Late Holocene Palaeoseismicity in South-Central Chile

在地球构造板块在俯冲带上发生碰撞时，会发生特大地震（震级>8级）和相关海啸，对断裂区和邻近海洋大部分人口稠密的海岸线造成重大危害。对最近发生在苏门答腊（2004年）、智利（2010年）和日本（2011年）的特大地震的预测不足，突出表明我们对沿着俯冲带的特大逆冲地震仍然知之甚少，并强调了能够现实地估计未来地震潜在规模的重要性。评估未来的地震和海啸风险需要了解特大地震发生的频率、间隔时间以及不同事件中陆地运动的模式如何变化。历史和仪器记录太短，无法充分评估最大震级地震灾害的重现性，我们只能从过去4000年积累的沉积物的地质调查中获得长期模式。我建议从智利中南部沿海的潮汐沼泽地沿着收集新的沉积物，并使用其中保存的微化石来量化多个地震周期的陆面变化。这里提出的工作将使用来自潮汐沼泽地的沉积物，因为其他地方的沿海湿地和潮汐沼泽地是记录大地震期间发生的陆面变化的绝佳环境。我将分析在沉积物中发现的微观藻类（称为硅藻），因为不同的物种对潮汐洪水有不同的耐受性。我将利用这些信息开发一个简单的数学模型，可以预测不同类型的硅藻生活在相对于目前的海平面，并利用硅藻目前的分布信息，它将有可能解释过去和量化与过去的大地震有关的海平面和陆地平面变化，这些地震保存在潮汐沼泽沉积物中。在多个地震周期内精确的相对海平面和陆平面重建。我将使用潮汐沼泽沉积物的成熟可靠的方法，因为我以前曾成功地用它来重建与阿拉斯加过去大地震有关的陆地运动。然而，我的方法是新颖的，因为我将把这些方法应用到一个相对缺乏研究的板块边界上的新地点。这项研究将提供独特的沉积物证据，以量化智利中南部至少在最近三次特大地震期间发生的陆地变化量。这将使我能够确定每次地震受地表变形影响的区域，并确定最大陆地水平变化的位置。追踪过去地震事件的空间范围将提供关于每次破裂的长度和破裂的板块段的数量的信息。如果多个板块同时破裂，它们可能会产生更大规模的地震。因此，这是一个关键的辩论，在评估地震灾害，海啸的产生，和长期发展的边界，其中板块碰撞。该项目具有实际和社会经济效益，提供的信息将有助于预测智利未来的单段和多段地震和海啸。了解智利巨型逆冲断层系统的空间和时间将有助于了解收敛速度更慢的巨型逆冲断层区的运作方式。因此，这些结果对智利和世界其他易受地震影响的地区都有影响。

Mega-earthquakes (magnitude >8) and related tsunami, generated where the Earth's tectonic plates collide on subduction zones, produce major hazards for both the area of rupture and heavily populated coastlines across much of the adjacent ocean. Inadequate anticipation of recent mega-earthquakes in Sumatra (2004), Chile (2010) and Japan (2011) highlights how little we still know about megathrust earthquakes along subduction zones and underscores the importance of being able to realistically estimate the potential size of future earthquakes. Evaluating future earthquake and tsunami risk requires knowing how frequently mega-earthquakes occur, at what intervals, and how the patterns of land movement vary in different events. Historical and instrumental records are too short to adequately assess the recurrence of the greatest magnitude seismic hazards, and we can only obtain the long-term patterns from geological investigations of sediments accumulating over the last ~4000 years. I propose to collect new sediments from tidal marshes along the coast of south-central Chile, and use microfossils preserved within them to quantify land-level changes over multiple earthquake cycles.The work proposed here will use sediments from tidal marshes, as elsewhere coastal wetlands and tidal marshes are excellent environments for recording land-level changes that occur during large earthquakes. I will analyse microscopic algae (called diatoms) that are found in the sediments, as different species have distinct tolerances to tidal flooding. I will use this information to develop a simple mathematical model that can predict where different types of diatoms live with respect to present sea-level, and using information on the present distribution of diatoms, it will be possible to interpret the past and quantify sea- and land-level changes associated with past mega-earthquakes that are preserved in tidal marsh sediments.This approach provides a powerful means of developing robust, precise relative sea- and land-level reconstructions over multiple earthquake cycles. I will use the well-established and reliable methodology of using tidal marsh sediments, as I have previously used this successfully to reconstruct land-level movements associated with past great earthquakes in Alaska. However, my approach is novel as I will apply these methods to new sites on a relatively poorly studied plate boundary. The research will provide unique sedimentary evidence for quantifying the amount of land-level change that occurred during at least the last three mega-earthquakes in south-central Chile. This will enable me to define the area affected by surface deformation for each earthquake and identify the location of maximum land-level change. Tracing the spatial extent of past seismic events will provide information on the length of each rupture and the number of plate segments that ruptured. If multiple plate segments rupture together, they may potentially produce earthquakes of greater magnitude. This is therefore a critical debate in assessing earthquake hazard, tsunami generation, and the long-term development of the boundaries where tectonic plates collide. This project has practical and socio-economic benefits by providing information that will aid forecasting of future single- and multiple-segment earthquakes and tsunamis in Chile. Understanding the Chilean megathrust system in space and time will aid understanding of how more slowly converging megathrust zones operate. The outcomes therefore have implications for both Chile and other vulnerable seismic regions worldwide.