Earthquake Grade 8 Science and techn ppt
- 2. EARTHQUAKES • Caused by plate tectonic stresses sudden movement or shaking of the Earth • 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 WAVES produced 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 Body P waves S waves waves AKA Moves through Movement of rock Primary (1st to arrive) Longitudinal, Compression all states of matter (solid, liquid, gas) • back and forth movement of rock • push/pull or compression/stretch out • Vibration is same as the direction of travel Secondary (2nd to arrive - larger) Transverse, Shear Can go through solids only • 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!)