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

合作研究：新西兰阿尔卑斯断层的物理特性：脆性断层核心及周围损伤区的机械和水文过程

• 批准号: 1215856
• 负责人: Demian Saffer
• 金额: $ 31.6万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1215856&HistoricalAwards=false
• 关键词: Collaborative; Research; Physical; properties; Alpine

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.

科学家们早就知道，大多数大型破坏性地震是由构造板块边界断层带上的应力缓慢积累引起的。断层两侧之间的摩擦力将断层固定在一起并防止滑动，同时应力累积直至断裂点，从而引发地震。然而，人们对这种破坏如何以及为何发生并发展成大地震的本质仍然知之甚少。人们认为它在很大程度上是由构成断层带的物质决定的？因过去的地震而破裂和分解的岩石和填充岩石孔隙空间的水，以及地震深度的构造应力。为了进一步了解断层如何运作，一个国际科学家团队正在开展一个分三阶段的项目，钻探新西兰的高山断层，这是一个类似于加利福尼亚州圣安德烈亚斯的主要断层带，历史上的震级为 7- 8 次地震，未来还有可能发生更多地震。钻探阿尔卑斯断层将提供来自断层带的新鲜样本，这些样本不会受到地表风化和侵蚀的负面影响。第一阶段已钻探至 150 米深度，获取了横跨断层带的岩心样本，并通过放置在孔中的仪器对岩石特性进行了测量。下一阶段，将钻一个或多个深度超过1500米的孔，目的是在地震深度跨断层进行采样。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的合作伙伴关系将测量这些样品的一系列特性，包括它们的强度（基于摩擦的防滑性和储存应变而不断裂的能力）、渗透性孔隙水运动，以及它们在现实条件下传输两种类型的地震波（一种广泛使用的远程测量岩石特性的方法）的速度。此外，降低钻孔的仪器将用于在更广泛的范围内测量类似和附加的特性。利用样本结果和钻孔数据，研究人员将评估有关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的情况，以及断层如何变化导致未来的地震活动。他们还将评估断层带内部和周围深度的地下水流（或缺乏）的性质，这对于了解断层活动期间的压力和温度条件非常重要。这项研究与新西兰合作者和其他人的补充工作相结合，将对断层带如何运作以及地震为何以这种方式发生产生新的认识。它还可能为了解阿尔卑斯断层（特别是高山断层）和主要断层未来的地震危险提供新的线索。