Earthquake in Southern Caribbean

[Steve Wooler]

I've just received an email from a reader. While typing his message to me, he received two calls from Trinidad. Apparently there's just been an earthquake of around 6.3 scale. Buildings were evacuated and the tremour felt up the chain of islands and as far south as Guyana.

This is the first and only report I've heard. Can anyone on Tobago confirm what was felt and any damage.

[Steve Wooler]

Sorry - I didn't mean to scare anyone about to leave for Tobago (in response to the emails I've already received).

The U.S.Geological Survey reports that a "strong earthquake with a preliminary magnitude of 6.0" rattled Trinidad and northern Venezuela earlier today. No damage or injuries were immediately reported. The 9:08am (local time) tremor swayed buildings in the Trinidadian capital, Port-of-Spain, and some schools were evacuated. The earthquake was centred 26 miles north-west of Port-of-Spain in the Caribbean Sea, according to the USGS.

It was also felt in Grenada, 100 miles north of Trinidad, and would clearly have been felt in Tobago. I have received no reports of damage or injury on Tobago at this time.

[Patrick Dankou]

Hi Steve,
we felt that earthquake here in Crown Point for sure, it was gentle enough not to make us run out of the building, felt more like a gentle swinging of Mother earth's hips ( "slow wine").
Consequently a 2 1/2 hours islandwide blackout gave us time for a lime.
The epicentre was closer to Trinidad than Tobago and a couple of buildings were damaged. I did not here about any persons being injured , over here we only had a few cracks in the wall.

[Steve Wooler]

felt more like a gentle swinging of Mother earth's hips

Are you still fantasising about big women, Patrick?

Let's be honest, it doesn't take much to make the local power company give up the ghost - the foreman dropping his fag is probably all it takes.

Seriously, though, thanks for the update. Yes, I believe the epicentre was out in the Caribbean Sea on the other side of Trinidad. The cracks in the wall were probably caused when Tanja chucked you out of the office for getting in their way.

[Patrick Dankou]

Hi Steve,
I am starting to enjoy this gentle rocking, we just had the next earthquake, interesting to watch my staff's reactions, half of them ran outside the other half including me did not move. T& Tec did not switch off electricity this time.

[Roger D.]

Here's the latest from Today's Trinidad Guardian Online:
Quite a scare but no serious damage or injuries. Paul Any comments ?

BY KAYODE JAMES

T&T was spared tragedy once again as yet another explosion of nature failed to inflict major structural damage or injury across either island.

However, the mid-morning 5.8 earthquake caused widespread disruptions in public utilities, and dozens of reports of minor damage to buildings emerged before a weaker 5.1 aftershock hit in the early afternoon.

According to reports from the Office of Disaster Preparedness and Management (ODPM) and the UWI Seismic Research Unit, the quake hit at 9.08 am, and emanated from an epicentre less than 5km off the north coast of Trinidad.

The earthquake also sent thousands of Venezuelans scampering out into the streets, and was felt as far as Grenada.

The T&T Electricity Commission (T&TEC) reported interruptions in its supply to most of the north-east of the island, much of the East-West Corridor, and Tobago, as six of its generating units tripped. Pt Lisas was particularly affected by the power outages.

The power disruptions stalled operations at more than a dozen WASA water treatment plants, including those in Caroni, Aripo, Valsayn, Maraval and Fyzabad.

As late as yesterday evening, T&TEC maintenance personnel were working on the affected equipment.

Cable television was similarly affected by the electrical interruptions, but Columbus spokesman Rhea Yaw Ching said the company would be working throughout the day to stabilise any outages in the service.

The Fire Service was only called to tend to a handful of trouble scenes in the aftermath of the quake, including a minor gas leak at the International School in Westmoorings, and a stuck elevator at the Agricultural Development Bank on Henry Street.

Seismic unit: 5.8 on Richter scale

Early reports from United States Geological Survey cited the quake’s magnitude as 6.0 on the Richter scale, and the figure was widely reported throughout the day.

However, a release from the UWI Seismic Research Unit indicated a preliminary magnitude of 5.5.

“Our instruments are closer to the epicentre and we also have a better distribution of instruments near the source of the earthquake so we are confident that our magnitude of 5.5 is accurate,” stated the release.

The unit later amended its figure to 5.8.

The unit also noted the possibility of similar or weaker aftershocks, but emphasised that it had not issued warnings that a larger earthquake would occur later that day.

“We hope that the earthquake will serve as a strong reminder (to the general public) that both (of our) islands lie in an area of high earthquake activity in the Caribbean,” said unit education officer Stacy Edwards.

“It’s not a surprise, sudden, or an unusual event,” she said.

Neither was it, said Edwards, the strongest earthquake to hit the island in recent decades.

