In traditional empirical Green's function method, the difference between corner frequencies of large and small events is seldom considered. Since the simulation is performed by the superposition of the small events records, the results would have same corner frequencies as the small events, which contradict the fact that the corner frequency decreases with the moment magnitude. The results by traditional empirical Green's function method underestimate the low-frequency content when n² small events are added. Assuming the corner frequency of a sub-fault is inversely proportional to the square root of the numbers of ruptured sub-faults, we construct a new function to apply the dynamic corner frequency to empirical Green's function method based on the ω² source model. In the constructed function, the corner frequency of each sub-fault changes with the rupture propagation. We also develop a schematic diagram to show how the improved empirical Green's function method works.
To validate the empirical Green's function method with dynamic corner frequency, we simulate the near fault strong ground motion of Wenchuan earthquake. Three aftershocks of Wenchuan earthquake are used as Green's functions of the asperities based on their magnitude and locations. Then ground motions of Wenchuan earthquake are synthesized by traditional empirical Green's function method and the empirical Green's function method with the dynamic corner frequency respectively. Comparison between the simulated results and observed data indicates that the traditional empirical Green's function method underestimates the low-frequency content of ground motions. While the empirical Green's function method with the dynamic corner frequency boosts the low-frequency motions without changing the high-frequency content. The results from the empirical Green's function method with the dynamic corner frequency show good agreement with the observed records after the low-frequency contents are improved, which proves that the dynamic corner frequency is valid to eliminate the underestimation due to the difference between the corner frequencies of large events and small ones.
This study also proves that the empirical Green's function method with the dynamic corner frequency is a powerful tool to synthesize the near fault strong ground motions from M_W7.9 earthquake.

Complex spatial distribution of seismic motion near faults has always been a concern to scientists,and it still remains as an uncertain problem due to insufficiency of events and information.The paper presents the main cases of seismic disaster by field investigations of M_S 8.0 Wenchuan earthquake,analyzes and discusses the relationship among earthquake fault,ground motion and earthquake disaster near the fault fractured zone,based on previous research of source rupture processes and source inversion of Wenchuan earthquake.Intensive deformation and ground surface rupture along the earthquake fault have caused obvious damage to buildings,so it is necessary to introduce the safety distance away from active fault and other measures.Possible reasons for buildings near surface rupture zone having withstood the strong earthquake are as follows:other than their performance of seismic resistance,firstly,most of them locate at hard sites or on bedrock in the surface rupture zone,and secondly,the effective stress drop and low rupture velocity may exist in the shallow asperities,resulting in a relatively lower ground motion at the period about 1 sec.