5 quakes jolt Mindanao, felt as far as Bicol region

07/26/2010 - A total of five earthquakes, three of them strong ones with two aftershocks, shook the southwestern quadrant of Mindanao island yesterday morning, the Philippine Institute of Volcanology and Seismology and the US Geological Survey said.

While the epicenters of the quakes were out at sea, residents of Mindanao reported being awakened by the quakes, one of which was strong enough to be felt as far north as the Bicol region.

The first earthquake occurred at around 6:08 a.m. with a magnitude of 7.3. with the epicenter estimated at 100 kilometers southwest of Cotabato or 120 kilomenters south of Pagadian City. The quake had a depth of 604.5 kilometers.

The next quake occurred 18 minutes later at 6:19 a.m. but was relatively weaker with a magnitude of 5.4. This quake had a depth of 594.8 kilometers with the epicenter estimated at 95 kilometers west southwest of Cotabato City or 115 kilometers south of Pagadian.

Around 30 minutes later, a magnitude 7.6 earthquake struck at 6:51 a.m. The epicenter was estimated at 115 kilometers southwest of Cotabato City or 145 kilometers south of Pagadian City. The quake had a depth of 576.3 kilometers.

The last earthquake occurred at 7: 15 a.m. wtth a magnitude of 7.4. The epicenter was estimated at 120 kilometers south of Pagadian City or 120 kilometers west southwest of Cotabato City. The quake had a depth of 616.7 kilometers.

An aftershock occurred at 8:50 a.m. and was measured at magnitude 4.9 with the epicenter estimated at 100 kilometers southwest from Cotabato City or 142 kilometers south of Pagadian City.

The Philippines has an average of around 20 earthquakes a day due to its location in the Pacific Ring of Fire, where there is a high degree of volcanic and seismic activity.

Phivolcs Director Renato Solidum noted that the earthquakes emanated from very deep in the bowels of the earth, at depths ranging from 570 kilometers to over 600 kilometers.

According to Solidum, the first earthquake at 6:08 a.m. was felt at Intensity 2 in General Santos City, Surigao City, Butuan City, Cagayan de Oro City and Tacloban City.

The weaker earthquake at 6:19 a.m. was also was felt in Butuan and Surigao.

At 6:52 a.m., another tremor with a magnitude 6.8 struck the area. It was felt at Intensity 4 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.

Around 6:45 a.m., Genely Eborde, 22, an ESL teacher who lives in barangay y Banilad in Cebu City just went out after taking a bath when her boardmates panicked. They told her there was an earthquake.

“I didn't believe them because I never felt it while I was inside the shower,” Eborde said.

About 7:10 a.m., however, she was sitting outside their room when she saw the cabinet shake and felt the ground under her shake. She said it lasted for almost a minute.

She said she sat down and did not move for fear she might lost her balance.

“It was not really a strong quake but it’s strong enough that you can really feel its intensity,” she said.

Another stronger quake occurred at 7:15 a.m. with a magnitude of 6.7. Solidum said this quake was felt in many parts of the Visayas and even in the Bicol Region in Luzon.

It was felt at Intensity 4 in Tanhay, Negros Oriental and San Jose City, Negros Oriental; Intensity 3 in Irosin, Sorsogon, General Santos City and Antique; Intensity 2 in Legazpi City, Tacloban City, Cebu, Kidapawan, Dipolog, Antipolo and Manila.

Solidum said a deeper quake is felt over a wider 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 said deep earthquakes, while felt by people, do not tend to be damaging because the shaking at the surface of the earth is diminished. They also do not cause tsunamis, Solidum added.

He said earthquakes in the area of Saturday's swarm of tremors are mostly caused by movement between the Moluccas sea plate and Mindanao island. (Inquirer.net)

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