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Shonel Dwyer | Jamaica’s seismic dilemma

A looming earthquake threat

Published:Sunday | December 3, 2023 | 12:06 AM
Shonel Dwyer
Shonel Dwyer
Volcanoes in the Lesser Antilles and America arcs (red triangles) and Earthquakes (USGS database) magnitude 5–8 (circles with increasing diameter) for the last 20 years
Volcanoes in the Lesser Antilles and America arcs (red triangles) and Earthquakes (USGS database) magnitude 5–8 (circles with increasing diameter) for the last 20 years
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An undercurrent of seismic upheaval has been set in motion. Recent months have witnessed a subtle but discernible surge in seismic activities, an uptick, sending tremors of concern throughout the country. Are we on the brink of a major earthquake?

In my previous article, published on October 15, I touched on the vulnerability to seismicity, which now seem like prescient warnings, an eerie premonition of an imminent catastrophe. In fact, Jamaica has had two earthquakes since. Notwithstanding the veneration of an ability I do not have (regrettably), the opportunity, and obligation no less, presents for a deeper and more sophisticated look at the fault systems as well the trending energy releases in space (location) and time.

The geological dynamics now relay a narrative of shifting and escalating tectonic stress and sporadic energy release/ruptures within Jamaica.

Picture this: Faults, usually resistant to movement due to friction, transform into vulnerabilities under the relentless pressure of tectonic stress. My understanding of the tectonic and paleo-environmental history of the Caribbean Plate is speculative of an origin and movement from the Pacific Ocean into its present day position. Quite a tale but one that has tremendous evidentiary support.

Presently, Jamaica and Hispaniola are precariously and partially located on the Gonâve Microplate which is wedged (essentially stuck), against the continental North American Plate. The shear of the North American Plate sliding to the west and our inability to get past it, has produced mounting tectonic stress in our respective geologic provinces. The island of Puerto Rico, by some mechanism, was able to get past the North American plate and move on with the Caribbean Plate proper.

The remarkable stress from the constrained plate motion is transferred along the previously indicated and prominent Enriquillo-Plantain Garden fault. This left-lateral fault strike-slip fault extends for approximately 1,000km from Hispaniola, trending westward into and through Jamaica. As a result, the stress from our lodged resident plate must be transferred, and, in fact, has a direct conduit-type structure for energy release in our island nation, known as the Yallahs-Plantain Garden Fault.

SEISMIC EVENTS

The seismic events recorded in eastern Jamaica (2023) have occurred in the Blue Mountains Block, geologically described as the Blue Mountain (positive) flower structure, and also within the Yallahs-Plantain Garden Zone. Focal mechanism monitoring and studies (tracking the epicentres), have shown the progressive step and migration of energy (seismic, that is) from Haiti into Jamaica over the past 15 years.

The Fault Systems of the Blue Mountain Block have terminated the seismic giant/conduit, the Plantain Garden Fault, and have transferred the energy unto the Blue Mountain Fault (BMF) and into the structural Blue Mountain Block/Flower Structure. The BMF is a reactivated oblique/thrust fault (perpendicular to the strike-slip fault) which supports compressional forces and causes uplift of the mountain territory under any such fault rupture. These are the Magnitude five earthquakes we’ve had over the past two months, near Hope Bay in Portland.

On the other hand, the rupturing of the Plantain Garden Fault zone presents a major concern. On April 15, an epicenter in the region of this vulnerability occurred in St. Thomas. The greater hazard exists here because the Plantain Garden fault has in fact been propagated to the South Coast Fault Zone (SCFZ). The SCFZ is one other extensive and laterally continuous E-W strike-slip fault (much like the Plantain Garden Fault) which has been mapped throughout our southern parishes (from the eastern point into St. Elizabeth parish). From St. Elizabeth the fault then trends westward into the offshore.

Unlike the Blue Mountain Fault, which attenuates stress transfer and produces modest uplift, the SCFZ’s uninterrupted lateral continuity raises fears of substantial devastation. The potential for an earthquake of greater magnitude than experienced this year is a stark reality.

In light of the potential threat, preparedness becomes the cornerstone of resilience for Jamaica. Establishing and practising earthquake readiness protocols at individual, community, schools and national levels is crucial. Implementing robust building codes, conducting regular seismic assessments of infrastructure, and creating awareness programmes to educate citizens on safety measures during earthquakes are imperative steps.

Additionally, fostering partnerships between government bodies, emergency services, and international relief agencies can strengthen response capabilities in the event of a seismic disaster.

The clock is ticking, urging us to heed the warnings of geology and history.

Shonel Dwyer is senior technology officer at the National Commission on Science and Technology (NCST). She is a geologist who has worked as a specialist in natural/water resources management and the local oil and gas sector. Send feedback to columns@gleanerjm.com.