[Photo: The remains of a village in Aceh after it was hit by the Tsunami.]

While being hit by a tsunami does not rate as one of the greatest fears of Singaporeans, the repercussions of being caught unawares will no doubt be devastating.

It was with this in mind that, after the destructive Indian Ocean tsunami struck in 2004, the National Environment Agency (NEA) with the National University of Singapore and the Nanyang Technological University embarked on a study to evaluate the probability and impact of a tsunami on Singapore.

The finding is not unexpected as Singapore is sheltered by the surrounding land masses.

Moreover, the shallow waters in the Malacca Straits and South China Sea - unlike the deep waters in the Indian Ocean and the Pacific Ocean - will significantly slow down any tsunami propagation and dissipate its energy.

However, the study considered two possible occurrences that might generate a tsunami that will affect Singapore - these include an undersea landslide near Singapore, and great earthquakes of the order 9.0 and above.

The study found that the likelihood of major undersea landslides near Singapore is very low.

In addition, numerical simulations of a tsunami triggered by undersea landslides show that the impact on Singapore is expected to be minimal.

Seismic zones

The study also identified two seismic zones, namely the Sunda Arc at the Andaman Sea (north and west of Sumatra) and the Manila Trench at the South China Sea (northern Philippines), that have the potential of producing large earthquakes.

Simulations showed that tsunami triggered by earthquakes along these two seismic zones are expected to take more than ten hours to arrive at the Singapore coast.

By the time the tsunami waves arrive in Singapore, the wave energy will have largely been dissipated and hence, the likely impact on Singapore will be minimal.

In addition, great earthquakes of magnitude 9.0 and above have been infrequent events. The Indian Ocean tsunami is the only earthquake of such magnitude in recorded history.

There has also been no known record of a tsunami affecting Singapore. During the 2004 Indian Ocean tsunami, measurements at the coastal waters west of Singapore did not record any significant rise in the sea level.

Possible impact

However, some of Singapore's beach areas are still potentially vulnerable to tsunami inundation in the scenario of a magnitude 9.0 earthquake at the Manila Trench.

These include beaches at West Coast Park, Labrador Park, Sentosa and the Southern Islands, East Coast Park and Pasir Ris Park.

The projected rise in sea level in the unprotected beach areas is estimated to be between 0.4m and 0.7m, and the inundation level is estimated to be less than 50m from the shore.

Tsunami response plan

While the potential of a tsunami impact on Singapore is low, those at unprotected beach areas can still be exposed to some risk in the event of a tsunami.

NEA has developed a tsunami response plan with the cooperation of the relevant agencies, namely the Singapore Police Force, Maritime Port Authority (MPA), Jurong Town Corporation (JTC), Sentosa Development Corporation (SDC).

Due to our sheltered geographical location, there is an expected long lead time before the first wave arrives in Singapore.

The Tsunami Response Plan is able to leverage on this lead time to provide early alerts to the public, and activate evacuation at the vulnerable public beach areas.

In terms of specific roles, NEA will continue to monitor the regional seismic activities for possible occurrence of tsunamis.

In the event that a tsunami is assessed to affect Singapore, NEA will issue early alerts and warnings to the respective agencies and provide the public with information on the tsunami.

The police and SDC will ensure that the public at the vulnerable public beach areas are alerted and facilitate the evacuation from these areas.

The agency also advises the public to stay away from these unprotected beach areas and heed the advisory to evacuate should a tsunami warning be issued.