A note on the motion of a large area on ground surface during passage of synthetic strong motion waves

•Synthetic earthquake motions of a large surface area 100×100 m2.•Role of site conditions on motion of a large surface area.•Dependence of rocking and torsional excitations on site conditions.•Coherency of synthetic body and surface waves in parallel layers.

It is shown that the synthetic earthquake displacements over a large area (100×100 m2) on ground surface can be described well by a plane surface undergoing translations and rotations, with only minor departures of displacements from those of a plane flat surface. Rotational motions are largest on deep soil sites over sediments and smallest for motions on the geological basement rocks.