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The physical properties of an active subduction megathrust

活跃俯冲巨型逆冲断层的物理特性

基本信息

批准号：
NE/S015531/1
负责人：
Daniel Faulkner
金额：
$ 8.94万
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：
2019
资助国家：
英国
起止时间：
2019 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FS015531%2F1
关键词：
physical properties active subduction megathrust

项目摘要

Subduction zone megathrust earthquakes are the largest and most destructive on Earth, with many rupturing the seafloor and generating devastating tsunamis such as those produced after the M9.0 Tohoku-Oki earthquake in 2011. Subduction zones are also some of the most inaccessible places to study and consequently our understanding of their structure and physical properties is very limited. To address this gap in our knowledge, IODP Expedition 358 NanTroSEIZE (the Nankai Trough SEIsmic Zone Experiment) aims to drill to ~5200 mbsf in Spring 2019 and intersect the subduction megathrust, which hosted the 1944 Tonankai M8.1 earthquake, collecting data and core samples along the way. This project will elucidate the conditions that could lead to earthquake rupture along megathrusts by conducting post-cruise research, using samples and shipboard data collected from the expedition, to characterize the physical properties of the fault zone materials. The work will utilize a range of high-pressure deformation apparatus at the Rock Deformation Laboratory, University of Liverpool, to replicate the in situ conditions of the megathrust, including a new high-pressure rotary shear apparatus that can apply slip velocities from microns/s to m/s (i.e. earthquake slip speeds). Accretionary wedges are primarily comprised of clay-rich seafloor sediments that are scraped off the down-going slab during subduction. 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 illustrated by a lack of seismicity seen in accretionary forearcs of many subduction zones. However it is observed that earthquakes do periodically propagate through these regions including at the Nankai Trough, the subject of the IODP Exp. 358 (e.g. the 1944 Tonankai M8.1 earthquake), and more recently on the nearby Japan Trench where the M9.0 Tohoku-Oki earthquake in 2011 occurred, producing the largest co-seismic slip ever recorded (~50m) and generating a devastating tsunami. Therefore, by sampling directly from an active subduction megathrust at seismogenic depths, it is important to characterize the physical properties of the fault zone materials in order to elucidate the conditions where an earthquake might occur in materials that would typically be expected to inhibit rupture propagation. 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 megathrust fault material develops under different stress conditions and sliding velocities. It will allow for frictional sliding to be simulated under fully confined conditions, approximating to up to 15km depth, thus achieving pressures associated with the in situ conditions of the megathrust in nature. In a different set of experiments the physical properties of the accretionary wedge material away from main fault core will be determined. This will include strength, permeability and seismic velocities. The results from these experiments will provide insights into behaviour of the wider damage zone which can act as energy sink during earthquake rupture.

俯冲带巨型逆冲断层地震是地球上最大和最具破坏性的地震，许多地震会使海底破裂，并产生毁灭性的海啸，例如2011年东北-冲木M9.0地震后产生的海啸。俯冲带也是一些最难以进入的地方进行研究，因此我们对它们的结构和物理特性的了解非常有限。为了解决我们知识中的这一空白，IODP Expedition 358 NantroSEIZE（南开海槽地震带实验）的目标是在2019年春季钻探到约5200 mbsf，并与1944年Tonankai M8.1地震的俯冲巨型逆冲断层相交，沿途收集数据和岩心样本沿着。该项目将利用从考察中收集的样品和船上数据进行考察后研究，以确定断层带物质的物理特性，从而阐明可能导致沿着巨型断层发生地震破裂的条件。这项工作将利用利物浦大学岩石变形实验室的一系列高压变形仪器来复制巨型逆冲断层的现场条件，包括一种新的高压旋转剪切仪器，该仪器可以施加从微米/秒到米/秒的滑动速度（即地震滑动速度）。增生楔主要由俯冲过程中从下行板片上刮下的富含粘土的海底沉积物组成。我们从缓慢滑动的实验室实验中知道，地震不会在富含粘土的断层上成核，因为随着滑动开始加速，断层会加强，从而阻止任何潜在的破裂。许多俯冲带的增生前弧缺乏地震活动性就说明了这一点。然而，据观察，地震确实周期性地通过这些地区传播，包括在南海海槽，IODP Exp的主题。358（例如1944年东南海8.1级地震），以及最近发生在附近的日本海沟，2011年发生了M9.0东北冲地震，产生了有史以来最大的同震滑动（约50米），并产生了毁灭性的海啸。因此，通过直接从活跃的俯冲巨型逆冲断层在孕震深度采样，重要的是要表征断层带材料的物理性质，以阐明地震可能发生的条件下，通常预计将抑制破裂传播的材料。这项研究将使用最近在利物浦开发的独特实验室设备，这些设备可以复制地震期间的条件，并使我们能够测量在不同应力条件和滑动速度下巨型逆冲断层材料的摩擦强度如何发展。它将允许在完全封闭的条件下模拟摩擦滑动，接近高达15公里的深度，从而实现与大规模逆冲断层的现场条件相关的压力。在一组不同的实验中，将确定远离主断层核的增生楔物质的物理性质。这将包括强度、渗透率和地震速度。从这些实验的结果将提供更广泛的破坏区，可以作为地震破裂过程中的能量汇的行为的见解。