Collaborative Research: Quantifying Megathrust Earthquake Ruptures with Coastal Stratigraphy and Tsunami Simulations, South-Central Chile

合作研究：通过海岸地层学和海啸模拟量化巨型逆冲地震破裂，智利中南部

• 批准号: 1624533
• 负责人: Benjamin Horton
• 金额: $ 25.81万
• 依托单位: Rutgers University New Brunswick
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2022-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1624533&HistoricalAwards=false
• 关键词: Collaborative; Research; Quantifying; Megathrust; Earthquake

On February 27, 2010, a great earthquake of magnitude 8.8 struck the coast of Chile. The uplift of the seafloor during the earthquake triggered a tsunami that swept over the coast. More than 525 people were killed and estimates of total economic losses were US $15-30 billion. Worldwide, only five great earthquakes since 1900 have been larger, including the largest earthquake ever recorded, which also occurred in southern Chile in May 1960. It is difficult to fully understand the behavior and effects of great earthquakes based on the handful that have occurred since scientific measurements began 100 years ago. A research team from Central Washington University and Rutgers University are using the long historical record (500 years) and geologic evidence of past earthquakes and tsunamis in Chile to investigate the effects of great earthquakes and tsunamis. Unusual sand deposits indicate that powerful tsunami waves swept landward multiple times in the last 2,000 years. Changes in the soil above and below the tsunami sand layers also indicate rising or sinking of the coastal landscape during earthquakes. Microscopic algae (diatoms) that live in coastal sediments are very sensitive to changes from fresh to salt water and vice versa. By identifying changes in the fossil diatoms present within ancient sediment layers, the amount of land-level change during past earthquakes can be precisely determined. The researchers are also using computer models of tsunami waves to calculate the locations and sizes of the fault ruptures that produced the past earthquakes based on these results. This combination of evidence will improve understanding of the frequency, location, and size of ancient earthquakes, and thus of the long-term behavior of the ocean-floor faults that produce them. The research team will engage in diverse activities to increase public awareness and education about earthquake and tsunami hazards in both the U.S. and Chile that include: production and distribution of a public service handbook in Spanish and English on preparing for and surviving a tsunami; presentations to the public, government officials, and local stakeholders; earthquake and tsunami activities for U.S. grade school children; and workshops for Hispanic and low-income students who are underrepresented in science careers. Graduate, undergraduate, and postdoctoral researchers will gain valuable research experience in the project.Understanding the physics of subduction-zone deformation and accurately assessing the hazards from megathrust earthquakes and their accompanying tsunamis requires earthquake and tsunami histories of considerable detail over multiple earthquake cycles. Accurate and precise estimates of the amounts and timing of coseismic uplift and subsidence over multiple earthquake cycles are critical to understanding the long-term history of strain accumulation and release at subduction zones. South-central Chile was the site of two of Earth?s largest earthquakes (1960, Mw 9.5; 2010, Mw 8.8). However, prior to the past century, the 500-year written history of earthquakes and tsunamis provides limited information on rupture extent and magnitude. This research project uses coastal stratigraphic evidence of subsidence, uplift, and tsunami deposits to measure coseismic and interseismic vertical deformation and construct tsunami chronologies at sites along 600 km of the south-central Chilean subduction zone. Comparisons with forward simulations of tsunamis will identify best-fit rupture parameters (length, location, depth, magnitude) for megathrust earthquakes during the last 2000 years. Two new paleoseismic methods will be developed in this project. First, Bayesian diatom transfer functions that employ the relation between diatoms and salinity, tidal elevation, and life form will be used to reconstruct records of vertical land-level change during large earthquakes. The expanded modern diatom dataset, combined with new Bayesian diatom-based transfer functions, will significantly increase the accuracy and precision of microfossil-based reconstructions of coseismic and interseismic coastal deformation in south-central Chile. Second, tsunami simulation models will be used to create forward simulations of tsunamis and match them with the distributions of paleotsunami deposits to differentiate the rupture locations and lengths responsible for past tsunamis. By combining the deformation reconstructions with mapped tsunami-deposit inundation and latitudinal extent, the researchers will use numerical simulations to evaluate different rupture scenarios for past megathrust earthquakes. Such rupture modeling has not been attempted in south-central Chile, or published elsewhere at this large spatial scale. Maps of the deposits of the 1960, 2010, and earlier tsunamis in a variety of coastal geomorphic settings will provide important calibration comparisons for identifying prehistoric tsunami deposits and using them to infer inundation extent at other coastal sites subject to tsunami hazards.

