ABSTRACT

Along the northeast coast of New Zealand’s South Island, a 7.8 Mw earthquake on the 14th of November 2016 induced instantaneous uplift of approximately 1 m around the Kaikōura Peninsula. This paper documents a unique field study examining short-term responses in the Mixed Sand and Gravel (MSG) beaches of Kaikōura to a relative sea level fall as a result of this event. We present two conceptual response pathway models which consider the pre-earthquake trends of 18 coastal sites, and two surveys taken over a 22 month period following the earthquake to define the short-term response of MSG beaches to instantaneous relative sea level fall. This study found MSG beach responses vary strongly according to their pre-quake sediment supply, source connectivity and open coast exposure characteristics. Overall, there were two predominant trends in which the beaches were responding in the short-term post-earthquake environment: accretionary profiles and erosional profiles. The difference between these two profile response types can be summarised as pre-earthquake erosional profiles were found to be retreating to pre-earthquake extents 22 months post-earthquake, whilst pre-earthquake accretional and dynamic beaches had an increased or stable trend which promoted stability or growth in beach volume post relative sea level fall.

摘要

沿着新西兰南岛的东北海岸，2016 年 11 月 14 日发生的 7.8 Mw 地震导致凯库拉半岛周围瞬时隆起约 1 米。本文记录了一项独特的实地研究，该研究考察了凯库拉混合砂砾 (MSG) 海滩对该事件导致的相对海平面下降的短期响应。我们提出了两个概念性响应路径模型，考虑了 18 个沿海地点的震前趋势，以及地震后 22 个月内进行的两项调查，以确定 MSG 海滩对瞬时相对海平面下降的短期响应。这项研究发现，MSG 海滩的响应根据震前沉积物供应、源连接性和开阔海岸暴露特征而有很大差异。全面的，海滩在短期震后环境中的反应有两种主要趋势：增生剖面和侵蚀剖面。这两种剖面响应类型之间的差异可以概括为震前侵蚀剖面被发现在震后 22 个月后退到震前程度，而震前增生和动态海滩有增加或稳定的趋势，这促进了稳定性或相对海平面下降后海滩体积的增长。