A 6.0 magnitude earthquake – updated from the previous 6.1 – rocked the Central Maluku region on Seram Island to Ambon on the afternoon of Wednesday 16th June.
The Meteorology, Climatology, and Geophysics Agency (BMKG) explained why its early warning system and modelling results did not mention the existence of a tsunami, even though a small one did occur.
“Because its strength was 6.0, its position was also on the sea border with the beach. It’s tectonic, thus there was no potential for a tsunami,” said BMKG head Dwikorita Karnawati.
However, a tsunami was confirmed by the tidal monitoring tool belonging to the Geospatial Information Agency, indicating a rise in sea level after the earthquake.
“In Tehoru, the sea level rose by half a metre, allegedly due to an underwater cliff landslide,” said Dwikorita.
The maximum rise in sea level in Tehoru was about half a metre at 11:47am, or four minutes after the earthquake. As for Banda, the maximum height was seven centimetres at 12:02pm, 19 minutes after the earthquake.
Up to 4pm, there were 16 aftershocks with magnitudes ranging from 1.9 to 3.7. BMKG recommended that the public, especially in areas along the Japutih Coast to Atiahu Beach in Central Maluku Regency on Seram Island, to be aware of the potential for a tsunami due to underwater landslides.
“It is feared that it will still happen,” Dwikorita added.
Those living on the coast are asked to immediately move away from the beach to a high place if a strong shock is felt, even without having to wait for an early warning from BMKG.
“Because warnings based on tsunami tectonic earthquakes from underwater landslides cannot be detected with the current early warning system,” she explained.
Dwikorita added that BMKG is monitoring the Maluku region specifically based on tsunamis occurring quite often which could be due to non-tectonic triggers.
The tsunami that is generated can also happen quickly – breaking the formula that has been known so far, namely 20-20-20 or within 20 seconds after the shock, run to a place more than 20 metres away because the tsunami will come in 20 minutes.
“This theory collapsed with the Palu tsunami and the incident in Seram,” said Dwikorita.
Early warnings from BMKG and agencies in developed countries have not been able to detect such a fast tsunami. Instead, the community is asked to use local wisdom. Apart from that, there are other ways to measure strong earthquakes.
“If you stand up and you want to fall or if you stand but swing, immediately find a high place,” he said.
The BMKG Earthquake and Tsunami Mitigation Coordinator, Daryono, added data on the destructive earthquake and tsunami in the southern region of Seram Island. Among them are a destructive earthquake and tsunami in Ambon in 1950 and another in 2019 which left 31 people dead.