The Nankai Trough 南海トラフ is a submarine trough located south of the Nankaidō region of Japan's island of Honshū, extending 900 km offshore. The underlying fault, the Nankai megathrust, is the source of the devastating Nankai megathrust earthquakes, while the trough itself is a major source of hydrocarbon fuel, in the form of methane clathrate. In plate tectonics, the Nankai Trough marks a subduction zone, caused by subduction of the Philippine Sea Plate beneath Japan, part of the Eurasian plate; this plate boundary would be an oceanic trench except for a high flux of sediments that fills the trench. Within the Nankai Trough there is a large amount of deformed trench sediments, making one of Earth's best examples of accretionary prism. Furthermore, seismic reflection studies have revealed the presence of basement highs that are interpreted as seamounts that are covered in sediments; the northern part of the trough is known as the Suruga Trough, while to the east is the Sagami Trough. The Nankai trough runs parallel to the Japan Median Tectonic Line.
Conventional geologic estimates of plate movement velocities are difficult in the Nankai Trough because there are no spreading ridges that bound the tectonic plate. This area was not in the original NUVEL models. However, a more recent study that included the Philippine Sea plate was based on data from the NUVEL-1A model; this study estimates. REVEL-based calculations indicate; the rates of movement have been calculated to be in a range of 3.0 ± 1.8 mm/yr to 11.1 ± 1.7 mm/yr. As mentioned the NUVEL-1A plate motion model does not include the Philippine Sea plate; this is because the mathematics of this model only used twelve plates, the Philippine Sea and Eurasian convergent margin were not included. However, using the Eurasia to North America plate motion, the estimated rate was 2–4 mm/yr; this is not in agreement with the REVEL model indicating that the NUVEL-1A model may need further revision. The deposits are trench-wedge turbidites. There are indications of an increase in the retention of porosity within the rock.
Porosity reduces with increasing depth. However, there is an anomalous preservation of porosity at depth at drill site 1173; this has been attributed to post-depositional opal cementation, preserving the porosity. The detrital clays smectite, display variation over time and location in the Nankai Trough as well as the Shikoku basin. At depth there is an increase in the smectite clay content in the sediments, inferring that there has been a change in the deposition source rock. Furthermore, there is a geothermal alteration of the smectite; the Nankai Trough is deforming and marks a region of seismic activity. Deformation is concentrated in the outermost imbricate zone, with a significant amount of "out of sequence" thrusting occurring landward. Based on the work of Operto et al. 2006, several areas of intense tectonic activity in the Nankai Trough were identified using full waveform tomography. The upper portion of the upper accretionary prism and the underlying backstop are undergoing a great deal of compressional pressure.
Several thrust faults were identified by al.. 2006, of which the thrust faults closest to the subduction zone are active. Furthermore, Pisani et al. 2006, identified protothrusts and decollement surfaces along the Nankai Trough. There has been an increase in interest in the release of water from illite clays in subducting sediments; the conversion of smectite to illite in subduction zones is driven by the higher temperature found in the subduction zone as opposed to non-subducting sediments. IODP Expedition 370 will seek to find the temperature limit of the deepest life on Earth by drilling in the Nankai Trough, where heat flow is high near its boundary with the subducting young, hot Philippine Sea tectonic plate. At the targeted site, the geothermal gradient is about four times steeper than elsewhere in the Pacific Ocean. Reaching temperatures of 130 °C in other areas would require collecting cores from 4 kilometers below the seafloor, rather than 1.2 kilometers as planned. The Nankai Trough is the near-surface extension of a zone of active seismicity that dips beneath SW Japan.
