Earthquake Engineering 2012 Lecture 0102 Nature of Earthquakes

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  • 1. EARTHQUAKEENGINEERING 1.2. N Nature of f Earthquakes 1.2.1. Causes of Earthquakes 1.2.2. Faults 1.2.3. Earthquake Effects
  • 2. 1.2.1. Causes of EarthquakesTectonic Earthquakesare caused by the sudden dislocation of large rock masses alonggeological faults within the earths crust. The Earth is formed ofseveral l l layers that h h have very diffdifferent physical and chemical h i l d h i lproperties. The outer layer, which averages about 70 kilometersin thickness, consists of about a dozen large, irregularly shapedplates that slide over under and past each other on top of the over,partly molten inner layer .Most earthquakes occur at theboundaries where the plates meet . Plate Tectonic Interactions Flash movieDr. Osman Shalan Dr. Tharwat Sakr
  • 3. 1.2.1. Causes of EarthquakesTectonic Earthquakes Dr. Osman Shalan Dr. Tharwat Sakr
  • 4. 1.2.1. Causes of EarthquakesVolcanic Earthquakes Earthquakes that can be reasonably associated with volcanoes are relatively rare and fall into three categories: (i) volcanic explosions, (ii) shallow earthquakes from magma movements, and (iii) sympathetic tectonic earthquakes Dr. Osman Shalan Dr. Tharwat Sakr
  • 5. 1.2.1. Causes of EarthquakesVolcanic Earthquakes Dr. Osman Shalan Dr. Tharwat Sakr
  • 6. 1.2.1. Causes of EarthquakesVolcanic Earthquakes Dr. Osman Shaalan Dr. Tharwat Sakr
  • 7. 1.2.1. Causes of EarthquakesExplosions Earthquakes may be produced q y pby the undergrounddetonation of chemical ornuclear devices When a devices.nuclear device is detonated ina borehole underground,enormous nuclear energy isreleased .Dr. Osman Shalan Dr. Tharwat Sakr
  • 8. 1.2.1. Causes of EarthquakesCollapse Earthquakes Collapse earthquakes are small earthquakes occur in regions of underground caverns and mines. The immediate cause of ground shaking is the sudden collapse of the roof g g p of the mine or cavern. Dr. Osman Shalan Dr. Tharwat Sakr
  • 9. 1.2.1. Causes of EarthquakesLarge Reservoir-induced Earthquakes Reservoir- The idea that earthquakes might be triggered by impounding q g gg y p g surface water is not new. The first detailed evidence of such an effect came with the filling of Lake Mead behind Hoover Dam (height 221 m. After impounding began , reports of local shaking became prevalent. b l t Dr. Osman Shalan Dr. Tharwat Sakr
  • 10. 1.2.1. Causes of EarthquakesTsunamiUnderwater earthquakes,volcanoes, or landslidescan produce a tsunami ortidal wave. This wave cantravel very rapidlythousands of miles acrossthe ocean. In deep waterthe tsunami may only raisethe ocean level by a fewcentimeters,centimeters hardly enoughto notice. But as itapproaches land, theshallower water causes thewave to build in height toas much as 10-20 metersor more and suddenlyflood coastal areas Dr. Osman Shalan Dr. Tharwat Sakr
  • 11. 1.2.2. FaultsDefinition A fault is a fracture within some particular rocky mass within the earths crust. Th d h and h The depth d length of faults vary greatly. Faults may range in length from few meters to many kilometers and are drawn on a geological map as continuous or broken lines. Earthquakes are caused by q y active faults, that is, faults along faults which the two sides of the fracture move with respect to each other. S an earthquake i h th So, th k is caused by the sudden movement of the two sides of a fault with respect to another . Dr. Osman Shalan Dr. Tharwat Sakr
  • 12. 1.2.2. FaultsActive FaultsProf.Dr. Osman Shaalan Dr. Tharwat Sakr
  • 13. 1.2.2. FaultsTectonic Plates Dr. Osman Shalan Dr. Tharwat Sakr
  • 14. 1.2.2. Faults Types of Faults a) Normal faults These occur in response to pulling or tension: the overlying bl k i h l i block moves down the dip of the fault plane. movie b) Thrust (reverse) faults These occur in response to squeezing or compression: the overlying block moves up the dip y g p p of the fault plane. movie c) Strike‐slip (lateral) faults Strike‐ These occur in response to either type of stress: th bl k move t f t the blocks horizontally past one another . movieProf.Dr. Osman Shaalan Earthquake Engineering Dr. Tharwat Sakr
  • 15. 1.2.2. Faults Earthquake Focus The point on the fault where rupture initiates is referred to as the f h focus or h hypocentert of an earthquake. The hypocenter of an earthquake is described by q y its depth in kilometers, its map location in latitude and The term epicenter is the longitude, its date and time point on the earth’s surface earth s of occurrence, and i f d its directly above the magnitude hypocenterProf. Dr. Osman Shaalan Earthquake Engineering Dr. Tharwat Sak
  • 16. 1.2.3. Earthquake Effects How do Earthquakes affect Structures? q 1‐ By inertial forces generated b severe d by ground shaking Overturning collapse of a high-rise building Chi Chi Chi-Chi earthquake, Taiwan, September 20, 1999, Magnitude 7.6Prof.Dr. Osman Shaalan Earthquake Engineering Dr. Tharwat Sakr
  • 17. 1.2.3. Earthquake Effects How do Earthquakes affect Structures? q 2. By earthquake‐ induced fires:  i d d fi Damage caused by the earthquake induced fires Hanshin (Kobe) earthquake, January 17, 1995, Japan, Magnitude 6.9Prof.Dr. Osman Shaalan Earthquake Engineering Dr. Tharwat Sakr
  • 18. 1.2.3. Earthquake Effects How do Earthquakes affect Structures? q 3. By changing the physical properties of the foundation soils such as Liquefaction: Overturning due to liquefaction g q Damage due to liquefaction Kocaeli earthquake, Turkey, 1999, Magnitude 7.4 1964 Niigata, Japan, earthquake.Prof.Dr. Osman Shaalan Earthquake Engineering Dr. Tharwat Sakr
  • 19. 1.2.3. Earthquake Effects How do Earthquakes affect Structures? qProf.Dr. Osman Shaalan Earthquake Engineering Dr. Tharwat Sakr
  • 20. 1.2.3. Earthquake Effects How do Earthquakes affect Structures? qProf.Dr. Osman Shaalan Earthquake Engineering Dr. Tharwat Sakr
  • 21. 1.2.3. Earthquake Effects How do Earthquakes affect Structures? q 4. By direct fault displacement at the site of a structure:Prof.Dr. Osman Shaalan Earthquake Engineering Dr. Tharwat Sakr
  • 22. 1.2.3. Earthquake Effects How do Earthquakes affect Structures? q 5. By landslides, or other movement:Prof.Dr. Osman Shaalan Earthquake Engineering Dr. Tharwat Sakr
  • 23. 1.2.3. Earthquake Effects How do Earthquakes affect Structures? q 6. By seismic sea waves (tsunamis) or fluid motions in reservoirs and lakes (seiches):Prof.Dr. Osman Shaalan Earthquake Engineering Dr. Tharwat Sakr