The Ryukyu Trench (琉球海溝 Ryūkyū kaikō), 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.
An east-west planar seismic zone associated with the Ryukyu Trench occurs off the east coast of Taiwan. This seismic zone is continuous laterally for 50 km and to 150 km depth. The hypocenters of earthquakes at this location outline a Benioff zone indicating that the Philippine Sea Plate is subducting at an angle of about 45° beneath the Eurasian plate in this area; the dip of the slab changes dramatically from one end of the trench to the other as noted in the next section. Such depth and dip inferences of this area are consistent with the positions of the overlying Tatun and Chilung volcano groups of Taiwan.
The region behind (N and NW of) the Ryukyu Arc is a bathymetric low known as the Okinawa Trough. The Yilan Plain of Taiwan could be the westward continuation of this trough, but the Yilan Plain sits on the forearc side of the Ryukyu Trench system. This may indicate that the Ilan Plain represents a former spreading centre that sits trench-ward of the current spreading centre and volcanic arc.
Near 122°E (about 100 km East of the Taiwan Coast), the Ryukyu Arc is displaced to the north relative to the eastern extent of the arc. One hypothesis is that a north trending dextral transform faults has displaced this section of the arc to the north. A competing hypothesis claims that no transform fault motion is involved in the displacement, but rather the trench is continuous up to the northeast continental margin of Taiwan. A third hypothesis maintains that the trench is continuous through the continental margin right up to the northeastern Taiwan coastline, also without the existence of a dextral north-south trending fault.
Ocean bottom seismography methods combined with earthquake studies of the Benioff zone constrain the dip angle of the Philippine Sea Plate along the Ryukyu trench. In the Northern part of the Ryukyu trench, the dip of the Philippine Sea Plate is shallow at shallow depth, reaching only about 11° in the first 50 km, and steeper at deeper depths, reaching 70° below about 70 km. In contrast, the slab dip in the central and southern parts of the Ryukyu trench is more gentle, reaching only 40-50° at 70 km depth.
Ocean bottom seismography studies of the Ryukyu trench provide insight into the P-wave velocity structure of the area. In the northern part of the trench, several transects have been studied, including a profile of the back arc region parallel to the trench, a transect spanning the trench, fore arc and back arc region, and a transect spanning the Ryukyu volcanic arc. The transect perpendicular to the length of the trench images many distinct velocity layers. The sedimentary wedge created by subduction has four distinct layers with p-wave velocities of 1.8 km/s, 2.8-2.9 km/s, 3.5 km/s, and 4.5–5 km/s. In the area of this transect, the wedge reaches a thickness of 9 km at 50 km from the trench. Beneath the wedge are several seismic layers within the oceanic crust.
Separate ocean bottom seismography and multi-channel seismic studies provide insight into the structure of the northern end of the Ryukyu trench region. Features of note include a thick (7–12 km) low velocity (4–5 km/s) zone on the landward side of the trench, the existence of subducting paleo-arc crust near the top of the trench in contrast to simple oceanic crust located at the middle of the trench, and a zone in which the Philippine Plate subducts beneath low P-wave velocity material (Vp = 5 km/s) that coincides with the location of the Mw 7.5 1968 Hyuganada earthquake. It has been hypothesized that the above structural heterogeneity, in particular the subducting paleo-arc crust and its associated bathymetric highs, is one reason why earthquakes in this region are not larger i.e. exceeding Mw 8.0. The exact mechanism by which the subduction of paleo-arc crust prevents sufficient stress build up for a larger earthquake is unknown.
