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

俯冲断裂带，地球的一个构造板块被压在另一个板块之下，产生了地球上最强大和最具破坏性的地震和海啸。是什么控制了这种断层滑动行为几乎是未知的，但它对于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钟到几分钟内释放出地震能量，但最近的发现揭示了另一种被称为慢滑地震(SSE)的断层运动形式，需要几天、几周或几个月的时间才能发生。虽然不像大地震那样具有破坏性，但这些慢滑地震被认为是应变积累并随后在俯冲带断层系统上释放的关键过程。慢滑地震也可以作为可能在哪里以及何时发生大的破坏性地震的指标。新西兰北岛东海岸的俯冲带定期(每4年)会发生异常浅的(海平面以下4-5公里)慢滑地震，而其他地区，如美国西海岸的卡斯卡迪亚和阿拉斯加俯冲带，通常深度为20-50公里。该项目将进行三维地震调查，旨在对新西兰俯冲带的浅层慢滑区域成像，绘制断层系统图，确定哪些条件与慢滑行为有关，以及它们与产生大地震的俯冲带有关的条件有何不同。该项目包括与新西兰、日本和英国的研究人员在地震成像方面进行大量国际合作，以及与旨在钻探慢滑带的国际海洋钻探计划直接联系。该项目涉及一名早期职业科学家和几名研究生，他们将在论文工作的各个方面进行研究。更多的学生将参与从所有参与国收集的实地数据。通过媒体报道、新闻报道、公开讲座和参观船只等形式进行的公众宣传将与新西兰组织和合作者协调。与记录到的地震有关的板块边界断层滑动通常无法解释大地测量方法或全球模型预测的所有预期板块运动。在过去的十年中，令人振奋的进展已经认识到并记录了瞬时慢滑地震是适应俯冲边缘板块会聚的另一种模式。该项目通过首次在以无地震蠕变为主的俯冲推覆上采集的三维地震数据集，研究俯冲推覆的机制和导致各种滑动行为的条件。该项目将使用R/V朗塞特考察船在新西兰Hikurangi海沟和弧前15 x 60公里的近海区域获取开放访问的3D地震反射数据集。这些数据将提供瞬间滑动板块边界巨型逆冲的高分辨率图像和地震属性，被研究界确定为主要锁定的俯冲冲断带，如南开、东北、卡斯卡迪亚和哥斯达黎加的重要比较点。与高流体压力有关的地震属性是慢滑地震有利条件的一个有希望的指标，北希库兰吉边缘有充分记录的4-5公里深的慢滑地震--足够浅，可以进行详细的地震成像和地震属性测量。3D地震图像和属性将允许准确记录导致沿俯冲巨型逆冲产生慢滑地震的构造、地层和水文地质条件。国际合作实验将在3D采集过程中记录朗塞特镜头，并使用3D全波形反演开发有史以来第一个跨俯冲带的高分辨率3D速度模型，该模型将重叠并延伸到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.