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Seismology

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Omal Vindula

on 3 July 2013

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Transcript of Seismology

Seismology
Seismology is the study of earthquakes and seismic waves that move through and around the earth. A seismologist is a scientist who studies earthquakes and seismic waves. They play a major role in predicting the behavior of the crust and core of the earth. They also warn about the disastrous events that occurs in nature related to seismic activities such as Tsunamis and earth quakes and helps to save numerous human and wild life...
What is seismology?
What Are Seismic Waves?
Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs. The place where the explosion of the earth occurred is known as the epicenter. Seismic waves are generated from these epicenter mainly due to volcanic eruptions and shifting of tectonic plates.
Seismic waves can be categorized into 2 types according to the way they travel through the earth.
They are,
Body Waves
Surface Waves


Seismic waves are.. Two types... They are....
Body Waves
Traveling through the interior of the earth, body waves arrive before the surface waves emitted by an earthquake. These waves are of a higher frequency than surface waves.There are two types of body wave
Primary waves
Secondary waves






Surface Waves
A surface wave is a mechanical wave that propagates along the interface between differing media, usually two fluids with different densities. Its motion is restricted to near the ground surface. A surface wave can also be an electromagnetic wave.
Surface waves in earthquakes can be divided into two types.
Love Waves
Rayleigh Waves


Pressure waves or Primary waves, are longitudinal waves that involve compression and rarefaction in the direction that the wave is traveling. P-waves are the fastest waves in solids and are therefore the first waves appear on a seismogram. When subjected to a P-wave, particles will move to the same direction of the wave which the direction of the wave energy is traveling.
S-waves, also called secondary waves, are transverse waves that involve motion perpendicular to the direction of propagation. S-waves appear later than P-waves on a seismogram. Fluids cannot support this perpendicular motion, so S-waves only travel in solids. P-waves travel in both solids and fluids. S-waves will move the particles up and down and side by side, perpendicular to the direction of the wave. Therefore S-wave is a type of a transverse wave.
Love waves were named in respect for A.E.H Love, who discovered these type of waves. Love wave is the fastest surface wave among the two. Its motion is essentially that of S waves that have no vertical displacement; it moves the ground from side to side in a horizontal plane but at right angles to the direction of propagation. The horizontal shaking of Love waves is particularly damaging to the foundations of structures.
P-Waves
S-Waves
The second type of surface wave is known as a Rayleigh wave. This type of waves were discovered by John William Rayleigh.
Like rolling ocean waves, Rayleigh waves wave move both vertically and horizontally in a vertical plane pointed in the direction in which the waves are traveling. Shaking effect of earthquakes are mainly caused by Rayleigh waves. They can be much larger than other types of waves.
Rayleigh Wave
Love Wave
Rayleigh waves
Earthquakes
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes are measured using observations from seismometers.
Earthquakes may occur due to shifting of tectonic plates and also due to volcanic eruptions. Earthquakes usually occur in the places where tectonic plates meet.
The strength of the earthquake varies from one to another. The strength of an earthquake is measured by using a scale known as the Richter scale. Earthquakes with a value higher than 6.0 in the Richter scale are considered as strong earthquakes. The largest earthquake recorded was in Chile 1960(9.5 magnitude)
Earthquakes can also occur due to gigantic bomb explosions. They can occur in the ground as well as in the sea. When earthquakes occur in the sea, Tsunamis may rise from the ocean.
Earthquakes claim thousands of lives every year. There's no way to prevent them but to stay away from it.
Definitions in Seismology
Epicenter
is the place where earth quake occurs.
A
seismic shadow zone
is an area of the Earth's surface where seismographs cannot detect an earthquake after its seismic waves have passed through the Earth.
Fault
is a crack on earth's surface, along which rocks move.
Tsunami
is a very big wave created in the ocean due to an underwater earthquake
There are 2 scales that we use to measure the magnitude of earthquakes. They are Mercalli scale(not commonly used) and the Richter scale(commonly used)
Seismograph
is a tool used to measure and record vibrations of the earth and ground.
Seismograph
is a piece of paper that seismograph records its information
Tsunami
Volcanic Eruptions
Deep within the Earth it is so hot that some rocks slowly melt and become a thick flowing substance called magma. Because it is lighter than the solid rock around it, magma rises and collects in magma chambers. Eventually some of the magma pushes through vents and fissures in the Earth's surface. A volcanic eruption occurs! Magma that has erupted is called lava.
There are two types of volcanic eruptions,explosive and non explosive. How explosive an eruption is depends on the density of the magma. If density of magma is less, gases can escape easily from the volcano. When this type of magma erupts, it flows out of the volcano. Lava flows rarely kill people because they move slowly enough for people to get out of their way. Lava flows, however, can cause considerable destruction. If density of magma high, gases cannot escape easily. Pressure builds up until the gases escape violently and explode. In this type of eruption, the magma blasts into the air and breaks apart into pieces called 'tephra' which can range in size from tiny particles of ash to boulders.
Explosive volcanic eruptions can be dangerous and deadly. They can blast out clouds of hot tephra from top of a volcano. These fiery clouds race down mountainsides destroying almost everything in their path. Ash erupted into the sky falls back to Earth like powdery snow, but snow that won't melt. If thick enough, blankets of ash can suffocate plants, animals, and humans.This can cause the death of the plants in that area because when plants are covered with ash the photosynthesis stops due to lack of sunlight. When hot volcanic materials mix with water from streams or melted snow and ice, mudflows form. Mudflows have buried entire communities located near erupting volcanoes. Because there may be hundreds or thousands of years between volcanic eruptions or even more.
Volcanic eruption of Mount Pelée(Martinique island) in 1902 is considered as the deadliest volcanic eruption in 20th century .It caused 33000 causalities and a vast destruction to the island.
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water. It is caused mainly by earthquakes and volcanic eruption under the sea. Its can also occur due to the detonation of bombs under the sea.
Tsunami waves do not resemble normal sea waves, because their wavelength is far longer. Rather than appearing as a breaking wave, a tsunami may initially resemble a rapidly rising tide, and for this reason they are often referred to as tidal waves. But, tides do not play any part in the generation of tsunamis.
Geologists, oceanographers, and seismologists analyze each earthquake and based on many factors may or may not issue a tsunami warning. However, there are some warning signs of an impending tsunami, and automated systems can provide warnings immediately after an earthquake in time to save lives.
Thank you...
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