According to the pilot of the motorized glider, he was flying at an altitude of 6,000 feet mean sea level (msl) en route to his home airport when he noted an episode of turbulence on the avionics logs for his flight path. He climbed to an altitude of 6,500 feet msl to avoid the turbulence and continued to his destination; however, the glider subsequently encountered severe turbulence that lasted for a few seconds. The pilot reported that during that time he heard a cracking noise in the rear of the glider, which he attributed to a loose quart of oil in the baggage compartment. He continued the flight and landed at his home airport uneventfully. While he was cleaning the glider after the flight, the pilot noted substantial damage to the empennage, which included a 12-inch crack to the composite structure under the right side of the vertical stabilizer. The pilot reported no mechanical malfunctions or failures that would have precluded normal operation before the turbulence encounter; further, he stated that he noted no controllability problems with the glider after the turbulence encounter.