Category: Geography

What is an Earthquake

In general, earthquake refers to any volcanic activity which results in producing seismic waves. When rocks deep inside the earth are caused to experience a lot of stress due to tectonic forces acting on them. As a result of this severe stress, these rocks undergo a change in their shape and store energy within them. Now as these deformed rocks come back to their original shape, they release energy on their return. This energy is in the form of waves called seismic waves. Thus, these waves cause the earth to shake, leading to an earthquake.

This theory that explains how energy is stored inside rocks when they deform as they are caused to undergo extreme force and then release energy upon coming back to their original position is known as elastic rebound theory.

Illustration

The cause of an earthquake is similar to the bending of a flexible stick. When you twist a stick at its maximum point so much so that it may snap off once you push it any further, it will store energy inside it. Now as soon as you let it free, it gets back to its original shape releasing the energy in the process.

Terms and Definitions

1. The bending of rocks into a new position is known as strain.
2. The point (inside the earth’s crust) from where the energy of the rocks is released due to volcanic activity is called focus. It is also known as hypocenter and it refers to the precise location of an earthquake.
3. The point that lies directly above the focus and on the surface of the earth is known as epicenter.
4. The field of science that studies earthquake and seismic waves is called seismology. The scientist who examines earthquake and follows a line of inquiry into this discipline is known as seismologist.
5. The scientific devices that record vibrations of the earth are called seismometers.
6. The energy released by an earthquake (in the form of seismic waves) is usually assigned a specific magnitude number so that the precise amount of released energy can be calculated. The device that designates this number is known as Richter magnitude scale.
7. The size of earthquake is measured by calculating the amount of energy released by it. The instrument that measures its size is called moment magnitude scale.
8. When a volcanic activity or earthquake occurs beneath the body of water, a huge mass of water is displaced and in this way it gives rise to a series of waves known as Tsunami. It is also called Tidal Wave.
9. The distance from the epicenter downward up to a point of focus is called focal depth.
10. At times, an earthquake of relatively smaller magnitude occurs in the same location where main earthquake has just taken place. This smaller earthquake is referred to as aftershock.
11. If one earthquake sparks off several other big earthquakes in the same location, this phenomenon is known as earthquake storm.
12. The intensity of the earthquake varies according to the depth of the hypocenter. The deeper an earthquake is, the less likely it is to cause any damage and vice versa.

Tectonic Plates

1. When the crust is merged with the uppermost part of the mantle, it forms lithosphere. The lithosphere is divided into a number of pieces called tectonic plates. Majority of earthquakes take place along boundaries of tectonic plates.
2. Tectonic plates are attached with one another like pieces of a jigsaw puzzle. At times, one of the plates makes an effort to slip over the adjacent plate and like so the strain develops. This process in which one plate glides over another eventually results in producing seismic waves. This type of an earthquake is known as interplate earthquake.
3. Almost 90 percent of the total seismic energy is released through interplate earthquakes.

Seismic Waves

1. When earthquake occurs within rocks of the Earth’s crust, it emits energy in the form of waves. The frequency of these waves is low as they pass through three layers of the earth (The Crust, The Mantle and The Core). These waves are called seismic waves. It is only because of these waves that we get to know that earth’s interior is composed of three layers.
2. Scientists believe that less than ten percent of the energy given off by an earthquake is in the form of seismic waves. Much of the rest of the energy is transformed into heat energy.
3. The very first wave a seismograph records is called P-wave. The letter ‘P’ denotes ‘pressure’ or ‘primary’. The speed of these waves within solid rocks inside the earth is 6 – 7 km/s.
4. The second wave to be recorded on a seismograph is known as S-wave. The letter ‘S’ denotes ‘secondary’ or ‘shear’. These waves are unable to pass through outer core (which is in molten state) but they can cross inner core (which is in solid state). The velocity of S-waves in the interior of the earth is slower as compare to P-waves. These waves travel at a speed of 4 – 5 km/s.

Earthquakes with a magnitude number of less than or equal to 3 are weak and cannot be noticed. The earthquakes having more than number 7 on magnitude scale are destructive and cause severe damage.

Types of Earthquakes  

Based on focal depth, earthquakes are classified into three kinds.

1. Shallow-focus earthquakes are those quakes that occur less than 70 km deep inside the earth. Thus their focal depth is less than 70 kilometers.
2. Intermediate-depth earthquakes are those that lie between 70 km and 300 km deep. They are also known as mid-focus earthquakes.
3. Deep-focus earthquakes develop inside the mantle and vary from 300 km to 700 km.

Location of Earthquakes

1. The location with maximum number of earthquakes lies in the Pacific Ocean and is called Ring of Fire. It is 40,000 km long and consists of more than 75 percent of the volcanic eruptions of the world. Almost 90 percent of the underground eruption in the world takes place in this region. It is the world’s most active volcanic region.
2. The second most active region of volcanic activity is called Alpine-Himalayan orogenic belt. About 17 percent of the biggest earthquakes of the world lie in this area.
3. The world’s third most active area for volcanic activity is Mid-Atlantic Ridge.

Human Causes of Earthquakes

There are four kinds of human actions that may also trigger earthquakes. These are:

1. When huge amount of water is collected to the backside of dams;
2. when making a hole deep inside the ground and inserting liquid into the wells;
3. when digging ground for extracting coal from deep inside the earth;
4. when digging out oil from the earth.

