Integrating Marine Seismic and Ocean Drilling Results with three-dimensional dynamic models of Subduction Initiation

这个项目试图更好地理解一种称为俯冲的过程。俯冲是冰冷的海洋板块返回地球内部的地方。板块俯冲是一种关键的地质过程，负责构造板块上最大的力量，构造板块是地球上破坏性最强的地震的所在地，并导致地球表面的大部分火山活动。该项目将着眼于形成一个新的俯冲带的过程，这被称为俯冲启动。俯冲开始被理解得很少，但与驱动和抵制板块构造运动的力量的最大变化有关。尽管板块构造的许多方面都已被了解，但俯冲的启动仍然是一个关键的未知因素，过去几年来一直在共同努力通过海洋地质和地球物理研究来了解这一过程。该项目将把最近的海洋研究与所谓的板块构造重建结合起来，并将这些信息纳入计算模型。制约这一过程的一些关键证据来自深海钻探和海洋地震调查。这些数据分别限制了俯冲起始点的地质演化和现代结构的细节。该项目将侧重于最近或正在进行的四个俯冲启动点：日本南部的伊祖-博宁马里亚纳岛、西南太平洋的汤加·克尔马德克、新西兰南部的普伊塞格尔和斐济附近的马修斯-亨特，也位于西南太平洋。最近通过大洋钻探发现，尽管相距数千英里，伊祖-博宁-马里亚纳俯冲带和汤加-克尔马德克俯冲带可能是同时开始的，并与太平洋板块运动的重大变化有关。这个项目将根据固体和流体力学的基本物理原理来研究这些俯冲带如何形成的细节。在俯冲开始的过程中，形成了所谓的巨型逆冲断层，也就是破坏性大地震的所在地。据认为，这样一个新的巨型逆冲正在新西兰南部形成。在这个项目中，将使用复杂的计算方法，称为有限元，并将使用由国家科学基金会支持的最大的超级计算机。在项目期间，一名研究生将接受计算方法方面的培训，这些方法广泛适用于许多科学和工程领域。这位调查员将与加州理工大学地震实验室外联和社交媒体办公室合作，向洛杉矶社区广泛、多样化的社区传播科学，包括访问当地公立学校。新俯冲带的形成是板块构造的重要组成部分，但仍是一个悬而未决的问题。俯冲板块是板块运动的主要驱动力，新俯冲带的形成和现存俯冲带的消亡与板块作用力的最大变化有关。太平洋在50 Ma左右发生了洋盆范围的构造变化，IBM和Thoma-Kermadec的启动与板块运动的变化是同步的。该项目将通过利用最近扩大的深海钻探和海洋地震调查的观测记录，正视这些根本问题。地球科学家团队将通过将观测结果与新一代依赖时间的3D地球动力学模型进行比较，来测试启动俯冲的概念。随着过去六年来对通过大洋钻探和海洋地震调查引发俯冲的观测限制跃升，同时软件和计算硬件也相应成熟，现在是重新研究俯冲引发机制的理想时机。研究人员将为四个西太平洋俯冲起始事件建立详细的区域板块构造重建(数据模型)：Izu-Bonin Mariana(IBM)、Thoma Kermadec、Puysegur和Matthews-Hunter。普伊塞格俯冲带(新西兰近海)是测试俯冲启动力学的理想天然实验室，它具有良好的板块运动学、构造控制、应力演化、垂直运动和断层分布。这些重建提供了基本的初始条件和边界条件，并允许在地球动力学模型与地质和地球物理观测之间进行严格的比较。有限元方法将被用来解决这些固有的、时间相关的、多尺度的问题，并达到跟踪塑性失效系统变形关键部位所需的分辨率。粘弹塑性模型将具有热浮力和成分浮力，以及弱化、位错蠕变和部分熔化的显式次尺度模型。该团队将从15 Ma以来Puysegur和2 Ma以来Matthews-Hunter的板块运动的时间依赖模型中约束板片强度、应力传播、塑性破坏和断裂带成核(与颗粒演化和精子化相关的削弱机制)。该小组将确定在100-1000公里的走向上以52 Ma的速度启动IBM弧所需的条件，以便初始岩浆信号在几个MyR内是同步的。对于IBM来说，驱动力增长并传递到太平洋板块的速度将得到解决。该项目将把动态流动模型、板块运动学和MG&amp；G数据之间的集成达到一个新的水平，具有广泛的应用前景。这项工作可能会影响几个大型项目。地球动力学假说可能会导致预测，这些预测可以在IOP的主持下用深海钻探进行测试。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。

This project seeks to better understand a process called subduction. Subduction is where cold oceanic plates return to Earth’s interior. Plate subduction is a key geological process responsible for the largest forces on tectonic plates, the site of the most destructive earthquakes on the planet and leads to much of the volcanism on Earth’s surface. The project will look at the process of forming a new subduction zone, which is called subduction initiation. Subduction initiation is poorly understood but is associated with the largest changes in the forces which both drive and resist plate tectonic motions. Although many aspects of plate tectonics are understood, subduction initiation remains a key unknown and there has been a concerted effort in the last few years to understand this process through marine geological and geophysical research. This project will synthesize the recent marine research with what are called plate tectonic reconstructions and incorporate that information into computational models. Some of the key evidence that constrains the process has come from deep sea drilling and through marine seismic surveys. These data constrain the details of the geological evolution and present-day structure of the sites of subduction initiation, respectively. The project will focus on four sites of recent or on-going subduction initiation: Izu-Bonin Mariana south of Japan, Tonga Kermadec in the southwest Pacific, Puysegur south of New Zealand and Matthews-Hunter near Fiji also in the southwest Pacific. It has recently been discovered through ocean drilling that the Izu-Bonin-Mariana and the Tonga-Kermadec subduction zones may have initiated at the same time despite being separated by several thousand miles and were associated with a major change in the motion of the Pacific Plate. This project will look at the details of how these subduction zones formed in terms of the basic physics of solid and fluid mechanics. During subduction initiation, the so-called