July 11, 2011

6.2-magnitude earthquake rocks Philippines Negros Islands

At least three predawn quakes, with the most powerful measuing magnitude-6.2, jolted the Negros area in Western Visayas, with the quake felt as far as Central Visayas and Mindanao.

Philippine Institute of Volcanology and Seismology director Renato Solidum Jr. said the quake was recorded at 4:47 a.m. even as Phivolcs warned of possible aftershocks.

"Most likely siguro dapat disaster manager ng iba't ibang bayan tingnan mabuti. (Pero) kung Intensity V walang damage. Kung Intensity VI ang report baka may damage (Most likely, disaster managers of the areas concerned should conduct inspections. If the most powerful felt is Intensity V, there is not likely to be damage. But if the intensity is Intensity VI, that's the time there will likely be damage)," Solidum said in an interview on dzBB radio.

Solidum said a magnitude-6.2 quake is considered "moderately strong."

He also reminded residents to be always prepared since there is no way of telling when a powerful quake will hit.

"The approach is always to be prepared. We must review our preparedness measures and know how to respond. We do not know when a powerful quake will hit," he said in Filipino.

The United States Geological Survey initially measured the first quake at magnitude 6.4.

It said the epicenter was 126 km west northwest of Dumaguete; 135 km south southwest of Iloilo, Panay; 151 km south southwest of Bacolod; or 576 km south southeast of Manila.

3 quakes

For its part, Phivolcs said the first quake was felt at 4:47 a.m., with the epicenter at 93 km southwest of Dumaguete City.

It was felt at:
  • Intensity V: Sipalay City, Negros Occidental
  • Intensity IV: Oton, Iloilo; Dumaguete City; Binalbagan and Hinigaran; Sibulan
  • Intensity III: San Jose, Antique; Dapitan City; Talisay City, Negros Occidental
  • Intensity II: Cagayan de Oro City; Dipolog City; La Carlota City, Negros Occidental and
  • Intensity I: La Castellana, Negros Occidental
While no damage was expected, Phivolcs warned of possible aftershocks.

Phivolcs also recorded at least two more quakes after the 4:47 a.m. quake.

The first measuring magnitude 5.5 was recorded at 5:03 a.m., while the second measuring magnitude 5.7 was recorded at 5:05 a.m.

Both were at 112 km southwest of Dumaguete City, Phivolcs said.

However, the USGS measured the second quake at magnitude 5.1 and the third at magnitude 4.9.

Intensity scale

In its intensity scale, Phivolcs describes an Intensity V quake as "strong."

An Intensity V quake is "generally felt by most people indoors and outdoors" while many sleeping people are awakened.

"Some are frightened, some run outdoors. Strong shaking and rocking felt throughout building. Hanging objects swing violently. Dining utensils clatter and clink; some are broken. Small, light and unstable objects may fall or overturn. Liquids spill from filled open containers. Standing vehicles rock noticeably. Shaking of leaves and twigs of trees are noticeable," it said.

An Intensity IV quake is "moderately strong," felt generally by people indoors and by some people outdoors.

"Light sleepers are awakened. Vibration is felt like a passing of heavy truck. Hanging objects swing considerably. Dinner, plates, glasses, windows and doors rattle. Floors and walls of wood framed buildings creak. Standing motor cars may rock slightly. Liquids in containers are slightly disturbed. Water in containers oscillate strongly. Rumbling sound may sometimes be heard," it said.

An Intensity III quake is "weak," felt by many people indoors especially in upper floors of buildings.

An Intensity II quake is "Slightly felt," felt by few individuals at rest indoors. — RSJ, GMA News

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