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Quantifying the relationship between the Earth?s convecting interior, plate motions, and earthquakes in Alaska using three-dimensional numerical simulations

使用三维数值模拟量化地球内部对流、板块运动和阿拉斯加地震之间的关系

基本信息

批准号：
1736153
负责人：
Lucy Flesch
金额：
$ 29.43万
依托单位：
Purdue University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-08-15 至 2022-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1736153&HistoricalAwards=false
关键词：
Quantifying relationship between Earth convecting

项目摘要

It is important to understand the levels of mantle coupling that drives intraplate continental deformation, a fundamental question in geophysics, as it will aid in seismic hazard analysis for earthquakes that occur far away from plate boundaries. How mantle flow drives surface deformation and motions in oceanic lithosphere is well established and has been key in further understanding many aspects of plate tectonics, however, within intraplate continental lithosphere the quantification of this coupling remains poorly understood. Alaska provides a unique opportunity to assess the level of continental lithospheric/mantle coupling due to its thin lithosphere and surface motions that are not easily explained by relative plate motions and gravity acting on high topography. The diffuse Pacific - North America plate boundary zone in Alaska is related to the subduction of the Pacific plate and Yakutat microplate beneath the North American plate and clockwise rotation of the Bering plate to the west, and has been used as an analog for an early Tibet. Observed surface motions in Alaska, however, illustrate that it is unlike any other convergent continental plate boundary. For example, all convergence of the approximately 5 cm/yr of Pacific - North America relative plate motion is accommodated within a 500 km zone, and surface motions beyond this zone are directed southward towards the plate boundary. Because the of the long time scale over which significant intraplate earthquakes occur it is vital to understand how stress is transferred form the mantle into these regions, this study will to address that fundamental question This project will also support the research of a graduate and undergraduate student. We will perform 3-D finite element geodynamic modeling to investigate the role mantle flow in driving intraplate surface motions and deformation in Alaska. These numerical experiments will be constrained using geophysical observations and have a physically accurate model volume (geometry) for the diffuse Pacific-North American plate boundary zone in Alaska. The resolution of this 3D geometry will allow us to determine the level of coupling between the Alaskan lithosphere and convecting mantle beneath it. We will differentiate between physically viable models by comparing our various model's predicted surface velocities to the observed surface deformation field, constrained by GPS and Quaternary fault slip data, This work will seek to answer the following questions: (1) What are the driving forces of the Bering plate? (2) What are the relative contributions of lithospheric thickness, lithospheric rheology and mantle flow in driving intraplate deformation in northern and central Alaska? (3) What force(s) is/are responsible for compression and uplift of the Mackenzie Mountains?

重要的是要了解驱动板内大陆变形的地幔耦合水平，这是地球物理学的一个基本问题，因为它将有助于对发生在远离板块边界的地震进行地震危险性分析。地幔流如何驱动海洋岩石圈的地表变形和运动已经得到了很好的证实，并已成为进一步理解板块构造的许多方面的关键，然而，在板内大陆岩石圈内，这种耦合的量化仍然知之甚少。阿拉斯加提供了一个独特的机会，以评估大陆岩石圈/地幔耦合的水平，由于其薄的岩石圈和表面运动，不容易解释的相对板块运动和重力作用于高地形。阿拉斯加的太平洋-北美板块扩散边界带与太平洋板块和雅库塔特微板块向北美板块俯冲以及白令板块向西顺时针旋转有关，并被用作早期西藏的类比。然而，观测到的阿拉斯加的地表运动表明，它不同于任何其他会聚的大陆板块边界。例如，太平洋-北美相对板块运动的约5 cm/年的所有会聚都容纳在500 km的区域内，而超过该区域的表面运动则指向南向板块边界。由于重大板内地震发生的时间尺度很长，因此了解应力如何从地幔转移到这些地区至关重要，本研究将解决这一基本问题。我们将进行三维有限元地球动力学模拟研究地幔流在驱动阿拉斯加板内表面运动和变形中的作用。这些数值实验将使用地球物理观测的约束，并有一个物理上准确的模型体积（几何形状）的扩散太平洋-北美板块边界带在阿拉斯加。这个三维几何的分辨率将使我们能够确定阿拉斯加岩石圈和它下面的对流地幔之间的耦合程度。我们将通过比较我们各种模型的预测表面速度与观测到的表面变形场来区分物理上可行的模型，这些模型受到GPS和第四纪断层滑动数据的约束。这项工作将寻求回答以下问题：（1）白令板块的驱动力是什么？(2)在阿拉斯加北方和中部，岩石圈厚度、岩石圈流变学和地幔流动在驱动板内变形中的相对贡献是什么？(3)是什么力量造成了麦肯齐山脉的挤压和抬升？