Disaster Management U 2_Lecture - IV.pptx

Unit II

1. Disaster Preparedness & Planning Management Unit – II Disasters Lecture 4 - Earthquakes

2. Earthquakes Earthquakes are sudden, violent, lateral movement of Earth surface due to movement of Earth’s Tectonic Plates.

3. Earth’s Architecture

4. Process of Earthquake The tectonic plates are always slowly moving, but they get stuck at their edges due to friction.  When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel.

5. Earthquake waves When an earthquake occurs, it releases waves of energy, which are known as  Seismic waves. Based on the medium they travel in, earthquake waves can be classified under two categories: Body waves Surface waves Body waves are those waves that travel through the earth. They originate at the epicentre of the earthquake and travel through the earth at amazing speeds. There are two types of body waves namely, P waves S waves Surface waves are those waves that travel on the surface of the earth. The destruction caused by earthquakes is primarily done by these waves.

6. Earthquake waves

7. Earthquake waves P waves  or  Primary waves  are the first waves to hit the seismographs when an earthquake strikes. They are longitudinal waves which means that the direction of motion and propagation are the same. S waves  also called  secondary waves  and  shear waves,  are the second waves to hit the seismographs. They are transverse waves, which means that the motion is perpendicular to the direction of  wave propagation . S waves can only travel through solids and scientists have been successful to map the interior of the earth by studying the routes of these waves.

8. Types of Earthquakes Tectonic Earthquakes: A tectonic earthquake is one that occurs when the earth's crust breaks due to geological forces on rocks and adjoining plates that cause physical and chemical changes.

9. Types of Earthquakes Volcanic Earthquakes: Results from tectonic forces which occur in conjunction with volcanic activity.

10. Types of Earthquakes Collapse Earthquakes: A collapse earthquake are small earthquakes in underground caverns and mines that are caused by seismic waves produced from the explosion of rock on the surface

11. Causes of Earthquakes There are 5 main Causes of Earthquakes: Volcanic Eruptions. The main cause of the earthquake is volcanic eruptions. Tectonic Movements. Geological Faults. Man-Made reasons. Meteorite Impacts.

12. Earthquake Measurements The vibrations produced by earthquakes are detected, recorded, and measured by instruments call seismographs. The zig-zag line made by a seismograph, called a "seismogram," reflects the changing intensity of the vibrations by responding to the motion of the ground surface beneath the instrument.

13. Measuring Size of Earthquakes The severity of an earthquake can be expressed in terms of both intensity and magnitude. Magnitude: The magnitude is a number that characterizes the relative size of an earthquake. Magnitude is based on measurement of the maximum motion recorded by a seismograph. Most Commonly used Magnitude Scales are Local Magnitude Scale Surface Wave Magnitude Scale Body Wave Magnitude Scale Moment Magnitude Scale

14. Richter Scale Richter scale (ML), quantitative measure of an earthquake’s magnitude (size), devised in 1935 by American seismologists Charles F. Richter. The earthquake’s magnitude is determined using the logarithm of the amplitude (height) of the largest seismic wave calibrated to a scale by a seismograph. The Richter Scale was replaced because it worked largely for earthquakes in Southern California, and only those occurring within about 370 miles of seismometers. In addition, the scale was calculated for only one type of earthquake wave. It was replaced with the Moment Magnitude Scale, which records all the different seismic waves from an earthquake to seismographs across the world.

15. Richter Scale

16. Measuring Size of Earthquakes Intensity: The severity of Earthquake is measured in terms of Intensity There are several earthquake intensity scales. The most common scale was “ Modified Mercalli Intensity Scale”. Modified Mercalli Intensity Scale: This scale, composed of 12 increasing levels of intensity that range from imperceptible shaking to catastrophic destruction, is designated by Roman numerals3

17. Protective measures from Earthquakes Advance Preparations: Improve your home’s earthquake resilience Stockpile water and Food Stuffs Participate in Disaster Training Discuss Disaster Preparedness with your Family