The results of the on-site investigation of the 6.9 magnitude earthquake in Qinghai Menyuan were released

After the 6.9-magnitude earthquake in Menyuan, Qinghai, Lanzhou University and the Science and Technology Department of Gansu Province, together with the Lanzhou Earthquake Research Institute of the China Earthquake Administration, Sun Yat-sen University and the Qinghai Provincial Earthquake Bureau, rushed to the earthquake area on the same day to conduct on-site inspections of the surface rupture zone, seismic structure and earthquake damage of the earthquake, and released the phased results on January 18.

According to Professor Yuan Daoyang of the College of Geological Sciences and Mineral Resources of Lanzhou University, after on-site investigation, it was found that the length of the surface rupture zone of the 6.9 earthquake exceeded 22 kilometers, which was mainly composed of two rupture zones. Among them, the main rupture zone on the north side is distributed along the western section of the Lenglongling fault in the middle section of the Guangyi Haiyuan Fault Zone, roughly passing through the Sulphur Valley Brain Watershed, the Lanxin High-speed Railway Girder Tunnel, the Daogou to the West Branch Ditch of the Lower Daquan Ditch from east to west, and the overall direction is NWW (North West West), with a length of more than 17 kilometers, and the maximum horizontal fault measured in the field is about 2.1-2.3 meters, gradually decaying to both ends; the secondary rupture zone on the south side is distributed on the local section of the East Section of the Tole Mountain Fault in the middle and west section of the Guangyi Haiyuan Fault Zone, and is roughly distributed along the line of DaxiGou and Lion Cliff. Towards near EW (east-west), with a length of about 5 km and a horizontal dislocation of about 0.5-1 m, the secondary branch rupture of the left diagonal column of the western section of the main rupture zone should be the end effect of the westward rupture of the earthquake.

Yuan Daoyang said that the surface rupture nature of the 6.9 magnitude earthquake is mainly left-handed slippage, and the secondary rupture section is mainly a combination of left-handed left-order tensioning or right-order extrusion. It forms a typical faulty landform of the slip activity fault, such as the left-handed fault groove, the riverbed and the barbed wire fence in the pastoral area, the road subgrade, the rut, the sidewalk, the animal footprint, etc., and also forms the extrusion ridge, tension crack, fault steep ridge, etc., and its deformation style is rich and typical.

"In addition to damage to house buildings, this earthquake also caused a variety of secondary disasters such as local slope collapse, rolling stones, cracking of frozen soil and deformation of ice arches." Xie Hong, an associate researcher at the Lanzhou Institute of the China Earthquake Administration, told reporters. Xie Hong said that the earthquake also caused the Bridge deck of the Lanxin High-Speed Railway Girder Tunnel and the Sulfur Gully Bridge that crossed the Lenglongling Fault to be damaged and stopped, and some road subgrades were deformed.

After the earthquake, the problem of deformation of the bridge deck of the Lanxin high-speed railway attracted attention, and the inspection team preliminarily believed after the on-site investigation around the piers that since the railway bridge across the sulfur ditch was located in the north plate of the surface rupture zone of the earthquake, the north plate mainly moved westward. Due to the different distances between different piers from the seismic surface fracture zone, the instantaneous westward vibration amplitude may be different, resulting in different deformation amplitudes of beams and rails between different piers, resulting in the illusion of right-handed misalignment, which is actually more likely to be a deformation effect of unsynchronized westward vibration.

It is understood that at present, the on-site emergency investigation work is basically over, and the data collation, drawing processing and comprehensive analysis related to this scientific expedition are underway. (Science and Technology Daily reporter Jie Manbin)

Source: Science and Technology Daily