Chapter 3 - Earthquake and Volcanoes by CareerIAS.in Free IAS online coaching
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EARTHQUAKE &
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VOLCANO
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Chapter - 3
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Objectives
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An earthquake is the perceptible shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's crust that creates seismic waves. Earthquake intensity is measured on the modified Mercalli scale, which ranges from one to 12, depending upon the intensity. Earthquake magnitude is measured on the Richter scale (named after the seismologist who devised it), which rates them on a scale of one to nine. Earthquakes waves are transmitted through materials in Earth and along Earth’s Surface. Earthquake waves are called seismic waves. In its most general sense, the word earthquake is used to describe any seismic event — whether natural or caused by humans — that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults, but also by other events such as volcanic activity, landslides, mine blasts, and nuclear tests.
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Introduction
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Earthquake Features of Earthquake Earthquake Zones Volcano and its Types Hotspot
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CareerIAS.in
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An earthquake is the perceptible shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's crust that creates seismic waves.
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Movement along a fault releases strain energy is potential energy that builds up in rock when it is bent. When this potential energy is released, it moves outward from the fault in the form of seismic waves. The Point inside Earth where this movement first occur and energy is released is called the focus of an earthquake. The point on Earth’s Surface located directly above the Earthquake focus is called the Epicentre of the Earthquake.
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There are three main stages to an earthquake: • Foreshocks relate to the initial shattering of obstructions or bonds along the failure plane. • Principal shock is the most severe shock. It may last from just a few seconds to a couple of minutes. • Aftershocks recur as the shockwaves travel around the Earth. They generally decrease in frequency and intensity over time, but may occur over a period of several days to several months. They have great potential to cause damage, as structures have already been weakened by the principal shock.
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Earthquake Focus and Epicentre
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Earthquake features
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There are three main types of fault, all of which may cause an earthquake: normal, reverse and strike-slip.
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Normal and reverse faulting are examples of dip-slip, where the displacement along the fault is in the direction of dip and movement on them involves a vertical component. Normal faults occur mainly in areas where the crust is being extended such as a divergent boundary. Reverse faults occur in areas where the crust is being shortened such as at a convergent boundary. Strike-slip faults are steep structures where the two sides of the fault slip horizontally past each other; transform boundaries are a particular type of strike-slip fault. Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip; this is known as oblique slip.
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These are huge ‘tidal waves’ caused by the displacement of the sea bed. Displacement may be caused by an earthquake, but may also be caused by the slumping of sediments around the coast, or especially near to deep-sea trenches. Whole series of waves may be set up, which have wavelengths of several hundred kilometres. Because they posses so much energy, they may race across the ocean for thousands of kilometres at speeds of up to 900 km per hour – a large tsunami can cross the Pacific in about 24 hours. The height of a tsunami is directly proportional to the depth of the water across which it is travelling. In the middle of the deep ocean, a tsunami wave may be relatively unnoticeable. Therefore its effects are at their most intense in shallow waters, so shelving coastlines are particularly vulnerable to damage should a tsunami hit. Most dangerous tsunamis occur in the Pacific Ocean, as it is surrounded by tectonic plate margins. The Pacific Tsunami Warning System has been set up, which triggers warning alarms if an earthquake greater than 6.5 on the Richter scale is detected by one of its 69 seismic stations across the area. Tsunami warnings can then be issued, and appropriate action taken in areas at risk.
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Earthquake fault types
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Earthquake Causing Tsunami
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4
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earthquake zoning map of India divides India into 4 seismic zones
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Zone 5 Zone 5 covers the areas with the highest risks zone that suffers earthquakes of intensity MSK IX or greater. Structural designers use this factor for earthquake resistant design of structures in Zone 5. It is referred to as the Very High Damage Risk Zone. The region of Kashmir, the western and central Himalayas, North and Middle Bihar, the North-East Indian region and the Rann of Kutch fall in this zone.
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Earthquake zones of India
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5
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Zone 4 This zone is called the High Damage Risk Zone and covers areas liable to MSK VIII. The Indo-Gangetic basin and the capital of the country (Delhi), Jammu and Kashmir fall in Zone 4. In Maharashtra, the Patan area (Koyananager) is also in zone no-4. In Bihar the northern part of the state like- Raksaul, Near the border of India and Nepal, is also in zone no-4. Zone 3 The Andaman and Nicobar Islands, parts of Kashmir, Western Himalayas fall under this zone. This zone is classified as Moderate Damage Risk Zone which is liable to MSK VII. and also 7.8 Zone 2 This region is liable to MSK VI or less and is classified as the Low Damage Risk Zone.
