Series of Earthquakes continues
The series of Earthquakes off the coast of Zambales continues. Since the initial magnitude 6.0 hit, yesterday at 08:26, 12 more shocks were recorded. Their intensities were from magnitude 2.3 to 4.5.
All Quakes occurred in the Manila trench. The Manila Trench is an ocean trench in the South China Sea West Philippines Sea). It reaches a depth of about 5,400m, in contrast with the average depth of the South China Sea of about 1,500m. It is created by subduction, in which the Eurasian Plate is subducting under the Philippine Mobile Belt.
The Philippine Mobile Belt is a complex portion of the tectonic boundary between the Eurasian Plate and the Philippine Sea Plate, comprising most of the country of the Philippines. It includes two subduction zones, the Manila Trench to the west and the Philippine Trench to the east, as well as the Philippine Fault System. Within the Belt, a number of crustal blocks or microplates which have been sheared off the adjoining major plates are undergoing massive deformation.
Already in March 2011, PHIVOLCS informed that the Manila trench, could actually trigger earthquakes with magnitudes as high as 8.2.
Here is a schema of a subduction zone like the one found in the Manila trench.
When two oceanic plates collide, the younger of the two plates, because it is less dense, will ride over the edge of the older plate. Oceanic plates grow more dense as they cool and move further away from the Mid-Ocean Ridge. The older, heavier plate bends and plunges steeply through the athenosphere, and descending into the earth, it forms a trench that can be as much as 70 miles wide, more than a thousand miles long, and several miles deep.