M7.8 Philippines Earthquake: An Alarm for the Forgotten Megathrust Zone in Eastern Indonesia
The magnitude 7.8 earthquake that shook southern Mindanao, Philippines, on Monday (8/6) serves as a serious warning for Indonesia regarding the massive potential threat of earthquakes and tsunamis from active subduction systems in the eastern region of the country. This is because the zone receives significantly less attention than the Sumatra and Java megathrust zones.
Daryono, a member of the Indonesian Disaster Expert Association (IABI), stated that the Mindanao earthquake is not an isolated event, but rather part of a process of releasing tectonic energy that has long been stored undersea. “The M7.8 earthquake that shook southern Philippines and parts of North Sulawesi should not be read as a single event. It is a loud alarm, not only for the Philippines but also for Indonesia,” he said in a written statement on Tuesday (9/6).
According to Daryono, the region spanning from southern Philippines to North Maluku and North Sulawesi is one of the most tectonically complex areas in the world. This area features the interaction of three major earthquake sources: the Philippine Sea Plate Subduction, the Cotabato Subduction, and the Molucca Sea Double Subduction system. He explained that these subduction zones continuously accumulate energy over decades or even centuries. When the stored pressure can no longer be sustained, the energy is released in the form of massive earthquakes with the potential to trigger tsunamis.
Daryono highlighted that several studies indicate the North Maluku, North Sulawesi, and Philippines regions have the potential to produce earthquakes of up to magnitude 8.2. However, these areas have not received as much attention as the megathrust zones in western Indonesia. “It is as if the subduction system in this zone has become the forgotten megathrust zone in eastern Indonesia,” he remarked.
History records several devastating earthquakes and deadly tsunamis in the region. An 8.3 magnitude earthquake in 1918 and an 8.1 magnitude earthquake in 1976 in the Cotabato region of the Philippines triggered massive tsunamis that killed over 5,000 people. Additionally, a 7.6 magnitude earthquake off the eastern coast of the Philippines in 2012 and the 7.6 magnitude Hinatuan earthquake in 2023 also triggered tsunamis. In the Molucca Sea and surrounding areas, large earthquakes such as the 7.2 magnitude Halmahera earthquake in 2019 and the 7.9 magnitude Minahasa earthquake in 1996 demonstrate the high level of seismic activity in the region.
Based on analysis of the epicentre location, hypocentre depth, and earthquake source mechanism, Daryono believes the M7.8 Mindanao earthquake on 8 June 2026 originated from the Cotabato Subduction Zone via a thrust fault mechanism. He assessed that the series of earthquake activities indicates that the southern Philippines to the Molucca Sea region is one of the most active tectonic systems in the world, with the potential for large earthquakes and tsunamis that must remain a constant concern.
Consequently, Daryono urged the government and the public not to be reactive to disasters. He emphasised the importance of increasing disaster education, implementing risk-based spatial planning, and strengthening mitigation systems down to the community level. “The earthquake occurring now is not merely news. It is a stern warning, and ignoring warnings from the earth is a mistake that is always paid for dearly,” he asserted. He noted that preparedness is key to reducing the risk of casualties and losses should a major earthquake from the megathrust zone recur in eastern Indonesia.