Animation of the 2004 Sumatra Tsunami
We are only into the third month of 2011 and so far there has been unrest in some of the African countries, an earthquake that has ruined New Zealand’s capital Christchurch and now a tsunami that has hit Japan. Donovan Hand asks is 2011 the start of the omen that the ancient Mayans warned us about?
I know that the Mayan prophecy as well as any other predictions about the end of the world are more than likely false. Also, I know that true scientists use the MMS rather than Richter Scale. Unfortunately, I doubt the people marking my work would actually know the difference.
They say that the end of the world will happen in 2012. People have already started to believe that this ancient prophecy is happening a year earlier than expected. The devastating tsunami that hit Japan is the latest piece of ‘evidence’ that some people are using to support claims that the apocalypse is nigh.
The tsunami, however, was the result of a major earthquake that occurred offshore at around 0607 GMT (around 1500 local Japanese time). The first shock recorded by the USGS (United States Geological Survey) was a mighty 8.9 on the Richter scale.
But what is a tsunami and how do they occur? Firstly, a tsunami and a tidal wave are technically two different things. A tidal wave is caused by changing tides; a tsunami on the other hand is often caused by water being displaced. In the case of the Sumatra Boxing day tsunami (2004), it was caused by an earthquake that measured between 9.1-9.3 that ruptured anywhere between 1200 to 1600km of fault line. It is this action that displaces water and thus causes a tsunami to occur.
In the Sumatra example, there was an average vertical displacement of ten meters along the whole length of ruptured fault line. This is a very large area to be displaced and is the reason why the waves caused so much destruction.
Tsunami waves have a long wavelength and out to sea and they have very low amplitudes. They can travel very quickly (over 500mph in open ocean) but they slow down as they reach the coastline due to increased friction with the sea bed (and whatever else there may be on it e.g. coral reefs). This causes them to ‘rear up’ and their amplitudes to increase. This is why when tsunamis are often depicted, they appear over ten feet tall when they reach shore. Due to the immense amount of energy that they carry, it is not unusual for them to move far inland. A tsunami wave is also incredibly heavy. The force of the wave can derail and carry a fully laden freight train which typically weighs over a hundred tonnes.
At the time of writing, we believe that the area affected and the displacement that caused the Japanese tsunami was much less than Sumatra, but there are still tsunami warnings in place for New Zealand, the Philippines, Indonesia, Papua New Guinea and Hawaii. The worrying issue is that Sendai is home to over a million people and that in the past, parts of the city would flood due to the Hirose-gawa River. Sendai was affected by an earthquake offshore 2005 which registered 7.2 on the Richter scale but in that case there was no tsunami and few casualties or fatalities.
The Japanese are well prepared for tsunamis and often run drills as they live on one of the most tectonically active areas of the planet. The island sits on the ‘Pacific Ring of Fire’ is the most tectonically active area on the planet. Here the Pacific crust subducts under the Eurasian plate.
This causes immense pressure and when the pressure is released we have an earthquake.
That is what hit Christchurch earlier this year. New Zealand, like Japan, sits on top of a plate boundary but in this case it’s the Pacific and the Indo-Australian plate. The Pacific plate in this case is subducting under the Indo-Australian plate. The 2011 earthquake was approximately 6.3 on the Richter Scale but what made it devastating was that it was a shallow focus earthquake. The epicentre was just 5km below the Earth’s surface.
To understand how the energy dissipates, scientists use this analogy:
• There is a speaker that is playing a sound at 100dbs.
• The closer you are to the source, the louder the sound would appear.
• The further you are, the quieter the sound would appear.
In this case, the focus was so shallow so more of that energy was felt without it muffled by bedrock or water. This is the reason why even the earthquake was a much lower magnitude earthquake and caused such damage.
Christchurch was hit by a much larger magnitude earthquake last year which registered a 7 on the scale but it was deeper (around 10km). This demonstrates that by classifying an earthquake using only the Richter scale is not the complete story. Like everything in science, there are many things that make up the effect. At the time of writing, there have been 166 confirmed deaths but more and more are being bodies are being pulled from the rubble. The main issue that the re-development team is faced with now is the bed rock that the city is built on. There are layers of silt that sit on top of bedrock in the area and this can amplify any seismic waves. Many sedimentologists will tell you that silt has a high electro-static charge that on a small scale are very powerful at holding particles together, but when subjected to larger forces the bonds holding the particles together break down. This causes the particles to behave more like a liquid; hence the term liquefaction.
This is the concern with Mexico City. It is built on top of old lake bed sediments and aquifers that become unstable during tectonic events such as earthquakes. The effect of liquefaction is increased where there is presence of water (or other liquids) in the rock. Both New Zealand and Japan sit upon the ‘Pacific Ring of Fire’. It is also no coincidence that west coast USA is also overdue for a major earthquake.
Scientists have noticed that there has been a steady rise in tectonic activity over the years and so it is not surprising that the earthquakes have happened in the world’s most active tectonic fault zone. What scientists can say for sure is that there is more than likely a direct link between these recent events but what they cannot explain is what is causing the earthquakes or if there are going to be any more in the not so distant future.
The Mayan prophecy was based on the stars from god-fearing shamans, but the facts we know now are based on science we can prove. Our knowledge of how the world works is constantly expanding. So, do I believe that the world will end in 2012? I wouldn’t put my money on it.
Related articles
- 2011: Apocalypse now? (donovanhand.wordpress.com)
- Strong Earthquake Strikes North-East Japan; Tsunami Alert Sounded (techie-buzz.com)
- 6.0 magnitude earthquake strikes SW of Sumatra, Indonesia(theextinctionprotocol.wordpress.com)
- Scientists: Japan’s Tsunami Broke Off Chunks of Antarctica (newsfeed.time.com)
