Collaborative Research: A community 3D seismic investigation of fault property controls on slow-slip along the Hikurangi megathrust

俯冲断裂带，地球上的一个构造板块被挤压到另一个板块之下，会产生地球上最强大、最具破坏性的地震和海啸。控制这种断层滑动行为的原因几乎是未知的，但它对理解和评估全球地震危害至关重要。虽然这些巨大的俯冲带地震在几秒到几分钟内释放地震能量，但最近的发现揭示了另一种类型的断层运动，称为慢滑地震（sse），需要几天、几周或几个月才能发生。虽然不像大地震那样具有破坏性，但这些慢滑地震仍然被认为是在俯冲带断层系统上应变积聚并随后释放的关键过程。慢滑地震也可以作为大地震可能发生的地点和时间的指示器。俯冲带沿美国东海岸的新西兰北岛定期(每4年~)生产异常浅(4 - 5公里海面以下)缓慢滑动地震相比,典型的20 - 50公里深处发现在其他领域如卡斯卡底古陆西海岸和阿拉斯加俯冲带美国的这个项目将进行3 d地震勘测设计形象的浅慢滑移区域新西兰俯冲带,绘制出断层系统,确定与慢滑行为相关的条件，以及它们与产生大地震的俯冲带相关的条件有何不同。该项目包括与新西兰、日本和英国研究人员在地震成像方面的大量国际合作，以及与国际海洋钻探计划的直接联系，该计划旨在钻探到慢滑带。该项目涉及一名早期职业科学家和几名研究生，他们将在论文工作中研究研究的各个方面。其他学生将参与所有参与国的实地数据收集。将与新西兰各组织和合作者协调以媒体报道、新闻报道、公开讲座和游船等形式进行的公众宣传。与记录的地震相关的板块边界断层滑动通常不能解释大地测量方法或全球模型预测的所有预期板块运动。近十年来令人振奋的进展已经认识到并记录了瞬态慢滑地震是另一种适应板块在俯冲边缘汇聚的模式。该项目通过开展首个以地震蠕变为主的俯冲逆冲区域的三维地震数据集，解决了俯冲逆冲的机制以及导致各种滑动行为的条件。该项目将使用研究船R/V Langseth在新西兰Hikurangi海沟和前弧附近15 x 60公里的区域获取开放的3D地震反射数据集。这些数据将提供高分辨率图像和瞬变滑动板块边界大逆冲断层的地震属性，这是研究团体与南开、东北、卡斯卡迪亚和哥斯达黎加等主要锁定俯冲逆冲断层进行比较的重要点。与高流体压力相关的地震属性是有利于慢滑地震条件的一个有希望的指标，北Hikurangi边缘在4-5公里深度有充分记录的慢滑地震-足够浅，可以进行详细的地震成像和地震属性测量。三维地震图像和属性将允许对构造、地层和水文地质条件进行准确的记录，这些条件会导致沿俯冲巨型逆冲带产生慢滑地震。国际合作实验将在3D采集过程中记录Langseth镜头，并使用3D全波形反演开发跨俯冲带的第一个高分辨率3D速度模型，这些模型将重叠并扩展到3D体积之外。

Subduction fault zones, where one of Earth's tectonic plates is forced beneath another plate, produce the most powerful and destructive earthquakes and tsunamis on the planet. What controls this fault slip behavior is virtually unknown and yet it is critical for understanding and assessing global seismic hazards. While these great subduction zone earthquakes release seismic energy in a matter of seconds to minutes, recent discoveries reveal another style of fault movement called slow slip earthquakes (SSEs) that take days, weeks or months to occur. While not as damaging as major earthquakes, these slow slip earthquakes are nonetheless thought to be a critical process in how strain builds up and is subsequently released on subduction zone fault systems. Slow slip earthquakes may also act as indicators of where, and possibly when, large damaging earthquakes might occur. The subduction zone along the east coast of the New Zealand North Island regularly (~ every 4 years) produces unusually shallow (4-5 km below the sea surface) slow slip earthquakes compared to the typical 20-50 km depths found in other areas such as the Cascadia and Alaska subduction zones on the west coast of the U.S. This project will conduct a 3D seismic survey that is designed to image the shallow slow slip region of the New Zealand subduction zone, map the fault systems, determine what conditions are associated with slow slip behavior and how they differ from conditions associated with subduction zones that generate great earthquakes. The project includes substantial international collaboration with New Zealand, Japanese and United Kingdom researchers on the seismic imaging as well as direct links with an international ocean drilling program designed to drill into the zone of slow slip. The project involves an early career scientist and several graduate students who will work on various aspects of the research for their thesis work. Additional students will be involved in the field data collection from all participating countries. Public outreach in the form of media coverage, news stories, public lectures and ship tours will be coordinated with New Zealand organizations and collaborators.Slip on plate boundary faults associated with recorded earthquakes typically fails to account for all of the expected plate motion predicted by geodetic methods or global models. Exciting advances in the last decade have recognized and documented transient slow slip earthquakes as another mode to accommodate plate convergence at subduction margins. This project addresses the mechanics of subduction thrusts and the conditions that lead to the wide variety of slip behaviors by carrying out the first-ever 3D seismic dataset acquired over a subduction thrust dominated by aseismic creep. The project will use the research vessel R/V Langseth to acquire an open-access 3D seismic reflection data set in a 15 x 60 km area offshore New Zealand's Hikurangi trench and forearc. These data will provide high-resolution images and seismic attributes of a transient-slip plate boundary megathrust identified by the research community as an important point of comparison to predominantly locked subduction thrusts such as Nankai, Tohoku, Cascadia, and Costa Rica. Seismic attributes linked to high fluid pressures are a promising indicator of conditions favorable for slow slip earthquakes and the Northern Hikurangi margin has well-documented slow slip earthquakes at 4-5 km depth - shallow enough for detailed seismic imaging and seismic attribute measurements. The 3D seismic images and attributes will allow for an accurate documentation of the structural, stratigraphic, and hydrogeologic conditions that lead to generation of slow slip earthquakes along a subduction megathrust. International collaborative experiments will record Langseth shots during 3D acquisition and develop the first ever high-resolution 3D velocity models across a subduction zone using 3D full-waveform inversion, which will overlap and extend beyond the 3D volume.