Earthquakes and How They Are Measured
How Earthquakes Occur <ul><li>earthquake: a vibration, or shaking, of Earth’s crust </li></ul><ul><li>fault: found in the ...
<ul><li>earthquakes  happen where plates are moving past each other </li></ul><ul><ul><li>rocks get stuck and don’t move <...
How Earthquakes Are Measured <ul><li>energy from a earthquake travels as waves through the Earth </li></ul><ul><ul><li>ene...
<ul><li>the  Mercalli  scale : measures movement and damage that an earthquake causes </li></ul><ul><ul><li>scale uses Rom...
Summary <ul><li>fault in Earth’s crust is a break along which rocks move </li></ul><ul><li>earthquake is the vibrations pr...
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Chap C1.2

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Earthquakes Measurement

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  • Well described.
    In ancient time Aristotle said that earthquakes were caused by winds trapped in subterranean caves.

    Small tremors were thought to have been caused by air pushing on the cavern roofs, and large ones by the air breaking the surface.
    A later theory stated that earthquakes occurred in calm, cloudy conditions, and were usually preceded by strong winds, fireballs, and meteors.
    But now we all know the reason behind this.
    I agree that it is unstoppable but safety preparations are not impossible.
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Chap C1.2

  1. 1. Earthquakes and How They Are Measured
  2. 2. How Earthquakes Occur <ul><li>earthquake: a vibration, or shaking, of Earth’s crust </li></ul><ul><li>fault: found in the crust – a break along which rocks move </li></ul><ul><ul><li>rocks on either side of the fault move up/down, side/side, or both </li></ul></ul>
  3. 3. <ul><li>earthquakes happen where plates are moving past each other </li></ul><ul><ul><li>rocks get stuck and don’t move </li></ul></ul><ul><ul><li>plates continue to move – building pressure on rocks </li></ul></ul><ul><ul><ul><li>when enough pressure is put on the rocks, they break and the plates move suddenly </li></ul></ul></ul><ul><ul><ul><li>the sudden movement causes vibrations in the Earth’s crust </li></ul></ul></ul><ul><ul><li>focus : the point underground where the movement first took place </li></ul></ul><ul><ul><ul><li>when rocks slip at focus, energy moves out in all directions through the rock around it </li></ul></ul></ul><ul><ul><li>epicenter: the point on the surface that is right above the focus </li></ul></ul><ul><ul><ul><li>the damage from the vibrations is caused by the release of energy at the epicenter </li></ul></ul></ul>
  4. 4. How Earthquakes Are Measured <ul><li>energy from a earthquake travels as waves through the Earth </li></ul><ul><ul><li>energy can be measured in different ways </li></ul></ul><ul><li>seismograph: an instrument that records earthquake waves </li></ul><ul><ul><li>2 main parts – a pen and paper covered rotating drum </li></ul></ul><ul><ul><ul><li>as the drum turns, the pen marks – when an earthquake happens the line gets jagged </li></ul></ul></ul><ul><ul><ul><ul><li>the more jagged the line, the stronger the earthquake </li></ul></ul></ul></ul>
  5. 5. <ul><li>the Mercalli scale : measures movement and damage that an earthquake causes </li></ul><ul><ul><li>scale uses Roman numerals from I to XII </li></ul></ul><ul><ul><ul><li>earthquake measuring III makes hanging objects swing back and forth </li></ul></ul></ul><ul><ul><ul><li>earthquake measuring X causes brick buildings to crumble </li></ul></ul></ul><ul><li>Richter scale : uses numbers 1 to 9 to measure the energy an earthquake releases </li></ul><ul><ul><li>earthquake measuring 3.0 releases 30 times the energy as an earthquake measuring 2.0 and 900 times the energy as an earthquake measuring 1.0 </li></ul></ul>
  6. 6. Summary <ul><li>fault in Earth’s crust is a break along which rocks move </li></ul><ul><li>earthquake is the vibrations produced when energy builds up and is quickly released along a fault </li></ul><ul><li>Mercalli and Richter scale measure earthquake intensity </li></ul>
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