The earth surface is made up of many huge pieces of rock, like a jigsaw puzzle, call tectonic plates. An Earthquake is a sudden violent shaking of the ground, typically causing great destruction, as a result of movements within the earth's crust or volcanic action
For hundreds of millions of years, the forces of plate tectonics have shaped the earth, as the huge plates that form the earth's surface slowly move over, under and past each other. Sometimes, the movement is gradual. At other times, the plates are locked together, unable to release accumulated energy. When the accumulated energy grows strong enough, the plates break free. If the earthquake occurs in a populated area, it may cause many deaths and injuries and extensive property damage
Types of tectonic plate activity
Earthquake activity in St. Vincent and the Grenadines is a result of various types of movements taking place within boundary zones of the Caribbean Plate.
There are generally three kinds of plate movements which can cause an earthquake:
Spreading: when plates are spreading or separating from each other, we call the movement divergent
Colliding: when plates are colliding, or pushing each other, we call the movement convergent
Sliding: when plates are sliding past each other we call this movement lateral
Magnitude is related to the energy generated when a fault ruptures and produces an earthquake. There are different ways to determine magnitude. In one method, three characteristics of the fault zone are used in the calculation:
- The area that ruptures during the earthquake.
- The amount of displacement during the earthquake.
- The stifness of the rocks that break.
When we multiply these numbers, we obtain a number called the seismic moment. The seismic moment is then converted into another number called the moment magnitude (or simply magnitude). In our region, we use the duration of the earthquake recording, and the distance of the recording station from the hypocentre to find magnitude e.g. magnitude 5.8.Â For any given earthquake, the magnitude is a fixed number that does not vary regardless of which island you are located.
Intensity scales describe the severity of an earthquake by grading the effects on people, structures and geological formations. Each degree of intensity is described by a Roman numeral, (I, II, III etc.) and the effects of the earthquake roughly double in severity for each one-division increase in intensity. In the Western hemisphere, including the Eastern Caribbean, the most widely used scale is called the Modified Mercalli or MM scale. In the rest of the world an almost identical scale called the MSK scale is more common.Â
For any given earthquake, the Intensity may vary depending where you are in relation to the earthquake's epicenter.
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Earthquakes cannot be predicted so it is important to prepare yourself as soon as possible:
- Become aware of fire evacuation and earthquake plans for all of the buildings you occupy regularly.
- Pick safe places in each room of your home, workplace and/or school. A safe place could be under a piece of furniture or against an interior wall away from windows, bookcases or tall furniture that could fall on you.
- Practice drop, cover and hold on in each safe place. If you do not have sturdy furniture to hold on to, sit on the floor next to an interior wall and cover your head and neck with your arms.
- Keep a flashlight and sturdy shoes by each person's bed.
- Make sure your home is securely anchored to its foundation.
- Bolt and brace water heaters and gas appliances to wall studs.
- Bolt bookcases, china cabinets and other tall furniture to wall studs.
- Hang heavy items, such as pictures and mirrors, away from beds, couches and anywhere people sleep or sit.
- Brace overhead light fixtures.
- Install strong latches or bolts on cabinets. Large or heavy items should be closest to the floor.
- Learn how to shut off the gas valves in your home and keep a wrench handy for that purpose.
- Learn about your area's seismic building standards and land use codes before you begin new construction.
If you are inside when the shaking starts you should:
- Drop, cover and hold on. Move as little as possible.
- If you are in bed, stay there, curl up and hold on. Protect your head with a pillow.
- Stay away from windows to avoid being injured by shattered glass.
- Stay indoors until the shaking stops and you are sure it is safe to exit. If you must leave the building after the shaking stops, use stairs rather than an elevator in case there are aftershocks, power outages or other damage.
- Be aware that fire alarms and sprinkler systems frequently go off in buildings during an earthquake, even if there is no fire.
If you are outside when shaking starts you should:
- Find a clear spot and drop to the ground. Stay there until the shaking stops (away from buildings, power lines, trees, streetlights).
- If you are in a vehicle, pull over to a clear location and stop. Avoid bridges, overpasses and power lines if possible. Stay inside with your seatbelt fastened until the shaking stops. Then, drive carefully, avoiding bridges and ramps that may have been damaged.
- If a power line falls on your vehicle, do not get out. Wait for assistance.
- If you are in a mountainous area or near unstable slopes or cliffs, be alert for falling rocks and other debris. Landslides are often triggered by earthquakes.
- After an earthquake, the disaster may continue. Expect and prepare for potential aftershocks, landslides or even a tsunami. Tsunamis are often generated by earthquakes.
- If you are near the ocean and you feel an earthquake then you should leave immediately. Move to higher ground. More information can be found on the tsunami section of the website.
- Each time you feel an aftershock, drop, cover and hold on. Aftershocks frequently occur minutes, days, weeks and even months following an earthquake.
- Look quickly for damage in and around your home and get everyone out if your home is unsafe.
- Open closet and cabinet doors carefully as contents may have shifted.
- Watch out for fallen power lines or broken gas lines and stay out of damaged areas. Stay out of damaged buildings.
Please follow these links for further advice and information on earthquakes:
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