Is Sabah really tsunami free?

After the disastrous 2004 Boxing Day Asian tsunami that wiped out 300,000 in a blink of an eye, is Sabah at risk of any similar disaster in the future?

As Sabah is lapped by three different seas, French geophysicist and seismologist Jean-Paul Boeldieu thinks the potential risk may apply differently to the South China Sea, the Sulu Sea and the Celebes Sea.

What’s his projection? “I hope you understand why you live in a ‘kind of sanctuary’ regarding seismic and water waves,” he said in a written synopsis to his scheduled talk tonight (Thursday) at the Kota Kinabalu City Bird Sanctuary at 7.30pm, organised by the Malaysian Nature Society under President Kadir Omar. He cited the South China Sea.

But it may pay the East Coast folks to opt for serious long-term tsunami water through seismic recording. Read on.

“Don’t be scare. Be happy,” he cautioned against alarmism.

“The South China Sea is totally protected from any tsunami waves,” said Jean-Paul, Head of the Seismological Laboratory and correspondent of the international tsunami watch net, who was also a member of the 18th French Polar expedition to Antarctica from 1967 to 1969.

“It is completely closed by high grounds, there are no subduction areas, no faults in relation with subduction areas beyond its limits,” he pointed out.

“In other words, it is the most stable part of the Eurasian Plate,” he added. A very remote possibility for any tsunami in the South China Sea would rather have its origin from space, such as a big asteroid collision, than from underground. This risk is very minimal,” he explained.

In the case of the Sulu Sea, there is a “higher probability of big waves.”

“The record of historic earthquakes in the “Sulu Sea” shows the epicentres were in fact below the Bohol Sea. That sea is rather shallow water, far above the epicentres. The Bohol Sea is partly closed so waves, if any, could only escape towards the Sulu Sea as interference. Therefore, risk seems to be very limited,” he said.

The Celebes Sea, on the other hand, is somewhat different and “maybe affected by a local tsunami,” he said.

“Here, the water column is important. The earthquakes count is high, some being quite energetic,” he noted.

“The fault system is very complex, close to three plates,” he added. Hence, he opined: “Around the Sea, there are serious risk of tsunami water waves, as it happened, in a short time after any big intensity earthquake.” So, in Sabah, only Lahad Datu, the Tawau bays maybe concerned. “The reefs and low coasts of Sulawesi Island are at very serious risk,” he reckoned.

Jean-Paul said earthquakes represent successive relaxation of tensions along the plate boundaries.

“The tsunamis are transmission of movements to the water column above the fault emergence at the seabed level and their propagation,” he said.

Hence, a high magnitude quake and a thick water column above such quakes are conditions for tsunami occurrence. The tsunami water waves are propagated at the ocean surface at the speed of a jet plane or few hundred kilometres per hour.

On the other hand, the speed of the seismic waves within the earth is much higher, in excess of 40,000km per hour, he pointed out.

“This is the reason why the tsunami watch by seismic recording is helpful,” he recommended.

“The people who experience the earthquake should deduct that a tsunami wave may arise very soon,” he suggested.

“It will affect them only if they are not protected by land, shallow water, mangrove on the way of the waves. The purpose of tsunami watch is to warn people close to coasts that are far away from the epicentre as they will have time to go up to the hills if they get the information,” Jean-Paul said.

He said when the earthquake epicentres are deep, that is, more than 100km in the bowel of the earth, there is likely to be no fault on the seabed. But when the epicentres are shallow and far from the coastline and into the oceans, the generated waves can propagate across the oceans.

“The waves are guided by the deep channels. They maybe reflected by cliffs. They explode on shallow waters and high grounds. They are destructed by mangroves,” he said.

Thus underscoring the importance of maintaining and maybe restoring mangrove forests all around Sabah, particularly Sabah’s East Coast where future tsunamis are probably more likely.

In his coming talk, Jean-Paul will examine the mechanisms that cause tsunami waves and the conditions that must prevail for their occurrence.

Resource: Daily Express, 6th April 2006

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