Philippine Trench

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The Philippine Trench, in the middle of the picture.

The Philippine Trench (also Philippine Deep, Mindanao Trench, and Mindanao Deep) is a submarine trench to the east of the Philippines. The trench is located in the Philippine sea of the western North Pacific Ocean and continues NNW-SSE [1] It has a length of approximately 1,320 kilometres (820 miles) and a width of about 30 km (19 mi) from the center of the Philippine island of Luzon trending southeast to the northern Maluku island of Halmahera in Indonesia.

Immediately to the north of the Philippine Trench is the East Luzon Trench. They are separated, with their continuity interrupted and displaced, by Benham Plateau on the Philippine Sea Plate.[2]

Formation[edit]

The Philippine trench is hypothesized to be younger than 8-9 Ma. The central part of the Philippine fault formed during the Plio-Pleistocene times [3] is considered to be an active depression of the earth’s crust.[4] The trench formed from a collision between the Palawan and Zamboanga plates. This caused a change in geological processes going from a convergent zone to a subduction zone. The subduction zone is located west to east of the Philippine Islands.[3] The rate of subduction on these plates is estimated to be about 15 cm per year.[2] A convergent zone borders an estimate of 45% of the Philippine Trench today.[3] Although there are vast regions of subduction zones, until 2012, there has been no recorded large earthquake activity since the 1600s.[5] This region is considered to have low seismic activity however, in 2012 the Philippine Trench experienced an earthquake of Mw 7.6. The earthquake hit the trench at 10.838°N, 126.704°E, with a hypocenter depth of 34.9 km.[5] Areas adjacent to the subduction zones however, have experienced large seismic activity. In 1897 northern Samae experienced a Ms 7.3 earthquake and in 1924 south east of Mindanao experienced a Ms 8.2 earthquake.[5]

Depth[edit]

The trench reaches one of the greatest depth in the ocean, third only to the Mariana trench and the Tonga trench. Its deepest point is known as Galathea Depth and reaches 10,540 meters (34,580 ft) or (5,760 fathoms).[2]  At these depths, it is believed that deuterium, an isotope of hydrogen, resides near the bottom of the trench from deep-sea hydrothermal vents and is in high commercial interest.

Sedimentation[edit]

Sedimentation of the Philippine trench contains slightly metamorphosed, calc-alkalic, basic, ultrabasic rock and sand grains.[4] The southern area of the trench contains homogenous, blue, clay silt and was poor in lime. Sand grains that were also found contained fresh basaltic andesite.[4] The sediments found in the trenches are hypothesized to have been deposited by turbidity currents.[4] A turbidity current is an underwater current that moves rapidly and carries sediment.

References[edit]

  1. ^ Hessler, R.R., Ingram, C.L., Yayanos, A.A., and Burnett, B.R (1978). "Scavenging amphipods from the floor of the Philippine trench". Deep sea research. 25: 1029–1047. 
  2. ^ a b c Deschamps: Lallemand (2003). Intra-oceanic subduction systems: tectonic and Magmatic processes.
  3. ^ a b c Lallemand, S.E., Popoff, M., Cadet, J., Bader, A., Pubellier, M., Rangin, C., Deffontaines, B, 1998. "Genetic relations between the central and southern Philippine Trench and the Sangihe Trench.". Journal of geophysical research. 103: 933–950. 
  4. ^ a b c d Larsen, B (1968). "Sediment from the central Philippine trench". Institute of applied geology. 
  5. ^ a b c Ye, L., Lay, T., Kanamori, H (2012). "Intraplate and interpolate faulting interactions during the August 31, 2012, Philippine trench earthquake (Mw 7.6) sequence". Geophysical research letter. 39.