Plate Tectonics Information Report

 

Plate Tectonics Information Report on the Japan Trench

The Japan Trench is an oceanic trench located beneath the Pacific Ocean alongside the coastline of eastern Japan. Most science and geography textbooks in Japan have a description or at least mentions this oceanic trench. In the north, it makes a huge bend eastwards at Cape Erimo near Hokkaido and after reaching Erimo seamount continues on as the Kuril–Kamchatka Trench. In the south, it begins to bend slightly at Bōsō Peninsula and continues on as the Izu-Ogasawara Trench. The Kuril–Kamchatka Trench and the Izu-Ogasawara Trench used to be part of the Japan Trench. The three oceanic trenches were all known as the Japan Trench. The style of earthquakes near the Izu-Ogasawara Trenchwas and still is changing, which resulted in scientists differentiating this trench from the Japan Trench in 1962. There were other pieces of evidence that supported the differentiation. The Izu-Ogasawara Trench continues on southwards across 5000 metres of the Ogasawara plateau before joining the Mariana Trench. The total length of the Japan Trench is approximately 800km. The average depth is 7000～8000m. The depth at its deepest is 8020～8200～8412m. (デジタル大辞泉By Shogakukan ©2010 【日本海溝】.)(ブリタニカ国際大百科事典小項目電子辞書版By Britannica Japan Co., Ltd.©2010日本海溝Japan Trench.) The deepness of the Japan Trench changes and varies between sources much like the lengths of major rivers. Some areas in the south near the Izu-Ogasawara Trench can reach up to 9000m and above. However, it is not considered as the Japan Trench’s deepest depth because it is too close to the Izu-Ogasawara Trench. (百科事典マイぺディア電子辞書版 By Hitachi Solutions, Ltd. ©2010 にほんかいこう【日本海溝】.)

According to the ocean floor spreading hypothesis and plate tectonics, the force of the ocean floor sinking into the mantle creates oceanic trenches and island arcs such as the Japan Trench and the Japanese archipelago. Hence, most oceanic trenches are located in and around the Pacific Ocean (around 20) with some in the Atlantic Ocean and the Indian Ocean. That is not the only contributing factor which creates archipelagos. Many things happen which have not yet been confirmed. Around 65 million years ago Gondwana split apart and most of the continents began looking like they are now. (Williamson & Garton 2011, p.240.) 40,000 years ago, humans arrived on the Japanese archipelago. (数研出版2014, p.494.) The Japan Trench has been roughly where it is now ever since the Japanese archipelago began forming. It used to be right next to Korea and below what eventually became Japan. The Japan Trench has existed for three hundred million years.It developed when the plates that existed in the past began to diverge, converge and transform. (百科事典マイぺディア電子辞書版 By Hitachi Solutions, Ltd. ©2010 にほんれっとう【日本列島】.)

The oceanic Pacific plate sinks into the mantle under the continental Okhotsk Plate and creates a subduction zone which includes the Japan Trench. It sinks into the mantle because oceanic plates are made of a heavier material than continental plates. (石井and others 2009, p.378.)Continental plates are less dense and floats on top. The continental Okhotsk Plate used to be known as the North American plate but has been differentiated. In Japan it is still known as the North American plate sometimes because it is easier. Both names are used in some cases. There are four main plates around Japan. Two of them are oceanic plates and the other two are continental plates. The oceanic Pacific plate also sinks under the Philippine (Sea) Plate which in turn sinks under the Eurasian plate. The type of movement at the boundary of the oceanic Pacific plate and the continental Okhotsk Plateis convergent. Frequent earthquakes occur in this area. Big earthquakes occur when the continental plate is pulled down with the oceanic plate and reaches a limit which takes over five-hundred years. The continental plate then moves up with all the accumulated stress and causes devastating earthquakes and tsunamis. There are many ways earthquakes occur and the processes are unlimited. (National Geographic Japan 2008, Chapter 2) Volcanoes are also present throughout Japan.

The Japanese archipelago was created by the strain caused by the Pacific plate against the North American plate. The force of this made the earth crust bend and fold thus creating a huge anticline as well as metamorphic rock. Some also say that dirt and sand from the continental plates got mixed with the sandstone and other materials from the Pacific plate. The sandstonekept on piling up onto the continental plates as the Pacific plate is pushed under them. The Japan Trench was formed because both the continental and the oceanic plate bend inwards to create a belt-shaped cavity. The term ‘trench’ was not officially used on textbooks until after the 1960s. (Wikipedia, Oceanic trench2. History of the term "trench".) 海溝means a gulf, gap or groove in the sea. If a person was to stand inside any ocean trench and look up at the corresponding archipelago it would look like a huge 10,000m mountain range. (石井and others 2009, p.377～386.)

