Most dense in U.S.: California. Least dense: The Dakotas.
Most dense Canada: Toronto, Montreal. Least dense: Northwest territories
I would recommend going on Amazon.com and buying this book to help you study and prioritize.
When geologists want to study an active earthquake fault, they often rely on a trenching study. ... They brace the walls, if needed, to prevent cave-ins, then they climb down into the trench and carefully map its walls, looking for signs of past earthquakes and ground movement.