As of 8?AM on Tuesday, 174 aftershocks were recorded in Zhongba County in southwestern Tibet, following a 6.8-magnitude earthquake late on Monday, the Tibet Autonomous Regional Earthquake Bureau said.

No casualties have been reported from any of these quakes.

Of the 174 aftershocks, only two were at or above 5.0 magnitude: one 5.2-magnitude quake at 9:29?PM on Monday and a 5.0-magnitude quake at 3:13?AM on Tuesday, said the regional quake bureau.

The 6.8-magnitude quake took place at 9:22 p.m. on Monday, with the epicenter being fixed about 10 km underground at 31 degrees north latitude and 83.6 degrees east longitude, according to the China Earthquake Networks Center.

Gerze and Coqen counties in Ali prefecture also felt the quake. But the county seats sustained no damage, said the regional earthquake bureau.

A Zhongba county government worker said the quake was strongly felt in some townships and cracks had appeared in some buildings.

An official from the regional flood control and drought relief headquarters said a local hydropower station was slightly damaged in the 6.8-magnitude quake. The damage included the flood control levee shifting 5 m from its original location and cracks in workshop walls.

The plant maintained normal power generation.

Zhu Jiang, the Zhongba County Communist Party head, said they had contacted all 13 townships but received no reports of fatalities.

The official said the county sent staff to townships and villages to assess the situation and carry out relief work.

Zhu Quan, the regional earthquake bureau chief, said the tremor would have no effect on the Qinghai-Tibet railway, which is several hundred kilometers from the quake zone.

Zhongba, in the west of Xigaze with a population of 18,000 and covering 43,594 square kilometers, is located in an area with frequent quakes. It is 4,700 meters above sea level.

A 6.7-magnitude quake occurred in the same area in 2004, followed by a 6.5-magnitude quake on April 8, 2005, but neither caused casualties, according to the regional earthquake bureau.

(Xinhua News Agency August 26, 2008)