Glance at any map of the Caribbean and one cannot but notice the distinctive arc of the small islands elegantly sweeping the blue sea. Yet this clear curve is due to the constant geologic process of plate tectonics, with the relentless movement of the Earth’s viscous mantle against South America steadily shoving the crescent chain east over the last 50 million years.
Covering the globe’s entire surface, the seven major chunks of solid stone have essentially carved continents and created majestic mountain chains, enabling complex chemistry, valuable minerals and the endless recycling of key compounds like carbon dioxide while crucially stabilising the climate. Scientists believe it is no coincidence, this, the largest rocky planet in the solar system, remains the only known with prevalent, vibrant life hence the habitability term – the “Goldilocks” zone meaning it is just right, neither too hot nor too cold to support liquid water, too immense nor too small for plate tectonics, and the perfect distance from our central star, the sun.
With the usual demands of daily life, it is easy to forget that deep under our feet the restless interior of the planet is in motion especially at plate boundaries such as subduction zones where a region of the Earth’s crust sinks below another causing volcanic eruptions and earthquakes.
During this month we were once again reminded that many of us live within or close to a seismically active area. Last weekend, unusually, I slept through the slight night shake of a magnitude 4.7 tremor registered out in the Gulf of Paria, about 50 miles from Port of Spain, Trinidad, perhaps growing dangerously accustomed to the frequent rattles this side of the world.
However on the afternoon of December 6 last year, as I noticed the concrete walls of the house suddenly vibrate loudly, and heard the low rumbling, staring momentarily transfixed as our giant packed bookcases swayed and ceiling mouldings snapped, I darted down the shaking wooden staircase to the outdoors in time to check on our terrified dogs and spy them racing to the empty part of the compound. Near west of Tobago, that magnitude 6.1 quake was thankfully about 17 miles in depth and outside of densely populated cities so damage was minimal and no one died but numerous aftershocks have ensued. TT has at least six seismogenic zones including the risky Central Range fault previously thought to be inactive.
Running through the middle of the country from one end at Manzanilla in the east to Claxton Bay in the central west and extending offshore, the line studied by the United States Geological Survey is capable of unleashing monsters similar to the catastrophic 7.0-magnitude quake that devastated Port-au-Prince, Haiti, in January 2010. A major part of the boundary between the Caribbean and South American tectonic slabs, the former is moving at roughly 0.79 inches (20 millimeters) per year with scientists estimating enough stress has accumulated for the fault to rupture and lead to a comparable disaster following the last strike between 550 to 2700 years ago.
This week the seas in the Eastern Caribbean continued to show seismic unease following a cluster which intensified early on the morning of April 17, 2017 with a 5.8 magnitude quake off Antigua-Barbuda’s coast, the second in this range since 2011, according to the University of the West Indies (UWI) Seismic Research Centre (SRC).
Referring to the 120 felt reports from as far west as St. Kitts and south to Guadeloupe, the SRC disclosed the series has been followed by more than 500 events in the same general area, two of which were in the magnitude range of 5.1-5.5, warning that jolts should continue for some time. Just Tuesday, the islands were jarred by another 4.5M.
“Although this most recent earthquake sequence may not necessarily signal a larger earthquake, the public should be reminded that the Leeward Islands region is an area of high earthquake activity for the Caribbean. Moderate to significant sized earthquakes may occur in this region at any time which may impact islands in this area (St. Kitts-Nevis, Antigua-Barbuda, Montserrat etc). For this reason measures must always be in place at an individual, community and national level to protect against the impact of earthquakes,” the Centre stressed.
We had not long moved to Antigua-Barbuda, our former home, when the Eastern Caribbean was hit in November 2007 by a 7.3M quake in the nearby Martinique Passage, the strongest I have ever endured, that was felt across the region from Puerto Rico to Guyana, Suriname and Cayenne. Listening to the advice of our veteran Dominican helper, I stood with her calm but wide-eyed under a creaking doorway, as the heavy wooden roof and beams rattled, thick masonry walls cracked and the ground groaned, vowing to take my chances and roll outside under open skies, in the future. It is the fifth earthquake in the magnitude 7 range to occur there since 1727. In October 1974, a 7.5M quake struck the islands damaging among other landmarks its Deep Water Harbour and famous Cathedral of St John the Divine. Historian Dr Reginald Murphy would tell the Antigua Observer newspaper, “I remember the refrigerator and the stove danced across the kitchen swapping places.”
