Collaborative Research: Unraveling the habitat and dynamics of slow slip events through integrated borehole observations in the northern Hikurangi subduction margin

俯冲带板块边界，一个构造板块俯冲或俯冲到另一个构造板块之下，产生了世界上最大的地震和海啸，2004年印度洋9.2级地震和2011年日本北方近海9.0级东北冲地震就是明证。最近，科学家们已经认识到，俯冲巨型逆冲断层在幕式慢动作地震中经历滑动，或持续数天至数月的慢滑动事件。在某些情况下，已经观察到慢滑动事件发生在（并可能触发）大俯冲地震之前，这增加了了解它们的必要性。在靠近地球表面（5-15公里深）的地方发生的缓慢滑动事件存在于新西兰近海的Hikurangi俯冲带，是近源调查的唯一途径。2018年，在Hikurangi俯冲带的国际海洋发现计划科学钻探考察期间安装了两个观测站（穿透至海底以下400米）。观测站中的传感器现在正在持续测量慢滑事件源附近地壳性质的时间变化，并将有助于揭示其原因、后果以及与破坏性地震的关系。该项目提供资金，分析从观测站收集的数据，并支持对观测站的另一项使命，以恢复和更换观测站的仪器弦，使其能够继续运行五年。 该项目支持研究生和本科生的培训。慢滑动事件（SSEs）涉及断层上的瞬时非稳态滑动（持续数周至数月），滑动速度介于板块边界位移速率和产生地震波所需速率之间。导致SSE的物理机制，它们在板块边界应变积累和释放中的作用，以及它们与俯冲逆冲断层上破坏性地震滑动的关系知之甚少，部分原因是大多数研究充分的俯冲带SSE发生得太深，无法进行近场调查。一个值得注意的例外是新西兰的北方希库朗吉俯冲带，在那里，特征明显的SSE发生在海底以下5-15公里的范围内，并可能传播到海沟。2018年初，作为IODP Expedition 375的一部分，在北方Hikurangi SSE的近场安装了两个钻孔观测站，以通过多个SSE周期监测变形，热，水文和地球化学响应。该项目将：（2）于2023年初的拟议研究巡航期间，更换其中一个钻孔的地球化学采样和温度传感仪器串，跨越变形前沿附近的活动逆冲断层。这些数据将与海底传感器网络集成（绝对压力计、地震仪和流体流量计），在2019年的一次大型缓慢滑动事件中，它们也在沿着钻井断面记录，提供了一个前所未有的机会，整合多个海底和海底下的观测，在近，该奖项反映了NSF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 plate boundaries, where one tectonic plate dives or subducts beneath another tectonic plate produce the world’s largest earthquakes and tsunami, as starkly demonstrated by the M9.2 Indian Ocean earthquake in 2004, and the 2011 M9.0 Tohoku-Oki earthquake offshore northern Japan. Recently, scientists have recognized that subduction megathrust faults undergo slip in episodic slow-motion earthquakes, or slow slip events lasting days to months. In some cases, slow slip events have been observed to precede (and possibly trigger) major subduction earthquakes, increasing the need to understand them. Slow slip events occurring close to Earth's surface (5-15 km depth) exist at the Hikurangi subduction zone offshore New Zealand and are uniquely accessible to near-source investigations. In 2018, two observatories (penetrating up to 400 m below the seafloor) were installed during an International Ocean Discovery Program scientific drilling expedition at the Hikurangi subduction zone. Sensors in the observatories are now continuously measuring temporal changes in properties of Earth's crust near the source of slow slip events and will help reveal their causes, consequences, and relationship to destructive earthquakes. This project provides funding to analyze the data collected from the observatories, and to support another mission to the observatories to retrieve and replace the instrument strings at the observatories to enable their continued operation for another five years. The project supports the training of graduate and undergraduate students.Slow slip events (SSEs) involve transient aseismic slip on a fault (lasting weeks to months) at sliding velocities intermediate between plate boundary displacement rates and those required to generate seismic waves. The physical mechanisms leading to SSEs, their role in plate boundary strain accumulation and release, and their relationship to destructive seismic slip on subduction thrusts are poorly known, due in part to the fact that most well-studied subduction zone SSEs occur far too deep for near-field investigations. A notable exception to this is the northern Hikurangi subduction zone, New Zealand, where well-characterized SSEs occur within 5-15 km below the seafloor, and possibly propagate to the trench. In early 2018, as part of IODP Expedition 375, two borehole observatories were installed in the near field of northern Hikurangi SSEs to monitor deformation, thermal, hydrological, and geochemical responses through multiple SSE cycles. This project will: (1) recover and conduct analyses of data and samples recovered from the observatories; and (2) replace the geochemical sampling and temperature sensing instrument string in one of these boreholes, spanning an active thrust near the deformation front, during a proposed research cruise in early 2023. These data will be integrated with a network of seafloor sensors (absolute pressure gauges, seismometers, and fluid flowmeters) that were also recording along the drilling transect during a large slow slip event in 2019, offering an unprecedented opportunity to integrate multiple seafloor and subseafloor observations in the near-field of a large slow slip event.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.