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Understanding Earthquakes: Causes, Types, and Seismic Hazards

Earthquakes are caused by stress along faults in the Earth's crust, leading to the release of energy as seismic waves. The main types of stress that contribute to earthquakes include tension, compression, and shearing. Faults, such as normal, reverse, and strike-slip, are breaks in the crust where rocks slide past each other. The energy buildup from deformed rocks results in the movement that generates earthquakes. Seismic waves, including primary, secondary, and surface waves, propagate through the Earth, causing vibrations that can lead to significant destruction. Understanding these concepts is vital for assessing earthquake risks.

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Understanding Earthquakes: Causes, Types, and Seismic Hazards

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Presentation Transcript

  1. Earthquakes • Stress • Faults they cause • Seismic Waves • Hazards of an Earthquake

  2. Types of Stress • Tension • Pulls crust apart • Compression • Squeezes rock until it folds or breaks • Shearing • Pushes a mass of rock in two opposite, horizontal direction

  3. Fault a break in Earth’s crust where slabs of crust slip past each other 3 types: normal, reverse, strike-slip

  4. Hanging wall Foot wall Normal Fault • caused by tension forces • rock above the fault moves down compared to the rock below the fault Hanging Wall – rock that is above the fault line Foot Wall – rock that is below the fault line

  5. Hanging wall Foot wall Reverse Fault • caused by compression forces • rock above the fault moves upward compared to rock below the fault.

  6. Strike-Slip Fault -Caused by shear forces, rock on either side of the fault moves past one another in opposite directions.

  7. Elastic Rebound • When rocks strain and then break, the broken pieces snap back. • Potential energy builds up as the rocks deform over long periods of time. • Energy is suddenly released when the rocks break and move. • Movement causes vibrations

  8. Mountain Building • Fault-block Mountains

  9. Mountain Building • Folded Mountains Syncline – Maryland road cut (I-68)

  10. Mountain Building • Folded Mountains Anticline – Route 55 in West Virginia

  11. Parts of an Earthquake Focus – point inside earth where movement along a fault first occurs and energy is released Epicenter – the point on the Earth’s surface located directly above the focus.

  12. Seismic Waves • Primary waves– cause rock to move back and forth in the same direction other waves are moving • Secondary waves– cause rock to vibrate at right angles to the direction the waves are moving • Surface waves– slowest, largest, most destructive

  13. Shadow Zone

  14. Seismograph • Instrument that records an earthquake’s vibrations. • Richter scale – measures an earthquake’s size, or magnitude. 10 is the greatest.

  15. Tsunamis

  16. Earthquake Zones

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