Fault behavior and lower crustal rheology inferred from the first seven years of postseismic GPS data after the 2008 Wenchuan earthquake
Fault behavior and lower crustal rheology inferred from the first seven years of postseismic GPS data after the 2008 Wenchuan earthquake
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根据2008年汶川地震后前七年的震后GPS数据推断的断层行为和下地壳流变学
DOI：
10.1016/j.epsl.2018.05.020
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发表时间：
2018-08
影响因子：
5.3
通讯作者：
Walter Thomas R.
中科院分区：
文献类型：
--
作者：
Diao Faqi;Wang Rongjiang;Wang Yuebing;Xiong Xiong;Walter Thomas R.
长期和大面积的大地测量观测可以识别大地震后不同的震后变形过程，从而可以揭示断层行为，并允许量化岩石圈流变学的复杂性。本文利用2008年汶川7. 9级地震后前7年的GPS（Global Positioning System）位移数据，研究了震后变形的相关机制。首先对两种简单的模型进行了试验，这两种模型分别考虑了震后滑移和粘弹性松弛作为震后变形的统一机制。在分析了两种机制各自的局限性和互补性后，提出了一种融合两种机制的组合模型。在以往的研究中，这主要是假设后滑和粘弹性松弛是独立的，我们的组合模型包括瞬态后滑引起的二次粘弹性松弛效应。模拟结果表明，中远场的震后变形主要是由下地壳同震应力变化的粘弹性松弛引起的，而近场的位移主要是由应力驱动的震后后滑引起的。瞬变后滑释放的地震矩相当于Mw7.4级地震，约为Mw7.9级主震释放地震矩的25%。随着1.2年的特征衰变时间，大多数后滑（类似于80%）是在前2年释放。汶川地震与芦山地震之间的空区存在轻微的余震后滑，表明该段断裂处于闭锁状态。青藏高原东部的有效下地壳粘度估计为2.0 × 10 ~（18）Pa·s，比邻近的四川盆地至少小两个数量级。这一发现与以往在该地区观测到的低地震速度和高电导率相一致，支持了青藏高原东部地壳增厚主要是由下地壳韧性流动引起的假设，对理解长期和短期地壳变形过程具有重要意义。(C)2018爱思唯尔B. V.保留所有权利。
Long-term and wide-area geodetic observations may allow identifying distinct postseismic deformation processes following large earthquakes, and thus can reveal fault behavior and permit quantifying complexities in lithospheric rheology. In this paper, the first 7 years of GPS (Global Positioning System) displacement data following the 2008 Mw7.9 Wenchuan earthquake are used to study the relevant mechanisms of postseismic deformation. Two simple models that consider either afterslip or viscoelastic relaxation as the unitary mechanism of the postseismic deformation are tested at first. After analyzing the limitations and complementarity of these two separated models, a combined model incorporating the two main mechanisms is presented. In contrast to previous studies, which mostly assume that afterslip and viscoelastic relaxation are independent, our combined model includes the secondary viscoelastic relaxation effect induced by transient afterslip. Modeling results suggest that the middle- to far-field postseismic deformation is mainly induced by viscoelastic relaxation of the coseismic stress change in the lower crust, whereas the near-field displacement is dominantly caused by stress-driven aseismic afterslip. The seismic moment released by the transient afterslip corresponds to an Mw7.4 earthquake, or 25% of that released by the Mw7.9 main shock. With a characteristic decay time of 1.2 yr, most afterslip (similar to 80%) is released in the first 2 years. Negligible aseismic afterslip is observed in the seismic gap between the Wenchuan and Lushan earthquakes, indicating the locked state of the fault within this segment. The effective lower crustal viscosity of the eastern Tibetan Plateau is estimated to be 2.0 x 10(18) Pas, at least two orders of magnitude smaller than that of the adjacent Sichuan Basin. This finding is consistent with previous observations of low seismic velocity and high electrical conductivity in this region, all of which support the assumption that the crustal thickening in the eastern Tibetan Plateau is dominantly caused by ductile lower crustal flow, with important implications for understanding both long- and short-term crustal deformation processes. (C) 2018 Elsevier B.V. All rights reserved.
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发表时间：
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