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EARTHQUAKES: WHY? AND HOW?

Learn about the causes of earthquakes, the damage they can cause, and the different types of seismic waves. Discover how to read seismograms to calculate the magnitude of an earthquake and its distance from the epicenter.

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EARTHQUAKES: WHY? AND HOW?

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  1. EARTHQUAKES:WHY? AND HOW?

  2. EARTHQUAKES sudden movement or shaking of the Earth • Caused by plate tectonic stresses • Located at plate boundaries • Resulting in breakage of the Earth’s brittle crust

  3. PLATE TECTONIC STRESSES • Plate boundaries and faults (= cracks where plate sections are moving in different directions) cause friction as plates move • Plates in a fault zone have STICK-SLIP motion • Periods of no movement (stick) and fast movement (slip) • Energy stored as plates stick, • Energy released as plates slip

  4. EARTHQUAKE DAMAGE • Landslides • Building damage • Liquefaction

  5. EARTHQUAKE DAMAGE Most caused by SURFACE waves (arrive last)

  6. EARTHQUAKE WAVES • FOCUS = place deep within the Earth and along the fault where rupture occurs • EPICENTER = geographic point on surface directly above focus • SEISMIC WAVESproduced by the release of energy • move out in circles from the point of rupture (focus) • 2 types: surface & body (travel inside & through earth’s layers) • P waves: back and forth movement of rock; travel through solid/liquid/gas • S waves: sideways movement of rock; travel through solids only

  7. EARTHQUAKE WAVES • 3 types of seismic waves show up on seismogram • P waves: shake earth in same direction as wave; travel through solid, liquid, gas • S waves: Shake earth sideways to wave direction; travel through solids only • Surface waves: circular movement of rock; travel on surface – cause most damage!!

  8. EARTHQUAKE WAVES P waves move through solids & liquids S waves move through solids only!!!

  9. EARTHQUAKE WAVES Primary (1st to arrive)Longitudinal, Compression Secondary (2nd to arrive - larger) Transverse, Shear all states of matter (solid, liquid, gas) Can go through solids only • back and forth movement of rock • push/pull or compression/stretch out • Vibration is same as the direction of travel • Move sideways • perpendicular to direction of wave travel • Like snake

  10. EARTHQUAKE WAVES Lets test your understanding!! Is this a P or an S wave? P wave! S Wave

  11. EARTHQUAKE WAVES • Seismographs record earthquake waves • Seismograms show: • Amplitude of seismic waves (how much rock moves or vibrates) • Distance to the epicenter • (indirectly)

  12. DISTANCE TO THE EPICENTER Difference in time of arrival between S&P wave  distance to the epicenter • Time-Travel Chart (in ESRT): matching time difference provides the distance • Small time difference  • close to epicenter • Large time difference  • far from epicenter • What you need: • Estimate the time of arrival of the P and S wave • Subtract to get time difference

  13. HOW TO READ SEISMOGRAMS P & S (body waves) move through earth & arrive first • P & S waves used to calculate magnitude of earthquake and distance to the epicenter • Examples (you try it!)

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