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    Earthquakes Earthquakes Presentation Transcript

    • Earthquakes
    • An Earthquake is…
      • the shaking and trembling that results from the movement of rock beneath Earth's surface
      • The movement of Earth's plates produces strong forces that squeeze or pull the rock in the crust
      • This is an example of stress, a force that acts on rock to change its volume or shape
    • Stress
      • There are three different types of stress that occur on the crust, shearing, tension, and compression
      • These forces cause some rocks to become fragile and they snap
      • Some other rocks tend to bend slowly like road tar softened by the suns heat
    • Faults
      • A fault is a break in the crust where slabs of crust slip past each other. The rocks on both sides of a fault can move up or down or sideways
      • When enough stress builds on a rock, the rock shatters, creating faults
      • Faults usually occur along plate boundaries, where the forces of plate motion compress, pull, or shear the crust too much so the crust smashes
    • Strike-Slip Faults
      • Shearing creates this fault
      • In this fault, rocks on both sides of the fault slide past each other with a little up and down motion
      • When a strike-slip fault forms the boundary between two plates, it becomes a transform boundary
    • Normal Faults
      • Tension forces in Earth's crust causes these types of faults
      • Normal faults are at an angle, so one piece of rock is above the fault, while the other is below the fault
      • The above rock is called the hanging wall, and the one below is called the footwall
      • When movement affects along a normal fault, the hanging wall slips downward
      • Normal faults occur along the Rio Grande rift valley in New Mexico, where two pieces of Earth's crust are diverging
    • Reverse Faults
      • Compression forces produce this fault
      • This fault has the same setup as a normal fault, but reversed, which explains it’s name
      • Just like the normal fault, one side of the reverse fault is at an angle of the other
      • This fault produced part of the Appalachian Mountains in the eastern United States
    • How Do Mountains Form?
      • The forces of plate movement can build up Earth's surface , so over millions of years, movement of faults can change a perfectly flat plain into a gigantic mountain range
      • Sometimes, a normal fault uplifts a block of rock, so a fault-block mountain forms
      • When a piece of rock between two normal faults slips down, a valley is created
    • Mountains Formed by Folding
      • Sometimes, under current conditions, plate movement causes the crust to fold
      • Folds are bends in rock that form when compression shortens and thickens part of Earth's crust
      • The crashing of two plates can cause folding and compression of crust
      • These plate collisions can produce earthquakes because rock folding can fracture and lead to faults
    • Anticlines and Synclines  
      • Geologists use the terms syncline and anticline to describe downward and upward folds in rock
      • An anticline is a fold in a rock that arcs upward
      • A syncline is a fold in a rock that arcs downward
      • These folds in rocks are found on many parts of the earths surface where compression forces have folded the crust
    • How Earthquakes Form
      • Everyday, about 8,000 earthquakes hit Earth, but most of them are too little to feel
      • Earthquakes will always begin in a rock beneath the surface
      • A lot of earthquakes begin in the lithosphere within 100 km of Earth's surface
      • The focus triggers an earthquake
      • Focus : the point beneath Earth's surface where rock that is under stress breaks
    • Seismic Waves
      • Seismic Waves: vibrations that travel through Earth carrying the energy released during an earthquake
      • an earthquake produces vibrations called waves that carry energy while they travel out through solid material
      • During an earthquake, seismic waves go out in all directions to the focus
      • They ripple like when you through a stone into a lake or pond
    • Seismic Waves Ctd.
      • There are three different types of seismic waves: P waves, S waves, and surface waves
      • An earthquake sends out two of those waves, P and S waves
      • When they reach the top of the epicenter, surface waves form
    • Primary Waves
      • Also known as P Waves
      • The first waves to come are these waves
      • P waves are earthquake waves that compress and expand the ground like an accordion
      • P waves cause buildings to expand and contract
    • Secondary Waves
      • Also known as S Waves
      • After p waves, S waves come
      • S waves are earthquake waves that vibrate from one side to the other as well as down and up
      • They shake the ground back and forth
      • When S waves reach the surface, they shake buildings violently
      • Unlike P waves, which travel through both liquids and solids, S waves cannot move through any liquids
    • Surface Waves
      • When S waves and P waves reach the top, some of them are turned into surface waves
      • Surface waves move slower than P waves and S waves, but they can produce violent ground movements
      • Some of them make the ground roll like ocean waves
      • Other surface waves move buildings from side to side
    • Detecting Seismic Waves
      • Geologists use instruments called seismographs to measure the vibrations of seismic waves
      • Seismographs records the ground movements caused by seismic waves as they move through the Earth
    • Mechanical Seismographs
      • Until just recently, scientists have used a mechanical seismograph
      • a mechanical seismograph consists of a heavy weight connected to a frame by a wire or spring
      • When the drum is not moving, the pen draws a straight line on paper wrapped around the drum
      • Seismic waves cause the drum to vibrate during an earthquake
      • the pen stays in place and records the drum's vibrations
      • The higher the jagged lines, the more severe earthquake
    • Measuring Earthquakes
      • There are many things to know about the measures of an earthquake
      • 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 Mercalli Scale
      • 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
      • The Mercalli scale uses Roman numerals to rank earthquakes by how much damage they cause
    • The Richter Scale
      • 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
    • The Moment Magnitude Scale
      • 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
    • Locating the Epicenter
      • Sine the P waves travel faster than the S waves, scientists can use the difference in arrival times to see how far away the earthquake occurred.
      • It does not tell the direction however.
    • Determining Direction
      • One station can only learn how far away the quake occurred.
      • They would draw a circle at that radius.
      • If three stations combine their data, the quake occurred where the three circles overlap.
    • How Earthquakes Cause Damage
      • 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.