6.7 earthquake strikes: current seismicity in the Philippines as tectonic plate agitation increases

 

February 5, 2012 – PHILIPPINES – The Philippines, like Japan, sits in one of the most volatile tectonic areas on Earth but unlike Japan, the Philippines is under geological assault from plate movements on all sides. The Philippine plate is squeezed in between the Eurasian plate and the Pacific Plate, but the situation is more complex than that. The Philippine Islands are surrounded by complex plate boundaries, and the Philippines Plate rather consists of several micro-plates – squeezed in between two convergent plate margins. The lines with black triangles are active subduction zones with teeth on the over-riding plate. Lines with white triangles are passive subduction zones with teeth on the over-riding plate. The major Philippine fault zone is shown as a black line with arrows showing the movement direction. The volcanoes Pinatubo and Mayon are shown as red dots. The volcanoes of the Philippines are probably the most deadly in world. Both Pinatubo and Mayon are both capable of producing VEI6 type eruptions. Because the moon’s tidal influence is so great in the Pacific, volcanologists warned in 2006 that Mount Mayon could explode at any time and that the gravitational pull of a full moon could provide the final push. A full moon coincided with at least three of Mayon’s nearly 50 explosions over the last four centuries, including the two most recent in 2000 and 2001. The volcanoes  are concentrated in a northern volcanic arc above and east of the north-western subduction zone (Manila Trench) and in a southern volcanic arc above and west of the south-eastern subduction zone (Philippine trench). The Sulu trench also produce a (discontinuous) line of active volcanoes. The Mayon volcano may be associated with the transform fault that connects the eastern and the western subduction zones. This transform fault is offset by the younger north-south directed Philippine Fault. The Eurasian Plate is being subducted along the western side of Luzon and Mindoro at a rate of 3cm/year. The Philippine Fault Zone decouples the northwestward motion of the Pacific with the southwestward motion of the Eurasian Plate. Movements along other active faults are responsible for the present-day high seismicity of the Philippine Archipelago. –The Extinction Protocol

A 6.8 (6.7 downgraded by USGS) magnitude earthquake, at a depth at 29 miles, struck off the Philippines on Monday, northeast of Dumaguete, Negros island, at 0349 GMT, the U.S. Geological Survey reported. There were no immediate reports of casualties or damage, and the U.S. National Oceanic and Atmospheric Administration said that based on all available data a Pacific-wide tsunami is not expected.