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GEO1011

GEO1011. Chap. 19 : Earthquakes. Chap 19: Earthquakes. What is an earthquake and its relation to plate tectonics The seismic waves Location and focal mechanism The sizes of an earthquake and how to measure them Earthquake prediction Seismic hazard and seismic risk. Chap 19: Earthquakes.

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GEO1011

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  1. GEO1011 Chap. 19 : Earthquakes

  2. Chap 19: Earthquakes • What is an earthquake and its relation to plate tectonics • The seismic waves • Location and focal mechanism • The sizes of an earthquake and how to measure them • Earthquake prediction • Seismic hazard and seismic risk

  3. Chap 19: Earthquakes • What is an earthquake and its relation to plate tectonics • The seismic waves • Location and focal mechanism • The sizes of an earthquake and how to measure them • Earthquake prediction • Seismic hazard and seismic risk

  4. Plategrenser og kildedyp

  5. Earthquakes in continental regions

  6. Earthquakes occur in the cold, brittle parts of the Earth: • the upper part (upper crust and upper part of the upper mantle) • the subducted lithosphere

  7. The theory of the elastic rebound Forces associated with plate motion act on plates, but friction inhibits motion until a given stress is reached. Then, slip occurs suddenly.

  8. Friction in the fault plane

  9. Cycles of the elastic rebound

  10. JordskjelvsyklusTektoniske krefter deformasjon spenningskrefter jordskjelv

  11. Description of a fault plane

  12. Three angles to characterize a fault plane and its slip

  13. Normal faults in extension regions like on mid-oceanic ridges, graben structures • Reverse faults in regions under compression, like subduction zones • Strike-slip faults along transform faults or in regions with shear

  14. Plate Boundaries

  15. Trace of the Fuyun earthquake (Mongolia) Fault trace 60 years after an M=8 earthquake

  16. Lamia fault, Greece.

  17. Izmit, Tyrkia

  18. Strike-slip earthquake in Landers (California)

  19. Surface traces of faults after erosion

  20. The tectonic setting of the North-Anatolian fault

  21. Focus: where the slip starts at depth Epicenter: its projection on the surface

  22. The rupture propagates along the fault plane at a velocity of about 3km/s. The rupture lasts a few seconds for moderate earthquakes.

  23. Dimensions of earthquake fault planes: • largest dimensions: 1000km (Chile 1960) • smallest: no lower limit. Any small crack is an earthquake. Thrust Fault Example

  24. Thrust Fault Example

  25. Chap 19: Earthquakes • What is an earthquake and its relation to plate tectonics • The seismic waves • Location and focal mechanism • The sizes of an earthquake and how to measure them • Earthquake prediction • Seismic hazard and seismic risk

  26. The waves propagate away from the earthquake, also called source

  27. Seismic waves Distinguish between the earthquake itself (some motion on a fault) and the vibrations that this sudden motion generates in the surrounding media: the seismic waves. Destruction comes from the seismic waves associated with the earthquake.

  28. Seismic waves = vibrations • Equivalent to sound waves in the air or waves in the water. The earthquake is the stone you throw in the water.

  29. In the air or in fluids, we have pressure waves only. In queues also. • In solids, we have pressure and shear waves: http://www.whfreeman.com/understandingearth

  30. VolumbølgerP-bølger (øverst) og S-bølger (nederst)

  31. OverflatebølgerRayleigh øverst, Love nederst

  32. The periods of these waves: from around 0.01s (local earthquakes) to 53 mn (maximum on Earth)

  33. Seismic waves propagate at velocities of a few km/s: much faster than water waves or sound waves in the air, for which the velocity is 0.3km/s. • At a few km from an explosion, the ground vibration will arrive before the sound.

  34. How are these waves registered? They are registered by seismographs. You have different types of seismographs: • Short-period: for rapid vibrations • Long period: for slow vibrations • Broadband: for all vibrations

  35. Prinsippet for registrering av jordskjelvbølgerVertikal- (øverst) og horisontalbevegelse + clock

  36. Long period electromagnetic seismographs at ATD (Djibouti)

  37. The electronic equipment at ATD:

  38. The entrance to the ATD station (Djibouti)

  39. Globalt nettverk av seismologiske målestasjoner

  40. Wave paths for regional earthquakes

  41. Wave propagation for distant earthquakes

  42. Main layers in the Earth

  43. P S P

  44. Wavepaths for distant earthquakes

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