The earthquake lasted for about two minutes in total. In the twenty-four hours immediately after the event, there were eight major aftershocks, measuring between 5.5 and 6.0. It was the second-largest earthquake in the world since 1964; only the December 26, 2004 Indian Ocean earthquake earthquake was stronger. A debate arose among seismologists over whether this should be considered an aftershock of the December 2004 event, or a "triggered earthquake" as it was larger than typical aftershocks and on a different fault.

On the Indonesian island of Nias, off the coast of Sumatra, hundreds of buildings were destroyed by the earthquake. The death toll on Nias was at least one thousand, with 220 dying in Gunungsitoli, the island's largest town. Nearly half of Gunungsitoli's population (27,000) fled the town. The control tower at the nearby airport (Banaka) collapsed, forcing relief flights to operate out of Sibolga on nearby Sumatra.

The earthquake was strongly felt across the island of Sumatra, and caused widespread power outages in the Indonesian city of Banda Aceh, already devastated by the December 2004 tsunami, and prompted thousands to flee their homes and seek higher ground [2]. It was also strongly felt along the west coast of Thailand and Malaysia, and in Kuala Lumpur high-rise buildings were evacuated. The earthquake was felt less strongly in the Maldives, India, and Sri Lanka.