Azimuthal Anisotropy of the Crust and Uppermost Mantle Beneath Alaska
Azimuthal Anisotropy of the Crust and Uppermost Mantle Beneath Alaska
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DOI：
10.1029/2020jb020076
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发表时间：
2020-12-01
影响因子：
3.9
通讯作者：
Ritzwoller, M. H.
中科院分区：
文献类型：
--
作者：
Feng, L.;Liu, Chuanming;Ritzwoller, M. H.
本研究提出了一个方位各向异性剪切波速度模型的地壳和上地幔阿拉斯加，根据瑞利波相速度观测记录在500多个宽带站从10到80秒的周期。我们测试的假设，由两个均匀的各向异性层组成的模型可以解释这些测量。这种“两层模型”将方位各向异性限制在从莫霍面到200 km深度的脆性上地壳沿着与最上层地幔。该模型通过了大部分研究区域的假设检验，从中我们得出两个结论。(a)这些数据是一致的地壳方位各向异性的主要控制变形对齐的裂缝和裂缝在上地壳进行脆性变形。(b)这些数据也与阿拉斯加和周围经历垂直相干变形的最上层地幔一致。该模型解决了几个突出的特点。(1)在上地壳，快速方向主要与主要断裂的方向一致。(2)在上地幔中，在挤压构造域中，快方向与挤压方向对齐，在张性构造域中，快方向与张性方向对齐。(3)位于阿拉斯加-阿留申俯冲带附近的地幔快速方向和周围的弧后地区形成一个环形图案，是一致的地幔流动方向的最新地球动力学模型预测。最后，地幔各向异性是非常一致的SKS快速方向，但要适应SKS分裂时间，各向异性必须延伸到200公里以下的深度在大多数研究区域。
This study presents an azimuthally anisotropic shear wave velocity model of the crust and uppermost mantle beneath Alaska, based on Rayleigh wave phase speed observations from 10 to 80 s period recorded at more than 500 broadband stations. We test the hypothesis that a model composed of two homogeneous layers of anisotropy can explain these measurements. This "Two-Layer Model" confines azimuthal anisotropy to the brittle upper crust along with the uppermost mantle from the Moho to 200 km depth. This model passes the hypothesis test for most of the region of study, from which we draw two conclusions. (a) The data are consistent with crustal azimuthal anisotropy being dominantly controlled by deformationally aligned cracks and fractures in the upper crust undergoing brittle deformation. (b) The data are also consistent with the uppermost mantle beneath Alaska and surroundings experiencing vertically coherent deformation. The model resolves several prominent features. (1) In the upper crust, fast directions are principally aligned with the orientation of major faults. (2) In the upper mantle, fast directions are aligned with the compressional direction in compressional tectonic domains and with the tensional direction in tensional domains. (3) The mantle fast directions located near the Alaska-Aleutian subduction zone and the surrounding back-arc area form a toroidal pattern that is consistent with mantle flow directions predicted by recent geodynamical models. Finally, the mantle anisotropy is remarkably consistent with SKS fast directions, but to fit SKS split times, anisotropy must extend below 200 km depth across most of the study region.