earthquakes and sulfur

What in plate tectonics explains the characteristic sulfur fumes surrounding an earthquake?[1] This is a question I do not see being asked, much less answered.

  1. Mr. Axel Bojanowski. "A Continent Splits Apart" Spiegel Online 2006-03-15. http://service.spiegel.de/cache/international/spiegel/0,1518,405947,00.html