The 1771 Great Yaeyama Tsunami (also called 明和の大津波, the Great Tsunami of Meiwa) was caused by the Yaeyama Great Earthquake at about 8 A.M. on April 24, 1771, south-southeast of Ishigaki Island, part of the former Ryūkyū Kingdom and now forming part of present-day Okinawa, Japan. According to records, 8,439 persons were killed on Ishigaki Island and 2,548 on Miyako Island.1911 Kikai Island earthquake
The 1911 Kikai Island earthquake (1911年喜界島地震 Sen-kyūhyaku-jyūichi-nen Kikai-jima Jishin) occurred on June 15 at 14:26 UTC (23:26 local time). The earthquake was located near Kikai Island, Japan. It had a magnitude of Ms 8.1.The earthquake occurred near the northern end of the deepest region in Ryukyu Trench. The hypocenter was located near 28.00°E, 130.00°N, about 30 km south of the Kikai Island, with a depth of about 100 km. However, due to the instrumental precision of that time, the location of the hypocenter was just an approximation, and estimations differ. A recent study estimated that the hypocenter was located near 28.90°E, 130.25°N, about 60 km NNE of the Kikai Island, with a depth of about 30 km.Twelve people were reported dead, including one on Kikai Island. Four hundred and twenty two houses were completely destroyed, 401 of which on Kikai Island. Damage was also reported on Amami Ōshima, Toku-no-shima, and Okinawa Island. The wall of Shuri Castle in Shuri was damaged. This earthquake could be felt as far as in Shanghai, China, Tainan, Taiwan (then under Japanese rule), and Fukushima, Japan.1968 Hyūga-nada earthquake
The 1968 Hyūga-nada earthquake (Japanese: 1968年日向灘地震) occurred on April 1 at 09:42 local time. The earthquake had a magnitude of Mw 7.5, and the epicenter was located in Hyūga-nada Sea, off the islands of Kyushu and Shikoku, Japan. The magnitude of this earthquake was also given as MJMA 7.5. A tsunami was observed. There were 15 people reported injured. The intensity reached shindo 5 in Miyazaki and Kōchi.Benthic comb jelly
The benthic comb jelly is a comb jelly living in the Ryukyu Trench near Japan. Found at a depth of 7,217 metres (23,700 ft), it is the deepest dwelling ctenophore discovered.Cold seep
A cold seep (sometimes called a cold vent) is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool. Cold does not mean that the temperature of the seepage is lower than that of the surrounding sea water. On the contrary, its temperature is often slightly higher. The "cold" is relative to the very warm (at least 60 °C or 140 °F) conditions of a hydrothermal vent. Cold seeps constitute a biome supporting several endemic species.
Cold seeps develop unique topography over time, where reactions between methane and seawater create carbonate rock formations and reefs. These reactions may also be dependent on bacterial activity. Ikaite, a hydrous calcium carbonate, can be associated with oxidizing methane at cold seeps.Geology of Japan
The islands of Japan are primarily the result of several large ocean movements occurring over hundreds of millions of years from the mid-Silurian to the Pleistocene as a result of the subduction of the Philippine Sea Plate beneath the continental Amurian Plate and Okinawa Plate to the south, and subduction of the Pacific Plate under the Okhotsk Plate to the north.
Japan was originally attached to the eastern coast of the Eurasian continent. The subducting plates, being deeper than the Eurasian plate, pulled Japan eastward, opening the Sea of Japan around 15 million years ago. The Strait of Tartary and the Korea Strait opened much later.
Japan is situated in a volcanic zone on the Pacific Ring of Fire. Frequent low intensity earth tremors and occasional volcanic activity are felt throughout the islands. Destructive earthquakes, often resulting in tsunamis, occur several times a century. The most recent major quakes include the 2011 Tōhoku earthquake and tsunami, the 2004 Chūetsu earthquake and the Great Hanshin earthquake of 1995. Hot springs are numerous and have been developed as resorts.Geology of Taiwan
The island of Taiwan is active geologically, formed on a complex convergent boundary between the Yangtze Subplate of the Eurasian Plate to the west and north, the Okinawa Plate on the north-east, the Philippine Plate on the east and south, and the Sunda Plate to the southwest. Subduction changes direction at Taiwan.
