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

关于日本海沟北方和中部的海啸地震，有大量的仪器、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。这场地震沿着海沟的北方和中部破裂了沿着五个部分，但未能通过靠近东京大都市的南部破裂。由于2011年地震期间应力可能向南转移，并且俯冲带的这一部分被锁定，因此海沟这一部分的地震风险不确定。此外，仪器和历史记录稀少，只有一个海啸地震记录（CE 1677 Empo地震），缺乏长期的地质数据。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，将采用现场、实验室（沉积物、微化石和放射性分析）、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，这些数据对预测未来灾害非常重要。除了提高对东京地区地震风险的认识外，通过对中学生的宣传，提高了STEM教育水平，通过培养研究生、本科生和博士后导师，培养了具有全球竞争力的STEM人才队伍，这些都为社会带来了额外的好处。对保存在海岸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。该项目的重点是三个候选海啸砂，这些砂保存在位于东京以东约50公里的房总半岛海滨平原的Kujukuri海滩的沿海稻田中。利用代用分析（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，将解决海沟南部未来是否会发生与2011年东北地震规模相似的地震。每个候选海啸的约束年龄将允许海岸线位置的准确估计，因此，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先前开发的海啸模拟模型中（例如，2011 Tohoku和CE 1677 Empo模型），研究小组将测试以前的中部/北方或南部海沟破裂是否可能在房总半岛沉积海啸砂。

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.