Collaborative Research: Subduction Zone Segmentation over Multiple Seismic Cycles, South-Central Chile

合作研究：智利中南部多个地震周期的俯冲带分割

• 批准号: 1357756
• 负责人: Benjamin Horton
• 金额: $ 12.35万
• 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: 2013
• 资助国家: 美国
• 起止时间: 2013-08-01 至 2016-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1357756&HistoricalAwards=false
• 关键词: Collaborative; Research; Subduction; Zone; Segmentation

The possible segmentation of subduction zone faults currently presents one of the most significant questions to the physics and geology of earthquake occurrence and the assessment of future earthquake hazards. How will future large earthquakes be arrayed along a fault? How and why will individual earthquake ruptures stop? Subduction zone faults form the tectonic plate boundaries that parallel the coastlines of many countries around the world. Advances in instrumentation and modeling in recent decades have produced important insights into fault behavior, yet these measurements span only fractions of the time interval between major earthquakes. The goal of this research project is to use an interdisciplinary array of evidence preserved in coastal landforms and sediments to investigate whether segmentation of subduction zone faults is maintained over multiple earthquake cycles spanning hundreds to thousands of years. The field are, the Arauco Peninsula coast of south-central Chile, crosses the boundary between the rupture zones of two of the largest subduction zone earthquakes in the worldwide historic record, on May 22, 1960 (Mw 9.5) and February 27, 2010 (Mw 8.8). Prior to 2010, the study area for this project in south-central Chile was one of the most accepted hard fault segment boundaries along the Peru-Chile trench; it was believed to bound several historical ruptures, including the Great Chilean earthquake of 1960. The Chilean earthquake in February 2010 called this hypothesis into question, when the rupture extended south of this boundary and only partially overlapped with the previous earthquake in AD 1835. The combination of geological evidence of past earthquakes over the last 4000 years, frequent large subduction zone earthquakes, and an unusually long and comprehensive historic record of earthquakes in south-central Chile makes this region a natural laboratory to address fundamental questions about fault segmentation. This research project will test multiple hypotheses regarding earthquake behavior and coastal response: (1) fault ruptures over multiple earthquake cycles could terminate at fixed (hard), variable (soft), or random boundaries, or could include multiple segments; (2) large subduction zone earthquakes will produce a tsunami deposit simultaneous with an abrupt change in land level; and (3) the Holocene coastal evolution in this region reflects a modest net change in relative sea level in which the vertical uplift or subsidence during large earthquakes is largely reversed during the periods between earthquakes. To address these hypotheses the research team will reconstruct vertical land-level changes and tsunami history associated with multiple earthquake cycles using geomorphic, sedimentological and microfossil analysis. They will characterize the optimal environmental settings for the preservation of land-level changes and tsunami deposits in sedimentary sequences and analyze the impacts of these land-level changes on the coastal landscape.Ruptures on subduction zone faults have created some of the largest earthquakes and tsunamis in the world, such as the catastrophic earthquake in Japan in 2011 that killed thousands of people and destroyed coastal cities. The practical importance of this investigation for assessing future earthquake hazards in other similar geological settings was underscored by the unforeseen extent of fault ruptures and resulting earthquake magnitudes in the recent devastating earthquakes in Sumatra in 2004, Chile in 2010 and Japan in 2011. The project will build on strong existing collaboration with Chilean scientists. The results will inform the construction of earthquake and tsunami risk maps through established contacts in Chile, and we will arrange public presentations on earthquake and tsunami hazards. The general concepts will advance knowledge of earthquake behavior over time periods that exceed the relatively short period of the instrumental record.This project is supported by the Tectonics Program and Geomorphology and Land Use Dynamics Program in the Division of Earth Sciences and the Office of International Science and Engineering.

俯冲带断层的可能分割目前对地震发生的物理和地质学以及未来地震危害的评估提出了最重要的问题之一。未来的大地震将如何沿着断层排列？个别地震破裂如何以及为何会停止？俯冲带断层形成与世界许多国家海岸线平行的板块边界。近几十年来仪器和建模的进步对断层行为产生了重要的见解，但这些测量仅涵盖大地震之间时间间隔的一小部分。该研究项目的目标是利用沿海地貌和沉积物中保存的一系列跨学科证据来调查俯冲带断层的分割是否在跨越数百年至数千年的多个地震周期中得以维持。该区域位于智利中南部的阿劳科半岛海岸，跨越了世界历史记录中两次最大俯冲带地震的破裂带之间的边界，分别发生在1960年5月22日（兆瓦9.5）和2010年2月27日（分子量8.8）。 2010年之前，该项目位于智利中南部的研究区域是秘鲁-智利海沟沿线最受认可的硬断层段边界之一；人们相信它限制了历史上的几次断裂，包括 1960 年的智利大地震。2010 年 2 月的智利地震使这一假设受到质疑，当时断裂延伸到该边界以南，并且仅与公元 1835 年的上一次地震部分重叠。过去 4000 年过去地震的地质证据、频繁发生的大型俯冲带地震以及智利中南部异常漫长和全面的地震历史记录，使该地区成为天然的实验室解决有关故障分段的基本问题。该研究项目将测试有关地震行为和海岸响应的多种假设：（1）多个地震周期的断层破裂可能终止于固定（硬）、可变（软）或随机边界，或者可能包括多个段； (2) 俯冲带大地震会在陆地平面突变的同时产生海啸沉积物； (3)该地区的全新世海岸演化反映了相对海平面的适度净变化，其中大地震期间的垂直隆起或沉降在地震之间的时期很大程度上发生了逆转。为了解决这些假设，研究小组将利用地貌、沉积学和微化石分析来重建与多个地震周期相关的垂直陆地水平变化和海啸历史。他们将描述在沉积序列中保存陆地平面变化和海啸沉积物的最佳环境设置，并分析这些陆地平面变化对沿海景观的影响。俯冲带断层的破裂造成了一些最大的地震和海啸在世界范围内，例如2011年日本发生的灾难性地震导致数千人死亡并摧毁了沿海城市。最近 2004 年苏门答腊岛、2010 年智利和 2011 年日本发生的毁灭性地震中断层破裂的不可预见程度​​以及由此产生的地震震级，凸显了这项调查对于评估其他类似地质环境中未来地震危害的实际重要性。该项目将建立在与智利科学家现有的强有力合作的基础上。研究结果将为通过在智利建立的联系来构建地震和海啸风险地图提供信息，我们将安排有关地震和海啸灾害的公开演讲。一般概念将增进对超过仪器记录相对较短时期的地震行为的了解。该项目得到了地球科学部和国际科学办公室的构造学计划和地貌学和土地利用动力学计划的支持和工程。