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首页> 外文期刊>ICES Journal of Marine Science >Active faults, paleoseismology, and historical fault rupture in northern Wairarapa, North Island, New Zealand
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Active faults, paleoseismology, and historical fault rupture in northern Wairarapa, North Island, New Zealand

机译：新西兰北岛怀拉拉帕北部的活动断层，古地震学和历史断层破裂

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摘要

Active faulting in the upper plate of the Hikurangi subduction zone, North Island, New Zealand, represents a significant seismic hazard that is not yet well understood. In northern Wairarapa, the geometry and kinematics of active faults, and the Quaternary and historical surface-rupture record, have not previously been studied in detail. We present the results of mapping and paleoseismicity studies on faults in the northern Wairarapa region to document the characteristics of active faults and the timing of earthquakes. We focus on evidence for surface rupture in the 1855 Wairarapa (M_W 8.2) and 1934 Pahiatua (M_W 7.4) earthquakes, two of New Zealand's largest historical earthquakes. The Dreyers Rock, Alfredton, Saunders Road, Waitawhiti, and Waipukaka Faults form a northeast-trending, east-stepping array of faults. Detailed mapping of offset geomorphic features shows the rupture lengths vary from c. 7 to 20 km and single-event displacements range from 3 to 7 m, suggesting the faults are capable of generating M >7 earthquakes. Trenching results show that two earthquakes have occurred on the Alfredton Fault since c. 2900 cal. BP. The most recent event probably occurred during the 1855 Wairarapa earthquake as slip propagated northward from the Wairarapa Fault and across a 6 km wide step. Waipukaka Fault trenches show that at least three surface-rupturing earthquakes have occurred since 8290-7880 cal. BP. Analysis of stratigraphic and historical evidence suggests the most recent rupture occurred during the 1934 Pahiatua earthquake. Estimates of slip rates provided by these data suggest that a larger component of strike slip than previously suspected is occurring within the upper plate and that the faults accommodate a significant proportion of the dextral component of oblique subduction. Assessment of seismic hazard is difficult because the known fault scarp lengths appear too short to have accommodated the estimated single-event displacements. Faults in the region are highly segmented, disconnected, and probably structurally immature, which implies that apparent geometric discontinuities at the surface may not be significant barriers to rupture propagation at depth and that the surface rupture record significantly under-represents the seismic slip on faults in the region.
机译：新西兰北岛Hikurangi俯冲带上板的活动断裂代表着重大的地震危险，目前尚未充分了解。在怀拉拉帕北部，活动断层的几何学和运动学，以及第四纪和历史地表破裂记录，以前没有进行过详细研究。我们提供北部怀拉拉帕地区断层的制图和古地震研究结果，以记录活动断层的特征和地震时机。我们重点研究1855年怀拉拉帕（M_W 8.2）和1934年Pahiatua（M_W 7.4）地震中的地表破裂证据，这是新西兰最大的两次历史性地震。德雷尔斯岩，阿尔弗雷德顿，桑德斯路，威塔瓦蒂和威普卡卡断层构成了东北向，东移的断层。偏移地貌特征的详细映射显示，破裂长度与c不同。 7至20 km，单事件位移范围为3至7 m，表明这些断层能够产生M> 7地震。开沟结果表明，自c。以来，阿尔弗雷德断层发生了两次地震。 2900卡路里BP。最近的事件可能发生在1855年怀拉拉帕地震中，滑移从怀拉拉帕断层向北传播，并跨越了6公里宽的台阶。威普卡卡断层沟显示，自8290-7880 cal以来，至少发生了三次表面破裂地震。 BP。地层和历史证据分析表明，最近的破裂发生在1934年的Pahiatua地震中。这些数据提供的滑移率估计值表明，上板内部发生的走滑分量比以前怀疑的大，并且断层占斜向俯冲的右旋分量的很大一部分。地震危险性的评估很困难，因为已知的断层陡峭长度似乎太短，无法容纳估计的单事件位移。该地区的断层高度分段，不连贯，并且可能在结构上不成熟，这意味着表面上明显的几何不连续性可能不是深度破裂传播的重要障碍，并且表面破裂记录明显不足以表示该地区断层的地震滑动。该区域。

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