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。在过去的二十年里，在陆地-海洋边界附近产生的海啸已经造成25万人死亡（2004年的苏门答腊岛海啸，地球上最近最致命的自然灾害），损失超过2000亿美元（2011年的日本海啸，历史上最昂贵的自然灾害之一）。在未来的某个时候，类似的事件可能会袭击美国俄勒冈-华盛顿海岸。不幸的是，预测这些灾难性事件的能力不是很好。该项目将部署和测试几种类型的仪器，用于测量可能是地震前兆的海底小运动。研究结果将用于提高对俯冲带地震和海啸的预测和认识。该项目将在中美洲海上部署新的、具有成本效益的最先进的海底大地测量设备，对俯冲带的两个相邻部分进行取样。这两个板块在重要的地质和地球物理特征上形成对比，为检验巨型逆冲构造在海啸发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，浅层滑动亏缺的积累是否是发生与俯冲有关的海啸的必要条件？这个问题可以通过比较中美洲俯冲带两个相邻近海段的应变率剖面来回答，这些剖面在地震特征、锁定行为和海啸历史上形成了对比。尽管哥斯达黎加尼科亚半岛近海的地震带频繁发生7.2 - 7.8级地震，但在有记录的历史中，该地震带并未产生重大海啸，而尼加拉瓜和萨尔瓦多北部的地震带在1992年和2012年引发了海啸。假设滑差积累是海啸的必要条件，该项目预计在哥斯达黎加北部近海地区没有滑差，但在尼加拉瓜南部观察到浅滑差（锁定？），表明未来几十年那里可能发生另一次海啸。其中一个微妙之处是应力阴影效应的可能性，即前弧的上倾部分不是摩擦“锁定”的，而是与板块界面上更深的锁定凸起“一起行驶”，尽管摩擦稳定，但仍积累了部分滑动赤字。与海沟垂直的大地测量样条应允许对这种可能性进行评估。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.