TEMPO.CO, Jakarta - The complexity of Central Sulawesi's fault lines is reflected in conflicting scientific assessments over what triggered last Tuesday's magnitude 6.7 earthquake on June 16, 2026. While the Meteorology, Climatology, and Geophysics Agency (BMKG) attributed the seismic event to the Sausu Fault, the Geological Agency pointed instead to the Palolo Fault.
This geological complexity is inherited from Sulawesi’s tectonic history, with the island essentially forming from a chaotic collision of small tectonic plates. While the region is crisscrossed by an immense number of fractures, scientists face difficulties in determining which specific fault lines remain active.
"Many of these plate boundaries manifest directly as faults," explained Astyka Pamumpuni, a geology lecturer at the Bandung Institute of Technology (ITB), on Thursday, June 18, 2026.
A house collapsed due to the magnitude 6.7 earthquake in Kamarora A Village, Nokilalaki District, Sigi, Central Sulawesi, June 17, 2026. ANTARA/Basri Marzuki
Astyka explained that seismic activity in Sulawesi is driven by the westward movement of the massive Pacific plate, which has its southern boundary in northern Papua. The movement of the Pacific plate intersects with the Eurasian plate, creating a boundary along the Sorong Fault that extends to the Palu area.
"This is what causes the Palu-Koro Fault to be quite large due to the rapid movement of the plates," she said, referring to one of the two main faults in Central Sulawesi.
The earthquake's epicenter in Palu, June 16, 2026. Doc. BMKG
Tuesday's strong earthquake occurred on the eastern side of the Palu-Koro Fault, located between Palu City and the eastern coast of Sausu. According to Astyka, the tremor was triggered by plate thrust from the east across smaller local faults, where both the Sausu Fault and the Palolo Fault are situated. "We cannot confirm the location until it is proven in the field," Astyka said.
The earthquake shook Central Sulawesi, with the most severe impact felt in Sigi Regency. Three people died, and over a hundred others were injured in the disaster. Additionally, more than 1,600 residential houses and dozens of public and government buildings were damaged, including the Sigi Regent's Office.
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