Earthquake nucleation on rate and state faults: Theory (mostly) and some observations
速率和状态断层的地震成核:理论(主要)和一些观察
基本信息
- 批准号:0538156
- 负责人:
- 金额:$ 19.4万
- 依托单位:
- 依托单位国家:美国
- 项目类别:Continuing Grant
- 财政年份:2005
- 资助国家:美国
- 起止时间:2005-12-01 至 2009-11-30
- 项目状态:已结题
- 来源:
- 关键词:
项目摘要
Earthquakes do not begin at a single point in space, but via accelerating slip over a region of finite size termed the nucleation zone. The nucleation process is important because it determines whether or under what conditions detectable precursory signals may be produced, as well as the response of the fault to a suddenly-applied stress step, such as from a nearby large earthquake. Despite the fact that the "rate and state" formulation for fault friction has been widely used for over two decades, there is currently no general theory for determining the size of the nucleation zone on natural (elastically deformable) faults. In a recent numerical and analytical study, the PI and post-doc Jean-Paul Ampuero mapped out two regimes of earthquake nucleation on faults governed by the "aging law" (the more popular of two commonly used empirical laws for the evolution of the "state variable" part of "rate and state" friction). In one regime, the nucleation zone spontaneously evolves to a state of accelerating slip on a patch of fixed length. For laboratory values of the relevant constitutive parameters "a" (pertaining to "rate" effects) and "b" (pertaining to "state" effects), on the other hand, the nucleation zone takes the form of an expanding crack that asymptotically approaches a length that for a/b=0.95 is 100 times larger. This would lead to nucleation events that might sometimes be detectable using surface seismometers. However, these large sizes are a direct consequence of the rapid increase in effective fracture energy with increasing slip speed that the aging law implies. In fact, such a rapid increase has little experimental support, suggesting that despite its popularity the aging law is a poor descriptor of nucleation. In contrast, and in better agreement with relevant experiments, under the "slip law" the effective fracture energy of nucleation increases more slowly with slip speed. Preliminary calculations show that for laboratory values of a/b, nucleation under this law takes the form of a unidirectional slip "pulse" that is most active over a much smaller region.The PI is currently investigating, numerically and analytically, earthquake nucleation under the slip law and other classes of evolution laws, much as was done for the aging law. Because current laws for the evolution of the "state variable" are strictly empirical, trying to obtain a fundamental understanding of what distinguishes different classes of laws is quite important. Although this study is primarily theoretical, the results are also being applied to the analysis of several clusters of small repeating earthquakes that were activated by the M6.2 Morgan Hill, California, earthquake and that "turned off" within a year. These earthquakes may have occurred on nearly velocity-neutral (a/b~1) patches of the Calaveras fault with a size close to the nucleation length. The results of this study have already proven useful for the design of laboratory experiments that can distinguish between different proposed evolution laws, and should be useful for interpreting observations expected to come from two major NSF-sponsored projects to image earthquake nucleation at seismogenic depths - the SAFOD borehole along the San Andreas fault, and the NELSAM experiment in deep South African mines. The study will also support a first-year graduate student, Yue Tian to work
