Poster of the Jiaokui, China Earthquakes of 7 September 2012 - Magnitude 5.6
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.
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