This year marks 20 years since the devastating Indian Ocean earthquake and tsunami, an event that led to far-reaching impacts for millions of people across the Indian Ocean.
A recent review study led by researchers from the Earth Observatory of Singapore (EOS) and Asian School of the Environment (ASE) at Nanyang Technological University Singapore (NTU) highlights some lessons learnt from the event. These include key scientific advancements made in understanding the tectonics of the region, as well as improvements surrounding disaster preparedness. The study, which was published in Nature Reviews Earth & Environment, also involved collaborators from National Research and Innovation Agency (Indonesia), Universitas Syiah Kuala, ETH Zurich, Université Grenoble-Alpes, and University of California, Berkeley.
Recapping the event, the authors explain the nature and devastating impacts of the disaster. First, an earthquake of magnitude Mw 9.1-9.3 struck offshore northern Sumatra, Indonesia on 26th December 2004. Considered one of the largest earthquakes in recorded history, the event was caused by a rupture longer than 1,500 kilometres that occurred along the Sunda megathrust, the plate boundary between the Indo-Australian and the Sunda plates. It generated a tsunami that reached more than 50 m above normal sea level in some coastal cities, and devastated coastal communities bordering the Indian Ocean. The aftermath to the event saw approximately 230,000 fatalities, 1.7 million people displaced, and US $9.9 billion in damages.
Beyond the impacts on human societies, the authors highlight the effects this event had on the Earth’s systems. For example, beyond the Indian Ocean, the event triggered tsunami waves throughout the world’s oceans. It also generated acoustic and gravity waves in the atmosphere.
Caption: A graphic that shows the regional and global impacts of the 2004 Indian Ocean earthquake and tsunami (Source: Figure 2 from the paper published in Nature Reviews Earth & Environment)
By studying the aftershocks of the 2004 event and the earthquakes that occurred in the decades since, scientists now have a better understanding of the different tectonic processes and ruptures along the Sunda megathrust. For example, scientists found that the 2004 event, along with subsequent megathrust events including two earthquakes of magnitude greater than 8, triggered immediate afterslip on the Sunda megathrust and viscoelastic relaxation in the mantle. After large earthquakes, the Earth's mantle, which is a layer beneath the crust, slowly adjusts to the stress caused by these quakes, causing the Earth's surface to continue deforming over time. This postseismic deformation due to viscoelastic relaxation is still ongoing, even after 20 years.
Scientists have also constructed a more complete historical record of past earthquakes in the Sunda megathrust, spanning back thousands of years, which has helped unravel the patterns and cycles of earthquake rupture in the region. A key advancement is the identification of barriers to earthquake rupture along the Sumatran subduction zone. Barriers to rupture refer to features or conditions along a fault line that consistently prevent or slow down the spread of an earthquake rupture. So far, scientists have identified two well-defined and documented persistent rupture barriers along the Sunda megathrust: the Simeulue Saddle, and the Batu Barrier.
Looking towards the future, scientists have also identified a 200-km stretch along the Sunda megathrust offshore Sumatra that has not ruptured in more than 200 years. Located in northern Mentawai, between the southernmost Batu Islands to Sipora Island, this region, called a ‘seismic gap’, has the potential to produce a large earthquake.
In the following video, Dr Gina M. Sarkawi, Research Fellow at EOS and lead author of the study, summarises these key research advancements since the 2004 event.
Research that focuses on improving our understanding of this Mentawai seismic gap is ongoing, including the recent installation of low-cost Global Network Navigation System (GNSS) stations in Siberut island. “We hope that having a denser network will help us better monitor the current status of the Mentawai Seismic Gap, determine how much strain has accumulated, and whether any strain is being quietly released through slip without generating big earthquakes,” said Assistant Professor Lujia Feng from ASE and EOS, who is one of the authors of the paper and involved in the Mentawai seismic gap research.
Finally, beyond scientific advancements, the authors note how the 2004 event led to the formation of new agencies, including the National Disaster Management Agency (BNPB) of Indonesia, and stress the importance of continuing to improve early warning systems and preparedness, as well as public education about seismic and tsunami hazards. “By applying lessons learned from this tragic event, we can enhance early warning systems, improve disaster response, and raise public awareness to better support vulnerable coastal communities living near subduction zone systems worldwide,” said Dr Sarkawi,
Professor Emma Hill, Chair of ASE, Principal Investigator at EOS, and one of the authors of the paper, adds how the study relates to current efforts in the region. “So much has been learned about the Sumatran subduction zone and hazards in our region, but there is still a lot left to learn,” she said. “Our current project Integrating Volcano and Earthquake Science and Technology (InVEST) in Southeast Asia, is bringing together scientists from across Singapore and the region to further understand these hazards.”
The hope is that the lessons from the 2004 Indian Ocean earthquake and tsunami can help better prepare for future events and protect coastal populations around the world.