The rupture zone has been subdivided into five areas with respect to seismic modelling. These five subdivisions show interesting differences in earthquake behavior: frequency of earthquakes varying on a 90 to 150-year cycle, similar slip occurrences along the fault segments, the order of subdivision faulting, different failure features. Hydrologic observatories were placed in boreholes drilled in 2000 in an attempt to quantify changes in pore-fluid pressure that are a result of the oncoming Philippine Sea plate. Site 808 is located in the front section of the main thrust fault, while site 1173 is located 11 km from the frontal thrust zone. Other interesting results of the pressure measurements were the pressure changes that resulted from sediment deformation near boreholes and the effect of low earthquake swarms at the time of pressure changes; the working hypothesis is that pressure changes indicate a change in the elastic str
Hokkaido known as Ezo, Yeso, or Yesso, is the second largest island of Japan, the largest and northernmost prefecture. The Tsugaru Strait separates Hokkaido from Honshu; the two islands are connected by the undersea railway Seikan Tunnel. The largest city on Hokkaido is its capital, its only ordinance-designated city. About 43 km north of Hokkaido lies Russia. To its east and north-east are the disputed Kuril Islands; the Nihon Shoki, finished in 720 AD, is said to be the first mention of Hokkaido in recorded history. According to the text, Abe no Hirafu led a large navy and army to northern areas from 658 to 660 and came into contact with the Mishihase and Emishi. One of the places Hirafu went to was called Watarishima, believed to be present-day Hokkaido. However, many theories exist in relation to the details of this event, including the location of Watarishima and the common belief that the Emishi in Watarishima were the ancestors of the present-day Ainu people. During the Nara and Heian periods, people in Hokkaido conducted trade with Dewa Province, an outpost of the Japanese central government.
From the Middle Ages, the people in Hokkaido began to be called Ezo. Hokkaido subsequently became known as Ezogashima; the Ezo relied upon hunting and fishing and obtained rice and iron through trade with the Japanese. During the Muromachi period, the Japanese created a settlement at the south of the Oshima Peninsula; as more people moved to the settlement to avoid battles, disputes arose between the Japanese and the Ainu. The disputes developed into a war. Takeda Nobuhiro killed the Ainu leader and defeated the opposition in 1457. Nobuhiro's descendants became the rulers of the Matsumae-han, granted exclusive trading rights with the Ainu in the Azuchi-Momoyama and Edo periods; the Matsumae family's economy relied upon trade with the Ainu. They held authority over the south of Ezochi until the end of the Edo period in 1868; the Matsumae clan rule over the Ainu must be understood in the context of the expansion of the Japanese feudal state. Medieval military leaders in northern Honshū maintained only tenuous political and cultural ties to the imperial court and its proxies, the Kamakura Shogunate and Ashikaga Shogunate.
Feudal strongmen sometimes located themselves within medieval institutional order, taking shogunal titles, while in other times they assumed titles that seemed to give them a non-Japanese identity. In fact, many of the feudal strongmen were descended from Emishi military leaders, assimilated into Japanese society; the Matsumae clan were of Yamato descent like other ethnic Japanese people, whereas the Emishi of northern Honshu were a distinctive group related to the Ainu. The Emishi were conquered and integrated into the Japanese state dating back as far as the 8th century, as result began to lose their distinctive culture and ethnicity as they became minorities. By the time the Matsumae clan ruled over the Ainu most of the Emishi were ethnically mixed and physically closer to Japanese than they were to Ainu; this dovetails nicely with the "transformation" theory that native Jōmon peoples changed with the infusion of Yayoi immigrants into the Tōhoku rather than the "replacement" theory which posits that one population was replaced by another.
There were numerous revolts by the Ainu against the feudal rule. The last large-scale resistance was Shakushain's Revolt in 1669–1672. In 1789, a smaller movement, the Menashi–Kunashir rebellion, was crushed. After that rebellion, the terms "Japanese" and "Ainu" referred to distinguished groups, the Matsumae were unequivocally Japanese. In 1799–1821 and 1855–1858, the Edo Shogunate took direct control over Hokkaido in response to a perceived threat from Russia. Leading up to the Meiji Restoration, the Tokugawa Shogunate realized there was a need to prepare northern defenses against a possible Russian invasion and took over control of most of Ezochi; the Shogunate made the plight of the Ainu easier, but did not change the overall form of rule. Hokkaido was known as Ezochi until the Meiji Restoration. Shortly after the Boshin War in 1868, a group of Tokugawa loyalists led by Enomoto Takeaki temporarily occupied the island, but the rebellion was crushed in May 1869. Ezochi was subsequently put under control of Hakodate Prefectural Government.
