On 26 December 2004, nature reminded us of its power. A series of tsunami waves swept across the coastal areas of Indonesia, the islands in the Bay of Bengal, Malaysia, Thailand, India, Sri Lanka and the Maldives. Indonesia was the hardest hit, where the waves surged about 2 km inland in Banda Aceh. The tsunami is described as the deadliest ever, with 230,000 lives lost.

The disaster began with a powerful underwater earthquake just before 8 a.m. local time, 160 km west of Sumatra in Indonesia. The earthquake, with a magnitude of 9, generated within 10 minutes a 20-metre-wide rupture in the earth's crust over an area of about 1500 km. This was the world's strongest earthquake in 40 years. Several powerful aftershocks followed, the largest with a magnitude of 7.1.

Figure. The earthquake that caused the 2004 Sumatra tsunami was recorded at all NORSAR stations, in Svalbard, Karasjok, Jan Mayen and Løten. On the right, you can see the distance between the measuring station and the earthquake's epicentre.

The earthquake occurred in the Ring of Fire, an area with high seismic activity encircling the Pacific Ocean. About 80% of the world's earthquakes occur here. The 26 December earthquake took place in the subduction zone where the Indian Plate is thrust beneath the Burma Plate, and the tsunami was generated because the entire water column – from the seabed to the surface – was set in motion. When the waves reached shallow water, their height increased up to 30 metres, with catastrophic consequences.

Could this happen again?
Large tsunamis like the one in 2004 are rare, but they do occur. Most recently, in 2011, an underwater earthquake followed by a tsunami struck the coast near Fukushima in Japan, where 19,000 lives were lost. Since 2004, the warning systems for earthquakes and tsunamis have improved significantly. Technological advances have made it possible to monitor more precisely and send real-time alerts. In Japan in 2011, a warning was issued just three minutes after the earthquake, saving many lives. Nonetheless, timely evacuation remains a challenge, even with better warnings.

Earthquakes cannot be predicted, but improved warning systems help save lives and reduce the risk of major destruction. One organisation that contributes data to these warning systems is the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) in Vienna. Their data centre continuously receives seismic, infrasound and hydroacoustic data from national data centres around the world. NORSAR is Norway’s national data centre and operates the Norwegian stations that are part of the CTBTO’s international monitoring system.

This system, known as the verification regime for the Comprehensive Test Ban Treaty, is designed to detect nuclear test explosions. After the 2004 Sumatra tsunami, data from the CTBTO’s seismic and hydroacoustic stations were made available in 2006 to national tsunami warning centres (NTWCs). These data, now transmitted in real time, enable more accurate and timely warnings of potential tsunamis. The Sumatra tsunami stands as a powerful example of the importance of knowledge about the movements of the Earth. As Norway’s leading expert in seismology, NORSAR has over 50 years of experience analysing the Earth’s tremors. Sharing insights with authorities, industry and research communities is a central part of our societal mission.

Through monitoring, research and technology, we contribute to a safer world.