地震并不是从空间中的一个单一点开始开始的,而是通过在一个被称为成核区的有限大小的区域上加速滑动而开始的。 成核过程很重要,因为它决定了是否或在什么条件下可以产生可检测的地震信号,以及断层对突然施加的应力阶跃的反应,例如附近的大地震。 尽管断层摩擦的“速率和状态”公式已经被广泛使用了二十多年,但目前还没有确定天然(弹性变形)断层上成核区大小的一般理论。 在最近的一项数值和分析研究中,PI和博士后Jean-Paul Ampuero绘制了两种由“老化定律”(两种常用的经验定律中更流行的“速率和状态”摩擦的“状态变量”部分的演变)控制的断层上的地震成核机制。 在一个政权,成核区自发地演变成一个固定长度的补丁上的加速滑移的状态。 另一方面,对于相关本构参数“a”(与“速率”效应有关)和“B”(与“状态”效应有关)的实验室值,成核区采取扩展裂纹的形式,其渐近地接近a/B=0.95时的长度大100倍。这将导致核化事件,有时可以使用地面地震仪检测到。然而,这些大的尺寸是随着老化规律所暗示的滑移速度的增加有效断裂能快速增加的直接结果。 事实上,这种快速增长几乎没有实验支持,这表明,尽管它的普及,老化规律是一个穷人的成核描述。 与此相反,在“滑移定律”下,形核的有效断裂能随滑移速度的增加而缓慢增加,这与相关实验结果吻合得更好。 初步计算表明,对于实验室值的a/B,成核在此法律下采取的形式是一个单向的滑移“脉冲”,是最活跃的一个小得多的region.The PI目前正在调查,数值和分析,地震成核下的滑移法律和其他类的演变规律,就像是做了老化的法律。 由于目前的法律演变的“状态变量”是严格的经验,试图获得一个基本的理解是什么区分不同类别的法律是相当重要的。 虽然这项研究主要是理论性的,但其结果也被应用于分析几个由加州摩根山6.2级地震激活并在一年内“关闭”的小型重复地震群。 这些地震可能发生在Calaveras断层的近速度中性(a/B~1)斑块上,其大小接近成核长度。 这项研究的结果已经被证明是有用的实验室实验的设计,可以区分不同的建议的演变规律,并应是有用的解释观测预期来自两个主要的NSF赞助的项目,以图像地震成核在孕震深度-SAFOD钻孔沿着圣安德烈亚斯断层,和NELSAM实验在南非深部矿井。这项研究还将支持一名研究生一年级学生Yue Tian工作
项目成果
期刊论文数量(0)
专著数量(0)
科研奖励数量(0)
会议论文数量(0)
专利数量(0)
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Allan Rubin其他文献
Allan Rubin的其他文献
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{{ truncateString('Allan Rubin', 18)}}的其他基金
The granular physics contribution to rate- and state-dependent fault friction
颗粒物理对速率和状态相关的断层摩擦的贡献
- 批准号:
1946434 - 财政年份:2020
- 资助金额:
$ 19.4万 - 项目类别:
Standard Grant
Collaborative Research: What Processes Cause State Evolution in Rate and State Friction?
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- 批准号:
2024766 - 财政年份:2020
- 资助金额:
$ 19.4万 - 项目类别:
Standard Grant
Catalog-constrained models of tremor and slow slip
颤动和慢滑移的目录约束模型
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1645145 - 财政年份:2017
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$ 19.4万 - 项目类别:
Continuing Grant
Collaborative Research: Laboratory and Theoretical Investigations of the Micro-Mechanical Origins of Rate and State Friction on Tectonic Faults
合作研究:构造断层上速率和状态摩擦的微机械起源的实验室和理论研究
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1547286 - 财政年份:2016
- 资助金额:
$ 19.4万 - 项目类别:
Continuing Grant
Developing high-resolution tremor catalogs to constrain numerical models of slow slip
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- 批准号:
1344948 - 财政年份:2014
- 资助金额:
$ 19.4万 - 项目类别:
Continuing Grant
Mechanical Erosion of Frictionally Locked Fault Patches Due to Creep: ObservationalEvidence and Modeling
蠕变引起的摩擦锁定断层块的机械侵蚀:观测证据和建模
- 批准号:
1214900 - 财政年份:2012
- 资助金额:
$ 19.4万 - 项目类别:
Continuing Grant
A (mostly) Observational Study of Microearthquakes on a Bimaterial Interface
双材料界面上微地震的(主要)观测研究
- 批准号:
1113579 - 财政年份:2011
- 资助金额:
$ 19.4万 - 项目类别:
Standard Grant
Theoretical earthquake nucleation, with applications to creep fronts, tremor, and slow slip
理论地震成核,及其在蠕变前沿、颤动和慢滑移中的应用
- 批准号:
0911378 - 财政年份:2009
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$ 19.4万 - 项目类别:
Standard Grant
An Observational Study of Microearthquakes on a Bimaterial Interface
双材料界面微地震的观测研究
- 批准号:
0710896 - 财政年份:2007
- 资助金额:
$ 19.4万 - 项目类别:
Continuing Grant
Studies of Fault Fabrics and Earthquake Mechanics from the Precise Relative Locations of Microearthquakes
从微地震精确相对位置研究断层组构和地震力学
- 批准号:
0126184 - 财政年份:2002
- 资助金额:
$ 19.4万 - 项目类别:
Continuing Grant
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