Caribbean earthquakes
Martinique, 2007
On Wednesday, 29 November 2007, at 15:00:19 Atlantic Standard Time, the earth under the eastern Caribbean shook.
I was talking to Mandella, a friend from home. It was our first semester at the University of the West Indies, Cave Hill, Barbados. She was studying law and I was studying comp sci and maths (or maybe it was comp sci and psych; I don't remember when exactly I switched from psych to maths). As I remember it, I was on my way back to my room on hall after finishing a class in the Faculty of Pure and Applied Sciences, and I met her on the Guild Lawn, a rectangle of green that was a social if not geographic centre of the campus. We must've been talking about how we were finding Barbados and university so far, or maybe about whichever student society's week it was, or maybe our plans for the Barbados independence day holiday, which was the following day, when the earth shook.
"Do you feel that?", she asked. I had.
The Caribbean is seismically active. The islands of the Eastern Caribbean, including St Vincent where I grew up and Barbados where I was during this quake, were all formed as a result of the North American tectonic plate and South American plate subducting between the Caribbean plate. In the south eastern Caribbean, there are often harmless tremors – magnitudes 4 and below – which, in my memory, always happened at night, and which my father always claimed to feel and which I never did. (In his defence, he'd generally claim there was an earthquake before the news confirmed it.) This was not a tremor.
"Yeah, I think so", I said. We looked around. Others around us seemed to have noticed something as well, but we still weren't sure.
And then there was a jolt, and some people at a picnic bench near us got up.
"What do we do?", she asked.
I thought quickly. "You're supposed to get outside if you can. But we're already outside. Move away from buildings." We were already outside and away from buildings. "Maybe move further away from them?" So we did, and moved towards the centre of the Lawn. (Another friend later told me that she remembered that the campus is called Cave Hill because it's on a hollow hill and worried that the earthquake would dump us all into that cave, but thankfully that didn't happen, and neither Mandella nor I remembered that for it to worry us.)
The rest of my memory is hazy. At some point the fire alarm went off in my Halls of Residence; I found out later that one of my friends had pulled it as he evacuated it. At another point I called my father back in St Vincent, 100 miles away, to see if he could also feel it; he said yes he could and he was leaving the building he was in. Maybe I also tried calling my mother, but I don't remember. I do remember trying to call someone – maybe my father again, maybe my mother – and the call not going through.
It was a magnitude 7.4 quake, centred a few miles to the northwest of Martinique (about 140 miles from Barbados) and unusually deep at 96 miles below the surface. News reports say the earth shook for over a minute. Its depth seems to have reduced its damage – it only directly killed one person (in Martinique), caused other injuries, and caused some structural damage – but it might have extended its range. It was felt from Puerto Rico in the Greater Antilles to its northwest, throughout the islands of the eastern Caribbean and as far away as Georgetown, Guyana over 570 miles away to its southeast, in South America. And in my recollection – though I wasn't able to find sources of this while writing this post – it initially confused the US Geological Survey's triangulation algorithms such that they issued (and then withdrew) an alert that it was in California.
Some older, bigger ones
As well as being seismically active, the Caribbean occasionally gets very big earthquakes. In school, we learned of the Port Royal earthquake, which destroyed the city of Port Royal, Jamaica in 1692. It was a shallow quake, estimated at about 7.5 magnitude, that killed about 5,000 people and sank most of the city. That Wikipedia article has some terrifying details about it.
Before the earthquake the town consisted of 6,500 inhabitants living in about 2,000 buildings, many constructed of brick and with more than one storey, and all built on loose sand. During the shaking, the sand liquefied and the buildings, along with their occupants, appeared to flow into the sea.[9] More than twenty ships moored in the harbour were capsized. One ship, the frigate HMS Swann, was carried over the rooftops by the tsunami.[10] During the main shock, the sand was said to have formed waves. Fissures repeatedly opened and closed, crushing many people. After the shaking stopped the sand again solidified, trapping many victims.
I later learned as well of the strongest earthquake known to have ever occurred in the Caribbean. That was the 1843 Guadeloupe earthquake, which is estimated to have been about magnitude 8.5. (That's 10 times more shaking and 32 times more energy than the 7.5 I felt and the 7.5 that destroyed Port Royal.) It was felt as far away as Guyana hundreds of miles to the south and New York City to the north, almost 2,000 miles away. It triggered an eruption of Guadeloupe's volcano, and together the earthquake and eruption killed a few thousand people, including one third of the population of Guadeloupe at the time.
The next big one
Everything I've written up to this point I've known for a while before writing this article. But one new thing just came to my attention. To set up context for this, here's a link to an article that I first read years ago.
Kathryn Schulz
It's primarily about an expected big earthquake in the Pacific Northwest of the USA along the Cascadia subduction zone. If you're at all interested in earthquakes you should read it. I mention it here because it says this:
Every fault line has an upper limit to its potency, determined by its length and width, and by how far it can slip. For the San Andreas, one of the most extensively studied and best understood fault lines in the world, that upper limit is roughly an 8.2...
It then goes on to talk about the Cascadia subduction zone in detail. (Its upper limit is in the 9s.) When I first read it, one thing that article left me wondering is: how do I find the upper limit for the fault lines in the Caribbean? And I searched on and off for a bit, finding the reports of the massive Guadeloupe quake and other big ones in the Leeward Islands, but I never found a scientific estimate for the limit. But while reading around a bit for this article, I came across one in the Wikipedia article on the 1839 Martinique earthquake (another big historic earthquake):
At the present moment, the Lesser Antilles subduction zone...has the potential to generate an earthquake of Mw 8.95 to 9.58.
🌎🤯
- Major earthquake shakes Caribbean – BBC Caribbean
- M 7.4 - 18 km WNW of Basse-Pointe, Martinique – US Geological Survey
- Anniversary of Martinique Earthquake – UWI Seismic
- Quantifying potential earthquake and tsunami hazard in the Lesser Antilles subduction zone of the Caribbean region – Geophysics Journal International
