Basic characteristics of co-seismic geological hazards induced by Jishishan M_s 6.2 earthquake and suggestions for their risk control

On December 18, 2023, an M_s 6.2earthquake occurred in Jishishan County, Linxia Prefecture, Gansu Province, causing a large number of geological disasters and threatening people's lives and the safety of infrastructure. After the earthquake, Gansu and Qinghai provincial governments quickly deployed hundreds of geology professionals to carried out the investigation and verification geological disasters in the earthquake area. Based on the results of the earthquake geohazard investigation and verification, this paper analyses the characteristics, control factors and development trend of the earthquake-induced geohazards, and puts forward suggestions on disaster prevention and risk mitigation measures. Till December 23, a total of 2044 geohazards have been checked, including 78 new geohazards, 88 existing geohazards with intensified deformation due to earthquake, and 1 878 existing geohazards without obvious different from before. Most of new and intensified deforming geohazards are collapse, accounting for 67.5%, followed by landslide, accounting for 31.9%. Most of new and intensified deforming geohazards are small in scale, accounting for 84.9%, followed by medium, accounting for 10.8%. Disaster mode of new and intensified deforming geohazards are mostly small collapse threatening houses and roads. The co-seismic geohazards are densely distributed along the seismic fault, and the spatial density increases with the enhancement of earthquake intensity. Data from 206 groups of accelerate-meters within 50 km from the epicenter of the National Geological Safety Monitoring Network showed that the peak acceleration of the earthquake area was 30.4～1969.7 mg. and decayed logarithm with the increase of the distance from the epicenter. In addition, the surface deformation monitoring equipment also recorded the co-seismic displacement curve of a typical landslide. Analysis shows, earthquake put a deteriorate effect to rock and soil, which decreased their integration and strength. There is a magnificent geohazard after-effect of earthquake; collapse, landslide and debris flow will be much often than before. So the authors suggest: (1) update earthquake geohazard database as soon as possible, (2) work out targeted prevention and control measures for the geohazards with large potential danger, (3) conduct comprehensive remote sensing monitoring and research of earthquake-induced geohazard mechanism, (4) improve the meteorological early warning model and threshold. By all this efforts the risk of geohazards after earthquake will be reduced and controlled.