WHY WAS T&T NOT DESTROYED YESTERDAY... A SEISMOLOGIST EXPLAINS
By Richard Charan http://www.trinidadexpress.com/
Why did Trinidad and Tobago's 6.1 magnitude earthquake leave only negligible damage, but that same day, a 6.5 magnitude earthquake devastate Indonesia, killing more than 100 and destroying buildings. It has to do with location, magnitude and geological factors, says head of UWI's Seismic Research Centre, seismologist Dr Joan Latchman, who explained why this country was not ruined yesterday.
Latchman said that had an earthquake with the same intensity occurred under one of our built-up areas at a shallow depth, the damage would have been far different.
“It's the magnitude and depth in relation to population centres” she said, using the example of the catastrophic 7.0 magnitude earthquake that struck Haiti in 2010, killing an estimated 250,000 people and taking down 30,000 buildings.
With Haiti, said Dr Latchman, the quality of the construction played a big part in the level of destruction, as did the distance between the epi-centre and the heavily population area affected – Port-au-Prince.
She said seismologists have also noted that soil conditions can amplify the effects of an earthquake, as in the case of magnitude 7.0 Mexico City tremor in 1985 that killed thousands. In that event, the energy from the quake was amplified through the areas of reclaimed land, with areas further away from the epi centre suffering more damage and deaths.
WHY NO TSUNAMI?
As to why there was no threat of a tsunami despite the earthquake happening under the seabed off Tobago on Tuesday, Dr Latchman said there would have to be a rupture causing a vertical (up and down) movement of the earth's crust under the sea, displacing a large column of water above it.
This is what happened in 2004 in the Indian Ocean, causing tsunamis in 14 countries, killing an estimated 280,000 people.
Dr latchman said that a 6.1 magnitude quake would not be expected to cause such a fault, and she does not believe a rupture occurred. For thousands of citizens on Tuesday evening, a fake Tsunami alert terrified people along the low lying east coast of Trinidad.
EXPECT AFTERSHOCKS
Dr Latchman said that since Tuesday's tremor, UWI had recorded more than 100 aftershocks, the largest of which occurred just before and after midnight Tuesday. She said that the country could expected many more in the coming days, weeks and months, since a 6.1 magnitude quake is expected to general a high level of aftershock activity.
She noted what happened after the two quakes in 1997, centered in Tobago, which caused $18 million in building damage. On that occasion, aftershocks continued into November of that year.
CAN WE EXPECT A BIGGER QUAKE?
Dr Latchman said studies have shown that a quake of the magnitude experienced yesterday meant that the country could expect several quakes measuring between 5 and 5.9 on the Richter Scale, which can occur at any time. So be prepared.