Indonesia's Megathrust Zone Map Updated, Japanese Expert Points to Danger Areas

The risk of a major earthquake in Indonesia is back in the spotlight following the update of the 2024 Indonesian Earthquake Source and Hazard Map, which records an increase in the number of megathrust zones to 14 points. This latest map shows a higher potential hazard compared to the 2017 release, marked by increasingly dense hazard contours in several regions. The increase in megathrust zones in Indonesia has also attracted attention from Japan. Professor Kosuke Heki from Hokkaido University assesses that Indonesia’s geological characteristics are similar to the Nankai Trough zone, one of the most active megathrust areas in the world. “We understand that magnitude 8 earthquakes in Japan occur at intervals of about 50 to 100 years. This was our classic view before the occurrence of large earthquakes,” Heki said while serving as a Visiting Researcher at the National Research and Innovation Agency (BRIN) at the end of December 2025. According to Heki, although the timing of a major earthquake is difficult to predict, long-term monitoring of crustal deformation is a key element in disaster mitigation. He emphasised the role of the Global Navigation Satellite System (GNSS) and seabed geodetic measurements to read stress accumulation in subduction zones. “We see inter-seismic coupling that locks almost along the entire trough axis. Even in the very shallow parts of the plate boundary, strain continues to accumulate for the next earthquake,” he explained. Heki also highlighted the phenomenon of slow slip events, which often appear before large earthquakes. Although they move very slowly, this phenomenon is considered a potential early indicator. “This phenomenon has been observed repeatedly in the Nankai Trough and other areas in Japan. One of these slow slip events could trigger the next major earthquake,” he said. He believes Indonesia has a great opportunity to develop a similar monitoring system, given the many active subduction zones from Sumatra, Java, Bali, Lombok to Maluku. By strengthening GNSS networks and seabed monitoring technology, Indonesia can read tectonic stress accumulation more precisely. “I am currently working on this problem in Indonesia,” Heki said. In the latest map, the Aceh-Andaman Megathrust zone is recorded as having the largest earthquake potential with a maximum magnitude of 9.2. Meanwhile, the Java Megathrust has the potential to trigger an earthquake of up to magnitude 9.1. Several other zones such as Mentawai-Siberut, Mentawai-Pagai, and Enggano each hold the potential for earthquakes of up to magnitude 8.9. The Meteorology, Climatology, and Geophysics Agency (BMKG) previously also highlighted the existence of two megathrust zones that are still in a seismic gap condition, namely the Sunda Strait and Mentawai-Siberut. These two areas have not released large amounts of energy for hundreds of years, since the last major earthquakes in 1757 and 1797 respectively. BMKG stressed that the term “waiting for the time” is not intended as a prediction of when an earthquake will occur. “What is meant is the accumulation of energy that is still stored because there has not been a large earthquake for a long time. It does not mean that an earthquake will occur in the near future,” BMKG wrote in an official statement.