'Just a matter of time' megathrust earthquake hits Indonesia, as government agency urges mitigation efforts

JAKARTA: Indonesian authorities, including local governments, must get serious about disaster mitigation as it is “just a matter of time” before a powerful earthquake caused by two converging tectonic plates hits the country, its meteorology and geophysics agency has warned.

Local governments should prepare mitigation measures including spatial planning on earthquake-proof buildings that can accommodate the community in case of megathrust earthquakes, Indonesia’s Meteorology, Climatology and Geophysics Agency (BMKG) said this week.

“There should be restrictions on development on the coast; no buildings should be built. If a hotel is built, the hotel must be ready to face (a megathrust earthquake), requiring the building to be able to withstand 8.5 magnitudes,” said BMKG head Dwikorita Karnawati in a press conference on Tuesday (Aug 20).

On its part, the BMKG has put in place monitoring, processing and information dissemination systems for earthquake and tsunami early warnings that have been increasingly fast and accurate.

Earthquake preparedness has drawn renewed attention in Indonesia in the wake of Japan’s megaquake alert earlier this month. 

After a 7.1 magnitude earthquake occurred on the Nankai subduction zone and hit Japan’s island of Kyushu on August 8, the Japan Meteorological Agency issued a megaquake advisory for the first time, indicating the quake could be a precursor to an even larger one that could cause significant loss of lives.

The agency ended the alert a week later and said people were free to return to their normal lifestyles.

TWO ZONES OF CONCERN

Referring to the events in Japan, Mr Daryono, head of the BMKG’s Earthquake and Tsunami Centre, said that it was a matter of time before Indonesia experienced earthquakes at two megathrust zones, as it had been a while since they had occurred.

Mr Daryono was referring to two megathrust zones known as the Sunda Strait and Mentawai-Siberut segments, which are off the southern coasts of Sumatra and Java islands. 

A megathrust is the meeting zone between the earth's tectonic plates that has the potential to trigger strong earthquakes and tsunamis.

“The release of earthquakes in these two segments can be said to be 'just a matter of time' because it has been hundreds of years since a major earthquake occurred,” he wrote on  X, formerly known as Twitter, on August 11.

According to Mr Daryono, the concerns of Japanese scientists about the Nankai Megathrust are identical to those of Indonesian scientists for the Sunda Strait and the Mentawai-Siberut megathrusts, which have not experienced earthquakes or seismic gaps for a long time.

“The Sunda Strait seismic gap has been 267 years and the Mentawai-Siberut has been 227 years, while other segments have experienced earthquakes; my job is to remind (of the need for) vigilance,” Mr Daryono said in another post.

His observation resulted in “megathrust” becoming a trending topic on social media in the country, as well as local media reports.  

Indonesia is located at the intersection of the world's major tectonic plates and several small plates, and has experienced many earthquakes and volcanic eruptions. 

According to an earthquake hazard source map released by BMKG in 2017, there are 13 megathrust zones that have the potential to trigger earthquakes of more than magnitude 8 and tsunamis.

Mr Daryono added that public discussion about the megathrust is not new as it was discussed even before the Aceh tsunami disaster in 2004, which killed more than 220,000 people.

While earthquakes are usually hard to predict, they have to be anticipated with mitigation measures, experts and politicians said in recent days.

House of Representatives member Daniel Johan said the potential of a megathrust earthquake in Indonesia should be of serious concern to the government.

“Do not let the initial information conveyed by BMKG be dismissed and (as a result) we do not make preparations,” Mr Daniel said, as quoted by news outlet Jawa Pos.

In response to the BMKG’s warning, the Ministry of Social Affairs said that it has sent a team to Mentawai Island in West Sumatra to map out areas that are potentially vulnerable to megathrust earthquakes and tsunami disasters.

The team consists of personnel from the ministry's Disaster Preparedness Cadets (Tagana) and BMKG.  

Social Affairs Minister Tri Rismaharini said that apart from mapping the area, the team will also counsel and brief residents regarding disaster response and evacuation preparedness.