• The plate tectonics in the Philippines is complex and includes plate boundaries that are changing rapidly. Several micro-plates are getting squeezed between two convergent plate margins.

• Stratigraphic evidence indicates cessation and reactivation of subduction at some trenches. The currently active volcanoes in the Philippines define two north-south trending arcs.

• The scale and type of volcanism varies from monogenetic cinder cone fields to large stratovolcanoes and calderas. Composition of volcanic rocks range from tholeiitic basalt to andesite to shoshonite.

• The scale and type of volcanism varies from monogenetic cinder cone fields to large stratovolcanoes and calderas. Composition of volcanic rocks range from tholeiitic basalt to andesite to shoshonite.

• Black triangles = active subduction zones with "teeth" on the over-riding plate, white triangles = inactive subduction zones with "teeth" on the over-riding plate, arrows = transform or major strike-slip faults, red triangles = volcanoes active in the last 10,000 years. Plates and micro-plates shown in different colors. Based on Divis (1983). Volcanoes from Simkin and Siebert (1994).

Indeed the 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. They 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.

In the west, more steeply east-dipping subduction of the Eurasian Plate (South China Sea basin and the transitional oceanic-continental crust of the Palawan block) along the 560 mile (900 km) length of the Manila and Sulu trenches produces a discontinuous line of active volcanoes from Taal in the south to Iraya in the north. Volcanism associated with this subduction zone began about 10 million years ago.

In the east, shallow west-dipping subduction of the Philippine Plate at the Philippine Trench produces a line of volcanoes from Balut in the south to Mayon in the north. Based on Divis (1983).

Volcanoes in an east-west zone across central Luzon may be associated with a "leaky" transform fault that connects the two subduction zones. The transform fault is offset to the right by the younger Philippine Fault. Based on Divis (1983).

Map of Philippine Plate from USGS marking one of the many eartquakes in the area.

Major Tectonic Boundaries: Subduction Zones -purple and Transform Faults -green

The Philippine Fault Zone which trends N40°w is widely accepted as a major strike-slip fault comparable to the San Andreas fault. An area in south-eastern Luzon, commonly regarded as part of the main fault zone, has been studied in an effort to date the faulting and to establish its nature and extent.

• Two main episodes of faulting are recognized, one late Miocene on northerly faults, one Plio-Pleistocene on north-westerly faults. Both these episodes involve considerable dip-slip movements and the two principal Recent faults which have been recognized are also of dip-slip type. 

• Geomorphological evidence shows that the whole area has been subjected to Recent episodic but areally uniform uplift.

• Direct evidence of strike-slip movements is slight and the structural relations argue against major post-Miocene strike-slip movements. The possibility of earlier strike-slip cannot be excluded and the fault and fold systems show a good correlation with those predicted following the theory of Moody & Hill (1956).

• Possibly therefore the faults on which the main Miocene and later dip-slip movements occurred were initiated during earlier strike-slip episodes. A pre-Tertiary episode of left-lateral strike-slip in the Rift followed by a Miocene episode of right-lateral strike-slip on conjugate primary faults can be tentatively inferred. The direct evidence of faulting in the Rift, however, relates only to the Plio-Pleistocene activity of the morphogenic phase.

• Luzon is situated in a Plate Boundary Zone (PBZ), an actively deforming region where earthquakes and tectonic motion are prevalent  .

• These are direct consequences of rapid convergence between the Philippine Sea Plate and the Sundaland Plate (part of the Eurasian Plate) along dual, opposing subduction in the Manila Trench (western margin), and along the East Luzon Trough-Philippine Trench (eastern margin).

• The Philippine Fault System is an inter-related system of faults throughout the whole of the Philippine Archipelago, primarily caused byt ectonic forces compressing the Philippines into what tectonic geophysicists call the Philippine Mobile Belt

• The Philippine Mobile Belt is composed of a large number of accretionary blocks and strips. Most strips are long and narrow like the Zambales ophiolites which is at least 400 km long and 50 km wide.

• The strips generally run north-south and the zones of convergence are usually demarkated by fault lines. The Philippine Mobile Belt is compressed on the west by the Eurasian Plate and two arms of the Sunda Plate, and on the east by the Philippine Sea Plate. 

•  These tectonic plates have compressed and lifted parts of the Philippines causing extensive faulting, primarily on a north-south axis. The main fault runs most of the length of the Philippines and is called the Philippine Fault.

• In northern Luzon, the fault has become braided and is no longer single. All faults in the Philippines are inter-related by the tectonic forces causative of the Philippine Mobile Belt, or its tectonic induced volcanism. 

Tectonic Map of Far Northern Philippines including the Philippine Fault System

Tectonic Map of Northern Central Philippines including the Philippine Fault System

Tectonic Map of Central Philippines including the Philippine Fault System

Tectonic Map of Southern Philippines including the Philippine Fault System

Tectonic Map of Far Southern Philippines including the Philippine Fault System

Tectonic Map of the Philippines showing the Philippine Fault System generally

Northern and Central portions of Philippine Fault System

Northwest Luzon segment of Philippine Fault System