Unit 5 - Disaster Management
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This document provides an overview of seismicity and earthquakes. It discusses seismic waves, earthquakes and faults, measures of earthquakes including magnitude and intensity, ground damage from earthquakes, tsunamis caused by earthquakes, and earthquake resistant construction. Specific topics covered include the 2001 Gujarat earthquake in India and the devastating 2004 Indian Ocean tsunami. The document aims to introduce students to key concepts regarding seismicity and earthquakes.
Unit 5 - Disaster Management
- 1. UNIT FIVE: SEISMICITY As per the Syllabus According to our Omnibus Seismic waves Introduction to Earth Earthquakes and faults Tectonic Plates Measures of an earthquake - Faults magnitude & intensity Fundamentals of Earthquakes Ground damage Earthquakes and Tsunamis Tsunamis and earthquakes Ground Damage and Failure Earthquake Resistant Design and Construction The Great Indian Ocean Tsunami, 2004 Gujarat Earthquake, 2001
- 2. INTRODUCTION TO EARTH
- 3. SOME FACTS ABOUT THE EARTH Earth is the only planet to be named in English. The word ‘Earth’ is Old English word for "land“ Earth belongs to the Milky Way Galaxy, Local Group Cluster and Virgo Super Cluster Earth is the only planet to sustain life Earth is believed to be existent for 450 million years & evidences are from 225 million years
- 4. SOME FACTS ABOUT THE EARTH
- 5. SOME FACTS ABOUT THE EARTH Earth is the third planet from the sun Earth is the fifth largest planet in the universe The distance of the earth from the sun is 149,600,000 km The diameter of the sun is 100 times the diameter of the earth The mass of the earth is 5.972 x 1024 kg The Surface area of earth is 510,072,000 km²
- 6. SOME FACTS ABOUT THE EARTH Before 500 BC, people thought that earth was flat. But thanks to scientists like Aristotle and Pythagoras, people know that the shape of the earth is spherical. However Sir Isaac Newton showed that the earth was not a perfect sphere, but a compressed spheroid. The correct technical term to use will be oblate spheroid, a type of ellipsoid solid formed when an ellipse is rotated about its minor axis. The study of size and shape of earth is called geodesy. The diameter of earth at poles is 12715 km (minor axis) The diameter of earth at equator is 12763 km (major axis)
- 7. STRUCTURE OF EARTH The structure of earth (also referred as cross–section) is divided into mainly four layers namely Crust, Mantle, Inner Core and Outer Core.
- 8. STRUCTURE OF EARTH Divisions,Thickness & Materials of the layer
- 9. STRUCTURE OF EARTH CRUST The outermost layer of the Earth is the crust. It is also the surface of the earth. This comprises the continents and ocean basins and therefore it has been classified into continental crust and oceanic crust. The oceanic crust extends up to a distance of 0-10 kms (5-12 taken as average) whereas the continental crust would extend up to 0-75 kms (20-70 taken as average). The oceanic crust is mainly composed of basaltic igneous rocks, mainly of silica and magnesium and therefore also called SIMA layer. The continental crust is composed of crystalline and granitic rocks mainly of silica and aluminum and therefore also called SIAL layer.
- 10. STRUCTURE OF EARTH MANTLE The next layer is the mantle, which is composed mainly of iron and magnesium silicates. It is been referred as FeMa layer. Mantle is also where most of the internal heat of the Earth is located. It is about 2900 km thick. It can be subdivided into four layers namely (1) Lithosphere (70 – 100 kms) (2) Asthenosphere (100 - 350 kms) (3) Upper Mantle (350 – 670 kms) (4) Lower Mantle (670 – 2900 kms) Mohorovičić discontinuity, usually referred to as the Moho is the transition boundary between the Earth's crust and the mantle.
