The low-frequency nature of the great 1960 Chilean earthquake, the Earth's largest recorded event, is characterized and a source model composed of three events with a combined seismic moment of 5.5¿1023 N m and a duration of 1500 s is presented. The results show conclusively that large-scale slip, which is only observed at low frequencies, preceded the main shock. Complex amplitude measurements of normal mode data in the band 1.0--5.0 mHz, recorded at eight vertical component stations, comprise the data set. In this band the earthquake source is assumed to be described by a line source propagating at a constant rupture velocity. The data set is the basis for a sequence of least squares inversions to determine the seismic moment, rupture velocity, spatial slip distribution, and the temporal slip function. The data are best explained by a source model that begins 1150 s before the main shock with an event of moment 1.9¿1023 N m and rise time of 300 s, a main shock with moment of 3.2¿1023 N m and for which most of the low-frequency energy was released beginning about 50 s after the short-period origin time, and an event 350 s later with moment of 0.4¿1023 N m. The uncertainty in the moment estimate of the great 1960 Chilean earthquake is about 50% and is due primarily to the probable range of fault plane dip, which is not well constrained at this time. ¿ American Geophysical Union 1989