Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second plate, the heavier plate dives beneath the other and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with rates of convergence as high as 11 cm/year.
A convergent boundary is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a plane where many earthquakes occur, called the Wadati–Benioff zone. These collisions happen on scales of millions to tens of millions of years and can lead to volcanism, earthquakes, orogenesis, destruction of lithosphere, and deformation. Convergent boundaries occur between oceanic-oceanic lithosphere, oceanic-continental lithosphere, and continental-continental lithosphere. The geologic features related to convergent boundaries vary depending on crust types.
The Australian plate is a major tectonic plate in the eastern and, largely, southern hemispheres. Originally a part of the ancient continent of Gondwana, Australia remained connected to India and Antarctica until approximately 100 million years ago when India broke away and began moving north. Australia and Antarctica had begun rifting by 96 million years ago and completely separated a while after this, some believing as recently as 45 million years ago, but most accepting presently that this had occurred by 60 million years ago.
Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate is forced underneath another. The earthquakes are caused by slip along the thrust fault that forms the contact between the two plates. These interplate earthquakes are the planet's most powerful, with moment magnitudes (Mw) that can exceed 9.0. Since 1900, all earthquakes of magnitude 9.0 or greater have been megathrust earthquakes.
The Ryukyu Trench, also called Nansei-Shotō Trench, is a 1398 km (868 mi) long oceanic trench located along the southeastern edge of Japan's Ryukyu Islands in the Philippine Sea in the Pacific Ocean, between northeastern Taiwan and southern Japan. The trench has a maximum depth of 7460 m (24,476 ft). The trench is the result of oceanic crust of the Philippine Plate obliquely subducting beneath the continental crust of the Eurasian Plate at a rate of approximately 52 mm/yr. In conjunction with the adjacent Nankai Trough to the northeast, subduction of the Philippine plate has produced 34 volcanoes. The largest earthquake to have been recorded along the Ryukyu Trench, the 1968 Hyūga-nada earthquake, was magnitude 7.5 and occurred along the northernmost part of the trench on 1 April 1968. This earthquake also produced a tsunami.
The Manila Trench is an oceanic trench in the Pacific Ocean, located west of the islands of Luzon and Mindoro in the Philippines. The trench reaches a depth of about 5,400 metres (17,700 ft), in contrast with the average depth of the South China Sea of about 1,500 metres (4,900 ft). It is created by subduction, in which the Sunda Plate is subducting under the Philippine Mobile Belt, producing this almost N-S trending trench. The convergent boundary is terminated to the north by the Taiwan collision zone, and to the south by the Mindoro terrane. It is an area pervaded by negative gravity anomalies.
The Philippine Trench 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 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.
The Izu–Bonin–Mariana (IBM) arc system is a tectonic plate convergent boundary in Micronesia. The IBM arc system extends over 2800 km south from Tokyo, Japan, to beyond Guam, and includes the Izu Islands, the Bonin Islands, and the Mariana Islands; much more of the IBM arc system is submerged below sealevel. The IBM arc system lies along the eastern margin of the Philippine Sea Plate in the Western Pacific Ocean. It is the site of the deepest gash in Earth's solid surface, the Challenger Deep in the Mariana Trench.
The 1976 Moro Gulf earthquake and tsunami occurred on near the islands of Mindanao and Sulu, in the Philippines. It measured 8.0 on the moment magnitude scale occurring at a depth of 20 km (12 mi). The earthquake was accompanied by a destructive tsunami that resulted in a majority of the estimated 5,000 to 8,000 fatalities. It was the deadliest and strongest earthquake in the Philippines in 58 years since the 1918 Celebes Sea earthquake.
Located in the western Pacific Ocean near Indonesia, the Molucca Sea Plate has been classified by scientists as a fully subducted microplate that is part of the Molucca Sea Collision Complex. The Molucca Sea Plate represents the only known example of divergent double subduction (DDS), which describes the subduction on both sides of a single oceanic plate.
In the geology of the Philippines, 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 shorn off the adjoining major plates are undergoing massive deformation.
The 2002 Mindanao earthquake struck the Philippines at 05:16 Philippine Standard Time on March 6. The world's sixth most powerful earthquake of the year, it registered a magnitude of 7.5 and was a megathrust earthquake. It originated near the Cotabato Trench, a zone of deformation situated between the Philippine Sea plate and the Sunda plate, and occurred very near to the Philippines' strongest earthquake for the 20th century, the 1918 Celebes Sea earthquake.
The 1897 Mindanao earthquakes occurred on September 20, 1897, at 19:06 UTC and September 21, 1897, at 05:12 UTC. The estimated epicentres of the two earthquakes are identical, lying just off the southwestern coast of Mindanao in the Philippines, south of Basilan island. The earthquakes were originally given estimated magnitudes of 8.6 and 8.7 on the surface wave magnitude scale by Charles Richter, but these were revised downwards by Katsuyuki Abe to 7.4 and 7.5 , respectively. Contemporary reports noted that with few exceptions, all the masonry buildings in Zamboanga and Basilan were left in ruins.
The 1918 Celebes Sea earthquake occurred on August 15 at 12:18 UTC near the Moro Gulf coast of Mindanao. It had a magnitude of 8.3 on the moment magnitude scale and a maximum perceived intensity of X (Extreme) on the Mercalli intensity scale. It triggered a tsunami of up to 7 m in height and the combined effects of the earthquake and tsunami led to the deaths of 52 people.
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 also known as the Philippine Mobile Belt due to its complex tectonic setting.
Oblique subduction is a form of subduction for which the convergence direction differs from 90° to the plate boundary. Most convergent boundaries involve oblique subduction, particularly in the Ring of Fire including the Ryukyu, Aleutian, Central America and Chile subduction zones. In general, the obliquity angle is between 15° and 30°. Subduction zones with high obliquity angles include Sunda trench and Ryukyu arc.
The East Luzon Trough is an oceanic trench north of the Philippine Trench and east of the island of Luzon. The trench is located near the Philippine orogeny and located in the southeastern region of the Philippine Sea Plate. The depth of the trough is 5,700 meters. The East Luzon Trough formed during the Eocene and Oligocene epoch, 40–24 million years ago.
The 1955 Lanao earthquake struck Lanao del Sur on April 1 at 02:17 local time. The earthquake measuring 7.4 on the moment magnitude scale and assigned a maximum intensity of VIII (Severe) on the Modified Mercalli intensity scale was one of the largest to hit Mindanao. It caused immense damage around the northern and central parts of Mindanao, as well as the southern reaches of Visayas. It killed at least 465 individuals and injured a further 898.
The 1867 Keelung earthquake occurred off the northern coast of Taiwan on the morning of December 18 with a magnitude of 7.0. It produced strong shaking that seriously damaged the cities of Keelung and Taipei. A tsunami, thought to be the only confirmed destructive of its kind in Taiwan, drowned hundreds and had a run-up exceeding 15 m (49 ft). The total death toll was estimated to be 580 while more than 100 were injured. It was followed by aftershocks that were felt on average ten times a day.
