Being vigilant will help:

Earth tremors - no cause for alarm, says GSMB

By Ranil Wijayapala

As a country considered free from earthquakes in its recorded history, Sri Lankans hardly bothered about facing disasters caused by earthquakes. But the 2004 December 26 Tsunami which brought us disastrous effects of a huge earthquake near Indonesia, compelled us to be ever vigilant on earthquakes happening around the globe.

The constant vigilance of Sri Lankans for Tsunami warnings has made them more sensitive towards any tremor after the tragedy the country faced on Boxing Day in 2004. Therefore, the earth tremors reported in the Ampara district since November 2012, has made the people more vigilant about the situation.

Though there are no major damages to properties due to these low level tremors people are more concerned about the situation as they have felt nearly five such tremors within a day since November 2012. The Geological Survey and Mines Bureau (GSMB) is also concerned about the situation as they receive seismic data from the seismic station in Pallekele about these tremors.

Commenting on the situation, Chairman of the GSMB, Dr. N.P. Wijayananda said that the GSMB is continuing its efforts to trace the real cause behind these tremors after deploying their teams in the Ampara district.

According to Dr. Wijayananda during the year 2012, 21 earth tremors have been recorded in different parts of the country in the seismic stations. They have been reported in Kothmale, Maduru Oya national Park, Allanmulla in Moneragala and near Veheragala reservoir. Nearly 15 tremors have been recorded in Ampara area since November 24.

The Seismic Data and Tsunami Alert Centre (SDTAC) of the GSMB is receiving all these data through the seismic station at Pallekele, Kandy and 10 other global stations.

"We had reported more tremors during 2012. It doesn't mean that these tremors are more frequent. The reason for the number of incidents reported to be high is that people are more aware about these incidents. Almost all the people have mobile phones and they report to us or they report to the media when there is such an event. There is a better flow of information", he said.

"We have very advanced and sophisticated equipment at our seismic stations and it picks up even the very low level tremors. Some tremors recorded here are even without the knowledge of the people there", he added.

"People are saying a lot of things about earth tremors but we go only by our recordings. It is difficult to rely solely on the reports from the people. If there is any earth tremor that is recorded at our centre", Dr. Wijayananda said, pointing to a computer which constantly indicate the earth tremors and earthquakes around the world.

"What I can say is that none of the tremors reported in the country are damaging. They are only vibrations", he said.Explaining further, Dr. Wijayananda said if such tremors have to be damaging it has to have the effect to cause a glass on a table fall, or cause glass windows to crack. But non of these tremors had such effects.

"Some people say that some walls of the houses were cracked due to these tremors. This can happen because of the tremor as well as due to the weakness of a structure or the foundation. If the tremor is powerful to crack a wall it should first shatter the glass on windows.

At least the tiles on the roof had to fall. If someone is complaining their walls are cracked that may not be due to the tremor but due to the weakness of foundation. So far people have not reported of such thing", he said.

According to Dr. Wijayananda there are two possibilities for these tremors. One is natural reasons and the other, man made.

"We earlier had experience about man made tremors. One such incident was reported in Colombo when an underwater blast was carried out to deepen the Colombo harbour. That was known to us and people did not panic when they were told about the reason for the tremor", he said.

The Ports Authority had informed the GSMB about these underwater blasts and it had given them the required parameters to carry out the underwater blasts. The operations at the Colombo harbour had gone on for more than two months and something went wrong with the particular blast causing tremors in Colombo, he said.

"A situation similar to Ampara was also reported in Kirinda area in Hambantota district in 2011 also, and the GSMB observed the situation. When we carried out the investigations we found that the blasting program carried out in the harbour tallied with the tremors reported in Hambantota area. We were not aware of the situation and one company had undertaken to carry out those blasts from the Ports Authority. People got panicked. But later we found that it was the reason for these tremors", he added.

One unusual things reported by the people in Ampara is that they hear a vibration along with the tremor.

" If it is a natural tremor there will be no unusual sound. According to our observations most of these tremors were reported during week days and day time.

Therefore there is a good possibility that these tremors are relating to man made incidents", he said.

When the tremors were reported in Ampara, the first reaction of the GSMB was to check with the construction work of the Oluvil harbour but they said no such activity was taking place there.

"Again we double checked with the Government Agent and asked whether there are any deep piling in Ampara. The answer to that also was not positive. If there is such activity there may be tremors but there cannot be a sound", he said.

The next reaction of the GSMB was to establish mobile seismic units there. But with the rainy season the teams could not travel to the areas where these tremors were reported. Therefore they had to withdraw from the area in the first week of December.

"What we tried through these mobile units was to check whether they can detect the tremors that cannot be detected by the Pallekele station. But the tremors detected by these mobile units were also recorded at the Pallekele station", he said.

The other doubt the GSMB had was whether these tremors were caused by blasts at the metal quarries, since there were a huge demand for construction material."Therefore we carried out an artificial blast at a metal quarry. But it also did not create such a tremor", he said."When the water levels of the reservoirs increased also there is a possibility of experiencing such tremors. This may happen in Victoria reservoir as the water column is very high. In Ampara we have the Senanayaka Samudra.

There is no such water column in Senanayaka Samudra as in Victoria, and there was no such water level in Senanayaka Samudra in November to cause such tremor.

However, these tremors have been reported around Senanayaka Samudra and the exact locations of the tremors are scattered around the jungle terrain around Senanayaka Samudra.

"During the rainy season our teams could not reach these places to carry out investigations.

Therefore with the two tremors reported in the area on January 25, we have decided to carry out a long term investigation by deploying two teams in the area. They are ready to start their investigations on Wednesday", he said.

The Government Agent in Ampara and the Sri Lanka Army will also extend their assistance to carry out these investigations. "What we request the public or any other company is that if they are engaged in activities in these areas that may cause such tremors please let us know about it and if the activity is legal we can help them. The bureau has the capacity to do that. Then people will not panic. People believe us if they are informed of the real situation", Dr. Wijayananda said.