Abstract :
Computer simulation was used to study the nature of the strong ground motion near a
strike-slip fault. The faulting process was modeled by stress release with fixed rupture velocity in a
uniform elastic half-space or layered half-space. The fourth-order 3-D finite-difference method with
staggered grids was employed to compute both ground motions and slip histories on the fault. The fault
rupture was assumed to start from a point and propagate circularly with 0.8 times shear-wave velocity.
In the present paper, we focused on the spatial pattern of ground velocity vectors, i.e., the direction of
strong motions. In the case of bilateral rupture propagation, the strong fault parallel ground motion
appeared near the center of the fault. The fault normal motions of ground velocity appeared near the
edges of the fault. In the case of unilateral rupture, the fault parallel motion appeared near the starting
point however, the amplitude was lower than that for the bilateral rupture case. The fault normal
motion was predominant near the terminal point of the rupture. The results were applied to the
earthquake damage data, especially the directions that simple bodies overturned and wooden houses
collapsed, caused by the 1927 Tango, the 1930 Kita-Izu, and the 1948 Fukui earthquakes. The spatial
distributions of the direction data were found to reflect the strong ground motions generated from the
earthquake source process.
