Analyses Of Strong Ground Motion Intensity And Its Characteristics

The strength of strong ground motion was generally scaled by intensity, or strong ground motion parameters like Peak Ground Acceleration(PGA) and Peak Ground Velocity(PGV). However, as a typical non-stationary signal whose amplitude and frequency components varied with time, the instantaneous peak amplitude of strong ground motion could not represent its destructive power perfectly. Statistical analyses had proved that whether PGA or PGV was linked closely to intensity, which indicated that reliable estimation of intensity distribution could not be available soon after PGA and PGV were determined.Meanwhile, rapid and reliable distribution of intensity was strongly needed by emergency rescue for destructive earthquakes. Parameters much more significantly related to intensity should be chosen, and the corresponding attenuation relationships should be determined in order to improve the reliability of the instrumental intensity distribution.Besides the acceleration history, the velocity history and the displacement history were another two important characteristics of strong ground motion. But because of baseline shifts, sometimes the velocity history and the displacement history of ground could not be achieved by simple integration of acceleration. Filtering in frequency domain could obviate baseline shifts, but could not achieve co-seismic permanent displacement for any record, which was inconsistent with the observation data.In this article, accelerograms and their corresponding intensity materials of recent destructive earthquakes in West China were collected. The relativity between various strong ground motion parameters and intensity was compared with a method based on hypothesis testing, which indicated that Spectral Intensity(SI0.2) was the parameter that most significantly related to intensity. As an improvement, SI0.2 was modified depending on the predominant period of spectral acceleration and the site condition of the station. The instrumental intensity determined by modified SI0.2 was identical with the actual intensity for 70 percents of the stations, and the difference between instrumental intensity and actual intensity for 99 percents of the stations was within 1 degree of intensity.By statistical analyses of acceleration records obtained in several destructive earthquakes and after shocks of Wenchuan MS8.0 earthquake, attenuation relationships for SI0.2, modified SI0.2, PGA and spectral acceleration in Sichuan-Yunnan region of China were determined. This might be the first time that reliable attenuation relationships for strong ground motion parameters were determined by statistics of accelerograms in China. In this article, the first order error term of acceleration recorder was found to be proportional with the ground displacement history. A baseline correction method was suggested based on this finding, with which ground velocity and ground displacement of several stations were obtained. But this method needed improvement because of the divergence in its iterative process.A time-frequency analysis method based on Single-Cosine Wave(SCW) convolution and Hilbert transform was proposed, with which several acceleration records of tall buildings were analyzed.In summary, an instrumental intensity determination method for West China and the strong ground motion attenuation characteristics for Sichuan-Yunnan region were obtained by statistical analyses, and an explorative attempt was made on the acceleration baseline correction method as well as on the time-frequency analysis method.