The two earthquakes felt in the Cayman Islands earlier this month, along with the unusually high tides over the past few weeks, have focused attention on the issues of sea levels and landmass elevation – and the correlation between those two geographical factors.

Both quakes were detected south of Grand Cayman on Wednesday, 3 September. The first, registering 5.1 on the Richter scale, was felt at 5:01a.m. It was centered 23 miles (37 kilometers) south of George Town, the capital. The aftershock was felt that evening at 6:34p.m. It measured 5.2 and was located 28 miles (45 kilometers) south of George Town.

Addressing subsequent speculation, the Department of Lands and Survey (L&S) has stated that there were no horizontal or vertical changes in position recorded for these Islands after the two events. It should be noted that although overall seismic monitoring operations are the responsibility of Hazard Management Cayman Islands (HMCI), it partners with L&S and other agencies.

L&S Director Rupert Vasquez noted that his department’s Land Survey section is responsible for “accurate and efficient land surveying in the Cayman Islands”, adding that the National Control Network is a critical component of local infrastructure services.

In the case of the recent quakes, data from the Cayman Islands’ Continuously Operating Reference Stations (see description in Sidebar story below) was compared with data from Florida, Mexico and Jamaica.

The results showed no notable local differences detected before or after the earthquakes. In both cases, the differences measured in our geographic position varied by only a few inches (few centimeters), which is within the limit of achievable measurement accuracy, and is considered “normal”.

On the issue of rising tides, L&S is reassessing mean sea level data. Several tide gauges have already been installed throughout Grand Cayman and the Sister Islands. “This is a high-priority, long-term project,” added Mr. Vasquez.

The tide gauges measure the extent of the recent high tides and compare them to data from previous years. Data collected recently indicates that, whilst sea levels at high tide have indeed been higher in recent days, there has been no discernable long-term upward or downward movement of the sea level of Grand Cayman or the Sister Islands.

Mr. Vasquez reassures the public that L&S staff members will continue to conduct detailed investigations and intensive monitoring, especially following these occurrences.

The Cayman Islands’ ‘National Control Network’

The Cayman Islands’ intricate Lands and Survey (L&S) monitoring network remains largely out of public view. It consists of hundreds of traditional ground-based monuments, as well as four continuously-operating GPS /GNSS base stations, otherwise known as CORS (Continuously Operating Reference Stations), that form our National Control Network (NCN).

These survey controls are positioned relative to each other to within-centimeter accuracy, with the exact coordinates available to all licensed land-surveyors, utility surveyors, Government surveyors, and anyone else involved in positioning or mapping in the Cayman Islands.

Strategically positioned throughout these Islands, the CORS receive and process signals from American GPS satellites and Russian GLONASS satellites. The receivers operate 24/7 and are at the core of local surveying and mapping infrastructure. They are the foundation of the National Geodetic Network (NGN).

The Cayman Islands’ four CORS are part of a wider Caribbean network of similar GNSS receivers. All data is collected in real-time, monitored and stored locally, then shared online with the international community through the United States National Geodetic Survey (NGS).

Lands and Survey monitors the positions of all local monuments and the CORS system to ensure that their published positions remain correct. Any significant changes are noted and investigated as part of maintaining a comprehensive and efficient network

The Department notes that tectonic movement is a natural phenomenon, ongoing throughout the globe. For instance, the CORS positioned on the roof of the Government Administration Building indicates that the Cayman Islands is moving steadily but slightly towards the west, at a velocity of less than half of an inch annually. This is natural for the Cayman Islands.

If otherwise sudden and unexpected tectonic plate movements were to occur, it would be detected by one, or all, of these CORS. This change would be immediately shared with the American National Geodetic Survey, who would then correlate this data to all CORS in the local network as well as with the many CORS stations on different tectonic plates and countries throughout our entire hemisphere.

For details on local earthquake monitoring, and to see the live graphs, charts and maps, visit: http://earthquaketrack.com/r/cayman-islands/recent

Photo credits: Photo by Information Officer Lennon Christian

Lands and Survey staff check the CORS equipment located on the roof of the Government Administration Building.