Insights into tectonic hazards since the 2004 Indian Ocean earthquake and tsunami

In 2004, an earthquake of moment magnitude Mw 9.1–9.3 ruptured over 1,500 km of the Sunda megathrust under the Indian Ocean, producing a devastating tsunami and resulting in 230,000 fatalities and the displacement of nearly 1.7 million people. In this Review, we explore the lessons learned since the 2004 event, including advances in understanding Sumatran subduction-zone hazards and related disaster preparedness and risk communication. The 2004 earthquake triggered a series of aftershocks, including over 6,000 Mw ≥ 4.5 earthquakes in the first 10 years, two of which were Mw 8.6 and Mw 8.4 events, that ruptured much of the remaining Sumatran subduction interface. Ruptures of the Sumatran subduction interface are often bounded by persistent barriers associated with structural features, including fracture zones and seamounts, on the subducting oceanic plate. Although the entire plate boundary zone should always be prepared for earthquakes and tsunamis, the seismic gap in the Mentawai Islands highlights the need for enhanced preparedness in this region. The lack of tsunami early warning systems in the Indian Ocean before the 2004 tsunami prompted international efforts to help coastal populations protect themselves, which remain ongoing. Future communication efforts should ensure the public understands that no warning system is perfect, and it is safest to evacuate when there is any indication of a potential tsunami. Understanding of the Sumatran subduction zone and its hazards has increased since the 2004 Indian Ocean earthquake and tsunami. This Review commemorates the 20th anniversary of this event by outlining these insights and how they can inform future strategies to improve tsunami preparedness.