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

大型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。了解活动断层内部普遍存在的条件对于阐明控制长期断层演化的机制，特别是地震破裂过程至关重要。该项目包括对新西兰南岛阿尔卑斯断裂带及其周围的微地震和地壳结构进行详细研究，该断裂带位于Whataroa断裂带钻探点周围。它将与一组新西兰科学家密切合作。本课题研究的关键科学问题包括：(1)确定AF -中地壳深度和发震带基底深度的几何形状；(2)确定震源机制和估计主应力方向；(3)利用多种方法进行地壳结构地震成像；(4)寻找可能的非火山震颤（NVT）。我们的项目旨在测试一些假设，包括：(1)地表断层迹线的复杂性并不反映断层在深度上的迹线，而是在地表看到的分割合并成一个具有上地壳斜滑的贯穿断层；(2)在Whataroa地区下方的AF上，震源带底部的深度上升到15公里，或者可能更浅；(3) AF倾角与孕震带基底保持在50°附近；(4)主应力方向不随距AF的距离而变化；(5)与电阻率模型相似，在大尺度上通过大部分地壳沿SIGHT样带成像的相对低速带实际上是靠近AF的较窄带；(6)在af下面不存在NVT。本项目的目的是研究新西兰南岛阿尔卑斯断层这一主要活动大陆断层的结构和微震特征。阿尔卑斯断层在其地震周期中孤立，是长期多学科科学研究的焦点。在这个项目中，我们将进行与高山断层相关的地震现场工作和后续的微地震分析。这项研究将与一个雄心勃勃的断裂带钻探项目同时进行，该项目的重点是阿尔卑斯断层和邻近地壳的机械特性。他们的工作将有助于(1)确定断层深度的几何形状，(2)确定地震活动的深度范围（“发震区”），(3)为解释钻孔观测和岩心建立三维结构背景，(4)潜在地有助于确定浅层地震的破裂带，作为未来的钻探目标。

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.