- 11. STRUCTURE OF EARTH MANTLE The lithosphere is the outermost part of the mantle immediately below the Mohorovičić discontinuity. It has a part of the tectonic plates that cover surface of Earth. Asthenosphere is a low seismic velocity zone where rocks are at or near melting point. It also has a part of tectonic plates. The lower mantle is probably mostly silicon, magnesium and oxygen with some iron, calcium and aluminum. The upper mantle is made up of mostly olivine and pyroxene (iron/magnesium silicates), calcium and aluminum
- 12. STRUCTURE OF EARTH OUTER CORE The third layer is outer core. The outer core is a hot and liquid layer comprising mainly of Nickel and (liquid) Iron. Therefore it is referred as NiFe Layer. The outer core may also contain lighter elements such as Si, S, C, or O. The outer core ranges from 2900 kms to 5150 kms and is 2300 km thick. The Earth's magnetic field is believed to be controlled by the liquid outer core. It is also believed to be the responsible force of earth’s rotation and electric currents. The transition space between outer core and mantle is called Gutenberg discontinuity
- 13. STRUCTURE OF EARTH INNER CORE The fourth layer is inner core. This layer stretches from 5150km to 6370 km and is nearly 1200 km thick. The inner core is mostly made of solid iron and has little amounts of nickel. It is unattached to the mantle and is suspended in the molten outer core. The inner core is believed to have the extreme temperature and pressure conditions. The transition region between outer core and inner core is called Lehmann discontinuity
- 15. What is tectonic plates? What are the different tectonic plates? What is the history of tectonic plates? Do the tectonic plates move? Briefly explain the movement of plates? What is continental drift? What is the evidence of tectonic plate movement? How do tectonic plates cause earthquakes? What are intraplate and interplate earthquakes?
- 16. The lithosphere is divided into several slabs or blocks or plates. These plates are supported from below by Asthenosphere. These plates are called Lithosphere plates or Tectonic Plates. Some of these plates encompass continents, some of these plates encompass oceans and some of the plates encompass both oceans and continents.
- 18. The plates are divided into three categories Primary Plates Secondary Plates Tertiary Plates The primary plates and secondary plates are together called major plates. The tertiary plates are sub divisions of Primary and Secondary Plates
- 19. Primary African Plate Antarctic Plate Eurasian Plate Indo-Australian Plate (sometimes Indian and Australian) North American Plate Pacific Plate South American Plate Secondary Arabian Plate Caribbean Plate Cocos Plate Juan de Fuca Plate Nazca Plate Philippine Sea Plate Scotia Plate
- 23. 225 million years ago (Permian) PANGAEA 200 million years ago (Triassic) LAURASIA, GONDWANA 125 million years ago (Jurassic) NENA,COLUMBIA,ZEALANDIA 65 million years ago (Cretaceous) LEMURIA CURRENT 150 million years later AMASIA
- 29. FUTURE
- 31. The movement of tectonic plates is believed to be induced by the asthenosphere which induces heat and convection currents. The plates are capable of drifting with respect to each other along their plate boundaries. Based on the plate movement, there are 3 principal type of boundaries namely Diverging Boundaries Converging Boundaries Transform Boundaries
- 32. Divergent Boundary – moving _____ Convergent Boundary – moving ________ Transform Fault Boundary – moving _____________
- 36. EXAMPLES Divergent Boundaries North American Plate & Eurasian Plate Convergent Boundaries South American Plate & Nazca Plate Transform Boundaries North American Plate & Pacific Plate near the JDF Plate
- 38. PLEASE NOTE When two continental plates diverge, a rift is created. Eg. East African Rift When two oceanic plates diverge, a ridge is created. Sea Floor Spreading is said to occur. Eg. Mid Atlantic Ridge When two oceanic plates converge, an island arc and trench are created. When an oceanic and convergent plate converge, a volcano and trench are created. When two continental plates converge, a mountain range is formed.
- 39. PLEASE NOTE When two continental plates or oceanic plates or continental/oceanic plates transform, EARTHQUAKE HAPPENS If one plate is trying to move past the other, they will be locked until sufficient stress builds up to cause the plates to slip relative to each other. The slipping process creates an earthquake .
