The dynamic rupture propagation of the 1995 Kobe earthquake (Mw 6.9) is simulated using the boundary integral equation method to investigate the physical condition of earthquake dynamic rupture. From several numerical experiments, a small fault is found to be required beneath the Akashi Kaikyo Bridge, which is located near the hypocenter and between the Nojima and Suma faults. The existence of this small fault was originally proposed by Koketsu et al. (1998, Earth Planets Space). In the present physical modeling, it plays an important role in making the rupture propagate bilaterally along both faults. In addition, the principal stress direction should be rotated 30° clockwise from the tectonic stress direction in this region. This suggests that an aseismic slip before the earthquake might occur in order to disturb the stress field in this region from the global stress field. © 2009 by Academic Press, Inc.