XINING; Secondary geological hazards triggered by the magnitude-7.0 earthquake in Drachen county, Nagchu city, in the Xizang autonomous region have been limited so far, but the risks over the medium to long term should not be ignored, experts from the Ministry of Natural Resources told Xinhua News Agency on Monday.
The natural resources system completed surveys of all geological hazard sites within 50 kilometres of the epicentre as of Monday. Remote-sensing analysis of 80 glacial lakes and 145 glaciers within the quake-affected zone showed minimal impact, with no signs of glacial lake outburst floods.
Gao Yanchao, a senior engineer at the Chengdu Centre of China Geological Survey, said the occurrence of new geological hazards and the worsening of existing hazard sites triggered by the earthquake had been relatively limited.
Gao attributed this to the area's gentle plateau terrain, characterised by small differences in elevation and slope, making it less susceptible to geological hazards. In addition, the fault responsible for the earthquake is a normal fault, which typically triggers fewer and smaller landslides than thrust or strike-slip faults.
On Sunday, a small landslide occurred on the north-western side of Maru township in Drachen county, blocking a local river and forming a barrier lake. The lake is now discharging naturally, with limited impact on upstream and downstream areas. Situated about 110 kilometres from the epicentre, the site and its surrounding glaciers have remained mostly stable.
However, Gao cautioned that the landslide was likely triggered by a combination of aftershocks and gradual slope deformation, suggesting that risks would persist in the aftermath of the earthquake.
He pointed out that earthquakes can fracture rock and ice masses, forming seepage channels that increase the likelihood of geological hazards. In addition, some herders' settlements and cordyceps harvesting sites move into potentially hazardous areas during the summer melt season, highlighting the need for continued monitoring.
All temporary tent and prefabricated housing settlements have been established in open, flat areas, at a safe distance from steep slopes. Technical personnel from natural resources departments have conducted on-site safety assessments and confirmed that these locations are secure.
Since the earthquake, 18 teams comprising 78 personnel, 21 vehicles and 13 drones have been deployed to the site. Their work focuses on assessing geological safety at resettlement sites, monitoring slope stability around residential areas and observing deformation at known hazard points. Preventive measures have been implemented at all identified high-risk sites, and no casualties from secondary geological hazards have been reported.
Chen Hongqi, a senior engineer at the geological disaster technical guidance centre of the Ministry of Natural Resources, noted that the earthquake occurred in a typical highland mountainous region characterised by high overall elevation but relatively small variations in terrain elevation. While surface ruptures resulting from the earthquake are expected, landslides and collapses are not predicted to be particularly severe.
Chen added that the region is widely covered by glaciers, glacial lakes and permafrost. As the ice and snow begin to thaw next year, he stressed the importance of closely monitoring the stability of glaciers and glacial lakes, while also taking precautions against landslides triggered by melting permafrost. - Xinhua
