SPECTRAL ANALYSIS AND MIGRATION OF MAJOR EARTHQUAKES: APPLICATION TO SOUTH AMERICA

e develop two new techniques to detect migration of seismic activity. First we use a stacking procedure to explore common seismicity trends preceding great earthquakes. The seismicity is described in coordinate systems (space vs. time) each having a great earthquake as origin. The seismic belt forms the spatial axis with distances measured from one end of the belt. Then the diagrams are superimposed by matching their axes and origin: common features appear as clustering. Second, we use a two dimensional spectral analysis to detect migration trends. We sample the earthquake point process by filtering the points in the space-time domain prior to sampling. This permits conventional one- and two-dimensional spectral analysis on both the space-time and stacking diagrams.;Forecasting great earthquakes in South America requires a combination of both McCann's seismic potential gaps and the observed migration trends; although, the presence of migration trends during the last 80 years do not automatically guarantee that they will continue in the future.;Using Duda-Bath's catalog {1965, 1979}, we find three well-defined trends among great South American earthquakes (M (GREATERTHEQ) 7.7) migrating from south to north at about 1(DEGREES)/yr. The first migration trend started in 1914 and ended in 1958. The second trend started in 1939 and is now just north of the equator (McCann et al. {1979} gap of category...