Indonesia’s Megathrust Map Identifies 14 Zones, but No Earthquake Date

Indonesia’s 2024 earthquake-source and hazard map identifies 14 megathrust zones, more than the 2017 map showed, according to CNBC Indonesia. The revised count describes how the hazards are mapped; it does not mean new faults have suddenly formed. Geologist Gayatri Indah Marliyani told BBC News Indonesia that megathrust zones have existed for millions of years as part of the country’s tectonic system.

A megathrust is a fault at a boundary where one tectonic plate moves beneath another, Gayatri explained. Indonesia’s mapped system extends along western Sumatra and south of Java and the Nusa Tenggara islands, according to BBC News Indonesia. CNBC Indonesia reported that the new map assigns a maximum potential magnitude of 9.2 to the Aceh–Andaman zone and 9.1 to the Java zone. Those figures describe potential scenarios, not forecasts of an earthquake’s size or timing.

Indonesia’s Meteorology, Climatology and Geophysics Agency has drawn attention to seismic gaps in the Sunda Strait and Mentawai–Siberut zones, CNBC Indonesia reported. In an official statement cited by the outlet, the agency said that a long interval without a major earthquake indicates stored energy, not that one will occur soon. The Bandung Institute of Technology has also reported that evidence from historical earthquakes is less complete for the Sunda Strait than for Mentawai, while stressing that this does not remove the Sunda Strait’s earthquake potential.

Researchers are looking at ways to measure strain more closely. Kosuke Heki of Japan’s Hokkaido University told Indonesia’s National Research and Innovation Agency that satellite-navigation measurements and seafloor geodesy can track deformation around subduction zones, according to CNBC Indonesia. Drawing on observations from Japan’s Nankai Trough, he also discussed slow movements along a plate boundary that researchers are studying for their possible relationship to larger earthquakes. He did not offer a date for an Indonesian earthquake.

For communities near the coast, the distinction between monitoring a hazard and predicting a disaster matters. Gayatri told BBC News Indonesia that discussion of megathrust risk should focus on whether people are prepared if an earthquake occurs. Avianto Amri, head of the Indonesian Disaster Management Society, told the BBC that spending on prevention and mitigation can reduce future casualties and losses.