The 1931 Fuyun earthquake (富蕴地震) occurred on August 10 at 21:18 UTC. The epicenter was near Fuyun County of northern Xinjiang, China. It had a moment magnitude (Mw ) of 8.0 and had a surface rupture of 171 km with a maximum horizontal displacement of 14 m along the Koktokay-Ertai fault zone (可可托海-二台断裂带). The Koktokay-Ertai fault has a slip rate of 4±2 mm per year. The rupture of this earthquake was caused by right-lateral strike-slip movement with normal component. The rupture is well preserved and becomes one of the main features of the Koktokay National Geopark (可可托海国家地质公园) located in Koktokay.