Time-dependent deformation: bridging the strain rate gap in brittle rocks.

地震破裂和火山喷发是临界应力地壳动力破坏最壮观的表现形式。然而，这些实际上是相当罕见的，在空间和时间上离散的事件。地壳的大部分时间都处于高应力的亚临界状态。此外，水在地壳中无处不在。众所周知，水岩化学反应可导致随时间的变形，使岩石在远低于其短期破坏强度的应力下长期破坏；这种现象被称为“亚临界裂纹扩展”。量化亚临界裂纹扩展对于揭示脆性地壳演化和动力学的复杂性至关重要。裂缝的存在使地壳能够储存和输送流体，即使裂缝的大小、密度或联系的微小变化也会产生流体输送特性的重大变化。因此，随时间变化的岩石变形具有科学和社会经济影响，因为它控制着地震破裂和火山爆发等重要地质灾害前兆阶段的持续时间和可探测性。这种变形机制导致压实和开裂，两者都会影响孔隙度和渗透率。因此，研究结果也可能与有效回收碳氢化合物和地热能资源以及危险废物长期储存设施的完整性有关。联合国教科文组织最近强调了我们目前对这一领域缺乏了解，而“在动态破坏之前了解缓慢变形”是其国际地球年自然灾害主题中两个优先研究领域之一。因此，我们正在为一项综合实验室实验、深海观测和随时间变化的脆性岩石变形的定量分析研究寻求资金，涉及伦敦大学学院地球科学系的岩石与冰物理实验室（RIPL）、爱丁堡大学地球科学学院（EdU）和意大利国家地球物理与火山学研究所（INGV）。该项目的目的是区分不同的随时间变化的岩石变形模型。鉴于传统实验室实验中可实现的应变速率范围，这在目前是不可能的。因此，我们的主要目标是利用深海环境来弥合实验室应变率和地壳应变率之间的差距。该项目将以小组之间先前的合作工作为基础，并利用实验方法（RIPL）和理论分析（EdU）的最新发展，以及由NERC资助的深海观测站试点研究中取得的初步结果，其中基础设施支持由INGV提供。试点研究最初是作为目前提案的可行性研究提出的，并取得了积极成果。我们现在有了一个及时的机会，可以在早先的合作基础上进一步发展，并利用INGV在西西里岛东岸爱奥尼亚海海底建立的一个独特的、新的、价值数百万欧元的深海观测设施。

Earthquake rupture and volcanic eruptions are the most spectacular manifestations of dynamic failure of critically-stressed crust. However, these are actually rather rare, discrete events in both space and time. Most of the crust spends most of its time in a highly-stressed but sub-critical state. Furthermore, water is ubiquitous in the crust. It is well-known that water-rock chemical reactions can lead to time-dependent deformation enabling rocks to fail over extended periods of time at stresses far below their short-term failure strength; a phenomenon known as 'sub-critical crack growth'. Quantifying sub-critical crack growth is crucial to unravelling the complexities of the evolution and dynamics of the brittle crust. The presence of cracks allows the crust to store and transport fluids, and even modest changes in crack size, density or linkage can produce major changes in fluid transport properties. Time-dependent rock deformation therefore has both a scientific and a socio-economic impact since it controls the duration and detectability of any precursory phase of important geohazards such as earthquake rupture and volcanic eruptions. Such deformation mechanisms cause compaction and cracking, both of which affect porosity and permeability. The results may therefore also be of relevance in the effective recovery of hydrocarbon and geothermal energy resources, and the integrity of long-term storage facilities for hazardous waste. Our current lack of understanding in this area has recently been highlighted by UNESCO, and 'Understanding Slow Deformation before Dynamic Failure' is one of the two priority areas for study within the Natural Hazards theme of its International Year of Planet Earth. We are therefore seeking funds for an integrated laboratory experiment, deep-sea observatory and quantitative analysis study of time-dependent brittle rock deformation, involving the Rock & Ice Physics Laboratory (RIPL) in the Department of Earth Sciences at University College London (UCL), the School of Geo-Science at Edinburgh University (EdU) and the Italian National Institute of Geophysics and Volcanology (INGV). The aim of the project is to discriminate between competing models of time-dependent rock deformation. That is currently not possible given the range of strain rates achievable in conventional laboratory experiments. Our main objective is therefore to use the deep-sea environment to bridge the strain rate gap between laboratory and crustal strain rates. The project will build on previous collaborative work between the groups, and take advantage of recent developments in experimental methodology (RIPL) and theoretical analysis (EdU), and preliminary results achieved during a deep-sea observatory pilot study funded by NERC, where infrastructural support was provided by INGV. The pilot study was originally proposed as a feasibility study for the current proposal, and achieved positive results. We now have a timely opportunity to build on this earlier collaboration and take advantage of access to a unique, new, multi-million Euro deep-sea observatory facility established by INGV on the bed of the Ionian Sea off the east coast of Sicily.