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Recording Earthquakes

Recording Earthquakes. Chapter 6.2. Recording Earthquakes. A seismograph is an instrument that is used to detect and record seismic waves. A seismograph records motion by tracing wave-shaped lines on a paper or by translating the motion into electronic signals. Recording Earthquakes.

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Recording Earthquakes

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  1. Recording Earthquakes Chapter 6.2

  2. Recording Earthquakes • A seismograph is an instrument that is used to detect and record seismic waves. • A seismograph records motion by tracing wave-shaped lines on a paper or by translating the motion into electronic signals.

  3. Recording Earthquakes • A seismograph consists of three main recording devices that measure motion in the following directions. • Vertical motion of the ground. • Horizontal motion in East-West direction • Horizontal motion in North-South direction

  4. Seismic Waves • Scientists have determined that earthquakes generally produce three major types of seismic waves. • Each type of wave travels at a different speed and causes different motion in the earth’s crust.

  5. Primary WAves • Primary waves, or P-waves, move the fastest and are therefore the first to be recorded by a seismograph. • P-waves can travel through solids and liquids. • The more rigid the material the faster the p-wave travels. • P-waves are compression waves which means they cause rock particles to move together and apart along the direction of the waves.

  6. Secondary WAves • Secondary waves, or S-waves, are the second waves to be recorded by a seismograph. • S-waves can only travel through solid material. • S-waves are shear waves which means that they cause rock particles to move at right angles to the direction in which the waves are traveling.

  7. Surface Waves • Surface waves are created when p-waves and s-waves reach the earth’s surface. • Surface waves are the slowest moving waves and are the last to be recorded on a seismograph. • Surface waves travel over the earth’s surface similar to ocean waves. • Surface waves are destructive when traveling through loose earth.

  8. Locating an Earthquake • Locating an Earthquake • The difference between the arrival times of the p-waves and s-waves can be used to determine the epicenter of an earthquake. • P-waves travel about 1.7 times faster than s-waves. • Therefore, if the s-waves arrive shortly after the p-waves we know that the earthquake occurred close, and if the s-waves arrive a long time after the p-waves we know the earthquake occurred far away.

  9. Locating an Earthquake • To determine the exact location of the epicenter scientists plot the difference between the arrival times of the two waves and compare them to a standard graph that turns the times into distances from the epicenter. • In order to determine the distance you must have information from at least three seismograph stations at different locations. • Circles are drawn on a map using the distances recorded. • Where the circles intersect is the epicenter of the earthquake.

  10. Earthquake measurement • Earthquake Measurement • Magnitude is a measure of the energy released by an earthquake and is also described as the amount of ground motion. • Magnitude is measured using the Richter scale or the Moment Magnitude Scale. • The Richter scale is related to the effect of the earthquake while the moment magnitude scale is related to the cause of the earthquake.

  11. Earthquake measurement • Earthquakes with a magnitude less than a 2.5 are called microquakes and are usually not felt by people. • The Mercalli scale expresses the intensity of an earthquake, or the amount of damage it causes through roman numerals and description of damage. • The Mercalli scale describes an earthquake with a scale from I to XII, where a rating of II is a low intensity.

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