LEGAZPI CITY, Philippines -- A magnitude 5 earthquake struck off Legazpi City at 1:38 p.m. Wednesday, the US Geological Survey said, about four-and-a-half hours after Albay and Sorsogon were hit by a 4.8 magnitude tremor.

There were no immediate reports of damage or injury.

The latest undersea quake was located 45 kilometers south of Bicol region?s southeastern city and 50 kilometers north-northeast of Masbate island at a depth of 31.6 kilometers, the USGS said.

Alex Baloloy, senior science research analyst of the Philippine Institute
of Volcanology and Seismology (Phivolcs) in Bicol, said the first quake, with a 4.8 magnitude, struck at 8:59 a.m.

It was measured at intensity 5 in Bulan, Sorsogon, and intensity 3 in Legazpi City.

He said the earthquake's epicenter was detected 41 kilometers south and 17 kilometers west of Legazpi City with a depth of 21 kilometers.

The earthquake, caused by the movement of tectonic plates under the earth's surface, was not destructive since it was below magnitude 6, Baloloy said.

He added it had nothing to do with any activity on Mayon Volcano, which had been showing an intensified crater glow during the past weeks.

"The intensified crater glow is a sign of rising magma. But Mt. Mayon's alert warning is maintained at level 1," Baloloy said in a mobile phone interview.

He said visual observation of the crater glow is just one parameter in determining volcanic activity.

"We are now monitoring other parameters such as seismic activity, ground deformation, and sulfur dioxide emission," Baloloy said.

He added that the alert level status may only be heightened when all the parameters show a significant increase.

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