Earthquakes Earthquakes and the Earth’s Structure • Focus is the point within Earth where the earthquake starts. • Epicenter is the location on the surface directly above the focus. An earthquake is the vibration of Earth produced by the rapid release of energy Focus and Epicenter • Faults are fractures in Earth where movement has occurred. Faults
Earthquakes. Earthquakes and the Earth’s Structure. An earthquake is the vibration of Earth produced by the rapid release of energy. Focus and Epicenter. • Focus is the point within Earth where the earthquake starts. . - PowerPoint PPT Presentation
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Earthquakes
Earthquakes and the Earth’s Structure
• Focus is the point within Earth where the earthquake starts.
• Epicenter is the location on the surface directly above the focus.
An earthquake is the vibration of Earth produced by the rapid release of energy
Focus and Epicenter
• Faults are fractures in Earth where movement has occurred.
Faults
What causes an earthquake?• Caused by sudden slip on a fault, and the
resulting ground shaking and radiated seismic energy caused by the slip
• Caused by volcanic or magmatic activity, • Caused by other sudden stress changes in the
earth.
Focus, Epicenter, and Fault
Cause of Earthquakes
Earthquakes
Elastic Rebound Hypothesis• Most earthquakes are produced by the rapid
release of elastic energy stored in rock that has been subjected to great forces.
• When the strength of the rock is exceeded, it suddenly breaks, causing the vibrations of an earthquake.
1) Elastic deformation – rock stretches then reaches a breaking point, releasing energy, causes earthquakes.
2) Plastic deformation – does not cause earthquakes
Elastic Rebound Hypothesis
Elastic deformation – rock stretches then reaches a breaking point, releasing energy
Plastic deformation – does not cause earthquakes
SeismographSeismographs—Instruments that records the vibrations of the earth during an Earthquake.
How Seismographs Work
the pendulum remains fixed as the ground moves beneath it
Seismogram
Earthquake Terms
• Seismographs—Instruments that records the vibrations of the earth during an Earthquake.
• Seismologists—People who study earthquakes.
• Richter Scale— Scale used to measure the strength of an earthquake.
• Magnitude—The strength of an earthquake.
Seismic Waves Body Waves
• P waves• Identified as P (primary) waves or S (secondary) waves
- Have the greatest velocity of all earthquake waves 8 km/sec
- Are push-pull waves that push (compress) and pull (expand) in the direction that the waves travel
- Travel through solids, liquids, and gases
Surface Waves
• S waves
- Slower velocity than P waves 4.5 km/sec
- Shake particles at right angles to the direction that they travel
- Travel only through solids. Cannot travel through liquids
- L or Love waves- Rayleigh waves
Primary Waves (P Waves)
• A type of seismic wave that compresses and expands the ground
• The first wave to arrive after an earthquake 8 km/sec