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

研究人员开发了复杂的数值模型，探索了产生地震的断层，无论大小，如何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预先存在的断层上的快速滑动产生的，并受到构造板块运动的影响。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。这几种现象往往存在于同一个地方，并且可以相互影响。该项目将模拟几个大地震周期，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学知识，观察慢事件以及小地震和大地震的作用方式。他们将进行模拟，并将其与实验室和自然界中的观察结果进行比较。这些研究将有助于更好地了解地震成核、断层性质和前震序列的预测价值，从而有助于减轻地震灾害。结合波传播、场地和建筑物响应的规范，模拟慢滑和地震序列的方法可以成为地震危险性分析基于物理的模拟能力的重要组成部分。这些类型的模型为我们的灾害研究增加了另一种工具。为了研究缓慢滑动与地震发生断层斑块的相互作用，研究人员将使用一种独特的数值方法，能够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，震后滑动，以及包括瞬变在内的震间滑动。慢滑将产生作为长期故障模拟的一部分，使用几种物理机制，使它们之间的比较：（一）由标准的速度弱化率和状态摩擦控制的故障上的成核过程，（二）由于非弹性剪切阻尼的修改，以及（iii）速度加强故障上的慢滑。断层模型将包括一个或多个被定义为具有不同摩擦特性的区域的块。几种类型的差异，可能会导致地震活动将进行探讨，包括有效的正应力，率弱化性能，渗透性和渗透性的变化。这里的重点是模拟和表征慢滑和地震事件在其辐射谱，应力降，潜在的地震活动复发补丁在一个单一的情节慢滑，空间范围内产生的事件有关补丁大小，修改慢滑由所产生的地震活动及其震后影响，以及相邻斑块之间相互作用的结果。将这些特征与观测（包括实验室研究）进行比较，将有助于确定与观测现象相关的情景，并澄清自然和实验室断层的异质性性质。 所开发的详细模型的慢滑相互作用与异质补丁将被用来创建简化表示的微震用于未来的模拟地震和慢滑，包括前震序列和震颤，在现实的故障设置。

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.