Bring out the relevance of seismic study in determining the structure of the interior of the earth. (150 Words)
The behavior of seismic waves in different layers of the earth provides the most authentic evidence about the composition & structure of the earth. The different types of waves generated during the occurrence of earthquake , are generally divided into 3 broad categories;-
a)Primary waves, b)Secondary waves ,c)surface waves.
Seismic Waves- both P-waves & S-waves travel faster through rigid material than through soft or plastic material. The velocities of these waves travelling through specific part of earth gives an indication of type of rocks there. Abrupt changes in seismic wave velocities indicate significant changes in earth’s interior.
Seismic waves passing through the earth are refracted in ways that show distinct discontinuities within earth’s interior & provide basis for the belief that earth has
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- a solid inner core,
- a liquid outer core,
- a soft asthenosphere,
- a rigid lithosphere.
Seismic vibrations follow property of light waves being reflected & refracted with change in medium. interference:-
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- NON HOMOGENEOUS- If earth were homogeneous solid, seismic waves would travel in straight line with a constant speed. But seismic waves arriving sooner at distant stations & later at closer stations indicate that earth is not a homogeneous , uniform mass but has physical properties that change with depth.
- SHADOW ZONE- Refraction at the boundary between the core & the mantle thus causes a p-wave shadow zone over part of earth’s surface i.e. zone where no P-waves are received between 103 & 143 deg. S- waves do not pass through the core . there is a huge shadow zone therefore outer core is liquid (as S-waves do not pass through liquid)
- SEISMIC TOMOGRAPHY – Here seismic waves are used as X-rays to analyse the velocity of seismic waves as they pass through earth in different directions with different temperatures. The tomography thus can be interpreted as “temperature maps”. Hot parts of the mantle being less dense than their surroundings will rise, whereas cool mantle will sink. Thus tomography can be used to outline the pattern flow in mantle
Thus seismic waves act as probes of earth’s Interior.
Write a note on the science and effectiveness of earthquake early warning system. (200 Words)
Earthquake can cause massive destruction. Hence, Early Earthquake warning system are required at places prone to earthquake to reduce the loss to life and property as caused by the recent Nepal earthquake. Such systems are operational in several countries like Japan, Mexico.
Earthquakes are caused by sudden release of energy from the Earth’s crust that creates seismic waves. However, different types of waves are sent out. Sensors detect the fast moving “P-wave” which is first to arrive and immediately transmit data to earthquake alert center where the size and location of quake is determined. Damage is caused by the “S-waves” and surface waves which arrive later and leaves a time gap for a message to be transmitted from the alert center to devices.
The seconds of early warning can allow people to take actions to protect life and property. Actions taken can include evacuating buildings, moving to safe locations, safely stopping vehicles, protecting sensitive devices. Even a few seconds of warning can enable protective actions such as:
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- Public: Citizens, including schoolchildren, drop, cover, and hold on; turn off stoves, safely stop vehicles.
- Businesses: Personnel move to safe locations, automated systems ensure elevators doors open, production lines are shut down, sensitive equipment is placed in a safe mode.
- Medical services: Surgeons, dentists, and others stop delicate procedures.
- Emergency responders: Open firehouse doors, personnel prepare and prioritize response decisions.
- Power infrastructure: Protect power stations and grid facilities from strong shaking.
However, there should be proper awareness among people through mock-drills to prevent situations of chaos and ensure right information regarding the use of the system. Any delay from sending the data must be reduced. Also, as same model cannot work for different regions, tailor-made systems for local fault system should be adopted after adequate research.
With suitable examples, write a note on the impact of earthquakes on the geography of an affected region. (200 Words)
Earthquakes can be disastrous to humans as well as the environment. They have immediate i.e. primary and secondary effects causing much destruction the effects on the geography of a region includes
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- Surface faulting – displacement of rocks along faults
- Subsidence: the earth‘s surface subsides or moves down in comparison to previous or sea level Ex : seen at many places in japan after 2011 Tohoku earthquake
- Tectonic uplift.
- Shifting of landmasses – Sumatra shifting due to the earthquake of 2004
- Liquefaction : when soils with a high water content are violently shaken they lose their mechanical strength and behave like a fluid and so buildings can literally sink. Ex: 2011 Japan earthquake
- Avalanches : avalanche is a rapid flow of snow down a sloping surface. occurred in the Himalayan region during the recent Nepal Earthquake
- Landslides – earthquakes often cause landslides, especially in steep river valleys and areas of weak rocks.
- Tsunami – an earthquake on the sea floor or close to the coast may cause huge waves. Ex : tsunami of 2004
- Change in course of rivers : generally occurs due to tectonic upliftment or subsidence Ex: change in course of Mississippi river following the Madrid earthquake
- Changes in the ocean, like formation of islands or submerging of existing islands due to earthquakes. (Formation of Islands in the Banda Aceh region of Indonesia)
What is ‘Pacific Ring of Fire’? Examine its relevance to recent natural disasters in Japan and Ecuador. (200 Words)
Pacific Ring of Fire is a geologically and volcanically active region that stretches from one side of the Pacific to the other.
It is also known as the circum-Pacific belt, a horseshoe-shaped basin that is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements
Formation:
The Ring of Fire is the direct result of plate tectonics and the movement and collisions of lithospheric plates. These plates, which constitute the outer layer of the planet, are constantly in motion atop the mantle. Sometimes they collide, pull apart, or slide alongside each other; resulting in convergent boundaries, divergent boundaries, and transform boundaries.
Its relation with disasters in Japan and Ecuador:
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- The island nation of Japan lies along the western edge of the Ring of Fire, and is one of the most tectonically active places on Earth Mount Fuji, Japan’s tallest and most famous mountain, is an active volcano in the Ring of Fire, which is situated at the tri junction of three plates((the Amur Plate, Okhotsk Plate, and Philippine Plate)
- Ecuador, which is situated on south American east pacific ocean, faces the boundary between the Nazca and South American tectonic plates. The Nazca plate, which makes up the Pacific Ocean floor in this region, is being pulled down and under the South American coast.