Geology and Earth Structure

Isoseismic Line is the line connecting all points on the surface of the earth where the intensity is the same. These lines show great irregularity in their form. 

According to the Bureau of Indian Standards, India is divided into four seismic zones (II, III, IV, and V) based on the intensity of earthquake risk.

During an earthquake, surface waves are the seismic waves that cause the most damage. Unlike other seismic waves that move deep inside the Earth, surface waves move along just under the surface of the Earth like waves in water. Surface waves are the slowest seismic waves and are the final waves to hit an area after an earthquake. First, P-waves move through compression through the deep layers of the Earth. They result in minimal damage. The second group of waves is S-waves. They move up and down starting deeper in the Earth. Stronger S-waves do some damage when they reach the surface. Surface waves move in last. Their slow roll just under the surface provides the greatest risk for damage to man-made structures and changes to natural landforms

• Earth's crust is divided into various plates which float on hot magma layer called asthenosphere. When these plates move, they interact with each other which releases energy, that is felt on the surface of earth as tremors or shaking movement, which is termed as earthquake.
  
• Cyclones, thunderstorms and lightenings are the atmospheric phenomena and are not related with earth's surface, hence these 3 options are incorrect.

An earthquake  is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves.

An earthquake's point of initial rupture is called its focus or hypocenter. The epicenter is the point at ground level directly above the hypocenter

Underwater earthquakes push water upward to create the initial movement, then gravity pulls the water downward, creating the horizontal force that forms the tsunami. The waves travel through the ocean in a similar fashion to ripples created by throwing a stone into a body of water.

Earthquakes occur often on the earth's crust that forms the sea floor; however, not all result in a tsunami. For a tsunami to form, the magnitude of the earthquake must measure a minimum of 7.0 on the Richter scale. Below this magnitude, the earthquake does not displace enough water to create the big wave. The movement must also lift or lower the sea bed. Sideways movement does not create the initial wave to start the process. The epicenter of the earthquake must be near the surface of the sea floor to cause the correct movement.

The biosphere is the global sum of all ecosystems. It includes lithosphere, atmosphere and hydrosphere. Earth's lithosphere includes the crust and the uppermost mantle, which constitute the hard and rigid outer layer of the Earth.

The lithosphere is the rigid outermost shell of a terrestrial-type planet, consisting of the crust and the uppermost part of the mantle.

The lithosphere is the rigid outer part of the earth, comprising the crust and the solid, outermost part of the upper mantle.

The oceanic lithosphere is generally thinner than the continental lithosphere, typically ranging from 5 to 100 km, with 10-12 km being a common textbook figure for the crustal portion.

The solid portion of the earth is called the Lithosphere. It comprises the rocks of the earth’s crust and the thin layers of soil that contain nutrient elements which sustain organisms.

The lithosphere is the solid, outer part of the Earth. The lithosphere includes the brittle upper portion of the mantle and the crust, the outermost layers of Earth's structure. It is bounded by the atmosphere above and the asthenosphere below.

The lithosphere is the rigid, outermost shell of the Earth, consisting of the crust and the upper mantle.

During an earthquake, surface waves cause the most damage. Unlike other seismic waves that move deep inside the Earth, surface waves move along just under the surface of the Earth like waves in water. Surface waves are the slowest seismic waves and are the final waves to hit an area after an earthquake. 

First, P-waves move through compression through the deep layers of the Earth. P-waves are also carried by air and water, causing them to make a sound when they hit the Earth's surface. They result in minimal damage. The second group of waves is S-waves. They move up and down starting deeper in the Earth, and they cannot travel through air or water. Stronger S-waves do some damage when they reach the surface. Surface waves move in last. Their slow roll just under the surface provides the greatest risk for damage to man-made structures and changes to natural landforms.

The oceanic crust is much thinner, ranging from 5 to 10 km thick. The continental crust has an average density of 3.0 g/cm3 and is composed primarily of felsic rock.