I used these books to find out about Earthquakes:

Plate Tectonics by Alvin, Virginia and Laura Silverstein

Atlas of Geology and Land Forms by Cally Oldershaw

Friend or Foe by William Muñoz

Website:  
http://earthquake.usgs.gov/4kids
  RESOURCES
Earthquake "Where and When"
Earthquake "Personal Safety"
Earthquake Resources
Earthquake Photo Gallery
Earthquake Activities