April 15th Earth Tremor – A Messenger of an Impending Disaster?
A minor Earth tremor occurred on the 15th April 2009, which was felt at several areas of Central, Eastern and Uva provinces in Sri Lanka. (1) The Communty Tsunami Early-warning Centre (CTEC) in Peraliya received a number of inquiries from Hambantota, Matara and Galle Districts as well. (2)
It is interesting to note that on the evening of April 14th, 1615, (just a day prior to April 15th) a strong earthquake struck Sri Lanka unleashing widespread damage and casualties in western sections of the island, most notably in Colombo. It is thought that 200 houses collapsed. A part of the western city wall of the Colombo Fort collapsed destroyed. A bastion also collapsed and destroyed a neighboring house killing 4 persons. A stone bridge was also destroyed in the earthquake. Deep fissures opened in the earth. According to a historical text (reproduced below), flames and sulphur are said to have been emitted from these fissures. It is thought that 2000 persons were killed in and around Colombo as a result of this earthquake. If the description of the damage described in this text is to be believed, this earthquake would most likely have a maximum intensity (MMI) of VIII or perhaps even IX. (3)
Knowledge of this earthquake is derived from a 4 page pamphlet published in Lisbon in 1616, the contents of which were brought to light by late Fr. S.G. Pereira, SJ a pioneer historian, proficient in several languages, Prof. in Missionology Georgian University Rome, etc. (3)
The 15th April, 2009 earth tremor was not reported by the USGS earthquake notification service. (4) There was no Tsunami threat due to this event. This incident has been recorded by the Pallekele Seismic station, which is part of the Global Seismic network, a Geological Survey and mines bureau person stated, as a response to a a telephone inquiry. The magnitude of this quake is to be around Magnitude 4.
Sri Lanka is located in a considerably inactive zone , free of large earth quakes. Sri Lanka lies on a thick and old crustal block with no neo-tectonic activity. However, over the last few decades, our country felt minor earth tremors, one or two every year (5).
The source of these earth tremors could be three fold:
1. The active zone near the Zundra trench, which was responsible for the Indian ocean Tsunami – No significant earth quake activity was recorded around the 15th Of April 2009 event.
2. There is a seismically active zone from about three degrees south of Sri Lanka and extends four degrees down to the southern hemisphere. The dynamics of this region are under study. – Any activity in this region needs to be studied to determine the origin of the 15th November 2009 earth tremor.
3. Localized seismic activity –These are not generally picked up by regional or global networks. High seismic activity has been reported in Hambegamuwa area in past instances, which is a part of localized activity.
This earth tremor is an eye opener to the Disaster Risk Management professionals especially to the experts of Geology and Seismology at the Geological Survey and Mines Bureau of Sri Lanka, to determine the Earth Quake Risk of Sri Lanka. It is high time that Disaster Risk Management practices are incorporated into the routine development activities of the country. It is better to be prepared, as we have not, as a nation, forgotten the tragedy of Tsunami which would have been easily prevented.
References:
- 1. http://www.colombopage.com/archive_09/April1545738RA.html
- 2. www.communitytsunamiwarning.com
- 3. http://www.lankalibrary.com/geo/portu/earthquake.htm
- 4. http://earthquake.usgs.gov/eqcenter/recenteqsww/
- 5. Nalin de Silva, Earthquake hazards, Project on Determination of the outer edge of the Continental margin of Sri lanka under “UNCLOS”, DEOCOM Project.
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