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: 1558440
• 负责人: Eli Silver
• 金额: $ 5.96万
• 依托单位: University of California-Santa Cruz
• 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 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1558440&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.

俯冲断层带是地球的一个构造板块被迫位于另一个板块之下，会产生地球上最强大、最具破坏性的地震和海啸。 是什么控制了这种断层滑动行为几乎是未知的，但它是理解和评估全球地震灾害的关键。虽然这些巨大的俯冲带地震在几秒钟到几分钟内释放地震能量，但最近的发现揭示了另一种称为慢滑地震（SSE）的断层运动，这种地震需要几天，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，但这些缓慢滑动的地震仍然被认为是一个关键的过程，在应变如何建立和随后释放到俯冲带断层系统。慢滑地震也可以作为大破坏性地震可能发生的地点和时间的指标。 沿着新西兰北岛东海岸的俯冲带（~每4年）产生异常浅的（海面以下4-5公里）慢滑地震与典型的20-在美国西海岸的卡斯卡迪亚和阿拉斯加俯冲带等其他地区发现的50公里深处。新西兰俯冲带的浅慢滑区，绘制断层系统图，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条件的区别。 该项目包括与新西兰、日本和联合王国的研究人员就地震成像进行大量国际合作，以及与旨在钻探缓慢滑动区的国际海洋钻探方案建立直接联系。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、公开讲座和船舶图尔斯参观等形式开展公众外联活动。与记录地震相关的板块边界断层上的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。在过去的十年里，令人兴奋的进展已经认识到并记录了瞬态慢滑地震作为另一种模式，以适应板块会聚在俯冲边缘。该项目通过执行在以无滑动蠕变为主的俯冲逆冲断层上采集的第一个三维地震数据集，解决俯冲逆冲断层的力学和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海沟和前弧近海15 x 60公里区域获取开放式三维地震反射数据集。这些数据将提供高分辨率图像和地震属性的瞬态滑动板块边界巨型逆冲断层确定的研究界作为一个重要的比较点，主要锁定俯冲逆冲断层，如南开，东北，卡斯卡迪亚，和哥斯达黎加。与高流体压力相关的地震属性是有利于慢滑动地震的条件的有希望的指标，并且北方希库朗吉边缘在4-5 km深度处有充分记录的慢滑动地震-足够浅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准确记录导致沿着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拍摄，并使用3D全波形反演开发第一个高分辨率的3D俯冲带速度模型，该模型将重叠并延伸到3D体积之外。