Collaborative Research: Paleoseismic Evidence of Earthquakes and Tsunamis along the Southern Part of the Japan Trench

关于源自日本海沟北部和中部的海啸地震，有大量的仪器、历史和地质记录，其中记录了过去数千年的地震和海啸，包括2011年发生的9级东北地震。这次地震使海沟北部和中部的五个部分破裂，但未能穿过东京大都市附近的南部。这部分海沟的地震风险是不确定的，因为在2011年地震期间，应力向南转移的可能性，以及这部分俯冲带被锁定。此外，仪器和历史记录很少，只有一次海啸地震(CE1677年EMPO地震)有记录，而且缺乏长期的地质数据。南密西西比大学和罗格斯大学的一个研究小组将与日本研究人员合作，利用现场、实验室(沉积、微化石和辐射分析)、统计和建模技术的创新组合，对一系列可能的海啸沉积物进行研究，以确定日本南部海沟的海啸和地震历史，这一数据对预测未来的灾难非常重要。除了提供对东京地区地震风险的更好了解外，对社会的其他好处还包括通过向中学生拓展来改善STEM教育，通过培训研究生和本科生以及博士后指导来发展具有全球竞争力的STEM劳动力。对保存在沿海沉积物中的海啸沉积物的检测和表征提供了过去地震的长期记录。该项目的重点是保存在久久库里海滩沿海稻田中的三个候选海啸沙子，久久库里海滩是位于博索半岛东京以东约50公里的滨海平原。使用替代分析(粒度和微化石)、贝叶斯年龄深度模型和海啸模拟模型确定海啸沉积物，将确定海沟南部未来能否发生与2011年东北地震规模类似的地震。对每一次候选海啸的良好限制年龄将使准确估计海岸线位置，从而在沉积时的淹没距离。通过将这些不断变化的海岸线位置整合到以前开发的海啸模拟模型中(例如，2011东北和CE 1677 EMPO模型)，研究小组将测试之前的中部/北部或南部海沟破裂是否可能在博索半岛沉积了海啸沙。

There is an extensive instrumental, historical, and geological record of tsunamigenic-earthquakes originating from the northern and middle parts of the Japan Trench that documents the last several thousand years of earthquakes and tsunamis, including the magnitude 9 Tohoku earthquake in 2011. This earthquake ruptured five segments along the northern and middle parts of the Trench, but failed to rupture through the southern part, which is near metropolitan Tokyo. The seismic risk for this portion of the trench is uncertain because of the possibility that stress transferred southwards during the 2011 earthquake and that this part of the subduction zone is locked. Furthermore, the instrumental and historical record is sparse with only one tsunamigenic-earthquake on record (CE 1677 Empo earthquake) and lack of long-term geological data. A research team from University of Southern Mississippi and Rutgers University in collaboration with Japanese researchers will employ an innovative combination of field, laboratory (sedimentary, microfossil, and radiometric analyses), statistical, and modeling techniques to a series of possible tsunami deposits in order to determine the tsunami and earthquake history of the southern Japan Trench, data which is very important for anticipating future disasters. Besides providing an improved understanding of seismic risk in the Tokyo region, additional benefits to society include improved STEM education though outreach to middle school students and development of a globally competitive STEM workforce through training of graduate and undergraduate students and post-doctoral fellow mentoring.The detection and characterization of tsunami deposits preserved in coastal sediments provides a long-term record of past earthquakes. This project focuses on three candidate-tsunami sands that are preserved in coastal rice fields in the Kujukuri beaches, a strand plain located on the Boso Peninsula approximately 50 km east of Tokyo. The identification of tsunami deposits using proxy analyses (grain size and microfossil), with Bayesian age-depth models and tsunami simulation models, will resolve whether the southern part of the trench can produce future earthquakes that are similar in size as the 2011 Tohoku event. Well-constrained ages for each candidate tsunami will permit an accurate estimation of the shoreline position, and thus, inundation distance at the time of deposition. By integrating these changing shoreline positions into previously developed tsunami simulation models (e.g., 2011 Tohoku and CE 1677 Empo models), the research team will test whether previous middle/northern or southern trench ruptures could have deposited the tsunami sands on the Boso Peninsula.