Slowing down on acceleration - Chile seismic hazard

Thank you to the anonymous commentator on my last post. Although it was not explicit in the USGS poster, it makes sense that the figure on acceleration would not represent actual data from the Chile quake.

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: