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，智利海岸发生里氏8.8级大地震。地震期间海底隆起引发了席卷海岸的海啸。超过 525 人死亡，总经济损失估计为 15-300 亿美元。自 1900 年以来，全球范围内仅发生过五次较大地震，其中包括 1960 年 5 月在智利南部发生的有史以来最大的地震。仅凭自 1900 年以来发生的几次大地震，很难完全了解大地震的行为和影响。科学测量始于 100 年前。来自中央华盛顿大学和罗格斯大学的研究小组正在利用智利过去地震和海啸的悠久历史记录（500年）和地质证据来研究大地震和海啸的影响。不寻常的沙沉积表明，在过去 2000 年里，强大的海啸浪潮多次席卷陆地。海啸沙层上方和下方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小藻类（硅藻）对淡水和咸水的变化非常敏感，反之亦然。通过识别古代沉积层中硅藻化石的变化，可以精确确定过去地震期间陆地平面的变化量。研究人员还利用海啸波的计算机模型，根据这些结果计算出过去发生地震的断层破裂的位置和大小。这些证据的结合将提高对古代地震的频率、位置和规模的理解，从而提高对产生地震的海底断层的长期行为的理解。研究小组将参与各种活动，以提高公众对美国和智利地震和海啸灾害的认识和教育，其中包括：制作和分发西班牙语和英语的关于海啸准备和生存的公共服务手册；向公众、政府官员和当地利益相关者进行介绍；为美国小学生举办的地震和海啸活动；以及为在科学职业中代表性不足的西班牙裔和低收入学生举办的研讨会。研究生、本科生和博士后研究人员将在该项目中获得宝贵的研究经验。了解俯冲带变形的物理原理并准确评估巨型逆冲地震及其伴随海啸的危害需要多个地震周期的相当详细的地震和海啸历史。准确和精确地估计多个地震周期内同震隆起和沉降的数量和时间对于了解俯冲带应变积累和释放的长期历史至关重要。智利中南部是地球上两次最大地震的发生地（1960 年，兆瓦 9.5；2010 年，兆瓦 8.8）。然而，在上个世纪之前，500 年的地震和海啸历史记录提供的有关破裂程度和震级的信息有限。该研究项目利用沉降、隆起和海啸沉积物的沿海地层证据来测量同震和震间垂直变形，并在智利俯冲带中南部 600 公里沿线的地点构建海啸年代表。与海啸的正向模拟比较将确定过去 2000 年巨型逆冲地震的最佳破裂参数（长度、位置、深度、震级）。该项目将开发两种新的古地震方法。首先，利用硅藻与盐度、潮汐高程和生命形式之间关系的贝叶斯硅藻传递函数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与新的基于贝叶斯硅藻的传递函数相结合，将显着提高智利中南部同震和震间海岸变形基于微化石重建的准确性和精确度。其次，海啸模拟模型将用于创建海啸的正向模拟，并将其与古海啸沉积物的分布相匹配，以区分造成过去海啸的破裂位置和长度。通过将变形重建与绘制的海啸沉积淹没和纬度范围相结合，研究人员将使用数值模拟来评估过去巨型逆冲地震的不同破裂情景。这种破裂模型尚未在智利中南部尝试过，也没有在其他地方以如此大的空间尺度发表过。 1960 年、2010 年和早期海啸在各种沿海地貌环境中的沉积物地图将为识别史前海啸沉积物并利用它们来推断其他遭受海啸灾害的沿海地点的淹没程度提供重要的校准比较。