Japan Tsunami 2011
What Causes a Tsunami?
A tsunami is a large ocean wave that is caused by sudden motion on the ocean floor. This sudden motion could be an earthquake, a powerful volcanic eruption, or an underwater landslide. The impact of a large meteorite could also cause a tsunami. Tsunamis travel across the open ocean at great speeds and build into large deadly waves in the shallow water of a shoreline.
Subduction Zones are Potential Tsunami Locations
Most tsunamis are caused by earthquakes generated in a subduction zone, an area where an oceanic plate is being forced down nto the mantle by plate tectonic forces. The friction between the subducting plate and the overriding plate is enormous. This friction prevents a slow and steady rate of subduction and instead the two plates become "stuck".
Accumulated Seismic Energy
As the stuck plate continues to descend into the mantle the motion causes a slow distortion of the overriding place. The result is an accumulation of energy very similar to the energy stored in a compressed spring. Energy can accumulate in the overriding plate over a long period of time - decades or even centuries.
Earthquake Causes Tsunami
Energy accumulates in the overriding plate until it exceeds the frictional forces between the two stuck plates. When this happens, the overriding plate snaps back into an unrestrained position. This sudden motion is the cause of the tsunami - because it gives an enormous shove to the overlying water. At the same time, inland areas of the overriding plate are suddenly lowered.
The Tohuku Earthquake and Tsunami
The 2011 earthquake off the Pacific coast of Tohoku known as the 2011 Tohoku earthquake, the Great East Earthquake, and the 3.11 Earthquake, was a magnitude 9.03 (Mw) undersea mega thrust earthquake off the coast of Japan that occurred at 14:46 JST (05:46 UTC) on Friday, 11 March 2011, with the epicentre approximately 70 kilometres (43 mi) east of the Oshika Peninsula of Tohoku and the hypocenter at an underwater depth of approximately 32 km (20 mi). It was the most powerful known earthquake ever to have hit Japan, and one of the five most powerful earthquakes in the world since modern record-keeping began in 1900. The earthquake triggered powerful tsunami waves that reached heights of up to 40.5 metres (133 ft) in Miyako in Tohoku's Iwate Prefecture, and which, in the Sendai area, travelled up to 10 km (6 mi) inland.[17] The earthquake moved Honshu (the main island of Japan) 2.4 m (8 ft) east and shifted the Earth on its axis by estimates of between 10 cm (4 in) and 25 cm (10 in).
Geophysical Effects
The quake moved portions of north eastern Japan by as much as 2.4 m (7.9 ft) closer to North America,[18][19] making portions of Japan's landmass wider than before.[19] Portions of Japan closest to the epicentre experienced the largest shifts. A 400 km (250 mi) stretch of coastline dropped vertically by 0.6 m (2.0 ft), allowing the tsunami to travel farther and faster onto land.[19] One early estimate suggested that the Pacific plate may have moved westward by up to 20 m (66 ft), and another early estimate put the amount of slippage at as much as 40 m (130 ft). On 6 April the Japanese coast guard said that the quake shifted the seabed near the epicentre 24 meters (79 ft) and elevated the seabed off the coast of Miyagi prefecture by 3 meters. A report by the Japan Agency for Marine-Earth Science and Technology, published in Science on 2 December 2011, concluded that the seabed in the area between the epicentre and the Japan Trench moved 50 meters east-southeast and rose about 7 meters as a result of the quake. The report also stated that the quake had caused several major landslides on the seabed in the affected area
The earthquake shifted the Earth's axis by estimates of between 10 cm (4 in) and 25 cm (10 in). This deviation led to a number of small planetary changes, including the length of a day, the tilt of the Earth, and the Chandler wobble. The speed of the Earth's rotation increased, shortening the day by 1.8 microseconds due to the redistribution of Earth's mass.
Fatalities
The National Police Agency has confirmed 15,870 deaths, 6,114 injured, and 2,814 people missing across twenty prefectures.
Of the 13,135 fatalities recovered by 11 April 2011, 12,143 or 92.5% died by drowning.
Of the total confirmed victims, 14,308 drowned, 667 were crushed to death or died from internal injuries, and 145 perished from burns.
Save the Children reports that as many as 100,000 children were uprooted from their homes, some of whom were separated from their families because the earthquake occurred during the school day. 236 children were orphaned in the prefectures of Iwate, Miyagi and Fukushima by the disaster; 1,580 children lost either one or both parents,846 in Miyagi, 572 in Iwate, and 162 in Fukushima. The quake and tsunami killed 378 elementary, middle-school, and high school students and left 158 others missing. One elementary school in Ishinomaki, Miyagi, Okawa Elementary, lost 74 of 108 students and 10 of 13 teachers and staff.
