Collaborative Research: Can Low-Angle Normal Faults Produce Earthquakes? Reading a Pseudotachylyte 'Rosetta Stone'

合作研究:低角度正断层能否产生地震?

基本信息

  • 批准号:
    1630130
  • 负责人:
  • 金额:
    $ 29.04万
  • 依托单位:
  • 依托单位国家:
    美国
  • 项目类别:
    Standard Grant
  • 财政年份:
    2016
  • 资助国家:
    美国
  • 起止时间:
    2016-08-01 至 2022-07-31
  • 项目状态:
    已结题

项目摘要

The physics of earthquake-producing fault rupture has been studied for over a hundred years, a period marked by dramatic advances in the instrumentation and analytical techniques required to understand both the ground shaking (seismicity) caused by fault failure and the physical properties of fault rocks. This research addresses a discrepancy between the long-term rock record of ancient earthquakes and the short-term historical seismic record. Specifically, it focuses on representatives of a class of faults that appear to be poorly oriented for breakage according to the current earthquake mechanics paradigm and Andersonian mechanical theory for the rupture of rocks. According to established theory, normal faults that form at low angles (i.e., less than 30 degrees) should not produce significant earthquakes because the tectonic forces that cause failure are oriented at a high angle to the fault surface. The historical seismicity record generally supports this argument, suggesting that such faults produce only microearthquakes. However, the geologic record contains numerous examples of normal faults that appeared to have slipped at low (less than 30 degree) dips. The presence of pseudotachylite, an extremely quickly cooled, glassy melt rock that generally forms as the result of frictional heating during seismic slip, has been found to be associated with some of these low angle faults, and thus preserves a record of 'fossil earthquakes.' In this study, the principal investigators have identified an unusually rich record of 'fossil earthquakes' on a low angle normal fault in the South Mountains, Arizona. This research is exploring this fossil record with the goal of determining whether or not such faults produce significant earthquakes in non-Andersonian orientations, thus addressing a first-order question in fault mechanics. The research will not only result in a deeper understanding of the earthquake record and the potential seismic hazard of 'misoriented' faults, but also has the potential to transform our understanding of fault mechanics. In addition to the scientific objectives of this research, the project will contribute to the training of graduate and undergraduate students in a STEM (science, technology, engineering, and mathematics) discipline, thus contributing to a more scientifically literate and vibrant society. It represents a collaborative effort between investigators from two research-intensive public universities. Research results will be disseminated by presentation at national geoscience meetings and through the peer-reviewed scientific literature. The results will also be used to engage and educate the public regarding geologic concepts and earthquake hazards through a partnership with the University of Wisconsin Geology Museum to produce participatory exercises and videos and online teaching modules. Low-angle normal faults (LANFs) are poorly oriented for slip according to Andersonian fault mechanics. The geologic record generally supports slip at current low (less than 30 degrees) dips; however, the seismic record generally suggests such faults cannot produce earthquakes greater than magnitude 5.5. One explanation for the discrepancy between these data sets is that the large size and greater efficiency of LANFs result in recurrence intervals longer than the seismic record. A second is that LANFs were re-oriented by isostatic rebound as they were exhumed, allowing them to slip at steeper dips