Study On Double Stationary Ground Motion Characteristics Of Wenchuan Earthquake

The 2008 Wenchuan earthquake caused a huge number of personal injury and death,property damage and natural environment destruction.It is the common goal of the researchers to analyze the causes of the serious structural damage caused by the earthquake,improve and perfect the existing seismic design concept and method,improve the seismic capacity of the engineering structure and reduce the earthquake damage in the future.The analysis of the focal mechanism of Wenchuan earthquake shows that the earthquake was caused by the joint rupture of Yingxiu-Beichuan fault,Guanxian-Jiangyou fault and so on.The seismic damage investigation found that the damage at the corner of the fault surface rupture and the superposition of each other were relatively serious.The large earthquakes formed by the rupture of multiple fault zones contain two or more peaks in the acceleration recording time history.In order to reveal the spatial distribution law of ground motion corresponding to the multi-fault rupture model of the large earthquake,the single and double stationary ground motion of the Wenchuan earthquake records were identified by the phase identification method.The two-stationary seismic records were distinguished from the front and the back.By comparative analyzing the attenuation characteristics of the seismic amplitude,spectrum and duration of the whole,single and double stationary ground motions with the fault distance,further understanding of the characteristics of the amplitude,spectrum and duration of the two-stationary ground motion was provided,which provides a theoretical basis and a practical model for the simulation of the near-field strong ground motion.The main work and the results are as follows:(1)76 groups of Wenchuan earthquake records were selected for analysis.After the baseline correction of 228 records,40 sets of double-stationary seismic records and 36 sets of single-stationary seismic records were distinguished by using the phase identification method,and according to the waveform characteristics,the two-stationary seismic records was divided into two parts,namely front and rear.(2)By analyzing the fitting goodness and residual graph of the peak acceleration attenuation relation,the attenuation model of the ground motion parameters used in this study was determined.(3)The nonlinear least square method was used to fit the attenuation relationship between the peak acceleration and the peak velocity of the whole,single and double stationary ground motions.The correlation between peak acceleration and peakvelocity was discussed.The results showed that the peak of the double-stationary vibration was larger than that of the single-stationary vibration.The peak value of the whole,single and double stationary ground motions had the same attenuation trend,that was decreasing with the increase of the fault distance.The double stationary ground motion with large energy was more likely to cause high intensity damage.(4)The attenuation characteristics of duration of the single and double stationary ground motion were studied.The trend of the energy duration of double stationary ground motion was significant,which increased with the increase of the fault distance,however,the single stationary ground motion tends to be gentle;The absolute duration decay rate of the single stationary ground motion was faster than that of the double stationary ground motion;Compared with Lu Shunan model,the difference of the energy duration fitting curve of the two models was very small,but the absolute time curve of the two models was different significantly,the fitting curve of the attenuation model tends to be gentle in this study.(5)The attenuation characteristics of the peak of the acceleration response spectrum of the single and double stationary ground motion were studied.The peak of the absolute acceleration response spectrum of the two types of ground motions with damping ratio of 0.05 was calculated,and the attenuation trend of the two types of ground motion was the same,which decreased with the increase of the fault distance.The decay rate of the peak of the acceleration response spectrum of the single stationary ground motion was larger than that of the double stationary ground motion.