When establishing the Development Commission, the Meiji Government introduced a new name. After 1869, the northern Japanese island was known as Hokkaido; the primary purpose of the development commission was to secure Hokkaido before the Russians extended their control of the Far East beyond Vladivostok. Kuroda Kiyotaka was put in charge of the venture, his first step was to journey to the United States and recruit Horace Capron, President Grant's Commissioner of Agriculture. From 1871 to 1873 Capron bent his efforts to expounding Western agriculture and mining with mixed results. Capron, frustrated with obstacles to his efforts returned home in 1875. In 1876, William S. Clark arrived to found an agricultural college in Sapporo. Although he only remained a year, Clark left a lasting impression on Hokkaido, inspiring the Japanese with his teachings on agriculture as well as Christianity
Sea of Japan
The Sea of Japan is the marginal sea between the Japanese archipelago, the Korean Peninsula and Russia. The Japanese archipelago separates the sea from the Pacific Ocean, it is bordered by Japan and Russia. Like the Mediterranean Sea, it has no tides due to its nearly complete enclosure from the Pacific Ocean; this isolation reflects in the fauna species and in the water salinity, lower than in the ocean. The sea has bays or capes, its water balance is determined by the inflow and outflow through the straits connecting it to the neighboring seas and Pacific Ocean. Few rivers discharge into the sea and their total contribution to the water exchange is within 1%; the seawater has an elevated concentration of dissolved oxygen that results in high biological productivity. Therefore, fishing is the dominant economic activity in the region; the intensity of shipments across the sea has been moderate owing to political issues, but it is increasing as a result of the growth of East Asian economies. Sea of Japan is the dominant term used in English for the sea, the name in most European languages is equivalent, but it is sometimes called by different names in surrounding countries reflecting historical claims to hegemony over the sea.
The sea is called Rìběn hǎi or Jīng hǎi in China, Yaponskoye more in Russia, Chosŏn Tonghae in North Korea, Donghae in South Korea. A naming dispute exists about the sea name, with South Korea promoting the English translation of its native name as the East Sea; the use of the term "Sea of Japan" as the dominant name is a point of contention. South Korea wants the name "East Sea" to instead of or in addition to "Sea of Japan; the primary issue in the dispute revolves around a disagreement about when the name "Sea of Japan" became the international standard. Japan claims the term has been the international standard since at least the early 19th century, while the Koreas claim that the term "Sea of Japan" arose while Korea was under Japanese rule, before that occupation other names such as "Sea of Korea" or "East Sea" were used in English; the International Hydrographic Organization, the international governing body for the naming bodies of water around the world, in 2012 recognized the term "Sea of Japan" as the only title for the sea, stated they would will review the issue again in 2017.
For centuries, the sea had protected Japan from land invasions by the Mongols. It had long been navigated by Asian and, from the 18th century, by European ships. Russian expeditions of 1733–1743 mapped Sakhalin and the Japanese islands. In the 1780s, the Frenchman Jean-François de Galaup, comte de Lapérouse, traveled northward across the sea through the strait named after him. In 1796, a British naval officer, William Robert Broughton explored the Strait of Tartary, the eastern coast of the Russian Far East and the Korean Peninsula. In 1803–1806, the Russian navigator Adam Johann von Krusenstern while sailing across the globe in the ship Nadezhda explored, in passing, the Sea of Japan and the eastern shores of Japanese islands. In 1849, another Russian explorer Gennady Nevelskoy discovered the strait between the continent and Sakhalin and mapped the northern part of the Strait of Tartary. Russian expeditions were made in 1853–1854 and 1886–1889 to measure the surface temperatures and record the tides.
