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: 1215711
• 负责人: Harold Tobin
• 金额: $ 23.4万
• 依托单位: University of Wisconsin-Madison
• 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 2017-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1215711&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，大多数大的破坏性地震是由构造板块边界的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其固定在一起，防止滑动，而应力则积累到破裂点，从而引发地震本身。然而，对于这种故障如何以及为何发生并发展成为大地震的性质仍然知之甚少。它被认为在很大程度上是由构成断层带的物质所控制的？被过去的地震破碎的岩石和填充在岩石孔隙中的水，以及地震深度的构造应力。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三阶段的项目，以钻探新西兰？阿尔卑斯山断层，一个类似于加州圣安德烈亚斯的主要断层带，历史上发生过7-8级地震，未来可能发生更多地震。钻探阿尔卑斯断层将提供来自断层带的新鲜样本，这些样本未受地表风化和侵蚀的负面影响。第一阶段，已经钻到150米深，获得了整个断裂带的岩心样本，并通过放置在孔中的仪器测量了岩石的性质。在下一阶段，将钻一个或多个孔，深度超过1500米，并打算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合作将测量这些样品的一系列特性，包括它们的强度（基于摩擦的滑动阻力和储存应变而不断裂的能力），孔隙水运动的渗透性，以及它们在实际条件下传输两种地震波（一种广泛使用的远程测量岩石特性的方法）的速度。此外，将使用从钻孔下放的仪器在更大范围内测量类似和额外的性能。利用样本和钻孔数据的结果，研究人员将评估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。他们还将评估断层带内部和周围深度的地下水流（或缺乏地下水流）的性质，这对于了解断层活动期间的压力和温度条件很重要。这项研究与新西兰合作者和其他人的补充工作相结合，将对断层带的工作方式以及地震发生的方式产生新的理解。它也可能产生新的线索，以了解未来的地震危险，特别是对阿尔卑斯山断层和一般的主要断层。