Decadal Viscoelastic Postseismic Deformation of the 1964 Mw9.2 Alaska Earthquake
Decadal Viscoelastic Postseismic Deformation of the 1964 Mw9.2 Alaska Earthquake
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1964年Mw9.2阿拉斯加地震的年代际粘弹性震后变形
DOI：
10.1029/2020jb019649
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发表时间：
2020-09-01
影响因子：
3.9
通讯作者：
Freymueller, Jeffrey T.
中科院分区：
文献类型：
--
作者：
Huang, Kejing;Hu, Yan;Freymueller, Jeffrey T.
1964年阿拉斯加9.2级地震后的粘弹性震后形变从破裂区域延伸数千公里，持续数十年，为更好地了解阿拉斯加俯冲带的三维流变特性提供了独特的机会。我们优化了一个三维粘弹性有限元模型，以研究控制1964年地震震后变形的过程。该模型包括一个弹性大陆板块和一个弹性海洋板块、一个双层粘弹性大洋上地幔和一个均匀粘弹性地幔楔体。应力驱动的余滑用薄的弱剪切带模拟。上地幔和剪切带的粘弹性松弛表现为双粘性Burgers流变学。模型确定地幔楔体和剪切带的粘度分别为3×10(19)PaS和8×10(16)PaS。余滑主要发生在地震后的头5年内，长达4米，相当于一次8.5米的模拟地震。模型结果揭示了余滑分布与后期慢滑事件之间的时空相关性。该模型预测，震后约200年的地表形变将主要受断层再闭锁的控制。进一步的地幔楔体粘度横向变化影响试验表明，距断裂区数千公里的大陆上地幔的粘度可能比俯冲带中的地幔楔体的粘度高一个数量级。
Viscoelastic postseismic deformation after the 1964 Mw9.2 Alaska earthquake extends thousands of kilometers from the rupture region and lasts for decades, providing unique opportunities to better understand the three-dimensional rheological properties of the Alaska subduction zone. We have optimized a three-dimensional viscoelastic finite element model to study processes that control the postseismic deformation of the 1964 event. The model includes an elastic continental plate and an elastic oceanic plate, a two-layered viscoelastic oceanic upper mantle, and a uniform viscoelastic mantle wedge. Stress-driven afterslip is simulated by a thin weak shear zone. The viscoelastic relaxation of the upper mantle and shear zone is represented by the bi-viscous Burgers rheology. The model has determined the viscosities of the mantle wedge and shear zone to be 3 x 10(19) Pa s and 8 x 10(16) Pa s, respectively. The afterslip takes place mostly within the first 5 years after the earthquake and is up to 4 m, equivalent to a modeled earthquake of Mw8.5. Model results reveal a spatial and temporal correlation between the afterslip distribution and later slow slip events. The model predicts that the surface deformation about 200 years after the earthquake will be controlled mostly by the relocking of the fault. Further tests on the impact of lateral variation in the mantle wedge viscosity indicate that the viscosity in the continental upper mantle thousands of kilometers from the rupture area may be about an order of magnitude higher than that of the mantle wedge in the subduction zone.