Jakarta. Indonesia should be cautious of the potential impact from an earthquake originating from the Nankai megathrust, located off the eastern coast of Kyushu, Shikoku, and Kinki in southern Japan.

Daryono, Head of the Earthquake and Tsunami Center at the Indonesian Meteorology, Climatology, and Geophysics Agency (BMKG), explained that the Nankai megathrust is one of the seismic gaps—a zone with a potential earthquake source but has not experienced a significant earthquake in decades or even hundreds of years. Currently, this zone is suspected to be accumulating stress in the Earth's crust.

He continued that the Japanese experts’ concerns about the potential earthquake are justified. Such a massive earthquake would not only be destructive but also likely to trigger a tsunami.

"If a massive earthquake on the Nankai megathrust does occur and generates a tsunami, we need to be vigilant, as a large tsunami in Japan could potentially reach Indonesian territories," Daryono said on Monday.

However, he emphasized that a major earthquake on the Nankai megathrust would not affect the tectonic plate system in Indonesia due to its considerable distance. Typically, tectonic dynamics in the Nankai subduction zone are confined to local or regional scales.

Historical data compiled by BMKG shows that the Nankai megathrust has previously generated several devastating earthquakes. Examples include the Hakuho Nankai tsunami (684), Ninna Nankai earthquake (887), Kōwa Nankaido earthquake (1099), Shōhei Nankaido 8.4 magnitude tsunami (Aug. 3, 1361), Keichō Nankaido 7.9 magnitude tsunami (Feb. 3, 1605), Hoei 8.7 magnitude tsunami (Oct. 28, 1707), Ansei Nankai 8.4 magnitude tsunami (Dec. 24, 1854), and the Nankaido 8.4 magnitude tsunami (Dec. 21, 1946).

Daryono noted that almost all of these massive earthquakes triggered tsunamis, indicating the high potential activity of the Nankai megathrust system.

According to historical earthquake data, this earthquake source zone is capable of producing catastrophic earthquakes with magnitudes of 8.0 or higher every one to two centuries.

As believed by Japanese scientists, the Nankai Trough has several megathrust segments, which, if all the fault edges slip simultaneously, could generate an earthquake of up to 9.1 magnitude.

This scenario is also a concern among Japanese scientists, especially following the 7.1 magnitude Miyazaki earthquake on Aug. 8, 2024, as this major earthquake was triggered by one of the segments in the Nankai megathrust.

This megathrust zone features an 800-kilometer-long undersea trench that stretches from Shizuoka, west of Tokyo, to the southern tip of Kyushu Island. Thus, the recent 7.1 magnitude earthquake raises concerns as a potential precursor or trigger for the next major earthquake in the Nankai Subduction System.