This article reviews studies on ground motion characteristics during the 2004 earthquake sequence off the Kii peninsula and the Tokai district occurred on September 5. Long-period ground motions are observed at stations in the large sedimentary basins such as Kanto, Nobi, and Osaka. Typical predominant periods of ground motions at each basin are approximately 8-10s for Kanto basin, 3s for Nobi, and 6s for Osaka, respectively, which corresponds to thickness of sedimentary layers of each basin. Long-period ground motion modelings for the event were done by several authors for confirming and improving underground velocity structure models. The reliable underground structure model confirmed by this waveform modeling shall be used for strong ground motion simulation of the anticipated Tokai, Tonankai and Nankai earthquakes.