Magnitude 5.5 earthquake strikes Aceh's Gayo Lues, no tsunami threat

Magnitude 5.5 earthquake strikes Aceh's Gayo Lues, no tsunami threat

A magnitude 5.5 earthquake struck Gayo Lues Regency in Aceh Province on Wednesday morning, sending tremors across the region and into neighboring North Sumatra Province. The Meteorology, Climatology, and Geophysics Agency (BMKG) confirmed the inland quake posed no tsunami threat and urged residents to remain calm while avoiding damaged structures.

The earthquake occurred at 11:18 a.m. local time at a shallow depth of 9 kilometers, with its epicenter located 36 kilometers northeast of Gayo Lues, a sparsely populated regency covering 5,549.91 square kilometers in Aceh's interior. Home to approximately 106,136 residents as of mid-2024, the regency represents less than 2% of Aceh's total population and serves as the capital district of Blangkejeren.

Tectonic cause and fault system

Wijayanto, BMKG's Director of Earthquakes and Tsunamis, attributed the seismic activity to movement along the Oreng Fault. The fault forms part of the Great Sumatran Fault system, a 1,900-kilometer dextral strike-slip zone that accommodates tectonic motion between the Indo-Australian and Sunda plates along the length of Sumatra. Source mechanism analysis indicated strike-slip movement triggered the quake.

Intensity of shaking across regions

Residents in Gayo Lues experienced the strongest shaking at intensity V on the Modified Mercalli Intensity scale. At this level, nearly all residents felt the tremors, glassware shattered, and large objects swayed noticeably. Moderate shaking measuring IV MMI affected several other Aceh districts, including Southwest Aceh, Southeast Aceh, North Aceh, Lhokseumawe, East Aceh, Bener Meriah, and Central Aceh.

Weaker tremors rated at II to III MMI reached Pidie district in Aceh and crossed provincial boundaries into North Sumatra, where they were felt in the cities of Medan and Sibolga.

Aftershocks and ongoing monitoring

By 11:30 a.m., BMKG had recorded one magnitude 3.8 foreshock preceding the main event, followed by two aftershocks. The largest aftershock measured magnitude 4.3. The agency continues monitoring seismic activity in the region.

Indonesia's seismic landscape

Indonesia experiences frequent seismic activity due to its position along multiple tectonic boundaries. Historical data from the past 26 years shows the country averages approximately 264 earthquakes of magnitude 5.0 or higher annually, equivalent to 22 such events per month. The archipelago sits near 13 identified megathrust zones capable of producing earthquakes ranging from magnitude 7.8 to 9.2, located off the coasts of western Sumatra, southern Java, Bali, Nusa Tenggara, northern Sulawesi, Halmahera, and Papua.

Aceh's devastating earthquake history

Aceh Province has experienced devastating earthquakes in recent decades. The December 26, 2004 earthquake and tsunami, measuring magnitude 9.1, ranks as the third-largest earthquake in recorded history. That disaster claimed approximately 227,000 lives across the Indian Ocean region and displaced more than 1.7 million people, with over 120,000 deaths occurring in Aceh Province alone. More recently, a magnitude 6.5 earthquake struck the regencies of Bireun, Pidie, and Pidie Jaya on December 7, 2016, killing at least 97 people and causing widespread structural damage.

Paleoseismological research on fault systems in the region has revealed evidence of at least three ground-rupturing earthquakes over the past 1,000 years, with major fault lines extending 250 kilometers from Tripa to Banda Aceh, underscoring the area's long history of seismic activity.

BMKG emphasized the importance of ignoring unverified rumors and following official information channels as monitoring of the situation continues.