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  1. 1. Earthquakes
  2. 2. An Earthquake is… <ul><li>the shaking and trembling that results from the movement of rock beneath Earth's surface </li></ul><ul><li>The movement of Earth's plates produces strong forces that squeeze or pull the rock in the crust </li></ul><ul><li>This is an example of stress, a force that acts on rock to change its volume or shape </li></ul>
  3. 3. Stress <ul><li>There are three different types of stress that occur on the crust, shearing, tension, and compression </li></ul><ul><li>These forces cause some rocks to become fragile and they snap </li></ul><ul><li>Some other rocks tend to bend slowly like road tar softened by the suns heat </li></ul>
  4. 4. Faults <ul><li>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 </li></ul><ul><li>When enough stress builds on a rock, the rock shatters, creating faults </li></ul><ul><li>Faults usually occur along plate boundaries, where the forces of plate motion compress, pull, or shear the crust too much so the crust smashes </li></ul>
  5. 5. Strike-Slip Faults <ul><li>Shearing creates this fault </li></ul><ul><li>In this fault, rocks on both sides of the fault slide past each other with a little up and down motion </li></ul><ul><li>When a strike-slip fault forms the boundary between two plates, it becomes a transform boundary </li></ul>
  6. 6. Normal Faults <ul><li>Tension forces in Earth's crust causes these types of faults </li></ul><ul><li>Normal faults are at an angle, so one piece of rock is above the fault, while the other is below the fault </li></ul><ul><li>The above rock is called the hanging wall, and the one below is called the footwall </li></ul><ul><li>When movement affects along a normal fault, the hanging wall slips downward </li></ul><ul><li>Normal faults occur along the Rio Grande rift valley in New Mexico, where two pieces of Earth's crust are diverging </li></ul>
  7. 7. Reverse Faults <ul><li>Compression forces produce this fault </li></ul><ul><li>This fault has the same setup as a normal fault, but reversed, which explains it’s name </li></ul><ul><li>Just like the normal fault, one side of the reverse fault is at an angle of the other </li></ul><ul><li>This fault produced part of the Appalachian Mountains in the eastern United States </li></ul>
  8. 8. How Do Mountains Form? <ul><li>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 </li></ul><ul><li>Sometimes, a normal fault uplifts a block of rock, so a fault-block mountain forms </li></ul><ul><li>When a piece of rock between two normal faults slips down, a valley is created </li></ul>
  9. 9. Mountains Formed by Folding <ul><li>Sometimes, under current conditions, plate movement causes the crust to fold </li></ul><ul><li>Folds are bends in rock that form when compression shortens and thickens part of Earth's crust </li></ul><ul><li>The crashing of two plates can cause folding and compression of crust </li></ul><ul><li>These plate collisions can produce earthquakes because rock folding can fracture and lead to faults </li></ul>
  10. 10. Anticlines and Synclines   <ul><li>Geologists use the terms syncline and anticline to describe downward and upward folds in rock </li></ul><ul><li>An anticline is a fold in a rock that arcs upward </li></ul><ul><li>A syncline is a fold in a rock that arcs downward </li></ul><ul><li>These folds in rocks are found on many parts of the earths surface where compression forces have folded the crust </li></ul>
  11. 11. How Earthquakes Form <ul><li>Everyday, about 8,000 earthquakes hit Earth, but most of them are too little to feel </li></ul><ul><li>Earthquakes will always begin in a rock beneath the surface </li></ul><ul><li>A lot of earthquakes begin in the lithosphere within 100 km of Earth's surface </li></ul><ul><li>The focus triggers an earthquake </li></ul><ul><li>Focus : the point beneath Earth's surface where rock that is under stress breaks </li></ul>
  12. 12. Seismic Waves <ul><li>Seismic Waves: vibrations that travel through Earth carrying the energy released during an earthquake </li></ul><ul><li>an earthquake produces vibrations called waves that carry energy while they travel out through solid material </li></ul><ul><li>During an earthquake, seismic waves go out in all directions to the focus </li></ul><ul><li>They ripple like when you through a stone into a lake or pond </li></ul>
  13. 13. Seismic Waves Ctd. <ul><li>There are three different types of seismic waves: P waves, S waves, and surface waves </li></ul><ul><li>An earthquake sends out two of those waves, P and S waves </li></ul><ul><li>When they reach the top of the epicenter, surface waves form </li></ul>
