Abstract
The spatiotemporal deformation response of a seismogenic fault to a large earthquake is of great significance to understanding the nucleation and occurrence of the next strong earthquake. The Longmeshan fault, where the 2008 Wenchuan MS 8.0 earthquake and 2013 Lushan MS 7.0 earthquake occurred, provides an opportunity for us to study this important issue. Based on the GPS observations, we exploit the deformation response of the Southern Segment of the Longmenshan Fault (SSLMF) to the Wenchuan earthquake. The results are as follows: (1) during the co-seismic and post-seismic processes of the Wenchuan earthquake, the deformation is dominated by a continuous pattern in the SSLMF, which is different from the rupture pattern in the middle-northern segment of the Longmenshan Fault (LMF). Quantitatively, the compressive strain present between 2008 and 2013 was equal to the strain accumulation of 69 years during the interseismic period in the SSLMF. If the statistics scope is restricted to the eastern region of the Anxian-Guanxian Fault (AGF), which covers the Lushan source area (Abbr.: Eastern Region), the value is about 25 years; (2) After the Wenchuan earthquake, the strain accumulation pattern changes significantly. First, the deformation adjustment (especially the shear deformation) in the region that crosses the Maoxian-Wenchuan Fault (MWF) and Beichuan-Yingxiu Fault (BYF) (Abbr.: Western Region) is significantly greater than that in the Eastern Region. Furthermore, the crustal shortening is significant in the Eastern Region with minor adjustments in shear deformation. Second, the azimuth angles of the principal compressive strain rate in both regions show significant adjustments, which change fast in the first year of the observation period and then turn into the stable state. In general, the deformation responses of the SSLMF reveal that the Wenchuan earthquake promotes the occurrence of the Lushan earthquake. Their differences in the spatiotemporal domain can be attributed to the influence of afterslip, viscous relaxation of the lithosphere, mechanical parameters and block movement.
Highlights
The ongoing collision of the Indian and Asian plates dominates the tectonics of South and East Asia [1] and causes intense seismicity on the margins of the Tibetan Plateau [2]
We focus on exploiting the dynamic deformation of the Southern Segment of the Longmenshan Fault (SSLMF) and its major faults relating to the Wenchuan earthquake
The crustal shortening is −87.7 mm in the co-seismic period which is equal to the strain accumulation of 44 years during the interseismic period
Summary
The ongoing collision of the Indian and Asian plates dominates the tectonics of South and East Asia [1] and causes intense seismicity on the margins of the Tibetan Plateau [2]. The co-seismic rupture of Wenchuan earthquake is characterized by reverse thrusting along with dextral slip, mainly located in the central and northern section of the BYF [12,13,14,15,16]. For the correlation between the Wenchuan earthquake and the Lushan earthquake that occurred in the SSLMF, some groups suggest that Coulomb stress increases by about 5–15 kPa for the SSLMF [19,20,21,22,23,24], while near the epicenter of Lushan earthquake, it increases by about 0.9 kPa. Besides, the geodesy surveying can play an important role in the study of this important issue as it can describe the dynamic deformation process in detail and can provide powerful data sets for constraining models. The GPS campaign and continuous data are processed to get the movement results under a unified reference frame firstly, and the spatiotemporal deformation responses of SSLMF to the Wenchuan earthquake are analyzed
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