At 7:58 am local time on December 26, 2004 an earthquake of moment magnitude Mw 9.1–9.3 ruptured a over 1,500 kilometers long section of the seafloor off the western shores of the island of Sumatra (Indonesia).
It was the third strongest earthquake ever recorded, after Chile 1960 and Alaska 1964 (Mw 9.5 and 9.2 respectively). The earthquake started on the Great Sumatran Fault, a fault system linked to the subduction of the Indian Plate underneath the Sunda Plate. The earthquake propagated along the fault northwards taking ca. 8 to 10 minutes to travel the entire fault—the longest length and duration of any such recorded event.
The rupturing fault created an approximately 20 meters (or 65 feet) high new scarp on the seafloor, which in turns caused the water displacement and a series of six tsunami moving both east towards Sumatra, and west towards Sri Lanka, India and Africa—eventually reaching the Atlantic and Pacific.
According to the official data by the United Nations, casualties were in excess of 126,000, with 94,000 people still missing. The tsunami displaced more than 1.5 million people and more than 100,000 houses were destroyed in Aceh alone, the Indonesian province located nearest to the earthquake epicenter.
The lack of tsunami early warning systems in the Indian Ocean before the 2004 tsunami had made the disaster’s impact worse. There were no seismic stations covering the entire area and no systems to warn the coastal populations in time.
The 2004 earthquake triggered over 6,000 aftershocks 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 zone. Seismic gaps, where no earthquakes occur, highlight the need for enhanced preparedness in this region as tectonic tensions continues to build up.
Advancements in earthquake and tsunami science since 2004 have prompted improvements in coastal protection, early warning systems and risk communication. However, challenges persist especially at locations near the tsunami source. Here, warning time between the detection of an earthquake and the first tsunami waves reaching the coast can be only minutes.
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.
The study, “Insights into tectonic hazards since the 2004 Indian Ocean earthquake and tsunami,” was published in nature reviews earth & environment and can be found here.
