The viscoelastic lower crust beneath Kyushu Island, influenced by the volcanic arc, interplays with active crustal faults in this region and helps to shape local tectonics. In this study, we employed a three-dimensional viscoelastic finite element model to gain insights into the lithospheric rheology and crustal faulting kinematics, through modeling the postseismic deformation processes of the 2016 Mw 7.1 Kumamoto earthquake. Our model reveals a viscosity of 2 × 10²⁰ Pa s for the lower crust and 2 × 10¹⁹ Pa s for the upper mantle. A reduced lower crust viscosity of 2 × 10¹⁹ Pa s in the volcanic arc area is required for better reproducing the Global Positioning System data. The stress-driven afterslip decays rapidly over time and is up to 0.3 m within 5 years after the earthquake. We propose additional normal-component afterslip to better explain the complex postseismic deformation in the near field, which may be due to the interaction between the fault and volcano Aso.

中文翻译：

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九州非均质下地壳流变学及2016年Mw7.1熊本地震后滑流行为综合研究

九州岛下方的粘弹性下地壳受火山弧的影响，与该地区的活动地壳断层相互作用，有助于塑造当地的构造。在这项研究中，我们采用三维粘弹性有限元模型，通过对 2016 年 Mw 7.1 熊本地震的震后变形过程进行建模，深入了解岩石圈流变学和地壳断层运动学。我们的模型显示 下地壳的粘度为 2 × 10 ²⁰ Pa s， 上地幔的粘度为2 × 10 ¹⁹ Pa s。 为了更好地再现全球定位系统数据，需要将火山弧区域的下地壳粘度降低至 2 × 10 ¹⁹ Pa s。应力驱动的后滑随着时间的推移迅速衰减，震后 5 年内达到 0.3 m。我们提出额外的法向分量后滑以更好地解释近场中复杂的震后变形，这可能是由于断层和阿苏火山之间的相互作用造成的。