During the 1999 Chi-Chi, Taiwan, earthquake (Mw7.6), large amplitude fundamental-mode Love wave with a predominant period of around 5 sec was observed in the Ilan Basin, northeastern Taiwan. The Love wave was generated near the edge of the basin and propagated toward its center during which its amplitude and duration increased and its phase velocity decreased. Numerical 2-D modelings of SH-wave propagation using a structural model of the Ilan Basin reproduced the generation process and propagation characteristics of the Love wave from multiple SH-wave reflections between the free-surface and dipping sediment/basement interface. The simulation results also suggest that long-period Love wave was not generated during aftershocks, because the predominant period of the incident S-wave was too short to resonate in the thick sediments of the Ilan Basin. ¿ 2001 American Geophysical Union