Field and excavation investigations show that at least two paleo- (historic) seismic events occurred along the northeastern segment of the Chelungpu fault during the period between 1800 AD and 500 AD before the 1999 Chi-Chi earthquake. The principal indicators of paleo-seismic faulting events are : (1) termination of secondary faults, (2) deformation of deposits related to faulting, and (3) liquefaction of deposits. The observational results show that the offset produced by an individual faulting event is ~ 1m. It is inferred that the probable magnitude of these two paleo-earthquakes is 7.0-7.5.