The eastward expansion of the Tibetan Plateau has resulted in different earthquake types in the eastern Tibetan Plateau, but the mechanism remains unclear. Here, we construct a three-dimensional visco-elastoplastic finite element model considering the topography to investigate the influence of fault geometry and rheological heterogeneity on stress fields. In our best-fitting model, the minimum principal stress is nearly vertical around the southern Huya fault zone, which is adjacent to the Longmen Shan fault zone, due to the significant mid-lower crust lateral rheological heterogeneity, and the thrust stress regime accounts for the reverse fault and thrust-dominated earthquakes. In this scenario, the eastward horizontal motion of the mid-lower crust is obstructed and facilitates thrust faulting, suggesting the limited eastward expansion of the Tibetan Plateau. In contrast, the northern Huya fault zone, one of the terminal branches of the East Kunlun fault, accommodates the continuous eastward extrusion of the East Kunlun fault, where the stress regime under a more homogenized crust favors the strike-slip faulting process, along with the dominant strike-slip earthquakes. Moreover, the best-fitting of stress regime explains the thrust-dominated 2008 Ms. 8.0 Wenchuan and 2013 Ms. 7.0 Lushan earthquakes on the Longmen Shan fault zone. Combining geophysical and geodetic observations and model analyses, we propose that the hybrid deformation mode in the eastern Tibetan Plateau is accommodated by upper crustal shear and thrusting deformation and mid-lower crustal thickening driven by the gravitational potential energy gradient. Our results elucidate the mechanism for differences in strong historical earthquakes and, more importantly, isolate the effect of fault geometry from those of heterogeneous viscosity on crustal deformation and stress heterogeneity in the eastern Tibetan Plateau.

中文翻译：

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青藏高原东部的应力异质性及其对当今高原扩张的影响


青藏高原东扩导致青藏高原东部发生不同类型的地震，但其机制尚不清楚。在这里，我们构建了一个考虑地形的三维粘弹塑性有限元模型，以研究断层几何形状和流变异质性对应力场的影响。在我们的最佳拟合模型中，由于显著的中下部地壳横向流变异质性，最小主应力在毗邻龙门山断裂带的南沪亚断裂带周围几乎垂直，而逆冲应力状态是逆断层和逆冲为主的地震的原因。在这种情况下，中下地壳的东向水平运动受阻，促进了逆冲断层，表明青藏高原的东向扩张有限。相比之下，沪雅北部断裂带是东昆仑断裂的末端分支之一，容纳了东昆仑断层的连续东向挤压，在更均匀的地壳下，应力状态有利于走滑断层过程，以及占主导地位的走滑地震。此外，应力状态的最佳拟合解释了龙门山断裂带上 2008 年以逆冲为主的 8.0 毫秒汶川地震和 2013 年 7.0 毫秒芦山地震。结合地球物理和大地测量观测和模型分析，提出青藏高原东部的混合形变模式由重力势能梯度驱动的上地壳剪切和逆冲变形以及中下地壳增厚所容纳。 我们的研究结果阐明了历史上强烈地震差异的机制，更重要的是，将断层几何形状与非均质粘度对青藏高原东部地壳变形和应力非均质性的影响分离出来。