  14. 14. Primary Waves <ul><li>Also known as P Waves </li></ul><ul><li>The first waves to come are these waves </li></ul><ul><li>P waves are earthquake waves that compress and expand the ground like an accordion </li></ul><ul><li>P waves cause buildings to expand and contract </li></ul>
  15. 15. Secondary Waves <ul><li>Also known as S Waves </li></ul><ul><li>After p waves, S waves come </li></ul><ul><li>S waves are earthquake waves that vibrate from one side to the other as well as down and up </li></ul><ul><li>They shake the ground back and forth </li></ul><ul><li>When S waves reach the surface, they shake buildings violently </li></ul><ul><li>Unlike P waves, which travel through both liquids and solids, S waves cannot move through any liquids </li></ul>
  16. 16. Surface Waves <ul><li>When S waves and P waves reach the top, some of them are turned into surface waves </li></ul><ul><li>Surface waves move slower than P waves and S waves, but they can produce violent ground movements </li></ul><ul><li>Some of them make the ground roll like ocean waves </li></ul><ul><li>Other surface waves move buildings from side to side </li></ul>
  17. 17. Detecting Seismic Waves <ul><li>Geologists use instruments called seismographs to measure the vibrations of seismic waves </li></ul><ul><li>Seismographs records the ground movements caused by seismic waves as they move through the Earth </li></ul>
  18. 18. Mechanical Seismographs <ul><li>Until just recently, scientists have used a mechanical seismograph </li></ul><ul><li>a mechanical seismograph consists of a heavy weight connected to a frame by a wire or spring </li></ul><ul><li>When the drum is not moving, the pen draws a straight line on paper wrapped around the drum </li></ul><ul><li>Seismic waves cause the drum to vibrate during an earthquake </li></ul><ul><li>the pen stays in place and records the drum's vibrations </li></ul><ul><li>The higher the jagged lines, the more severe earthquake </li></ul>
  19. 19. Measuring Earthquakes <ul><li>There are many things to know about the measures of an earthquake </li></ul><ul><li>There are at least 20 different types of measures </li></ul><ul><li>3 of them are the Mercalli scale, Richter scale, and the Moment Magnitude scale </li></ul><ul><li>Magnitude is a measurement of earthquake strength based on seismic waves and movement along faults </li></ul>
  20. 20. The Mercalli Scale <ul><li>Developed in the twentieth century to rate earthquakes according to their intensity </li></ul><ul><li>The intensity of an earthquake is the strength of ground motion in a given place </li></ul><ul><li>Is not a precise measurement </li></ul><ul><li>But, the 12 steps explain the damage given to people, land surface, and buildings </li></ul><ul><li>The same earthquake could have different Mercalli ratings because of the different amount of damage in different spots </li></ul><ul><li>The Mercalli scale uses Roman numerals to rank earthquakes by how much damage they cause </li></ul>
  21. 21. The Richter Scale <ul><li>The Richter scale is a rating of the size of seismic waves as measured by a particular type of mechanical seismograph </li></ul><ul><li>Developed in the 1930’s </li></ul><ul><li>All over the world, geologists used this for about 50 years </li></ul><ul><li>Electric seismographs eventually replaced the mechanical ones used in this scale </li></ul><ul><li>Provides accurate measurements for small, nearby earthquakes </li></ul><ul><li>Does not work for big, far ones </li></ul>
  22. 22. The Moment Magnitude Scale <ul><li>Geologists use this scale today </li></ul><ul><li>It’s a rating system that estimates the total energy released by an earthquake </li></ul><ul><li>Can be used for any kind of earthquakes, near or far </li></ul><ul><li>Some news reports may mention the Richter scale, but the magnitude number they quote is almost always the moment magnitude for that earthquake </li></ul>
  23. 23. Locating the Epicenter <ul><li>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. </li></ul><ul><li>It does not tell the direction however. </li></ul>
  24. 24. Determining Direction <ul><li>One station can only learn how far away the quake occurred. </li></ul><ul><li>They would draw a circle at that radius. </li></ul><ul><li>If three stations combine their data, the quake occurred where the three circles overlap. </li></ul>
  25. 25. How Earthquakes Cause Damage <ul><li>The severe shaking provided by seismic waves can damage or destroy buildings and bridges, topple utility poles, and damage gas and water mains </li></ul><ul><li>With their side to side, up and down movement, S waves can damage or destroy buildings, bridges, and fracture gas mains. </li></ul>