Collaborative Research: Physical properties of the Alpine Fault, New Zealand: Mechanical and hydrological processes in the brittle fault core and surrounding damage zone

科学家们早就知道，大多数具有破坏性的大地震是由构造板块之间边界的断裂带上缓慢积累的应力引起的。断层两侧的摩擦力将断层结合在一起，防止滑动，同时应力累积到断裂点，从而引发地震本身。然而，这种破坏是如何发生的，以及为什么会发展成一场大地震，其本质仍然知之甚少。它被认为在很大程度上是由构成断裂带的物质控制的？在过去的地震中破裂和破碎的岩石，填满岩石孔隙的水，以及地震深处的构造应力。为了进一步了解断层是如何运作的，一个国际科学家团队正在进行一个分三个阶段的项目，以钻探新西兰的S阿尔卑斯山断层，这是一个类似于加利福尼亚州圣安德烈亚斯的主要断裂带，历史上曾发生7-8级地震，未来可能会发生更多地震。钻探阿尔卑斯山断层将提供断裂带的新样本，不受地表风化和侵蚀的负面影响。第一阶段已经钻探到150米深，获取了断层带上的岩心样本，并通过放置在孔中的仪器测量了岩石性质。在下一阶段，将钻一个或多个洞，深度超过1500米，目的是在地震深度穿过断层进行采样。作为这项工作的一部分，威斯康星大学麦迪逊分校和宾夕法尼亚州立大学将合作测量这些样品的一系列特性，包括它们的强度(基于摩擦的抗滑能力和不破裂存储应变的能力)、对孔隙水运动的渗透性以及它们在现实条件下传播两种类型地震波的速度(一种广泛使用的远程测量岩石特性的方法)。此外，向下放下钻孔的仪器将被用来在更大范围内测量类似和额外的特性。利用样本和钻井数据的结果，调查人员将评估关于断裂带强度和其中条件的相互竞争的假说，帮助发现地震之间在断层内发生的事情，以及它们可能如何变化，从而导致未来的地震活动。他们还将评估断层带内部和周围深层地下水流动的性质(或缺乏)，这对于了解断层活动期间的压力和温度条件很重要。这项研究与新西兰的合作者和其他人的补充工作相结合，将对断裂带是如何工作的以及地震为什么会以这种方式发生产生新的理解。它还可能提供新的线索，以了解未来特别是阿尔卑斯断层和主要断层上的地震危险。

Scientists have long known that most large, destructive earthquakes are caused by the slow buildup of stress on fault zones at the boundaries between tectonic plates. Friction between the two sides of the fault holds it together and prevents slip while stress accumulates until the point of failure, precipitating the earthquake itself. However, the nature of how and why that failure occurs and grows into a large earthquake remains poorly understood. It is thought to be governed in large part by the materials that make up the fault zone ? the rock that is fractured and broken down by past earthquakes and the water that fills pore spaces in that rock, as well as the tectonic stresses at the depth of earthquakes. To further our understanding of how faults work, an international team of scientists is conducting a 3-stage project to drill into New Zealand?s Alpine Fault, a major fault zone similar to the San Andreas of California, with a history of magnitude 7-8 earthquakes, and future potential for more. Drilling into the Alpine Fault will provide fresh samples from the fault zone unaltered by the negative effects of earth-surface weathering and erosion. The first stage, already drilled to 150 meters depth, obtained core samples across the fault zone and made measurements of the rock properties made by instruments placed down the holes. In the next stage, one or more holes will be drilled to more than 1500 meters depth, and is intended to sample across the fault at earthquake depths. As part of that effort, the University of Wisconsin-Madison and Penn State University partnership will measure a range of properties of these samples, including their strength (friction-based resistance to slip and the capacity to store up strain without breaking), permeability to pore water movement, and the speeds with which they transmit two types of seismic waves (a widely used way to measure rock properties remotely) under realistic conditions. Furthermore, instruments lowered down the drill holes will be used to measure similar and additional properties at a broader scale. Using the results of sample and the drillhole data, the investigators will evaluate competing hypotheses for the strength of fault zones and the conditions therein, helping discover what happens inside faults between earthquakes, and how they may change leading up to future seismic activity. They will also evaluate the nature of groundwater flow (or lack thereof) in and around the fault zone at depth, important for understanding the pressure and temperature conditions during fault activity. This research, when combined with the complementary work by New Zealand-based collaborators and others, will yield a new understanding of how fault zones work and why earthquakes happen in the ways that they do. It will likely also yield new clues to understanding the future earthquake hazard on the Alpine Fault in particular and on major faults in general.