- 40. 6. WHAT IS CONTINENTAL DRIFT? The movement of earth’s continents with respect to each other due to the movement of tectonic plates is called continental drift.
- 41. 7. EVIDENCES FOR TECTONIC PLATE MOVEMENT SIMILAR PLANT & ANIMAL FOSSILS IN CONTINENTS SIMILAR LIVING ORGANISMS SIMILAR ROCK TYPES ON CONTINENTS COMPLEMENTARY ARRANGEMENT OF FACING SIDES OF SOUTH AMERICA & AFRICA SEAFLOOR SPREADING DATA
- 42. 8. INTRAPLATE & INTERPLATE EARTHQUAKES 1. An intraplate earthquake is an earthquake that occurs in the interior of a tectonic plate, whereas an interplate earthquake is one that occurs at a plate boundary or a plate margin. 2. Intraplate earthquakes are very rare whereas interplate earthquakes are quite normal. The recurrence interval of intraplate earthquake is 10 – 30 years while that of interplate earthquakes is 100 – 1000 years. 3. The effect (magnitude and intensity) of intraplate earthquakes is less when compared with interplate earthquakes. 4. Notable examples of damaging intraplate earthquakes are the devastating Gujarat earthquake in 2001 while that for interplate earthquakes are Chile 1960 Earthquake and
- 43. FAULTS
- 44. THE TWO MOST IMPORTANT REASONS FOR EARTHQUAKES 1. TECTONIC PLATES 2. FAULTS
- 45. FAULTS FAULTS ARE ONE OF THE STRUCTURAL FEATURES OF ROCKS WHILE ROCKS AT OR NEAR THE SURFACE OF THE EARTH ARE COOL & BRITTLE, ROCKS BELOW THE SURFACE OF THE EARTH ARE HOT AND TEND TO MOVE
- 46. FAULTS A LOT OF EXTERNAL FORCES ACT UPON THE ROCKS AND CAUSE STRESS ON THEM DUE TO THIS STRESSES, ROCKS EITHER UNDERGO DUCTILE DEFORMATION(BEND) OR BRITTLE DEFORMATION(BREAK) IF THEY UNDERGO DUCTILE DEFORMATION, ROCKS DEVELOP FOLDS. IF THEY UNDERGO BRITTLE DEFORMATION, THEY DEVELOP FAULTS.
- 47. FAULTS
- 48. FAULTS FAULT IS DEFINED AS A SPLIT OR CRACK OR FRACRTURE IN THE ROCK PRESENT IN EARTH’S CRUST CHARACTERISED BY RELATIVE DISPLACEMENT OF ONE SIDE OVER THE OTHER. The two sides of a non-vertical fault are known as the hanging wall and footwall. By definition, the hanging wall occurs above the fault plane and the footwall occurs below the fault
- 49. FAULTS
- 50. FAULT LINE A FAULT LINE IS THE INTERSECTION OF A FAULT PLANE AND EARTH SURFACE IT IS THE SURFACE TRACE OF A FAULT
- 51. FAULT LINE
- 52. TYPES OF FAULTS FAULTS ARE CLASSIFIED INTO THREE TYPES NAMELY DIP SLIP FAULTS (VERTICAL MOTION) STRIKE SLIP FAULTS (HORIZONTAL MOTION) OBLIQUE SLIP FAULTS (OBLIQUE MOTION)
- 53. TYPES OF FAULTS
- 54. DIP SLIP FAULTS A fault where the relative movement on the fault plane is approximately vertical is known as a dip-slip fault. Dip Slip Faults are divided into Normal Faults (Extension) Reverse Faults/Thrust Faults (Compression)
- 55. NORMAL FAULTS
- 56. REVERSE FAULTS
- 57. DIP SLIP FAULTS When the hanging wall moves down with respect to the footwall, it is called a normal fault. When the hanging wall moves up relative to the footwall, it is called a reverse fault
- 58. STRIKE SLIP FAULTS A fault where the relative movement on the fault plane is approximately vertical is known as a strike-slip fault. Strike Slip Faults are divided into Left Lateral Faults (Sinistral Faults) Right Lateral (Dextral Faults)
- 61. STRIKE SLIP FAULTS If you stand on one side of a fault and the other side slips to the right, then it is called a right- lateral fault. In a left-lateral fault, the movement occurs to your left.
