Philippines issues tsunami warning after powerful 7.8-magnitude earthquake strikes off Mindanao coast

A powerful magnitude 7.8 earthquake struck off the coast of southern Mindanao on Monday morning, prompting Philippine authorities to warn of aftershocks and a possible tsunami in several coastal provinces.

The Philippine Institute of Volcanology and Seismology, known as Phivolcs, said the offshore quake was recorded at 7.37am on 8 June at a depth of 33 kilometres. The agency placed the epicentre 32 kilometres south, four degrees west, of Maasim town in Sarangani province.

Phivolcs had initially reported the earthquake as magnitude 7.0, with the epicentre located off General Santos City, before upgrading it to magnitude 7.8.

The US Geological Survey also reported a magnitude 7.8 earthquake in the Mindanao region, while the Pacific Tsunami Warning Center said tsunami waves were possible on some coasts in the region.

Phivolcs warned that tsunami waves of more than one metre above normal tide levels could affect coastal areas. The first waves were expected between 7.37am and 9.37am and could continue for several hours.

Residents in coastal communities in Sarangani, Davao Occidental, Tawi-Tawi, Sulu, Basilan, Zamboanga del Sur, Zamboanga Sibugay, Sultan Kudarat and South Cotabato were advised to evacuate immediately to higher ground or move farther inland.

The agency also advised owners of boats in harbours, estuaries and shallow coastal waters in the affected provinces to secure their vessels and move away from the waterfront. Boats already at sea were told to remain offshore in deep waters until further notice.

The strongest reported shaking was felt in General Santos City, where Phivolcs recorded Intensity VII, classified as “destructive” on the agency’s earthquake intensity scale. Intensity VI, or “very strong” shaking, was reported in Palimbang and Senator Ninoy Aquino in Sultan Kudarat.

Intensity V, described as “strong”, was felt in Davao City; Kidapawan City and Carmen in Cotabato; Bagumbayan, Kalamansig and President Quirino in Sultan Kudarat; and Sibuco and Siocon in Zamboanga del Norte.

Moderately strong shaking, or Intensity IV, was reported in Mati City in Davao Oriental, Buug in Zamboanga Sibugay, and the Davao Oriental towns of Caraga, Manay and Tarragona.

Weaker shaking was also reported in Butuan City, parts of Surigao del Norte, Zamboanga del Norte, Zamboanga del Sur, Leyte, Southern Leyte, Bukidnon, Misamis Oriental and Cagayan de Oro.

Instrumental readings recorded even higher shaking in some areas. Phivolcs said Instrumental Intensity VIII was recorded in Malapatan, Sarangani, while Instrumental Intensity VII was recorded in Koronadal City, South Cotabato, and Santa Maria, Davao Occidental. Instrumental Intensity VI was recorded in General Santos City and T’boli, South Cotabato.

President Ferdinand Marcos Jr. said the Office of Civil Defence and the National Disaster Risk Reduction and Management Council were coordinating disaster response and monitoring across affected areas. He said the Department of Social Welfare and Development had been directed to preposition relief goods and ensure evacuation centres were ready.

The Department of Public Works and Highways was also placed on standby to assess damage to roads, bridges and critical infrastructure, and to clear routes needed for rescue and relief operations.

Marcos suspended classes at all levels across affected areas in Mindanao until further notice.

Public schools across the Philippines had opened for the new school year on Monday.

There was no immediate confirmed information on casualties or damage in the initial reports. Phivolcs said damage and aftershocks were expected following the offshore tremor.

The Philippines lies along the seismically active Pacific Ring of Fire and regularly experiences earthquakes and volcanic activity.