EARTHQUAKE - GEOGRAPHY

EARTHQUAKE - GEOGRAPHY

News: Powerful earthquakes in Turkey and Syria leave over 3,800 dead

What's in the news?

●       A major earthquake struck Turkey and Syria on February 6, killing more than 3,800 people and flattening thousands of buildings as rescuers dug with bare hands for survivors.

●       Dozens of nations pledged aid after the 7.8-magnitude quake, which hit as people were still sleeping and amid freezing weather that has hampered emergency efforts.

Earthquake:

●       An earthquake is the shaking of the Earth when two blocks of the earth suddenly slip past one another.

●       The surface where they slip is called the fault or fault plane.

●       The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.

Types of Earthquakes:

1. Tectonic: A tectonic earthquake is one that occurs when the earth's crust breaks due to geological forces on rocks and adjoining plates that cause physical and chemical changes.

2. Volcanic: A volcanic earthquake is any earthquake that results from tectonic forces which occur in conjunction with volcanic activity.

3. Collapse: A collapse earthquake are small earthquakes in underground caverns and mines that are caused by seismic waves produced from the explosion of rock on the surface.

4. Explosion: An explosion earthquake is an earthquake that is the result of the detonation of a nuclear and/or chemical device.

5. Reservoir induced Earthquakes: These occur in the areas of huge reservoirs like dams.

What are seismic waves?

1. Any elastic material when subjected to stress, stretches in a proportional way, until the elastic limit is reached. When the elastic limit is crossed, it breaks.
2. Similarly, the Earth also has an elastic limit and when the stress is higher than this limit, it breaks. Then there is a generation of heat, and energy is released.
3. Since the material is elastic, the energy is released in the form of elastic waves. These propagate to a distance determined by the extent of the impact. These are known as seismic waves.

Seismic Zones of India:

●       Seismic zones in Indian subcontinent is divided into four seismic zones (II, III, IV, and V) based on

○       scientific inputs relating to seismicity

○       earthquakes occurred in the past and

○       tectonic setup of the region.

●       The Bureau of Indian Standards is the official agency for publishing the seismic hazard maps and codes.

●       Seismic Active Zones:

○       Seismic Zone II

○       Seismic Zone III

○       Seismic Zone IV

○       Seismic Zone V

Richter Scale:

●       This is a measure of the magnitude of an earthquake was first defined by Charles F. Richter of the California Institute of Technology, U.S., in 1935.

●       Richter scale magnitudes are expressed as a whole number and a decimal part, for example 6.3 or 5.2.

●       Since it is a logarithmic scale, an increase of the whole number by one unit signifies a tenfold increase in the amplitude of the wave and 31 times increase of the energy released.

Types of Seismic Waves:

1. Body waves:

●       Traveling through the interior of the earth, body waves arrive before the surface waves emitted by an earthquake. These waves are of a higher frequency than surface waves.

●       Body waves are of two types such as

○       Primary waves (also called P-waves, or pressure waves)

○       Secondary waves (S-waves, or shear waves).

2. Surface waves:

●       Travelling only through the crust, surface waves are of a lower frequency than body waves. Though they arrive after body waves, it is surface waves that are almost entirely responsible for the damage and destruction associated with earthquakes.

●       The two types of surface waves are named Love waves and Rayleigh waves.

Speed of different waves in descending order: Primary Waves > Secondary Waves > Love Waves > Rayleigh Waves.

Emergence of Shadow Zone:

●       Earthquake waves get recorded on seismo- graphs located at far-off locations.

●       However, there exist some specific areas where the waves are not reported. Such a zone is called the ‘shadow zone’.

●       P and S waves radiate spherically away from an earthquake's hypocenter (or focus) in all directions and return to the surface by many paths. However, P waves are refracted by the liquid outer core and are not detected between 105° and 145°.

●       S waves cannot pass through the liquid outer core and are not detected beyond 103°.

●       Thus, a zone between 105° and 145° from the epicentre (approximately) is identified as the shadow zone for both the types of waves.

Causes of Earthquakes in India:

1. North-East region: Collision zones of the Himalayan belt and Sumatran belt. Kopili fault is currently the most active seismic zone in North East India.

2. Himalayan belt: Collision between Indo-Austral plate with Eurasian plate and Burma Plate with Java Sumatra.

3. Andaman and Nicobar Islands: Seafloor displacement and underwater volcanoes.

4. Deccan Plateau: Fault line and energy build-up along the fault line of the river Bhima (Krishna) near Latur and Osmanabad (Maharashtra).

5. Anthropogenic: Increasing population and unscientific land use in construction.

Impact of Earthquakes:

●       Loss of Human Lives

●       Change in River Course

●       Landslide

●       Tsunami

●       Floods

●       Avalanches

●       Damage to property

STEPS TAKEN BY GOVERNMENT TO MANAGE EARTHQUAKES:

1. National Center for Seismology, Ministry of Earth Sciences: For Earthquake surveillance and Hazard Reporting.
2. National Earthquake Risk Mitigation Project.
3. National Building Code (NBC): To regulate building construction.