September 7, 2012 Earthquake: Yiliang, Zhaotong, Yunnan Province, China

Felt Report

At least 81 people killed, 821 injured, 37,000 buildings destroyed, 133,000 houses damaged and landslides and power outages occurred in the epicentral area. Felt strongly at Zhaotong and (II) at Chengdu.

Tectonic Summary

The two September 7, 2012 earthquakes to the SSE of Jiaokui, China (03:19 UTC; 04:16 UTC) occurred as a result of oblique-reverse faulting within the shallow crust of the Eurasia plate. The moment tensors of these earthquakes, describing their faulting mechanisms, are consistent with slip on either SW-NE trending faults with moderate dips towards the northwest, or approximately N-S trending faults steeply dipping towards the east. The events occurred in the boundary region between the South China Block and the southeastern Tibetan Plateau to the west. The principal boundary is commonly taken to be the well-expressed Xiaojiang fault system; the September 7 earthquakes occurred along faults approximately 100 km further east. Further work is necessary to identify the causative faults for these earthquakes, though active structures have been mapped in the surrounding region.

Many parts of southeastern China have a history of damaging earthquakes, and the area surrounding the September 7, 2012 earthquakes is no exception. 30 earthquakes of M5 or above have occurred within 100 km of these events over the past 40 years. Three had magnitudes greater than 5.5, and each of these caused damage and fatalities. The largest, a M 6.8 earthquake 80 km to the north of the September 7 events in May 1974, caused over 1500 fatalities. A M 5.6 earthquake just 30 km to the south of these events also caused several fatalities in November 2003. While the September 7, 2012 events are not considered large earthquakes, the high population density and high vulnerability of structures in the region make such shallow earthquakes particularly damaging.

(above from reference #1053)

Officials from the local seismological authority in Yunnan Province said Sunday massive losses caused by recent earthquakes were mainly due to the special topography of the area, and rejected speculation that it should be attributed to human error such as jerry-built buildings. The death toll in a series of earthquakes in Yiliang county, Zhaotong, in Southwest China's Yunnan, increased to 81 on Saturday after a 2-year-old boy failed to survive serious injuries received in a 3.7-magnitude aftershock on Saturday, according to the Zhaotong city government. Another 821 people were injured in the quakes, after the first one of 5.6 magnitude hit an area near Yiliang at 11:19 am on Friday, and more than 200,000 people have been relocated, said a press release sent to the Global Times Sunday. The disaster caused about 4 billion yuan ($631 million) in direct losses. (reference #9976)

2012, July 9. 81 killed, 744,821 affected, $1000 million damage. (reference #1250)