Indonesia's Megathrust Zones Shifting, Japanese Expert Identifies Danger Areas
The threat of major earthquakes in Indonesia has returned to the spotlight after the 2024 Indonesian Earthquake Source and Hazard Map showed changes in the distribution of megathrust zones. In the latest map, the number of megathrust zones in Indonesia is recorded at 14 points, an increase compared to the map released in 2017.
This change indicates that more regions require attention regarding the potential for large earthquakes. Indonesia’s geological conditions have also caught the attention of Japanese experts, as they possess characteristics deemed similar to the Nankai Trough, one of the active megathrust regions in Japan.
Professor Kosuke Heki from Hokkaido University believes that long-term monitoring of the Earth’s crust conditions is essential for understanding the potential for large earthquakes. According to him, technologies such as the Global Navigation Satellite System (GNSS) and seabed geodetic measurements can assist in monitoring stress accumulation in subduction zones.
“We understand that magnitude 8 earthquakes in Japan occur at intervals of approximately 50 to 100 years. This is our classic view before a major earthquake occurs,” said Heki while serving as a Visiting Researcher at the National Research and Innovation Agency (BRIN) in late December 2025.
According to Heki, although the timing of large earthquakes 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 the accumulation of stress in subduction zones.
“We see seismic coupling that is locked almost along the axis of the trench. Even at very shallow plate boundaries, strain continues to accumulate for the next earthquake,” he explained.
Heki also highlighted the phenomenon of ‘slow slip events’ or slow shifts that frequently appear before major earthquakes. Although moving very slowly, this phenomenon is considered a potential early indicator.
“This phenomenon has been observed repeatedly in the Nankai Trough and other regions in Japan. One of these slow slip events could potentially trigger the next major earthquake,” he said.
He believes Indonesia has a great opportunity to develop similar monitoring systems, given the many active subduction zones ranging from Sumatra, Java, Bali, and Lombok to Maluku. By strengthening the GNSS network and seabed monitoring technology, Indonesia is considered capable of reading tectonic stress accumulation more precisely.
“Currently, I am working on this issue in Indonesia,” said Heki.
In the latest map, the Aceh-Andaman megathrust zone is recorded as having the greatest earthquake potential, with a maximum magnitude reaching 9.2. Meanwhile, the Java Megathrust has the potential to trigger earthquakes up to magnitude 9.1. Several other zones, such as Mentawai-Siberut, Mentawai-Pagai, and Enggano, each hold earthquake potential of up to magnitude 8.9.
The Meteorology, Climatology, and Geophysics Agency (BMKG) previously highlighted the existence of two megathrust zones that remain in a seismic gap condition, namely the Sunda Strait and Mentawai-Siberut. Both regions have not released significant energy for hundreds of years, since the last earthquakes in 1757 and 1797, respectively.
BMKG emphasised that the term “waiting for time” is not intended as a prediction of when an earthquake will occur.
“What is meant is the accumulation of energy that remains stored because a large earthquake has not occurred for a long time. It does not mean an earthquake will occur in the near future,” BMKG wrote in an official statement.