A tsunami is a large ocean wave that is caused by sudden motion on the ocean floor. This sudden motion could be an earthquake, a powerful volcanic eruption, or an underwater landslide. The impact of a large meteorite could also cause a tsunami. Tsunamis travel across the open ocean at great speeds and build into large deadly waves in the shallow water of a shoreline.
Subduction Zones are Potential Tsunami Locations
Most tsunamis are caused by earthquakes generated in a subduction zone, an area where an oceanic plate is being forced down nto the mantle by plate tectonic forces. The friction between the subducting plate and the overriding plate is enormous. This friction prevents a slow and steady rate of subduction and instead the two plates become "stuck".
Accumulated Seismic Energy
As the stuck plate continues to descend into the mantle the motion causes a slow distortion of the overriding place. The result is an accumulation of energy very similar to the energy stored in a compressed spring. Energy can accumulate in the overriding plate over a long period of time - decades or even centuries.
Earthquake Causes Tsunami
Energy accumulates in the overriding plate until it exceeds the frictional forces between the two stuck plates. When this happens, the overriding plate snaps back into an unrestrained position. This sudden motion is the cause of the tsunami - because it gives an enormous shove to the overlying water. At the same time, inland areas of the overriding plate are suddenly lowered.
The Tohuku Earthquake and Tsunami
The 2011 earthquake off the Pacific coast of Tohoku known as the 2011 Tohoku earthquake, the Great East Earthquake, and the 3.11 Earthquake, was a magnitude 9.03 (Mw) undersea mega thrust earthquake off the coast of Japan that occurred at 14:46 JST (05:46 UTC) on Friday, 11 March 2011, with the epicentre approximately 70 kilometres (43 mi) east of the Oshika Peninsula of Tohoku and the hypocenter at an underwater depth of approximately 32 km (20 mi). It was the most powerful known earthquake ever to have hit Japan, and one of the five most powerful earthquakes in the world since modern record-keeping began in 1900. The earthquake triggered powerful tsunami waves that reached heights of up to 40.5 metres (133 ft) in Miyako in Tohoku's Iwate Prefecture, and which, in the Sendai area, travelled up to 10 km (6 mi) inland.[17] The earthquake moved Honshu (the main island of Japan) 2.4 m (8 ft) east and shifted the Earth on its axis by estimates of between 10 cm (4 in) and 25 cm (10 in).
Geophysical Effects
The quake moved portions of north eastern Japan by as much as 2.4 m (7.9 ft) closer to North America,[18][19] making portions of Japan's landmass wider than before.[19] Portions of Japan closest to the epicentre experienced the largest shifts. A 400 km (250 mi) stretch of coastline dropped vertically by 0.6 m (2.0 ft), allowing the tsunami to travel farther and faster onto land.[19] One early estimate suggested that the Pacific plate may have moved westward by up to 20 m (66 ft), and another early estimate put the amount of slippage at as much as 40 m (130 ft). On 6 April the Japanese coast guard said that the quake shifted the seabed near the epicentre 24 meters (79 ft) and elevated the seabed off the coast of Miyagi prefecture by 3 meters. A report by the Japan Agency for Marine-Earth Science and Technology, published in Science on 2 December 2011, concluded that the seabed in the area between the epicentre and the Japan Trench moved 50 meters east-southeast and rose about 7 meters as a result of the quake. The report also stated that the quake had caused several major landslides on the seabed in the affected area
The earthquake shifted the Earth's axis by estimates of between 10 cm (4 in) and 25 cm (10 in). This deviation led to a number of small planetary changes, including the length of a day, the tilt of the Earth, and the Chandler wobble. The speed of the Earth's rotation increased, shortening the day by 1.8 microseconds due to the redistribution of Earth's mass.
Fatalities
The National Police Agency has confirmed 15,870 deaths, 6,114 injured, and 2,814 people missing across twenty prefectures.
Of the 13,135 fatalities recovered by 11 April 2011, 12,143 or 92.5% died by drowning.
Of the total confirmed victims, 14,308 drowned, 667 were crushed to death or died from internal injuries, and 145 perished from burns.
Save the Children reports that as many as 100,000 children were uprooted from their homes, some of whom were separated from their families because the earthquake occurred during the school day. 236 children were orphaned in the prefectures of Iwate, Miyagi and Fukushima by the disaster; 1,580 children lost either one or both parents,846 in Miyagi, 572 in Iwate, and 162 in Fukushima. The quake and tsunami killed 378 elementary, middle-school, and high school students and left 158 others missing. One elementary school in Ishinomaki, Miyagi, Okawa Elementary, lost 74 of 108 students and 10 of 13 teachers and staff.