Several earthquakes and aftershocks shook parts of Visayas and Mindanao in the Philippines Saturday (July 24) morning, authorities said.

While the epicentres of the quakes were out in the sea, residents were reportedly awakened by the tremors.

The first earthquake occurred at around 6:08 am with a magnitude of 7.3 and the epicentre estimated at 100 kilometres southwest of Cotabato or 120 south of Pagadian. The quake had a depth of 604.5 kilometres, according to the US Geological Survey and the Philippine Institute of Volcanology and Seismology.

Phivolcs director Renato Solidum said the tremor was also felt in the cities of Zamboanga, Pagadian, Koronadal, General Santos and in Manila although there have been no reports of casualties or damages.

He said the quake was intensity 2 in General Santos City, Surigao City, Butuan City, Cagayan de Oro City and Tacloban City.

The next quake occurred at 6:19 am but was relatively weaker, with a magnitude of 5.4, a depth of 594.8 kilometres, and an epicentre estimated at 95 kilometres west southwest of Cotabato City or 115 kilometres south of Pagadian City, the USGS and Phivolcs said.
A magnitude 7.6 earthquake followed at 6:51 am. The epicentre was estimated at 115 kilometres southwest of Cotabato City or 145 kilometres south of Pagadian City. The quake had a depth of 576.3 kilometres, the USGS said.

Phivolcs recorded the tremor at 6:52 am with a 6.8 magnitude. Intensity 4 was registered in General Santos City; ; Intensity 3 in Davao City and Davao del Sur; Intensity 2 in Tacloban City, Palo in Leyte, Cagayan de Oro, Cebu and Davao.

At 7: 15 am, a magnitude of 7.4 quake was recorded, with the epicentre estimated at 120 kilometres south of Pagadian City or 120 kilometres west southwest of Cotabato City. The quake had a depth of 616.7 kilometres, the USGS said.

Phivolcs recorded the same quake at a magnitude of 6.7. Solidum said this quake was felt in many parts in the Visayas and even in the Bicol Region in Luzon. It was felt as Intensity 4 in Tanhay, Negros Orienal and San Jose City, Negros Oriental; Intensity 3 in Irosin, Sorsogon, General Santos City and Antique; Intensity 2 in Legaspi City, Tacloban City, Cebu, Kidapawan, Dipolog, Antipolo and Manila.

Solidum said a deeper quake reaches a wide area. “Because of the depth, the shaking is amplified. Plus you have other factors. Antipolo is kind of high so it can be felt there. Manila has a soft bedrock so you might be able to feel it too.”

He also said deep earthquakes, while being felt by people, did not tend to be damaging because the shaking at the surface would diminish.

He explained that due to the depth records of the quakes, tsunamis were unlikely.

He also said earthquakes in the area were mostly caused by movement between the Molucca sea plate and the Mindanao island.
Meanwhile, the USGS said an aftershock occurred at 8:50 am and was measured at magnitude 4.9 with the epicenter estimated at 100 kilometres southwest from Cotabato City or 142 kilometers south of Pagadian City.

A magnitude 5.3 occurred at 9:44 am with a depth of 592.2 kilometres, an epicentre estimated at 91 kilometres southwest of Cotabato City and 136 kilometres south Pagadian City, the USGS said.

Yolly Andrias, a resident here, said they were still sleeping when the strong quake awoke them.

“Some of our Muslim neighbors fired their weapons to drive away bad spirits,” she said.

But Monisa Tulawie, a staff member at the Cotabato City mayor’s office told Agence France-Presse that the quake was "kind of mild."

Other residents contacted by phone were unaware of what had happened, saying they had not been woken by the tremors.

"We have received no reports of damage or casualties," said local fire official Marlon Macapili of the Autonomous Region in Muslim Mindanao, a self-ruled area that includes four provinces around Cotabato.

The Philippines sits on the Pacific "Ring of Fire" where continental plates collide causing frequent seismic and volcanic activity.

The worst earthquake in the country happened on Aug 16, 1976 after a tsunami caused by a quake killed between 5,000 and 8,000 people in the Moro Gulf region in southern Philippines.