The upper part of the crust on the island is primarily made up of a series of terranes, mostly old island arcs which have been forced together by the collision of the forerunners of the Eurasian Plate and the Philippine Sea Plate, which is moving to the northeast. These have been further uplifted as a result of the detachment of a portion of the Eurasian Plate as it was subducted beneath remnants of the Philippine Sea Plate, a process which left the crust under Taiwan more buoyant.South of Taiwan, the Philippine Sea Plate is subducting under the Sunda Plate, forming the Luzon Volcanic Arc (including Green Island and Orchid Island). The east and south of the island are a complex system of belts formed by, and part of the zone of, active collision between the North Luzon Trough portion of the Luzon Volcanic Arc and the Eurasian Plate, where accreted portions of the Luzon Arc and Luzon forearc form the eastern Coastal Range and parallel inland Taitung Longitudinal Valley of Taiwan respectively.To the northeast, the Philippine Sea Plate is subducting under the Okinawa Plate, forming the Ryukyu Volcanic Arc.Island arc
Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries (such as the Ring of Fire). Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle along the subduction zone. They are the principal way by which continental growth is achieved.
Island arcs can either be active or inactive based on their seismicity and presence of volcanoes. Active arcs are ridges of recent volcanoes with an associated deep seismic zone. They also possess a distinct curved form, a chain of active or recently extinct volcanoes, a deep-sea trench, and a large negative Bouguer anomaly on the convex side of the volcanic arc. The small positive gravity anomaly associated with volcanic arcs has been interpreted by many authors as due to the presence of dense volcanic rocks beneath the arc. While inactive arcs are a chain of islands which contains older volcanic and volcaniclastic rocks.The curved shape of many volcanic chains and the angle of the descending lithosphere are related. If the oceanic part of the plate is represented by the ocean floor on the convex side of the arc, and if the zone of flexing occurs beneath the submarine trench, then the deflected part of the plate coincides approximately with the Benioff zone beneath most arcs.Kaikō ROV
Kaikō (海溝, "Ocean Trench") was a remotely operated underwater vehicle (ROV) built by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) for exploration of the deep sea. Kaikō was the second of only four vessels ever to reach the bottom of the Challenger Deep, as of 2010. Between 1995 and 2003, this 10.6 ton unmanned submersible conducted more than 250 dives, collecting 350 biological species (including 180 different bacteria), some of which could prove to be useful in medical and industrial applications. On 29 May 2003, Kaikō was lost at sea off the coast of Shikoku Island during Typhoon Chan-Hom, when a secondary cable connecting it to its launcher at the ocean surface broke.Another ROV, Kaikō7000II, served as the replacement for Kaikō until 2007. At that time, JAMSTEC researchers began sea trials for the permanent replacement ROV, ABISMO (Automatic Bottom Inspection and Sampling Mobile). ABISMO is currently one of only three ROVs rated to 11,000-meters (the other two being Nereus, built and operated by the Woods Hole Oceanographic Institution, and Deepsea Challenger, piloted by director James Cameron).List of tectonic plate interactions
Tectonic plate interactions are of three different basic types:
Divergent boundaries are areas where plates move away from each other, forming either mid-oceanic ridges or rift valleys. These are also known as constructive boundaries.
Convergent boundaries are areas where plates move toward each other and collide. These are also known as compressional or destructive boundaries.
Subduction zones occur where an oceanic plate meets a continental plate and is pushed underneath it. Subduction zones are marked by oceanic trenches. The descending end of the oceanic plate melts and creates pressure in the mantle, causing volcanoes to form.
Obduction occurs when the continental plate is pushed under the oceanic plate, but this is unusual as the relative densities of the tectonic plates favours subduction of the oceanic plate. This causes the oceanic plate to buckle and usually results in a new mid ocean ridge forming and turning the obduction into subduction
Orogenic belts occur where two continental plates collide and push upwards to form large mountain ranges. These are also known as collision boundaries.
