An excellent, comprehensive data source is the National Earthquake Information Center (NEIC) of the U.S. Geological Survey. The NEIC home page includes links to many other sources of data, maps, and information on earthquakes.
Information on the Canadian National Earthquake Hazards Program-including a link to information on use of seismology in monitoring compliance with the nuclear test ban treaty
The National Information Service for Earthquake Engineering maintains an online database of over 10,000 images of photos and art works (some hundreds of years old) relating to earthquakes.