Tag: earthquake

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

Earthquake is a movement of tremor of the earth's crust. It originated naturally and below the surface. An earthquake produces infrasound before the mainshock wave begins. Infrasound is low-frequency sound less than 20hz. It can travel hundreds of km through the earth's surface. So by detecting this sound, we can predict an earthquake.

• 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

The processes for building new land and coastal plains are called constructive forces. Three of the main constructive forces are crustal deformation, volcanic eruptions, and deposition of sediment.

Crustal deformation occurs when the shape of land (or crust) is changed or deformed. One of the main causes is movement of the Earth's plates. When the plates collide or push toward each other, pressure builds. This can cause two things to happen. The rock can either fold or fault.

Both A and B

Coastal plains are formed when ocean levels fall on continental shelves that are at sea level, or when rivers carry sediment to areas of the ocean. These plains can take hundreds of years to form, and a few are found hundreds of miles inland.

1. Earthquake may sometimes create new coastal plains, by the emergence of a portion of ocean floor.

2. Submergence of coastal land may result in the formation of bays and gulfs which are favorable sites for the development of ports harbors.

3.Earthquakes result in the formation of hot springs and geyser beneficial for medicinal purposes

• Vertical displacement of overlying water causes a stark difference between the elevation of the ocean floor due to which water from higher elevation quickly move towards lower elevation seafloor. 
• This generates very high waves which travel towards the coastal regions and are known as tsunami or harbour waves. Hence option C is correct.
• Note- Horizontal displacement does not cause displacement of a very significant amount of water hence cannot generate tsunamis.

July 9, 1958

On 9 July 1958, a 7.8Mw strike-slip earthquake in southeast Alaska caused 90 million tonnes of rock and ice to drop into the deep water at the head of Lituya Bay. The block fell almost vertically and hit the water with sufficient force to create a wave that surged up the opposite side of the head of the bay to a height of 524 m, and was still many tens of metres high further down the bay, when it carried eyewitnesses Howard Ulrich and his son Howard Jr. over the trees in their fishing boat. They were washed back into the bay and both survived

• The primary effect of the earthquake- shaking of earth's surface.
• Secondary effects- effects caused by primary effect i.e. effects caused by the shaking of the earth's surface viz tsunami, landslides, and fires.
• Hence all options are correct.

The primary destructive effect of Earthquakes include the damage to man-made structures, such as roads, bridges, dams, and buildings from the ground motion depends on the type of construction:

1. concrete and masonry structures are brittle and thus more susceptible to damage and collapse

2. damage to wood and steel structures is far less because of its flexibility.