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

合作研究：新西兰高山断层瓦塔罗阿断层带钻探现场周围微地震和地壳速度结构的地震特征

• 批准号: 1114228
• 负责人: Clifford Thurber
• 金额: $ 20.74万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-10-01 至 2015-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1114228&HistoricalAwards=false
• 关键词: Collaborative; Research; Seismic; characterization; microearthquakes

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.

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。了解活动断层内部普遍存在的条件对于阐明控制断层长期演化的机制，特别是地震破裂过程至关重要。该项目涉及对新西兰南岛沃塔罗阿断层带钻探地点周围阿尔卑斯断层内部及其周围的微地震和地壳结构进行详细研究。它将与新西兰科学家团队密切合作。本研究项目要解决的关键科学问题包括：（1）确定地壳中部深度的AF的几何形状和发震带底部的深度；（2）确定震源机制并估计主应力方向；（3）使用多种方法对地壳结构进行地震成像；（4）寻找可能的非火山震颤（NVT）。我们的项目旨在检验一些假设，包括：（1）地表断层痕迹的复杂性并不反映深层的断层痕迹，而是地表看到的分区合并成上地壳中带有斜滑的贯穿断层； (2) 在 Whataroa 地区下方的 AF 上，到发震带底部的深度升高到 15 公里，或者可能更浅； (3) AF倾角与震源底面保持接近50°； (4) 主应力方向不随距 AF 的距离而变化； (5) 沿着 SIGHT 横断面通过大部分地壳大范围成像的相对低速区域实际上是更靠近 AF 的较窄区域，类似于电阻率模型； (6) NVT 不存在于 AF 之下。该项目的目标是研究主要活动大陆断层——新西兰南岛阿尔卑斯断层的结构和微地震特征。阿尔卑斯断层处于地震周期，是长期、多学科科学调查的焦点。在这个项目中，我们将开展地震现场工作以及与阿尔卑斯断层相关的微地震的后续分析。该研究将与一个雄心勃勃的断层带钻探项目结合进行，该项目重点关注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）定义断层深度的几何形状，（2）确定地震活动的深度范围（“发震带”），（3）建立用于解释钻孔观测和岩心的三维结构背景，以及（4）可能有助于将浅层地震的破裂带定义为未来的钻探目标。