Earthquakes

1. What are earthquakes?

The ground beneath our feet seems rock-solid, but the surface of our planet is in fact a dynamic grid of sections, which are moving very slowly, these sections are known as tectonic plates. When these large tectonic plates start breaking and shifting they cause the ground to shake, the shaking is called an earthquake.

2. Where are they most likely to happen?

Earthquakes mostly occur on, or near, plates of earth crust. For example; about 200 kilometres off the west coast of Vancouver Island, at the Juan de Fuca plate and Pacific plate. The plates of the world: this is a map showing the Earth and its plates and plate boundaries the Earth consists of. 

3. Why do they occur?

Earthquakes are usually caused when rock underground suddenly breaks along a fault. This sudden release of energy causes (seismic) waves which make the ground shake. When two blocks of rubber for example rub against each other, they don’t slide that smoothly. The rocks catch on each other. This means the rocks are still pushing against each other, but they aren’t moving. After a while, the rocks break because of all the pressure that’s built up. An earthquake occurs when the rocks break. After and even during the earthquake the plates or rocks will start to move again, till they break and another earthquake occurs. The spot underground where the rock breaks is called the focus of the earthquake. The place which is right above the focus (it’s above the ground) is called the epicenter of the earthquake.

Seismic waves can also be caused by explosions underground. Such an explosion may occur when people are making tunnels for roads, railroads, subways and mines. They explode it to let some rock break away. These explosions, however, don’t cause very strong seismic waves. Most of the time you won’t even feel them. Sometimes seismic waves occur when the roof or walls of a mine collapse. This can (sometimes) be felt by people near the mine. The largest underground explosions, from tests of nuclear warheads (bombs), can create seismic waves very much like large earthquakes.

It’s a bit like this small experiment:

  • Break a block of foam rubber in half.
  • Put the pieces on a smooth table.
  • Put the rough edges of the foam rubber pieces together.
  • While pushing the two pieces together lightly, push one piece away from you along the table top while pulling the other piece toward you. See how they stick?
  • Keep pushing and pulling smoothly. Soon some of the foam rubber along the crack (the fault) will break and the two pieces will suddenly slip past each other. In this experiment the sudden breaking of the foam rubber is the earthquake. This happens along a strike-slip fault.

4. How are earthquakes measured?

The vibrations which are produced by an earthquake are detected, recorded, and measured by special instruments called seismographs. A seismograph makes zig-zag lines, these lines together make a “seismogram.” The seismogram reflects the (changing) intensity of the vibrations. It reflects them by responding to the movement of the surface beneath the seismograph. From the date expressed in the seismogram, scientists can decide the time, the epicentre, the (focal) depth, and the type of faulting of an earthquake and then they can estimate how much energy was released.

The two most common types of vibrations produced by earthquakes are surface waves and body waves. Surface waves travel along the Earth’s surface. Body waves travel through the Earth. Most of the times the surface waves have the strongest vibrations and cause most of the damage done by earthquakes.

5. Can earthquakes be predicted?

It’s very hard to predict them. But scientists have a pretty good idea why they happen and we can trace a history of when they have happened in the past. But it’s not as obvious as when they look at animals. They do predict them. Animals behave differently when they sense earthquakes. E.g.: a group of elephants that were near the area which had a lot of damage after the Tsunami, left the area before the Tsunami hit that area. How elephant knew about the earthquake? The answer is elephant feet have sensors that can sense waves travelling beneath the earth, this explains how the elephants (and other animals) can predict an earthquake is going to happen.

6. What can people do to keep the damage caused by earthquakes as little as possible?

As I just said are earthquakes hard to predict. But there are some things you can do to keep the damage as little as possible.

What to Expect:

What happens when an earthquakes it a certain area. It depends of how big the earthquake is. News reports from all over the world show that it’s not always the earthquake itself which causes the damage. An earthquake may cause only a little damage on one place but on another it may be a great disaster. There are some different factors that affect how much damage a given earthquake can cause. Soft soils will shake a lot more than bedrock, and cause a lot more damage. Building methods will also affect how well a building will ride out the quake. There are things you can do to keep the damage as little as possible before, during and after an earthquake.

Before:

  • Take care that you got enough food en water for a couple of days. You may be on your own for quite a long time before authorities can get a relief system set up.
  • Know how to turn off the gas, water and electricity if necessary. You may need a special tool for the gas. Keep it where you will be able to find it quickly in an emergency. Authorities generally advise against turning off the gas unless you smell gas or have reason to believe that there may be a leak.
  • Make a plan which you can follow during the earthquake.

During:

  • Stay Calm – remember your earthquake plan (if you’ve got one) and follow it.
  • Take shelter under a table or an area protected from falling objects and glass.

After:

  • Check for fires.
  • Clean up broken glass or other dangerous materials that may have spilled. Keep people away from dangerous places till everything is cleaned up.
  • Stay away from downed power lines.
  • Of course there are more things to do, but I would be busy with that too long. So this are some important ones.

This was my project concerning earthquakes. I hope you liked it! I liked to working at it!

 

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