Question 1

Question 1Describe the distribution of Earthquakes in the world.

Accepted Answer

The distributional pattern of earthquakes shows that there are three major belts in the world in which the earthquakes frequently occur. These earthquake belts are:The Circum-Pacific Belt (Convergent Plate Boundaries) — It extends in west from Alaska to Kurile, Japan, Mariana and the Philippine trenches. Its one branch goes towards the Indonesian trench and the other goes towards the Kermadec-Tonga trench to the north-west of New Zealand. On the eastern side of the Pacific the earthquake zone follows the west coast of North America and continues southward along Pem and Chile trench on the west coast of South America.The Mid-Atlantic Belt (Divergent Plate Boundaries) — This belt of earthquakes extends along the mid-oceanic ridges and several islands near the ridges of Atlantic Ocean. Earthquakes of moderate to mild intensity with shallow focus are recorded in this belt. The Rift Valley of East Africa and the Red Sea are considered as an extension of this belt.The Mid-Continental Belt — This belt extends along the Alpine mountain system of Europe, Rocky mountains in North America, through Asia Minor, Caucasia, Iran, Afghanistan and Pakistan to the Himalayan mountain system including Tibet, the Pamir, Tien-Shan, Altai and the mountains of China, Myanmar and eastern Siberia. This zone is characterised by larger earthquakes of shallow origin and some of intermediate origin.

Question 2

Question 9Mention any two destructive effects of earthquakes.

Accepted Answer

Two destructive effects of earthquakes are:Building Collapse — The earthquakes of high intensity lead to collapse of buildings. People can be trapped under the rubble. There is loss of lives and properties.Landslides — Earthquake causes landslides in hilly areas or liquefaction of soils resulting in damage of properties and loss of lives and disturb the transport system. This occurs due to liquefaction of soils.

Question 3

Question 10Mention two constructive effects of earthquakes.

Accepted Answer

Two constructive effects of earthquakes are:Earthquakes may result in fissure opening causing a Geyser or hot spring which are useful from medicinal point of view as it contain sulphur.Sometimes earthquakes result in formation of coastal submergence and changing the coastal forms, forming bays and may prove to be helpful in navigation.

Question 4

Question 11What is a Tsunami?

Accepted Answer

The seismic waves travelling through the ocean resulting in long wavelength shallow water wave caused by rapid displacement of water is called Tsunami. Its velocity can reach 800 km per hour. It causes massive destruction and flood in coastal areas.

Question 5

Question 6How are earthquakes useful?

Accepted Answer

Earthquakes are useful for the following reasons-1. Energy release — They help the earth to release its stored up energy which helps to keep the earth in good shape.2. Landforms — Earthquakes help in the formation of various landforms.

Question 6

Question 1(c)Give a geographical reason for each of the following:(i) Most earthquakes occur on account of plate movements.(ii) Primary waves are the first earthquake waves to be recorded on a seismogram.(iii) Volcanic activity and earthquakes occur in the same belt.

Accepted Answer

(i) Most earthquakes occur on account of plate movements because when two plates slip past each other or collide against each other, their edges produce faults along the lines of weakness.(ii) Primary waves are the first earthquake waves to be recorded on a seismogram because they travel at the greatest speed and can pass through solids, liquids and gases.(iii) Volcanic activity and earthquakes occur in the same belt because earthquakes and volcanoes are formed along faults between tectonic plates, where the crust is weakest.

Question 7

Question 1(d)Explain the three types of earthquake waves.

Accepted Answer

The three types of earthquake waves are-1. P or Primary wave — These are the first earthquake waves to be recorded on a seismogram of an earthquake. They are compressional,i.e., the particles vibrate in the direction of movement of the wave. They can pass through solids, liquids and gases.2. S or Secondary wave — These waves are recorded on a seismogram after the P waves. They are distortional waves in which the particles vibrate at right angles to the direction of movement of the wave. S waves travel through the earth's interior but cannot be transmitted by liquids.3. L or Surface waves — These waves travel along the surface of the earth and are recorded after the P and S waves. Two types of L waves are identified- Love waves and Rayleigh waves.

Question 8

Question 2(a)The destructive effects of an earthquake are far more than its constructive effects. Give reasons to support your answer.

Accepted Answer

Constructive effects of earthquakes are-Release of stored up energy of the earthVertical and lateral displacement of the earthFormation of lakesDestructive forces of earthquakes are-Collapse of structures causing great loss of life and propertySubmergence of coastal areasChanged course of rivers, rendering many areas unsuitable for irrigation and agricultureResulting landslides disrupt the transport systemAccidental fires cause damage to life and propertyIn geographical terminology, earthquakes are a part of endogenic forces and are regarded as constructive movements of the earth's crust but from human point of view, earthquakes are regarded as destructive causing loss of life and property.

Question 9

Question 2(c)Is it possible to predict an earthquake? Give reasons to support your answer.

Accepted Answer

No, it is not possible to predict an earthquake.The Russians were the first ones to discover the P and S waves on the basis of which predictions were made. The theory of Plate Tectonics offers another means of prediction on scientific lines. Japanese use the methods of measuring the changes in sea level and variations in Earth's magnetic field to predict earthquakes.However, no method is foolproof as has been proved by recent earthquakes in Japan, India and USA.

Question 10

Question 2(d)How are earthquakes distributed over the globe?

Accepted Answer

The main earthquake belts in the world are-1. The Circum Pacific Mountain Belt — This belt has 70% of all earthquakes. A part of San Andreas Fault in the USA lies in this belt. The area of Japan, the Philippines and Indonesia all form parts of this belt.2. The Midworld Mountain Belt — It stretches from Eastern Europe covering Alpine-Himalayan ranges in Europe and Asia. About 20% of all earthquakes occur in this zone.3. The Mid-Atlantic Ridge — This belt comprises areas along the mid-oceanic ridges as well as many island near the ridges of the Atlantic Ocean and the remaining 10% of earthquakes occur in this belt. The Rift Valley of East Africa is considered an extension of the belt.

Question 11

Question 2Imagine you were sitting in the balcony of a seaside resort, when you suddenly noticed waves rising high in the sky. Suddenly there was a surge in the height of the waves and they turned into a tsunami. What could have caused this tsunami and what were its consequences.

Accepted Answer

A tsunami can be caused by:Underwater earthquakes — When an earthquake occurs on the ocean floor, it can create powerful waves that can travel long distances and cause a tsunami.Underwater landslides — A large landslide on the ocean floor can also displace a significant amount of water and create a tsunami.Volcanic eruptions — A volcanic eruption that occurs underwater can also cause a tsunami.The consequences of a tsunami can be severe:Flooding — A tsunami can cause extensive flooding in low-lying areas, leading to significant damage to infrastructure and loss of life.Destruction of buildings and homes — The force of the tsunami waves can cause significant damage to buildings and homes, leaving people homeless and without access to essential services.Loss of life and property— Tsunamis can be deadly, causing the loss of life. It also affects industries such as tourism, fishing, and agriculture.

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