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NSFGEO-NERC Earthquake nucleation versus episodic slow slip: what controls the mode of fault slip?

NSFGEO-NERC 地震成核与幕式慢滑移：什么控制断层滑移模式？

基本信息

批准号：
NE/V011804/1
负责人：
Daniel Faulkner
金额：
$ 52.02万
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：
2021
资助国家：
英国
起止时间：
2021 至无数据
项目状态：
未结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FV011804%2F1
关键词：
NSFGEO NERC Earthquake nucleation versus

项目摘要

Earthquakes, produced by rapid slip on faults, account for the majority of deaths from a range of natural disasters which amounts to about 60,000 people a year worldwide - around 90 percent of which occur in developing countries. Slip can occur in three ways on faults. These are (1) earthquake slip; (2) stable fault creep driven by plate tectonic loading rates; and (3) episodic slow slip events, where fault slip spontaneously accelerates but never reaches earthquake slip speeds. Episodic slow slip events can release the same amount of energy as earthquakes but over days to weeks rather than seconds to minutes. They most commonly occur in certain regions of subduction zones and have been linked to elevated pore pressures. These three modes of fault slip are vital to understand, as episodic slow slip and fault creep relieve stress build up and reduce seismic hazard, yet also transfer stress from one part of the fault to another, ultimately affecting the nucleation of destructive earthquakes.In this project, we will provide physical constraints from combined experiments and numerical modelling to determine the controlling factors leading to stable fault creep, episodic slow slip, or earthquakes. As yet, it is not understood what puts the brakes on some instabilities creating slow fault slip yet allows others to accelerate to rapid slip speeds that cause earthquakes. A transition of some sort from unstable frictional sliding (typically viewed as leading to earthquakes) to stable frictional sliding (typically viewed as leading to fault creep) while the sliding velocity is increasing must promote sustained slow slip on faults. The nature of this stability transition is widely debated and the range of conditions under which it may occur are ill defined. We will investigate the key hypotheses proposed to explain such stability transition and the resulting slow slip events, which include (1) evolution in friction properties related to very slow slip rates at elevated temperatures, (2) the role of pore fluid pressure on stability transitions, where small increases in pore volume of the granular shearing material in the fault produces a large decrease in pore pressure resulting in increase in the shear resistance (dilatant strengthening), and (3) spatial variation in fault properties and conditions leading to a situation where nucleation of an earthquake can occur but is limited by adjacent regions with stable frictional properties. The work will involve integrated laboratory experiments and numerical modelling. Controlled lab experiments will measure the evolution of fault friction under previously unexplored temperature, pore fluid pressure, and slip rate conditions relevant to natural faults. We will quantify the evolution of frictional properties from very slow, tectonic fault slip rates of millimetres per year, to those through the episodic slow slip range of millimetres per day, and into the slip rates of meters per second where earthquakes occur. Fluid pressure changes promoted by compaction and dilation during slip will also be characterized. Numerical modelling of the experiments at the laboratory scale will help to ensure that the coupled physical mechanisms involved are understood and captured in our mathematical descriptions. The large-scale behaviour of faults with the properties defined by the experiments will be explored by numerical modelling at the scale of natural faults. The numerical modelling will relate the experimental findings to field observations of episodic slow slip and earthquake nucleation and investigate the role of spatial variations in fault properties on the occurrence of episodic slow slip events vs. earthquakes. A key deliverable for this work would be identification of the range of fault conditions and physical mechanisms under which episodic slow slip, fault creep, or earthquakes can occur, leading ultimately to improved seismic hazard forecasting.

由断层快速滑动产生的地震是一系列自然灾害造成的死亡的主要原因，全世界每年约有6万人死亡，其中约90%发生在发展中国家。断层滑动有三种方式。它们是（1）地震滑动;（2）板块构造加载速率驱动的稳定断层蠕动;（3）幕式缓慢滑动事件，其中断层滑动自发加速，但从未达到地震滑动速度。间歇性的缓慢滑动事件可以释放与地震相同的能量，但需要几天到几周，而不是几秒到几分钟。它们最常出现在俯冲带的某些区域，并与孔隙压力升高有关。断层滑动的这三种模式对于理解是至关重要的，因为幕式缓慢滑动和断层蠕动可以缓解应力积累并降低地震危险性，但也可以将应力从断层的一部分转移到另一部分，最终影响破坏性地震的成核。在这个项目中，我们将通过结合实验和数值模拟来提供物理约束，以确定导致稳定断层蠕动的控制因素，阶段性缓慢滑动或地震。到目前为止，人们还不知道是什么阻止了一些造成缓慢断层滑动的不稳定性，但又允许其他断层加速到导致地震的快速滑动速度。当滑动速度增加时，从不稳定的摩擦滑动（通常被视为导致地震）到稳定的摩擦滑动（通常被视为导致断层蠕动）的某种转变必然会促进断层上持续的缓慢滑动。这种稳定性转变的性质是广泛争论的，它可能发生的条件范围是不明确的。我们将研究解释这种稳定性转变和由此产生的缓慢滑动事件的关键假设，包括（1）与高温下非常缓慢的滑动速率相关的摩擦特性的演变，（2）孔隙流体压力对稳定性转变的作用，断层中粒状剪切物质孔隙体积的小幅度增加会导致孔隙压力的大幅度降低，剪切阻力（剪切强化），以及（3）断层性质和条件的空间变化，导致地震成核可能发生，但受到具有稳定摩擦性质的相邻区域的限制。这项工作将涉及综合实验室实验和数值模拟。受控实验室实验将测量在以前未探索的温度、孔隙流体压力和与天然断层相关的滑动速率条件下断层摩擦的演变。我们将量化摩擦特性的演化，从非常缓慢的构造断层滑动速率（毫米/年），到那些通过幕式缓慢滑动范围（毫米/天），再到发生地震的滑动速率（米/秒）。流体压力的变化，促进了压实和扩张过程中滑动的特点。在实验室规模的实验的数值模拟将有助于确保所涉及的耦合物理机制的理解和捕获在我们的数学描述。将通过自然断层尺度的数值模拟来探讨断层的大尺度行为与实验确定的性质。数值模拟将把实验结果与现场观测的幕式慢滑和地震成核联系起来，并研究断层性质的空间变化对幕式慢滑事件与地震发生的作用。这项工作的一个关键成果是确定断层条件和物理机制的范围，在这些条件和机制下，可能发生幕式缓慢滑动、断层蠕动或地震，最终改善地震灾害预测。