How is a Tsunami Formed?

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The various earthquakes in different parts of the world call for greater awareness on natural hazards caused by mother earth. The recent ones in Sabah reminds us that Malaysia is also not free from earthquakes and tsunamis.

The memory of Acheh-Andaman earthquake and its tsunami on 26 Dec 2004 which has cost 230,000 lives and affected many more millions lives and reached the shores of Malaysia may still be fresh on our mind. History repeated itself in September 2009 where an earthquake in South West Pacific produced an earthquake and tsunami that killed nearly 200 people. And in March 2011 a big earthquake and subsequent tsunami hit Japan.

These disasters remind us of a need to understand the basics of Earthquake Science and to find ways to make prediction before it strikes and to deal with it when it finally hits us.

In particular, the Acheh-Andaman earthquake catastrophe changed the perspective of people regarding earthquake dangers in oceans. Its magnitude with the damage and destruction caused are the biggest in recent times.

What is a tsunami? It is defined as a big wave or a series of big waves. Tsunamis are different from the normal sea waves that are generated by the wind. Tsunami is caused by big disturbance in the ocean or other body of water. For example, during an earthquake under water, an enormous amount of energy is released when a fault slips. The crust can move up and down, therefore forcing a great column of water to follow it. This can creates a total imbalance in water body and forms a tsunami. Tsunami can also be caused by a meteorite or a land slide.

The normal wind generated waves have ‘small period’ ( time between two successive waves ) of 5 to 20 seconds and wavelengths of 100 to 200 meters. In a tsunami, the period increases significantly to the range of 10 minutes to 2 hours, and wavelengths can be greater than 500 km! Due to this large wavelength, a tsunami loses very little energy as it moves forward. As the leading edge of the fast moving wave comes into the shallow water near the shore, the resistance causes it to slow down. The water behind, however, continues to push forward.  As the fast moving waves push into the slowing wave front, its edge gets higher and steeper. Eventually, it can become a moving vertical wall of water, may be as high as a multi-storey building, and swallows everything that stands in its way! Its height depends on the geometry of the shore and the characteristics of the tsunami.

As such, it is advisable not to rush to the beach to watch a tsunami when it occurs. Many people had lost their lives during the Aceh-Andaman tsunami as a result of this. Unlike earthquake on land, tsunamis have one advantage: they give us time to evacuate because the waves take some time to travel to reach the coast, thus provide an opportunity to save lives. However, in all the above cases, there was no tsunami warning in place because people tend to forget about disasters of the past!

Some time ago, government announced Malaysian plan to set up an Earthquake Monitoring Centre. This is timely and research can be done in collaboration with regional fraternities in earth science such as the Earth Observatory of Singapore which was established in 2009. It has successfully conducted research in most of the South East Asia.

According to its Research Fellow Dr Afroz Ahmad Shah, it is extremely important for us to map all the active faults in Malaysia, just as it has been done in other earthquake –prone areas of the world, so that we can understand the potential of earthquake and subsequent tsunami risk in the country and surrounding areas in the future.

There is also a need for the general public to thoroughly understand earthquakes and tsunamis to enable necessary precautions be taken at the community levels. Currently, there is a warning system on tsunamis installed in the pacific region. It is essential for such warning to be able to reach out to the public extensively and promptly when the need arises.

Malaysia has been well-loved by mother nature with our abundance of natural resources and generally free from natural disasters so far. We, however, need to take heed of the recent warnings to protect ourselves against any impending calamity and learn how best to co-exist with mother nature.

About Earth Observatory of Singapore (www.earthobservatory.sg)

The Earth Observatory of Singapore (EBOS) is an autonomous institute of Nanyang Technological University. It conducts fundamental research on earthquakes, volcanic eruptions, tsunamis and climate change in and around Southeast Asia for safer and more sustainable societies. It runs a Ph.D Programme and works with world-renowned scientists on topics such as earthquakes, climate change, coastal processes, tsunami, environmental changes, volcanology, geodesy, tectonics, ocean chemistry and paleoclimate.

It also operates undergraduate programme majoring in Environmental Earth Systems Science and minor in Environmental Sustainability.

Scholarships are available for both the Ph.D and undergraduate programmes. For more information, refer to its Asian School of Environment website: www.ase.ntu.edu.sg. For undergraduate scholarships, please refer to: admissions.ntu.edu.sg/UndergraduateAdmissions/Pages/FreshmenSingaporeSPR.aspx

 

Written by:
Ms Wee Hui Bieh, AFMSA, September 2016

Original author:
Dr Afroz Ahmad Shah, Research Fellow, Earth Observatory of Singapore, Nanyang Technological University.

Full article available at www.scientificmalaysian.com magazine, Issue No. 3

This post is also available in: zh-hans简体中文 (Chinese (Simplified))

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