Transform boundaries occur when two plates grind past each other with only limited convergent or divergent activity.Oceanic trench
Oceanic trenches are topographic depressions of the sea floor, relatively narrow in width, but very long. These oceanographic features are the deepest parts of the ocean floor. Oceanic trenches are a distinctive morphological feature of convergent plate boundaries, along which lithospheric plates move towards each other at rates that vary from a few millimeters to over ten centimeters per year. A trench marks the position at which the flexed, subducting slab begins to descend beneath another lithospheric slab. Trenches are generally parallel to a volcanic island arc, and about 200 km (120 mi) from a volcanic arc. Oceanic trenches typically extend 3 to 4 km (1.9 to 2.5 mi) below the level of the surrounding oceanic floor. The greatest ocean depth measured is in the Challenger Deep of the Mariana Trench, at a depth of 11,034 m (36,201 ft) below sea level. Oceanic lithosphere moves into trenches at a global rate of about 3 km2/yr.Okinawa Plate
The Okinawa Plate, or Okinawa Platelet, is a minor continental tectonic plate in the northern and eastern hemispheres stretching from the northern end of Taiwan to the southern tip of the island of Kyūshū. The Okinawa Plate hosts typical earthquakes, like the 1911 Kikai Island earthquake, and various types of slow earthquakes, including low frequency earthquakes, very low frequency earthquakes, tremor, and slow slip events.Okinawa Trough
The Okinawa Trough (沖縄トラフ, Okinawa Torafu) (also called Chinese: 中琉界沟, literally China-Ryukyu Border Trough ) is a seabed feature of the East China Sea. It is an active, initial back-arc rifting basin which has formed behind the Ryukyu arc-trench system in the West Pacific. It developed where the Philippine Sea Plate is subducting under the Eurasia Plate.Philippine Sea
The Philippine Sea is a marginal sea east and northeast of the Philippines occupying an estimated surface area of 5 million square kilometres (2 million square miles). The Philippine Sea Plate forms the floor of the sea, which forms a portion of the western North Pacific Ocean. It is bordered by the Philippine archipelago (Luzon, Catanduanes, Samar, Leyte and Mindanao) on the southwest; Halmahera, Morotai, Palau, Yap, and Ulithi (of the Carolines) on the southeast; the Marianas, including Guam, Saipan, and Tinian, on the east; the Bonin and Iwo Jima on the northeast; the Japanese islands of Honshu, Shikoku, and Kyūshū on the north; the Ryukyu Islands on the northwest; and Taiwan in the west.The sea has a complex and diverse undersea relief. The floor is formed into a structural basin by a series of geologic faults and fracture zones. Island arcs, which are actually extended ridges protruding above the ocean surface due to plate tectonic activity in the area, enclose the Philippine Sea to the north, east and south. The Philippine archipelago, Ryukyu Islands, and the Marianas are examples. Another prominent feature of the Philippine Sea is the presence of deep sea trenches, among them the Philippine Trench and the Mariana Trench, containing the deepest point on the planet.Photobacterium profundum
Photobacterium profundum is a deep sea Gammaproteobacterium, belonging to the family Vibrionaceae and genus Photobacterium. Like other members of this genus, P. profundum is a marine organism and has two circular chromosomes. P. profundum is a gram-negative rod with the ability for growth at temperatures from 0 °C to 25 °C and pressures from 0.1 MPa to 70 MPa depending on the strain. It has a requirement for salt, is able to metabolise a wide range of simple and complex carbohydrates and has two flagella systems. Cells are rod shape, 2-4μm long and 0.8-1.0μm wide, with a single unsheathed flagella. This bacterium was originally isolated in 1986 from the Sulu Sea and there are currently 4 cultured wild-type strains of P. profundum, (strains SS9, 3TCK, DJS4 and 1230).P. profundum strain SS9 has optimal growth at 15 °C and 28 MPa making it both a psychrophile and a piezophile. P. profundum strain 3TCK, isolates from San Diego Bay, grows optimally at 9 °C and 0.1 MPa and P. profundum strain DSJ4, isolated from the Ryukyu Trench off of Japan at a depth of 5110 m, grows optimally at 10 °C and 10 MPa. Based on 16S rRNA sequence P. profundum is closely related to the genus Vibrio, the most prominent species being the human pathogen Vibrio cholerae.
