Sediment signatures of the 25th December 2016 Chile earthquake to constrain detection thresholds of tidal marsh records

2016年12月25日，智利中南部发生7.6级俯冲带地震。这次地震发生在公元1960年9.5级地震的破裂带内，这是有仪器记录以来最大的地震。12月25日的地震是自1960年地震以来在破裂带内记录到的最大地震。虽然人口稀少使该地区免于死亡或重大经济损失，但这次地震为研究地震断裂带的变异性以及这种震级的地震对释放累积应变的贡献提供了重要机会。全新世沉积物的古地震学研究为评估阿拉斯加、卡斯卡迪亚、智利、日本、印度尼西亚和新西兰等多个俯冲带不同地震破裂模式的时空变异提供了一种手段。至关重要的是，我们试图评估使用已建立的古地震学方法检测20世纪前地震的下限，以及地质记录低估大地震频率的可能性。我们寻求紧急资金，以便对12月25日地震造成的同震地表变形和沉积进行快速评估。在南方冬季两侧的两个实地活动将测试任何记录的同震信号在合并到沉积物剖面的前几个月的保存潜力，包括在冬季风暴和地震后板块界面蠕变引起的任何震后垂直变形中存活下来。沉积和微化石分析将揭示地震的沉积特征，约束变形探测的下限。这一建议建立在我们之前的研究和最近海岸古地震学的转变上，从识别晚全新世地震破裂段内最大的地壳变形到寻求破裂段的空间范围，因此限制。这就需要一种侧重于确定地壳垂直变形下限的方法。我们最近根据自己的研究和对古地震学文献的全面回顾，提出了一个修订的研究框架来完成这一任务，但注意到缺乏足够详细的现代等效。2015年智利地震提供了一个难得的机会，从受小型同震垂直陆地运动、地面震动和任何相关海啸影响的沿海地区的当代环境中收集时间关键型样本。

On 25th December 2016 a magnitude 7.6 subduction zone earthquake struck south central Chile. The earthquake occurred within the rupture zone of the AD 1960 magnitude (M) 9.5 earthquake, the largest earthquake ever recorded during the instrumental era. The 25th December earthquake is the largest recorded within the 1960 rupture zone since the original event. While the sparse population spared the region from fatalities or substantial economic losses, this earthquake provides a critical opportunity to investigate variability in earthquake rupture zones and the contribution of earthquakes of this magnitude to releasing accumulated strain. Paleoseismological investigations Holocene sediments provide a means to assess the temporal and spatial variability of different earthquake rupture modes in many subduction zones, including Alaska, Cascadia, Chile, Japan, Indonesia and New Zealand. Crucially, we seek to assess the lower limit for detecting pre-20th century earthquakes using established paleoseismological methods and the potential for geological records to underestimate the frequency of major earthquakes.We seek urgency funding to make a rapid assessment of the coseismic surface deformation and sedimentation resulting from the 25th December earthquake. Two field campaigns, either side of the austral winter, will test the preservation potential of any recorded coseismic signal through the first few months of incorporation into the sediment profile, including survival through winter storms and any post-seismic vertical deformation caused by post-seismic creep on the plate interface. Sedimentary and microfossil analysis will reveal the sedimentary signature of the earthquake and constrain the lower limit of deformation detection. This proposal builds on our previous research and the recent shift in coastal paleoseismologgy from identifying the largest amounts of crustal deformation within the rupture segments of late Holocene earthquakes to seeking the spatial extent, therefore limits, of a rupture segment. This requires a methodology focussed on identifying the lower limit of vertical crustal deformation. We recently proposed a revised research framework to accomplish this, based on our own research and a comprehensive review of the paleoseismological literature, but noted the lack of sufficient detailed modern equivalents. The 2015 Chile earthquake provides a rare opportunity to collect time-critical samples from the contemporary environments in coastal areas affected by small coseismic vertical land motions, ground shaking and any associated tsunami.