关键词: 漾濞地震, 强震动特征, 空间分布, 衰减关系

Abstract: The 6.4 earthquake occurred in Yangbi County, Dali Prefecture, Yunnan Province on May 21, 2021, the National Strong-Motion Observation Network System (NSMONS) of China has obtained a batch of strong motion acceleration recordings. In this paper, 29 sets of strong motion recordings of the earthquake were processed, and the spatial distribution maps of peak ground acceleration (PGA) and peak ground velocity (PGV) were drawn. We compare the observed ground motion parameters with the calculated values of the ground motion attenuation relationships commonly used in western China and Sichuan-Tibet, and analyze the amplitude and time-frequency characteristics of the observed ground motions, and compare and analyze the spectral acceleration recorded by the near-field station with the design spectra of Code for seismic design of buildings in China. Combined with the on-site earthquake damage investigation, the main reasons for the lighter structural damage in the meizoseismal area are analyzed. The results show that the maximum horizontal PGA and PGV of the Yangbi 6.4 earthquake recorded by the station located near the epicenter, and the ground motion attenuates the slowest along the north-northwestern direction. The actual observation values on the soil site in the Yangbi earthquake are in good agreement with the calculated values of the horizontal ground motion attenuation relationships commonly used in western China and Sichuan-Tibet, while the observation values on the bedrock site are relatively small. The horizontal acceleration recording energy of 53YBX station is mainly concentrated in the period range 0.07~0.13 s. When T<0.14 s, the spectral acceleration is significantly higher than the design spectra of Code for seismic design of buildings in China, and the remarkable period of the acceleration response spectra is 0.1 s. The natural periods of the main buildings near the epicenter are 0.1~0.3 s. The above ground motion characteristics well explain that the most serious damage of this earthquake is the 1-story old wooden frame structure, while the 2~3 story brick and concrete frame structure has little damage or very light damage phenomenon.

Key words: Yangbi earthquake, strong ground motion characteristics, spatial distribution, attenuation relationship