Collaborative Research: Unlocking the secrets of slow slip by drilling at the northern Hikurangi subduction margin, New Zealand: CORK observatory development and installation

合作研究：通过在新西兰 Hikurangi 俯冲边缘北部钻探解开慢滑移的秘密：CORK 天文台的开发和安装

• 批准号: 1929120
• 负责人: Patrick Fulton
• 金额: $ 2.11万
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-01-01 至 2020-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1929120&HistoricalAwards=false
• 关键词: Collaborative; Research; Unlocking; secrets; slow

The Hikurangi subduction zone offshore the eastern North Island of New Zealand has characteristics that provide a globally unique window into a fundamental aspect of how stress builds up and is relieved as an oceanic plate thrusts (or "subducts") beneath continental crust. Recently, seismologists have recognized that subduction megathrust faults undergo slip in episodic "slow slip events". Prior to the discovery of slow slip events in the last decade, our paradigms of fault slip were focused on seismic slip in major earthquakes. Since the discovery of slow slip, most studies have focused on deep (20-40 km depth) slow slip events, but we now realize that shallow slow slip events (5-15 km depth) exist that are much more accessible to near-source investigations. These shallow slow fault slip events are centered beneath the ocean so onshore instruments have not been able to measure how much surface deformation occurs. This study takes advantage of planned International Ocean Discovery Program drilling to install sensors in two boreholes that will measure properties indicative of change in the shallow crust that the episodic fault activity causes. Senior researchers in borehole instrumentation will mentor mid-early career scientists, passing along extensive knowledge of such complex implementation and research. Japanese, New Zealand, and German collaborators will participate with the US investigators in this international study, and local communities will benefit from scientist outreach associated with cruises off New Zealand. This study is being undertaken as a ?community proposal?, whereby all data will be immediately publicly available. The shallowest, well-documented slow slip events on Earth occur at the northern Hikurangi margin, offshore Gisborne, New Zealand, at 5-15 km depth. They recur approximately every 1-2 years, with slip on the plate boundary interface of up to 15-20 cm. The unusually close proximity of the Gisborne slow slip events to the seafloor, the large slow slip event magnitudes (equivalent to an earthquake magnitude Mw ~6.3-6.8), and short recurrence intervals makes this the ideal setting for evaluating the near-source hydrological, geochemical, and thermal response of the offshore subduction margin to large, frequent, well-documented deformation transients. The borehole observatory data will clarify the role that fluid pressures, fluid flow, and temperature play in the occurrence of slow slip events, as well as the influence of slow slip event deformation on fluid and geochemical cycling within the forearc. This project will establish the borehole facility and set-up open data access. Analysis of the first two years of data, recovered by ROV, will evaluate the deformation, hydrological, and geochemical responses near the source of slow slip, as well as document the thermal regime of shallow slow slip. One of the borehole installations will target the region surrounding the shallow portion of the megathrust fault , while sensors in a second borehole will target the over-riding plate ~5 km above the slow slip event source.

新西兰北岛东部近海的Hikurangi俯冲带具有全球独特的特征，为了解大洋板块在大陆地壳下逆冲（或“俯冲”）时应力是如何形成和释放的基本方面提供了一个窗口。最近，地震学家已经认识到，俯冲巨型逆冲断层在幕式的“慢滑事件”中发生滑动。在近十年来发现慢滑事件之前，我们的断层滑动范式主要集中在大地震中的地震滑动上。自慢滑发现以来，大多数研究都集中在深部（20-40 km深度）慢滑事件上，但我们现在意识到存在浅层慢滑事件（5-15 km深度），近源调查更容易获得。这些浅层缓慢断层滑动事件的中心位于海洋之下，因此陆上仪器无法测量地表变形的程度。这项研究利用计划中的国际海洋发现计划钻井，在两个钻孔中安装传感器，测量间歇性断层活动引起的浅层地壳变化的特征。井眼仪器领域的资深研究人员将指导处于职业生涯中期的科学家，传授此类复杂实施和研究的广泛知识。日本、新西兰和德国的合作者将与美国研究人员一起参与这项国际研究，当地社区将从与新西兰外游相关的科学家外展中受益。这项研究是作为一项社区的建议呢?，所有数据将立即公开。地球上最浅、记录最充分的慢滑事件发生在新西兰吉斯本近海的Hikurangi边缘北部，深度为5-15公里。它们大约每1-2年发生一次，在板块边界界面上的滑动可达15-20厘米。吉斯本慢滑事件与海底的异常接近，大的慢滑事件震级（相当于地震震级Mw ~6.3-6.8）和短的重复间隔使其成为评估近海俯冲边缘近源水文、地球化学和热响应的理想环境，这些响应是大的、频繁的、有充分记录的变形瞬变。井眼观测资料将阐明流体压力、流体流动和温度在慢滑事件发生中的作用，以及慢滑事件变形对弧前流体和地球化学循环的影响。该项目将建立钻孔设施并建立开放的数据访问。通过ROV对前两年的数据进行分析，将评估慢滑源附近的变形、水文和地球化学响应，并记录浅层慢滑的热状态。其中一个钻孔装置将定位于大逆冲断层浅层部分周围的区域，而另一个钻孔的传感器将定位于慢滑事件源上方约5公里处的覆盘。