Out Of The Blue SHE Came!

For thousands of people in Japan one day would begin as any other, little knowing that by the time the sun had set that cool evening their lives would be changed forever.

On March the 11th 2011 out of the blue SHE came. First the 9.0-magnitude under sea earthquake hit making it the equal fifth largest earthquake ever recorded and the largest in Japan, since records began. This took just over two minutes and the length of time required for most of the 500–km fault to rupture. However, the shaking experienced at greater distances from the epicentre would have lasted longer as the vibrations or seismic waves spread out. devastating and destroying as it did so. 

To give you some idea of just how powerful this quake was on a basic scale here are some facts known. The amount of energy released by a magnitude 9 earthquake is roughly equivalent to 32 gigatons of TNT. Now imagine being there. It must have been quite literally terrifying. 

G.P.S data from the Geospatial Information Authority (G.S.I) of Japan shows that the north-east coast of Japan moved east by up to 4 metres. And the coast of north-east Japan moved eastward up to 4 meters, and consequently the coastline subsided by about 0.5 meters. 

These tremors were the result of a violent uplift of the sea floor 80 miles off the coast of Sendai, where the Pacific tectonic plate slides beneath the plate Japan sits on. Tens of miles of crust ruptured along the trench where the tectonic plates meet. The earthquake occurred at the relatively shallow depth of 15 miles, meaning much of its energy was released at the seafloor. 

tsunami heights

The Pacific plate moves fast in tectonic terms, at a rate of 9cm (3.5 inches) a year. This leads to the rapid buildup of huge amounts of energy. As the Pacific plate moves down, it sticks to the overhead plate and pulls it down too. Eventually, the join breaks, causing the seafloor to spring upwards several metres.

The plate tectonics of the region are complex, and geologists are not sure which plate Japan sits on. Candidates include the Eurasian plate, the North American plate, the Okhotsk plate, and the Honshu microplate.

The warning for the general public was delivered about 8 seconds after the first P.Wave was detected, or about 31 seconds after the earthquake occurred. It is difficult to explain just how this may have looked to those in the midst of this event so I will let the below video do the talking.  

http://www.youtube.com/watch?v=4DVTLzKkVh0&feature=youtu.be

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 m (9.8 ft) at the following locations and times on 11 March 2011, following the earthquake at 14:46 J.S.

15:12 JST – off Kamaishi– 6.8 m (22 ft)

15:15 JST –  Ofunato – 3.2 m (10 ft) or highest 

15:20 JST – Ishinomaki- shi  Ayukawa – 3.3 m (11 ft) or higher

15:21 JST – Miyako – 4.0 m (13.1 ft) or higher

15:21 JST – Kamaishi – 4.1 m (13 ft) or higher

15:44 JST – Erimo cho Shoya– 3.5 m (11 ft)

15:50 JST –  Soma - 7.3 m (24 ft) or higher

16:52 JST – Oarai – 4.2 m (14 ft)