The first of the 2009 Sumatra earthquakes occurred on 30 September off the coast of Sumatra, Indonesia with a moment magnitude of 7.6 at 17:16:10 local time. The epicenter was 45 kilometres (28 mi) west-northwest of Padang, West Sumatra, and 220 kilometres (140 mi) southwest of Pekanbaru, Riau. Government and authorities confirmed 1,115 dead, 1,214 severely injured and 1,688 slightly injured. The most deaths occurred in the areas of Padang Pariaman (675), Padang (313), Agam (80) and Pariaman (37). In addition, around 135,000 houses were severely damaged, 65,000 houses were moderately damaged and 79,000 houses were slightly damaged. An estimated 250,000 families have been affected by the earthquake through the total or partial loss of their homes and livelihoods.

The Sunda megathrust is a fault that extends approximately 5,500 km (3300 mi) from Myanmar (Burma) in the north, running along the southwestern side of Sumatra, to the south of Java and Bali before terminating near Australia. It is a megathrust, located at a convergent plate boundary where it forms the interface between the overriding Eurasian plate and the subducting Indo-Australian plate. It is one of the most seismogenic structures on Earth, being responsible for many great and giant earthquakes, including the 2004 Indian Ocean earthquake and tsunami that killed over 227,000 people. The Sunda megathrust can be divided into the Andaman Megathrust, Sumatra(n) Megathrust and Java(n) Megathrust. The Bali-Sumbawa segment is much less active and therefore does not have the "megathrust" term associated with it.