Modeling slow slip and earthquake nucleation on heterogeneous faults: implications for foreshocks and repeating earthquakes

模拟异质断层上的慢滑移和地震成核：对前震和重复地震的影响

• 批准号: 1520907
• 负责人: Nadia Lapusta
• 金额: $ 44.7万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-07-01 至 2018-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1520907&HistoricalAwards=false
• 关键词: Modeling; slow; slip; earthquake; nucleation

The researchers have developed sophisticated numericals models that explore how faults that produce earthquakes, large and small, also produce movements that are slow, and look different from typical earthquakes. Earthquakes are typically generated by rapid slip on pre-existing faults inside the Earth, loaded by tectonic plate motion. Observations show that the rapid slip, with the average velocity of the order of 1 m/s, coexists with much slower slip that can be measured, e.g. using GPS. These types of phenomena often exist in the same place and can influence each other. This project will look to simulate several cycles of large earthquakes and, by incorporating what we know about how the Earth deforms, the physics of seismic waves and faults, observe how slow events and both small and large earthquakes work. They will take their simulations and compare them with observations made in experimental labs and in nature. The studies will lead to better understanding of earthquake nucleation, fault properties, and the predictive value of foreshocks sequences, and hence help mitigate seismic hazard. Combined with codes for wave propagation and site and building response, the methodology for simulating slow slip and earthquake sequences can become a vital ingredient of physics-based simulation capability for seismic hazard analysis This kind of modeling could have transformative impacts on our understanding of earthquakes and their hazards. These types of models add another tool to our study of hazards.To study the interaction of slow slip with seismicity-producing fault patches, the researchers will use a unique numerical approach capable of resolving all stages of slip: accelerating slip during earthquake nucleation, dynamic rupture with all inertial (wave) effects, postseismic slip, and interseismic slip including transients. Slow slip will be generated as a part of long-term fault simulations using several physical mechanisms to enable comparison between them: (i) nucleation processes on faults governed by standard velocity-weakening rate-and-state friction, (ii) modifications of such processes due to inelastic shear dilatancy, and (iii) slow slip on velocity-strengthening faults. The fault models will include one or multiple patches defined as areas of different frictional properties. Several types of differences that may lead to seismicity will be explored, including variations in effective normal stress, rate-weakening properties, dilatancy, and permeability. The focus here is on simulating and characterizing well-resolved interactions of slow slip and seismic events in terms of their radiated spectra, stress drops, potential for seismicity recurrence on a patch during a single episode of slow slip, spatial extent of the generated events in relation to the patch sizes, modification of slow slip by the resulting seismicity and its postseismic effects, and the consequences of interaction between nearby patches. Comparison of these features with observations (including laboratory studies) will allow identification of scenarios relevant to the observed phenomena as well as clarify the nature of heterogeneity on natural and laboratory faults. The developed detailed models of slow slip interaction with heterogeneous patches will be used to create simplified representations of microseismicity for use in future simulations of earthquakes and slow slip, including foreshock sequences and tremor, in realistic fault settings.

研究人员开发了复杂的数值模型，探索断层如何产生地震，无论大小，也会产生缓慢的运动，并且看起来与典型的地震不同。地震通常是由地球内部已经存在的断层在构造板块运动的作用下快速滑动而产生的。观测表明，平均速度为1 m/s的快速滑动与可以测量的慢得多的滑动共存，例如使用GPS。这些类型的现象往往存在于同一个地方，并且可以相互影响。这个项目将模拟大地震的几个周期，并通过结合我们对地球如何变形的了解，地震波和断层的物理特性，观察慢地震和小地震和大地震是如何发生的。他们将进行模拟，并将其与实验室和自然界的观察结果进行比较。这些研究将有助于更好地理解地震成核、断层性质和前震序列的预测价值，从而有助于减轻地震危害。结合对波传播、场地和建筑反应的规范，模拟慢滑和地震序列的方法可以成为地震灾害分析中基于物理的模拟能力的重要组成部分。这种建模可以对我们对地震及其危害的理解产生革命性的影响。这些类型的模型为我们的危害研究增加了另一种工具。为了研究慢滑动与产生地震的断层块的相互作用，研究人员将使用一种独特的数值方法来解决滑动的所有阶段：地震成核期间的加速滑动，所有惯性（波）效应的动态破裂，地震后滑动，以及包括瞬态在内的地震间滑动。慢滑将作为长期断层模拟的一部分产生，使用几种物理机制来对它们进行比较：(i)由标准速度减弱速率和状态摩擦控制的断层上的成核过程，（ii）由于非弹性剪切膨胀对这些过程的修改，以及（iii）速度增强断层上的慢滑。故障模型将包括一个或多个块，定义为不同摩擦特性的区域。将探讨几种可能导致地震活动性的差异，包括有效正应力、速率减弱特性、膨胀性和渗透率的变化。这里的重点是模拟和描述慢滑和地震事件之间的良好解决的相互作用，包括它们的辐射光谱、应力降、单次慢滑期间一个地块上地震活动性复发的可能性、与地块大小相关的产生事件的空间范围、由此产生的地震活动性及其震后效应对慢滑的修正，以及附近地块之间相互作用的后果。将这些特征与观测结果（包括实验室研究）进行比较，将有助于确定与观测到的现象相关的情景，并澄清自然和实验室断层的异质性本质。已开发的与非均匀斑块的慢滑相互作用的详细模型将用于创建微地震活动性的简化表示，用于未来在实际断层设置中模拟地震和慢滑，包括前震序列和震颤。

项目成果

Microseismicity Simulated on Asperity‐Like Fault Patches: On Scaling of Seismic Moment With Duration and Seismological Estimates of Stress Drops

• DOI: 10.1029/2018gl078650
• 发表时间: 2018-08
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Yen‐Yu Lin;N. Lapusta

Microseismicity on Patches of Higher Compression During Larger‐Scale Earthquake Nucleation in a Rate‐and‐State Fault Model

速率和状态断层模型中较大规模地震成核过程中较高压缩斑块的微震活动

• DOI: 10.1029/2018jb016395
• 发表时间: 2019
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Schaal, Natalie;Lapusta, Nadia
• 通讯作者: Lapusta, Nadia