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: 2022832
• 负责人: Demian Saffer
• 金额: $ 3.54万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-01-01 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2022832&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.

新西兰北部北部岛的海库兰吉俯冲带的特征为全球独特的窗口提供了一个基本方面的压力，并随着大陆地壳下方的海洋板块推力（或？俯冲？）而放松。最近，地震学家认识到，俯冲的巨型缺陷会在情节性的慢速事件中受到打滑？在过去十年中发现缓慢的事件之前，我们的断层滑移范式集中在主要地震中的地震滑移上。自从发现缓慢滑移以来，大多数研究都集中在深（20-40 km深度）慢速事件上，但是我们现在意识到，存在浅慢速事件（5-15公里深），这些事件对于近源调查更容易访问。这些浅的慢断层滑移事件以海洋为中心，因此陆上仪器无法测量发生多少表面变形。这项研究利用计划的国际海洋发现计划钻探将传感器安装在两个钻孔中，这些传感器将测量表明情节性断层活动造成的浅层地壳变化的属性。 钻孔仪器的高级研究人员将在中期的职业科学家中指导人们对这种复杂的实施和研究的广泛知识。日本，新西兰和德国合作者将与美国调查人员一起参加这项国际研究，当地社区将受益于与新西兰巡游相关的科学家宣传。这项研究是作为“社区建议”进行的，其中所有数据都将立即公开可用。地球上最浅，有据可查的慢速事件发生在新西兰吉斯伯恩近海北部的北部，深度为5-15公里。它们大约每1 - 2年重现一次，在板边界界面上滑动高达15-20厘米。 Gisborne缓慢滑动事件与海底的异常接近，大型慢速事件大小（等效于地震幅度MW〜6.3-6.8），并且短期复发间隔使得这是评估近距离水文，地球化学和热响应的理想设置，该响应量很大。钻孔天文台数据将阐明流体压力，流体流量和温度在慢滑动事件发生中的作用，以及慢滑动事件变形对前臂内流体和地球化学循环的影响。该项目将建立钻孔设施并设置开放数据访问。 ROV回收的最初两年数据的分析将评估慢速滑移来源附近的变形，水文和地球化学响应，并记录了浅慢滑层的热状态。钻孔装置之一将针对大型断层浅层浅层区域周围的区域，而第二个钻孔中的传感器将瞄准慢速事件源上方约5 km的过度骑行板。