May 21, 2021 Earthquake: Yangbi, Yongping, Yunnan Province, China

Tectonic Summary

The May 21, 2021 M6.1 earthquake in south-central China near the cities of Dali and Lijiang occurred as the result of strike-slip faulting at relatively shallow depths. The earthquake occurred on either a southeast striking right-lateral fault, or on a southwest striking left-lateral fault. The regional geologic context is consistent with right-lateral strike slip motion. The earthquake occurred within a broad zone of strike-slip faults that demark, in part, the boundary between the Eurasia and India plates. These seismically active strike-slip faults and smaller faults in their vicinity produce frequent, yet often moderate (smaller than M7.0) earthquakes. In the past century, 24 earthquakes of M6.0 or greater have occurred within 250 km of the May 21 earthquake, with one of those earthquakes (May 29, 1976) being M7.0. The most recent moderate magnitude earthquake in this region occurred on August 30, 2008 (M6.0). The August 2008 M6.0 earthquake led to extensive regional damage and at least 43 fatalities. Other earthquakes in this region with similar magnitudes have led to tens to hundreds of fatalities. The steep regional topography can also lead to earthquake shaking-induced landslides and liquefaction (ground failure).

Generally, strike-slip faults and earthquakes in south-central China result from the southeastward motion of the Earth's crust that is driven by the collision of the Indian and Eurasian continental plates beneath the Himalaya Mountains and the Tibetan Plateau farther to the west. The Tibetan Plateau exhibits east-west oriented extension, as evidenced by faults, earthquake normal faulting mechanisms, and geodetic observations. The extension of the Tibetan Plateau is further accommodated by extrusion of crustal material southward in south-central China along the strike-slip faults where the May 21 earthquake occurred.

(all above from ref #1053)

The quakes, including a 6.4-magnitude one, has claimed three lives and injured 28 others by early Saturday. Two deaths were reported in Yangbi county and one in Yongping county [...] As of 3 am Saturday, the expressway, which was blocked by landslides and falling rocks, had been cleared, opening way for rescue vehicles, according to the local transportation department. (ref #12940)

Total damages USD 49 million (reference #1250)