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The Dynamic Earth

The Dynamic Earth. The most common cause of Earthquakes is FAULTING. A Fault is a break in the earth’s crust. Earthquakes occur when rocks slip past each other along the fault line. This releases a tremendous amount of energy. Part 1: Understanding Earthquakes. Studying Earthquakes.

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The Dynamic Earth

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  1. The Dynamic Earth The most common cause of Earthquakes is FAULTING. A Fault is a break in the earth’s crust. Earthquakes occur when rocks slip past each other along the fault line. This releases a tremendous amount of energy. Part 1: Understanding Earthquakes

  2. Studying Earthquakes • Seismology – the study of earthquakes. • Seismograph – an instrument used to detect and measure the shock (seismic) waves sent out by an earthquake. • Seismogram – a recording of the three types of seismic waves. (S, P and L) Seismograph

  3. Types ofSeismic Waves • Primary Waves (P Waves) – Push / pull waves. (like a slinky) Can travel through solids liquids or gases. FASTEST WAVES! • Secondary Waves (S Waves) Move at right angles to the direction of the wave (like a rope) Can travel through solids but not liquids or gases. Not as fast as P waves. (Arrive after the P Wave) • Surface Waves (L Waves) Travel like waves in water. (up and down) Slowest wave but most destructive kind of wave.

  4. Seismograms The Lag Time or S - P Interval is 4 seconds. Magnitude - 3.1Distance -34 km(Only about 25 miles away from the epicenter.) S Waves arrive after the P Wave. The lag time between the arrival of the two waves is called the S-P Interval P Waves arrive at the recording station first.

  5. Earthquake Terms • Focus – the point beneath the earth’s surface where the earthquake occurs. • Epicenter – the point on the earth’s surface above the focus.

  6. Locating the Epicenter To locate the epicenter seismologists record the seismic waves from three different recording stations. They measure the time between the arrival of the P waves and the S waves. Circles are drawn based on this measurement. The epicenter is located where all three circles meet.

  7. Are We At Risk? New Madrid Fault New Madrid, Missouri You better believe it!

  8. New Madrid Earthquakes 1811 - 1812 - Changed the course of the Mississippi River.- Created Reelfoot Lake in Tennessee.- Rang church bells as far away as Boston, Mass. Several earthquakes occurred between December 1811 through February 1812. Estimated magnitudes as high as 8.1

  9. United States Geological Survey

  10. QUAKES Activity Finding the Epicenter of an Earthquake

  11. When an earthquake occurs both P Waves and S Waves are sent out in all directions. Since P Waves travel faster than S Waves, the waves do not reach a distant point at the same time. This difference in time is known as the S/P Interval or Lag Time.

  12. A P Wave travels through the earth at an average of 6.1 kilometers per second (km / sec.) How many kilometers would a P wave travel in 6 seconds? 6.1 km / sec.X 6 sec.____________ Multiply 6.1 times 6 seconds 36.6 km

  13. An S Wave travels through the earth at an average of 4.1 km/sec. How many kilometers would a S wave travel in 6 seconds? 4.1 km / sec.X 6 sec.__________ Multiply 4.1 km / sec. times 6 seconds 24.6 km

  14. If P Waves travel at an average of 6.1 km/sec. then in 16 Seconds a P Wave will travel about 100 km. If S Waves travel at an average of 4.1 km/sec. then in 24 Seconds an S Wave will travel about 100 km. 6.1 km / sec. X 16 sec.__________ 4.1 km / sec. X 24 sec.__________ 97.6(100 Km) 98.4(100 km)

  15. Using this knowledge, we can see that the S-P Interval or Lag Time is about 8 seconds if the epicenter of an earthquake is 100 km away. This means that the epicenter is 12.5 km away for every single second of Lag Time 100 ÷ 8 = 12.5 Remember! It takes data from three recording stations to determine the epicenter of an earthquake.

  16. An Earthquake has been detected…………………… Stand by for data You will now begin the QUAKES Practice Activity. Wait for further instructions.

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