- 63. OBLIQUE SLIP FAULTS A fault where the relative movement on the fault plane is both horizontal and vertical is known as a oblique-slip fault.
- 65. FAULTS & EARTHQUAKES FAULTS CAN CAUSE TREMENDOUS EARTHQUAKES STRIKE SLIP FAULTS CAUSE MAJOR EARTHQUAKES WHILE OBLIQUE SLIP FAULTS AND DIP SLIP FAULTS CAUSE MINOR EARTHQUAKES. THE OCCURRENCE OF EARTHQUAKES DUE TO FAULTS IS EXPLAINED BY ELASTIC REBOUND THEORY.
- 68. ELASTIC REBOUND THEORY The elastic rebound theory is an explanation for how energy is spread during earthquakes. As plates on opposite sides of a fault are subjected to force and shift, they accumulate energy and slowly deform until their internal strength is exceeded. At that time, a sudden movement occurs along the fault, releasing the accumulated energy, and the rocks snap back to their original undeformed shape.
- 69. FUNDAMENTALS OF EARTHQUAKES
- 70. CONTENTS 1. DEFINITION OF AN EARTHQUAKE 2. EARTHQUAKES & SEISMICS 3. CENTRES AND SHOCKS 4. INTENSITY AND MAGNITUDE OF EARTHQUAKES 5. CAUSES OF EARTHQUAKE 6. SEISMIC WAVES 7. EFFECT OF EARTHQUAKES 8. WORLD SEISMIC ZONES 9. SEISMIC ZONES OF INDIA
- 71. Earthquake may simply expressed as a momentary shock experienced by the earth at a particular location and time. Earthquake may be technically defined as the vibrations induced in the earth’s crust due to internal or external causes that give a shock to a part of the crust and all things existing on it
- 72. The greek word for earthquake is Seism and therefore the term seismic is associated with earthquakes. The science dealing with the study of earthquakes is called seismology The word seismic is used to qualify anything related to earthquake such as seismic intensity, seismic zoning, seismic waves etc.
- 73. FOCUS OR HYPOCENTRE The point of origin of an earthquake below the surface of earth. EPICENTRE The point on the surface directly above the focus where the vibrations are felt.
- 74. SHOCKS A large earthquake is generally preceded and followed by many smaller shocks. The largest earthquake is called the main shock. The smaller ones that occur before the main shock are called foreshocks and the shocks that occur after the main shock are called aftershocks.
- 75. INTENSITY MAGNITUDE Intensity is a term used to Magnitude is a term used measure the impact of to establish the size of an earthquake. earthquake. Intensity measures the It is a measure of the strength of shaking amplitude of a seismic produced by the wave and is related to the earthquake at a certain amount of energy released location. during an earthquake. Intensity is determined Magnitude is the total from effects on energy released by an people, human earthquake at its focus. structures, and the natural environment. The Richter Scale is most famous to express the Mercalli Scale was used magnitude of an to predict intensity. earthquake.
- 76. INTENSITY AND MAGNITUDE Magnitude and Intensity measure different characteristics of earthquakes. Magnitude is quantitative and measured using instrument called seismograph. Intensity is qualitative and can be measured using assessment of the damages.
- 77. INTENSITY AND MAGNITUDE The analogy of tube light is used to differentiate between magnitude and intensity.
