ABSTRACT

The hill country of west central North Island, west of Te Kuiti and Otorohanga, is recognised to be slowly uplifting and relatively stable. The New Zealand national seismic hazard model shows the area to be in a low-risk zone and the New Zealand active faults database recognises no active faults in the region. However, dated evidence provided by speleothems in a cave near Waitomo indicates the intermittent movement of the Okohua fault from before the Last Interglacial until around 38 kyrs ago. Evidence of older movement along the Waipa Fault near Te Kuiti is also apparent from the vertical displacement of the Ngaroma ignimbrite (1.55 Myrs) by about 150 m in the interval prior to the deposition of the Ongatiti ignimbrite at 1.21 Myrs. Net uplift in the West Waikato Hills and Ranges, by about 0.1 mm/yr in the Late Quaternary, is accommodated in a series of NNE-trending faults and transverse faults, resulting in a staircase of fault-bound blocks rising westwards from Waitomo to the western watershed of the Waipa basin. Geomorphologically fresh cliffed lineaments on the Okohua and Hikurangi faults convey evidence of mid to late Quaternary fault activity.

摘要

北岛中西部的丘陵地带，Te Kuiti 和 Otorohanga 以西，被认为缓慢抬升且相对稳定。新西兰国家地震灾害模型显示该地区处于低风险区，新西兰活动断层数据库认为该地区没有活动断层。然而，怀托摩附近洞穴中的洞穴提供的过时证据表明，从末次间冰期之前到大约 38 公里前，奥科华断层的间歇性运动。从 Ngaroma 熔凝凝灰岩 (1.55 Myrs) 在 1.21 Myrs 的 Ongatiti 熔凝凝灰岩沉积之前的间隔中垂直位移约 150 m，也可以明显看出沿 Te Kuiti 附近的 Waipa 断层存在更早运动的证据。西怀卡托山和山脉的净隆升，在第四纪晚期每年约 0.1 毫米，被容纳在一系列北北东向断层和横向断层中，导致从怀托摩向西上升到怀帕盆地西部分水岭的断层块阶梯。Okohua 和 Hikurangi 断层上地貌上新鲜的悬崖构造提供了第四纪中晚期断层活动的证据。