They documented the cyclonal character of the sea currents. Other notable expeditions of the 19th century include the American North Pacific Exploring and Surveying Expedition and British Challenger expedition; the aquatic life was described by V. K. Brazhnikov in P. Yu. Schmidt in 1903–1904; the Japanese scientific studies of the sea became systematic since the 1920s. American and French whaleships cruised for whales in the sea between 1848 and 1892. Most entered the sea via Korea Strait and left via La Pérouse Strait, but some entered and exited via Tsugaru Strait, they targeted right whales, but began catching humpbacks as right whale catches declined. They made attempts to catch blue and fin whales, but these species invariably sank after being killed. Right whales were caught from March with peak catches in May and June. During the peak years of 1848 and 1849 a total of nearly 160 vessels cruised in the Sea of Japan, with lesser numbers in following years; the Sea of Japan was a landlocked sea.
The onset of formation of the Japan Arc was in the Early Miocene. The Early Miocene period corresponds to the Japan Sea starting to open, the northern and southern parts of the Japanese archipelago separating from each other. During the Miocene, there was expansion of Sea of Japan; the north part of the Japanese archipelago was further fragmented until orogenesis of the northeastern Japanese archipelago began in the Late Miocene. The south part of the Japanese archipelago remained as a large landmass; the land area had expanded northward in the Late Miocene. The orogenesis of high mountain ranges in northeastern Japan started in Late Miocene and lasted in Pliocene also. Nowadays the Sea of Japan is bounded by the Russian mainland and Sakhalin island to the north, the Korean Peninsula to the west, the Japanese islands of Hokkaidō, Honshū and Kyūshū to the east and south, it is connected to other seas by five straits: the Strait of Tartary between the Asia
Three earthquakes, which occurred off the coast of Kamchatka Peninsula in far eastern Russia and the Soviet Union in 1737, 1923 and 1952, were megathrust earthquakes and caused tsunamis. They occurred where the Pacific Plate subducts under the Okhotsk Plate at the Kuril-Kamchatka Trench; the depth of the trench at the point of the earthquakes is 7,000–7,500 m. Northern Kamchatka lies at the western end of the Bering fault, between the Pacific Plate and North American Plate, or the Bering plate There are many more earthquakes and tsunamis originating from Kamchatka, of which the most recent was the 1997 Kamchatka earthquake and tsunami originating near the Kronotsky Peninsula; the epicentre of the 1737 earthquake was located at 52.5°N 159.5°E / 52.5. This earthquake occurred at a depth of 40 km. A magnitude of 8.3 Ms has been estimated. On February 4, 1923, an estimated magnitude 8.3–8.5 Mw earthquake with an approximate location of 54.0°N 161.0°E / 54.0. The tsunami was still 6 meters high. There was another earthquake and tsunami in April 1923, which caused locally high tsunami runup near Ust' Kamchatsk, leaving a deposit studied by Minoura and others.
The main earthquake struck at 16:58 GMT on November 4, 1952. Assigned a magnitude of 8.2, the quake was revised to 9.0 Mw in years. A large tsunami resulted, causing destruction and loss of life around the Kamchatka peninsula and the Kuril Islands. Hawaii was struck, with estimated damage of up to US$1 million and livestock losses, but no human casualties were recorded. Japan reported damage; the tsunami reached as far as Alaska and New Zealand. The hypocentre was located at 52.75°N 159.5°E / 52.75. The length of the subduction zone fracture was 600 km. Aftershocks were recorded in an area of 247,000 km2, at depths of between 40 and 60 km. A recent analysis of the tsunami runup distribution based on historical and geological records give some indication as to the slip distribution of the rupture. 1959 Kamchatka earthquake 2006 Kamchatka earthquakes Megathrust earthquake Землетрясения на Командорских островах. Землетрясения на Камчатке: информация, впечатления жетелей Камчатки
Sakhalin is Russia's largest island, lying in the North Pacific Ocean between 45°50' and 54°24' N. It is administered as part of Sakhalin Oblast. Sakhalin, about one third the size of Honshu, is just off the east coast of Russia, just north of Japan; the island's population was 497,973 as of the 2010 census, made up of ethnic Russians and a smaller Korean community. The indigenous peoples of the island are the Ainu and Nivkhs. Sakhalin was claimed by both Japan over the course of the 19th and 20th centuries; these disputes sometimes involved military conflict and divisions of the island between the two powers. In 1875, Japan ceded its claims to Russia in exchange for the northern Kuril Islands. In 1905, following the Russo-Japanese War, the island was divided, with the south going to Japan. Russia has held all of the island since seizing the Japanese portion—as well as all the Kuril Islands—in the final days of World War II in 1945. Japan no longer claims any of Sakhalin. Most Ainu on Sakhalin moved to Hokkaido, only 43 kilometres to the south, when the Japanese were displaced from the island in 1949.
