   | |
| Local date | 23 December 1738 (1738-12-23) |
|---|---|
| Magnitude | 7.6Mw[1] |
| Epicenter | 33°18′N96°36′E / 33.3°N 96.6°E /33.3; 96.6[2] |
| Fault | Xianshuihe fault system, Diangjiang Fault segment[1] |
| Type | strike-slip |
| Areas affected | China,Qinghai |
| Max. intensity | MMI VIII (Severe)[2] |
| Casualties | 261–500[2][1] |
On 23 December 1738 the province ofQinghai was struck by anearthquake with an estimated magnitude of 7.6Mw.[1] It ruptured the westernmost part of theXianshuihe fault system, the Dangjiang segment. It led to 261–500 deaths.[3][2][1]
Qinghai lies within the eastern part of theTibetan Plateau, which is a result of the ongoingcollision between theIndian Plate and theEurasian Plate. This huge area of thickenedcrust is spreading eastwards. The plateau is divided into several blocks bounded by large WNW-ESE trending left lateralstrike-slip fault zones. The Xianshuihe fault system separates theBayan Har block to the north from the Quiangtang Block to the south. The western part of the overall fault system has three main segments, from the west the Dangjiang, Yushu and Ganzi faults. The estimated slip rate on the Dangjiang segment is about 6–7 mm per year.[3]
The magnitude of this earthquake has been calculated from observations ofsurface rupture and estimates of co-seismic (during the earthquake) slip. A total of about 100 km of rupture have been mapped on the Dangjiang fault segment. A maximum left-lateral offset of 3.3 m has been measured and an average offset of 2.2 m. These measurements have been used to calculate a magnitude of Mw 7.6.[1]
Estimates of casualties for this event vary. Sources mention death tolls of 261, 336 and 500.[2][1]
The Dangjian segment shows evidence of several previous ruptures. The lack of seismic activity on this fault since 1738 means that sufficient slip has occurred to generate an earthquake of Mw 7.3.[3]