In strain SS9 it has been shown that several stress response genes are up regulated in response to atmospheric pressure, these include htpG, dnaK, dnaJ, and groEL. The types and abundance of fatty acid chains in the cell membrane also respond to changes in pressure and temperature. At low temperature and high pressure strain SS9 increases the abundance of mono- and polyunsaturated fatty acids. This has the effect of increasing membrane fluidity by reducing packing of the fatty acid chains which results in a liquid crystal structure in the membrane rather than a gel structure. The outer membrane protein OmpH has been shown to be up regulated at elevated pressures, the opposite is true for the outer membrane protein OmpL which is up regulated in response to low pressures.In 2005 Vezzi et al. published the genome sequence for P. profundum strain SS9. The genome of P. profundum consists of a 4.1-Mbp circular chromosome, a 2.2-Mbp minor circular chromosome, as well as an 80-kbp circular plasmid. Strain SS9 has 14 ribosomal RNA (rRNA) genes on chromosome 1, and 1 on chromosome 2; this is the largest number of rRNA genes found in any bacterium. Chromosome 1 consists largely of genes which are essential for growth whereas chromosome 2 appears to be a large plasmid, which, on an evolutionary time scale, has gained several transposable elements. Within the genome of P. profundum there is a large number of open reading frames (ORF) which are unique to SS9 and not found in other members of the family Vibrionaceae.
The genome sequence also highlighted a full Stickland pathway for the fermentation of amino acids; this was the first time this pathway has been identified in an aerobic bacterium. Two complete F1F0 ATP synthase pathways (one on each Chromosome) are also present in this bacterium: this might explain its ability to produce ATP at both high and low pressure.
This work was followed by another paper in 2005 by Campanaro et al. which detailed microarray work comparing gene expression at sub-optimal, optimal and supra-optimal temperatures and pressure for strains SS9, 3TCK and DSJ4. Campanaro et al. showed that there are 544 ORF’s divergent or missing from the 3TCK genome and 562 ORF’s divergent or missing from the DSJ4 chromosomes when compared to that of SS9. This paper also highlighted that 3TCK lacks the lateral flagella system which is up regulated in SS9 at elevated pressure as well as the absence of 3 phage-related regions from 3TCK and 4 phage-related regions from DSJ4.The transcriptional landscape of the wild-type DB110 strain and of the toxR mutant TW30 were investigated by means of next generation sequencing. ToxR is a transmembrane DNA-binding protein first discovered in Vibrio cholerae, where it regulates a considerable number of genes involved in environmental adaptation and virulence. In P. profundum the abundance and activity of this protein is influenced by hydrostatic pressure and its role is related to the regulation of genes in a pressure-dependent manner. Results obtained from RNA-seq experiments revealed a complex expression pattern with a group of 22 genes having expression profiles similar to OmpH that is an outer membrane protein transcribed in response to high hydrostatic pressure. Moreover, RNA-seq allowed a deep characterization of the transcriptional landscape that led to the identification of 460 putative small RNA genes and the detection of 298 protein-coding genes previously unknown. The genome-wide prediction of the operon structure, the transcription start and termination sites, revealed an unexpected high number of genes (992) with large 5’-UTRs, long enough to harbor cis-regulatory RNA structures, suggesting a correlation between intergenic region size and UTR length.Ryukyu Islands
The Ryukyu Islands (琉球諸島, Ryūkyū-shotō), also known as the Nansei Islands (南西諸島, Nansei-shotō, lit. "Southwest Islands") or the Ryukyu Arc (琉球弧, Ryūkyū-ko), are a chain of Japanese islands that stretch southwest from Kyushu to Taiwan: the Ōsumi, Tokara, Amami, Okinawa, and Sakishima Islands (further divided into the Miyako and Yaeyama Islands), with Yonaguni the westernmost. The larger are mostly high islands and the smaller mostly coral. The largest is Okinawa Island.
