page_title: Subduction tectonics of the Philippines
section_title: Formation of Philippine Trench
hierarchical_section_title: Subduction tectonics of the Philippines / Formation of the Philippine archipelago / Formation of Philippine Trench
caption_attribution_description: English: Volcanoes in the Philippines. Plotted by GeoMapApp.
context_page_description: The subduction tectonics of the Philippines is the control of geology over the Philippine archipelago. The Philippine region is seismically active and has been progressively constructed by plates converging towards each other in multiple directions. The region is bounded by subduction zones, where surrounding oceanic plates to the east and west slide towards the centre of the Philippine archipelago. Subduction results in deep oceanic trenches, such as the Philippine Trench and Manila Trench, bounding the eastern and western sides of the Philippine archipelago, respectively. The Philippine archipelago is also cut along its length by a left-lateral strike-slip fault known as the Philippine Fault. The region is also known as the Philippine mobile belt due to its complex tectonic setting.
  Active subduction disturbs the crust, leading to volcanic activity, earthquakes and tsunamis, making the Philippines one of the most hazard-prone regions on Earth.
context_section_description: The collision of Palawan Block to the Philippine Mobile Belt was related to the formation of the Philippine Trench. It is argued that the formation of the Philippine Trench was to entertain the stress resulted from the Palawan collision. Adding compressional stresses to the incipient subduction, it progressively developed into a subduction zone.
  The Philippine trench is known to be formed by recent subduction. It is deduced by the shallow subduction slab reflected by shallow seismicity and considering its subduction rate at the same time.
  Another hypothesis is that the Philippine Trench was originated near Bicol (around 13˚N) and propagates southwards to present termination abruptly at northeast Halmahera (2˚N). This is supported by evidence such as variation of the age of volcanoes along the trench, depth of subduction slap and geometry of the trench.
  The hypothesis is supported by evidence of the age of arc volcanism along the Eastern magmatic arc. The oldest volcano is located in Bicol, with age of 6.5 Ma. The progressive southwards younging trend of volcanoes along the trench from Bicol is observed, where the youngest subduction-related volcanic activities are observed right at the northeastern Halmahera. The younging trend is also observed northwards from Bicol to the northern termination of East Luzon Trough. Supporting the hypothesis of  northwards and southwards propagation of Philippine Trench from Bicol.
  The geometry of the trench also gives evidence supporting the hypothesis of both northwards and southwards propagation. Lallemand et al. (1990) proposed that the trench was first formed near 9˚N then propagated towards north and south, resulting in a relatively symmetrical geometry to the north and south of 9˚N. The deepest part of the trench could be found around 9˚N, where the average depth of the trench is over 10,000 meters. The trench depth is progressively shallower to the north and to the south,  with the depth near 8,000 meters at the southern terminal and around 6,000 meters at the northern terminal.
caption: Volcanoes in the Philippines.
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