The island is known in Russian as Sakhalin. In Chinese, it is known as Kuye. In Japanese, it is known as Karafuto or, as Saharin; the spelling Saghalien may be found in historical texts. Choka is another name found in the early literature and seems to have been the name used by the islanders themselves, but it is not clear whether these were the Gilyak or the Ainu; the European names derive from misinterpretation of a Manchu name ᠰᠠᡥᠠᠯᡳᠶᠠᠨᡠᠯᠠ ᠠᠩᡤᠠᡥᠠᡩᠠ sahaliyan ula angga hada. Sahaliyan, the word, borrowed in the form of "Sakhalin", means "black" in Manchu, ula means "river" and sahaliyan ula is the proper Manchu name of the Amur River, its Japanese name, Karafuto comes from Ainu kamuy kar put ya mosir, which means "the island a god has created at the estuary". The name was used by the Japanese during their possession of its southern part. Sakhalin was inhabited in the Neolithic Stone Age. Flint implements such as those found in Siberia have been found at Dui and Kusunai in great numbers, as well as polished stone hatchets similar to European examples, primitive pottery with decorations like those of the Olonets, stone weights used with fishing nets.
A population familiar with bronze left traces in earthen walls and kitchen-middens on Aniva Bay. Among the indigenous people of Sakhalin are the Ainu in the southern half, the Oroks in the central region, the Nivkhs in the north. Chinese chronicled the Hezhe tribes, which had a way of life based on fishing; the Mongol Empire made some efforts to subjugate the native people of Sakhalin starting in about 1264 A. D. According to Yuanshi, the official history of the Yuan dynasty, the Mongols militarily subdued the Guwei, by 1308, all inhabitants of Sakhalin had submitted to the Yuan; the Nivkhs and the Oroks were subjugated earlier, whereas the Ainu people submitted to the Mongols later. Following their subjugation, Gǔwéi elders made tributary visits to Yuan posts located at Wuleihe and Boluohe until the end of the Mongol Yuan dynasty in China. In the early Ming dynasty, the tributary relationship was re-established. By the middle of the 15th century, following the introduction of Chinese political and commercial institutions in the Amur region, the Sakhalin Ainu were making frequent tributary visits to Chinese-controlled outposts.
Chinese of the Ming dynasty knew the island as Kuyi or Kuwu, as Kuye, as it is known today. There is some evidence that the Ming eunuch Admiral Yishiha reached Sakhalin in 1413 during one of his expeditions to the lower Amur, granted Ming titles to a local chieftain. Under the Ming dynasty, commerce in Northeast Asia and Sakhalin was placed under the "system for subjugated peoples", or ximin tizhi; this suggests that the island was at least nominally under the administration of the Nurgan Regional Military Commission, established by Yishiha near today's village of Tyr on the Siberian mainland in 1411, continued operating until the mid-1430s. A Ming boundary stone still exists on the island. According to Wei Yuan's work Military history of the Qing dynasty, the Later Jin sent 400 troops to Sakhalin in 1616 in response to Japanese activity in the area, but withdrew, judging there to be no major threat to their control of the island. In an early colonization attempt, a Japanese settlement was established at Ootomari on Sakhalin's southern end in 1679.
Cartographers of the Matsumae clan created a map of the island and called it "Kita-Ezo". The 1689 Nerchinsk Treaty between Russia and China, which defined the Stanovoy Mountains as their mutual border, made no explicit mention of the island. Local people were forced to pay tribute at Qing posts, Qing officials sometimes granted titles to local elders, entrusting them with the task of "keeping the peace". By the mid-18th century, Qing officials had registered 56 surname groups.
