The Asian continent extends south from Thailand, Cambodia and Vietnam to form the Sunda Shelf. The southern end of the shelf is an active margin defined by the Java Trench. To the east it forms the South China Sea, a passive margin condition. The South China Sea itself is bounded to the east by the Philippine islands and the Philippine Trench, another active condition.

Which of the bounding conditions of the Sunda Shelf and the South China Sea are characterized by volcanic activity? Why?