Studies On Numerical Simulation Of Near-fault Large Velocity Pulse Based On Kinematic Source Model

Study on long-period velocity pulse plays an important role in analyzing the damage of engineering buildings.After the 1979 Imperial Valley earthquake,relevant scholars have gradually realized that the high-amplitude,long-period large velocity pulses contained in the near-fault strong ground motion will cause serious damage to large-scale civil engineering structures(bridges,tunnels,oil storage tanks,and high-rise buildings,etc.),because of the impact of seismic waves and the resonance effect of the carriers.The simulation of the near-fault pulse-like ground motions are extremely important for mitigating the disaster caused by future large earthquake and the engineering anti-seismic design of major projects.Qualitative and quantitative evaluation of the characteristics of pulse-like ground motion can provide a reference for earthquake prevention and disaster reduction.Most existing studies have used the equivalent velocity pulse models to simulate waveforms,and analyze the influence of velocity pulse on the engineering structure,but less on the relationship between the pulse and the focal mechanism.With the rapid development of the national economy,the long-period buildings are showing an increasing trend year by year.Therefore,numerical calculation of the near-fault large velocity pulse from the source,and analysis of the characteristics and formation mechanism of the pulse-like ground motion,it has important theoretical reference and application value in earthquake hazard analysis,earthquake damage assessment,and improve the ability of earthquake prevention and disaster reduction.The main research contents and results of this paper are as follows:(1)Take the Chi-Chi,Taiwan,China earthquake with rich velocity pulse data as an example.The setting of source parameters are based on the inversion data and empirical statistical relationship of actual earthquakes,and the source model with 6 asperities is established with reference to the fault rupture propagation process and the source kinematic model.Comparing the simulation results of 39 velocity pulses with the real records,it is found that the pulse waveforms and velocity response spectrum are close to the actual records obtained by the stations,which also verifies the feasibility of using this method to numerically simulate large velocity pulses.(2)The asperities and the background area affect the spatiotemporal distribution of the pulse-like ground motion.The seismic moment and rise time of the asperities together determine the pulse peak and pulse period.In the case of a given seismic moment,the pulse period is positively correlated with the rise time,the pulse peak is negatively correlated with the rise time,and the velocity waveform is mainly affected by the rise time of the background region.At the same time,it is found that the forward directivity effect of PGV is more significant than that of PGA.(3)In order to analyze the distribution characteristics of the near-fault large velocity pulse and the relationship between the pulses and the focal mechanism,estimating the large earthquake in a given region in the future,the intensity and distribution characteristics of the near-fault pulse-like ground motion may be generated.The Shuantung fault and its vicinity in western Taiwan were selected for research,and the near-fault pulse-like ground motions were estimated using 8 different kinematic source models.The results show that the double-sided velocity pulses generated by the directivity effect are mainly concentrated in the direction perpendicular to the fault sliding component,while the single-sided velocity pulses generated by the fling-step effect are concentrated in the direction parallel to the fault sliding component.(4)Because of the mutual modulation of the directivity effect,the fling-step effect,and the hanging wall effect,the pulse-like ground motion reflects the characteristics of asymmetric zonal distribution.The ground motion at the rupture front end and the hanging wall is large,and the attenuation of the horizontal ground motion component perpendicular to the fault strike is the slowest,and the velocity pulses are distributed in the range of the fault distance of about 15 km.