Earthquakes Can Occur Anywhere In the World… Prof. Kapila Dissanayake
By Niranjala Ariyawansha
Sri Lankans preparing for the Sinhala/ Tamil New Year were in for a shock on the 11th of April when they felt tremors of the earthquake that took place near Indonesia’s Sumatra Islands. It was 8.7 on the Richter scale.
An aftershock measuring 8.2 on the Richter scale followed two hours later with several more thereafter. Sri Lankans all over the island felt these tremors ranging from 2 to 5 minutes. A tsunami warning was issued and emergency measures were promptly put in place to handle such a disaster if it became a reality. By 6.30 p.m. the tsunami alert was removed.
Why was there no tsunami despite an earthquake measuring 8.7 on the Richter scale? What really is an earthquake? With the experience of the disastrous tsunami that took place in 2004 all Sri Lankans become apprehensive when an earthquake occurs anywhere in the region. It still is fresh in the minds of Sri Lankans, more like a bad dream. Most think that each earthquake would result in a tsunami.
We interviewed the acclaimed Professor Kapila Dahanayake, now retired from the University of Peradeniya to find out more on earthquakes and tsunamis.
Q: What is an earthquake?
A: It is a very active phenomenon under the earth. There are two kinds of plates that come into consideration.
a) Oceanic plates
b) Continental plates
The Oceanic plates are more dense and are beneath the sea. The Continental plates are on the surface of the earth. These plates have a definite tendency to move. Some plates move towards each other, some away from each other and others up and down against each other.
There are 12 such plates. Some say there are 13 in existence. However the geological fraternity has not accepted the 13th plate’s existence.
Earthquakes happen where these plates meet. When similar plates meet mountains form. The Himalayas is an example. When two plates move apart eathquakes occur, like what happens in the Atlantic ocean. When plates move apart the resultant earthquakes are not that devastating.
However as described earlier the more dangerous earthquakes happen when two plates move underneath one another or when they move in opposite directions. Therefore the serious earthquakes happen when a Continental plate moves over an Oceanic plate. Places close to Sumatra, California, and Japan are prone to and are situated in zones which are most vulnerable.
Every earthquake does not result in a tsunami. As I said earlier with some earthquakes mountains could be formed. Earthquakes due to Continental plate movement would result in destruction of buildings etc. Let us think in this fashion. If we draw a verticle line from one point deep into the earth the end point would be the epicentre of an earthquake. The fissure of geo chemicals deep within the earth results in earthquakes.
When a tsunami occurs the focus of such is a few kilometres deep in the earth. A tsunami occurs only when two bodies of geo chemicals collide in a verticle manner. In such a verticle collision the water is churned and displaced.
In otherwords awhen a collision takes place deep within the sea, say 25 to 30 kilometres underneath in a verticle fashion a tsunami can happen.
Another necessary feature is that such a quake should measure more than 6 or 6.5 on the Richter scale. In the 2004 tsunami all these took place. However on the 11th of April when an earthquake did happen near Sumatra the collision was not vertical hence no tsunami resulted.
Q: Is Sri Lanka in danger? There was a theory that the geo positioning of Sri Lanka may have changed after the battering it received in the 2004 tsunami hence a danger may persist.
A: We cannot say that Sri Lanka is definitely in danger now. Even scientists have not been able to say with any certainity what goes on deep down in the earth. That is why one cannot predict an earthquake. An earthquake can happen anywhere on earth. No one can say with any degree of certainity that earthquakes will not happen in a particular area.
In 1614 , 2000 died in Colombo Many do not know that there was an earthquake in 1614 in Sri Lanka. That was when the Portuguese were in occupation. Its impact was mainly seen in Colombo.
It is reported that around 2000 died in Colombo. If one takes the lifespan of earth (4.6 billion years) according to geological sciences and compares that with the life span of human beings, the human life cycle would be like a second.
Whilst a human’s life gets lesser with each passing moment the earth’s life expands. Therefore with such an ancient and yet growing earth no one can predict what would happen in the future.
However the frequency of earthquakes have increased as time passes. Even geological scientists cannot predict where and when an earthquake could happen.
Does that mean one is resigned to live with a lurking danger forever? Man has always attempted to control nature. In doing so man has had to suffer the consequences of nature hitting back.
We also spoke to R. M. S. Bandara, Chief of the National Building Research and Service Authority stated that buildings will have to be built to withstand earthquakes. “Sri Lankans have thus far taken note of earthslips, floods, hurricanes but its time to include earthquakes. We have started studies into this too. It is a wide field. This cannot be concluded overnight. We are working at it as quickly as possible,” he said.