Collaborative Research: SISIE: South Island, New Zealand, Subduction Initiation Experiment

在这个项目中，来自加州理工学院和德克萨斯大学奥斯汀分校的科学家将在新西兰南部进行一项实验，以调查板块构造如何运作的关键未知因素。板块构造描述了地球表面是如何运动的，并且非常成功地提供了对地球表面发生的大多数地震和火山喷发的了解。板块构造的一个关键方面是当冷板块(密度相对较大)俯冲到另一个板块下方时的俯冲作用。其中一个令人费解的因素是，新的俯冲区必须从过去不存在的地方开始。这个项目的目的是了解一个新的俯冲带是如何开始的。这项研究选择的区域是地球上唯一已知的我们可以看到新俯冲带的位置。第一个研究目标是澳大利亚板块，因为它第一次潜入地球内部。第二个目标是新的断层，它定义了澳大利亚板块和太平洋板块之间的边界。所有收集到的数据将被整合到一个动态模型中，该模型描述了新俯冲带的形成以及力量如何运作和变化。来自德克萨斯大学和加州理工学院的学生将在海上获得宝贵的经验，学习数据收集、计算技术和数据解释。新西兰科学家将在进行这项实验的同时，对俯冲板块的性质进行陆上地震记录。该项目是在新西兰南岛南部普伊塞格-菲奥德兰边界进行的综合有源地震实验。这项研究将检验这样一种假设，即这种早期俯冲的例子正在从被迫状态过渡到自我维持状态。该项目的目的是了解俯冲的驱动力，特别是通过一些模型，这些模型表明，在俯冲开始期间，从远场板块应力到板块的负浮力有一个根本的转变。所选择的俯冲带是麦格理山脊杂岩(澳大利亚板块和太平洋板块之间的边界)的一部分，可能是研究俯冲早期阶段的全球最佳边缘。该小组将解决几个基本问题，包括：在俯冲启动过程中，是什么控制着从被迫状态到自我维持状态的转变？那么，大洋板块在俯冲初期的力学条件是什么呢？PI将检验板拉力增强导致沿山脊下沉的假设。这一板块构造情景将通过普伊塞格尔地区精炼的重力模型以及地壳结构和沉积盆地历史的地震约束来处理。此外，在俯冲启动过程中，最初陡峭的断裂带和正断层过渡或演化为浅冲断面，这是地球动力学的关键方面。该项目是由震源-接收器配置的正演模拟指导的，它表明沿走向的两个位置的板的倾角和其他特征，每个具有不同的压缩程度，将可以用所采用的地震方法来解决。

In this project, scientists from the California Institute of Technology and The University of Texas at Austin will conduct an experiment south of New Zealand to investigate key unknowns about how plate tectonics works. Plate tectonics describes how the surface of the earth moves and has been very successful providing an understanding of the occurrence of most earthquakes and volcanic eruptions on the surface of Earth. One of the key aspects of plate tectonics is subduction when the cold plate (which is relatively dense) dips beneath another. A puzzling element of this is that new subduction zones must start where none existed in the past. The purpose of this project is to understand how a new subduction zone starts. The region selected for this study is the only known location on Earth where we can see a new subduction zone. The first target of study is the Australian plate as it first dives into Earth's interior. The second target is the new fault that defines the boundary between the Australian and the Pacific plates. All of the data collected will be integrated into a dynamic model of the formation of a new subduction zone and how the forces operate and change. Students from both the University of Texas and the California Institute of Technology will get valuable experience at sea learning about data collection, computational techniques, and data interpretation. New Zealand scientists will conduct onshore seismic recordings on the nature of the over-riding plate concurrent with this experiment. The project is an integrated, active-source seismic experiment on the Puysegur-Fiordland boundary south of South Island of New Zealand. The study will test the hypothesis that this type-example of incipient subduction is making a transition from a forced to a self-sustaining state. The project was motivated to understand the forces that drive subduction, specifically by models that suggest that during subduction initiation there is a fundamental transition from far-field plate stresses to the negative buoyancy of the slab. The subduction zone selected is a segment of the Macquarie Ridge Complex (the boundary between the Australian and Pacific plates), and is likely the best margin globally to study the early stages of subduction. The team will address several fundamental questions including: What controls the transition from a forced to self-sustaining state during subduction initiation? And, what are the mechanical conditions of the oceanic plate during incipient subduction? The PIs will test the hypothesize that a strengthening of the slab pull force causes the subsidence along the ridge. This plate tectonic scenario will be addressed with refined gravity models of the Puysegur region and seismic constraints on the crustal structure and sedimentary basin history. Moreover, initially steep fracture zones and normal faults transition or evolve to shallow thrust planes during subduction initiation, key aspects of the geodynamics. The project is guided by forward modeling of the seismic source-receiver configuration that shows that the dip and other features of the slab at two positions along strike, each with a different degree of compression, will be resolvable with the seismic methods employed.