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The simultaneous evolution of seismicity and permeability within geological faults

地质断层内地震活动性和渗透性的同时演化

基本信息

批准号：
NE/E004210/1
负责人：
Rebecca Lunn
金额：
$ 32.06万
依托单位：
University of Strathclyde
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2007
资助国家：
英国
起止时间：
2007 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FE004210%2F1
关键词：
simultaneous evolution seismicity permeability within

项目摘要

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.

所有的岩石内部都有孔（称为孔隙），里面充满了气体或水（两者一起被称为流体）。这些流体能够沿着岩石中相连的路径缓慢流动，并能携带化学物质。地质断层是一条共同的连通通道。这些区域有很多裂缝，如果它们没有被其他物质填充，就会为流体流动提供很多连通的孔隙空间。能够预测裂缝岩石中的流体流动速率对于开采地下水、石油、天然气和地热能至关重要。深层岩石也被用来掩埋废物，比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所安全性的一个重要部分是预测溶解在水中的泄漏废物迁移到地面所需的时间。如果我们能理解控制岩石裂缝形成的物理定律，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，为流体流动创造新的路径。但与此同时，如果流体流入地质断层线，它会使断层变弱，导致断层滑动。流体可以通过使断层在两次地震之间“愈合”来影响地震。当流经断层的水将其携带的化学物质倾倒以产生新的矿物质时（比如将裂缝的两侧粘合在一起），就会发生这种情况。下次地震时，这些水泥就会破裂。如果不进行修复，断层就会滑动而不会引起地震。科学家们以前就提出过流体流动和地震这两个过程之间的联系，但我们并不真正了解它们是如何紧密联系在一起的，以至于无法做出预测。该提案使用了巴西建造大型地表水水库引起的微地震数据。每年水库的水位都会上升，几个月后就会发生小地震。这表明水流入断层，导致地震沿着断层破裂。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，但不知道确切的位置。通过分析地震开始的时间和开始的地点，我们可以了解到水的路径，以及断层“愈合”需要多长时间。我们将使用新技术来精确地找到每次地震的位置，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，该模型可以模拟流体流过裂缝时裂缝的生长。我们需要检查这些模型是否产生了看起来像真正的岩石断层的裂缝，所以我们将绘制出巴西大坝遗址附近暴露的岩石断层的形状和大小。我们还将通过测试来检验我们的模型是否有效，看看它是否与同一水库的另外两个断层的地震模式相匹配。通过仔细检查我们的模型是否能制造出逼真的地震模式，我们将能够利用这些结果来预测地震对其他地方裂缝演变的影响。