The Pacific plate and the Philippine (Sea) Plate both move approximately 7～9cm each year. (石井and others 2009, p.377.) The Japan Trench causes earthquakes and tsunamis regularly. It caused the Great East Japan Earthquake (M9.0) that occurred in 2011. At first scientists were amazed and startled when it happened. Scientists had to collaborate to generate solutions for future unexpected tsunamis and earthquakes. They also discovered among many other things that M9.0 earthquakes had occurred in the past as well.(Wikipedia, 東日本大震災 2015.)

The Japanese deep sea research submarine SHINKAI 6500 officially began its career in 1989 when it went down 6,527m into the Japan Trench. That was only an official trial. SHINKAI 6500 is probably the submarine that is most closely related to the Japan Trench. In 1991, it went down 6,366m and discovered the chasm of the ocean floor from the oceanic plate side of the Japan Trench. The actual discovery led to an improved understanding of the Japan Trench and oceanic trenches in general. It also discovered several rare deep sea creatures. It discovered more strange species in 1997. By 2007, it had explored the ocean floors around the world 1,000 times. In 2011, after the devastating earthquake and tsunami that hit eastern Japan, it researched the epicentre of the earthquake and discovered a long crevice in the ocean floor. In 2012 it had been used 1,300 times and was renovated to keep up with the advanced technologies of today. There are only 7 manned deep sea research submarines around the world. The speed of the submarine is 2.7 knots. It requires 2 hours and 30 minutes to descend to a depth of 6,500m. It requires the same amount of time to rise to the surface. Research of the ocean floor does seem to be hard work. (Japan Agency for Marine-Earth Science and Technology 2012) I wonder if they have changed their Full HD video camera into a 4K video camera already. Although it has the ability to dive deeper than other submarines because it is needed for research of Japan’s earthquakes etc., the submarine itself is already behind the world standards with the Chinese research submarine breaking the deepest depth record.

There are 2～3 ocean floor terraces on the slope of the Okhotsk Plate. At the depth of 2400～3400m it becomes a steep staircase-shaped surface that leads down to the bottom. On the Pacific plate side, there is a concave shaped mini trench at the depth of 5600～6000m which is adjacent to the Japan Trench. It marks the beginning of the slope on the ocean side of the Japan Trench. The seabed of the Japan Trench is unlike most oceanic trenches. It is V-shaped when seen from the side and does not have many flat areas which typify oceanic trenches. (百科事典マイぺディア電子辞書版 By Hitachi Solutions, Ltd. ©2010 にほんかいこう【日本海溝】.)

Although the Izu-Ogasawara Trench and the Mariana Trench are deeper than the Japan Trench, the popularity of the Japan Trench is high. The name is easy to remember. It is the cause of most of the earthquakes of north-eastern Japan. The attention of the Japanese people is now at the Philippine Sea Plate and the surrounding area. A huge earthquake is expected to occur in south-western Japan at any time. Particular attention is paid to the warm, bottom-filled troughs, not the oceanic trenches. Troughs are shallower than oceanic trenches even though they are created the same way.

 

Bibliography

 

“日本海溝 Japan Trench” 2010, ブリタニカ国際大百科事典小項目電子辞書版, Britannica Japan Co., Ltd.

 

“にほんかいこう【日本海溝】” 2010, 百科事典マイぺディア電子辞書版,Hitachi Solutions, Ltd., Japan

 

“にほんれっとう【日本列島】” 2010, 百科事典マイぺディア電子辞書版, Hitachi Solutions, Ltd., Japan

 

石井忠浩and 5 others 2009、中学用/理科自由自在、受験研究社、Osaka

 

Japan Agency for Marine-Earth Science and Technology 2012, 「しんかい6500」. http://www.jamstec.go.jp/j/about/equipment/ships/shinkai6500.html, (accessed 1/08/2015).

 

National Geographic Japan 2008, ビジュアル化学大事典, “起源と地質” from Chapter 2 ‘地球’ (Earth)

 

“【日本海溝】” 2010, デジタル大辞泉, Shogakukan, Japan

 

“生物の起源と進化” 2014, 【新課程】チャート式®シリーズ　新生物　生物基礎・生物, 数研出版株式会社, Chapter 12 p.494, Tokyo & Kyoto

 

Wikipedia 30 June 2015, at 13:33, Oceanic trench. https://en.wikipedia.org/wiki/Oceanic_trench, (accessed 1/08/2015).

 

フリー百科事典『ウィキペディア（Wikipedia）』10 July 2015, at 23:11, 東日本大震災https://ja.wikipedia.org/wiki/東日本大震災, (accessed 2/08/2015).

 

Williamson, K & Garton, A 2011, Science Essentials 9, MACMILLAN EDUCATION AUSTRALIA PTY LTD, South Yarra

 

Noah Nishihara Homegroup 909

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