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，大多数大的、破坏性的地震是由构造板块之间边界的断层带上的应力缓慢积聚引起的。断层两侧之间的摩擦使其保持在一起，防止滑动，而应力积累直到破裂点，从而引发地震本身。然而，这种失败发生并发展成大地震的方式和原因，人们仍然知之甚少。人们认为它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的岩石和充满岩石孔隙空间的水，以及地震深处的构造应力。为了进一步了解断层是如何工作的，一个国际科学家团队正在进行一个分三个阶段的项目，钻探到新西兰？这是一个类似于加州圣安德烈亚斯的主要断层带，历史上曾发生过7-8级地震，未来还可能发生更多地震。在阿尔卑斯断裂带钻探将提供断裂带的新鲜样品，这些样品未受地球表面风化和侵蚀的负面影响。第一阶段，已经钻到150米深，获得了断层带的岩心样本，并通过放置在洞里的仪器测量了岩石的性质。在下一阶段，将钻一个或多个1500米以上的洞，目的是在地震深度的断层上取样。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的合作伙伴将测量这些样品的一系列特性，包括它们的强度（基于摩擦的抗滑移性和不破裂的储存应变的能力），孔隙水运动的渗透率，以及它们在现实条件下传输两种地震波的速度（一种广泛用于远程测量岩石特性的方法）。此外，在钻孔中放置的仪器将用于在更大范围内测量类似和额外的特性。利用样本和钻孔数据的结果，研究人员将评估关于断层带强度及其条件的相互竞争的假设，帮助发现地震之间断层内部发生了什么，以及它们如何变化导致未来的地震活动。他们还将评估深层断层带内及其周围地下水流动（或缺乏）的性质，这对于了解断层活动期间的压力和温度状况很重要。这项研究，当与新西兰合作者和其他人的补充工作相结合时，将产生对断层带如何工作以及地震为什么以这种方式发生的新理解。它可能还会提供新的线索，以了解未来的地震危险，特别是在阿尔卑斯断层和主要断层上。

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.