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，有广泛的仪器、历史和地质记录，记录了过去几千年的地震和海啸，包括2011年的9级东北地震。这次地震使海沟北部和中部的5个板块破裂，但东京附近的南部板块没有破裂。这部分海沟的地震风险是不确定的，因为在2011年地震期间应力可能向南转移，并且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-地震记录（公元1677年恩波地震），缺乏长期的地质资料。来自南密西西比大学和罗格斯大学的一个研究小组与日本研究人员合作，将采用实地、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分析，以确定日本南部海沟的海啸和地震历史，这些数据对预测未来的灾难非常重要。除了提高对东京地区地震风险的了解外，对社会的其他好处还包括通过向中学生推广STEM教育，以及通过培训研究生和本科生以及博士后指导培养具有全球竞争力的STEM劳动力。沿海沉积物中海啸沉积物的探测和特征提供了过去地震的长期记录。该项目重点研究了保存在Kujukuri海滩沿海稻田中的三个候选海啸沙滩，Kujukuri海滩是位于东京以东约50公里的博索半岛上的一个海滨平原。利用代理分析（粒度和微化石）、贝叶斯年龄深度模型和海啸模拟模型来识别海啸沉积物，将解决海沟南部未来是否会产生与2011年东北地震规模相似的地震。对每一个候选海啸进行精确的年龄约束，将允许对海岸线位置进行精确的估计，从而得到沉积时的淹没距离。通过将这些变化的海岸线位置整合到先前开发的海啸模拟模型中（例如，2011年东北和CE 1677 Empo模型），研究小组将测试先前的中部/北部或南部海沟破裂是否可能在博索半岛沉积海啸砂。

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.