One of the major problems associated with the application of the empirical Green's function (EGF) method is that the Fourier spectrum of the synthetic ground motion shows a quite evident fall-off in the frequencies between the corner frequencies of the large and small events. For the purpose of solving this problem, the author proposes an application of Sato and Hirasawa's (1973) circular crack model to the EGF method. It is shown that the synthetic ground motion with this model does not show any evident fall-off from the ω^-2 target spectrum, whose corner frequency is determined considering the rupture directivity effects. It is also revealed that the variable rise time assumed in the Sato and Hirasawa's model is the key to the solution of the problem. The validity of the model is discussed in terms of it's final-slip distribution and the area of high-frequency generation. Furthermore, the author proposes modeling the rupture heterogeneities of a large earthquake with the “multiple circular asperity model”. As an example, a multiple circular asperity model is constructed for the 1993 Kushiro-oki Earthquake.