The Alpine Fault zone in New Zealand marks a major transpressional plate boundary that is late in its typical earthquake cycle. Understanding the subsurface structures is crucial to understand the tectonic processes taking place. A unique seismic survey including 2D lines, a 3D array, and borehole recordings, has been performed in the Whataroa Valley and provides new insights into the Alpine Fault zone down to ∼2 km depth at the location of the Deep Fault Drilling Project (DFDP)-2 drill site. Seismic images are obtained by focusing prestack depth migration approaches. Despite the challenging conditions for seismic imaging within a sediment filled glacial valley and steeply dipping valley flanks, several structures related to the valley itself as well as the tectonic fault system are imaged. A set of several reflectors dipping 40°–56° to the southeast are identified in a ∼600 m wide zone that is interpreted to be the minimum extent of the damage zone. Different approaches image one distinct reflector dipping at ∼40°, which is interpreted to be the main Alpine Fault reflector located only ∼100 m beneath the maximum drilled depth of the DFDP-2B borehole. At shallower depths (z < 0.5 km), additional reflectors are identified as fault segments with generally steeper dips up to 56°. Additionally, a glacially over-deepened trough with nearly horizontally layered sediments and a major fault (z < 0.5 km) are identified 0.5–1 km south of the DFDP-2B borehole. Thus, a complex structural environment is seismically imaged and shows the complexity of the Alpine Fault at Whataroa.

中文翻译：

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新西兰高山断裂带和 Whataroa 冰川谷的 3D 活源地震成像

新西兰的高山断层带标志着一个主要的压压板块边界，该边界处于其典型的地震周期后期。了解地下结构对于了解正在发生的构造过程至关重要。在 Whataroa Valley 进行了一次独特的地震勘测，包括 2D 线、3D 阵列和钻孔记录，并提供了对深断层钻探项目 (DFDP) 位置深达 2 公里深的高山断层带的新见解-2 钻探现场。地震图像是通过聚焦叠前深度偏移方法获得的。尽管在充满沉积物的冰川山谷和陡峭的山谷侧翼内进行地震成像具有挑战性的条件，但仍对与山谷本身以及构造断层系统相关的几个结构进行了成像。在大约 600 m 宽的区域中确定了一组向东南倾斜 40°–56° 的反射器，该区域被解释为损坏区域的最小范围。不同的方法成像一个不同的反射体倾斜约 40°，这被解释为位于 DFDP-2B 钻孔最大钻孔深度以下仅约 100 m 的主要高山断层反射体。在较浅的深度（z  < 0.5 km)，附加反射器被识别为断层段，通常倾斜度高达 56°。此外， 在 DFDP-2B 钻孔以南 0.5-1 公里处发现了一个冰川过度加深的槽，具有近乎水平的层状沉积物和一个主要断层（z < 0.5 公里）。因此，一个复杂的结构环境被地震成像并显示了 Whataroa 高山断层的复杂性。