Shock and awe

The tremors felt by Grand Cayman residents over the weekend and yesterday are aftershocks to Tuesday’s earthquake.

Dr. Margaret Wiggins-Grandison of the University of the West Indies Earthquake Unit at the Mona Campus in Jamaica, who has been monitoring the tremors on Grand Cayman, said that there was unlikely to be a repeat of the big earthquake last week, which was 6.8 in magnitude.

‘Based on the sequence of events, it does appear that the main shock is gone,’ she said.

‘It is to be expected. It’s a normal part of the earthquake cycle… We located two aftershocks since Friday, one on Sunday and another today,’ she told the Caymanian Compass yesterday.

Both aftershocks were of a 4.6 magnitude, occurring at 5:29 am Sunday and 1:18 pm yesterday.

Dr. Wiggins-Grandison, who visited Grand Cayman over the weekend, confirmed her findings indicate that Tuesday’s earthquake was not on the island, but south where the Caribbean and North American Tectonic plates meet.

At this point there is a ridge known as the Cayman Rise, and just north of that is the Oriente Fracture.

The plates meet at the Oriente Fracture, which runs through southern Cuba and the Dominican Republic and Haiti.

The earthquake could have been triggered by movement at either the Cayman Rise or the Oriente Fracture, but Dr. Wiggins-Grandison believes it was at the Oriente Fracture.

Another indication of the distance of the earthquake was the slow vibrations Grand Cayman residents felt. ‘Once people say that the shake was not too rapid, that means it was some distance away.’

She said that owing to the distance there was some attenuation, or lessening of intensity as the waves of vibrations got to Grand Cayman.

A comforting factor she found is the practice of constructing on rock, which makes buildings safer during tremors than other structures that are placed on other material.

While here, the UWI professor also delivered a temporary seismograph to the Mosquito Research and Control Unit, marking a re-establishment of the link between the Cayman Islands and that centre.

Handing over of the equipment is a stop-gap measure, enabling the MRCU to record earthquakes. ‘We can say we have an event, but we can’t say the magnitude and location,’ the MRCU’s Dr. Alan Wheeler said yesterday as he explained the limited ability of seismograph.

He said that plans are under way for collaboration with the UWI Earthquake Unit to purchase in a few months three custom-built seismographs, which are needed for proper recording, locating, and measuring of earthquakes.

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