Characteristic Analysis Of Intensity Measure Of Ground Motion In Wenchuan

The 5.12 Wenchuan earthquake in 2008 was a major earthquake caused by the joint rupture of Yingxiu-Beichuan fault,Guanxian-Jiangyou fault and Xiaoyudong fault.The complex dynamic behavior of multi-fault rupture makes its seismic record waveform exhibit a distinct multimodal(double-plateau)feature.It has been shown that the damages caused by the double-plateau ground motion is more serious than them caused by the single-plateau ground motion.The engineering characteristics of the double-plateau ground motion and the difference in its influence on the structure compared with the single-plateau ground motion have attracted the attention of earthquake engineering researchers.In order to reveal the engineering characteristics of the double-plateau ground motion,the relationship between the intensity measures of the double-plateau ground motion and the seismic response of the structure,and the near-fault effect of various intensity measures,using the data of 240 records from 80 stations of the 5.12 Wenchuan earthquake,19 kinds of intensity measures with each record were calculated based on the corrected acceleration time history,and the seismic phase identification method and fitting envelope method are used to distinguish single-plateau and double-plateau ground motion.Then the attenuation law of various intensity measures of single-plateau and double-plateau ground motion are deduced,and the correlation between the intensity measure of the double-plateau ground motion and the seismic displacement of the frame structure is analyzed.Furthermore,in order to explore the attenuation difference of various intensity measures of the hanging-wall vs foot-wall,the attenuation laws of intensity measures of the hanging-wall and foot-wall are compared and analyzed.The main research contents and results are as follows:(1)The seismic acceleration time history was corrected by the Boore method,and the seismic phase identification method and the fitting envelope method are used to distinguish the single-plateau and double-plateau ground motion.Among the selected 240 seismic records of the 80 stations,114 records of 38 stations belong to the single-plateau ground motion,and 126 records of 42 stations belong to the double-plateau ground motion.(2)The 19 kinds of ground motion intensity measures with the 240 records were calculated.(3)The nonlinear least squares regression was used to analyze the attenuation laws of the 19 intensity measures of the hanging-wall and foot-wall ground motion.It is concluded that the intensity measures of the hanging-wall and foot-wall ground motions decrease with the increasing of the fault distance.The attenuation speed of the UD component of the hanging-wall of the acceleration intensity measures is significantly greater than the foot-wall,while the attenuation speed of the UD component of the hanging-wall of the velocity and the displacement intensity measures is slower than the foot-wall.Except for the EW component of the cumulative absolute velocity which shows that the attenuation speed of the hanging-wall ground motion is greater than the foot-wall;the other intensity measures show that the attenuation speed of the hanging-wall ground motion is slower than the foot-wall.(4)According to the logarithmic residuals obtained from the attenuation analysis of the intensity measures of the hanging-wall and foot-wall ground motion,the hanging-wall effects of 19 kinds of intensity measures are discussed.The results show that there are obvious hanging-wall effects with all 19 intensity measures.(5)The attenuation laws of 19 kinds of intensity measures of the single-plateau and double-plateau ground motion with distance were analyzed,and the attenuation relationships of various intensity measures are obtained.The results show that the intensity measures of the single-plateau and double-plateau ground motion decrease with the increasing of fault distance.Except for the displacement response spectrum peak,Root mean square displacement,the UD component of cumulative absolute velocity and the horizontal components of the Riddell displacement intensity measures,which show that the attenuation speed of single-plateau ground motion is greater than the double-plateau ground motion,the other intensity measures show that the attenuation speed of the double-plateau ground motion is greater than the single-plateau ground motion.(6)The correlations between the intensity measures of the double-plateau ground motion and the maximum seismic displacement of the frame structure were analyzed.According to the significance of the linear regression equation,the intensity measure which can reasonably describe the characteristic of the double-plateau ground motion is selected.The results show that among the three types of intensity measures,the correlation between the velocity intensity measures and the maximum seismic displacement of the frame structure is the strongest,the correlation between the displacement intensity measures and the maximum seismic displacement of the frame structure is the weakest.Among the velocity intensity measures,the peak velocity has the strongest correlation with the maximum seismic displacement of the frame structure.There regression equation between the peak velocity and the maximum seismic displacement of the frame structure is the most significant.It is recommended to use the peak velocity as the intensity measures for seismic analysis of engineering structures under the double-plateau ground motion.