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Natural Calamities - Earthquakes and Seismograph

Grade 5ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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An Earthquake is a sudden shaking or trembling of the Earth's surface caused by internal disturbances deep within the Earth's crust, mainly due to the movement of tectonic plates.

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The Focus (or Hypocentre) is the point deep inside the Earth where the earthquake actually originates.

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The Epicentre is the point on the Earth's surface located directly above the focus. The damage is usually most severe at this point.

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Vibrations that travel through the Earth during an earthquake are known as Seismic Waves.

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A Seismograph (also known as a Seismometer) is a scientific instrument used to detect and record the intensity, direction, and duration of seismic waves.

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The Richter Scale is used to measure the magnitude (strength) of an earthquake, typically ranging from 11 to 1010. It is a logarithmic scale, meaning an increase of 11 unit represents a 1010-fold increase in the amplitude of the shaking.

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Earthquakes with a magnitude of less than 3.03.0 are usually not felt, while those above 7.07.0 are considered major and cause widespread destruction.

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Safety measures during an earthquake include the 'Drop, Cover, and Hold on' technique, moving away from tall buildings, and staying away from windows or glass objects.

📐Formulae

Magnitude increase=10(M2−M1)\text{Magnitude increase} = 10^{(M_2 - M_1)}

Energy release increase≈32(M2−M1)\text{Energy release increase} \approx 32^{(M_2 - M_1)}

Richter Scale Range:0<M≤10\text{Richter Scale Range}: 0 < M \leq 10

💡Examples

Problem 1:

An earthquake is recorded with a magnitude of 6.06.0 on the Richter scale. Another earthquake is recorded with a magnitude of 4.04.0. How many times stronger is the amplitude of the 6.06.0 magnitude earthquake compared to the 4.04.0 magnitude one?

Solution:

The difference in magnitude is 6.0−4.0=26.0 - 4.0 = 2. Since each unit on the Richter scale represents a 1010-fold increase in amplitude, the increase is 102=10010^2 = 100. Therefore, it is 100100 times stronger.

Explanation:

The Richter scale uses a logarithmic base of 1010. For a difference of nn units, the intensity/amplitude increase is calculated as 10n10^n.

Problem 2:

During an earthquake, a Seismograph produces a graph showing the vibrations. What is this recorded graph called?

Solution:

The recorded graph or the output of a Seismograph is called a Seismogram.

Explanation:

While the instrument is the Seismograph, the paper or digital record of the earth's movements that it produces is specifically called a Seismogram.

Problem 3:

If the Focus of an earthquake is at a depth of 10 km10\text{ km} below the surface, where would the Epicentre be located?

Solution:

The Epicentre would be located on the surface of the Earth, at the point 0 km0\text{ km} altitude, directly vertical from the 10 km10\text{ km} deep Focus.

Explanation:

By definition, the Epicentre is the point on the Earth's crust that is geometrically perpendicular to the Focus.