EARTHQUAKE environment notes for geology.pptx

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1. Presenting by, R.PARIMALA I – M.Sc., - APPLIED GEOLOGY

2. EARTHQUAKE

3. CONTENTS INTRODUCTION TERMINOLOGY OF EARTHQUAKE CLASSIFICATION OF EARTHQUAKES WHY EARTHQUAKE FORMS MEASURES OF EARTHQUAKE EARTHQUAKE INTENSITY SCALE PREDICTION OF EARTHQUAKE CAUSES OF EARTHQUAKE EFFECTS OF EARTHQUAKE RISK OF EARTHQUAKES EARTHQUAKE OF INDIA

4. INTRODUCTION : Earthquakes constitute one of the worst natural hazards which often turn into disaster causing widespread destruction and loss to human life. An Earthquake is the sudden vibration of the earth’s surface by rapid release of energy. This energy is released when two parts of rock masses move suddenly in relation to each other along a fault.

5. TERMINOLOGY OF EARTHQUAKE: FOCUS : The Focus are otherwise called as hypocenter. The point of origin of and earthquake within the earth’s crust is called the “Focus”. From the focus the earthquake waves radiate in all direction. EPICENTER : The point lying vertically above on the earth’s surface, directly above the focus, is called the “Epicenter” Epicenter the shaking Is most intense. The intensity gradually decreases outwards.

6. ISOCLINAL LINES: The lines connecting points of equal intensity on the ground surface are called “ Isoseismal line”. If the focus is commonly a line, the isoseismal are generally elliptical. From the distribution of the lines, the epicenter of an earthquake can be determined. FAULTS: FAULT LINE: A fault line is the surface trace of a fault, the line of intersection between the earth’s surface FAULT PLANE: Fault plane are the crackers or sudden slips of the land. FAULT SCRAP: A fault scrap is the topographic expression of faulting attributed to the displacement of the land surface movement along faults.

7. TERMS OF EARTHQUAKE

8. CLASSIFICATION OF EARTHQUAKES: CLASSIFICATION-I: Depending upon their mode of origin, the earthquakes are classified into the following groups. 1 ) Earthquake due to surface causes: Earthquake may be generated by landslips and collapse of the roof of underground caverns. Most of these are very minor. 2 ) Earthquakes due to volcanic causes: Volcanic eruption may also produce earthquakes but such earthquakes are usually very feeble. 3) Earthquakes due to tectonic causes: Tectonic earthquakes are the most numerous and usually the most disastrous. They are caused by shocks which originate in the earth’s crust due to sudden movements along faults.

9. EARTHQUAKE SURFACE

10. CLASSIFICATION-II: On the basis of the depth of focus, the earthquakes are divided into the following 1) Shallow focus earthquakes: Earthquake having depth of focus upro 55km. 2) Intermediate focus earthquakes: Earthquakes having depth of focus between 55to 300 km. 3) Deep focus earthquakes: Earthquake shaving depth of focus between 300 to 650 km. The shallow earthquake s are more violent at the surface but affect a smaller area than deep earthquakes.

11. WHY EARTHQUAKE FORMS: Geological faults. Volcanic eruptions. Mine blasts. Nuclear tests. GEOLOGICAL FAULTS: A fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement. There are three main types of faults, namely a) Normal fault. b) Thrust fault. c) Strike slip fault. GEOLOGICAL FAULT

12. NORMAL FAULT: A normal fault occurs when the crust is extended . The hanging wall moves downward relative to the footwall. THRUST FAULT: A thrust fault occurs when the crust is compressed. The hanging wall moves upward relative to the footwall. STRKE SLIP FAULT: The fault surface is usually near vertical and motion results from shearing forces.

13. VOLCANIC ERUPTIONS: A volcanic tectonic earthquake is caused by the movement of magma beneath the surface of the earth. The movement results in pressure changes where the rock around the magma has experienced stress. At some point, this stress can cause the rock to break or move. MINE BLAST: The mine blast are caused by seismic waves produced from the explosion of rock on the surface. NUCLEAR TEST: A nuclear explosion an earthquake and an aftershock sequence.

14. MEASURES OF EARTHQUAKES: SEISMOGRAPHS: “Seismographs” are instruments which detect and record earthquake waves. Most seismographs contains a heavy weight suspended from a support which is attached to bed rocks. When waves from a distant earthquake reach the instrument, the intertia of the weight keeps it stationary, while the earth and the support vibrate. The movement of the earth in relation in the stationary weight is recorded on a rotating drum. Some seismograph detect horizontal motion while others detect vertical motion.

15. SEISMOGRAMS: The trace of the earthquake waves is usually recorded on a travelling photographic paper as a series of zig-zag lines. These recorded are called “Seismograms”. The seismograms the time interval between the arrival of the P and S waves can be calculated and with the help of the travel-time graph. The distance between the recording station and the epicenter is determined.

