By Kyle Aristophere T. Atienza, Reporter

AT LEAST one person died and four others were hurt after a magnitude 7.6 earthquake rocked the southern Philippine island of Mindanao on Saturday night, prompting authorities to issue a tsunami warning that forced coastal residents to flee their homes around midnight.

Nine people were still missing, while more than 500 families were affected, Defense Secretary Gilberto Eduardo Gerardo C. Teodoro, Jr. told a news briefing on Sunday.

The tremor struck at a depth of 32.8 kilometers (km) near the province of Surigao del Sur at 10:37 p.m., according to the US Geological Survey (USGS).

The quake occurred as a result of oblique reverse faulting at a shallow depth of about 75 km west of the Philippine Trench, it said on its website.

“While commonly plotted as points on maps, earthquakes the size of the Dec. 2 event are more appropriately described as slip over a larger fault area. Earthquakes of this size are typically about 100×35 km,” it added.

The Philippines lies in the so-called Pacific Ring of Fire, a belt of volcanoes around the Pacific Ocean where most of the world’s earthquakes strike. It also lies along the typhoon belt in the Pacific and experiences about 20 storms each year.

The Philippines frequently experiences moderate to large earthquakes, the USGS said, noting that 127 additional earthquakes of magnitude 6 or larger have occurred in the past 100 years within 250 km of Saturday’s quake. Fifteen of these were magnitude 7 or larger.

“Earthquakes in the Philippines exhibit diverse styles of faulting that are indicative of the locally complex tectonic motions,” the USGS said. “Moreover, this region experiences earthquakes across a range of depths, from shallow surface rupturing strike-slip earthquakes, to deep earthquakes located within subducting oceanic slabs.”

The Philippine Institute of Volcanology and Seismology (Phivolcs) measured the quake at magnitude 7.4, while the Japanese weather agency estimated it at 7.7.

It was followed by another quake at 3:43 a.m. on Sunday, which had a depth of 64.3 km, the USGS said on its website. It recorded three more aftershocks with magnitudes 6.2, 6.1 and 6.

The Pacific Tsunami Warning Center in Hawaii warned tsunami waves were expected to hit southern Philippines and parts of Indonesia, Palau and Malaysia. 

It later said the tsunami threat had passed. Minor sea level fluctuations might occur in some coastal areas, it added.

Right after the Saturday quake, people along the coast of Surigao Del Sur and Davao Oriental were told to leave their homes and seek higher ground.

In a separate tsunami warning, Phivolcs warned of a destructive tsunami “with life threatening wave heights” — more than a meter above normal tides, which could be higher in enclosed bays and straits.

It asked owners of boats in shallow coastal waters in the two provinces to secure their vessels and immediately move away from the waterfront. Boats already at sea were advised to stay offshore in deep waters.

One of the first videos that circulated on social media after the Saturday quake showed people shouting and rushing to leave a commercial bar in Davao City.

In Hinatuan town, where the 7.6-magnitude quake struck, crowds rushed to evacuation centers. In Butuan City, patients were evacuated from a hospital.

After the earthquake, tsunami waves of as high as 1.3 feet were seen on some outlying islands in Japan.

The Civil Aviation Authority of the Philippines (CAAP) said there was no major damage on Mindanao airports. The airports in Butuan, Surigao, Siargao, Tandag and Bislig had minor damage, it added.

“Except for a few wall tiles that fell off in the international arrival elevator area, Davao International Airport facilities did not incur damage,” it said, citing CAAP Manager Rex A. Obcena. “Passengers and duty personnel are also all safe and sound.”

Flight operations at these airports were normal, the agency said.

It said the quick response team of all other airports in Mindanao were conducting runway and passenger terminal building inspections to ensure any damage is repaired.