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Earthquakes

View the ODPM Earthquake Brochure.

What is an Earthquake?

An earthquake is a natural hazard which occurs when the ground shakes or rocks violently. An earthquake can take place at any time, day or night, without any forewarning at all and is capable of inflicting the same type of damage as a major hurricane. This makes it the most unpredictable and feared of all natural disasters.

How Earthquakes Occur?

The earth is made up of four major layers: the inner core, outer core, mantle and crust. The crust is the outermost and thinnest layer of the earth made out of rock. This layer of rock is not one smooth continuous layer, in fact the rock is broken into several large pieces that can fit together like a jigsaw puzzle (Figure 1). These pieces are known as tectonic plates. These tectonic plates are able to move around and interact with one another; sliding and bumping into each other. When two or more of these plates meet, they can lock or stick together, similar to when your fingers interlock with each other. The plates continue to move about trying to get themselves unstuck from one another and this causes energy to build up below the plates. When the plates are able to break free from each other, the built up energy is released moving through the Earth resulting in the shaking of the ground or what we call an earthquake. The region where two or more plates meet is known as a plate boundary.

An earthquake typically lasts under one (1) minute or sixty (60) seconds, but the shaking could be so violent at times to cause irreparable damage. When an earthquake first takes place, it is known as the main event. However, there may be a series of smaller earthquakes that could occur after the main one. These smaller earthquakes are known as the aftershocks and are capable of inflicting further damage. The aftershock is just as unpredictable as the main one.

 


Figure 1: Showing the different Tectonic Plates

How are earthquakes measured?

Scientists who study earthquakes (called seismologists) are NOT able to predict the exact time and location that an earthquake would strike. However, they are able to measure the magnitude of an earthquake or the amount of energy that is released from the earth when an earthquake takes place. Seismometers are used to record the seismic waves generated by an earthquake. Seismologists are then able to use these recordings to determine where the earthquake was located and how strong it was. Seismic waves may also be used to map the interior of the earth.

Magnitude is used to measure an earthquake’s size (usually on a Richter Scale) and is related to the amount of energy generated by the earthquake. The Mercalli Intensity Scale is used to categorize the levels of shaking observed during an earthquake.

Earthquake Terms:

A SEISMIC WAVE travels through the Earth, most often as the result of an earthquake, sometimes from an explosion. Seismic waves are also continually excited by the pounding of ocean waves and the wind.

INTENSITY describes the level of shaking during an earthquake.

MAGNITUDE is a measure of the strength of an earthquake and is related to the amount of energy released.

The HYPOCENTRE/FOCUS is the area within the crust where rocks ruptured and released their stored energy in an earthquake.

The EPICENTRE is the point on the earth’s surface that is directly above the hypocenter or focus. The epicenter is usually the location of greatest damage.

Some significant earthquakes that have affected Trinidad and Tobago

2010 (Dec 26) - 4.7 felt throughout Trinidad, from Carenage to Moruga to Matura. No reported injuries or damages.                                       

2009 - 4.8 occurred on land and felt in Sangre Grande and Penal, no reported injuries.

2008 – 5.6 located on the East Coast and felt mainly in Galeota, no reported injuries.

2007 – 7.3 felt throughout the Eastern Caribbean from Puerto Rico to Guyana; damage reported in Martinique, St. Lucia, St. Vincent and Barbados. This is the fifth earthquake in the magnitude 7 range to occur near Martinique since 1727.

2006 – 5.8 felt throughout Trinidad with 3 reported injuries in Point Lisas.

1997 (April 22) – 6.1 US # 25 million in damages to Tobago, 2 were injured and 15 were left homeless.

1996 – 5.2 North of Trinidad occurred New Year’s Day. No reported injuries.

1988 – 6.3 occurred off east Coast Trinidad. No injuries reported.

1982 – 5.2 largest earthquake near Tobago up to that time.

1968 - 7.0 significant damage in Venezuela with some damages to Port of Spain, Trinidad.

1954 – 6.5 one person was killed and many were injured.

1888 – 7.5 Damage occurring from Trinidad to St. Vincent.

1766 – 7.9 Destroyed Trinidad’s then capital San Jose.

Vulnerability to Earthquakes:

Physical Vulnerability:

  1. Not using building codes and the right type of material when constructing structures. Building codes are guides used to ensuring that structures can withstand the effects of earthquakes and hurricanes. Building structures according to building codes would ensure the integrity of the structure.
  2. Not building structures on the correct type of foundation. Some soil types are more susceptible to ground movements than others. The soil type of the land upon which a structure is to be erected, would dictate the type of foundation the building should have; be it a shallow or deep foundation.

Environmental Vulnerability:

  1. Soil type. As previously mentioned different soil types are more susceptible to soil and ground movements. It is important to know the soil type before constructing.
  2. Whether the area is located on or near a fault line. Areas away from fault lines can be affected by earthquakes; however areas located near or on fault line are more susceptible to the effects of an earthquake.

Economic Vulnerability:

  1. Unemployment, livelihoods and debt. People may not be able to afford to use the best materials or adhere to building codes when constructing their homes. This makes them more vulnerable.
  2. Increased population density. Due to lack of finances, the predominant density pattern in certain areas would be clusters; meaning that there would be a large number of houses being built very close together. Areas with a higher population density are more vulnerable to disasters.

Social Vulnerability:

  1. Lack of Information and beliefs. Citizens are unaware that there are six (6) seismogenic zones in Trinidad and Tobago; according to the University of the West Indies Seismic Research Centre. Some people still believe that Trinidad and Tobago would not be affected by a major earthquake.

Further Reading

United States Geological Survey

The University of the West Indies Research Centre

Incorporated Research Institutions for Seismology

Federal Emergency Management Agency

Caribbean Disaster Emergency Management Agency

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