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.
At 23:50 (UTC+8) on 6 February 2018, an earthquake of magnitude 6.4 on the moment magnitude scale hit Taiwan. The epicenter was on the coastline near Hualien, which was the most severely affected area, with a maximum felt intensity of VIII (severe) on the Mercalli intensity scale. At least 17 deaths were reported, with 285 injured. The maximum foreshock was recorded on 4 February 2018, at 21:56:40. The epicenter was located at Hualien County, Taiwan, reaching a scale of ML 5.8.Chilung Volcano Group
The Chilung Volcanoes (Chinese: 基隆火山群; pinyin: Jīlóng Huǒshān Qún) are a group of extinct volcanoes located in northern Taiwan, lying to the east of Taipei and Keelung (Chilung), and adjoining the northern coast of the island of Taiwan. Together with Mount Guanyin and the Tatun Volcano Group, it belongs to the northern Taiwan volcanic province, constituting the western end of the island chains of the Ryukyu arc. Five separate bodies can be distinguished: Chilungshan (Mount Keelung), Penshan, Wutanshan, Tsaoshan and Chimuling.The group is mainly composed of andesite, although there is some heterogeneity caused by the mixing between mantle-derived and continental material. Aging of andesite, biotite, and zircon samples have yielded age estimates between 0.8 and 1.7 Ma. It comprises the largest gold-copper deposits of Taiwan.Japanese archipelago
The Japanese archipelago (日本列島, Nihon Rettō) is a group of 6,852 islands that form the country of Japan. It extends over 3,000 km (1,900 mi) from the Sea of Okhotsk northeast to the Philippine Sea south along the northeastern coast of the Eurasia continent. It consists of islands from the Sakhalin Island Arc, the Northeastern Japan Arc to the Ryukyu Islands and the Nanpō Islands. Japan is the largest island country in East Asia and the 4th largest island country in the world with 377,973.89 km2 (145,936.53 sq mi). It has the 8th largest exclusive economic zone of 4,470,000 km2 (1,730,000 sq mi).Masaaki Kimura
Masaaki Kimura (木村 政昭, Kimura Masaaki, born 6 November 1940) is a Professor Emeritus from the Faculty of Science of the University of the Ryukyus, Okinawa, Japan.Mount Iō (Iōjima)
Mount Iō (硫黄岳, Iō-dake) also Mount Iwo is an active rhyolitic lava dome on Iōjima in Kagoshima Prefecture, Japan. It sits within the borders of the town of Mishima.
The mountain is made up of non-alkali felsic rock and pyroclasitic flows.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.Otake (Nakanoshima)
Otake (御岳, O-take) is a stratovolcano in the Tokara Islands of Japan. It is the largest mountain on Nakanoshima, which is part of the village of Toshima in Kagoshima District of Kagoshima Prefecture. Being the largest mountain on a small island, it is also referred to as Nakanoshima. It is also called "Tokara Fuji" from its shape.
The mountain is an andesitic volcano. The volcano had a minor mud eruption in January 1914. In October 1949 the summit crater produced an ash cloud. The rock of the mountain is non-alkali mafic rock produced in the last 18,000 years.Sulphur mining took place on the southeast flank until 1944. During the rainy season, the summit crater fills with water.The volcano last erupted in 2007Ryukyu 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 Trench
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.