More Earthquake Facts for Kids

1. The energy released by a single earthquake is so great that it amounts to energy released by tens of thousands of nuclear bombs.
2. Every year, our planet experiences more or less 500,000 earthquakes. However, 400,000 of these earthquakes are so small that we cannot feel them.
3. In U.S.A., the two states that experience most minor earthquakes are Alaska and California.
4. From the year 1900 and beyond, about 18 earthquakes occurred with a magnitude ranges from 7 to 7.9 and thus these were termed as ‘major’ earthquakes, as per United States Geological Survey.
5. With a magnitude of 9.5, the strongest earthquake of the world was taken place in Chile in May 22, 1960. It is known as ‘Great Chilean earthquake’.
6. The earthquake with the most number of casualties in the world was occurred on January 23, 1556 in China. It took lives of about 830,000 people and this incident is now known as Jiajing earthquake.

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Learn some more: Facts About The Earth

Hi kids! Are you looking for some of the interesting rainforest facts for kids? Yes, then don’t worry because you don’t have to hang around anymore. We’ll discover some of the hidden truths pertaining to the rainforests. To start with, do you know why they are called rainforests? Well, simply because they have maximum quantity of rainfall as compare to the ordinary ones and the presence of huge thick trees make it unique. Every rainforest is filled with compact trees, flowers and plants that make it possible to change the climatic conditions. But the darkest side of rainforests is that they are fading away at a staggering rate. Out of the two kinds of rainforests, Tropical rainforests are close to the equator and are also known as ‘Jewels of the Earth’. There are four layers of tropical rainforest and the lowest layer takes in as less as 2% of the daylight. Besides, rainforest facts for kids are exciting to know also because they give off as well as take in a lot of carbon dioxide which is beneficial for the environment.

Rainforest Facts For Kids

As is obvious from its name, rainforest takes in a huge spell of rain in a year. That’s why it is different from usual forest.

Rainforests are of two kinds; tropical rainforest and temperate rainforest.

The biggest rainforest in the world is called Amazon Rainforest.

Nearly forty to seventy five percent of all species are native to rainforests.

There was a time when the land of earth used to have around 14% of rainforests but not anymore as it has reduced by 8% over the years. Besides, these lingering rainforests would not be able to survive for more than 40 years, according to some biologists. What one of the woeful rainforest facts for kids!

Even now billions of species (animals and plants) are undiscovered in the rainforests.

After each second, nearly 65,340 square feet (equal to the area of a football field) of rainforest is destroyed. That’s why you need to be familiar with some of the rainforest facts for kids so that you may spread awareness among other people about the significance of rainforests for the planet.

All the species are dropping off at the rate of 50,000 species every year. If the rainforests continue fall off at this alarming rate, it may result in the extinction of almost 50% of all the species (animals, plants and other organisms) by the end of next 100 years. One of the pitiful rainforest facts for kids!

Currently 200,000 Indians are living in the Amazon Rainforest while 500 years before there had been 10,000,000 isolated tribes.

Amazon Rainforest is so huge in size that if it were a state, it would have been the 9th biggest country as a whole.

The turnover of global oxygen is 28% from the rainforests.

Since the Amazon Rainforest is incessantly reprocessing oxygen from carbon dioxide so it serves the purpose of ‘Lungs’ for the earth.

A lion’s share (almost 80%) of the vegetables and fruits comes from rainforests.

In previous times, rainforests used to have 3,000 species of fruits. But since Indians consumed most of these fruits, so today there are only 200 fruits available.

Tropical rainforests are known as the largest drugstore in the world because almost quarter of the remedies was unearthed from this region. It’s definitely one of the rarely known rainforest facts for kids.

The plant life in rainforest is full of alkaloids (metabolites) and these alkaloids are not only useful in safeguarding vegetation from bugs and diseases, but they are equally helpful for healing purposes.

There are 3,000 species of plants in the world that are extremely effective for dealing with cancer cells and seventy percent of these are located in the rainforest.

One of the medicines known as Vincristine was produced from the rainforest (plant name as periwinkle). It is the most effective and strong drug against cancer cells. So knowing about rainforest facts for kids is good from medical standpoint as well.

According to some environmentalists, if we manage to keep the rainforests safe from extermination it will be economically more profitable than to destroy them.

There are many rare species flowers in the rainforests of Australia so much so that you’ll not find 80% of these flowers in other parts of the world.

In the South American rainforests, there are over 2,000 butterflies.

Rainforests serve as the most important means of preparing drugs and so out of every four ingredients of medicine; one ingredient comes from the plants of rainforest.

The Central African forests contain over 8,000 plant species.

Every day the massive plants of bamboo in rainforests shoot up by nine inches.

There are tens of thousands of trees scattered all over the rainforest and their topmost layer is so thick that in case of shower, the drop of water touches the ground after ten minutes.

In the South American tropical rainforests, sloth creeps so lazily that algae begin to produce on its body.

Madagascar has been deprived of about 2/3^rd of its rainforests from the time when human beings started to settle on the earth.

A Quick Guide To Rainforest Facts For Kids

Rainfall per year: 68 to 78 inches

Layers of Tropical Rainforest: Emergent, Canopy, Understory, Forest Floor

Size of Biggest Trees in the Canopy Layer: 30m to 45m

Percentage of West African Rainforest Demolished: 90%

Rainforest Facts Info-graphic

Courtesy of Oak Furniture UK