Hazards posed by active major faults along the Golmud–Lhasa railway route, Tibetan Plateau, China

Abstract

The high number of active faults in the vicinity of the planned 1142-km-long Golmud–Lhasa railway line across the Tibetan Plateau poses a great hazard to the railway. This is not only from periodic fault offsets, measured in meters, and the effects from large to great earthquakes, but also from significant ground displacement from annual fault-controlled freeze–thaw features in the areas of permafrost. Twenty-seven major active faults in eight seismic zones were revealed by detailed mapping along the railway route. Most of the faults have strike–slip movement, with those in the northern plateau being sinistral and those in the southern part dextral, although some normal faults are associated with graben and pull-apart basins. Many faults have produced earthquakes in the Ms 6.0–8.0 range, and the high slip rates, of 4–15 mm/year, found on others indicate a potentially similar range. The Ms 8.1 Central Kunlun earthquake of 2001 had an associated left-lateral displacement of 7–14 m near the epicenter and a 4–5 m offset where the railway line was cut. Such earthquakes, which can cause serious damage to the railway and associated facilities, occur relatively frequently. Tectonic creep along the faults between earthquakes also causes problems and has destroyed a section of highway adjacent to the railway line. The Tibetan Plateau has an average elevation of 4500 m and the higher, northern part has permafrost with the usual problems of ground deformation from freeze–thaw effects and mass movement and the need to thermally isolate structures. Active faults in this region affect groundwater flow and thus control unusual permafrost features. Linear zones of ground deformation from freezing and thawing and extensive broad belts of ground fractures occur along faults to damage structures. Most importantly, the faults were found to control zones of pingos. Many of these ice-cored domes rise in the late fall and winter only to be drained in the spring by linear alignments of springs; some pingos occasionally migrate along the faults with time. The resulting deformation has bent pipelines and ruined roadways along the route. Overcoming these hazards to provide for the safety of passengers and maintain the integrity of the railway is a great challenge. Building in regions of severe climate and permafrost is always difficult and the problems associated with the many active faults here make for unusual conditions. No other large construction will be subjected to such extreme effects from direct and indirect fault movement, and the Engineering Geology community will learn much from the experience gained here.