The earthquake arrest zone
The earthquake arrest zone
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DOI：
10.1093/gji/ggaa386
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发表时间：
2021-01-01
影响因子：
2.8
通讯作者：
Kammer, David S.
中科院分区：
文献类型：
--
作者：
Ke, Chun-Yu;McLaskey, Gregory C.;Kammer, David S.
地震破裂通常被认为是在预先存在的断层上以断裂或摩擦滑动的形式传播的裂缝。裂缝模型已经被用来描述断层偏移的空间分布和相关的静态应力变化，并对摩擦演化和破裂过程的潜在物理特性有影响。然而，现场测量可以帮助完善理想的裂缝模型是罕见的。在这里，我们描述了大规模的实验室地震实验，其中所有的破裂过程都包含在一个3米长的锯切花岗岩断层中，我们提出了一个适合我们测量的解析裂缝模型。与自然地震类似，实验室测量显示同震滑动在破裂尖端附近逐渐减小。测量的应力变化显示，在破裂区域的中心，应力下降大致恒定，在靠近破裂尖端的地方，最大应力增加，两者之间有一个平滑的过渡，我们称之为地震止震区。该模型通过在破裂端加入逐渐变细的滑移，推广了目前广泛应用的椭圆裂纹模型。与断裂力学所描述的内聚带不同，我们认为止震带中应力变化的转变和相应的线性锥度是主要由初始应力分布控制的破裂终止条件的结果。非均质初始应力分布控制着实验室地震的停止，静应力变化特征控制着实验室地震的停止。我们还进行了动态破裂模拟，以确认止动条件如何影响滑移锥度和静态应力变化。如果适用于更大的自然地震，这种地震止震带（取决于应力条件）和内聚带（主要取决于强度演变）之间的区别对于如何解释地震断裂能的地震观测结果具有重要意义。
Earthquake ruptures are generally considered to be cracks that propagate as fracture or frictional slip on pre-existing faults. Crack models have been used to describe the spatial distribution of fault offset and the associated static stress changes along a fault, and have implications for friction evolution and the underlying physics of rupture processes. However, field measurements that could help refine idealized crack models are rare. Here, we describe large-scale laboratory earthquake experiments, where all rupture processes were contained within a 3-m long saw-cut granite fault, and we propose an analytical crack model that fits our measurements. Similar to natural earthquakes, laboratory measurements show coseismic slip that gradually tapers near the rupture tips. Measured stress changes show roughly constant stress drop in the centre of the ruptured region, a maximum stress increase near the rupture tips and a smooth transition in between, in a region we describe as the earthquake arrest zone. The proposed model generalizes the widely used elliptical crack model by adding gradually tapered slip at the ends of the rupture. Different from the cohesive zone described by fracture mechanics, we propose that the transition in stress changes and the corresponding linear taper observed in the earthquake arrest zone are the result of rupture termination conditions primarily controlled by the initial stress distribution. It is the heterogeneous initial stress distribution that controls the arrest of laboratory earthquakes, and the features of static stress changes. We also performed dynamic rupture simulations that confirm how arrest conditions can affect slip taper and static stress changes. If applicable to larger natural earthquakes, this distinction between an earthquake arrest zone (that depends on stress conditions) and a cohesive zone (that depends primarily on strength evolution) has important implications for how seismic observations of earthquake fracture energy should be interpreted.