Earthquakes - Major Causes of Earthquakes. Focus, Epicentre and seismic waves
Introduction and Causes of Earthquakes * Earthquakes are sudden vibrations of the lithosphere. * Over 10 million earthquakes occur each year, but most of them are too mild to be felt. * They cause loss of lives and property. Major Causes of Earthquakes * Most earthquakes are the result of plate movements. * When plates move, friction causes pressure to build up slowly in the plate and energy is stored. * When the pressure exceeds the strength of rock, the rock breaks. * This releases the stored energy and produces seismic waves. * These waves move out in all directions and cause the ground to shake, resulting in earthquakes. * Some earthquakes are caused by volcanic eruptions. Focus, Epicentre and seismic waves * Some earthquakes are mild, some others are rather destructive. * The severity of an earthquake depends on the amount of energy that is released. * The point of origin of shock waves is usually at a certain depth in the earth's crust, known as focus. * The epicentre is the point on the Earth's surface vertically above the focus. * Shock waves that travel outwards from the epicentre at different speeds in all directions are called seismic waves. * These waves cause the ground to shake, resulting in earthquakes. Ways of classification Types of Earthquakes . By intensity * Felt by Human * Unfelt By Human * Felt earthquakes * Unfelt earthquakes 2.
Earthquakes - overview.
Earthquakes General An earthquake is a shaking or trembling of the crust of the earth caused by underground volcanic action or by the breaking and shifting of rock beneath the surface. The volcanic action and shifting rocks create strain which continues to build to a sudden release of pressure resulting in a shock wave. The vibrations produced in the crust can vary from barely noticeable to enormously destructive. Shock waves can be classified into two broad categories. Waves that send particles oscillating back and forth in the same direction as the waves are traveling are called primary. Primary waves, sometimes called compressional waves, travel through the earth beneath the crust. Secondary waves cause vibrations which move perpendicular to the wave. These waves travel on the surface of the earth and move much slower than primary waves. Thus, when an earthquake occurs, seismic centers throughout the world record primary waves before the secondary waves arrive. Historical Overview Earthquakes have captured the imagination of people living in earthquake prone regions since ancient times. Ancient Greek philosophers thought quakes were caused by subterranean winds, while others blamed them on fires in the bowels of the earth. About AD 130, a Chinese scholar named Chang Heng reasoned that waves must ripple through the earth from the source of an earthquake. By 1859, an
What are Earthquakes?
What are Earthquakes? General An earthquake is a shaking or trembling of the crust of the earth caused by underground volcanic action or by the breaking and shifting of rock beneath the surface. The volcanic action and shifting rocks create strain which continues to build to a sudden release of pressure resulting in a shock wave. The vibrations produced in the crust can vary from barely noticeable to enormously destructive. Shock waves can be classified into two broad categories. Waves that send particles oscillating back and forth in the same direction as the waves are travelling are called primary. Primary waves, sometimes called compressional waves, travel through the earth beneath the crust. Secondary waves cause vibrations which move perpendicular to the wave. These waves travel on the surface of the earth and move much slower than primary waves. Thus, when an earthquake occurs, seismic centres throughout the world record primary waves before the secondary waves arrive. Historical Overview Earthquakes have captured the imagination of people living in earthquake prone regions since ancient times. Ancient Greek philosophers thought quakes were caused by subterranean winds, while others blamed them on fires in the bowels of the earth. About AD 130, a Chinese scholar named Chang Heng reasoned that waves must ripple through the earth from the source of an earthquake. By
Geography essay - earthquakes
At a conservative margin two plates try to slide past each other slowly. Quite often, the two plates stick and pressure builds up; the release of this pressure creates a severe earthquake. There are no volcanic eruptions along conservative plate margins because the crust is neither being created nor destroyed. The classic example of a conservative plate margin is the San Andreas Fault in California. The North American and Pacific Plates are moving past each other at this margin, which is the location of many earthquakes. These earthquakes are caused by the accumulation and release of strain as the two plates slide past each other. The vast majority of Earthquakes occur along plate margins. In fact the locations of the earthquakes and the kind of ruptures they produce help scientists define the plate margin. Many earthquakes form a narrow spread at some plate margins than others; generally speaking, the earthquakes at destructive plate margins have a greater spread and therefore affect more places than at conservative plate margins. According to plate tectonic theory, huge slabs of plates are in constant movement caused by convection currents, a lot of pressure builds up at the plate margins, which when released causes a sudden jolt or earthquake. This accounts for a large number of earthquakes that occur at plate margins. The fact that the most deadly earthquakes occur at
What Are Earthquakes?
What Are Earthquakes? Introduction: Living in England as a public we know next to nothing about earthquakes, compared to what people know about them in America, the reason they know so much about them is because they have to deal with them on a very regular basis. This article is put together to inform the public of Great Britain about what earthquakes do and how they are caused. So What Are Earthquakes: Earthquakes are, vibrations produced in the earth's crust when rocks in which elastic strain has been building up suddenly rupture, and then rebound. What Are Seismic Wave That Are Produced From Earthquakes? Seismic waves are waves of energy that are produced from the rebound of the earths crust after the rocks reach there elastic limit and rupture. There are two types of seismic waves these are P waves (primary Waves) and S Waves (Shear Waves). P Waves: P waves are longitudinal Waves. This means they cause the particles to vibrate in the direction of the shockwave. P waves are the faster of the two waves and therefore reach the epicenter of the earthquake faster than S waves. P waves also can travel through liquid and solids so this means that they can travel through any part of the earths
Hazard - Earthquakes.
