Experts warn of geohazard risks following 7.0-magnitude quake in Xizang

Secondary geological hazards triggered by the magnitude-7.0 earthquake in Drachen county in Nagchu city, Xizang autonomous region, have been limited so far, but mid-to-long-term risks 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 geohazard sites within 50 kilometers of the epicenter 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 Center of China Geological Survey, said the occurrence of new geological hazards and the exacerbation of existing hazard sites triggered by the earthquake have been relatively limited.

Gao attributed this to the gentle plateau terrain of the area, characterized by small elevation differences and slopes, making it a region with low susceptibility 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 northwest 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 km from the epicenter, 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 the gradual deformation of the slope, suggesting that risks will continue in the aftermath of the quake.

He pointed out that earthquakes can fracture rock and ice masses, forming seepage channels that heighten the likelihood of geohazards. Additionally, some herders' settlements and cordyceps harvesting sites shift into potentially hazardous areas during the summer melt season, emphasizing the need for ongoing monitoring.

All temporary tent and prefabricated housing settlements have been established in open, flat areas, safely distanced from steep slopes. Technical personnel from the natural resources departments have carried out on-site safety evaluations and confirmed that these locations are secure.

Since the quake, 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 for all identified high-risk sites, and no casualties from secondary geohazards have been reported.

Chen Hongqi, a senior engineer at the geological disaster technical guidance center of the Ministry of Natural Resources, noted that the earthquake took place in a typical highland mountainous region, characterized by a high overall elevation but minimal variation 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 with glaciers, glacial lakes and permafrost. As the ice and snow begin to thaw next year, he stressed the importance of monitoring the stability of the glaciers and glacial lakes closely, while also taking precautions against landslides triggered by the melting of permafrost.