Abstract:

Active strike-slip fault usually hosts major earthquakes. Therefore, studies on fault segmentation, which is controlled by geometric complexity, are very important for assessing the maximum magnitude of potential earthquakes. Based on previous literature, we summarized the behavior of earthquakes on strike-slip faults related to fault geometry, segmentation, and cascading rupture from the aspects of field investigation and numerical modeling.

Previous field investigations have shown that geometrically complex sections of a strike-slip fault usually play the role of barriers that can separate earthquake rupture segments and effectively stop the propagation of earthquake rupture. Statistical results based on the limited field investigations of the surface rupture illuminated semi-quantitatively the influence of geometrically complex sections on the rupture behavior of the earthquake. Since not all earthquakes can produce surface rupture zones, the case number of surface ruptures are unlikely to meet statistical requirements in the coming years. In addition, knowledge gained from field investigation is mainly statistical results based on fault geometry and kinematics. They have some consistency but vary greatly, indicating the complexity of seismic rupture modes on strike-slip faults. No simple threshold that can be used as a criterion to refine the capability of earthquake rupture propagation on strike-slip faults with complex geometry. Based on the statistical results of field surveys, geologists have applied the factor, that complex geometricity controls earthquake rupture behavior, in seismic risk assessment. Lacking support from dynamic analysis, it is necessary to develop and integrate physics-based dynamic models to help improve earthquake-rate models and probability models.

Numerical modeling can not only present the earthquake simulation scenario but also provide insights into the fundamental physics of dynamic rupture propagation. The modeling results improve our understanding of how the geometric complexity of the fault influences the dynamic rupture propagation. Different modeling approaches focus on different aspects of this challenging scientific problem, each with unique advantages and disadvantages. 2D modeling is relatively simple. They allow modelers to consider more complex physical processes, variated parameters, and constraints from the field and laboratory observation, etc. They provide a comparative benchmark on rupture dynamics on a strike-slip fault with complex geometry. 3D modeling can provide closer approximations to realistic faults and more direct comparisons to observations. The simulations of one earthquake rupture process may focus on the influence of single/multiple parameters on the rupture process. While the multicycle earthquake simulation can predict spatiotemporal patterns of earthquake ruptures on a strike-slip fault. Both simple 2D modeling and complex 3D modeling have shown that one of the most important factors affecting rupture behavior on strike-slip faults is the fault geometric complexity. In addition, other dynamic factors, such as the initial stress, the properties of the rock medium, and nucleation location, also affect dynamic fracture propagation on strike-slip faults. It indicates that rupture behavior on a certain strike-slip fault has its unique characteristics that are controlled by dynamic factors such as the regional tectonic environment and the properties of the fault itself. The numerical modeling provides a dynamic perspective on the complexity of rupture behaviors on strike-slip faults given by field investigations.

In the China Seismic Science Experimental Site, 3D dynamic modeling supported by fault detection, dense geophysical observations, and high-performance computation will provide new insights into the rupture behavior in the complex multi fault system. That is helpful in determining the maximum magnitude of a potential earthquake.

Key words: active strike-slip fault, fault geometric complexity, field investigation, dynamic rupture, numerical simulation

摘要：

活动走滑断裂带上强震频发, 对几何结构复杂区及其导致的分段破裂模式开展研究对于评估区域潜在地震的最大震级具有重要意义。文中从野外地质调查和数值模型研究2个方面入手, 对走滑断层上地震破裂行为中的几何结构、 断层分段和级联破裂等相关研究进行回顾总结。野外地质调查发现, 走滑断裂带上广泛存在的断层几何结构复杂区可能会终止地震破裂的传播。前人基于地表破裂带野外调查, 给出了走滑断裂带上几何结构复杂区对地震破裂方式的影响, 以及这种影响程度的统计分析结果。另一方面, 与断层动态破裂过程相关的数值模拟研究, 不仅从动力学角度展示了断层几何结构复杂区对断层动态破裂传播的控制作用, 还表明初始应力、 岩石介质性质等其他因素也影响了断层动态破裂的传播。在研究程度较高的中国地震科学实验场区, 基于断层探测、 地球物理场密集观测和高性能计算的3D动力学模拟有望进一步深化对区域复杂断层系统中破裂行为的认识, 并为判定区域最大潜在震级提供帮助。

关键词: 活动走滑断裂带, 断层几何结构复杂区, 野外调查, 动态破裂, 数值模拟