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.

在大的构造断层上，运动可以稳定地发生，产生断层蠕变，或者在地震发生时通过不稳定的滑移。断层蠕变通常与富含粘土的断层泥有关，这些断层泥可容纳断层上的滑动。人们通常认为它们比周期性发生地震的闭锁断层造成的地震危害要小。最近的研究表明，地震可以通过断层蠕变部分传播，从而造成灾难性后果。该项目将联合领先的实验学家和建模者来研究在什么条件下地震破裂可以通过“蠕动”断层传播。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响应，并且破裂模型可以预测大规模响应。实验和建模的结果将用于开发蠕动断层的新地震危险性评估，包括如何看待其潜在的地震活动性，以及破裂的性质将如何影响辐射波场——这会影响地震的破坏性我们从慢滑移实验室实验中得知，地震预计不会在富含粘土的断层上成核，因为随着滑移开始加速，断层会增强，从而阻止任何潜在的破裂。俯冲带弧前富含粘土的增生区域缺乏地震活动，很好地说明了这一点。然而，最近的事件表明，在断层带中粘土含量较低的区域形成核的大地震破裂可以穿透粘土丰富的区域，甚至大大增强滑移，例如在 Mw9.0 东北冲地震中所看到的那样2011年，有记录以来最大的同震滑动（~50m）发生在富含粘土的增生前弧，导致海底大幅偏移，导致毁灭性的海啸。地震通过蠕动断层传播的其他例子包括 1999 年台湾 Mw7.6 Chi Chi 地震，其中破裂的性质明显改变（破裂速度和滑移速度增加），以及 1944 年 Mw7.4 北安那托利亚地震断层地震。这项研究将使用利物浦最近开发的独特实验室设备，该设备可以复制地震期间的条件，并使我们能够测量断层的摩擦强度如何发展，这将决定地震是否破裂将在富含粘土的断层中传播或停止。它将允许在大约 15 公里深度的完全受限条件下模拟地震破裂的逼近。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特性。峰值加速度和应力减少将模拟不同规模的地震，并研究促进不稳定滑移所需的能量势垒。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富含粘土区域时，将对其进行监测。实验室中限制地震滑移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，这将决定小地震是否会发展成大事件以及（b）其特性将如何例如它的行进速度和释放的压力，用于概率地震危险评估。