16. EARTHQUAKE WAVES: During an earthquake seismic waves are generated which spread out wants in all direction from the focus. The seismic waves are of three types: P – Waves S – waves L – waves i ) P – WAVES OR PRIMARY WAVES: These are compressional waves which cause the particles of rocks to vibrate in the longtitunal direction. The P – waves travel fastest. They reach a seismic station firs. Their velocity is 1.7 times than that of S – waves. They passing through solids as well as liquids.

17. S – WAVES OR SECONDARY WAVES: These are shear waves which are transverse in nature. Their velocity is less than the P – Waves. The S – waves travel through solids only and do not pass through liquids. L – WAVES OR SURFACE WAVES: When P - Waves reach the eath’s surface, they are converted into L – Waves. The L – Waves travel along the surface and came earthquakes. They are transverse in nature and their velocity is much less than the P and S waves.

18. EARTHQUAKE INTENSITY SACLE: The intensity scales have been devised. The two commonly used intensity scale are , Rossi Forel scale Ritchter scale i )ROSSI FOREL SCALE: The Rossi Forel is based on how people behave and react, and howmuch destruction or disturbance is caused to man made structures and natural objects. The Rossi Forel scale has nine divisions. Intensity 1 is given to the weakest earthquake. The highest number 9 is assigned to the strongest earthquake. That cause massive destruction to man made structures and natural objects. Intensity above 4 is can damage to properties.

19. ii) RICHTER SCALE: The Richter scale was divised by Charles F. Richter, and American Seismologist. It is based on the total amount of energy released during an earthquake. The Richter scale is used to the Magnitude of an earthquakes. The Magnitude scale are the logarithmic unit. Increase in magnitude of one unit to a tenfold increased in the size of seismic waves and about 30-fold increase in the energy released. The intensity scale are increased of 5.5 - damage to man made structures. The intensity scale are increased of above 8 - major earthquakes are caused total destruction.

20. PREDICTION OF EARTHQUAKE: Earthquake prediction is usually 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.

21. CAUSES OF EARTHQUAKES: Earthquake are caused due to sudden tectonic movements in the earth’s crust. When the tectonic plates slide over one another, there is a cause of orogeny which result in earthquakes and volcanoes. These disturbances cause vibrations spread in all directions. As there is a relative motion of these plates, there is stress built up, which breaks releasing the stored energy known as shock waves.

22. PRIMARY EFFECTS: EFFECTS OF EARTHQUAKES: The destructive effects of an earthquakes can be classified into two divisions. Primary effects Secondary effects They are the immediate damage caused by the earthquake such as collapsing buildings, Roads and Bridges. Which may kill many people. Those lucky enough to survive can suffer badly from shock and panic.

23. SECONDARY EFFECTS: They are the after – effects of the earthquake. The secondary effects divided into five major effects of earthquake.

24. FIRE: Earthquakes destroy gas pipes and electric cables, causing fires to spread. Broken water mains prevent the fires being extinguished. Fires spread very quickly in cities, especially in poor – quality housing areas where wooden building are common TSUNAMIS:: An earthquake on the sea floor or close to the coast may cause huge waves.

25. LANDSLIDES: Earthquakes often cause landslides, especially in steep river valleys and areas of weak rocks DISEASE AND FAMINE: Fresh water supplies are often cut off causing typhoid and cholera. Lack of shelter and food causes much suffering.

26. SOIL LIQUEFACTION: When soil with a high water content are violently shaken they lose their mechanical strength and behave like a fluid and so building can literally sink.

27. RISKS OF EARTHQUAKES: Many seismologist have said that “Earthquake don’t kill people, buildings do”. This is because most deaths from earthquakes are caused by buildings or other human construction falling down during an earthquake. Earthquake located in isolated areas far from human population rarely cause any deaths. Thus, Earthquake hazard risk depends on, 1) Population density. 2) Construction standards (Building codes) 3) Emergency preparedness. Examples: Worst earthquake in recorded history occurred in 1556 in Shaanxi, China. Killed 8,30,000 peoples. Worst earthquake in the 20 th century also occurred in china. Killed 2,40000 in 1976. Occurred at 3:42 AM, Magnitude 7.1 aftershock. Death were due to collapse of masonry (bricks) building.

28. EARTHQUAKE OF INDIA: GUJARAT EARTHQUAKE: The earthquake was felt in most parts of the century and 20 districts in the state of Gujarat sustained damage. The entire kutch region of Gujarat, enclosed on three sides by the great Runn of Kutch, The little Runn of kutch and the Arabian sea sustained highest damage with maximum intensity of shaking as high magnitude intensity scale. 25 district of the state was affected in this earthquake. Around 18 towns, 182 talukas and 7904 villages in the affected. The affected areas even spread up to 300 km from the epicenter. Overall 450 villages are totally destroyed.

29. DAMAGES OF STRUCTURE DURING EARTHQUAKE: