Indonesia flags megathrust earthquake after M7.6 quake, tsunami warning lifted

Indonesia’s meteorology agency said a magnitude 7.6 earthquake that struck waters off North Sulawesi on Thursday was a powerful megathrust event with high tsunami potential, as authorities monitored aftershocks and assessed damage.

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JAKARTA — The earthquake, which hit at 05:48 WIB (2248 GMT Wednesday), occurred in the Molucca Sea at a relatively shallow depth, increasing the risk of strong ground shaking and sea disturbances, officials said.

BMKG’s earthquake and tsunami information director Rahmat Riyono said the quake was classified as a megathrust event due to its shallow depth and thrust fault mechanism.

“This is a shallow undersea earthquake in a subduction zone with a thrust mechanism, which carries a high tsunami potential,” Rahmat told a press conference.

The quake originated from tectonic activity along the Molucca Sea subduction zone, where one tectonic plate is forced beneath another, releasing large amounts of energy that can trigger destructive earthquakes and tsunamis.

Officials said three provinces were among the hardest hit by the tremors: North Sulawesi, Gorontalo and North Maluku.

BMKG initially issued a tsunami early warning following the quake, with wave heights recorded in several locations. The highest waves reached up to 0.75 metres in North Minahasa, while other areas reported smaller sea level changes.

The agency later lifted the tsunami warning at 09:56 WIB after assessing that the threat had subsided.

Following the alert’s cancellation, search and rescue teams and structural assessment units were deployed to affected areas to evaluate damage and assist local communities.

BMKG chief Teuku Faisal Fathani said monitoring showed at least 93 aftershocks by midday, with magnitudes ranging between 2.8 and 5.8, several of which were felt by residents.

“Aftershock activity will continue to be closely monitored. In some cases, aftershocks can be stronger than the initial quake,” Faisal said, adding that seismic activity could persist for up to two weeks depending on conditions.

Indonesia sits on the Pacific “Ring of Fire,” making it highly prone to earthquakes and volcanic activity, with megathrust zones posing some of the greatest risks due to their potential to generate large-scale tsunamis.