Earthquakes and Tsunamis | Geomorphology | Principle Of Geography

 

Geomorphology

Principle Of Geography

Geography Complete Study Material

(Paper - I)

Earthquakes

           When the Lithospheric plates move, the surface of the earth vibrates. The vibrations can travel all round the earth. These vibrations are called earthquakes. The place in the crust where the movement starts is called the focus. The place on the surface above the focus is called the epicentre. Vibrations travel outwards from the epicentre as waves. Greatest damage is usually closest to the epicentre and the strength of the earthquake decreases away from the centre.

            Although earthquakes cannot be predicted, the impact can certainly be minimised if we are prepared before-hand. Some common earthquake prediction methods adopted locally by people include studying animal behaviour; fish in the ponds get agitated, snakes come to the surface.

           An earthquake is measured with a machine called a seismograph. The magnitude of the earthquake is measured on the Richter scale. An earthquake of 2.0 or less can be felt only a little. An earthquake over 5.0 can cause damage from things falling. A 6.0 or higher magnitude is considered very strong and 7.0 is classified as a major earthquake. There are three types of earthquake waves: 

1. P waves or longitudinal waves 

2. S waves or transverse waves 

3. L waves or surface waves 

EARTHQUAKE PREPAREDNESS 

Where to take shelter during an earthquake — 

• Safe Spot – Under a kitchen counter, table or desk, against an inside corner or wall. 
• Stay Away from – Fire places, areas around chimneys, windows that shatter including mirrors and picture frames. 
• Be Prepared – Spread awareness amongst your friends and family members and face any disaster confidently.

Tsunamis

            ‘Tsunami’ is a Japanese term represented by two characters: “tsu” and “nami”. The character “tsu” means harbor, while the character “nami” means wave. which has been universally adopted to describe a large seismically generated sea wave. These waves are responsible for causing considerable destruction in certain coastal areas where submarine earthquakes occur. It is a series of waves of extremely long wavelengths and long periods generated in a body of water by an impulsive disturbance that displaces water.

Process of Generation of Tsunami

When a tsunami is generated, its steepness i.e. height to length ratio is very less.This enables it to pass unnoticed beneath the ships in the sea. As the wave approaches the shore, the height of the wave rapidly increases because of the rebound from the shallow surface.The period of the wave remains constant, velocity drops, and the height increases. In confined coastal waters relatively close to their point of origin, tsunamis can reach a height of more than 30m. Tsunamis travel at the speed of 100 -150 km/h which may pick up 650-900 km/h.When the tsunami enters the shoaling water of coastlines in its path, the velocity of its waves diminishes, and the wave height increases.As a tsunami leaves the deep water of the open sea and propagates into the more shallow waters near the coast, it undergoes a transformation.Since the speed of the tsunami is related to the water depth, as the depth of the water decreases, the speed of the tsunami diminishes.The change in the total energy of the tsunami remains constant. Therefore, the speed of the tsunami decreases as it enters shallower water, and the height of the wave grows.Because of this “shoaling” effect, a tsunami that was imperceptible in deep water may grow to be several feet or more in height.It may travel a considerable distance. The frequency of tsunami is highest in the Pacific Ocean.Since 1948, an International Tsunami Warning Network has been in operation around the Pacific Ocean to alert coastal residents to possible danger.

Causes of Tsunami

• EarthQuakes
• Landslides
• Under Sea Volcanos
• Meteors Asteroid
• Anthropogenic Factors

Earthquake and Tsunamis Management

Earthquake management is the organization and management of the resources and responsibilities for dealing with all humanitarian aspects of emergencies. The aim is to reduce the harmful effects of the hazards. The earthquake management includes steps from pre-earthquake risk reduction to post-earthquake recovery.

1. Risk Recognition – Certain areas are more vulnerable to earthquakes than others, so risk recognition is the first step.
2. Earthquake monitoring system/Early warning system– Making a precise forecast about the occurrence of an earthquake in a region is still a difficult proposition. Seismologists are increasingly concentrating on the aspect of earthquake forecasting.
   • It will help in reducing the impact of upcoming disasters.
   • Example: – Japan has an earthquake early warning system that uses electronic signals that reach faster than earthquake waves.
3. Structural Solution– Past earthquakes show that over 95% of the lives lost were due to the collapse of buildings that were not earthquake resistant. But, the construction of such quake-resistant buildings is more expensive than ordinary buildings. Therefore, a cost-effective solution remains a challenge for a country like India. Seismic strengthening can be done through prioritization of structures and to implement this, it is important to have an earthquake hazard map for various zones according to the vulnerability.