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A collapsed home following the April 1997 earthquake in Tobago.

Twenty-three years ago, on April 22, 1997, Trinidad and Tobago was rocked by one of its strongest earthquakes in recorded history.

At 5:31 am, the magnitude (Mw) 6.7 earthquake struck south of Tobago, shaking Trinidad, Tobago, and the Windward Islands.

Over 500 earthquakes occurred as a result of this seismic sequence, beginning with a foreshock early on April 2, 1997, registering at a magnitude (Mt) 5.6 north of Tobago.

While 200 events occurred during April 1997, it took the remainder of the year for aftershocks to return to background seismic levels.

Based on data recorded by both the United States Geological Survey and the University of the West Indies Seismic Research Centre, Tobago recorded “very strong” shaking, which had a moderate damage potential, registering a VII on the Modified Mercalli Intensity scale.

On the morning of April 22, six homes and several buildings collapsed.

Overall more than thirty buildings and homes were damaged across Tobago. Some of the severely damaged buildings included Scarborough’s PSTC bus terminal, the Scarborough Library, and the local post office.

Fifteen people were left homeless, with two persons injured.

Damage across Tobago was estimated in the millions, with figures ranging from $18-25 million.

Why was this

Based on research, the ground shaking from both quakes caused a significant increase in groundwater discharge, which in some cases threatened building foundations.

There was an increase in the mortality of trees in the area following the magnitude 6.7 quake.

This has been linked to the change in groundwater.

No damages were reported in Trinidad.

Likelihood of

another similar quake occurring in T&T?

According to Dr Ilias Papadopoulos, the Engineering Seismologist at the University of the West Indies Seismic Research Centre: “There is a high probability for similar events anywhere in the Trinidad & Tobago territory, as we are situated in the junction of the South American plate and the Caribbean plate.”

He continued: “Aside from the on-land faulting system (Arima Fault at the north, Central Range Fault Zone and Los Bajos at the south), which can give shallow events which may not be big in magnitude but due to vicinity to urban environment pose a high risk.

“We also have the event on the subduction, which may be further away but of higher magnitude and at greater depths.

“That means the energy will travel at greater lengths and affect the taller buildings.”

This means, according to Dr Papadopoulos: “The risk is high, although the return periods are low. But we need to be prepared at any time.”

Trinidad and Tobago, and the surrounding region are in a very seismically active area.

Across the Eastern Caribbean, over 2,200 earthquakes are recorded annually.

Since 1990, the University of the West Indies Seismic Research Centre records an annual average of 280 earthquakes in the Trinidad and Tobago region.

Of these 280 quakes, 50 of these seismic events are, on average, above magnitude 3.5.