The flight had reached an altitude of 14,000 feet mean sea level (MSL), when the crew reported a severe vibration in the number 1 engine. The crew shut down the engine, declared an emergency, and returned to the airport. After landing, the airplane was taxied to the gate without evacuating the passengers. Examination of the engine revealed that a turbine shroud had separated and penetrated the turbine exhaust case at the 6 to 9 o'clock position, exited the cowling, and punctured the #2 outboard reserve fuel tank plate. There was a fuel leak, but no fire.