Earthquake awareness a must:

Unpredictable, unpreventable - Prof. Kapila Dahanayake

by Manjula Fernando

With several high magnitude earthquakes recorded around the world within the past several months and an alarming 6.0 point earthquake close to our tiny island last Monday, the fear and uncertainty of devastating earthquakes in Sri Lanka, have again started to haunt us.

This fear is not unfounded given the fact that Sri Lanka recorded several mild tremors and some high magnitude earthquakes in the Indian Ocean close to our territory lately.

However, Peradeniya University’s senior Professor of Geology, Kapila Dahanayake refutes the common notion that Sri Lanka’s threat level is increasing due to a new plate boundary formation about 1000 km off Sri Lanka.

Prof. Dahanayake who has published several scientific presentations in international science journals and who had predicted ‘something big” a week before the devastating Boxing Day tsunami in 2004, says an earthquake threat had always been there for Sri Lanka.

“It should be noted that in 1614 an earthquake had killed 2000 people near the Colombo port. During the last 15 years or so, several earthquakes have been reported in the ocean around Sri Lanka. Earthquakes cannot be predicted accurately. The Current thinking is that earthquakes can occur anywhere at anytime without prior warning.”

He refuted the opinion that there may be an increased threat to Sri Lanka due to a suggested new plate formation near Sri Lanka.

The Indo-Australian Plate is a major tectonic plate that includes the Australian continent and extends northwest to include the Indian subcontinent and also Sri Lanka.

Recent studies have suggested that the Indo-Australian Plate may be in the process of breaking up into two separate plates primarily due to stresses induced by the collision of the Indo-Australian Plate with Eurasia along the Himalayas. The two subplates are generally referred to as the Indian Plate and the Australian Plate.

Explaining the occurrence of an earthquake, Prof. Dahanayake said the earth is a very dynamic planet. Its outermost shell (lithosphere) is made up of a patchwork of a dozen or so large, cool, rigid slabs (also called tectonic plates) that are moving horizontally relative to one another at speeds varying from less than 1 to 10cm per year.

The plates slide and collide with each other in very slow motion on top of the asthenosphere- a 200km thick layer of the mantle, thereby providing a mechanism for the tectonic plates to glide on top. Where the plates grind against each other, stress builds up and is relieved periodically through earthquakes that occur when the rocks break along faults. Near a plate boundary, molten material (magma) rises to the surface and is erupted along fissures or through vents from volcanoes.

The geologic processes associated with the plate movements are concentrated in the narrow boundary zones between tectonic plates so that most our planet’s earthquakes and volcanoes are found along or near plate boundaries.

The World’s earthquakes are not scattered at random over the earth’s surface. Most are concentrated along edges of certain continents or along island chains e.g.Japan.

Nevertheless some active volcanic areas and large earthquakes can also occur in the interior of plates (intra plate earthquakes).

Some of the recent earthquakes around Sri Lanka have recorded values of about 6 on the Richter scale and their epicentres located in areas South West and South East of Sri Lanka.

“Since the country has recorded several tremors-minor earthquakes of about magnitude 4 or less from different parts of the island, it is prudent to educate people about earthquakes, regularly so that casualties can be minimized,” Prof. Dahanayake said.

He is of the opinion that Sri Laka should introduce a proper building code, not because the country could experience more earthquakes in time to come but because of the booming construction industry in the country.

“Earthquakes cannot be predicted nor prevented. Only awareness programs and appropriate construction practices can reduce casualties.”

In 1988 there were 99 strong earthquakes worldwide above magnitude 6.0 on the Richter scale, many of them causing extensive damage if the epicenter was situated in a populated area.

He says rather than causing panic among the people by feeding them with wrong sensational information it was wise to create awareness of this natural phenomena and take precautions.

“Most of the casualties in earthquakes are due to ignorance of people about earthquakes,”

A 7.9 point earthquake in eastern Sichuan China on 5 May 2008 killed 87,587 people and the 7.0 point earthquake in Haiti on 12 January this year claimed a devastating 222,570 lives (Total Boxing-Day tsunami toll was 227,898). This was in contrast to a bigger 8.3 earthquake in Hokkaido Japan in September 2003 where there were no reported casualties.

Japan which is historically related to earthquakes has been constructing earthquake proof buildings from the old days and awareness begins at elementary school.