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

了解驱动板块内大陆变形的地幔耦合水平是很重要的，这是地球物理学中的一个基本问题，因为它将有助于对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表面变形和运动已经很好地建立起来，并且已经成为进一步了解板块构造许多方面的关键，然而，在板块内大陆岩石圈中，这种耦合的量化仍然知之甚少。阿拉斯加为评估大陆岩石圈/地幔耦合水平提供了一个独特的机会，因为它的岩石圈很薄，地表运动不容易用相对板块运动和作用于高地形的重力来解释。阿拉斯加的扩散太平洋-北美板块边界带与太平洋板块和雅库特微板块在北美板块下的俯冲和白令板块向西顺时针旋转有关，并被用来作为早期西藏的类比。然而，在阿拉斯加观测到的地表运动表明，它不同于任何其他汇聚的大陆板块边界。例如，太平洋-北美相对板块运动大约5厘米/年的所有辐合都被容纳在一个500公里的区域内，而超过这个区域的地表运动则被导向向南的板块边界。由于重大板内地震发生的时间跨度很长，因此了解应力如何从地幔转移到这些区域至关重要，本研究将解决这一基本问题。该项目还将支持研究生和本科生的研究。我们将进行三维有限元地球动力学建模，以研究地幔流动在驱动阿拉斯加板内表面运动和变形中的作用。这些数值实验将受到地球物理观测的约束，并具有阿拉斯加太平洋-北美扩散板块边界带的物理精确模型体积（几何形状）。这个三维几何图形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。在GPS和第四纪断层滑动数据的约束下，我们将通过比较各种模型预测的地表速度与观测到的地表变形场来区分物理上可行的模型。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)阿拉斯加州北部和中部岩石圈厚度、岩石圈流变和地幔流动对驱动板内变形的相对贡献是什么？(3)是什么力量造成了麦肯齐山脉的压缩和隆起？

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?