Taking stock of a catastrophe

December 26, 2024, marks the twentieth anniversary of one of the biggest disasters ever triggered by an earthquake: The “Boxing Day Tsumani” killed almost 230,000 people. The cause was a mega-quake off the coast of Sumatra, which was associated with a rupture of the ground beneath the sea over a distance of more than 1,000 kilometers. The magnitude was 9.3, making it the third strongest earthquake ever recorded worldwide.

Most of the fatalities were locals on the coasts of Indonesia, India, Sri Lanka and Thailand. Also, many tourists were among the dead. The two countries with the highest death toll among travellers were Sweden and Germany, with more than 500 deaths each.

Global sympathy was enormous in view of the massive scale of the disaster and the images. “It was also a shock for us in the geosciences,” recalls Andrey Babeyko, who models tsunamis at the GFZ. “Theoretically, we knew that such severe quakes could occur, but the extent of the rupture zone over more than 1,000 kilometres and the devastating floods in particular took us all by surprise.”

A detailed insight into the events surrounding the tsunami disaster 20 years ago can be found on our ‘Tsunami focus page’ in pageflow style: Anatomy of a catastrophe

One week to the concept for an early warning system

In the days following the disaster, GFZ researchers worked with a number of colleagues to prepare a concept for an early warning system to limit the extent of such disasters in the future. Until then, there had only been tsunami early warning systems for the Pacific in the US and Japan.

In January 2005, the German government commissioned a consortium of 9 partners led by the GFZ to develop a German-Indonesian Tsunami Early Warning System (GITEWS). The main scientific partner institutions were the German Aerospace Center (DLR), the Alfred Wegener Institute for Polar and Marine Research (AWI) and the then Leibniz Institute for Marine Research IfM-GEOMAR. Like the other consortium partners mentioned above, GEOMAR is now part of the Helmholtz Association. An important role was played by the “Deutsche Gesellschaft für Internationale Zusammenarbeit” (GIZ), which was responsible for capacity development in Indonesia, the so-called ‘last mile’ of the warning chain.

How the tsunami warning works

At the heart of the system is a specially developed software called SeisComP, which analyses data from several hundred seismic stations in the region and detects earthquakes that could trigger tsunamis. Coupled with several thousand pre-calculated tsunami simulations and a decision support system, warnings can be generated in the early warning centre in Jakarta within a few minutes. Trained experts there then decide whether to issue a warning. GITEWS was put into operation in 2008 and handed over to Indonesia in 2011. Since then, it has been called InaTEWS (Indonesia Tsunami Early Warning System) and is operated by Indonesia.

Balance sheet of the Indonesian tsunami early warning system

The tsunami early warning system has analysed several thousand quakes since 2007 and successfully warned of a good dozen tsunamis. Examples include a tsunami in 2007 near Benkulu in South Sumatra with tsunami heights of up to five meters and further tsunami in North Sumatra in 2010 and 2012.

However, there have also been tsunamis that could not be warned of in time or at all. In the 2010 Mentawei and 2018 Palu tsunamis, the waves reached the coasts just a few minutes after the triggering quake – even before any warnings could arrive. A different case was the landslide of a flank of the Anak Krakatau volcano. This large landslide in the Sunda Strait triggered a tsunami in 2018. There was no strong earthquake associated with the flank collapse, which is why the system did not detect any danger.

Jörn Lauterjung, the former head of GITEWS project, is still working as a consultant for UNESCO in the Indian Ocean after his retirement from GFZ. Lauterjung says that the disaster back then led to early warning and protection programmes all over the world, also in the Caribbean and the Mediterranean, most of them under the umbrella of UNESCO, the United Nations' scientific and cultural organization.

“UNESCO has launched the Tsunami Ready and Tsunami Ready Recognition Programme to ensure that vulnerable communities and districts prepare for tsunami warnings, with evacuation plans and evacuation drills, knowledge transfer, work in schools and much more,” Lauterjung says.

