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

合作研究：断层属性控制 Hikurangi 巨型逆冲断层沿线慢滑移的社区 3D 地震调查

• 批准号: 1558574
• 负责人: Harold Tobin
• 金额: $ 9.93万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-15 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1558574&HistoricalAwards=false
• 关键词: Collaborative; Research; community; 3D; seismic

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.

俯冲断层带，即地球的一个板块被迫压入另一个板块之下的地方，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因素实际上是未知的，但它对于理解和评估全球地震灾害至关重要。虽然这些大俯冲带地震会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），需要数天、数周或数月的时间才能发生。虽然这些慢滑地震的破坏性不如大地震，但它们仍然被认为是俯冲带断层系统应变积累和释放的关键过程。慢滑地震也可以作为破坏性大地震可能发生的地点和时间的指标。 与其他地区典型的 20-50 公里深度相比，新西兰北岛东海岸的俯冲带定期（大约每 4 年）产生异常浅（海面以下 4-5 公里）的慢滑地震。作为美国西海岸的卡斯卡迪亚和阿拉斯加俯冲带，该项目将进行 3D 地震勘测，旨在对新西兰俯冲带的浅层慢滑移区域进行成像，绘制断层系统地图，确定什么条件与慢滑移行为相关，以及它们与产生大地震的俯冲带相关条件有何不同。 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，以及与旨在钻探慢滑移区域的国际海洋钻探计划的直接联系。该项目涉及一名早期职业科学家和几名研究生，他们将致力于论文工作的各个方面的研究。更多的学生将参与来自所有参与国家的实地数据收集。将与新西兰组织和合作者协调以媒体报道、新闻报道、公开讲座和船舶游览等形式进行的公共宣传。与记录的地震相关的板块边界滑移通常无法解释大地测量学预测的所有预期板块运动方法或全局模型。过去十年令人兴奋的进展已经认识到并记录了瞬态慢滑地震作为适应俯冲边缘板块聚合的另一种模式。该项目通过在以地震蠕变为主的俯冲冲断层上获取有史以来第一个 3D 地震数据集，研究了俯冲冲断层的力学原理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 获取新西兰 Hikurangi 海沟和前弧近海 15 x 60 公里区域的开放式 3D 地震反射数据集。这些数据将提供研究界确定的瞬态滑移板块边界巨型逆冲断层的高分辨率图像和地震属性，作为与南海、东北、卡斯卡迪亚和哥斯达黎加等主要锁定俯冲逆冲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发生的条件的一个有希望的指标，北希库朗吉边缘在 4-5 公里深度有记录良好的慢滑地震，该深度足够浅，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断层产生慢滑地震的结构、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 Langseth 镜头，并使用 3D 全波形反演开发首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。