waves propagate through the Earth’s crust and mantle. They are used to investigate Earth’s interior in a similar way that sonography is used in medical imaging. The team investigates several regions where weak zones may exist, in Australia and the United States. It analyzes records to determine if seismic waves have lost energy on their path through the Earth. Indeed, when the waves pass through a weak zone, they lose a significant amount of energy which can be detected. This allows mapping the locations of possible weak zones, hence where stresses build up in continental interiors. These data are used as input for geodynamic models which reproduce the mechanics of continental plates and weak zones. To test the models, their outputs – i.e., modeled earthquake locations and characteristics - are compared to records of real earthquakes using statistical analysis tools. The project provides support for an early career scientist from a group underrepresented in Science. It also provides training for a postdoctoral associate and a graduate student at the University of Minnesota – Twin Cities. Aspects of this research are integrated with an educational component that uses sound and music to introduce concepts in signal analysis and Earth imaging.The researchers test the "weak zone" hypothesis in terms of lateral rheological variations. The work includes three phases: 1) Seismic imaging (primarily teleseismic attenuation) will constrain lateral variations in viscous strength in the studied areas; 2) Geodynamic modeling will determine where the imaged strength anomalies would lead to enhanced deviatoric stresses, given the regional stress field; 3) Molchan error analysis will quantitatively measure the ability of the expected deviatoric stresses to predict the seismogenic regions. Phase 3 will include testing of the results for statistical significance. The relative magnitudes of the principal stresses predicted by the modeling will also be compared to observations. The studied regions include Australia, the Eastern U.S. and the South-Central U.S. Target areas were chosen because of the availability of the requisite data. Preliminary imaging also shows that seismicity is consistent with the weak zone hypothesis in these regions. For the South-Central U.S., the focus is on induced seismicity; the team test there whether the existence of a weak zone can explain the disproportionately high occurrence of induced seismicity in Oklahoma.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.

大多数地震发生在构造板块的边缘。然而，大而破坏性的地震偶尔会发生在大陆内部。地震发生在远离构造板块边界的地方的原因尚不清楚。人们提出了几种可能的解释，并且争论了几十年。在这里，研究人员测试了一种主要的解释：大陆内部的“薄弱地带”可能导致压力积聚，从而导致地震。为了探索这种可能性，他们使用了遥远地震产生的地震波记录。这些波通过地壳和地幔传播。它们被用来研究地球内部，就像超声波被用于医学成像一样。该小组调查了澳大利亚和美国几个可能存在弱区的地区。它通过分析记录来确定地震波在穿过地球的过程中是否损失了能量。事实上，当波通过一个弱区时，它们会损失大量的能量，这是可以检测到的。这样就可以绘制出可能的薄弱地带的位置，从而在大陆内部形成压力。这些数据被用作重现大陆板块和弱带力学的地球动力学模型的输入。为了测试这些模型，它们的输出——即模拟的地震位置和特征——使用统计分析工具与真实地震的记录进行比较。该项目为来自《科学》杂志中代表性不足的群体的早期职业科学家提供支持。它还为明尼苏达大学双城分校的一名博士后和一名研究生提供培训。这项研究的各个方面都与一个教育组成部分相结合，使用声音和音乐来介绍信号分析和地球成像的概念。研究人员从横向流变变化的角度检验了“弱区”假说。这项工作包括三个阶段：1)地震成像（主要是远震衰减）将约束研究区域粘性强度的横向变化；2)在给定区域应力场的情况下，地球动力学建模将确定成像强度异常将导致偏应力增强的位置；Molchan误差分析将定量地衡量预期偏应力预测孕震区的能力。第三阶段将包括测试结果的统计显著性。模拟所预测的主应力的相对大小也将与观测结果进行比较。研究的地区包括澳大利亚、美国东部和美国中南部。选择目标地区是因为有必要的数据。初步成像还表明，这些地区的地震活动性符合弱带假说。对于美国中南部，重点是诱发地震活动；研究小组在那里测试了弱带的存在是否可以解释俄克拉何马州诱发地震活动的不成比例的高发生率。该奖项反映了美国国家科学基金会的法定使命，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。

项目成果

Evidence for Stress Localization Caused by Lithospheric Heterogeneity From Seismic Attenuation

• DOI: 10.1029/2021gc009987
• 发表时间: 2021-06
• 期刊: Geochemistry
• 影响因子: 3.7
• 作者: Zhao Zhu;M. Bezada;J. Byrnes;H. Ford