mega thrust fault, the site of destructive great earthquakes, forms. It is thought that such a new megathrust is in the process of forming south of New Zealand. In this project sophisticated computational methods, call finite elements, will be used and will use the largest supercomputers supported by the National Science Foundation. During the project, a graduate student will be trained in computational methods, which are widely applicable to many areas of science and engineering. The investigator will work with the Caltech Seismo Lab Outreach and Social Media office to communicate science to the broad, diverse community of the Los Angeles community, including through visits to local public schools. The initiation of new subduction zones is a key component of plate tectonics but remains an unsolved problem. With subducted slabs being the primary force driving plate motions, formation of new subduction zones and demise of existing ones are associated with the largest changes in the forces on tectonic plates. There was an ocean basin-wide tectonic change in the Pacific at about 50 Ma with initiation of IBM and Tonga-Kermadec synchronous with a change in plate motions. This project will squarely address these fundamental problems by exploiting the recently expanded observational record from deep sea drilling and marine seismic surveys. The team of geoscientists will test concepts for the initiation of subduction by comparing observations against a new generation of 3D, time-dependent geodynamic models. With the observational constraints on subduction initiation through ocean drilling and marine seismic surveys jumping forward over the last six years simultaneous with a commensurate maturing of software and computational hardware, the time is ideal to readdress the mechanics of subduction initiation. The investigators will build detailed regional plate tectonic reconstructions (data models) for four western Pacific subduction initiation events: Izu-Bonin Mariana (IBM), Tonga Kermadec, Puysegur and Matthews-Hunter. The Puysegur subduction zone (offshore New Zealand) is an ideal natural laboratory for testing the mechanics of subduction initiation with its well-constrained plate kinematics, structural controls, stress evolution, vertical motions, and distribution of faults. These reconstructions provide essential initial and boundary conditions and allow for rigorous comparisons between geodynamic models and geological and geophysical observations. The finite element method will be used for the solution of these inherently time-dependent, multi-scale problems and achieve the resolutions required to track the localization of deformation key for systems with plastic failure. The visco-elastoplastic models will have thermal and compositional buoyancy and explicit sub-scale models of weakening, dislocation creep, and partial melting. The team will constrain, slab strength, stress propagation, plastic failure and fault zone nucleation (weakening mechanisms associated with grain evolution and sperpentinization) from time-dependent models with plate motions for Puysegur since 15 Ma and Matthews-Hunter since 2 Ma. The team will determine the conditions needed to initiate the IBM arc at 52 Ma over 100-1,000 km of strike such that the initial magmatic signal is synchronous within a few Myrs. For IBM, the rate at which driving forces grow and are transmitted to the Pacific plate will be addressed. The project will reach a new level of integration between dynamic flow models, plate kinematics and MG&G data that could have broad application. The work could impact several large programs. The geodynamic hypotheses could result in predictions that could be tested with deep sea drilling under the auspices of IODP.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.