More aftershocks possible

Three holes reportedly caused by the Tuesday evening temblor may point to an earthquake fault line in Windsor Park.

University of Alberta’s Professor Brian Jones, who has conducted in-depth geological studies of the Cayman Islands, said yesterday that positioning of the holes in the same zone could mean they represent a fault on the Tectonic plate below Cayman.

‘If they are in a straight line, presumably what they represent is a fracture in the rock.’

The three holes roughly line up in a north-east south-westerly direction from Oakdale Close through a yard on Oak Mill Street to Norbrook Street.

Oakdale Close and Norbrook are parallel streets feeding off Oak Mill Street.

Mr. Jones said fault lines in Cayman usually run east to west, north-east south-west, and north-west south-east.

‘We know that there were lines of weakness that have those three orientations,’ he said.

Speaking to the Compass from Alberta, Mr. Jones at first speculated that the holes might have been caused by a weakness in the rock below, a cave or a hollow area. But he then asked whether they were in line, and upon confirmation said they probably represented a fracture in the plate

He said there is nothing to fear as Cayman has a long history of small earthquakes, which usually go unnoticed. He explained that sensing of most small earthquakes depends on where the person is located or in what building.

This professor and chair of the CR Stelck Chair in Petroleum Geology at the University said Tuesday evening’s earthquake was unusually large for Grand Cayman, but it let off much of the under ocean pressure, thereby lessening the likelihood of another in a long time. Of course the smaller ones are preferred.

‘Not that you want to have any, but if you have to have an earthquake, you prefer a series of small ones, because that will relieve the pressure.’

Some persons on Grand Cayman reported feeling aftershocks following the earthquake, and Mr. Jones said there could more measuring 2, 3 or 4 in magnitude in days to come.

Dr. Margaret Wiggins-Granderson of the University of the West Indies Mona Camp Earthquake Unit in Jamaica was further assuring: ‘It was not an earthquake that would have occurred on land’.

Dr. Wiggins-Granderson said information gathered by her unit put the earthquake as occurring 19.1 degrees north. ‘It’s probably associated with the Cayman Spreading Centre,’ she said.

That Spreading Centre is the point at which the Caribbean Tectonic Plate and the North American Tectonic Plate meet under the sea. These plates are locked together for a period and when lava, formed by the heat below, rises it breaks between them causing an Earthquake. This spreads the plate apart while adding another section to that submarine floor. It is similar to the San Andreas Spreading Centre in California.

Information coming from Professor Jones and Dr. Wiggins-Granderson corroborated.

There are two earthquake-causing areas close to the Cayman Islands. The Spreading Centre exists south-east of Grand Cayman. The other is Transform Fault, called the Orient Transform Fault, which is north of Grand Cayman and runs through Cuba to Haiti.

At Transform Faults the plates mostly slide past each other laterally, and are said to cause earthquakes of a magnitude no higher that 8.5.

An Earthquake of the magnitude that hit Grand Cayman Tuesday 20 miles off are said to have the potential to be in the category that is destructive up to 62.1 miles away. Tremors at a magnitude of 8 or above can cause serious damage more than 100 miles away.

Dr. Wiggins-Granderson agreed that the description of the holes found in Windsor Park fit those that can be caused by an earthquake, given the Grand Cayman topography, in which ironshore – or Microkarst – is covered by marl for construction.

‘The shaking can cause any kind of sedimentary material to displace. Just like shaking a bowl of sand.’

She said it could also be caused by liquefaction, where the shaking caused a rising of water from the island’s low water table, enabling it to dissolve topsoil.

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