Abstract:

After field geological survey on the scale of 1∶2,000 and comparative measurement in different seasons, four types of surface fractures, seismic fractures, fault fracturs, permafrost fractures and ice fractures, were discovered along the Golmud-Lhasa railway across the Tibetan Plateau after engineering geological mapping on the scale of 1∶2,000. Seismic fracture zones are consisted of and accompanied by seismic fractures, seismic scarps, pressure ridges, sag-ponds and pull-apart basins.Typical examples include the Xidatan palaeo-seismic fracture zone, seismic fracture zone of the Kunlun Ms 8.1 earthquake occurred in November 14,2001, the south Hohxil palaeo-seismic fracture zone, seismic fracture zone of the Bengcuo Ms 8.0 earthquake occurred in 1951 and seismic fracture zones along normal fault in east of the Nyainqentanglha Mts.caused by Jiuzila Ms 7.5 earthquake occurred in 1952 and Yangbajain Ms 8.0 earthquake occurred in 1411.Fault fracture zones often form in active fault zones and appear as long extension with stable trending, they are jointly controlled by active faulting, underground water concentration and freezing expansion.Permafrost fracture and ice fracture are both the result of freezing expansion without evident relation to tectonic deformation and regional structures. Seismic fracture, fault fracture and permafrost fracture all gave negative effects on engineering construction and formed geological hazards at many localities along the Golmud-Lhasa highway and railway. Ice fractures formed in freezing rivers and lakes and on the top of pingos have not shown any hazard effect on engineering constructions up to the present.

Key words: surface fracture, active fault, freezing-thawing deformation, geological hazard, Golmud-Lhasa railway