before rotating into their final, shallow orientations. A third explanation, one which reconciles the geologic and geophysical records, is that low angle normal faults fail by creep, producing microseismicity but not substantial earthquakes. Although a convincing explanation for the two active faults that demonstrably record creep, this does not account for the common occurrence of pseudotachylyte in exhumed low-angle normal fault zones worldwide. The purpose of the proposed research is to explore this fossil record of earthquakes using exposures from the South Mountains metamorphic core complex. This site was chosen because pseudotachylyte fault veins are plentiful and amenable to both rock magnetic and geochronologic analyses. This project will test the following hypotheses by integrated structural, thermochronologic, and paleomagnetic analyses and modeling: (1) Recurrence intervals of the largest earthquakes are sufficiently long that they can be distinguished within the error of 40Argon/39Argon isotopic ages (+/- ca. 0.25 million years). (2) Paleomagnetic remanence indicates that earthquakes occurred at current fault dips (less than 30 degrees). (3) Fault veins in the South Mountains record a range of earthquake sizes, the largest of which are greater than magnitude 5.5. The principal investigators will use the magnetic record preserved in pseudotachylyte to quantify fault rotation (tilting), if any, seismogenesis. The remanence vector recorded by each sample will be compared with the expected geomagnetic field direction by correlating the sample?s 40Argon/39Argon age with its concomitant geomagnetic north location and comparison with the North American apparent polar wander path. Any divergence between the two vectors will represent rotation of the system since seismic slip, ultimately allowing us to quantify the angle at which a LANF was active. The cooling history of the wall rock also will be determined using several thermochronometers. Modeling will incorporate these data and constrain earthquake magnitude based on pseudotachylyte fault vein thickness. The project addresses a first-order question in fault mechanics and will provide a deeper understanding of the record of ancient seismicity in the metamorphic core complexes of the western U.S.
产生地震的断层破裂的物理学已经研究了一百多年,这一时期的标志是仪器和分析技术的巨大进步,这些技术需要了解断层破坏引起的地面震动(地震活动性)和断层岩石的物理特性。这项研究解决了古地震的长期岩石记录与短期历史地震记录之间的差异。具体来说,它侧重于一类故障,似乎是面向坏根据目前的地震力学范式和安德森力学理论的岩石破裂的代表。根据已建立的理论,以低角度形成的正断层(即,小于30度)不应产生重大地震,因为导致断裂的构造力与断层表面成高角度定向。历史上的地震活动记录通常支持这一论点,表明这样的断层只产生微震。然而,地质记录包含了许多正断层的例子,这些正断层似乎在低倾角(小于30度)滑动。假玄武玻璃岩是一种冷却极快的玻璃状熔融岩石,通常是地震滑动过程中摩擦加热的结果,它的存在被发现与这些低角度断层中的一些有关,因此保存了“化石地震”的记录。在这项研究中,主要研究人员在亚利桑那州南部山脉的一个低角度正断层上发现了异常丰富的“化石地震”记录。这项研究正在探索这种化石记录,目的是确定这些断层是否会在非安德森方向产生重大地震,从而解决断层力学中的一阶问题。这项研究不仅将导致对地震记录和“错误定向”断层的潜在地震危险的更深入的理解,而且有可能改变我们对断层力学的理解。除了这项研究的科学目标外,该项目还将有助于培养STEM(科学、技术、工程和数学)学科的研究生和本科生,从而为建设一个更具科学素养和活力的社会做出贡献。它代表了来自两所研究密集型公立大学的研究人员之间的合作努力。研究结果将通过在国家地球科学会议上介绍和通过同行审查的科学文献传播。通过与威斯康星州大学地质博物馆合作,制作参与性练习、视频和在线教学模块,其结果还将用于就地质概念和地震灾害吸引公众并对其进行教育。根据安德森断层力学,低角度正断层(LANF)的滑动方向很差。地质记录通常支持当前低倾角(小于30度)的滑动;然而,地震记录通常表明这种断层不会产生大于5.5级的地震。对这些数据集之间差异的一种解释是,LANF的大尺寸和更高的效率导致重现间隔长于地震记录。第二个是,LANF被重新定向的均衡反弹,因为他们被挖出,让他们在更陡的倾角滑动之前旋转到他们的最终,浅的方向。第三种解释,一种调和地质和地球物理记录的解释,是低角度的正断层由于蠕动而破裂,产生了微震活动,但不是实质性的地震。虽然这是一个令人信服的解释,两个活断层,证明记录蠕变,这并不能解释常见的假玄武玻璃在世界各地的低角度正断层带的折返。拟议的研究的目的是探索这一化石记录的地震暴露从南部山区变质核杂岩。 之所以选择这个地点,是因为假玄武玻璃断层脉丰富,适合岩石磁性和地质年代学分析。本项目将通过综合构造、热年代学和古地磁分析和模拟来验证以下假设:(1)最大地震的重复间隔足够长,可以在40 Ar/39 Ar同位素年龄(+/- ca.)的误差范围内区分它们。0.25百万年)。(2)古地磁剩磁表明地震发生在当前的断层倾角(小于30度)。(3)南部山脉的断层脉记录了一系列地震规模,其中最大的大于5.5级。主要研究人员将使用保存在假玄武玻璃中的磁记录来量化断层旋转(倾斜),如果有的话,地震成因。将每个样品记录的剩磁矢量与预期的地磁场方向进行比较,并将样品与地磁场方向进行相关。s 40 Ar/39 Ar年龄及其伴随的地磁北向位置和与北美视极移路径的比较。两个矢量之间的任何分歧都将代表自地震滑动以来系统的旋转,最终使我们能够量化LANF活动的角度。围岩的冷却历史也将使用几个热计时器来确定。建模将结合这些数据,并根据假玄武玻璃断层脉厚度限制地震震级。该项目解决了断层力学中的一阶问题,并将提供对美国西部变质核杂岩中古代地震活动记录的更深入了解。

