Area or a specific site identified by the most recent USGS data (see United States Geological Survey (USGS) Peak Ground Acceleration (PGAPGAPeak Ground Acceleration as determined by the United States Geological Survey. ) Calculator Tutorial) as having a PGAPGAPeak Ground Acceleration as determined by the United States Geological Survey. equal to or greater than 0.15g (i.e., 15% of the acceleration of gravity (g) using a 10% probability of exceedance in a 50 year period).