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.

地震是由快速滑倒的断层产生的，这是一系列自然灾害的大部分死亡，每年约有60,000人在全球范围内，其中约有90％发生在发展中国家。滑移可以以三种方式发生故障。这些是（1）地震滑动；（2）由板构造载荷率驱动的稳定故障蠕变；（3）情节慢滑动事件，故障滑移会自发加速，但从未达到地震滑动速度。情节慢速事件可以释放与地震相同的能量，但在几天到几秒钟内而不是秒至几分钟。它们最常见于俯冲带的某些区域，并且与孔隙压力升高有关。这三种断层滑动模式对于理解至关重要，因为情节的缓慢滑移和断层蠕变减轻了压力的增加并减少了地震危险，但也将压力从断层的一个部分转移到另一部分，最终影响破坏性地震的成核。在该项目中，我们将从组合实验和数字模型中提供良好的速度较高的速度，以确定良好的缺陷型，以确定良好的缺陷。到目前为止，尚不理解是什么使制动器在某些不稳定性上造成了缓慢的断层滑动，但其他人则可以加速导致地震的快速滑移速度。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（通常被视为导致故障蠕变）的某种过渡，而滑动速度的增加必须促进故障持续缓慢滑倒。这种稳定过渡的性质被广泛争论，并且可能发生的条件范围不明。我们将调查提议解释这种稳定性过渡和结果缓慢的事件的关键假设，其中包括（1）与温度升高时摩擦速率非常缓慢的速率相关的摩擦特性的演变，（2）孔隙液压力对稳定性过渡的作用，在孔隙率过渡中，较小的孔隙剪切材料在断层中的孔隙较小和骨骼压力的增加，并降低了孔的孔隙率，并降低了孔的延伸（在骨骼中降低）（在骨骼中降低（在骨骼中增加），从而增加了（在骨骼中增加）（在骨骼中增加（在骨骼）上增加（在孔隙中增加），而造成的（在骨骼中增加，则在孔隙率上增加了，而造成了（在孔隙率上增加，而造成的，则在上升的压力降低了，而无需增加（降低）。（3）断层特性和导致地震成核的情况的空间变化可能会发生，但受到具有稳定摩擦特性的相邻区域的限制。这项工作将涉及集成的实验室实验和数值建模。受控实验室实验将测量在先前未开发的温度，孔隙流体压力以及与自然断层相关的滑移速率条件下的断层摩擦演变。我们将量化摩擦性能从每年毫米的非常缓慢的构造断层滑移速率，每天通过毫米的情节缓慢滑移范围，以及发生地震发生的每秒米的滑移速率。通过压实和扩张期间促进的流体压力变化也将被表征。实验量表的实验的数值建模将有助于确保在我们的数学描述中了解和捕获所涉及的物理机制。通过在自然断层的尺度上进行数值建模来探索故障的大规模行为。数值建模将将实验发现与情节慢滑和地震成核的现场观察有关，并研究空间变化在断层特性中的作用在情节慢滑动事件中与地震的发生。这项工作的一个关键可交付是确定可能发生的慢速滑移，断层或地震的断层条件和物理机制的范围，最终导致改善地震危险预测。