2010年2月27日，8.8袭击了智利海岸的巨大地震。地震期间海底的隆起引发了一条席卷整个海岸的海啸。超过525人被杀，总经济损失的估计为15-30亿美元。自1900年以来，全世界只有五场大地震较大，其中包括有史以来最大的地震，也发生在1960年5月在智利南部。华盛顿大学和罗格斯大学的一个研究小组正在使用悠久的历史记录（500年）和智利过去地震和海啸的地质证据来研究大地震和海啸的影响。不寻常的沙子沉积物表明，在过去的2000年中，强大的海啸波扫过了多次陆地。海啸砂层上方和下方的土壤的变化也表明地震期间沿海景观的上升或下沉。生活在沿海沉积物中的微观藻类（硅藻）对从新鲜到盐水的变化非常敏感，反之亦然。通过确定古代沉积物层中存在的化石硅藻的变化，可以精确确定过去地震期间的土地变化量。研究人员还使用海啸波的计算机模型来计算基于这些结果产生过去地震的断层破裂的位置和大小。这种证据的结合将提高人们对古代地震的频率，位置和大小的理解，从而对产生它们的海底断层的长期行为。研究团队将从事各种活动，以提高美国和智利的公众对地震和海啸危害的认识和教育，其中包括：以西班牙语和英语的制作和分发公共服务手册，以准备和幸存海啸；向公众，政府官员和当地利益相关者演讲；美国级儿童的地震和海啸活动；以及在科学职业中人数不足的西班牙裔和低收入学生的讲习班。研究生，本科和博士后研究人员将在项目中获得宝贵的研究经验。理解俯冲区变形的物理学，并准确地评估巨型地震的危害及其随附的海啸需要进行地震，需要在多个地震犬类上进行大量细节的历史。对多个地震周期中coseis震振及的数量和时间的准确和精确估计对于理解俯冲带的应变积累和释放的长期历史至关重要。智利中南部是地球两次地震的地点（1960，MW 9.5; 2010，MW 8.8）。但是，在过去的一个世纪之前，地震和海啸的500年书面历史提供了有关破裂程度和幅度的有限信息。该研究项目使用沿海地层的沉降，隆升和海啸沉积物的证据来测量吉利亚中南部俯冲区600 km的地点，测量coseis震动和跨视为垂直变形。与海啸的正向模拟进行比较，将在过去2000年中确定巨型地震的最佳拟合破裂参数（长度，位置，深度，幅度）。该项目将开发两种新的旧方法。首先，采用硅巧与盐度之间的关系，潮汐升高和生命形式之间的关系的贝叶斯硅藻转移功能将用于重建大地震期间垂直地面变化的记录。扩展的现代硅藻数据集，再加上新的贝叶斯硅藻转移功能，将显着提高基于微化石基于微化石的coseismisic和shoistseismseist沿海变形的精确性和精度。其次，海啸仿真模型将用于创建海啸的正向模拟，并将其与古植物沉积物的分布相匹配，以区分破裂位置和负责过去海啸的长度。通过将变形的重建与映射的海啸淹没和纬度范围相结合，研究人员将使用数值模拟来评估不同的破裂场景，以实现过去的巨型地震。这种破裂的建模尚未在智利中南部，或以这种大型空间规模出版。 1960年，2010年和早期海啸的沉积地图将提供重要的校准比较，以识别史前海啸沉积物，并使用它们来推断其他受到海啸危害的沿海地区的淹没程度。