Vibration of the Earth produced by the rapid release of energy


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Vibration of the Earth produced by the rapid release of energy.

    • Vibration of the Earth produced by the rapid release of energy.
    • ….. Massive energy!
  • Earthquakes occur along plate boundaries at points called faults.

  • Energy is stored in the rocks which produces stress and strain… until the rock breaks! Releasing stored energy in the form of seismic waves.





The focus is the earthquake's underground point of origin or hypocenter.

  • The focus is the earthquake's underground point of origin or hypocenter.

  • The epicenter is the point on the Earth’s surface that is directly above the point where an earthquake originates or focus.





As we are dealing with a generally solid rigid plates, we can expect tremendous stress, strain and tension to build up as the plates bend, especially in the areas around the boundary of the plates. These stresses, strains and tensions produce stress and strain cracks on the plates, which are called faults.

  • As we are dealing with a generally solid rigid plates, we can expect tremendous stress, strain and tension to build up as the plates bend, especially in the areas around the boundary of the plates. These stresses, strains and tensions produce stress and strain cracks on the plates, which are called faults.



Strain - the result of stress or deformation

  • Strain - the result of stress or deformation

    • elastic deformation - when stresses are removed, rock returns to original shape
    • plastic deformation - permanent deformation. when stresses are removed, rock stays bent
    • rupture - breakage and fracturing of the rock, causing an earthquake.
  • Brittle materials break during elastic deformation.



Tectonic forces apply stress to rock in three basic forms

  • Tectonic forces apply stress to rock in three basic forms

  • 1. Compression: pushing together or compression

  • 2. Tension/Extensional : Stress that acts to lengthen an object or pull it apart.

  • 3. Shear/Transform: Stress that acts parallel to a surface. It can cause one object to slide over another. The most general definition is that shear acts to change the angles in an object.







When stress and strain on certain parts of the plates exceed the threshold that can be sustained by the elasticity of the rocks in that area, the plate ruptures, releasing strain energy which is called an earthquake.

  • When stress and strain on certain parts of the plates exceed the threshold that can be sustained by the elasticity of the rocks in that area, the plate ruptures, releasing strain energy which is called an earthquake.

  • This energy is transmitted through the plates in the form of seismic waves, heat and sound. The amount of energy released will determine the magnitude or strength of the earthquake.



A fault is a large crack in the Earth's crust where one part of the crust has moved against another part.

  • A fault is a large crack in the Earth's crust where one part of the crust has moved against another part.



The fault plane is where the action is. It is a flat surface that may be vertical or sloping. The line it makes on the Earth's surface is the fault trace.

  • The fault plane is where the action is. It is a flat surface that may be vertical or sloping. The line it makes on the Earth's surface is the fault trace.



Where the fault plane is sloping, the upper side is the hanging wall and the lower side is the footwall. When the fault plane is vertical, there is no hanging wall or footwall.

  • Where the fault plane is sloping, the upper side is the hanging wall and the lower side is the footwall. When the fault plane is vertical, there is no hanging wall or footwall.



There are three basic fault types

  • There are three basic fault types

  • Normal faults form when the hanging wall drops down.

  • The forces that create

  • normal faults are pulling

  • the sides apart, or

  • extensional.



There are three basic fault types

  • There are three basic fault types

  • 2. Reverse faults form when the hanging wall moves up.

  • The forces creating reverse

  • faults are compressional,

  • pushing the sides together.



3. Strike-slip faults

  • 3. Strike-slip faults

  • have walls that move sideways,

  • not up or down.

  • That is, the slip occurs along

  • the strike, not up or down the

  • dip.

  • In these faults the fault plane is

  • usually vertical, so there is no

  • hanging wall or footwall. The f

  • orces creating these faults are

  • lateral or horizontal, carrying

  • the sides past each other.

















1. Seismic Deformation

  • 1. Seismic Deformation

  • When an earthquake fault ruptures, it causes two types of deformation: static; and dynamic. Static deformation is the permanent displacement of the ground due to the event.

  • After the earthquake, the formerly straight line is distorted into a shape having increasing displacement near the fault, a process known as elastic rebound.



2. Seismic Waves

  • 2. Seismic Waves

  • The second type of deformation, dynamic motions, are essentially sound waves radiated from the earthquake as it ruptures. While most of the plate-tectonic energy driving fault ruptures is taken up by static deformation, up to 10% may dissipate immediately in the form of seismic waves.



There are two types of body waves

  • There are two types of body waves

  • P-Waves or Primary Waves

  • S-Waves or Secondary Waves





P waves arrive first. Primary, pressure waves.

