Spatiotemporal Variation of Mantle Viscosity and the Presence of Cratonic Mantle Inferred From 8 Years of Postseismic Deformation Following the 2010 Maule, Chile, Earthquake
Spatiotemporal Variation of Mantle Viscosity and the Presence of Cratonic Mantle Inferred From 8 Years of Postseismic Deformation Following the 2010 Maule, Chile, Earthquake
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DOI：
10.1029/2018gc007645
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发表时间：
2018-09
期刊：
影响因子：
3.7
通讯作者：
Shaoyang Li;J. Bedford;M. Moreno;W. Barnhart;M. Rosenau;O. Oncken
中科院分区：
文献类型：
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作者：
Shaoyang Li;J. Bedford;M. Moreno;W. Barnhart;M. Rosenau;O. Oncken
大俯冲地震后的震后位移表现出显著的长波长和时间依赖模式，主要是由在深度广泛发生的瞬态粘弹性松弛过程引起的。然而，地球的粘性结构和随时间的变化仍然知之甚少，特别是在大地震之后的几年。在这里，我们调查的时空变化的地幔粘度近端和远端的南安第斯山脉使用8年的连续高分辨率GPS观测后，2010年在智利中南部的Mule 8.8地震。我们消除了重锁和后滑对远场GPS位移的潜在影响，并估计了可以解释三维位移的粘度。最佳粘度结构显示安第斯火山弧下的低粘度（~ 1018 Pa·s）地幔和高粘度（> 1022 Pa·s）地幔，表明瞬态粘度依赖于温度。不同时间的粘度分布的比较表明，地幔粘度随时间增加整个研究区域。一般来说，在安第斯山脉下的地幔楔中，粘度增加最快，随着与马乌莱地震震源区距离的增加而减慢。这种时间粘度演变可以指示接近破裂带的粘度的应力依赖性，而安第斯山脉以东的区域充当相对刚性的主体（即，粘性高得多的地幔）。因此，我们的结果表明，温度结构和应力状态有助于地幔粘度的时空变化。粘滞系数的不均匀时空变化似乎控制了震后变形的扩展和持续时间，从而控制了震后应力演化。
Postseismic displacements following great subduction earthquakes show significant long‐wavelength and time‐dependent patterns caused primarily by transient viscoelastic relaxation processes occurring broadly at depth. However, the Earth's viscosity structure and time‐dependent variations are still poorly understood, especially in the years immediately following a great earthquake. Here we investigate the spatiotemporal variation of mantle viscosity proximal and distal to the southern Andes using 8 years of continuous high‐resolution GPS observations following the 2010 Mw 8.8 Maule earthquake in south Central Chile. We remove the potential influences of relocking and afterslip on far‐field GPS displacements and estimate viscosities that can explain the 3‐D displacements. The optimal viscosity structure exhibits a low‐viscosity (~1018Pa s) mantle beneath the Andean volcanic arc and high‐viscosity (>1022Pa s) cratonic mantle, indicating a dependence of transient viscosity on temperature. Comparisons of the viscosity distributions at different times show that mantle viscosities increase with time throughout the study region. Viscosity increase is generally fastest in the mantle wedge beneath the Andes and slows down with increasing distance from the source region of the Maule earthquake. Such temporal viscosity evolution may indicate a stress dependence of the viscosity proximal to the rupture zone, while regions east of the Andes act as a relatively rigid body (i.e., cratonic mantle) with much higher viscosity. Our results thus suggest that both temperature structure and stress state contribute to spatiotemporal variations of the mantle viscosity. Heterogeneous spatiotemporal variations of viscosity seem to control the expansion and duration of the postseismic deformation and therefore the postseismic stress evolution.