About two years ago, Greg Sterling wrote a piece on Searching for Earthquakes. Since then, I believe Ask.com was the only search engine providing a “smart answer” for earthquake data. Ask.com continues to offer the smart answer, but recently, Google added their own.
The data Google uses for this OneBox is from U.S. Geological Survey Earthquake Hazards Program.
Postscript: A day or so after, Google posted information about this new OneBox and titled their post Shaking up earthquake searches.