1786 Kangding-Luding earthquake

Tectonic setting

Sichuan lies within the complex zone of deformation associated with the continuing collision between the India Plate and the Eurasian plate. The thickened crust of the Tibetan Plateau is spreading to the east causing the southward motion of the Sichuan-Yunnan block. The eastern side of this block is bounded by the Xianshuihe fault system, a major left lateral strike-slip fault zone. Movement on this fault zone has been responsible for many major damaging earthquakes, such as the 1981 Dawu earthquake.

Earthquake

An isoseismal map constructed for this earthquake shows that the zone of maximum shaking was elongated in a northwest–southeast direction, parallel to the trace of the Xianshuihe Fault. The magnitude of 7.5–8.0 has been estimated from the extent of the intensity VIII (Severe) zone. Remote sensing techniques, backed up by a field survey, identified a 70 km long zone of surface fault rupture thought to be associated with the earthquake. The active fault segment has been identified as the Moxi Fault.

Landslide dam

The earthquake triggered numerous landslides, one of which blocked the Dadu River, forming a temporary lake. The dam was about 70 m high, holding back an estimated water volume of about 50 e6m3. By 9 June the lake had started to flow over the dam and an aftershock on 10 June caused the dam to collapse suddenly, releasing the impounded water and devastating areas downstream. It is the second-deadliest landslide disaster on record, after the 1920 Haiyuan earthquake.

Damage

The earthquake caused widespread damage in the epicentral area. The city walls at Kangding collapsed and severe damage to many houses and government buildings caused 250 casualties. In Luding County 181 people were killed in collapsed buildings. At both Qingxi and Yuexi, parts of the city walls were destroyed and many buildings were severely damaged, causing further casualties.

The flood that resulted from the landslide dam failure reached the city of Leshan on 11 June, causing collapse of part of the city walls. Spectators who had gathered to watch the flood from the walls were thrown into the water. The destructive effects of the flood continued downstream at Yibin and Luzhou, with an estimated 100,000 people being killed overall. Local residents made a memorial tablet, describing these events, which is now kept at the Seismological Office in Luding.

References

References

1. National Geophysical Data Center/ World Data Service (NGDC/WDS): NCEI/WDS Global Significant Earthquake Database. NOAA National Centers for Environmental Information. (1972). "Significant Earthquake Information". NOAA National Centers for Environmental Information.
2. (2005). "The 1786 earthquake-triggered landslide dam and subsequent dam-break flood on the Dadu River, southwestern China". Geomorphology.
3. "Seismic hazard of the North-South Seismic Zone in China". First European Conference on Earthquake Engineering and Seismology.
4. Zhou, H.. (1983). "Source processes of large earthquakes along the Xianshuihe Fault in southwestern China". Bulletin of the Seismological Society of America.
5. (24–26 June 2002). "Landslides: Proceedings of the First European Conference on Landslides". A.A. Balkema Publishers.