A seismic hazard map shows the level of ground shaking expected from a given earthquake or from all earthquakes in a region with a specified likelihood of being exceeded (represented as a probability).
PGA stands for Peak Ground Acceleration. PGA is related to the force a building or structure has to withstand to remain standing. PGA is expressed as a percentage of the downward force of gravity at the surface of the Earth. At a PGA of 1G or higher, loose objects will leave the ground.