Stress changes associated with the significant first subevent of the 2008 Wenchuan earthquake and implications for the rupture behavior transition

IF 2.1 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Journal of Geodynamics Pub Date : 2021-07-01 DOI:10.1016/j.jog.2021.101859
Yujiang Li , Lianwang Chen , Hong Li , Yuanzhong Lu
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Abstract

The rupture process of the Wenchuan earthquake demonstrated a transition from thrust-dominated slip to northeastward strike-slip motion along the Longmen Shan Fault Zone. The initial stress has been reported as playing a critical role in this process; however, the stress changes, especially those caused by the significant first subevent of the Wenchuan earthquake are not well understood. Here, we employ a three-dimensional finite element model of the Sichuan-Yunnan region to analyze the stress change caused by the significant first subevent and explore the possible influence on the following ruptures. The results indicate that the auxiliary maximum principal compressive stress (SH) associated with the significant first subevent was horizontal and that the auxiliary stress regime was SH>Sh>Sv, supporting the ongoing regional thrust motion near the southwestern segment of the rupture plane. However, in the northeastern segment, the auxiliary stress regime transitioned to SH>Sv>Sh, demonstrating that the stress changes promoted the transition of the rupture behavior from predominantly thrust motion in the southwest to right-lateral strike-slip motion in the northeastern segment, which was also supported by the dominant shear stress change and the subtle normal stress change along the fault plane in the northeastern segment. In addition, our modeled results also indicate that the orientation of the maximum principal compressive stress changed from SEE to northeastward NEE along the strike of Longmen Shan Fault Zone. This anticlockwise rotation hastened the rupture behavior transition, suggesting that both the initial stress and the stress changes associated with the first subevent jointly controlled the following northeastward rupture of the Mw7.9 Wenchuan earthquake.

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2008年汶川地震第一次级地震的应力变化及其对破裂行为转变的影响
汶川地震的破裂过程表现为沿龙门山断裂带由逆冲主导滑向东北方向走滑运动的转变。据报道,初始应力在这一过程中起着关键作用;然而,应力变化,特别是由汶川地震的第一次次级地震引起的应力变化尚未得到很好的理解。本文采用川滇地区三维有限元模型,分析了第一次子事件引起的应力变化,并探讨了其对后续断裂的可能影响。结果表明,与第一次显著子事件相关的辅助最大主压应力(SH)是水平的,辅助应力区为SH> SH> Sv,支持断裂面西南段附近持续的区域逆冲运动。而在东北段,辅助应力状态转变为Sh >Sv>Sh,说明应力变化促进了断裂行为由西南主导逆冲运动向东北段右侧走滑运动转变,并得到了东北段主导剪应力变化和沿断裂面微妙的正应力变化的支持。此外,模拟结果还表明,沿龙门山断裂带走向,最大主压应力方向由东西向向东北东东方向转变。这种逆时针旋转加速了断裂行为的转变,表明初始应力和与第一次子事件相关的应力变化共同控制了随后的汶川7.9级地震东北向断裂。
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来源期刊
Journal of Geodynamics
Journal of Geodynamics 地学-地球化学与地球物理
CiteScore
4.60
自引率
0.00%
发文量
21
审稿时长
6-12 weeks
期刊介绍: The Journal of Geodynamics is an international and interdisciplinary forum for the publication of results and discussions of solid earth research in geodetic, geophysical, geological and geochemical geodynamics, with special emphasis on the large scale processes involved.
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