Collaborative Research: Improved Understanding of Subduction Zone Tsunami Genesis Using Sea Floor Geodesy Offshore Central America

俯冲带地震会引发海啸，这是一种致命的自然灾害。在过去20年中，在陆地-海洋边界附近产生的海啸造成25万人死亡(2004年的苏门答腊岛事件，这是地球最近最致命的自然灾害)，损失超过2000亿美元(日本2011年的事件，历史上代价最高的自然灾害之一)。类似的事件很可能在未来某个时候袭击美国俄勒冈州-华盛顿州海岸。不幸的是，预测这些灾难性事件的能力并不是很好。该项目将部署和测试几种测量海底微小运动的仪器，这些仪器可能是地震前兆。研究结果将用于改进对俯冲带地震和海啸的预测和理解。该项目将在中美洲近海部署新的、具有成本效益的最先进的海底大地测量设备，在两个横断面上采样俯冲带的相邻部分。这两个部分在重要的地质和地球物理特征上形成对比，为假设检验巨型逆冲性质在海啸产生中的作用提供了独特的机会。例如，在俯冲带的近海沟区域积累浅层滑动赤字是与俯冲相关的海啸的必要条件吗？这个问题可以通过比较中美洲俯冲带两个相邻近海区段的应变率剖面来回答，这些区段在地震特征、锁定行为和海啸历史方面存在差异。哥斯达黎加尼科亚半岛近海的地震孕育区在有记录的历史上没有发生过重大海啸，尽管经常发生7.2-7.8级地震，而尼加拉瓜和萨尔瓦多以北近海的地震孕育区在1992年和2012年引发了海啸。假设滑动赤字累积是海啸的必要条件，该项目预计在哥斯达黎加北部近海地区观察不到滑动赤字，但观察到浅滑动赤字(锁定？)在尼加拉瓜南部，预示着未来几十年那里可能会发生另一场海啸。一个微妙之处是应力阴影效应的可能性，即前弧形的上倾角部分不会被摩擦“锁定”，而是与板块界面上更深的锁定凹凸体一起“顺着”前进，尽管摩擦稳定，但仍积累了部分滑动赤字。海沟垂直的大地断面应该可以评估这种可能性。这一裁决反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Subduction zone earthquakes can cause tsunamis, a deadly natural disaster. In the last two decades tsunamis generated near the land-ocean boundary have caused a quarter of a million fatalities (the 2004 Sumatra event, Earth’s deadliest recent natural disaster) and losses more than $200 billion (Japan’s 2011 event, one of the most expensive natural disasters in history). A similar event is likely to hit the US Oregon-Washington coast sometime in the future. Unfortunately, the ability to forecast these catastrophic events is not very good. This project will deploy and test several types of instruments for measuring small motions of the seafloor that may be earthquake precursors. The results will be used to improve forecasts and understanding of subduction zone earthquakes and tsunamis. The project will deploy new, cost-effective state-of the art sea floor geodesy equipment offshore Central America, in two transects sampling adjacent segments of the subduction zone. The two segments contrast in important geological and geophysical characteristics, providing a unique opportunity for hypothesis testing of the role of megathrust properties in tsunami generation. For example, is accumulation of shallow slip deficit in the near-trench region of subduction zones a necessary condition for a subduction-related tsunami? The question can be answered by comparing strain rate profiles in two adjacent offshore segments of the Central America subduction zone that contrast in earthquake characteristics, locking behavior, and tsunami history. The seismogenic zone offshore the Nicoya peninsula of Costa Rica has not produced a significant tsunami in recorded history despite frequent M 7.2 – 7.8 earthquakes, while the one to the north offshore Nicaragua and El Salvador generated tsunamis in 1992 and 2012. Assuming slip deficit accumulation is a necessary condition for tsunamis, the project would expect to observe no slip deficit in the offshore region of northern Costa Rica but observe a shallow slip deficit (locking?) in southern Nicaragua, indicating the potential for another tsunami there in the next few decades. One subtlety is the possibility of stress shadow effects, whereby up-dip sections of the forearc are not frictionally ‘locked’ but rather ‘ride along’ with deeper locked asperities on the plate interface, accumulating a partial slip deficit despite being frictionally stable. The trench-perpendicular geodetic transects should allow assessment of this possibility.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.