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Uttarakhand became first Indian state to install a system to detect earthquakes and disseminate warnings. The first system has been installed in its capital Dehradun which will issue warnings 1-40 seconds before earthquakes of magnitude 5 or more occur. The system is designed and manufactured by Italian firm, Space Dynamics which already has installed it in Japan, Italy and US. Features of earthquake early warning The system is incorporated with sensors which are capable to detect P (Primary) and S (Secondary) waves generated during an earthquake. It is capable to detect the harmless P wave, which travels faster than the S wave for advance warning. The system has the earliest detection among those currently in use worldwide. The second system will be established at Pithoragarh in the Kumaon region of Uttarakhand. According to the Bureau of Indian Standards (BIS), Uttarakhand falls under seismic zone V i.e. High-Risk Seismic Zone. Apart from it, Jammu and Kashmir, Himachal Pradesh, Rann of Kutch (Gujarat), Northern Bihar and Andaman & Nicobar Islands also fall under this seismic zone.
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India’s first earthquake early warning system
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Volcano
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A volcano is a rupture on the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. Where does magma come from? Earth’s crust is so cool that it’s brittle. Nevertheless, hot, melted rock makes its way to Earth’s surface and comes out of volcanoes as lava. What makes rock melt so that it becomes magma and then explodes out onto Earth’s surface? Temperature You know that heating ice, butter, and a lot of other solids will make them melt. At high enough temperatures, solid rock will melt too. However, the lithosphere is not hot enough to melt rock. Pressure and water There are two other ways to make rock melt that are very important. One way is to reduce the pressure. The other way is to mix water with the hot rock. The conditions needed to melt rock are very special and they exist inside our planet.
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"Hotspots" is the name given to volcanic areas believed to be formed by mantle plumes, which are hypothesized to be columns of hot material rising from the core-mantle boundary in a fixed space that causes large-volume melting. Because tectonic plates move across them, each volcano becomes dormant and is eventually reformed as the plate advances over the postulated plume.
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Volcanoes have a lifetime Volcanoes are not permanent features on the surface of Earth. They have a lifetime that occurs in phases. Volcanoes are described according to the phase they are in. The three phases are active, dormant, and extinct. An active volcano is the most vigorous kind of volcano. Active volcanoes are erupting or have erupted recently, and are expected to erupt again in the near future. However, volcanic activity during the life of a volcano doesn’t last forever A dormant volcano is a quiet volcano. Dormant volcanoes are not active now, but may become active again in the future. Most of the volcanoes along the northern Pacific coast of North America are dormant. An extinct volcano is at the end of its life and is no longer able to erupt. As the volcano erodes, a core of now-solid magma, called a volcanic neck, may be exposed.
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Hotspot
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The life of a volcano
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Types of Volcanoes
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Cinder cone volcanoes also called scoria conesare the most common type of volcano and are the symmetrical cone shaped volcanoes we typically think of. They may occur as single volcanoes or as secondary volcanoes on the sides of stratovolcanoes or shieldvolcanoes.
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Shield volcano A shield volcano is a type of volcano usually built almost entirely of fluid magma flows. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from strato volcanoes. This results in the steady accumulation of broad sheets of lava, building up the shield volcano's distinctive form.
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Fissure Volcano fissure vent, also known as a volcanic fissure or eruption fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is often a few meters wide and may be many kilometers long. Fissure vents can cause large flood basalts which run first in lava channels and later in lava tubes.
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Caldera Volcano A caldera is a cauldron-like volcanic feature on large central volcanoes, a special sort of volcanic crater (from one to several kilometers in diameter), formed when a magma chamber was emptied. The depression then originated either in very big explosive eruptions or in erosion and collapse of the magma chamber roof. The previous emptying of this magma chamber is often accomplished during a series of effusive eruptions in the volcanic system, even kilometers away from the magma chamber itself.
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List of volcanoes in India Barren Island , Narcondam, Deccan Traps, Baratang, Dhinodhar Hills, Dhosi Hill
