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[COLOMBO] New computer modelling studies of possible earthquakes in the Indian Ocean, and the tsunamis they could trigger, suggest that the December 2004 tsunami that devastated parts of Sri Lanka’s coastline was about the worst the country could face.

Scientists from the University of Peradeniya modelled worst-case scenarios of earthquakes in each of the quake-prone zones in the Indian Ocean and the tsunamis that could result in each case. The study, led by Janaka Wijetunga, senior lecturer in the university’s department of civil engineering, was published on 7 March in Coastal Engineering.

The study, which provided estimates of arrival times and heights of sea waves reaching Sri Lanka following temblors in the quake-prone zones, identified the December 2004 event triggered by a mega temblor in the northern Sumatra-Andaman zone as the most destructive of nine possible scenarios.

"Estimating likely tsunami heights for an earthquake that has just occurred takes considerable time, unless you have an extensive database of a large number of pre-computed tsunami scenarios, which we do not have for Sri Lanka," Wijetunge told SciDev.Net.

Having such data on file is a critical part of tsunami hazard assessment for Sri Lanka, avoiding false alarms and preparing evacuation plans,  he said.

Subduction zones are portions of the earth's tectonic plates that dive into the earth's interior marked by deep oceanic trenches that extend landward.

Calculations by Wijetunga’s team suggested that even the largest credible earthquake scenarios from each of the other seismic zones in the Indian Ocean would result in tsunami wave heights around Sri Lanka that are only about 20—30 per cent of those created by the 2004 tsunami from the northern Sumatra-Andaman seismic zone.

The other seismic zones include southern Sumatra, Arakan and Markan.

Wijetunga explained that preparedness helps reduce the impact of such disasters.  "In 2004, deaths and destruction were immense because we (Sri Lanka) as a country were not prepared at all. When a 2004-like tsunami happens again, we must do better." 

Sri Lanka’s Disaster Management Centre (DMC) in Colombo oversees issue of tsunami warnings and initiated tsunami drills and a mix of communication techniques such as radio warnings, loud speakers and hand sirens, Pradeep Kodipilly, DMC’s assistant director said.

Wijetunge said that lack of high-resolution ground data was being compensated for with detailed coastal land surveys.

Link to abstract in Coastal Engineering: