By Ben Blanchard and Yimou Lee TAIPEI (Reuters) -A 6.8 magnitude earthquake hit the sparsely populated southeastern part of Taiwan on Sunday, the island’s weather bureau said, derailing train carriages, causing a convenience store to collapse and trapping hundreds on mountain roads. The weather bureau said the epicentre was in Taitung county, and followed a 6.4 magnitude temblor on Saturday evening in the same area, which caused no casualties. The U.S. Geological Survey measured Sunday’s quake at a magnitude 7.2 and at a depth of 10 km (six miles). Taiwan’s fire department said one person had …