An 8.6 magnitude earthquake struck 437km off the coast of Indonesia’s Banda Aceh on Wednesday, sparking a tsunami alert across the Indian Ocean region. The quake provided a test for the Deep-ocean Assessment and Reporting of Tsunami (DART) early warning system installed by Indonesia and its neighbors in the wake of the devastating 2004 tsunami. This animation explains how the DART system works.

Sources: UNISDR, BBC, NOOA, Australian Bureau of Meteorology,