TT still trembling

THERE have been more than 90 aftershocks following Thursday’s moderate 5.4 earthquake, the strongest occurring at 11.46 pm on Thursday. There have also been 14 earthquakes so far for the year,  including Thursday’s, most of which were felt in various parts of the country. The Seismic Research Unit (SRU) yesterday said the close to midnight aftershock, the magnitude of which was 5.1, would have awakened a number of people. There have however been no reports of structural damage or injuries. Seismologist Joan Latchman told Newsday the number of earthquakes recorded for the year is normal, explaining that the number of earthquakes varies, as it depended on the stresses which accumulated in the earth’s crust. She said the energy is released when the crust cannot hold it anymore.

Latchman said in the 1970s there was approximately one earthquake every month, then it decreased and now it seems to have picked up again. She said this country was on a “seismically active area.” According to the SRU’s website, the countries of the Eastern Caribbean are highly susceptible to earthquakes. The most striking example occurred in Trinidad in 1766. Although the population was small and the economy minuscule, the effects of the earthquake were devastating enough to cause the inhabitants to petition the King of Spain to allow settlers from other non-Spanish Caribbean islands. Prior to this event, there was another major earthquake in Jamaica (NW Caribbean) in 1692, which resulted in the death of over 2,000 persons and destroyed 90 percent of the then capital, Port Royal. According the site, such major earthquakes are likely to cause even more damage if they were to occur now or in the future, because of growing populations and large-scale poorly planned or unauthorised construction.

In 1954, Trinidad recorded an earthquake with a magnitude of 6.2 which resulted in one death. There was another in 1968, also of the same magnitude, which caused severe structural damage, including at the Hilton Hotel. Within recent times, the most destructive local earthquake was recorded in Tobago on April 23, 1997. It measured 5.9 with the epicentre located 15 kms south of Scarborough. There was significant damage and two persons were injured. It followed a 5.6 earthquake on April 2 of the same year. The website showed that before Thursday’s earthquake, the strongest and most widely felt earthquake was recorded on January 15 at 6.56 am. It was a 4.7 magnitude, and fortunately was not strong enough to cause damage except to extremely vulnerable buildings. It was widely felt in Trinidad, Tobago and the northern part of Grenada.

The others recorded for the year and their magnitudes were November 4, 4.4; October 11, 3.7; September 18, 4.0; two on August 28 at 3.5 and 4; July 23, 4.3; July 20, 3.7; June 10, 4; May 30, 3.8; May 14, 4.3 and April 26, 4.2. The SRU’s website also noted that the Eastern Caribbean was an example of an island arc system formed at a convergent plate boundary (more specifically, at a subduction zone, where two tectonic plates meet and the denser plate is forced beneath the lighter plate). Most of the earthquakes occurring in the Eastern Caribbean are either tectonic or volcanic in origin. Tectonic earthquakes are generated when plates move as accumulated energy is released. Volcanic earthquakes are generated by the movement of magma within the lithosphere. More than 75 percent of the world’s earthquakes occur at convergent plate boundaries.