A 6.7 ( 6.8) earthquake struck Luding County in Sichuan province, China on 5 September 2022 at 12:52:19 local time. The epicenter was located from Chengdu, or southeast of Kangding. Ninety-three people died, 424 were injured and 24 remained missing. More than 13,000 homes and other infrastructure were damaged or destroyed. It was the largest earthquake to strike the province since 2017.
Tectonic setting
Sichuan is situated in a complex zone of faulting created by the continued collision of the Indian Plate with the Eurasian Plate. As Himalayan underthrusting continues, the crust of the Eurasian Plate is deformed and uplifted to form the Tibetan Plateau. Instead of thrust faulting to its south, the Tibetan Plateau accommodates deformation through strike-slip escape tectonics. Large amounts of strike-slip motion are accommodated through major faults and their splays along the plateau, such as the Altyn Tagh Fault, Kunlun Fault, Haiyuan Fault, and Xianshuihe fault systems. Left-lateral strike-slip motion squeezes the crustal blocks of the Tibetan Plateau outwards, forcing it to move eastwards. Meanwhile, the strike-slip motion also results in an east-west extension of the plateau, causing normal faults to break within the thickened crust.
On a continental scale, the seismicity of central and eastern Asia is broadly the result of the northward convergence of the Indian Plate against the Eurasian Plate. The convergence of the two plates is accommodated by the uplift of the Asian highlands and by the motion of crustal material to the east away from the uplifted Tibetan Plateau. In the past 20 years, 25 other earthquakes M5.0+ have occurred within of the 5 September 2022, event. Most of this seismicity is related to aftershocks of previous destructive earthquakes in the western margin of the Sichuan Basin. This event is southwest of a cluster of seismicity following an M6.6 earthquake on 20 April 2013 that resulted in 196 fatalities. An M7.9 earthquake on 12 May 2008 occurred near the September event and resulted in over 87,000 fatalities, making it one of the most destructive earthquakes in recent history.
Earthquake
The earthquake measured 6.8 on the surface-wave magnitude scale (); on the moment magnitude scale (), it measured 6.7. According to the United States Geological Survey, the earthquake was a result of shallow strike-slip faulting on the western margin of the Sichuan Basin. The earthquake occurred on either an NNW–SSE striking, steep WSW dipping left-lateral fault, or a WSW–ENE striking, near vertical dipping right-lateral fault. The location and sense of motion are consistent with movement on or near the left-lateral Xianshuihe fault system, which runs for . Many faults in this region are related to the convergence of crustal material slowly moving from the high Tibetan Plateau to the west, against the strong crust underlying the Sichuan Basin and southeastern China.
Experts from the Sichuan Earthquake Administration said the earthquake occurred near the Moxi Fault, a segment of the southeastern Xianshuihe fault zone. They added that it is unlikely that a larger earthquake will occur near the epicenter, but aftershocks would persist. The Xianshuihe fault zone is a large active left-lateral fault that defines the margin between the Bayan Har and the Sichuan-Yunnan blocks. It produced destructive earthquakes in 1786 (M7.75), 1816 (M7.5), 1850 (7.5), 1893 (M7.0), 1904 (M7.0), 1923 (M7.3), 1948 (7.3), 1955 (M7.5), 1973 (M7.6), 1981 (M6.9) and 2014 (M6.3). No M7.0+ earthquakes have been recorded along the Moxi Fault since 1786. It runs north–south between Kangding and Shimian. The fault was considered a potential source for large earthquakes due to the absence of any since 1786.
A length along a NNW–SSE striking fault corresponded to the rupture with a maximum slip of . Most of the seismic moment was released within the first 10 seconds of the rupture initiating, which then propagated to the southwest. At least 2,715 aftershocks were recorded until 12 September, at depths of and distributed along a north–northwest trend. On 22 October, a 5.3 aftershock was recorded near Moxi Town. It had an epicenter away from the mainshock. By 22 October, 6,486 aftershocks had been recorded. A 5.5 aftershock occurred with an epicenter from that of the mainshock's on 26 January.
Using broadband seismic networks, the total rupture duration was calculated at 16 seconds, releasing 4.1×1014 J of energy. An energy magnitude () of 6.8 was determined. As the value is larger than (6.7), the earthquake likely released seismic energy in an efficient manner. It may have resulted in more extreme ground shaking compared to earthquakes with similar values.