EAGER: Search for a Paleotsunami Record in the Wetlands of Southern California

2004年，苏门答腊岛附近发生9.3级地震，引发海啸，摧毁了一个毫无防备的国家，造成超过15万印度尼西亚人死亡。七年后，在人口稠密的日本东海岸发生了一场规模略小的9.0级地震，引发了一场规模类似的海啸，但死亡人数要少得多。日本对过去的海啸有着丰富的地质和历史记录。这一记录提高了日本人民的意识，并催生了可以说是世界上最严格的建筑规范和最好的海岸工程——这两者都有助于减少日本的生命损失。在南加州，历史上的文字记录只能追溯到150-200年前，在地质记录中没有关于过去海啸的确凿证据。然而南加州有一个人口密集的沿海地区，有三个大型港口，包括洛杉矶港和长滩港，还有十个发电厂，包括圣奥诺弗雷核电站。即使是中等规模的海啸也会对南加州的经济产生巨大的影响。在过去的十年里，南加州近海的测绘和地震反射剖面揭示了一个密集的潜在发震断层网和大型海底滑坡。对这些假设的地震和滑坡源的建模表明，它们可能产生海啸，当地波高高达20米或更高。然而，没有海啸的地质记录，这些研究只能被认为是推测性的。南加州沿海湿地在全新世海平面上升期间形成，为捕获沙质海啸沉积物提供了一个理想的、以泥泞为主的沉积环境。该项目是对这些湿地沉积物进行系统搜索以寻找海啸沉积物候选物。在南加州找到海啸的记录将验证和证实过去十年来关于模拟由海底滑坡和近海地震引起的当地海啸的许多研究。沿海洪水的规模和频率对应急管理政策和发展有直接影响，特别是在人口密集、经济重要的南加州。建模只能提供估计的洪水规模，但海啸的地质记录代表了一项变革性的科学发现，它将有助于验证洪水的发生、规模和频率——这是规划海啸减灾的关键信息。该项目的数据提供了加利福尼亚湿地全新世历史的可靠记录，包括环境随时间的变化，以及对全新世海平面变化的限制。该项目还增加了该地区的古气候数据。该地区的许多湿地都是生态保护区，设有活跃的现场实验室和/或受欢迎的游客中心。监督这些地区的几个组织要求将该项目的结果与他们的现场展示结合起来。从该项目中获得的海啸信息将广泛传播到南加州社区。这些信息也将与地方政府和媒体分享，以确保公众了解这些结果的影响。该项目还具有很强的教育成分，培训三名本科生研究助理，他们将参与项目的各个方面，包括实地考察、实验室分析、解释和在会议上口头陈述结果以及通过共同撰写学术论文。

In 2004, a magnitude 9.3 earthquake off Sumatra triggered a tsunami that devastated an unaware and unprepared country, resulting in more than 150,000 Indonesian deaths. Seven years later, an only slightly smaller magnitude 9.0 earthquake off the densely populated East coast of Japan triggered a tsunami of similar size, but with a much lower death toll. Japan has a rich record, both geological and historical, of past tsunamis. This record has raised awareness in the population of Japan and fostered arguably the most stringent building codes and best coastal engineering in the world--both contributing to the reduced loss of life in Japan. In Southern California, historical written records extend back only 150-200 years, with no confirmed physical evidence for past tsunamis in the geological record. Yet Southern California has a densely populated coastal zone, and is home to three large ports, including the Port of Los Angeles and Long Beach Harbor and ten power plants, including the San Onofre nuclear power plant. Even a modestly sized tsunami would have an enormous impact of the economy of Southern California. In the past ten years, mapping and seismic reflection profiling of off-shore Southern California has revealed a dense network of potentialy seismogenic faults and large submarine landslides. Modeling of these hypothetical seismic and landslide sources suggests that they could generate a tsunami with local wave heights of up to 20m or more. However, without a geologic record of tsunamis, these studies can only be regarded as speculative. Coastal wetlands of Southern California, formed during the Holocene sea-level rise, provide an ideal, predominantly muddy sedimentary environment to capture a sandy tsunami deposit. This project is a systematic search of these wetland sediments for tsunami deposit candidates. Finding a record of tsunamis in Southern California will verify and validate much of the research of the last ten years on modeling local tsunamis from submarine landslides and offshore earthquakes. The scale and frequency of inundation along the coast has a direct impact on emergency management policy and development, especially in densely populated, economically important Southern California. Modeling can only provide an estimated scale of inundation, but a geologic record of tsunamis represents a transformative scientific discovery that would help verify the occurrence, scale, and frequency of inundation--critical information for planning tsunami hazard mitigation. Data from this project provides a robust record of the Holocene history of the California wetlands, including environmental changes through time, and places constraints on Holocene sea-level change. This project also adds to paleoclimate data for the region. Many of the wetlands in the area are ecological preserves with active on-site laboratories and/or popular visitors centers. Several of the organizations overseeing these areas have requested that the results from this project be integrated with their on-site displays. Tsunami information derived from the project will reach a broad cross-section of the Southern California community. This information will also be also shared with local governments and media to ensure the public is apprised of the implications of these results.The project also has a strong educational component, training three undergraduate research assistants, who will be included in all aspects of the project, including fieldwork, laboratory analyses, interpretation, and the presentation of the results both orally at conferences and through co-authorship of scholarly papers.