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Magnitude 9.0: When the Earth Quaked and the Ocean Raged

by Michelle Simon 12 Mar 2011
Magnitude 9.0: When the Earth Quaked and the Ocean Raged
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Honshu, Japan: At 05:46 UTC (02:46 PM - Local Time at the Epicentre) one of the most powerful earthquakes recorded in quake history, off the east coast of Japan, 130 km (80 miles) east of Sendai, Honshu, Japan.

Measured at an alarming magnitude of 9.0, the 11th March 2011, Honshu's Mega-trust EQ is marked as Japan's highest recorded magnitude, setting off a devastating tsunami that hit the eastern coastal towns approximately 1.5 hours after the EQ.

japan earthquake epicenter map

The main tsunami travelled up to 10 km (6 miles) inland in Japan. The destruction to life and property has taken its toll and the aftershocks and domino effect of the earthquake is still rippling through the Pacific Ocean with secondary tsunami wave impacts travelling as far as 2 100-7000 km hitting the North Pacific islands, North American west coast and western Canadian coastal areas at 16:30 UTC.

usgs google japan earthquake shockwave

japan earthquake wave height in cm

Today, 12th March 2011 continued with heightened seismic activity resulting in approximately 50 secondary-quakes or aftershocks in the order of as high as 6-magnitudes. The ensuing almost nonstop waves of seismic aftershocks and secondary tsunamis are continuing with warnings from the Japanese Meteorological Agency estimated throughout the day at heights of between 0.5m to 2m.

japan earthquake wave height analysis

The initial tsunami struck yesterday at approximately 14:50 JST at a height of 0.3m, followed at 15:12 JST by the maximum tsunami of 6.8m causing untold devastation to the east coast of Japan. Coastal cities could be viewed on global images being swiped by nature's powerful blow of ocean rage, as the rising super-wave moved across the ocean reaching almost 10 m at the intertidal zone, destroying everything in its path from human life to infrastructure. Boats, vehicles and built structures amongst other things were erased from the landscape in seconds as the wave engulfed them, leaving behind a trail of dead and injured bodies, rubble and chaos.

noaa japan earthquake tsunami travel times

The movement of the tsunami against the force of the rivers in Sendai and Kinagashima, breaking the rivers downstream flow and forcing the freshwater flow upriver to create an relentless waterforce of combined ocean-water and fresh-water. A tsunami can travel over the ocean at a speed of 500mph.

sendai tsunami

kinagashima tsunami river flow

Origin of the Earthquake

The 9.0 Earthquake originated off the east coast of Japan on the sea floor of the Pacific Ocean at a depth of 24.4 km (15.2 miles), where the Pacific Plate meets the North American Plate.

tectonic plates japan earthquake

Tectonic plates are the segmented blocks of the earth's outer crust upon which the oceans and continents lie. The oceanic crust is much thinner than the continental/terrestrial crust. There are 9 major plates with a number of minor ones. The Giant Pacific Plate is almost entirely ocean based while the North American plate is largely continently. Irrespective of size all plates have the potential to cause crustal unrest leading to earthquakes and volcanic eruptions.

According to the US Geological Society, Japan's EQ occurred as a result of thrust faulting on or near the subduction zone interface plate boundary between the Pacific and North American plates. The Pacific plate thrusts underneath Japan at the Japan Trench, and dips to the west beneath Eurasia. On March 11th 2011 the plate boundary subduction caused Japan's most catastrophic EQ.


Japan's EQ was preceded by a series of large foreshock as follows:

Two days Prior - 9th March 2011 - seismic activity creating a foreshock of M 7.2 approximately 40 km from Honshu EQ on the 11th March 2011.

9th March 2011 - a further 3 EQs greater than M 6 followed the M 7.2 foreshock.


Seismic activity continued past the main EQ, sending over a 100 aftershocks through the region as follows:

- Aftershock M 7.0 was reported at 15:06 (Local Time, LT).

- Aftershock M7.4 at 15:15 LT.

- Aftershock M7.2 at 15:26 LT.

- Second EQ M 6.7 occurred at 03:59 LT on the 12th March 2011 resulting in aftershocks.

- Over one hundred aftershocks of M 4.5 or greater have occurred since the initial quake.

usgs shake map japan earthquake

Japan - An EQ Hotspot

Japan is a noted earthquake, volcano and tsunami hotspot due to its location on the zone of several tectonic plate intersections. On the 1st September 1923, the Great Kanto Earthquake destroyed Tokyo, Yokohama and the surroundings. About 140,000 people fell victim to this earthquake and the fires caused by it. The Japan Trench subduction zone has hosted 9 events of M 7 or greater since 1973. The largest of these was an M 7.8 earthquake approximately 260 km to the north of the March 11 event, in December 1994, which caused 3 fatalities and almost 700 injuries. In June of 1978, an M 7.7 earthquake 35 km to the southwest caused 22 fatalities and over 400 injuries (USGC, 2011).

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Physical Destruction

The EQ-tsunami impacts are extensive and have rendered livelihoods of hundreds of people and economic activity non-functional with water and electricity supply being cut-off from millions of people. The power of water didn't end with the tsunami; the impact of the EQ-tsunami resulted in a dam failure in Fukushima Prefecture causing downstream homes to flood. Roads and rails were severely damaged.

sendai airport hit by tsunami

High Risk Impacts


A state of emergency was declared after the explosion of a nuclear plant, the Fukushima I

Nuclear Plant; at 12 March at 15:36 LT. Neighbouring residents within a 20 km (12 mile) radius of the Fukushima I plant were evacuated after the cooling system at the plant failed. Following this, the second nuclear plant, the Fukushima II's cooling system also failed resulting in authorities issuing an evacuation for residents within a 3 kilometers (1.9 mile) radius of the Fukushima II.

Oil Refinery

A fire broke out at the Chiba Oil Refinery resulting in an explosion.

Earthquake-Tsunami Death-Injury-Missing Persons Toll

Human Life impacts are estimated at a count of +600 confirmed dead, +780 missing, 1 040 injured. This count is sure to grow in the ensuing days as Japan tries to recover and proper statistics of the impacts are registered.

The loss of lives and destruction of Japan is shattering and the world needs to pool its resources in providing aid and disaster management support to help Japan back on its feet. The reality is we humans take the earth and nature for granted and only recognise our own fragility against forces of the planet when we are faced with natural disasters. Similarly the earth has to deal with our reckless onslaught to our natural landscapes, resources and fellow life-forms that we share the planet with. The difference is that nature is in no way strategically malevolent; the earth functions as any living organism does, it has it's days of natural good health and it's days when the rumblings in its internal system ruptures, cracks and rises up. The sooner we recognise the paradox of the earth's vulnerability and power, the sooner we will recognise that all life on the planet is precious and we should start developing a conscience about how we treat the planet.

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Copyright  © Michelle Simon 2011

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