Complex sentence: On December 26 2004, the earthquake struck off the western coast of Sumatra and subsequently produced tsunamis, the event of which had reportedly killed over 220,000 people around the rim of the Indian Ocean.
Split into simpler sentences: On December 26 2004, the Indian Ocean earthquake struck off the western coast of Sumatra. The earthquake and subsequent tsunamis reportedly killed over 220,000 people around the rim of the Indian Ocean.