The Study Of Rupture Directivity Effects On Near-field Ground Motion Based On Strong Motion Observation Records

There is a significant influence for the rupture directivity effects on the intensity and spatial distribution of near-field motion.It is of great significance to study the influence of rupture directivity effects on the understanding the engineering characteristics of strong ground motion and seismic fortification of engineering structures.The thesis investigates spatial variability and attenuation characteristics of observed near-field strong ground motion using strong ground motion records from important seismic events in recent years at home and abroad,and compares the observation with NGA-West2 prediction models to reveal the characteristics of long-period motion.We quantitatively investigate the influence of rupture directivity effects on spatial variability of Peak Ground Acceleration?PGA?,Peak Ground Velocity?PGV?and spectral accelerations of different periods based on statistical regression and residual analysis.There are 16 seismic events,which are selected from129 seismic events of the NGA-West2 database whose moment magnitude is more than 4.0 and the number of the seismic records is more than 50,having significantly rupture directivity effects.The influence of rupture directivity effects of different seismic events on the intensity and spatial distribution of ground motion at different periods is studied to reveal the narrow-band characteristics of the rupture directivity effects.The following research results are obtained:1.The rupture directivity effects of M_w6.4 Hualien earthquake,M_w7.9Wenchuan earthquake and M_w7.0 mainshock in Kumamoto earthquake series are studied.Using strong ground motions,we investigate spatial variability attentuation characteristics of PGA,PGV and spectral accelerations of different periods,and compare the observation with NGA-West2 prediction models.We study the long-period characteristics and formation mechanism of near-field ground motion during three seismic events,and the influence of amplification effects in the forward and de-amplification effects in the backward of rupture propagation is revealed.The study shows that rupture directivity mainly affects PGV and long-period motions above period 1.0s.2.The influence of rupture directivity on the ground motion at different periods is quantitatively analyzed based on the directivity quantitative predictor f_gand isochrone directivity predictor IDP.The study shows that directivity effects represent obvious narrow-band characteristic,that is,it is not uniform amplification of all frequency range,but the selective amplification of a certain frequency,with different amplification or de-amplification cofficients at different periods.The influence of rupture directivity durng M_w6.4 Hualien earthquake,M_w7.9 Wenchuan earthquake and M_w7.0 Kumamoto mainshock,including the amplification effects in the forward and de-amplification effects in the backward,reaches its maximum at the period T=3.0s,T=7.5s and T=10.0s,respectively.Due to strong directivity effects,the narrow-band peak period of M_w7.0 Kumamoto mainshock is higher than that of M_w7.9 Wenchuan earthquake,and the seismic response spectra in the rupture forward of Hualien and Kumamoto earthquakes exceeds that of Wenchuan earthquake at some frequency bands,which increases the uncertainty of the rupture directivity effects.3.According to the results from the M_w6.4 Hualien earthquake,M_w7.9Wenchuan earthquake,M_w7.0 Kumamoto mainshock and 16 seismic events from 129seismic events in the NGA-West2 database which have direcitivity effects,we investigate the variability of directivity effect model parameter C₁and direcitiviy effect residual term f _Dwith the increasing period,and statistical analysis is used to study the relationship between the peak period of rupture directivity effects on ground motions and seismic events and magnitude.Following conclusion can be made based on our study:?1?the variability trend of directivity effect residual term f _Dis consistent with slope parameter C₁.Every seismic event has their own peak period of narrow-band effects.?2?There is a obvious deviation,which overestimates or underestimates the prediction results of some typical earthquakes,and this model can't reflect the characteristic of narrow-band effect.?3?The peak periods of narrow-band effects during some seismic events often deviate from prediction results of Badie?2018?model.