North−south−trending structure in Jilong Valley, Xizang and its effect on engineering geological safety

This paper is the result of geological survey engineering.

Objective Jilong Valley will serve as an important segment for significant engineering construction across the Himalayas in Xizang in the coming years. However, the systematic understanding of the fundamental geological characteristics of this area remains insufficient, especially the inadequate comprehension of N−S−trending structures, which may cause unexpected risks during the engineering construction.

Methods This article systematically delineates the structural characteristics of the N−S−trending faults and joints in Jilong Valley through a combination of field geological surveys, joint statistics, audio−frequency magnetotellurics, geothermal investigations, and calcite U−series dating, in order to analyze the primary engineering geological risks associated with these N−S−trending structures.

Results The N−S−trending faults in Jilong Valley are generally small in scale, with a few cutting through the high Himalayan belt, and are also basin−controlling faults in the Jilong Basin. The formation and sedimentary evolution of the Jilong Basin are controlled by four N−S−trending normal faults in its eastern boundary and interior. The presence of seismic rocks near the eastern boundary faults and a large number of syn−sedimentary faults indicate intermittent activity in the basin. The N−S−trending joints exhibit a regional penetrative distribution, and the stress analysis reveals that they are controlled by a stress field similar to that of the N−S−trending rift.

Conclusions The potential engineering geological risk sources associated with the N−S−trending structure in Jilong Valley encompass Holocene activity, as well as the control exerted over regional geothermal activity and geological disasters, including landslide, debris flows and related hazards. It is proposed that the N−S oriented structure represents one of the key focal points for geological safety risk assessment in the planning and construction of major engineering projects in Jilong Valley.