DiscoverScroll article

On 11 March 2011, at 14:46:24 JST (05:46:24 UTC), a Mw 9.0–9.1 undersea megathrust earthquake occurred in the Pacific Ocean, 72 km (45 mi) east of the Oshika Peninsula of the Tōhoku region of Japan.

It triggered powerful tsunami waves that may have reached heights of up to 40.5 m (133 ft) in Miyako in Tōhoku's Iwate Prefecture, and which, in the Sendai area, traveled at 700 km/h (435 mph) and up to 10 km (6 mi) inland. The snowfall which accompanied the tsunami and the freezing temperature hindered rescue works; for instance, in Ishinomaki, the city with the most deaths, the temperature was 0 °C (32 °F) as the tsunami hit. The tsunami caused the Fukushima Daiichi nuclear disaster, primarily the meltdowns of three of its reactors, the discharge of radioactive water in Fukushima and the associated evacuation zones affecting hundreds of thousands of residents. Residents within a 20 km (12 mi) radius of the Fukushima Daiichi Nuclear Power Plant and a 10 km (6.2 mi) radius of the Fukushima Daini Nuclear Power Plant were evacuated.

The magnitude 9.1 (Mw) undersea megathrust earthquake occurred on 11 March 2011 at 14:46 JST (05:46 UTC) in the north-western Pacific Ocean at a relatively shallow depth of 32 km (20 mi), with its epicenter approximately 72 km (45 mi) east of the Oshika Peninsula of Tōhoku, Japan, lasting approximately six minutes.

This megathrust earthquake was a recurrence of the mechanism of the earlier 869 Sanriku earthquake, which has been estimated as having a magnitude of at least 8.4 Mw, which also created a large tsunami that inundated the Sendai plain.

The tsunami warning issued by the Japan Meteorological Agency was the most serious on its warning scale; it was rated as a "major tsunami", being at least 3 meters (9.8 ft) high. On 13 March 2011, the Japan Meteorological Agency (JMA) published details of tsunami observations recorded around the coastline of Japan following the earthquake. These observations included tsunami maximum readings of over 3 meters (9.8 ft) at the following locations and times on 11 March 2011, following the earthquake at 14:46 JST: The tsunami height that had been initially predicted by the tsunami warning system was lower than the actual tsunami height; this error contributed to the delayed escape of some residents.

The United States National Tsunami Warning Center issued a tsunami warning for the coastal areas in most of California, all of Oregon, and the western part of Alaska, and a tsunami advisory covering the Pacific coastlines of most of Alaska, and all of Washington and British Columbia, Canada.

The degree and extent of damage caused by the earthquake and resulting tsunami were enormous, with most of the damage being caused by the tsunami.

The reactors at the Fukushima Daiichi and Fukushima Dai-ni plants were automatically taken offline when the first earthquake occurred and sustained major damage from the earthquake and subsequent tsunami.

The Headquarters for Earthquake Research Promotion set up by the Japanese government then reassessed the long-term risk of trench-type earthquakes around Japan, and it was announced in November 2011 that research on the 869 Sanriku earthquake indicated that a similar earthquake with a magnitude of Mw 8.4–9.0 would take place off the Pacific coast of northeastern Japan, on average, every 600 years. Also, a tsunami-earthquake with a tsunami magnitude scales (Mt) between 8.6 and 9.0 (Similar to the 1896 Sanriku earthquake, the Mt for the 2011 Tōhoku earthquake was 9.1–9.4) had a 30% chance to occur within 30 years. The Japan Trench Fast Drilling Project, a scientific expedition conducted in 2012–2013, drilled ocean-floor boreholes through the fault zone of the earthquake and gathered important data about the rupture mechanism and physical properties of the fault that caused the 2011 earthquake and tsunami.

The 2011 Tōhoku earthquake and tsunami had a great environmental impact on Japan's eastern coast.

Quick Facts

• Also, a tsunami-earthquake with a tsunami magnitude scales (Mt) between 8.6 and 9.0 (Similar to the 1896 Sanriku earthquake, the Mt for the 2011 Tōhoku earthquake was 9.1–9.4) had a 30% chance to occur within 30 years.
• This megathrust earthquake was a recurrence of the mechanism of the earlier 869 Sanriku earthquake, which has been estimated as having a magnitude of at least 8.4 Mw, which also created a large tsunami that inundated the Sendai plain.
• Residents within a 20 km (12 mi) radius of the Fukushima Daiichi Nuclear Power Plant and a 10 km (6.2 mi) radius of the Fukushima Daini Nuclear Power Plant were evacuated.
• On 13 March 2011, the Japan Meteorological Agency (JMA) published details of tsunami observations recorded around the coastline of Japan following the earthquake.
• The 2011 Tōhoku earthquake and tsunami had a great environmental impact on Japan's eastern coast.

Source material: Wikipedia - "2011 Tōhoku earthquake and tsunami". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.