The development characteristics of surface fracture and secondary hazards at 5·22 Ms 7.4 earthquake in Maduo County Qinghai Province

At 2:04 on May 22,2021, an earthquake of magnitude 7.4 occurred in Maduo County,Guoluo Tibetan Autonomous Prefecture,Qinghai Province. In order to find out the characteristics of the surface rupture and associated secondary hazards caused by the earthquake,the survey team conducted surveys in the earthquake-affected area by means of remote sensing interpretation and field survey. The survey results showed that an active fault zone with a width of about 75 km and a length of about 230 km was formed between the Maduo-Gande fault and the Kunlun Mountain Pass-Jiangcuo fault; 653 ground fissures,1237 sand liquefaction and sand emitting,water spraying points,97 earthquake bulges and 2 collapse pits were found on the surface. The surface fractures were generally distributed in the north west -south east direction,with horsetail-like branches from west to east; the eastern section was oblique to the Maduo-Gande fault zone at a certain angle. The overall trend of the ground fractures was highly consistent with that of the Kunlun Mountain Pass-Jiangcuo fault. As indicated by the development characteristics of the earthquake surface fracture,the seismogenic fault of the Maduo Ms7.4 earthquake was Kunlun Mountain Pass-Jiangcuo fault,and the fault surface was generally inclined to the south,which featured left strike slip. As the earthquake broke out amid extrusion towards the Qinghai Tibet Plateau by the Indian Plate,the earthquake resulted from sinistral movement at strike-slip fault in the north under the tectonic action of strong eastward extrusion by Bayan Har block. The survey results provide the local government with first-hand basic information on the earthquake disaster loss assessment and post-disaster reconstruction in the disaster area.