The National Disaster Mitigation Agency (BNPB) has warned about a possible earthquake caused by the Walanae fault that runs underneath South Sulawesi province.

The Walanae fault is an active fault that moves between 2 to 4 centimeters per year.

Although the speed of the motion, at 5 cm per year, is not as significant as the Palu-Koro fault that caused the tsunami in 2018, it has the potential to cause an earthquake with an intensity of VIII to X Modified Mercalli Intensity Scale (MMI), BNPB head Doni Monardo said during an event in Makassar on Monday.

The MMI scores VIII, IX and X are considered severe and violent and can cause extreme structural damages, according to the United States Geological Survey. The score VIII means great damage in poorly built structures, while X means some well-built wooden structures are destroyed, frame structures destroyed with foundations and rails bent.

Doni said if there ever was a VIII to X MMI earthquake, eight regencies in the province — Pinrang, Enrekang, Sidenreng Rappang, Wajo, Soppeng, Bone, Sinjai and Bulukumba — would be affected.

During such an event, it is estimated that 1.1 million people would fall victim to the quake, according to research by Sarsito, a geologist from the Bandung Institute of Technology (ITB). It is also estimated that the catastrophe could destroy 137,000 houses and around 1,000 schools, health posts and hospitals.

“South Sulawesi will experience earthquakes, as the Walanae fault keeps moving,” Doni said.

The head of disaster mapping and risk analysis of the BNPB, Abdul Muhari, said the Walanae fault was detected as active last year by ITB research using the global positioning system (GPS).

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“What is certain is that an earthquake has a cycle. Once an area has a history of an earthquake, it will reoccur sometime in the future.”

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However, the time that the earthquake will take place cannot be predicted. “What is certain is that an earthquake has a cycle. Once an area has a history of an earthquake, it will reoccur sometime in the future,” said Trinirmalaningrum, an earthquake expert who is the head of the Palu-Koro expedition.

The Walanae fault was first discovered in 1976 and caused an earthquake a year later, with an intensity of V MMI.

The fault is connected with the Palu-Koro fault which jolted Palu and Donggala in Central Sulawesi in 2018, with a 7.4-magnitude earthquake and a tsunami, leaving more than 4,300 people dead or missing. The Walanae fault stretches from the Makassar Strait to Selayar Island, which is located in the southern part of Sulawesi.

In January, a 4.3-magnitude earthquake hit Selayar Island, which is equal to II or III MMI.

Doni suggested that the South Sulawesi administration immediately create a mitigation plan to minimize the damage and the number of victims.

Tri supported the notion, saying that the South Sulawesi Disaster Management Agency has no contingency plan for an earthquake to date. “The contingency plan is important to guide the next step, which is disaster management training.”

She added that the local administration also needed to check buildings, to ensure they met the standards of a quake-resistant building.

South Sulawesi Governor Nurdin Abdullah said he would immediately prepare a mitigation plan, and push forward the development of more resistant, safer settlements and infrastructure, and promote the plan to all regional heads in South Sulawesi, so they can prepare.

Besides the Walanae fault, there is potential for earthquakes along the Matano fault, on the western side of the Makassar Strait. Tri said the Matano fault was highly active and could cause a sea landslide, triggering an earthquake in Central Sulawesi and some parts of South Sulawesi, including Luwu regency.

The number of active faults across the nation has increased from 81 to 295 since 2010, according to the 2017 national earthquake map. Newly formed faults include one in Maluku, under Kairatu, West Seram and Haruku islands. The fault was the cause of the 6.9-magnitude earthquake that hit Ambon and the three aforementioned islands in September 2019. 

In Jayapura, Papua, the Meteorology, Climatology and Geophysics Agency (BMKG) said it would install 17 new seismographs for West Papua and Papua this year, to better mitigate against earthquakes.

“We’ve already installed 26. This year we will install 11 in West Papua and six in Papua, said Petrus Demon Sili, the head of BMKG’s Papua office.

Earthquakes have occurred frequently in Papua. A 6.3-magnitude earthquake hit Jayapura on the evening of Jan. 18 and later in the morning of Jan. 19. (aly)