How do earthquake ruptures propagate through clay-rich fault zones?

在大的构造断层上，运动可以稳定地发生，产生断层蠕动，或者在发生地震的地方通过不稳定的滑动。断层蠕动通常与富含粘土的断层泥有关，断层泥可容纳断层上的滑动。它们通常被认为比地震周期性发生的锁定断层造成的地震危险要小。最近的研究表明，地震可以通过断层的蠕动部分传播，造成毁灭性的后果。这个项目将结合联合收割机领先的实验和建模，以调查在什么条件下地震破裂可以传播通过'蠕动'断层。这项工作将利用一种独特的新型高压旋转剪切变形装置来复制和理解地震破裂时的物理反应，破裂模型预测大规模的反应。实验和建模的结果将用于对蠕动断层进行新的地震危险性评估，包括如何看待它们的地震活动潜力，以及破裂的性质将如何影响辐射波场--这将影响地震的破坏性。我们从缓慢滑动的实验室实验中得知，地震不会在粘土上成核--丰富的断层，因为他们加强滑动开始加速，从而阻止任何潜在的破裂。这是很好地说明了缺乏地震活动看到在增生弧前粘土丰富的部分俯冲带。然而，最近的事件表明，在断层带中粘土含量较少的区域发生的大地震破裂可以穿透粘土含量丰富的区域，甚至大大增强滑动，例如2011年的Mw9.0 Tohoku-Oki地震，有记录以来最大的同震滑动（~50米）发生在粘土中，丰富的增生前弧，产生了一个大的海底偏移，导致了毁灭性的海啸。地震通过蠕动断层传播的其他例子是1999年台湾集集7.6级地震，那里的破裂性质明显改变（破裂速度和滑移速度的增加），和1944年北安纳托利亚断层Mw7.4地震。这项研究将使用最近在利物浦开发的独特的实验室设备，可以复制地震时的条件，使我们能够测量断层的摩擦强度如何发展，这将决定地震破裂是否会在富含粘土的断层中传播或停止。它将允许在接近15公里深度的完全封闭条件下模拟地震破裂的接近。将进行实验，在不同的施加位移和位移速率下监测实验断层带的强度和性质。峰值加速度和应力降低将模拟不同大小的地震，并研究促进不稳定滑动所需的能量障碍。在不同类型的实验中，当粘滑不稳定性（实验室地震）传播到实验室断层带的粘土丰富区域时，将对其进行监测。实验室中限制地震滑动物理响应的结果将被添加到大尺度模型中，以帮助我们理解（a）破裂传播，这将决定小地震是否会发展为大事件，以及（B）属性将是什么，例如它将以多快的速度传播，以及释放多少应力，用于概率地震危险评估。

On large tectonic faults movement can occur stably, producing fault creep, or by unstable slip where earthquakes occur. Fault creep has typically been associated with clay-rich fault gouges that accommodate slip across a fault. They have typically been thought to pose less seismic hazard than locked faults where earthquakes occur periodically. Recent studies have demonstrated that earthquakes can propagate through creeping sections of faults, with devastating consequences. This project will combine leading experimentalists and modellers to investigate under what conditions earthquake ruptures can propagate through 'creeping' faults. The work will utilize a unique new high-pressure rotary shear deformation apparatus to replicate and understand the physical response as an earthquake rupture passes and rupture models predict the large-scale response. Results from experiments and modelling will be used to develop new seismic hazard assessment for creeping faults, both in terms of how their potential for seismicity is viewed, and how the nature of a rupture would affect the radiated wavefield - which influences how destructive an earthquake will be.We know from slow-slip laboratory experiments that earthquakes are not expected to nucleate on clay-rich faults as they strengthen as slip starts to accelerate, thereby arresting any potential rupture. This is nicely illustrated by a lack of seismicity seen in the accretionary forearc clay-rich parts of subduction zones. However, recent events have suggested that large earthquake rupture, nucleated on a less clay-rich region of a fault zone can punch through clay-rich regions, and even greatly enhance slip, such as was seen in the Mw9.0 Tohoku-Oki earthquake in 2011, where the largest co-seismic slip ever recorded (~50m) occurred in the clay-rich accretionary forearc that produced a large offset of the seafloor leading to a devastating tsunami. Other examples of where earthquakes have propagated through creeping faults are The 1999 Mw7.6 Chi Chi earthquake in Taiwan, there the properties of the rupture were clearly modified (increase in the rupture velocity and slip speed), and the 1944 Mw7.4 North Anatolian Fault earthquake.This research will use unique laboratory equipment recently developed at Liverpool that can replicate the conditions during earthquakes and allow us to measure how the frictional strength of the fault develops, which will dictate whether or not an earthquake rupture will propagate or arrest in clay-rich faults. It will allow the approach of an earthquake ruptures to be simulated under fully confined conditions approximating to 15km depth. Experiments will be conducted where the strength and properties of the experimental fault zone is monitored under different imposed displacements and displacement rates. The peak acceleration and stress reduction will mimic earthquakes of different size and investigate the energy barrier required to promote unstable slip. In a different type of experiment, a stick-slip instability (laboratory earthquake) will be monitored as it propagates into clay-rich region of a laboratory fault zone. Results constraining the physical response of earthquake slip from the laboratory will be added into large-scale models to aid our understanding of (a) rupture propagation, which will dictate if a small earthquake will grow into large event and (b) what the properties will be, such as how fast it will travel and how much stress will be released, for use in probabilistic seismic hazard assessment.