Damage characteristics and cause of Ms 6.4 earthquake in Yangbi, Yunnan Province on May 21, 2021

Yangbi area, located in the southeast margin of Qinghai-Tibet Plateau, is characterized by complex geological structure, which leads to the occurrence and behavior of earthquakes controlled by many factors.In order to clarify the intensity distribution characteristics, damage characteristics and influencing factors of Yangbi Ms 6.4 earthquake, the research work was carried out by means of interview, field investigation and statistical analysis.The results show that the intensity of the Yangbi Ms 6.4 earthquake in the extreme earthquake area can reach Ⅷ, and the major axis of the isoseismal ellipse deflects NW, which is consistent with the relocation of the earthquake sequence and the solution of focal mechanism, indicating that the seismogenic fault is a Caoping fault with NW-SE strike and SW dip and right-handed strike-slip property.Among them, the Ⅷ degree area deflects by about 30 at the southeast, which is affected by the tensile fracture effect at the tail end of the fault.The isoseismal line in the Ⅶ degree area is prominent in the opposite direction to the fracture tendency, and the overall range of intensity is much smaller than the previous survey results, which may be related to the difference of topography, physical properties on both sides of the fault, basin focusing effect and edge effect of seismic waves, as well as the influence of the intensity amplification effect caused by soft valley sediments, high groundwater level in the valley basin and high altitude of Cangshan Mountain.The earthquake damages developed in the above-mentioned intensity areas are mainly the destruction of houses and seismic geological disasters, in which the destruction of houses is more serious and the scale of seismic geological disasters is smaller.The types of geological disasters are mainly landslides and ground fissures.After investigation and analysis, it is found that they do not show the characteristics of concentrated development along faults or extreme earthquake areas, which are more affected by factors such as topography, surface media and groundwater.