Indonesian Regions with Megathrust Zones; Beware of Earthquakes and Tsunamis

TEMPO.CO, Jakarta - Social media has been flooded with megathrust earthquake discourses in the past few weeks. Especially after the warning of possible earthquakes that will cause tsunamis in parts of Indonesia. 

A megathrust earthquake is an earthquake that occurs due to the meeting of two tectonic plates in a subduction zone; a region where one tectonic plate is thrust under another, usually at the bottom of the ocean.

This earthquake occurs because the two plates continually move towards one another, yet become “stuck” where they are in contact. Eventually, the build-up of strain exceeds the friction between the plates and a huge megathrust earthquake occurs. 

In Indonesia, several megathrust zones are predicted and included in active subduction zones. These zones comprise the Sunda Subduction Zone which covers the areas of Sumatra, Java Island, Bali, Lombok, and Sumba. Other active subduction zones are the Banda Subduction Zone, the Maluku Sea Plate Subduction Zone, the Sulawesi Subduction Zone, the Philippine Sea Plate Subduction Zone, and the North Papua Subduction Zone.

There are also three megathrust segments in the Indian Ocean south of Java, which include the East Java, Central Java-West Java, and Banten-Sunda Strait segments. These segments could potentially trigger a major earthquake with an estimated magnitude of 8.7.

As reported by Antara, the Head of the Disaster Emergency Management Division of the Central Java Regional Disaster Management Agency (BPBD), Muhammad Chomsul, stated that four regions in Central Java are at risk of megathrust earthquake; Purworejo, Wonogiri, Cilacap, and Kebumen. Residents of these regions are advised to remain vigilant and follow situation updates from legitimate authorities to minimize the possible impact.

Quoted from the Journal of the Muhammadiyah University of Yogyakarta, regions along the southern coast of Java, especially in Pelabuhan Ratu, Pangandaran, Pacitan, and Banyuwangi, are at risk of megathrust-induced earthquakes and tsunamis. Although these regions have not logged any major earthquakes thus far, the tsunamigenic threat is real. 

This study used new data from the Indonesian Tsunami Early Warning System (InaTEWS) and International Seismological Center (ISC) catalogs to investigate the potential for a megathrust earthquake and tsunami in southern Java. Analysis of six years of seismic and GPS data shows a significant landslide deficit, which could trigger future earthquakes. These results are also used to model the height of a potential tsunami, reinforcing the need for an effective early warning system.

ANTARA | UMY

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