  • P waves arrive first. Primary, pressure waves.

  • Analogous to sound waves.

  • Particle motion is along the direction of travel (propagation) of the wave, i.e., longitudinal waves.

  • P waves can travel through solids, liquids or gases.



Push-Pull Motion

  • Push-Pull Motion





P waves are compression waves - the wave pulse or pulses travels through the rock in a series of compression pulses. On either side of the compression the rock is stretched. The stretching and compression of the rock is relatively small, allowing the wave to travel very quickly.

  • P waves are compression waves - the wave pulse or pulses travels through the rock in a series of compression pulses. On either side of the compression the rock is stretched. The stretching and compression of the rock is relatively small, allowing the wave to travel very quickly.

  • A P earthquake waves arrive first and are heard and felt as a sharp thud.



S-shake or shear wave

  • S-shake or shear wave



S waves are characterized by a sideways movement. The rock materials are moved from side to side as the wave passes.

  • S waves are characterized by a sideways movement. The rock materials are moved from side to side as the wave passes.

  • S waves are like water waves, the wave pulses travel along by moving the medium from side to side. As the pulse moves along, each section of rope moves to the side then back again in succession. Rocks are more resistant to sideways motion so the S wave travels more slowly.



The surface waves are the slowest of the three earthquake wave types.

  • The surface waves are the slowest of the three earthquake wave types.

  • Two basic types of surface waves

  • Long Waves

  • 2. Rayleigh Waves









P-Waves travel through solid and liquid

  • P-Waves travel through solid and liquid



However, it turns out that S waves cannot travel through the core, and only P waves are recorded in some places:

  • However, it turns out that S waves cannot travel through the core, and only P waves are recorded in some places:



Seismic waves travel faster through denser material.

  • Seismic waves travel faster through denser material.

  • Because of this, the path traveled by a seismic wave is bent towards the surface.







The record of an earthquake, a seismograph, as recorded by a seismometer, will be a plot of vibrations versus time. On the seismograph, time is marked at regular intervals, so that we can determine the time of arrival of the first P-wave and the time of arrival of the first S-wave.  

  • The record of an earthquake, a seismograph, as recorded by a seismometer, will be a plot of vibrations versus time. On the seismograph, time is marked at regular intervals, so that we can determine the time of arrival of the first P-wave and the time of arrival of the first S-wave.  





There are at least 20 different types of measures

  • There are at least 20 different types of measures

  • 3 of them are the Mercalli scale, Richter scale, and the Moment Magnitude scale

  • Magnitude is a measurement of earthquake strength based on seismic waves and movement along faults



The intensity or strength of an earthquake is measured by seismologist in two main ways:

  • The intensity or strength of an earthquake is measured by seismologist in two main ways:

  • 1.The Richter Scale

  • measures the amount of energy that an earthquake releases

  • Each number of magnitude is 10x stronger than the number below it.



The Richter scale is a rating of the size of seismic waves as measured by a particular type of mechanical seismograph

  • The Richter scale is a rating of the size of seismic waves as measured by a particular type of mechanical seismograph

  • Developed in the 1930’s

  • All over the world, geologists used this for about 50 years

  • Electric seismographs eventually replaced the mechanical ones used in this scale

  • Provides accurate measurements for small, nearby earthquakes

  • Does not work for big, far ones



2. The Mercalli Scale

  • 2. The Mercalli Scale

  • Measures the amount of damage from an earthquake

  • Ranges from I to XII

  • Based on common earthquake occurrences such as "noticeable by people" "damage to buildings" chimneys collapse" "fissures open in the ground”.



Developed in the twentieth century to rate earthquakes according to their intensity

  • Developed in the twentieth century to rate earthquakes according to their intensity

  • The intensity of an earthquake is the strength of ground motion in a given place

  • Is not a precise measurement

  • But, the 12 steps explain the damage given to people, land surface, and buildings

  • The same earthquake could have different Mercalli ratings because of the different amount of damage in different spots



Geologists use this

  • Geologists use this

  • scale today

  • It’s a rating system that estimates the total energy released by an earthquake

  • Can be used for any kind of earthquakes, near or far

  • Some news reports may mention the Richter scale, but the magnitude number they quote is almost always the moment magnitude for that earthquake



The severe shaking provided by seismic waves can damage or destroy buildings and bridges, topple utility poles, and damage gas and water mains

  • The severe shaking provided by seismic waves can damage or destroy buildings and bridges, topple utility poles, and damage gas and water mains

  • With their side to side, up and down movement, S waves can damage or destroy buildings, bridges, and fracture gas mains.


















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