What causes earthquakes?

Related: Technology & science

1. Headlines
   1. NASA funds 3-D printer project for space food

      NASA won't be printing out pizzas on Mars anytime soon, but the space agency is planning to pay out $125,000 to study the use of 3-D printing technology for food preparation in space.

   2. Neanderthal baby breast-fed for 7 months
   3. Teens' Facebook enthusiasm 'waning,' says study
   4. Solar Impulse takes fuel-free flight to Dallas
   5. Engagement ring glows when fiancee is near
   6. Creator of GIF files insists it's 'jif' - Internet in turmoil
   7. 'Europa Report' packs chills into movie trailer
2. Multimedia
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      Video
      Okla. victims find pets, photos through social media
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      Video
      Life Saving Invention
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      Video
      Mice, geckos, gerbils return from space
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      Ash spews from Costa Rica volcano