GPS Derived Evolution of Strain Rate in Sichuan Region

To study the impact of the Wenchuan earthquake on the stress re-distribution and corresponding seismic potential of the southeastern Tibetan Plateau and Sichuan Basin, In this study, 355 GPS sites in the Sichuan region of the southeastern Tibetan Plateau were used to calculate 4 sets (1997-2008, 2009-2011, 2011-2013, and 2013-2015) of GPS velocity fields for the period 1997-2015. These velocity results were used to deduce the corresponding dilatation, vertical rotation, and maximum shear strain rates, based on regular grid and splined interpolation methods. Subsequently, taking the 2008 Ms8.0 Wenchuan earthquake as the primary reference point and the subsequent 2013 Ms7.0 Lushan and 2014 Ms6.3 Kangding earthquakes as secondary reference points, the spatial and temporal evolution of the aforementioned strain rates and their relationships with the seismic events were analyzed. The results indicate that all types of strain rates, both in space and time, taper off along the Longmen Shan Fault with the passage of time after the Wenchuan earthquake. However, they have not yet recovered to their pre-seismic status, which implies that post-seismic relaxation of the Wenchuan earthquake is now dominated by ductile flow in the lower crust. The dilatation strain rate of the area enclosed by the Anninghe and Zemuhe faults shows an increase after the Wenchuan earthquake. This reveals the seismic hazard faced by the region and further detailed studies are required here. The location of maximum vertical rotation strain rate seems to transfer from the southern segment of the Xianshuihe fault to the Anninghe and Zemuhe faults, and even further southward to the Xiaojiang fault. However, the magnitude of this transfer is so small that detailed further studies are required to ascertain whether this transfer is realistic and the implications it bears, if so. The maximum shear strain rate indicates that the Daliang Shan sub-block and the northern segment of the Xianshuihe fault are still regions with high level seismic risk, and these should be the focus of future studies.