As of yesterday evening, the unit was still finalising its findings of the quake, and is expected to release a final result and comparisons today.

Edwards also dismissed fears that the quakes could cause a tsunami, explaining that they were both too weak.

She reiterated the need for disaster preparedness, and urged the public to head to the unit’s Web site at http://www.uwiseismic.com for earthquake survival tips.

[David Watkins]

I've always said Tobago rocks man,cool

[Steve Wooler]

I think that deserves a special award, David.

[Paul Tallet]

According to the USGS Earthquakes Hazard website the earthquake measurement has not been adjusted from 6.0 on the richter scale.

There has been just one after shock (so far) measuring 5.5 which came about 5 hours after the first quake.

Both quakes were within 5 miles of each other of the west coast of Trinidad and between 75 and 80 south west of Scarborough.

No Tsunami although there may have been a small ripple off the west coast of Trinidad.

I hope this helps all Earthquakes nerds.

Regards

[Roger D.]

Hey Paul

What else can you tell us about this earthquake ? Did it happen along the fault that runs up under the island chain - I think it's called the Caribbean Plate, which is bumping up against the North American plate ? Or did it occur along some other fault line?
Those plates in question are not sliding under one another, thereby creating what is known as a subduction zone, but rather they are climbing upwards, hence the creation of the Caribbean isles ? Right?

Roger

[Paul Tallet]

Hi Roger D

I wish I could draw you a picture.

It is not the North American Plate which is sliding under the Caribbean Plate to the east of the Windward Islands and rubbing against it to the north. The North American Plate causes most seismicity around Puerto Rico and the Virgin Islands where 'strike/slip' events occur as the 2 plates move in the opposite directions of each other.

The most likely Plate that is causing Tobago's seismicity is the South American Plate which is moving north under the Caribbean Plate.

So you have 3 main components ... the North American moving west, the Caribbean Plate moving east and the South American Plate moving north.

The area where the Caribbean Plate and the South American Plate meet is easily seen by the very straight looking coastline that you see on the map from the north coast of Trinidad and all the way across most of the north coast of Venezuela.

Having identified the main components ... we need to look at the complications and the local geography that creates the seismicity for Tobago.

Where these 3 plates converge, they create weaknesses as they crumple against each other and many faults occur at some distance from the area of convergence.

For example ... Monserrat has a very active Volcano that is oozing effluence from under the Caribbean Plate ... this is a weak spot (and, by the way, Monserrat is gearing up for a major collapse very soon).

Another weak spot is 'Kick em Jenny', just to the north of Grenada, another (underwater) Volcano. I will return to this one later.

The Caribbean Plate is rising over the other plates and as the Plate is pushed up over the South and North American Plates there is weakening that causes parts of the Plate to collapse.

Another complication is turning ... the Caribbean plate is being undermined from the south and the east and the pressures (or speed of movement) from these directions are not the same.

This has created Trinidad's own area of seismicity just to the north west of the island where there is a pressure centre that takes the strain of the Caribbean Plate turning and buckling as it moves over the other Plates ... this is associated with 'Kick em Jenny' who is likely to become more active and eventually another Island as movement progresses.

These pressure areas are where the Plate is moving in all kinds of directions.

Another similar area of pressure exists to the south east of Tobago and this caused the 5.8 earthquake of 1997 that was more widely felt as it occured only a few miles below ground level.

So ... the recent quakes can be attributed to a little pressure field just off the north west of Trinidad ... although it was a 6 ... it was 40 miles or so below the sea and therefore the quake is less likely to have been felt as much as the shallow 1997 Tobago quake.

I hope this helps.

Regards

[Roger D.]

Hey Paul;

As always, an excellent explaination - Seems as though there is more to come from Kick 'em Jenny and Monserrat
I read somewhere that Trinidad suffered a major earthquake in 1776 and of course we all know the Story of what happend to Port Royal in Jamaica, when most of it sank beneath the ocean. So I'm assuming that the Caribbean could suffer a major event(s) in the future.

One more question - Is the Volcanic activity on Monserrat relieving pressure that's building up on the plates thereby averting/postponing a major event?

[Paul Tallet]

Hi Roger

Monserrat is just a weak spot in the plate. It is made up of several volcanoes ... the old volcanoes represent the areas where the lava found the easiest path to the surface in the past and this is evidence of the plates moving.

As the Plate moves it may shut off one exit for the lava and then open another and then you get a new Volcano. Sometimes the exit route is shut off altogether for many years.

As you say, it does relieve pressure locally and can be linked to Earthquakes ... but then an Earthquake could set it off, just as there has been an increase in Volcano activity in Indonesia following the 9.1 Earthquake of Boxing Day 2004.

Monserrat is very unlikely to affect Tobago although a large dome collapse could have an effect on the weather depending on the wind direction.

Regards