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. 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. At its deepest point, the trench reaches 10,540 meters (34,580 ft) or (5,760 fathoms).
The Philippine trench is hypothesized to be younger than 8–9 million years ago. The central part of the Philippine fault formed during the Plio-Pleistocene times is considered to be an active depression of the Earth's crust. 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. The rate of subduction on these plates is estimated to be about 15 cm per year. A convergent zone borders an estimate of 45% of the Philippine Trench today.
Although there are vast areas of subduction zones, some authors have considered this region to have low seismic activity, though the USGS has recorded many earthquakes with magnitude ≥ 7.2 in the region as shown by the map to the side. Most recently, in 2012 the Philippine Trench experienced an earthquake of Mw 7.6 (the 2012 Samar earthquake). It hit the trench with a hypocenter depth of 34.9 km. Areas adjacent to the subduction zones have experienced large seismic activity. In 1897, northern Samar experienced a Ms 7.3 earthquake while in 1924 southern Mindanao experienced one with a Ms 8.2.
The trench reaches one of the greatest depths 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).
Sedimentation of the Philippine trench contains slightly metamorphosed, calc-alkalic, basic, ultrabasic rock and sand grains. 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. The sediments found in the trenches are hypothesized to have been deposited by turbidity currents. A turbidity current is an underwater current that moves rapidly and carries sediment.
Trenches in the Philippine region
Known trenches in LuzViMinda are:
- Hessler, Robert R.; Ingram, Camilla L.; Yayanos, A. Aristides; Burnett, Bryan R. (1978). "Scavenging amphipods from the floor of the Philippine trench". Deep Sea Research. 25 (11): 1029–1047. doi:10.1016/0146-6291(78)90585-4.
- Deschamps, A.; Lallemand, S. (2003). "Geodynamic setting of Izu-Bonin-Mariana boninites". In Larter, R.D.; Leat, P.T. (eds.). Intra-Oceanic Subduction Systems: Tectonic and Magmatic Processes. Geological Society, London, Special Publications. 219. pp. 163–185.
- "M 7.7 - Philippine Islands region". United States Geological Survey. 1911.
- "M 7.4 - Philippine Islands region". United States Geological Survey. 1921.
- "M 7.8 - Philippine Islands region". United States Geological Survey. 1943.
- "M 7.3 - Philippine Islands region". United States Geological Survey. 1952.
- "M 7.2 - Samar, Philippines". United States Geological Survey. 1975.
- "M 7.3 - Catanduanes, Philippines". United States Geological Survey. 1988.
- "M 7.6 - Mindanao, Philippines". United States Geological Survey. 1989.
- "M 7.2 - Samar, Philippines". United States Geological Survey. 1995.
- "M 7.5 - Mindanao, Philippines". United States Geological Survey. 2001.
- "M 7.2 - Samar, Philippines". United States Geological Survey. 2012.
- Lallemand, Serge E.; Popoff, Michel; Cadet, Jean-Paul; Bader, Anne-Gaelle; Pubellier, Manuel; Rangin, Claude; Deffontaines, Benoît (1998-01-10). "Genetic relations between the central and southern Philippine Trench and the Sangihe Trench". Journal of Geophysical Research: Solid Earth. 103 (B1): 933–950. doi:10.1029/97jb02620.
- Larsen, B. (1968). "Sediment from the central Philippine trench". Galathea Report. 9: 7–21.
- Ye, Lingling; Lay, Thorne; Kanamori, Hiroo (2012). "Intraplate and interplate faulting interactions during the August 31, 2012, Philippine Trench earthquake (Mw 7.6) sequence". Geophysical Research Letters. 39 (24): L24310. doi:10.1029/2012gl054164.