Torsional motion due to small-scale geological irregularity

M. R. Ghayamghamian, IIEES

The large variation in ground motions due to large and/or small scale basin-shape geological irregularities may introduce large amplitude rotational ground motions at the sites in the vicinity of basin edge. In this paper, the characteristics of rotational ground motions generated by small-scale basin were investigated. To this end, the small-scale basin was modeled using 2-D FLIP computer program. The surface motion at different positions with respect to basin edge was simulated by subjecting to an earthquake motion at engineering bedrock (shear wave velocity of 600-800 m/s). Then, the torsional ground motion was estimated from translational components between two adjacent sites. The results revealed that the torsional ground motion in the vicinity of basin edge show a large amplitude because of shear wave coupling between two shear waves propagating in different geological conditions at two sides of basin edge.