GPS-Derived Fault Coupling of the Longmenshan Fault Associated with the 2008 Mw Wenchuan 7.9 Earthquake and Its Tectonic Implications

Abstract

Abstract:Investigating relationships between temporally-and spatially-related continental earthquakes is important for a better understanding of the crustal deformation, the mechanism of earthquake nucleation and occurrence, and the triggering effect between earthquakes. Here we utilize Global Positioning System (GPS) velocities before and after the 2008 Mw 7.9 Wenchuan earthquake to invert the fault coupling of the Longmenshan Fault (LMSF) and investigate the impact of the 2008 Mw 7.9 Wenchuan earthquake on the 2013 Mw 6.6 Lushan earthquake. The results indicate that, before the 2008 Mw 7.9 Wenchuan earthquake, fault segments were strongly coupled and locked at a depth of~18 km along the central and northern LMSF. The seismic gap between the two earthquake rupture zones was only locked at a depth < 5 km. The southern LMSF was coupled at a depth of~10 km. However, regions around the hypocenter of the 2013 Mw 6.6 Lushan earthquake were not coupled, with an average coupling coefficient~0.3. After the 2008 Mw 7.9 Wenchuan earthquake, the central and northern LMSF, including part of the seismic gap, were decoupled, with an average coupling coefficient smaller than 0.2. The southern LMSF, however, was coupled to~20 km depth. Regions around the hypocenter of the 2013 Mw 6.6 Lushan earthquake were also coupled. Moreover, by interpreting changes of the GPS velocities before and after the 2008 Mw 7.9 Wenchuan earthquake, we find that the upper crust of the eastern Tibet (i.e., the Bayan Har block), which was driven by the postseismic relaxation of the 2008 Mw 7.9 Wenchuan earthquake, thrust at an accelerating pace to the Sichuan block and result in enhanced compression and shear stress on the LMSF.

Geodetic Constraints on the Crustal Deformation along the Kunlun Fault and Its Tectonic Implications

“…Probing the crustal deformation of the Tibetan Plateau has long represented a significant research focus [3][4][5][6]. Over the last 30 years, modern geodetic observations (i.e., Global Positioning System (GPS) and interferometric synthetic aperture radar (InSAR)) provided abundant data and sufficient precision to investigate the large-scale surface deformation of the Tibetan Plateau [7][8][9][10][11][12][13][14][15]; and the interseismic, coseismic and postseismic faulting behaviors of large crustal faults in and around the Tibet, including the Main Himalaya Thrust [16,17], the Longmenshan fault system [9,18,19], the Xianshuihe-Xiaojiang fault system [20], and the Altyn Tagh-Haiyuan fault system [5,21,22]. However, relatively few studies have focused on the regions along the Kunlun fault (Figure 1), owing to insufficient coverage of GPS sites [7,9,11,12], which is the focus of this study.…”

“…Furthermore, there is a need to investigate the temporal variations in crustal deformation following the 2001 large earthquake. For instance, the fault slip rate and fault coupling along the Kunlun fault, with implications for both seismic hazards and regional tectonic [17,19]. and the 2017 Mw 6.5 Jiuzhaigou earthquake, with all of them ruptured on the boundaries of the Bayanhar block [24], leaving the (eastern) Kunlun fault to be a potentially 'seismic gap.'…”

“…Studies of Coulomb stress triggering reported that both the 2001 Mw 7.8 Kokoxili earthquake and the 2008 Mw 7.9 Wenchuan earthquakes imposed a stress load along the Maqin-Maqu segment, eastern Kunlun fault, bringing the fault segment closer to rupture [35,36]. Interpreting the seismic potential along the Kunlun fault requires interseismic fault coupling estimates, which provide information for building future large earthquakes scenarios [19,37]. Recently, Li et al [38] and Zhu et al [39] reported heterogeneous fault coupling along the Kunlun fault.…”

Competing Effects of Mountain Uplift and Landslide Erosion Over Earthquake Cycles

“…Parameter β is defined here as the spatial decay factor, with higher values meaning more widely spread landsliding. Note that equation is analogous to the law of seismic wave attenuation accounting for both geometric spreading and quality decay, and has successfully reproduced the patterns of landslides caused by the Chi‐Chi, Northridge, Finisterre, and Wenchuan earthquakes (Li, Zhang, et al, ; Meunier et al, ). Based on current studies, 1/ β ranges from around 0 (Chi‐Chi) to 5 (Northridge).…”

“…We next consider the topographic effects of multiple earthquake cycles in the eastern Tibetan Mountains. Whereas the field observations from the Wenchuan event help determine the parameters describing landscape susceptibility to landsliding and fault geometry (Li et al, ; Li, Zhang, et al, ; Liu‐Zeng et al, ; Marc, Hovius, Meunier, Gorum, et al, ; Xu et al, ), major uncertainties exist in the effective elastic thickness ( T e ~7–40 km; Densmore et al, ; Fielding & McKenzie, ; Huang et al, ; Jordan & Watts, ) and earthquake depth ( R 0 , typically within 20‐km depth in this region; Xu et al, ). To account for these uncertainties, in our modeling, we conduct Monte Carlo random sampling of T e and R 0 for each earthquake magnitude bin ( M w ~5–8 and Δ M w = 0.1) and report the medians and the 16th and 84th percentiles of Ω over earthquake magnitude for 1,000 simulations (Figure a).…”