Tsunami warning system

A tsunami warning system (TWS) is used to detect tsunamis in advance and issue warnings to prevent loss of life and damage. It is made up of two equally important components: a network of sensors to detect tsunamis and a communications infrastructure to issue timely alarms to permit evacuation of the coastal areas. There are two distinct types of tsunami warning systems: international and regional. When operating, seismic alerts are used to instigate the watches and warnings; then, data from observed sea level height (either shore-based tide gauges or DART buoys) are used to verify the existence of a tsunami. Other systems have been proposed to augment the warning procedures; for example, it has been suggested that the duration and frequency content of t-wave energy (which is earthquake energy trapped in the ocean SOFAR channel) is indicative of an earthquake's tsunami potential.

History and forecasting

The first rudimentary system to alert communities of an impending tsunami was attempted in Hawaii in the 1920s. More advanced systems were developed in the wake of the April 1, 1946 (caused by the 1946 Aleutian Islands earthquake) and May 23, 1960 (caused by the 1960 Valdivia earthquake) tsunamis which caused massive devastation in Hilo, Hawaii^{source needed}. While tsunamis travel at between 500 and 1,000 km/h (around 0.14 and 0.28 km/s) in open water, earthquakes can be detected almost at once as seismic waves travel with a typical speed of 4 km/s (around 14,400 km/h)^{source needed}. This gives time for a possible tsunami forecast to be made and warnings to be issued to threatened areas, if warranted. Unfortunately, until a reliable model is able to predict which earthquakes will produce significant tsunamis, this approach will produce many more false alarms than verified warnings^{source needed}.

Japan

Coordinates: 35°N 136°E / 35°N 136°E / 35; 136

Japan (ⁱ/dʒəˈpæn/; Japanese: 日本 Nippon [nip̚põ̞ɴ] or Nihon [nihõ̞ɴ]; formally 日本国  Nippon-koku or Nihon-koku, "State of Japan") is an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, the East China Sea, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south. The kanji that make up Japan's name mean "sun origin", and Japan is often called the "Land of the Rising Sun".

Japan is a stratovolcanic archipelago of 6,852 islands. The four largest are Honshu, Hokkaido, Kyushu, and Shikoku, which make up about ninety-seven percent of Japan's land area. Japan's population of 126 million is the world's tenth largest. Approximately 9.1 million people live in Tokyo, the capital city of Japan, which is the sixth largest city proper in the OECD. The Greater Tokyo Area, which includes Tokyo and several surrounding prefectures, is the world's largest metropolitan area with over 35 million residents and the world's largest urban agglomeration economy.

Fukushima Prefecture

Fukushima Prefecture (福島県, Fukushima-ken) is a prefecture of Japan located in the Tōhoku region on the island of Honshu. The capital is the city of Fukushima.

History

Until the Meiji Restoration, the area of Fukushima prefecture was part of what was known as Mutsu Province.

The Shirakawa Barrier and the Nakoso Barrier were built around the 5th century to protect 'civilized Japan' from the 'barbarians' to the north. Fukushima became a Province of Mutsu after the Taika Reforms were established in 646.

In 718, the provinces of Iwase and Iwaki were created, but these areas reverted to Mutsu some time between 722 and 724.

The province of Fukushima was conquered by Prince Subaru in 1293. This region of Japan is also known as Michinoku and Ōshū.

The Fukushima Incident took place in the prefecture after Mishima Michitsune was appointed governor in 1882.

2011 earthquake and subsequent disasters

The 2011 Tōhoku earthquake and tsunami and the resulting Fukushima Daiichi nuclear disaster caused significant damage to the prefecture, primarily but not limited to the eastern Hama-dōri region.

Tsunami

A tsunami (plural: tsunamis or tsunami; from Japanese: 津波, lit. "harbor wave"; English pronunciation: /tsuːˈnɑːmi/) , also known as a seismic sea wave, is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), landslides, glacier calvings, meteorite impacts and other disturbances above or below water all have the potential to generate a tsunami. Unlike normal ocean waves which are generated by wind or tides which are generated by the gravitational pull of the Moon and Sun, a tsunami is generated by the displacement of water.

Tsunami waves do not resemble normal sea waves, because their wavelength is far longer. Rather than appearing as a breaking wave, a tsunami may instead initially resemble a rapidly rising tide, and for this reason they are often referred to as tidal waves, although this usage is not favored by the scientific community because tsunamis are not tidal in nature. Tsunamis generally consist of a series of waves with periods ranging from minutes to hours, arriving in a so-called "wave train". Wave heights of tens of meters can be generated by large events. Although the impact of tsunamis is limited to coastal areas, their destructive power can be enormous and they can affect entire ocean basins; the 2004 Indian Ocean tsunami was among the deadliest natural disasters in human history with at least 230,000 people killed or missing in 14 countries bordering the Indian Ocean.

List of earthquakes in Japan

This is a list of earthquakes in Japan with either a magnitude greater than or equal to 7.0 or which caused significant damage or casualties. As indicated below, magnitude is measured on the Richter magnitude scale (M_L) or the moment magnitude scale (M_w), or the surface wave magnitude scale (M_s) for very old earthquakes. The present list is not exhaustive, and reliable and precise magnitude data is scarce for earthquakes that occurred prior to the development of modern measuring instruments.

See also

References