Case Study: Earthquakes Name of Hazard: Earthquake Where: Kobe, Japan Date: 17 January 1995, 5:46am Causes: The earthquake due to Kobe being situated on a minor fault, known as the Nojima fault, which lies above a destructive plate margin. This is where the Pacific, Eurasian, and Philippine plates meet. On contact with the Eurasian plate, the Philippine plate gets forced downwards. This has created volcanic activity and means that Japan is under constant threat from severe earthquakes. As you can see from the diagram below Japan has 4 plate pushing against oneanother which could quadruple the size of an earthquake. The movement of these plates as showed in the diagrams below release a huge amount of pressure, which is released as waves. These waves move the earths crust both horizontally and vertically, as was the case with Kobe. Effects: As with most hazards there were two kinds of effects, Direct, and Secondary. Kobe is no exception and experienced both. Direct: When the quake struct many of the poorly constructed building in the area collapsed, over 200,000 buildings collapsing whilst the quake raged for 30 seconds. The many ports in the Kobe area were damaged instantly. Train lines and the famous expressway also received damage in the earthquake. One section of the line actually collapsed, and many others broke in places of large movement. This being because
Earthquakes and Volcanoes
Earthquakes and Volcanoes The 4 layers making up the Earth . The inner Core.This is the hottest part of the earth. It is solid. 2. The outer Core. This core is sorrounding the inner core. 3. The mantle.This is made up of semi- molten rock called magma. In the upper part of the mantle it is hard, but in the lower down it is soft and beginning to melt. 4. The crust is the outer layer of earth. It is the solid rock on which we live. It is divided into 2 : . The continental crust which carries land 2. The oceanic crust which carries water. Earthquakes and volcanic eruptions are caused by movements within the Earth. The crust is not all in one piece but is divided into alot of sections called plates. Underneath the plates there is the mantle. The plates float on the mantle and move about very slowly. The place where plates meat is called a plate boundary. Amongst those many gentle movements, occasionaly one may be violent. The movement of these plates boundaries can cause earthquakes and volcanic eruptions. The different types of plate movements . Constructive margins This is when two plates move away from eachother. Magma rises to fill the gap and forms new oceanic crust. This causes the formation of new volcanoes and earthquake activity. . Destructive margins This is when plates containing oceanic crust moves towards plates of continental crust. Where
Geography Coursework on Earthquakes
Geography Coursework on Earthquakes An earthquake is a shaking or trembling of the crust of the earth caused by underground volcanic action or by the breaking and shifting of rock beneath the surface. The volcanic action and shifting rocks create strain which continues to build to a sudden release of pressure resulting in a shock wave. The vibrations produced in the crust can vary from barely noticeable to enormously destructive. Shock waves can be classified into two broad categories. Waves that send particles oscillating back and forth in the same direction as the waves are traveling are called primary. Primary waves, sometimes called compressional waves, travel through the earth beneath the crust. Secondary waves cause vibrations which move perpendicular to the wave. These waves travel on the surface of the earth and move much slower than primary waves. Thus, when an earthquake occurs, seismic centers throughout the world record primary waves before the secondary waves arrive. Historical Overview Earthquakes have captured the imagination of people living in earthquake prone regions since ancient times. Ancient Greek philosophers thought quakes were caused by subterranean winds, while others blamed them on fires in the bowels of the earth. About AD 130, a Chinese scholar named Chang Heng reasoned that waves must ripple through the earth from the source of an earthquake.
Effects of Earthquakes.
Earthquakes General An earthquake is a shaking or trembling of the crust of the earth caused by underground volcanic action or by the breaking and shifting of rock beneath the surface. The volcanic action and shifting rocks create strain which continues to build to a sudden release of pressure resulting in a shock wave. The vibrations produced in the crust can vary from barely noticeable to enormously destructive. Shock waves can be classified into two broad categories. Waves that send particles oscillating back and forth in the same direction as the waves are traveling are called primary. Primary waves, sometimes called compressional waves, travel through the earth beneath the crust. Secondary waves cause vibrations which move perpendicular to the wave. These waves travel on the surface of the earth and move much slower than primary waves. Thus, when an earthquake occurs, seismic centers throughout the world record primary waves before the secondary waves arrive. Historical Overview Earthquakes have captured the imagination of people living in earthquake prone regions since ancient times. Ancient Greek philosophers thought quakes were caused by subterranean winds, while others blamed them on fires in the bowels of the earth. About AD 130, a Chinese scholar named Chang Heng reasoned that waves must ripple through the earth from the source of an earthquake. By 1859, an
Reasons for Earthquakes
Earthquakes Earthquake is one of the natural calamities. Its origin can be traced to the early days of earth formation. It is responsible for a lot of damage to living and non-living beings. For many centuries man didn’t know why earthquakes occur and how they occur and to what extent they would damage. He only felt that mother earth was angry with him and so caused the earthquake and he always feared it. It was left to Aristotle, the great Greek philosopher, to relate the phenomenon of earthquake to physical factors. According to Aristotle, when the air compressed within the arch escapes, it shakes some part of the land. This emission is called volcanic activity. When the volcano bursts, lots of lava, gas etc come out of the earth and fail out. This causes pressure and imbalance and results in producing earthquake waves in the surrounding areas. It was thus identified that volcanic activity is one of the reasons for earthquakes. The volcanic activity results in faulting. To fill up the new faults the movement of earth takes place. This causes tremor. The second reason is isocratic adjustment. The surface of the earth has certain raised up blocks and certain depressed blocks. They keep the balance of the earth, when it moves revolving on units of axis. These raised up blocks are washed down due to various reasons and cause imbalance. Then also the earthquakes occur to
