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Earthquakes

Earthquakes. Earthquake: shaking and trembling that results from the movement of rock beneath Earth’s surface The forces of plate movement cause earthquakes Most begin in the lithosphere. Forces that cause Earthquakes. Stress : force that acts on rock to change its shape or volume

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Earthquakes

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  1. Earthquakes Earthquake:shaking and trembling that results from the movement of rock beneath Earth’s surface The forces of plate movement cause earthquakes Most begin in the lithosphere

  2. Forces that cause Earthquakes Stress: force that acts on rock to change its shape or volume Types of Stress Tension: pulls on the crust, stretches the rock, becomes thinner in the middle (divergent) Compression: squeezes rock until it folds or breaks (Convergent) Shearing: pushes rock in two opposite directions

  3. Types of Faults A fault is a fracture in the earth’s crust where there has already been some movement. • Normal fault: occur where plates diverge, hanging wall lies below the footwall • Reverse fault: place where the rock of the crust is pushed together, hanging wall pushes over top of footwall • Strike-slip fault: rocks of the fault slip past each other sideways, little up or down motion.

  4. Folding Earth’s Crust • Anticline: rock that bends upward into an arch • Syncline: rock that bends downward to form a valley. • Plateau: a large area of flat land elevated high above sea level -Some of the worlds largest mountains formed from the folding of earth’s crust

  5. Where do they occur? Focus: place where the rock breaks, causing the earthquake Epicenter: point on Earth’s surface above the focus Seismic waves: vibrations that travel through the earth carrying the energy released during an earthquake

  6. Types of Waves P waves: primary waves, first to arrive; compress and expand the ground • Travel through solids and liquids • Look like coiled and stretched spring S waves: secondary waves, vibrate side to side as well as up and down • Cannot travel through liquids • Shakes structures violently Surface waves: move more slowly than P & S waves, roll the ground like ocean waves

  7. Earthquakes Measuring Scales Mercalli scale: rate earthquakes according to damage at a given place Richter scale: rate of an earthquake’s magnitude based on the size of the seismic waves • Magnitude: number based on earthquakes size (no max) Moment magnitude scale: a rating system that estimates the total energy released by an earthquake - Every point increase represents 32 times more energy

  8. How to locate the origin(epicenter) of an earthquake • Scientists measure the difference between the arrival times of P & S waves • Farther away an earthquake is, the longer the arrival time of the P & S waves USGS Website: http://earthquake.usgs.gov/ Track some earthquakes

  9. How to monitor earthquakes Seismograph: an instrument that records and measures seismic waves Seismogram: the record of an earthquakes seismic waves, produced by the seismograph

  10. Measuring fault zones Tiltmeters: measures the tilting or raising of the ground • Water level scale (like a carpenter’s level) • Measures vertical movement

  11. Creep Meter: uses a wire stretched across a fault to measure horizontal (side to side) movement of the ground - Works on a pulley system (stretches wire to move a weight)

  12. Laser-ranging device: uses a laser beam to detect horizontal fault movements - Laser beam is shot to reflector and sent back to origin of laser (timed test)

  13. GPS Satellites: use satellites to measure changes in tilt and horizontal movement - Global Positioning System - Satellite transmits signals to receivers(below) on both sides of faults

  14. What determines the intensity of an Earthquake? Friction: the force that opposes motion between two surfaces • Low friction = small earthquake • High friction = high stress on rocks = big earthquake • Scientists monitor stress on fault zones to try to predict earthquake, but NOTHING IS CERTAIN

  15. How can an Earthquake cause damage? • Shaking: triggers landslides or avalanches, can cause damage to or destroy structures • Liquefaction: causes building to sink and pull apart by changing soil to liquid mud • Aftershock: earthquake that occurs after a larger earthquake in the same area (could be hours, days, or months later) • Tsunami: water displaced by an earthquake that forms from subduction of the ocean floor

  16. A History of Earthquakes United States • Prince William Sound, Alaska – March 28, 1964 Magnitude 9.2 • San Francisco, California – April 18, 1906 Magnitude 7.8 Around the World • Sumatra, Indonesia – December 26, 2004 Magnitude 9.1 • Haiti – January 12, 2010 Magnitude 7.0

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