The Potential for Megathrust Earthquakes in Indonesia, Including Bali

It's no secret that Indonesia sits on the Ring of Fire, with many volcanoes dotted across its many islands. Seismic activities like earthquakes are common occurrences, from the smallest scale to the biggest, as with the 2004 Indian Ocean Earthquake. In 2023, Indonesia had more earthquakes than anywhere else, recording 2,203 events overall.

However, it was the 7.1 earthquake in Miyazaki, South Japan, on August 8 that showed the potential for a megathrust earthquake hitting Indonesia, predicted from Aceh to Maluku and North Sulawesi. In this article, we delve deeper into the megathrust dynamics in Indonesian regions, specifically Bali as a coastal area, and how to prepare yourself should a devastating disaster happen.

What is a Megathrust?

A megathrust earthquake occurs when the two tectonic plates along subduction zones collide. Most megathrust earthquakes occur at the bottom of ocean trenches and, thus, often generate more destructive tsunamis than the earthquake itself. Across history, all the earthquakes with a magnitude of 8.5 or more are megathrust earthquakes, the latest being the Japan earthquake of 2011 (M 9.1).

Megathrust Zones in Indonesia

Indonesia is located between two continental plates, the Sunda Plate and the Sahul Plate, and also two oceanic plates, the Pacific Plate and the Philippine Sea Plate. The potential threat of a megathrust comes from the Sunda Plate, which spans from the north of Myanmar to the southwestern side of Sumatra, to the south of Java and Bali. It is one of the most seismogenic structures on earth, and the Indian Ocean 2004 earthquake was one of the most devastating.

The seismic gap megathrust zones in the Sunda Strait and Mentawai‒Siberut are the ones with potential earthquakes. They haven't released any energy in hundreds of years (267 years in the Sunda Strait and 227 years in Mentawai‒Siberut). When released, however, powerful earthquakes happen and can trigger a massive tsunami.

The Potential of Megathrust Earthquakes

The Indonesian Meteorology, Climatology, and Geophysics Agency (BMKG) has predicted that megathrust earthquakes could happen anywhere alongside the Sunda Plate and has estimated which regions in Indonesia have the potential to experience earthquakes and tsunamis of maximum magnitude.

📍 Nias ‒ Simeulue: M 8.9

📍 Batu Islands: M 8.3

📍 Mentawai ‒ Siberut: M 8.7

📍 Mentawai ‒ Pagai: M 8.9

📍 Enggano: M 8.8

📍 Sunda ‒ Banten Strait: M 8.8

📍 West Java: M 8.8

📍 Central and East Java: M 8.9

📍 Bali: M 9.0

📍 West Nusa Tenggara: M 8.9

📍 East Nusa Tenggara: M 8.7

📍 South of Banda Sea: M 7.4

📍 North of Banda Sea: M 7.9

📍 Philippines ‒ Maluku: M 8.2

📍 North Sulawesi: M 8.5

Megathrust in Bali

Although the risks and threats of a megathrust in Bali are looming, they are not new; they have always been present. If you pay attention, you'll realise that earthquakes in Bali happen regularly, on smaller scales. As of 2024, no technology has yet been able to provide an early warning precisely and accurately before an earthquake occurs.

In 2023, the Executive Head of the Regional Disaster Management Agency (BPBD) advised that at least 41 tsunami warning siren points should be installed across Bali. As of June 2023, nine siren points were located on the southern coast of the island.

A Guide for Disaster Preparedness

Though we cannot predict when an earthquake will happen, we still need to prepare for potentially destructive natural disasters, including knowing what to do in our homes in a dangerous situation.

These are some of the things you need to pay attention to when major earthquakes and tsunamis happen in Bali:

1. Know your infrastructure well and how you decorate the house. Pay attention to heavy furniture or decorations such as bookshelves, cabinets, and wardrobes.

2. Prepare emergency kits in a bag. The emergency kits ideally consist of enough water for several days, dry food or canned goods, a first aid kit, hygiene and sanitation items (soaps, toothpaste, towels, etc.), a flashlight with extra batteries, and cash.

3. Make a copy of your important documents and keep them safe. Keep your important documents in one place and make copies of your passport, KITAS, ID cards, and other documents.

4. During earthquakes, take cover under sturdy furniture like tables or stairs. Stairs are considered the strongest part of a house. If you can get out of the building, do so immediately by avoiding any buildings or trees that could fall.

5. Run to higher ground or a building if you're in a coastal area to the evacuation routes or tsunami shelters. You will hear a boom sound from the ocean before a tsunami hits. A tsunami often occurs not long after an earthquake, and you will see the signs of it by the sudden low tide exposing the ocean floor.

6. Stay calm and get ready for the aftershock. Smaller earthquakes usually follow after a big one, so be alert and remain prepared.

7. Follow the authority updates. It is understandable to feel panic, but it is important to remain vigilant and follow reliable media and government updates during and after the quake.

Is It Safe to Visit Bali?

The possibility of megathrust earthquakes and large tsunamis may be worrisome, but we believe in science, and it is crucial to emphasise that no one will ever know when it will strike. It can happen next year, in the next 10 years, or tomorrow. And though it poses great danger, there is no need to worry excessively about it.

Bali is still a great place to visit and there are many things to do on the island. The only reminder we can give is to be prepared for the worst possibilities. Stay calm and stay safe!