The western coastal areas of Aceh, including the cities of Banda Aceh, Calang, and Meulaboh, were among the areas hardest-hit by the tsunami resulting from the magnitude 9.2 Indian Ocean earthquake on 26 December 2004. While estimates vary, over 170,000 people were killed by tsunami in Aceh and about 500,000 were left homeless. The tragedy of the tsunami was further compounded several months later, when the 2005 M8.6 Nias–Simeulue earthquake struck the sea bed between the islands of Simeulue Island in Aceh and Nias in North Sumatra. This second quake killed a further 1346 people on Nias and Simeulue, displaced tens of thousands more, and caused the tsunami response to be expanded to include Nias. the World Health Organisation estimates a 100% increase in prevalence of mild and moderate mental disorders in Aceh's general population after the tsunami.