Why are such "phenomena as hurricane katrina and rare" earthquakes in regions where oil shale is fracked called "hundred-year" events?

They are statistical outliers that typically do not occur within a normal human lifespan.

Explanation:

When a site is considered for oil shale fracking, various aspects of the area are evaluated including the geographical and climatic facets like the chances of earthquakes and hurricanes. It is normally assumed that when such a site is selected that any event that can lead to an emergency will not happen or at least the statistical chances are low. Hence, when an event like this happens it is assumed as rare or hundred year event because they are statistical outliers that typically do not occur within a normal human lifespan.

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