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Understanding Earthquakes: Causes, Waves, and Measurement Techniques

Earthquakes are seismic disturbances caused by the movement of tectonic plates. The Elastic Rebound Theory explains how friction affects forward motion, resulting in earthquakes, particularly at strike-slip boundaries like the San Andreas Fault. Focusing on the mechanics, the focus of an earthquake is the initial movement within the crust, while the epicenter is the surface point directly above it. Earthquakes generate three main wave types: Primary (P) waves, Secondary (S) waves, and Lateral (L) waves, each traveling differently through various materials. Their intensity is measured on the Richter scale.

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Understanding Earthquakes: Causes, Waves, and Measurement Techniques

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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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