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EARTHQUAKES

EARTHQUAKES. Elastic Rebound Theory: As tectonic plates move, friction interferes with forward motion. The plates shift, and this causes an earthquake.

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EARTHQUAKES

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  1. EARTHQUAKES • Elastic Rebound Theory: As tectonic plates move, friction interferes with forward motion. The plates shift, and this causes an earthquake. Strike-slip plate boundary: Some tectonic plates move past one another in opposite directions. This doesn’t build or destroy land forms, but it causes earthquakes.

  2. Example: San Andreas Fault in California Where does an earthquake begin? The focus of an earthquake is the location within the crust where movement begins. A subduction boundary (trench) has a deep focus, but a strike slip boundary has a shallow focus.

  3. More often, we find the epicenter of an earthquake. The epicenter is the location on the surface above the focus. How earthquakes travel: An earthquake is an energy pulse through the earth, so it travels in waves.

  4. Earthquakes generate three types of waves: • Primary waves: (P waves). These are quick longitudinal waves caused by compression. They travel in only one direction.

  5. P waves travel through solids and liquids. In liquids, they slow down and refract. 2. Secondary (S) waves. These are transverse waves caused by tension (stretching). S waves move in two directions, but never through liquids

  6. Lateral waves (L waves). L waves only travel on the Earth’s surface. They are the ones that actually damage buildings and other structures. Earthquakes are called seismic disturbances and are measured by seismographs. A seismograph measures movement in Earth’s crust, and can distinguish an S wave from a P wave.

  7. P waves arrive at a seismograph before S waves. The closer the S waves is to the P wave, the closer the seismograph is to the epicenter.

  8. Measuring an earthquake: 1. Richter scale. In the Richter scale, an earthquake is assigned a number. The higher the number, the stronger the earthquake. Each number increases exponentially. Less than 3.5 can’t be felt. 3.5 – 6 can be felt, causes little damage Over 6 causes damage.

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