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

地震破裂如何通过富含粘土的断层带传播？

基本信息

批准号：
NE/P002943/1
负责人：
Daniel Faulkner
金额：
$ 66.11万
依托单位：
University of Liverpool
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2017
资助国家：
英国
起止时间：
2017 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FP002943%2F1
关键词：
How do earthquake ruptures propagate

项目摘要

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.

在大型构造断层上，运动可以稳定地发生，产生断层蠕变，或者在地震发生的地方通过不稳定滑动进行。断层蠕动通常与富含粘土的断层泥有关，这些断层泥可容纳穿过断层的滑动。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风险更小。最近的研究表明，地震可以通过断层的爬行部分传播，造成毁灭性的后果。这个项目将联合领先的实验者和模型师来研究在什么条件下地震破裂可以通过“爬行”断层传播。这项工作将利用一种独特的新型高压旋转剪切形变装置来复制和理解地震破裂经过时的物理反应，并利用破裂模型预测大规模反应。实验和模拟的结果将被用来开发新的蠕动断层的地震危险性评估，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。我们从慢滑实验室实验中了解到，地震预计不会在富含粘土的断层上孕育，因为随着滑动开始加速，地震将加强，从而阻止任何潜在的破裂。俯冲带富含粘土的弧前增积部分缺乏地震活动就很好地说明了这一点。然而，最近的事件表明，在断裂带粘土含量较低的地区形成的大地震破裂可以穿透粘土丰富的地区，甚至可以极大地增强滑动，如2011年东北冲绳9.0次地震中所看到的那样，当时有记录的最大同震滑动(~50米)发生在粘土丰富的吸积弧前，产生了海底的大偏移量，导致了毁灭性的海啸。地震通过蠕动断层传播的其他例子有1999年台湾的Mw7.6集集地震，那里的破裂性质被明显改变(破裂速度和滑动速度增加)，以及1944年的北安纳托利亚断层地震。这项研究将使用利物浦最近开发的独特的实验室设备，它可以复制地震期间的条件，并允许我们测量断层的摩擦强度是如何发展的，这将决定地震破裂是在富含粘土的断层中传播还是滞留。它将允许在接近15公里深的完全受限条件下模拟地震破裂的接近过程。将进行实验，监测实验断裂带在不同外加位移和位移速率下的强度和性质。峰值加速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屏障。在另一种类型的实验中，粘滑不稳定性(实验室地震)将在它传播到实验室断层带的粘土丰富区域时进行监测。约束实验室地震滑动物理响应的结果将被添加到大型模型中，以帮助我们理解(A)破裂传播，它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，以及将释放多少应力，用于概率地震危险性评估。