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earthquake
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- 2. Earthquakes constitute oneof the worst natural hazards which often turn into disaster causing widespread destruction and loss to human life. The effects of earthquake vary upon the magnitude and intensity. Earthquakes occur every now and then all round the world, except in some places where earthquakes occur rarely. The devastation of cities and towns is one of the effects of earthquake.
- 3. What is Earthquake? •An Earthquake is the result of a sudden release of energy in the earth’s crust that creates seismic waves. • The seismic activity of an area refers to the frequency type and size of earthquakes experienced over a period of time.
- 4. Focus(Hypocenter): Focus is thepoint on the fault where rupture occurs and the location from which seismic waves are released. Epicenter: Epicenter is the point on the earth’s surface that is directly above the focus ,the point where an earthquake or underground explosion originates.
- 5. • Fault: Asurface across which two blocks can move relative to each other. • Fault Scrap: A Fault scrap is the topographic expression of faulting attributed to the displacement of the land surface by movement along faults. • Magnitude: A measure of the strength of an earthquake, as determined by seismographic observations.
- 6. Foreshocks and aftershocks •Relative measurement • Foreshocks: smaller earthquakes before the main event; – a portion of the fault moves • Aftershocks: larger earthquakes after the main event; – Adjustment of the fault plane
- 7. The primary causeof an earthquake is faults on the crust of the earth. “A Fault is a break or fracture b/w two blocks of rocks in response to stress.” This movement may occur rapidly, in the form of an earthquake or may occur slowly, in the form of creep. Some major causes of earthquakes are •Surface cause •Volcanic cause •Tectonic cause
- 8. • Surface cause: Greatexplosions, landslides, slips on steep coasts, dashing of sea waves avalanches , railway trains, heavy trucks, some large engineering projects cause minor tremors. some of them are man made, other are natural. • Volcanic cause: • Volcanic eruptions produce earthquakes. Earthquakes may precede, accompany and frequently follow volcanic eruptions. • They are caused by sudden displacements of lava within or beneath the earth crust. • There are general categories of earthquakes that can occur at a volcano: volcano-tectonic earthquakes long period earthquakes
- 9. • Tectonic cause: Structuraldisturbances resulting in the parts of the lithosphere is the main cause of this type of earthquake. Most of the disastrous earthquakes belong to this category and occur in areas of great faults and fractures. Sudden yielding to strain produced on the rocks of accumulating stress causes displacements especially along old fault zones known as great transform faults.
- 10. Seismic waves produceddue to earthquake are basically divided into two major types: Body waves Surface waves
- 11. Body waves: Body wavestravels through the interior(body) of earth as they leave the focus. Body waves are further divided into following types: Primary (P) waves Secondary(S) waves
- 12. Primary Waves (P-waves)Secondary Waves(S-wave) High frequency High frequency Short Wavelength Short Wavelength Longitudinal waves Transverse waves Pass trough both solids and liquids Can not move through liquids Move forwards and backwards as it compressed and decompressed Move in all direction from their source P-wave is faster S-wave is more slower than P- wave First P-wave arrive After P-wave,S-wave is arrive
- 13. Surface Wave: Surface wavestravels parallel to the earth’s surface and these waves are slowest and most damaging. Surface wave are divided into following types: Love waves Rayleigh waves
- 14. Love Waves Rayleighwave Guided waves Guided waves Displacement is parallel to the free surface Displacement is perpendicular to love-wave displacement Love wave is faster Rayleigh wave is slower Causes horizontal shifting of the earth surface. Ground move in circular motion.
- 15. How is anEarthquake’s Epicenter Located? Seismic wave behavior – P waves arrive first, then S waves, then L and R – Average speeds for all these waves is known – After an earthquake, the difference in arrival times at a seismograph station can be used to calculate the distance from the seismograph to the epicenter.