For years, really worried experts, such as SRC’s seismologist Dr Joan Latchman have warned about the need for proper building codes and to be always prepared given the increasing likelihood of an overdue great earthquake in certain vulnerable areas with traditionally high levels of seismic activity, noting that because the damage from recent shakes was minimal, this has led to a widespread sense of complacency.
Historically, the Eastern Caribbean including Trinidad and Tobago can generate large-magnitude earthquakes every century or so given the February 8, 1843 Lesser Antilles mega-event which came after a 6.9M shock in 1839. The 1843 convulsion rocked half the Atlantic including Demerara and Berbice in British Guiana, and New York City and Washington in the U.S, rivalling the Sumatra subduction zone 9.1-9.3M temblor of Boxing Day 2004 that generated deadly tsunamis and killed over 200 000, and another that manifested in the same district a year later measuring 8.7M.
The Guiana Times of February 8th 1843 would state hours later: “At ten minutes past eleven o’clock, this forenoon, occurred as severe an earthquake as some of the oldest inhabitants have any recollection of. Every moveable in every house was in motion, and every house shook violently; some old chimney stacks fell; people were seized with giddiness and nausea, similar to the feelings incidental to incipient sea sickness. As nearly as confusion would allow persons to judge the shock, or rather the two shocks lasted, altogether, forty seconds.” The last earthquake, of January 11 1839, “was severe, but not alarming in comparison of the convulsion of today. Yet, on the fatal morning, fell the town of St. Pierre in Martinique, killing, or miserably mangling in its ruins, a thousand of its inhabitants. Who can tell that multitudes in the neighbouring Colonies are not at this moment bewailing, in desolated habitations, amid dead or expiring relatives, the havoc which a few seconds have made?”
In its February 9 edition, the Guiana Herald wrote: “some of the tall chimnies of the boiling houses may have suffered. But, as the shock was accompanied with more of an undulating motion, than the sharp violent jar which generally marks these fearful phenomena of nature, the damage is not likely to be great in this colony… Our soil – our wooden tenements – the flatness of the land, whereby no buildings are erected on declivities, are all circumstances combining to lessen the desolating effects of earthquakes in Guiana.”
Geologists reported at a 2012 meeting of the American Geophysical Union that the 1843 and 2005 Indonesia events were similar, with the Antillean quake estimated at around a huge 8.5M. Sleuths Francois Beauducel and Nathalie Feuillet of the Paris Institute of Earth Physics revealed French maps proved that many palm-covered islets in the bay at Pointe-à-Pitre, the main city of Guadeloupe, disappeared between 1820 and 1869. The islets dropped below sea level given the flexing and warping of the earth’s crust with the heavy rupture far down in the subduction zone.
Portions of Antigua subsided up to 10 feet, wharves along Pointe-à-Pitre sunk, cliffs collapsed, and historic accounts describe five-foot-high mud fountains, Feuillet told OurAmazingPlanet. Earlier documented quakes close to Antigua in 1690 and 1766 are believed to have been equal to or greater than 8.0M with the later disaster causing considerable destruction to masonry structures even in Trinidad where the then capital San Jose (St Joseph) was flattened.
The University of Southern California study which confirmed the reason for the lovely islands’ characteristic loop, found that the minor Caribbean plate is being pushed by the three-times thicker 1.7 billion year-old stiff Guiana Shield section of the South American plate called a “cratonic keel.” Cratons are ancient, far-buried, stable continental pieces famed for their valuable deposits such as diamonds.
Upending previous hypotheses of the seismic activity beneath the Caribbean Sea and looking at the unique tectonic interactions that are causing the smaller plate to tear away from the mainland, the researchers said all the pushing and pulling 1 800 feet below the surface have established a complex system of strike-slip faults. In the south eastern end, the interaction of the subducted plate beneath the Antilles islands with the tougher continental keel has led to the El Pilar-San Sebastian Fault.
In the frequent words of Dr Latchman, as energy mounts at those key points and tectonic tension climbs, “sooner rather than later” and “when – not if” the next big one will strike as predicted. Still, we all hope and pray for something that continues the islands lucky song, along the lines of the 1954 blues classic, best performed by Bill Halley and his Comets.
ID reads the Guiana Herald’s riveting account of the 1843 mega-quake when Demerara’s “houses and churches were violently rocked to and fro” and in a certain Water Street wine-store “the bottles played such fantastic tricks, as their contents were apt to produce on mortals.”
