As best I can tell, the source of the information is probably Figure 6 from an article by Shedlock and Tanner: Seismic Hazard Map of the Western Hemisphere, part of the Global Seismic Hazard Assessment Program.
This seismic hazard map of South America depicts the median peak ground acceleration (PGA) with a 10% probability of exceedance in 50 year. "PGA, a short-period ground motion parameter that is proportional to force, is the most commonly mapped ground motion parameter because current building codes that include seismic provisions specify the horizontal force a building should be able to withstand during an earthquake. This seismic hazard map of the Americas depicts the likely level of short-period ground motion from earthquakes in a fifty-year window. Short-period ground motions effect short-period structures (e.g. one-to-two story buildings)."
"There are three major elements comprising the method used to calculate the PGAs: "1) the characterization of seismic sources; 2) the characterization of attenuation of ground motion; and 3) the actual calculation of probabilities."
Thank you, Anonymous.
Fig. 6 from Shedlock and Tanner: