Coulomb stress evolution along Xianshuihe–Xiaojiang Fault System since 1713 and its interaction with Wenchuan earthquake, May 12, 2008

Abstract

The curved left-lateral strike-slip Xianshuihe-Xiaojiang fault system (XXFS) in southwestern China extends at least 1400 km in the eastern margin of the Tibetan Plateau. Fieldworks confirm that the XXFS is one of the longest and most seismically active faults in China. The strain released by the slip motion on the XXFS is related to the convergence between the Indian and Eurasian plates. The entire fault system has experienced at least 35 earthquakes of M>6 in the recent 300 years and almost all segments of the system have been the locus of major historical earthquakes. Since the XXFS region is heavily populated (over 50 million people), understanding the migration of the large earthquakes in space and time is of crucial importance for the seismic hazard assessment in this region. We analyze a sequence of 25 earthquakes (M≥6.5) that occurred along the XXFS since 1713, and investigate their influence on the 2008 Mw7.9 Wenchuan earthquake occurred on the adjacent Longmenshan Fault. In our analysis, the relevant parameters for the earth crust are constrained by seismic studies. The locations and geometries of the earthquake faults as well as the rupture distributions are taken from field observations and seismological studies. Results from the Coulomb failure stress modeling indicate significant interactions among the earthquakes. After the 1713 earthquake, 19 out of 24 earthquakes occurred in the positive stress zone of the preceding earthquakes. The other 5 earthquakes located in the area without significant stress changes induced by the preceding events. In particular, we can identify 4 visible earthquake gaps with increasing seismic hazard along the XXFS, consistent with the findings from the paleo-seismological studies. The seismic activity and tectonic motion on the XXFS reduced the Coulomb stress accumulation at the hypocenter of 2008 Mw 7.9 Wenchuan earthquake, implying that the Wenchuan earthquake might not be triggered directly by the seismic activities on the XXFS. On the other hand, the Coulomb failure stress induced by the Wenchuan earthquake has increased in a region of 125-km-long segment of the XXFS, northwest of Kangding City.

Stressing Rates and Seismicity on the Major Faults in Eastern Tibetan Plateau

“…We calculate the Coulomb stress changes on faults using a range of effective friction coefficients from 0 to 0.8 and find that the general pattern of Coulomb stress changes does not change with the different effective friction coefficients. Hence, we show in most cases the results using an effective friction coefficient of 0.4, which is the commonly used value in studies of Coulomb stress changes (e.g., Freed et al, ; King et al, ; Luo & Liu, ; Shan et al, ). The results show that the Coulomb stress on northern and central Longmenshan fault, where the 2008 M w 7.9 Wenchuan earthquake occurred, was reduced by the preceding earthquakes on the Xianshuihe, Anninghe, and Zemuhe faults and the 1933 M 7.5 Diexi earthquake on the nearby Minjiang fault (Figures a and b).…”

“…However, estimating stressing rates on these faults is challenging. Some studies apply the deep‐slip or back‐slip models constrained by Global Positioning System (GPS) data to calculate stressing rates on faults (Loveless & Meade, ; Shan et al, ; Smith & Sandwell, ), but these studies have to assume a lithospheric deformation mechanism and rheology. Other studies directly use GPS data to calculate strain rates and apply the results to estimate stressing rates on faults by elastic Hooke's law (Freed et al, ; Jiang et al, ; Wang, Liu, et al, ; Wang, Wang, et al, ), but the GPS sites are usually sparse near fault zones and the near‐fault strain rates need to be extrapolated, leading to large uncertainty on the resulting stressing rates.…”

Crustal Deformation in the India‐Eurasia Collision Zone From 25 Years of GPS Measurements

“…Third, high strain rates occur along the whole Xianshuihe‐Xiaojiang fault system, where previous studies have identified four seismic gaps (Shan et al, ; Wen et al, ). The recent 2014 M w 5.9 Kangding earthquake struck the Kangding‐Daofu gap; however, the released strain energy was far less than that accumulated (Jiang et al, ).…”

Coseismic and postseismic deformation associated with the 2016 Mw 7.8 Kaikoura earthquake, New Zealand: fault movement investigation and seismic hazard analysis

“…The numerical results indicate that the amplitudes of ΔCFS vary depending on the different friction coefficients, but the spatial distribution patterns of Coulomb stress changes are highly consistent (Additional file 1: Figure S5). Therefore, we considered an empirical and moderate effective coefficient of friction of 0.4 (Shan et al 2013a, b;Xiong et al 2010Xiong et al , 2017 for our ΔCFS calculation and discussion.…”

“…The Coulomb failure criterion describes the fracture behavior of rock considering both shear and normal stress changes on a predefined surface (King et al 1994;Liu et al 2017;Shan et al 2013a;Stein 2000): where ΔCFS is the Coulomb failure stress (CFS) change; Δτ s and Δσ n are the shear stress and normal stress changes on the receiver fault, respectively; and µ ′ is the equivalent friction coefficient. Based on the seismic stress triggering theory, positive (increased) CFS change causes regional faults to be closer to failure and leads to seismic activity, whereas faults in stress shadow areas are further away from failure, reducing the possibility of seismicity (Freed 2005;Shan et al 2015).…”