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  1. 1. Suchitra Laishram MSc.II year Panjab University
  2. 2. OBJECTIVES  List the different types of seismic waves, their different properties and describe how seismologists can use them to learn about earthquakes and the Earth's interior.  Describe how to find an earthquake epicenter.  Describe the different earthquake magnitude scales and what the numbers for moment magnitude mean.  Describe how earthquakes are predicted and why the field of earthquake prediction has had little success.
  3. 3. WHAT ARE EARTHQUAKES?  The shaking or trembling caused by the sudden release of energy.  Usually associated with faulting or breaking of rocks.
  4. 4. STUDYING EARTHQUAKES Seismology --The study of earthquakes and the waves they create. Seismologists --Scientists who study and measure earthquakes to learn more about them and to use them for geological discovery.
  5. 5. SEISMOGRAPHS  Modern day scientists use a instrument called a seismograph to record earthquakes.  Seismogram is a graph output by a seismograph.  This instrument records earthquakes using waves.  The larger the waves the larger the earthquake.
  6. 6. ELASTIC REBOUND THEORY  Explains how energy is stored in rocks  Rocks bend until the strength of the rock is exceeded.  Rupture occurs and the rocks quickly rebound to an undeformed shape.  Energy is released in waves that radiate outward from the fault.
  7. 7. The Focus and Epicenter of an Earthquake  The point within Earth where faulting begins is the focus, or hypocenter.  The point directly above the focus on the surface is the epicenter.
  8. 8. WHERE DO EARTHQUAKES OCCUR AND HOW OFTEN?  Abt 80% of all earthquakes occur in the circum-Pacific belt.  Most of these result from convergent margin activity.  Abt 15% occur in the Mediterranean-Asiatic belt.  Remaining 5% occur in the interiors of plates and on spreading ridge centers.
  9. 9. SEISMIC WAVES  Seismic waves are waves of energy that travel through the Earth's layers, and are a result of an earthquake.  Two types: Body waves -- Primary(p) waves and -- Secondary(s) waves Surface waves -- Love waves and -- Rayleigh waves
  10. 10. BODY WAVES  Primary waves (p)  fastest waves.  travel through solids, liquids, or gases.  compressional wave, material movement is in the same direction as wave movement.  Secondary waves(s)  slower than P waves.  travel through solids only.  shear waves - move material perpendicular to wave movement.
  11. 11. SURFACE WAVE  Two types  Love waves-- are horizontally polarized shear waves existing only in the presence of a semi-infinite medium overlain by an upper layer of finite thickness.  travel slightly faster than Rayleigh waves.  Rayleigh waves--travel as ripples with motions that are similar to those of waves on the surface of water  They are slower than body waves.  In the layered medium (like the crust and upper mantle) it depends on their frequency and
  12. 12. TYPES OF EARTHQUAKES  Tectonic Earthquakes --occur when rocks in the earth's crust break due to geological forces created by movement of tectonic plates.  Volcanic Earthquakes occur in conjunction with volcanic activity.  Explosive Earthquakes result from the explosion of nuclear and chemical devices.  Collapse Earthquakes are small earthquakes in underground caverns and mines.
  13. 13. CLASSIFICATION OF EARTHQUAKE  Earthquakes are usually classified on the following bases: (a) Cause of origin; (b) Depth of focus; and (c) Intensity and magnitude of earthquake.
  14. 14. (A) CAUSE OF ORIGIN: (i) Tectonic Earthquakes occur when the plates move against one another. This movement can create stress that causes the Earth's exterior shell, the lithosphere, to shift or break. (ii) Non-tectonic earthquakes. The non-tectonic earthquakes are mainly of three types due to surface causes, volcanic causes and collapse of cavity roofs .
  15. 15. (B) DEPTH OF FOCUS (i) Surface-earthquakes : Surface-earthquakes are those in which the depth of the focus is less than 10,000 metres. (ii) Shallow-earthquakes : The earthquakes with the hypocentre at a depth of 10 to 50. (iii) Intermediate-focus earthquakes : When the earthquake is originated at a depth of 50 to 300 Kms. (iv) Deep-focus earthquakes : The deep-focus earthquakes or the plutonic earthquakes are those with hypocentres located at depths more than 300 kms. Majority of the deep focus earthquakes originate between 500 and 700 kms.
  16. 16. (C) INTENSITY AND MAGNITUDE OF EARTHQUAKES  Rossi-Forrel's Scale  Mercalli Scale  Richter Scale
  17. 17. (I) ROSSI-FORREL'S SCALE The 1873 version of the Rossi–Forel scale had 10 intensity levels: I. Microseismic tremor II. Extremely feeble tremor. III. Feeble tremor. IV. Slight tremor V. Moderate tremor VI. Strong tremor VII. Very strong tremor. VIII. Damaging tremor IX. Devastating tremor. X. Extremely high intensity tremor.
  19. 19. Magnitude  Richter scale measures total amount of energy released by an earthquake; independent of intensity.  Amplitude of the largest wave produced by an event is corrected for distance and assigned a value on an open-ended logarithmic scale .
  20. 20. TYPES OF DAMAGE CAUSE BY EARTHQUAKE  Physical Damage -- Landslides -- Tsunamis -- Fires -- Mudslides -- Liquefaction  Structural Damage -- Buildings Collapse -- Roadways Collapse  Emotional Damage -- Deaths
  21. 21. CAN EARTHQUAKES BE PREDICTED?  With the present state of scientific knowledge, it is not possible to predict earthquakes and certainly not possible to specify in advance their exact date, time and location.  However, a great deal of research is being conducted to develop reliable prediction methods such as Unusual behavior of animal. Radon gas emission. Electro-magnetic variations, etc .
  25. 25. TO DO BEFORE ,DURING ,AFTER EARTHQUAKE Before the Earthquake: -- Learn first aid,Be prepared to act. -- Stock up on emergency supplies. -- Arrange your work area for safety. During an Earthquake: -- Remain calm as the quake occurs. -- Don't use elevators. -- Drop down; take cover under a desk or table and hold on. After an Earthquake: --Remain calm and reassuring. -- ready to act without electricity or lights. -- If you must leave a building, use extreme caution -- Use telephones only to report a life-threatening emergency.
  26. 26. HELPLINE GIVEN  North and Central America UNESCO-HELP Basins.  Brazil National Water Agency Delegation.  USACE Global and Climate Scientists Featured.  PIANC USA Commissions.  U.S. Geological Survey.  U.S. Bureau of Reclamation and Sandia National  Upper Rio Grande Commissions.
  27. 27. THANK YOU