Also important: Natural warning signs

Lauterjung adds: “Natural warning signs, which can be perceived much earlier than an official warning, and the interpretation of these natural signs play an important role as well. For example, if you feel an earthquake for a long time – more than 30 seconds –, you should leave the beach and the coast at once.”

The people who live on the island of Simeulue off the north coast of Sumatra already knew this from local tradition in 2004. The legend of the monster “S'mong”, which killed thousands of people with a tidal wave in 1907, had been passed down through the generations. Although the 2004 tsunami also reached enormous heights on Simeulue, only seven people died there and several tens of thousands fled to higher ground and survived.

Positive outcome from the perspective of knowledge and technology transfer

“For the GFZ, the development of the GITEWS tsunami early warning system and the subsequent implementation of InaTEWS was also a great success in terms of knowledge and technology transfer,” says Dr Angelo Strollo, Head of the Global Earthquake Monitoring Programme GEOFON at the GFZ. “For us, the success is measured in particular by the fact that the Indonesian partners have been operating and developing the system independently as InaTEWS since 2011.”

The ‘SeisComP’ software for seismic monitoring, which was largely developed at the GFZ, has been developed very successfully by a GFZ spin-off company, gempa, since 2009. The software has not only been adopted in many of the tsunami early warning systems (TEWS) developed worldwide since then - including technical support from gempa and other companies and customised developments – but is now also used for monitoring volcanoes and critical infrastructure.

Current research for the further improvement of tsunami early warning

In recent years, the GFZ has developed additional technologies as part of research projects that can further improve tsunami early warning.

In the EWRICA project (2020-2023), the integration of data based on high-precision satellite navigation systems (GNSS) was developed in real time for tsunami early warning. In combination with local measurements, this is a way to improve the rapid and reliable estimation of seismic moments, depth and rupture direction of earthquakes, and thus also of secondary effects such as tsunamis. These developments are also being used for test purposes by the Indonesian Geospatial Information Agency (BIG) and the Meteorology, Climatology, and Geophysical Agency (BMKG).

In rare cases, tsunamis can also be triggered by volcanoes and landslides. To date, there are no operational tsunami early warning systems to detect these more subtle tsunami causes in real time. Improving this was the focus of the TsunamiRisk project (2021-2024), a scientific cooperation between 22 Indonesian partner institutions and seven German scientific institutions, including the GFZ, which was funded by the Federal Ministry of Education and Research. As part of the project, recommendations and a strategy were developed on how to tackle the problem in the future. Remote sensing methods, seismic monitoring of volcanoes, but also modelling, especially of flank instabilities, played a major role, as did social science research questions.

Outlook: Use of existing fibre optic cables as highly sensitive sensors

The use of existing underwater telecommunication cables as sensors for monitoring earthquake zones, volcanoes or oceans also opens up great potential for tsunami early warning. The underlying DAS technology (Distributed Acoustic Sensing) uses the optical fibres as strain sensors: movements in the subsurface cause them to deform, distorting the transmitted signals. Information about the movement of the earth can be derived from the analysis and both earthquake waves and processes in the water column above the ground, e.g. tsunamis, can be recorded. Promising preliminary work has been carried out across Europe in recent years.

This technology is being further developed, for example, in the EU project SUBMERSE (SUBMarine cablEs for ReSearch and Exploration), which was launched in 2023.

Also based on this technology, a major infrastructure project to set up a global monitoring and user centre ‘SMART Cables And Fibre-optic Sensing Amphibious Demonstrator’ (SAFAtor) has been applied for under the leadership of the GFZ and with the participation of other Helmholtz centres, which is scheduled to start in 2025 if approved.
 

Further information

An exciting insight into the events surrounding the tsunami disaster 20 years ago will be available from Monday, 23 December, 10 a.m., on our ‘Tsunami focus page’ in page-flow style.

Tsunami fact sheet (German only)

Tsunami info sheet (German only)

Tsunami warning info sheet (German only)

Experiment instructions #7 from the school lab for at home: Foam tsunami
With this experiment, you can observe the effects of a tsunami wave on a flat and a steep coast in slow motion. Suitable for children aged five and over. Video instructions. (German only)