A transform fault or transform boundary is a plate boundary where the motion is predominantly horizontal. It is connected to another transform, a spreading ridge, or a subduction zone. Most of these faults are hidden in the deep ocean, where they offset divergent boundaries in short zigzags resulting from seafloor spreading, the best-known being those on land at the margins of continental tectonic plates. A transform fault is the only type of strike-slip fault, classified as a plate boundary; these faults are known as conservative plate boundaries, since they neither create nor destroy lithosphere. Geophysicist and geologist John Tuzo Wilson recognized that the offsets of oceanic ridges by faults do not follow the classical pattern of an offset fence or geological marker in Reid's rebound theory of faulting, from which the sense of slip is derived; the new class of faults, called transform faults, produce slip in the opposite direction from what one would surmise from the standard interpretation of an offset geological feature.
Slip along transform faults does not increase the distance between the ridges it separates. This hypothesis was confirmed in a study of the fault plane solutions that showed the slip on transform faults points in the opposite direction than classical interpretation would suggest. Transform faults are related to transcurrent faults and are confused. Both types of fault are side-to-side in movement. In addition, transform faults have equal deformation across the entire fault line, while transcurrent faults have greater displacement in the middle of the fault zone and less on the margins. Transform faults can form a tectonic plate boundary, while transcurrent faults cannot; the effect of a fault is to relieve strain, which can be caused by compression, extension, or lateral stress in the rock layers at the surface or deep in the Earth's subsurface. Transform faults relieve strain by transporting the strain between ridges or subduction zones, they act as the plane of weakness, which may result in splitting in rift zones.
Transform faults are found linking segments of mid-oceanic ridges or spreading centres. These mid-oceanic ridges are where new seafloor is created through the upwelling of new basaltic magma. With new seafloor being pushed and pulled out, the older seafloor slides away from the mid-oceanic ridges toward the continents. Although separated only by tens of kilometers, this separation between segments of the ridges causes portions of the seafloor to push past each other in opposing directions; this lateral movement of seafloors past each other is where transform faults are active. Transform faults move differently from a strike-slip fault at the mid-oceanic ridge. Instead of the ridges moving away from each other, as they do in other strike-slip faults, transform-fault ridges remain in the same, fixed locations, the new ocean seafloor created at the ridges is pushed away from the ridge. Evidence of this motion can be found in paleomagnetic striping on the seafloor. A paper written by geophysicist Taras Gerya theorizes that the creation of the transform faults between the ridges of the mid-oceanic ridge is attributed to rotated and stretched sections of the mid-oceanic ridge.
This occurs over a long period of time with the spreading center or ridge deforming from a straight line to a curved line. Fracturing along these planes forms transform faults; as this takes place, the fault changes from a normal fault with extensional stress to a strike slip fault with lateral stress. In the study done by Bonatti and Crane and gabbro rocks were discovered in the edges of the transform ridges; these rocks are created deep inside the Earth's mantle and rapidly exhumed to the surface. This evidence helps to prove that new seafloor is being created at the mid-oceanic ridges and further supports the theory of plate tectonics. Active transform faults are between faults. Fracture zones represent the active transform-fault lines, which have since passed the active transform zone and are being pushed toward the continents; these elevated ridges on the ocean floor can be traced for hundreds of miles and in some cases from one continent across an ocean to the other continent. The most prominent examples of the mid-oceanic ridge transform zones are in the Atlantic Ocean between South America and Africa.
Known as the St. Paul, Romanche and Ascension fracture zones, these areas have deep identifiable transform faults and ridges. Other locations include: the East Pacific Ridge located in the South Eastern Pacific Ocean, which meets up with San Andreas Fault to the North. Transform faults are not spreading centers; the best example is the San Andreas Fault on the Pacific coast of the United States. The San Andreas Fault links the East Pacific Rise off the West coast of Mexico to the Mendocino Triple Junction off the coast of the Northwestern United States, making it a ridge-to-transform-style fault; the formation of the San Andreas Fault system occurred recently during the Oligocene Period between 34 million and 24 million years ago. During this period, the Farallon plate, followed by the Pacific plate, collided into the North American plate; the collision led to the subduction of the Farallon plate underneath the North American plate. Once the spreading ce