- 16. How is anEarthquake’s Epicenter Located? Time-distance graph showing the average travel times for P- and S- waves. The farther away a seismograph is from the focus of an earthquake, the longer the interval between the arrivals of the P- and S- waves
- 17. How is anEarthquake’s Epicenter Located? • Three seismograph stations are needed to locate the epicenter of an earthquake • A circle where the radius equals the distance to the epicenter is drawn • The intersection of the circles locates the epicenter
- 18. 3 Types ofEarthquakes (based on focus-depth): 1. shallow-focus depths <70km 2. intermediate-focus depths 70 to 300 km 3. deep-focus depths >300 km 90% of all EQs foci depths <100 km Only 3% are deep-focus.
- 19. Where Do EarthquakesOccur? • Majority (80%) occur in the circum-Pacific belt. (Along this belt, most EQs are assoc. with convergent plate boundaries but also occur along divergent & transform boundaries.) • 15% of EQs occur along the Mediterranean-Asiatic belt. (along a predominantly convergent zone) • 5% occur in plate interiors & along divergent margins. (Intraplate EQs take place along ancient faults commonly associated with buried plate margins.) • ~150,000 EQs strong enough to be felt are recorded each year. • Another 900,000 are recorded, but are too small to be cataloged individually. How Often Do Earthquakes Occur?
- 20. How is theSize of Earthquakes Measured? • A seismograph is the the tool used to measure the strength of an earthquakes • The seismograph prints out a seismogram that scientists read to determine the strength of the quake. • The data from the seismogram is translated into a 1-10 rating on the Richter Scale. Each step in the scale represents a tenfold increase in the size of the quake
- 21. What is aSeismograph • The Modern Seismograph • Seismic waves cause the seismograph’s drum to vibrate. But the suspended weight with the pen attached moves very little. Therefore, the pen stays in place and records the drum’s vibrations.
- 22. How are EarthquakesMeasured? Richter Scale A logarithmic scale used to express the total amount of energy released ___________ of an earthquake. Its values typically fall between 0 and 9, with each increase of 1 representing a _________ increase in energy. magnitude 10-fold
- 23. Mercalli Intensity Scale Goto http://tinyurl.com/13quake13 A scale of earthquake intensity based on ___________ and ranging from I (detectable only with instruments) to XII (causing almost total destruction). observed effects
- 24. • Zone -II: This is said to be the least active seismic zone. • Zone - III: It is included in the moderate seismic zone. • Zone - IV: This is considered to be the high seismic zone. • Zone - V: It is the highest seismic zone. The earthquake zoning map of India divides India into 4 seismic zones Based on the observations of the affected area due to Earthquake india divided into four types of zones:
- 26. Earthquake prediction isusually defined as the specification of the time , location , and magnitude of a future earthquake within stated limits. But some evidence of upcoming Earthquake are following: Unusual animal behavior Water level in wells Large scale of fluctuation of oil flow from oil wells Foreshocks or minor shocks before major earthquake Temperature change Uplifting of earth surface Change in seismic wave velocity
- 27. Loss of lifeand property Damage to transport system i.e. roads, railways, highways, airports, marine Damage to infrastructure. Chances of Floods – Develop cracks in Dams Chances of fire short-circuit. Communications such as telephone wires are damaged. Water pipes, sewers are disrupted Economic activities like agriculture, industry, trade and transport are severely affected.
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- 30. Date Place ScaleDamage Sept 2, 1993 Latur (maharashtra) 6.3 Large areas of Maharashtra rocked. 10,000 people lost lives. May 22, 1997 Jabalpur (Maharashtra) 6.0 40 person killed and over 100 injured. March 29, 1999 Nandprayag 6.8 widespread destruction in chamoli , rudraprayag and other areas. Massive loss of human life. Jan. 26, 2001 Bhuj (gujrat) 7.8 Tremors left by India and its neighboring countries. Over 1 lakh people killed. Huge loss to property and infrastructure. Oct. 8, 2005 Muzzaffarabad in Pakistan occupied Kashmir 7.4 Heavy damage to life and property. Death toll about one lakh in Pakistan and nearly 2000 in India.
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