Collaborative Research: Seismic characterization of microearthquakes and crustal velocity structure around the Whataroa fault zone drilling site, Alpine Fault, New Zealand

大断层的力学行为受热、化学和水力因素以及每个断层的内在结构和环境应力的控制。了解活动断裂内部的条件对于阐明控制长期断裂演化的机制，特别是地震破裂过程至关重要。该项目包括详细研究新西兰南岛阿尔卑斯断层内和周围的微震和地壳结构，这些断层位于瓦塔罗亚断裂带钻探现场周围。它将与一个新西兰科学家团队密切合作。这一研究项目要解决的关键科学问题包括：(1)确定AF到中地壳深度的几何形状和到孕震带底部的深度；(2)确定震源机制和估计主应力方向；(3)采用多种方法进行地壳结构的地震成像；(4)寻找可能的非火山地震(NVT)。我们的项目旨在检验一些假设，包括：(1)地表断层的复杂性并不反映深部的断层痕迹，而是在地表看到的分割合并成一个具有上地壳斜滑的贯通断层；(2)在瓦塔罗阿地区下的AF上，地震带底部的深度上升到15公里，或者可能更浅；(3)AF倾角保持接近50°；(4)主应力方向不随距离AF而变化；(5)沿视线在大部分地壳中大范围成像的相对低速带实际上是一个更靠近AF的较窄的带，类似于电阻率模型；(6)AF下不存在NVT。本项目的目标是研究新西兰南岛阿尔卑斯断裂这一主要活动大陆断裂的结构和微震特征。阿尔卑斯山断层处于地震周期的晚期，是一项长期、多学科科学调查的焦点。在这个项目中，我们将开展与阿尔卑斯断层相关的地震现场工作和后续的微震分析。这项研究将与一个雄心勃勃的断裂带钻探项目一起进行，该项目的重点是阿尔卑斯山断层和邻近地壳的力学性质。他们的工作将有助于(1)确定断层的几何形状，(2)确定地震活动的深度范围(“孕震带”)，(3)建立用于解释钻孔观测和岩心的三维结构背景，以及(4)潜在地有助于将浅层地震的破裂带定义为未来的钻探目标。

The mechanical behavior of large faults is controlled by thermal, chemical, and hydraulic factors,as well as each fault's intrinsic structure and the ambient stresses. Understanding what conditionsprevail within the interiors of active faults is crucial for elucidating the mechanisms governinglong-term fault evolution and, in particular, the earthquake rupture process. This project involvesa detailed study of microearthquakes and crustal structure within and surrounding the AlpineFault, South Island, New Zealand, around the Whataroa fault zone drilling site. It will be carriedout close collaboration with a team of New Zealand scientists. The key scientific issues to beaddressed by this research project include: (1) determining the geometry of the AF to mid-crustaldepths and the depth to the base of the seismogenic zone, (2) determining focal mechanisms andestimating principal stress orientations, (3) seismic imaging of crustal structure using multiplemethods, and (4) searching for possible nonvolcanic tremor (NVT). Our project is designed totest a number of hypotheses, including: (1) that the complexity of the surface fault trace does notreflect the fault trace at depth, rather the partitioning seen at the surface merges into a throughgoingfault with oblique slip in the upper crust; (2) that the depth to the base of the seismogeniczone is elevated to 15 km, or perhaps shallower, on the AF beneath the Whataroa area; (3) thatthe AF dip remains close to 50° to the base of the seismogenic zone; (4) that principal stressorientations do not vary with distance from the AF; (5) that the relatively low velocity zoneimaged at large scale through much of the crust along the SIGHT transects is actually a narrowerzone closer to the AF, similar to the resistivity model; (6) that NVT is not present beneath theAF.The goal of this project is to examine the structure and microearthquake characteristics of amajor active continental fault, the Alpine Fault, South Island, New Zealand. The Alpine Fault islate in its earthquake cycle and is the focus of a long-term, multidisciplinary scientificinvestigation. In this project, we will carry out seismic field work and subsequent analyses ofmicroearthquakes associated with the Alpine Fault. The research will be conducted inconjunction with an ambitious fault zone drilling project focused on the mechanical properties ofthe Alpine Fault and the adjacent crust. Their work will help (1) define the geometry of the faultat depth, (2) determine the depth range of seismic activity (the "seismogenic zone"), (3) establisha three-dimensional structural context for interpreting borehole observations and core, and (4)potentially help to define rupture zones of shallow earthquakes as future drilling targets.