About 500,000 earthquakes happen every year around the world. Most earthquakes are too small for people to notice. Discover more about this feature of the natural world in Earthquakes, a title in the Focus on Earth Science series. Focus on Earth Science is a series of AV2 media enhanced books. A unique book code printed on page 2 unlocks multimedia content. These books come alive with video, audio, weblinks, slideshows, activities, hands-on experiments,...