Abstract -- The result of an investigation on earthquake geology and active faults shows that the Changhua fault is not exposed on the surface and is overlaid by Quaternary deposits, whereas the Hsinchen, Chelungpu, Meishan and Hsinhua faults all crop out at the surface. Since the Hsinchen fault cuts through a non-lateritic fluvial terrace, it must have been reactivated in the Holocene, so that it should be reclassified as an active fault of the first category. Regarding the Changhua fault, it cannot be ascertained that it extends from subsurface to surface based simply on the data collected by drilling and geophysical exploration. An uplifted terrace was found next to the fault where it is a topographic high resulting from the process of a fault-propagation fold. Thus the Changhua fault is a blind fault. Historically there are records of earthquakes caused by the reactivation of Chelungpu, Meishan and Hsinhua faults. As for the Chelungpu fault it can be subdivided into two segments based on the activity deduced from the dating results. The northern segment was reactivated about 2000 years ago, whereas the southern segment was reactivated about 600 years ago. Continuing, the result of our study on the Meishan fault cannot account for its characterization by now. The topographic and geologic features in the area next to the fault were influenced by the Chukou fault and the Chiuchiungkeng fault. The latter has been re-classified as an active fault of the first category, for it cuts through the fluvial terrace. Finally, based on the shallow seismic data, the deformation zone of the Hsinhua fault is wide. The features observed in the trenching sites show that it has been reactivated several times in the past. The style of its recent activity is mainly confined to creeping.