Study of the impact of seamount subduction on the outer wedge of the Hikurangi margin from combined lab analyses of rock properties and marine seismic data

通过岩石特性和海洋地震数据的组合实验室分析研究海山俯冲对 Hikurangi 边缘外楔的影响

• 批准号: 1949171
• 负责人: Harm Van Avendonk
• 金额: $ 41.75万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-04-01 至 2025-03-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1949171&HistoricalAwards=false
• 关键词: Study; impact; seamount; subduction; outer

A subduction zone runs along the Hikurangi margin of New Zealand, and the faults along the margin move at different rates. Along this subduction zone, sediments on the incoming Pacific tectonic plate are either stripped off and transferred to the upper tectonic plate or carried down deep into the mantle on the lower, subducting tectonic plate. Some of this may be due to the distribution of seamounts on the subducting oceanic plate. Seamounts can enhance sediment subduction by taking the sediments with them. Fluids from the sediments may in turn affect movement on the faults. To improve understanding of how faults slip, this study looks at the effects of seamounts on subduction along the Hikurangi margin. This project uses existing marine seismic data to calculate seismic wave speeds and properties of rocks and sediments beneath the continental shelf of the Hikurangi margin to depths of 7-10 km. The study compares those properties with laboratory experiments on rock samples from the Hikurangi margin to get a better understanding of subduction zone processes. The study supports the training of graduate students. An educational model will be developed and used for undergraduate education and at local high schools. Through hands-on experiments, students will discover connections between rock properties and seismic hazards.The megathrust fault along the Hikurangi subduction zone of New Zealand changes its slip behavior dramatically from south to north along the margin. The megathrust along the southern section of the margin is geodetically locked and will likely slip coseismically. However, along the central and northern margin it appears to creep and generate regular slow-slip events. Recent studies have also shown that the ground motion of regional seismic waves is amplified much more at the northern Hikurangi margin than to the south. To gain a better understanding of these geological processes, likely factors that control slip behavior will be studied. These include accretionary wedge and underthrust sediment properties and the impact of seamounts on the accretionary prism of the Hikurangi margin. In this synthesis project existing marine active-source seismic data will be used to image seismic velocity structure and reflectivity of sediments and the underlying basement of the Hikurangi margin to depths of 7-10 km. The imaged properties of the shallow subduction zone will be compared with ultrasonic wavespeeds measured in rock samples from representative segments along the Hikurangi margin. Confining and pore pressures will be applied to the rock samples within the range expected for the subduction zone setting to determine their consolidation characteristics and stress history. In a two-year project the following hypotheses will be addressed: 1) Seismic velocities of the accretionary prism in southern Hikurangi are higher than northern Hikurangi in proportion to the differences in the degree of consolidation of Neogene rocks accreted along the margin. 2) The differences in compaction and dewatering inferred from seismic velocities along the Hikurangi margin is driven locally by the lateral stress imparted by subducting seamounts. 3) More severe shaking at the northern Hikurangi margin after the 2016 Kaikoura earthquake was caused by lower shear-wave velocities broadly distributed in the prism.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.

俯冲带沿着新西兰的希库兰吉边缘延伸，沿边缘的断层以不同的速度移动。沿着这个俯冲带，进入太平洋构造板块的沉积物要么被剥离并转移到上部构造板块，要么被带到下部俯冲构造板块的地幔深处。这在一定程度上可能是由于俯冲板块上的海山分布所致。海山可以通过带走沉积物来增强沉积物的俯冲作用。沉积物中的流体可能反过来影响断层上的运动。为了更好地理解断层是如何滑动的，这项研究着眼于海山对Hikurangi边缘俯冲的影响。该项目使用现有的海洋地震数据来计算7-10公里深度的希库兰吉边缘大陆架下岩石和沉积物的地震波速和性质。这项研究将这些特性与来自Hikurangi边缘的岩石样本的实验室实验进行了比较，以更好地了解俯冲带过程。这项研究为研究生的培养提供了支持。将开发一种教育模式，并将其用于本科教育和当地高中。通过动手实验，学生们将发现岩石性质与地震危险之间的联系。新西兰希库兰吉俯冲带上的巨型逆冲断层沿边缘从南向北急剧改变其滑动行为。沿边缘南段的巨型逆冲断裂受到大地测量的锁定，很可能会同震滑动。然而，沿着中部和北部边缘，它似乎爬行并产生定期的慢滑事件。最近的研究还表明，区域地震波的地面运动在Hikurangi北部边缘比在南部被放大得多。为了更好地了解这些地质过程，将研究控制滑动行为的可能因素。这些问题包括海积楔形和俯冲沉积性质，以及海山对希库兰吉边缘增积棱柱的影响。在这个综合项目中，现有的海洋活动震源地震数据将被用来成像7-10公里深处的沉积物和Hikurangi边缘的下伏基底的地震速度结构和反射率。浅俯冲带的成像特性将与在Hikurangi边缘具有代表性的部分的岩石样品中测量的超声波速度进行比较。围压和孔压将应用于俯冲带环境预期范围内的岩石样品，以确定其固结特征和应力历史。在一个为期两年的项目中，将提出以下假设：1)根据沿边缘沉积的新近系岩石固结程度的差异，Hikurangi南部的吸积棱镜的地震速度高于Hikurangi北部的地震速度。2)从Hikurangi边缘的地震速度推断的压实和降水的差异是由俯冲海山施加的侧向应力局部驱动的。3)2016年Kaikoura地震后，Hikurangi北部边缘发生的更严重的震动是由棱镜中广泛分布的较低剪切波速度引起的。这一裁决反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Permeability and Elastic Properties of Rocks From the Northern Hikurangi Margin: Implications for Slow‐Slip Events

北希库朗吉边缘岩石的渗透率和弹性特性：对慢滑事件的影响

• DOI: 10.1029/2023gl103696
• 发表时间: 2024
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Tisato, Nicola;Bland, Carolyn D.;Van Avendonk, Harm;Bangs, Nathan;Garza, Hector;Alamoudi, Omar;Olsen, Kelly;Gase, Andrew
• 通讯作者: Gase, Andrew