Indonesia Has 15 Megathrust Segments; BRIN Explains Potential Impacts

TEMPO.CO, Bandung - A megathrust zone, where oceanic and continental plates collide, poses a significant risk of powerful earthquakes and tsunamis. These events can cause widespread devastation due to the immense size of the thrust fault involved, often spanning hundreds of kilometers.

Nuraini Rahma Hanifa, an expert researcher at the Geological Disaster Research Center of the National Innovation Research Agency (BRIN), highlighted that Indonesia's megathrust zone extends from western Sumatra to southern Java, Bali, West Nusa Tenggara, East Nusa Tenggara, northern Sulawesi, and Papua. 

“It is divided into 15 segments,” she said in an online discussion on Monday, September 2, 2024.

After the 2024 Aceh Earthquake, she explained that several megathrust segments have released their energy, including the Nias Earthquake, Bengkulu Earthquake, Pangandaran Earthquake, and Pacitan Earthquake. 

According to the National Earthquake Study Center, the maximum earthquake estimate for the Aceh-Andaman segment is magnitude 9.2 (ruptured in 2004), while the Nias-Simeuleu segment has a maximum magnitude (Mmax) of 8.9.

Other segments with their respective maximum magnitudes include: Batu Islands (Mmax 8.2), Mentawai-Siberut (Mmax 8.7), Mentawai-Pagai (Mmax 8.9), Enggano (Mmax 8.8), Sunda-Banten Strait (Mmax 8.8), West Java (Mmax 8.8), Central Java-East Java (Mmax 8.9), Bali (Mmax 9.0), East Nusa Tenggara (Mmax 8.7), West Nusa Tenggara (Mmax 8.9), South Banda Sea (Mmax 7.4), northern Sulawesi (Mmax 8.5), and Philippines-Maluku (Mmax 8.2).

Based on the level of danger and the potential number of affected residents, Rahma identified the island of Java as facing the highest risk of megathrust events. The southern waters of Java feature a 1000-kilometer-long, 200-kilometer-wide megathrust field extending from the Sunda Strait to Bali. This region is where the Indo-Australian Ocean plate is subducting beneath the Eurasian continental plate at a depth of 60 kilometers.

Rahma provided a simulation of the potential impact of a magnitude 8.8 earthquake in the West Java segment. The main shock was estimated to last around two minutes. “The earthquake intensity is predicted to be VI-VIII MMI. Buildings that are not designed to withstand such strong shaking may collapse,” she said.

According to the Meteorology, Climatology, and Geophysics Agency (BMKG), a VI MMI earthquake intensity can cause widespread panic and damage to buildings, while an VIII MMI earthquake can lead to significant structural damage and even collapse.

Rahma emphasized that a shaking duration of 20 seconds could make it difficult for people to stand. Tsunami modeling indicated potential seawater heights of 5-20 meters along the coast, particularly in the Lebak area of Banten. “The estimated arrival time for the tsunami is 15-20 minutes,” she concluded.

ANWAR SISWADI (CONTRIBUTOR)

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