The simultaneous evolution of seismicity and permeability within geological faults

所有岩石内部都有洞（称为孔隙），充满气体或水（统称为流体）。这些流体能够沿着连接的路径缓慢地流过岩石，并能随其移动化学物质。一个共同的连接路径发生通过地质断层。这些区域有许多裂缝，如果没有其他物质填充，就会提供许多连通的孔隙空间供流体流动。能够预测裂缝岩石中的流体流动速率对于提取地下水、石油和天然气以及地热能至关重要。深层岩石也被用于掩埋废物，如放射性废物或温室气体。在这种情况下，评估地下废物处置场安全性的一个重要部分是预测溶解在水中的泄漏废物到达地面所需的时间。如果我们能理解岩石裂缝形成的物理规律，那么我们就能更好地预测地下的流动路径。当地震沿着地质断层线发生时，它们会破坏岩石，产生新的流体流动路径。然而，与此同时，如果流体流入地质断层线，它可以使它变弱并导致它滑动。流体可以通过使断层在地震之间“愈合”来影响地震。当水流通过断层时，它会将携带的化学物质倾倒出来，形成新的矿物质（比如将裂缝的两侧粘合在一起）。下一次发生地震时，它会使水泥破裂。如果没有愈合，断层只会滑动而不会发生地震。科学家们以前曾提出过流体流动和地震这两个过程的联系，但我们并不真正了解它们是如何联系得足够好，以便能够做出预测。该提案使用了从巴西建造大型地表水水库引起的微地震中获取的数据。每年水库的水位都会上升，几个月后就会发生小地震。这表明水正流入断层，并导致地震沿着断层带沿着破裂。我们非常幸运，在这种情况下，一些地震科学家收集了非常准确的数据来确定地震的位置，我们经常能感觉到地震，但不知道它们到底在哪里。通过分析地震开始所需的时间以及它们开始的位置，我们可以了解水所采取的路径以及断层“愈合”所需的时间。我们将使用新的技术来精确地找到每一次地震的位置，这将告诉我们早期的地震是如何产生新的裂缝并重新安排水流的路径的。为了理解这是如何发生的，我们将使用我们开发的一个模型，该模型可以模拟裂缝的生长，同时有流体流过它们。我们需要检查这些模型是否产生了看起来像岩石中真实的断层的裂缝，因此我们将绘制出巴西大坝附近暴露的岩石中断层的形状和大小。我们还将通过测试来检查我们的模型是否有效，看看它是否与同一水库的其他两个断层上的地震模式相匹配。通过仔细检查我们的模型是否能产生逼真的地震模式，我们将能够使用这些结果来预测地震对其他地方裂缝演化的影响。

All rocks have holes within them (called pores) that are filled with either gas or water (which together are referred to as fluids). These fluids are able to flow slowly along connected paths through the rock and can move chemicals with them. A common connected pathway occurs through geological faults. These are zones with lots of fractures which, if they are not filled with other material, provide lots of connected pore space for fluids to flow. Being able to predict the rate of fluid flow in fractured rocks is critical to extracting groundwater, oil and gas and geothermal energy. Deep rocks are also used for burial of waste materials, like radioactive waste or greenhouse gases. In this case an important part of assessing the safety of underground waste disposal sites is to predict the time taken for leaking waste dissolved in water to travel to the surface. If we can understand the physical laws that govern the formation of fractures in rocks, then we can make better predictions of flow paths beneath the ground. When earthquakes occur along geological fault lines they damage rocks, producing new paths for fluids to flow through. However at the same time, if fluids flow into a geological fault line, it can make it weaker and cause it to slip. Fluid can affect earthquakes by causing faults to 'heal' between earthquakes. This occurs when water flowing through a fault dumps the chemicals it's carrying to make new minerals (like cementing the two sides of the crack together). Next time there is an earthquake it will rupture this cement. If there is no healing, the fault will just slide without making an earthquake.The linking of the two processes of fluid flow and earthquakes has been suggested by scientists before, but we don't really understand how they are linked well enough to be able to make predictions. This proposal uses data taken from micro-earthquakes that have been caused by the construction of a large surface water reservoir in Brazil. Every year the water level in the reservoir rises and a few months later small earthquakes occur. This shows that the water is flowing into the faults and causing earthquakes to rupture along the fault zone. We are very lucky that in this case some earthquake scientists collected really accurate data to pin point the earthquake locations, often we can feel the earthquakes but don't know exactly where they are. By analysing the time it takes for the earthquakes to start and where they started we can learn something about the path the water has taken and how long it has taken for the faults to 'heal'. We will use new techniques to accurately find the position of each earthquake which will tell us how the earlier earthquakes have created new cracking and rearranged the paths for water to flow. To understand how this happens we will use a model we have developed that can simulate the growth of cracks while there is fluid moving through them. We'll need to check that these models are producing cracks that look like real faults in rock, so we will map out the shapes and sizes of faults in rocks that are exposed near the dam site in Brazil. We will also check that our model works by testing to see if it matches the earthquake patterns on two other faults at the same reservoir. By carefully checking that our model is making realistic looking earthquake patterns we'll be able to use these results to predict the affect of earthquakes on crack evolution at other locations.