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 × 10¹⁹ Pa s and 8 × 10¹⁶ 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.

中文翻译：

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1964年Mw9.2阿拉斯加地震的年代际粘弹性后地震形变

1964年阿拉斯加Mw9.2地震后的粘弹性地震后变形距破裂区域数千公里，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。我们优化了三维粘弹性有限元模型，以研究控制1964年地震后变形的过程。该模型包括一个弹性大陆板块和一个弹性海洋板块，一个两层粘弹性海洋上地幔以及一个均匀的粘弹性地幔楔。应力驱动的后滑由薄弱剪切带模拟。上地幔和剪切带的粘弹性松弛表现为双黏性伯格斯流变学。¹⁹  Pa s和8×10 ¹⁶  Pa s。滑移主要发生在地震发生后的前5年内，长达4 m，相当于模拟的Mw8.5地震。模型结果揭示了滑后分布与后来的慢滑事件之间的时空相关性。该模型预测，地震后约200年的表面变形将主要由断层的重新锁定来控制。对地幔楔粘度横向变化影响的进一步测试表明，距破裂区数千公里的大陆上地幔的粘度可能比俯冲带中地幔楔的粘度高约一个数量级。