项目成果

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Laurel Goodwin其他文献

Laurel Goodwin的其他文献

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{{ truncateString('Laurel Goodwin', 18)}}的其他基金

From damage zone to core: quantifying mechanical and hydrological coupling during fault-zone structural evolution
从损伤带到核心:量化断层带结构演化过程中的机械和水文耦合
  • 批准号:
    1951985
  • 财政年份:
    2020
  • 资助金额:
    $ 29.04万
  • 项目类别:
    Standard Grant
EAGER: Collaborative Research: Can Low-Angle Normal Faults Produce Earthquakes? A Paleoseismic Perspective
EAGER:合作研究:低角度正断层能否产生地震?
  • 批准号:
    1237105
  • 财政年份:
    2012
  • 资助金额:
    $ 29.04万
  • 项目类别:
    Standard Grant
Student Support for 2010 Electron Backscatter Diffraction Topical Conference
2010 年电子背散射衍射专题会议的学生支持
  • 批准号:
    1015246
  • 财政年份:
    2010
  • 资助金额:
    $ 29.04万
  • 项目类别:
    Standard Grant
Student Support for Electron Backscattered Diffraction Topical Conference
电子背散射衍射专题会议的学生支持
  • 批准号:
    0813918
  • 财政年份:
    2008
  • 资助金额:
    $ 29.04万
  • 项目类别:
    Standard Grant
Collaborative Research: Using Pore Fluid Pressure Gradients to Test the Relative Importance of Hydrologic Versus Mechanical Heterogeneity in Fracture Formation
合作研究:利用孔隙流体压力梯度测试裂缝形成中水文与力学非均质性的相对重要性
  • 批准号:
    0635965
  • 财政年份:
    2007
  • 资助金额:
    $ 29.04万
  • 项目类别:
    Standard Grant
Acquisition of a Versatile Scanning Electron Microscope
购买多功能扫描电子显微镜
  • 批准号:
    0447332
  • 财政年份:
    2005
  • 资助金额:
    $ 29.04万
  • 项目类别:
    Standard Grant
Localization of Deformation in Lithologically Heterogeneous Lower Crust, Arunta Block, Central Australia
澳大利亚中部阿伦塔地块岩性非均质下地壳变形局部化
  • 批准号:
    0440156
  • 财政年份:
    2005
  • 资助金额:
    $ 29.04万
  • 项目类别:
    Continuing Grant
Hydrogeologic Characterization of the Sand Hill Fault Zone, Albuquerque Basin, New Mexico
新墨西哥州阿尔伯克基盆地沙山断裂带的水文地质特征
  • 批准号:
    9706482
  • 财政年份:
    1998
  • 资助金额:
    $ 29.04万
  • 项目类别:
    Continuing Grant
RPG: Characterization of Pseudotachylyte Formed in an Extensional Tectonic Regime
RPG:伸展构造体系中形成的假速石的表征
  • 批准号:
    9304973
  • 财政年份:
    1993
  • 资助金额:
    $ 29.04万
  • 项目类别:
    Standard Grant

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