The climate of the islands ranges from humid subtropical climate (Köppen climate classification Cfa) in the north to tropical rainforest climate (Köppen climate classification Af) in the south. Precipitation is very high and is affected by the rainy season and typhoons. Except the outlying Daitō Islands, the island chain has two major geologic boundaries, the Tokara Strait (between the Tokara and Amami Islands) and the Kerama Gap (between the Okinawa and Miyako Islands). The islands beyond the Tokara Strait are characterized by their coral reefs.
The Ōsumi and Tokara Islands, the northernmost of the islands, fall under the cultural sphere of the Kyushu region of Japan; the people are ethnically Japanese and speak a variation of the Kagoshima dialect of Japanese. The Amami, Okinawa, Miyako, and Yaeyama Islands have a native population collectively called the Ryukyuan people, named for the former Ryukyu Kingdom that ruled them. The varied Ryukyuan languages are traditionally spoken on these islands, and the major islands have their own distinct languages. In modern times, the Japanese language is the primary language of the islands, with the Okinawan Japanese dialect prevalently spoken. The outlying Daitō Islands were uninhabited until the Meiji period, when their development was started mainly by people from the Izu Islands south of Tokyo, with the people there speaking the Hachijō language.
Administratively, the islands are divided into Kagoshima Prefecture (specifically the islands administered by Kagoshima District, Kumage Subprefecture/District, and Ōshima Subprefecture/District) in the north and Okinawa Prefecture in the south, with the divide between the Amami and Okinawa Islands, with the Daitō Islands part of Okinawa Prefecture. The northern (Kagoshima) islands are collectively called the Satsunan Islands, while the southern part of the chain (Okinawa Prefecture) are called the Ryukyu Islands in Chinese.Ryukyu arc
The Ryukyu arc (琉球弧, Ryūkyū-ko) is a volcanic island arc system of Japan's triple junction formed by the subduction of the Philippine Sea Plate beneath the Eurasian Plate between Ryukyu Trench to the south-east and the Okinawa Trough to north-west. It comprises the entirety of the Ryukyu Islands chain. The Ryukyu and Southwest Honshu arcs together form the southwest trending arm of the Boso Triple Junction.Shewanella violacea
Shewanella violacea DSS12 (S. violacea) is a gram-negative bacterium located in marine sediment in the Ryukyu Trench at a depth of 5,110m. The first description of this organism was published in 1998 by Japanese microbiologists Yuichi Nogi, Chiaki Kato, and Koki Horikoshi, who named the species after its violet appearance when it is grown on Marine Agar 2216 Plates.Shewanella violacea is a motile rod-shaped bacterium with flagella. It is a facultative anaerobic organism and considered an extremophile due to its optimal growing conditions at 8ᵒC and 30 MPa. Researchers are evaluating this species to better understand the specific mechanisms S. violacea uses in order to thrive in its unusually cold and high-pressure environment.Slow earthquake
A slow earthquake is a discontinuous, earthquake-like event that releases energy over a period of hours to months, rather than the seconds to minutes characteristic of a typical earthquake. First detected using long term strain measurements, most slow earthquakes now appear to be accompanied by fluid flow and related tremor, which can be detected and approximately located using seismometer data filtered appropriately (typically in the 1–5 Hz band). That is, they are quiet compared to a regular earthquake, but not "silent" as described in the past.Slow earthquakes should not be confused with tsunami earthquakes, in which relatively slow rupture velocity produces tsunami out of proportion to the triggering earthquake. In a tsunami earthquake, the rupture propagates along the fault more slowly than usual, but the energy release occurs on a similar timescale to other earthquakes.
|Faults and rift zones|
|Trenches and troughs|