Understanding postseismic processes following the 2016 Mw 7.8 Kaikōura earthquake remains challenging due to the time-dependent afterslip over the complex forearc system including crustal faults and megathrust, and the viscoelastic relaxation of the upper mantle. How the 2016 Mw 7.8 Kaikōura crustal earthquake interacts with the megathrust has yet to be better understood. Here we have derived the first 5-year postseismic displacements from Global Positioning System (GPS) time series of 75 stations to study postseismic processes through a three-dimensional viscoelastic finite element model. The optimal steady state viscosities of the crustal shear zone, megathrust shear zone, Australian upper mantle and Pacific upper mantle in the lowest-misfit model among test models are 10¹⁸ Pa s, 4 × 10¹⁷ Pa s, 2 × 10¹⁹ Pa s and 10²⁰ Pa s, respectively. The stress-driven afterslip within the first 5 years after the earthquake is up to 80 cm over crustal faults, and up to 70 cm over the megathrust. A Kapiti slow slip sequence is probably promoted with a shorter interval by the 2016 earthquake, and is up to ∼11 cm within the first year after the earthquake. Afterslip over crustal faults and the megathrust are both required to reproduce the first-order pattern of horizontal GPS observations. Coseismic rupture over the megathrust enhances shallow megathrust afterslip, which better fit the eastward postseismic displacement of sites near the rupture area. The southern end of Hikurangi megathrust may be activated during the 2016 earthquake and undergo continuous aseismic slip after the event.

中文翻译：

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2016 年 MW 7.8 凯库拉地壳地震约束的流变结构和应力触发的巨型逆冲滑移


由于 2016 年 Mw 7.8 凯库拉地震的后滑，包括地壳断层和大逆冲，以及上地幔的粘弹性松弛，理解 2016 年 Mw 7.8 凯库拉地震后的震后过程仍然具有挑战性。2016 年 Mw 7.8 凯库拉地壳地震如何与大逆冲相互作用还有待更好地理解。在这里，我们从全球定位系统 （GPS） 的 75 个站点的时间序列中得出了第一个 5 年地震后位移，以通过三维粘弹性有限元模型研究地震后过程。在测试模型中，最低失配模型中地壳剪切带、大逆冲剪切带、澳大利亚上地幔和太平洋上地幔的最佳稳态黏度分别为 10¹⁸ Pa s、4 × 10¹⁷ Pa s、2 × 10¹⁹ Pa s 和 10²⁰ Pa s。地震后前 5 年内，地壳断层上的应力驱动余滑高达 80 厘米，大逆冲上高达 70 厘米。2016 年的地震可能促进了 Kapiti 慢滑序列的间隔更短，并且在地震后的第一年内高达 ∼11 cm。地壳断层上的余滑和大推力都是再现水平 GPS 观测的一阶模式所必需的。大逆冲的同震破裂增强了浅层大逆冲后滑，这更适合破裂区附近场地的震后东移。Hikurangi 大逆冲的南端可能在 2016 年地震期间被激活，并在事件发生后经历持续的地震滑移。