earthquakes the rupture and sudden movement of rocks along a fault. 6.1 earthquakes and plate...
TRANSCRIPT
Earthquakes
Earthquakes
• The rupture and sudden movement of rocks along a fault.
6.1 Earthquakes and Plate Boundaries
• Majority of earthquakes occur in Earth’s crust.
• Part of the energy released from earthquakes spreads as complex waves.
• When rocks can no longer change shape—the fault breaks and slips, causing earthquakes.
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Focus & Epicenter
• The focus is the location on the fault where an earthquake begins.
6.1 Earthquakes and Plate Boundaries
• The closer the focus is to the surface, the stronger the shaking will be.
• The point on Earth’s surface directly above the focus is the epicenter.
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Plate Boundaries and Earthquakes• Lithospheric plates interact at different plate boundaries
and produce earthquakes.
6.1 Earthquakes and Plate Boundaries
• Earthquake size and depth and fault type depend on the type of plate boundary.
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Plate Boundaries and Earthquakes (cont.)
6.1 Earthquakes and Plate Boundaries
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Earthquakes Away from Plate Boundaries
6.1 Earthquakes and Plate Boundaries
• Not all earthquakes happen at plate boundaries.
• New Madris Earthquakes of 1911
• Millions of years ago, a long zone of intense faulting was formed when the crust began to pull apart, but did not break completely.
• Today, the crust is being compressed, or squeezed together. (p. 246) 1
Seismic Waves
Seismic Wave
• Waves move outwardfrom the focus in alldirections.
• 3 main types of seismic waves.
• Waves of energy that are produced at the focus of an earthquake.
6.2 Earthquakes and Seismic Waves
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1. Primary Waves (P-waves)
6.2 Earthquakes and Seismic Waves
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•Particles vibrate in same direction as wave
•Fastest seismic wave
•First to be detected by seismographs
•Travel through solids and fluids
• Particles vibrate perpendicular to wave
• Slower than P-waves
• Detected after the p-wave
• Travels through solids only
2. Secondary Waves (S-waves)
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• Slowest seismic wave
• Side-to-side swaying or rolling motion
• Cause the most damage
3. Surface Waves
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MeasuringEarthquakes
Measuring Earthquakes• Scientists determine size of earthquakes by measuring how much the rock slips
along the fault.
• They also analyze the heights of the seismic waves, which indicate how much energy is released by an earthquake.
6.3 Measuring Earthquakes
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Seismograph
• Records size, direction, and the movement time of ground
6.3 Measuring Earthquakes
• Records the arrival times of the P- and S-waves
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Seismogram
• Record of the seismic waves
6.3 Measuring Earthquakes
• Used to calculate the size and locations of earthquakes
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Reading a Seismogram• Wave heights indicate the amount of ground motion
for each type of wave.
• Difference between the arrival times of P-waves and S-waves determines the distance of the seismograph from the epicenter. (p.260)
6.3 Measuring Earthquakes
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Locating anEpicenter
Locating an Epicenter
• Triangulation is used to locate the epicenter.
• This method is based on the speeds of the seismic waves.
• At least three seismographs must record the distances.
6.3 Measuring Earthquakes
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1. Find the arrival time differences.
6.3 Measuring Earthquakes
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2. Find the difference from the epicenter.
6.3 Measuring Earthquakes
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3. Plot the distance on a map. (p. 263)
6.3 Measuring Earthquakes
• The epicenter is where the 3 circles overlap.
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Earthquake Scales
Measuring Earthquake Size• Magnitude measures the amount of energy released
by an earthquake.
• Magnitude scale is based on record of height of ground motion.
• Most values range from 0–9.
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Richter Scale
• First magnitude scale that used mechanical seismographs
• Good for earthquakes between 3.0-7.0 only.
• Not used today
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Moment Magnitude Scale• Used today
• More accurate scale for measuring earthquake size.
• Based on the amount of energy released during an earthquake.
• Uses electronic seismographs
6.3 Measuring Earthquakes
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Earthquake Intensity• Intensity refers to the amount of shaking and damage caused.
• Intensity varies depending on:
– Size of earthquake
– Distance from epicenter
– Type of ground surface
– Construction of building
• Mercalli Scale measures intensity
• Usually, the maximum intensity is found near the epicenter. (p. 264)
6.3 Measuring Earthquakes
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PredictingEarthquakes
Predicting Earthquakes• At this time, geologists cannot predict earthquakes.
• Geologists can, however, determine the seismic risk by locating active faults and where past earthquakes have occurred.
• Geologists create seismic risk maps.
6.3 Measuring Earthquakes
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Avoiding Earthquake Hazards (p.274)
6.4 Earthquake Hazards and Safety
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