Simon Mitchell | Why are there so many earthquakes in Jamaica? | In focus

Earthquakes are felt in Jamaica every year by many people. In some years there is a lot, some years there is a little. But why do earthquakes happen in Jamaica? This is related to plate tectonics. Plates are relatively full parts of the Earth’s crust, and within the plates there are relatively few earthquakes. But the plates move relative to each other, and there are three possibilities: the plates move towards each other (converging – that is, forming volcanoes, as in the Lesser Antilles); The plates move apart from each other (divergent – forming circumferential elevations); Or the panels slide sideways against each other (shift or slip faults).

A large part of the Caribbean and Central America falls on a relatively small plate that we call the Caribbean plate. Both the North American plate and the South American plate move to the west in relation to the Caribbean plate, meaning that we have sliding movements along the southern borders (for example, Trinidad and northern Venezuela) and the northern borders (Jamaica, Hispaniola and Puerto Rico) from the plate. The two American plates move at a rate of approximately 2 cm per year in relation to the Caribbean Plate, and over many years this leads to an increase in pressure in the areas of the plate margin.

But plate boundaries are never simple and often consist of multiple faults and / or crack areas. The northern boundaries of the Caribbean plate consist of several fault zones. In the west, the plate boundary is formed by the Pelican Island fault zone, which in the middle of the Cayman Basin splits into two groups of faults that extend to the west. The center of spread of the Cayman in the middle of the Cayman Basin represents a short portion of the divergent plate boundaries, and here volcanoes in depths of water five kilometers (the deepest part of the Caribbean) produce a new oceanic crust (the type of (basaltic) crust that lies beyond the oceans). The rift that runs westward along the northern edge of the Cayman Basin includes parts called the Orient Fault and the Seventh Rift Zone, which runs south of Cuba and across northern Hispaniola. Movement along these imperfections is approximately 11-12 mm per year.

The fracture that runs westward along the southern margin of the Cayman Basin has sectors called the Walton Fault Zone, the Plantin Park Fault Zone, and the Enriquio Fault Zone. It moves about 8-9 millimeters per year. The two rift regions and the center of the Cayman spread define the Gonâve microplate (Fig.1). The Enriquio Fault Zone passes through a peninsula in southwestern Haiti and was responsible for the Port-au-Prince earthquake, Haiti in 2010 (earthquake felt by Jamaica). The Walton Fault Zone and the Tongue Garden Fault Zone cannot be traced across Jamaica, as it breaks up in a series of faults across the island (and thus the boundaries between the Gonaf Plate and the Caribbean Plate are difficult to define in this region). Since there is not a single mistake, a stress field is created across the island of Jamaica, with the northeastern portion moving at a greater rate westward than the southwestern portion.

Releasing tension

When pressure builds up, it is released by earthquakes, which explains why earthquakes occur across many parts of the island. When an earthquake occurs, the pressure on this fault is released and transmitted to other faults, which in turn will produce more earthquakes. In this way, the tension is gradually released across Jamaica. If enough pressure builds up on a long fault (say 100 km) and a large portion of that fault ruptures, it results in a major earthquake. This is the cause of the major earthquakes in Jamaica: the Great Royal Harbor earthquake of 1692 and the Kingston earthquake of 1907.

2020 will always be known as the COVID-19 pandemic, but it was also a year in which Jamaica felt an earthquake of 18 people (Figure 2), which is a relatively large number. This is partly due to two earthquakes in the Orient fault zone in western Jamaica in January.

Regional earthquakes recorded by the seismic unit (Fig. 3) clearly show the earthquakes along the center of the Cayman propagation and the Orient fault zone. Note earthquakes in a wave line northeast and west northwest extending from southern Cuba directly to the south of the Cayman Islands. This trend decreases southward, west of the Cayman Islands, indicating the boundaries of the divergent plates (center of diffusion) in the middle of the Cayman Basin. In contrast, there is relatively little activity along the Walton and Enriquio Fracture regions.

Typical style

The earthquakes recorded across Jamaica (Fig.4) show a relatively typical pattern. A group of earthquakes is centered in southwest Portland at the eastern end of the island. These earthquakes are linked by a series of northwest and southeast faults that cause shortening in northwest and southeast Jamaica, which is responsible for the continuous rise of the Blue Mountains, which recent research indicates they are about 2 mm high per year. Elsewhere in Jamaica, earthquakes are linked to movements on faults across southern parishes, where active faults produce steep hills, such as the Spire Tree in western Manchester and the Santa Cruz Mountains in Saint Elizabeth. There are no earthquakes associated with the Walton and Plantain Garden faults (see Figure 1), and regionally, there appears to be little movement in the faults abutting the southern edge of the Gonâve Fine Plate in 2020.

Jamaica suffers from earthquakes due to tectonic plates and their location in relation to the northern margin of the Caribbean plate and the fine Gonaf plate. While none of us wants a major earthquake, just like in the past, it will happen in the future. We are still unable to predict earthquakes, and therefore, it is important to build with the correct building codes and to ensure that important infrastructure is placed in areas where earthquakes cause less damage. It should also be noted that without plate tectonics, there would be no Jamaica. Jamaica only emerged from the sea 10-12 million years ago due to the strength of tectonic plates.

Simon Mitchell is Professor of Sedimentary Geology, Department of Geography and Geology, and Director of Research, Seismology Unit, University of the West Indies, Mona. Send your feedback to [email protected]. January is Earthquake Awareness Month. This article is one in a series of articles highlighting earthquakes and Jamaica.

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