PORT-OF-SPAIN, Trinidad, September 30, 2006 – One is dead, three injured, several buildings structurally damaged and water and power disrupted in Trinidad and Tobago after a “very strong” earthquake yesterday.
The earthquake measured 5.8 on the Richter Scale and struck at 9:08 am said the Seismic Research Unit (SRU) at the St Augustine Campus of the University of the West Indies. However, the Richter Scale is used by scientists to measure seismic energy but for the average man on the street the Modified Mercalli Scale (MMC) is used to describe the intensity. This quake measured VI or “very strong” on the MMC which resulted on varying degrees of structural damage in buildings, depending on the strength of construction.
The Office of Disaster Preparedness and Management reported “serious structural damage” to at least seven schools as well as minor damage to a highway overpass.
In the capital, Port-of-Spain, which shook for about 15 to 20 seconds, thousands of screaming people poured out of offices and other buildings, construction workers scampered down scaffolding, and traffic came to a standstill.
At the Piarco International Airport as the buildings shook the airport authority activated its disaster management plan, shutting down operations and diverting incoming flights.
There were power outages across sections of the island which in turn affected the water distribution system. Mobile and telephone services were also disrupted which in turn knocked several Internet and web services off the air. Utilities worked overnight to restore service.
Some people contacted by Caribbean360 were badly shaken by the experience and were unsure about what would follow next and whether it was safe to return to their offices.
However, a few hours after the first quake, at 2:23 pm, as people thought it was safe to return to their offices and homes another quake struck. It was an aftershock measuring 5.3 on the Richter Scale, said the SRU. That is V or “strong” on the MMC.
It was the second aftershock that is believed to have shaken 52-year-old Anthony Sooklal from a scaffolding at Parforce Road in Gasparillo causing him to plunge to his death. Two other people were reported with minor injuries and hundreds more suffering from trauma.
The quake was also recorded by seismographs in Venezuela, St Vincent, Guyana, and Grenada.
The location of the earthquake and aftershock was different according to which agency was reporting it. The United States Geological Survey whose preliminary fix was 6.0 on the Richter Scale has now revised it to 5.5 which was the preliminary fix by the SRU. In a release the SRU said that it had instruments closer to the epicenter than the USGS and therefore they considered their reading as having a greater degree of accuracy. The SRU has since revised it to 5.8.
All seismology agencies get an initial reading from automated instruments and it is this figure that they issue immediately as a preliminary estimate. It then takes up to 12 hours for the record to be examined and calculations done by a seismologist to arrive at an accurate measurement. Both agencies collaborate and share data which is used to make a final fix.
The depth of the quake was also reported differently by the two agencies. The USGS reported a depth of 89.7 km (55.7 miles) while the SRU reported it as 40.0 km (24.8 miles). However given that the quake was just four to five kilometers (2 – 3 miles) offshore it’s impact would have been strongly felt.
The SRU said that the strength of the quake was not large enough to cause a tsunami.
The focal depth of the aftershock was reported by SRU as 32 km (19 miles). The USGS did not report the aftershock.