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

俯冲带沿着新西兰的希库朗吉边缘，断层沿着边缘以不同的速度移动。沿着这个俯冲带，太平洋构造板块上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。其中一些原因可能是海底山脉分布在俯冲洋板块上。海山可以带走沉积物，从而加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的运动。为了更好地了解断层如何滑动，本研究着眼于海山对希库朗吉边缘沿着俯冲作用的影响。该项目利用现有的海洋地震数据计算希库朗吉边缘大陆架下7至10公里深处的地震波速度和岩石及沉积物的性质。该研究将这些特性与Hikurangi边缘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。这项研究支持研究生的培训。将制定一个教育模式，用于本科教育和地方高中。通过动手实验，学生将发现岩石特性和地震危险之间的联系。新西兰希库朗吉俯冲带沿着巨型逆冲断层沿着边缘从南向北急剧改变其滑动行为。沿大陆边缘南段沿着的巨型逆冲断层在大地测量上被锁定，可能会同震滑动。然而，沿着中央和北方边缘，它似乎蠕动，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希库朗吉北方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。这些问题包括增生楔和俯冲带沉积物特性以及海山对希库朗吉边缘增生棱体的影响。在这一综合项目中，将利用现有的海洋主动源地震数据，对希库朗吉边缘7至10公里深处的沉积物和底层基底的地震速度结构和反射率进行成像。浅俯冲带的成像特性将与在希库朗吉边缘沿着代表性区段的岩石样本中测量的超声波速度进行比较。将在俯冲带设定的预期范围内对岩石样品施加围压和孔隙压力，以确定其固结特性和应力历史。在一个为期两年的项目中，将讨论以下假设：1）希库朗吉南部增生棱柱体的地震速度高于希库朗吉北方，这与沿着边缘增生的新近纪岩石固结程度的差异成比例。2)从沿着希库朗吉边缘的地震速度推断出的压实和脱水的差异是由俯冲海山施加的侧向应力局部驱动的。3)2016年凯库拉地震后希库朗吉北方边缘的更严重震动是由广泛分布在棱柱体中的较低剪切波速度引起的。该奖项反映了NSF的法定使命，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。

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.