Tōhoku Earthquake (2011): Aftershock, Tsunami & Warning System

In this article, we will discuss the Tōhoku Earthquake.

A tremor (Earthquake) may be defined as the sudden shock of the earth that emits the energy in the earth’s lithosphere causing the formation of seismic waves.

The earthquake can be caused due to volcanic eruption, moving of tectonic plates, formation of the cave in a small area, or due to explosions. It is determined with the help of a seismograph by Seismometers and is measured on the Richter Magnitude Scale.

  1. Tōhoku Earthquake (2011)  

On the date of 11 March 2011 Friday, at the time of 14:46 the local time (05:46 UTC), a massive undersea megathrust earthquake notes 1 off the coast of Japan happened. The earthquake set off a huge tsunami with waves up to 40.5 meters (133 feet) high.

It was one of the most dangerous disasters in human history, the waves moved inland as far as 6 miles (10 km) and generated huge and severe structural destruction in north-eastern Japan. Airports, roads, and railroads were damaged, 127,290 buildings totally failed, 272,788 buildings half-collapsed, and another 747,989 buildings were destroyed. A dam failed to resist.

The tsunami also happened nuclear accidents, firstly the level 7 meltdowns (means a huge accident, the peak level, look notes 2) at three reactors in the Fukushima Daiichi Nuclear Power Plant complex. On the date of 10 March 2015, it was reported that the confirmed loss was 15,894 deaths, 6,152 injured, and 2,562 people lost.

It was the strong tremor ever registered in Japan, and the fourth strong earthquake in the world since modern record-keeping started in 1900.

The earthquake activated strong tsunami waves that may have achieved heights of up to 40.5 meters (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.

Citizens of Sendai had only eight to ten minutes of forewarning, and more than a hundred evacuation areas were cleaned away.

The snowfall which attended the tsunami and the cool temperature hindered recovery performs seriously; for a point, Ishinomaki, the city with the most casualties, was 0 °C (32 °F) as the tsunami struck.

The authorized figures provided in 2021 noted 19,747 deaths, 6,242 injured, and 2,556 people lost, and a report from 2015 revealed 228,863 people were still living out of their homes in either temporary housing or due to enduring relocation.

  2. Tōhoku Earthquake Aftershocks  

Japan faced over 1,000 aftershocks since the earthquake, with 80 recording over magnitude 6.0 Mw and many of which have been more magnitude 7.0 Mw. A magnitude of 7.4 Mw at 15:08 (JST), 7.9 Mw at 15:15, and a 7.7 Mw quake at 15:26 all occurred on 11 March.

A month later, a major aftershock struck offshore on 7 April with a magnitude of 7.1 Mw. Its epicenter was underwater, 66 km (41 mi) off the coast of Sendai. The Japan Meteorological Agency assigned a magnitude of 7.4 MJMA, while the U.S. Geological Survey lowered it to 7.1 Mw.

A minimum of four people got dead, and electricity was stopped along much of northern Japan involving the loss of external power to the Higashidōri Nuclear Power Plant and Rokkasho Reprocessing Plant.

Four days later on 11 April, a magnitude 7.1 Mw aftershock hit Fukushima, causing extra damage and taking the lives of a total of three people.

  3. Tsunami Due To Tōhoku Earthquake 

An upthrust of the height of 6 to 8 meters (20 to 26 ft) across a 180 kilometers (110 mi) broad seabed at 60 kilometers (37 mi) offshore from the east coast of Tōhoku resulted in the main tsunami that carried devastation across the Pacific coastline of Japan’s northern islands.

Thousands of lives were lost and whole towns were destroyed. The tsunami multiplied throughout the Pacific Ocean area advancing the whole Pacific coast of North and South America from Alaska to Chile. Notices were given and evacuations were done in different countries bordering the Pacific. Although the tsunami impacted multiple of these places, the heights of the waves were small.

Chile’s Pacific coast, one of the most distant from Japan at about 17,000 kilometers (11,000 mi) far, was hit by waves 2 meters (6.6 ft) high, compared with a calculated wave height of 38.9 meters (128 ft) at Omoe peninsula, Miyako city, Japan.

  4. Earthquake Warning System  

One minute quick the earthquake was noticed in Tokyo, the Earthquake Early Warning System, which contains higher than 1,000 seismometers in Japan, sent out notifications of upcoming intense shaking to millions.

It is considered that the early notification by the Japan Meteorological Agency (JMA) protected many lives. The notification for the general public was provided about eight seconds after the first P wave was noticed, or about 31 seconds after the earthquake happened.

However, the estimated intensities were smaller than the actual ones in some places, especially in Kanto, Koshinetsu, and Northern Tōhoku regions where the populace warning did not trigger.

According to the Japan Meteorological Agency, reasons for the underestimation include a saturated magnitude scale when using maximum amplitude as input, failure to fully take into account the area of the hypocenter, and the initial amplitude of the earthquake being less than that which would be predicted by an empirical relationship.