"It's confirmed: The largest deep earthquake ever recorded happened in May off the coast of Russia. But this massive temblor is still a mystery to scientists.

The magnitude-8.3 earthquake occurred on May 24, 2013, in the Sea of Okhotsk, deep within the Earth's mantle. The earthquake, described today (Sept. 19) in the journal Science, is perplexing because seismologists don't understand how massive earthquakes can happen at such depths."


http://news.yahoo.com/earths-biggest-deep-earthquake-still-mystery-180428737.html