Exploring the geological signature of Slow Earthquakes through legacy experiments and field analysis

地球的外层是由板块组成的，这些板块相互滑动，相互移动或拉开。世界上很大一部分人口生活在这样的边界附近。过去二十年的遥感表明，我们对板块如何沿着这些边界变形的看法需要修正。我们现在认识到慢震（SEs），它的滑动速度比普通地震慢，但比正常的板块运动快得多。有趣的是，这些se似乎是由非常小的力触发的，相当于一个装满水的浴缸的重量，它们观察到的特征，目前还不能与我们目前对岩石变形的理解相一致。板块尺度的变形是由微观尺度上活跃的过程控制的，然而，使观测到的东南滑移率成为可能的过程的性质仍然是个谜。因为se可以影响破坏性地震的可能性，如果我们要更好地评估与板块边界运动相关的危害和风险，就需要了解se。目前应对这一挑战的方法在很大程度上依赖于来自敏感仪器的数据，这些仪器可以远程探测到非常微妙的地面运动。因为SEs发生在我们脚下许多公里的岩石中，所以没有直接的方法来检验那些用来解释SEs的理论。这种对推论而非直接证据的依赖，对我们理解社会经济学构成了一个主要障碍。幸运的是，地球为我们提供了另一组独立的观测结果。SEs应该在地质记录中留下印记；在许多俯冲带中，一个板块潜入另一个板块下面的地球内部，它们容纳了100公里宽区域内的大部分变形。因此，原则上，对在曾经受地球化学作用影响的地区出土的岩石进行深入分析，应该认为这一过程的特征是负责任的。但到目前为止，对这些签名还没有达成共识。我们假设se在地质记录中一直不可见，因为我们目前不知道要寻找什么。在我们的探索项目中，我们使用(1)地球物理学的SEs来帮助我们缩小可能产生它们的过程(2)可以重现SE行为的实验室实验-所得样品可以显示并告诉我们岩石在SEs之后的样子。(3)从合适的野外位置挖掘出SE岩石，允许我们测试我们的理论是否正确（即确定的过程确实负责SE）地球物理数据告诉我们，负责SE的过程必须使岩石像面团一样流动，突然破裂并快速移动。有趣的是，几十年的实验室变形实验已经准确地显示了这种行为。这种“缓慢裂缝”与东南断裂行为非常相似，发生在富含流体的岩石变形时。然而，这样的实验被认为是“失败的”，因为它们不能用来评估被解释为控制板块变形的岩石的缓慢流动行为。我们将利用这些迄今为止在很大程度上被忽视的实验来检验我们的假设。我们将使用目前可用的分析技术进行纳米级的分析。我们新近训练有素的眼睛能够识别预测的东南地震过程，我们将在目前被认为藏有慢震指纹的发掘区域进行实地工作，并对自然样本进行分析。如果我们的假设是正确的，我们将第一次能够使用地质记录来帮助约束以前只有地球物理数据才能看到的过程。与团队的慢滑密切讨论，遥感专家将确保推断的地质过程可以解释观测到的SE遥感数据。如果我们是正确的，我们的“概念验证”项目将为基本理解SE奠定基础，并允许团队建立知识库，以提出一个有充分基础的、更大的SE研究项目。

Earth's outer layer is made up of plates that slide past each other, move into one another or pull apart. A large percentage of the World's population is living close to such boundaries. The last two decades of remote sensing has shown that our view of how plates deform along these boundaries needs to be revised. We now recognise Slow Earthquakes (SEs), which slip more slowly than regular earthquakes, but significantly faster than normal plate movements. Intriguingly, these SEs seem to be triggered by very low forces equivalent to the weight of a filled bathtub and their observed characteristics cannot, at present, be reconciled with our current understanding of how rocks deform. Plate-scale deformation is governed by processes active at the microscopic scale, however the nature of the processes enabling observed SE slip rates remains enigmatic. Because SEs can influence the likelihood of damaging earthquakes, they need to be understood if we are to better assess hazards and risks associated with plate boundary motions. The current approach to this challenge relies heavily on data from sensitive instruments detecting remotely very subtle ground movement. Because the SEs are occurring in rocks that are many kilometres beneath our feet, there is no direct way to test the theories that have been put forward to explain SEs. This reliance on inferences rather than direct evidence poses a major barrier to our understanding of SEs. Luckily, the Earth presents us with another set of independent observations. SEs should leave an imprint in the geological record; they accommodate most of the deformation over 100-km-wide regions in many subduction zones, where one plate dives into the Earth's interior beneath another. Thus, in principle, in-depth analyses of exhumed rocks found in regions that were once subject to SEs should hold the signature of the processes responsible. But to date there is no consensus on these signatures.We hypothesise that SEs have remained invisible in the geological record because we currently do not know what to look for. In our exploratory project, we use (1) geophysics of SEs to help us to narrow down the processes likely to produce them(2) laboratory experiments that can reproduce SE behaviour - the resulting samples can show and teach us what rocks would look like following SEs. (3) exhumed SE rocks from suitable field locations, allowing us to test if our theory is correct (namely that the identified processes are indeed responsible for SEs)Geophysical data tells us that the process responsible for SE must enable rocks to flow like a dough and to suddenly crack and move fast. Interestingly, decades of laboratory deformation experiments have shown exactly this behaviour. Such "Slow Fractures" closely resemble SE behaviour and occur when deforming a fluid-rich rock. However, such experiments have been regarded as "failed" as they could not be used to assess the slow flow behaviour of rocks interpreted to govern plate deformation. We will test our hypothesis by utilising these so far largely neglected experiments. We will perform analyses down to the nanometer scale using only-now available analytical techniques. Equipped with our newly trained eye to recognise the predicted SE process, we will carry out field work in an exhumed area currently presumed to hold Slow Earthquake fingerprints and perform analyses on natural samples. If our hypothesis is right, we will for the first time be able to use the geological record to help constrain processes that have previously only been visible to geophysical data. Close discussion with the team's slow slip, remote sensing expert will ensure inferred geological processes can explain observed SE remote sensing data. If we are correct, our "proof of concept" project will lay the foundation for fundamental understanding of SEs and allow the team to build-up the knowledge-base to propose a well-founded, larger SE focused research project.