Using data collected by the U.S. Geological Survey, anyone can download historical data on earthquakes across the globe in various formats. Here’s a screenshot in Google Earth from a KML file downloaded today. It shows 30 years of earthquakes — in this extent focused on Japan — with colors representing depth and bubble size representing magnitude. (This obviously looks better in Google Earth):

Here’s an interactive version of the KML data uploaded to Google Fusion Tables:

View larger version | Source: USGS | Download the data