- 78. MAGNITUDE Magnitude is the logarithm to base 10 of maximum amplitude traced on the seismogram by an instrument placed at 100 km from the epicenter. It can be generally calculated by the formula M = log (A∆/Ao∆) where M is Richter magnitude ∆ is epicentral distance A is amplitude of the point to be measured Ao is the maximum amplitude of zero earthquake
- 79. INTENSITY Intensity is a space dependent descriptive rating of changes observed to the ground surface in terms of damaging effects. The damaging effects are ground damage, damage to built environment and to the humans. These effects are incorporated in a descriptive intensity scale by a group of experts and denoted by Roman numbers. Maximum intensity is usually close to the epicenter and it reduces as the epicentral distance increases. The lines of same intensity are plotted in a contour map called isoseismal map which is a very important data for earthquake analysis.
- 80. Nowadays intensity of earthquakes are not measured. They have been replaced by magnitude. Top 5 Earthquakes by Magnitude S. Date Place Magnitude No. 1 22 May 1960 Valdivia, Chile 9.5 2 27 March 1964 Alaska, USA 9.2 3 26 December Sumatra, Indonesia 9.1 2004 4 13 August 1862 Arica,Chile 9.0 5 26 January 1700 Cascadia, USA- 9.0 Canada
- 81. An earthquake may be caused by the following natural and artificial sources. NATURAL SOURCES Tectonic Plates Movement 90% Faults in Rocks (Elastic Rebound Theory) 6% Volcanic Explosions 1% ARTIFICIAL SOURCES Explosion 1% Mine Collapse 1% Reservoir Failure 1%
- 82. SEISMIC WAVES The energy released during earthquake travels to the earth in form of waves. The waves are called as P-Waves S-Waves L-Waves (Rayleigh Waves & Love Waves) P-Waves & S-Waves are called as body waves. L- Waves are also called as surface waves.
- 83. The seismic waves are very useful as follows They were used to establish the internal structure of the earth. They are used to calculate the magnitude of earthquake. Richter Scale is based upon the amplitude of the seismic waves. They are also used to locate the epicenter of earthquakes. They are also used for groundwater and other explorations.
- 85. Primary, or P waves are the first waves felt during an earthquake and they are the fastest. They move in a compressional, "push-pull" manner similar to a spring They are longitudinal in character. They move only in the direction of prorogation. They temporarily change the volume of the material they're moving through. They can travel through liquid, solid and gaseous matter. Their velocity increases with depth and decreases after the Gutenberg Discontinuity.
- 86. Secondary, or S waves, are felt next to P waves. These waves move in an oscillatory/distortional manner similar to shaking a rope. They are transverse in character. They move perpendicular to the direction of prorogation. They temporarily change the shape of the material they're traveling through They can travel through solids only. Their velocity increases with depth and they are absent beyond mantle.
- 87. L Waves or Long Waves or Surface Waves are finally felt, are felt next to S waves. They are of two types namely – Love Waves and Rayleigh Waves Rayleigh Waves move in a complex manner. They partly move in direction of propagation and partly perpendicular to the direction of prorogation. Love Waves move in the direction of propagation horizontally but in sideways. It is only the Surface Waves cause damage to the building.
- 91. The effects of earthquakes Loss of Life Building Collapse Ignition of Fire Ground Failure and Rupture Landslides and Avalanches Floods and Tidal Sources Tsunami Change in Soil and Rock Properties
- 92. WORLD SEISMIC ZONES or EARTHQUAKE HOTSPOTS Based on seismicity, the three most happening earthquake hotspots in the world are 1. PACIFIC RING OF FIRE 2. ALPIDE BELT 3. MID ATLANTIC RIDGE
- 96. EARTHQUAKES IN INDIA The major earthquakes in India are 2004 Sumatra Earthquake (9.1) 1934 Bihar Earthquake (8.7) 1950 Assam (Shillong Plateau) Earthquake (8.7) 1897 Assam (Tibetian Plateau) Earthquake (8.5) 2005 Kashmir Earthquake (7.6) 2001 Gujarat(Kutch) Earthquake (7.1)
- 98. EARTHQUAKE ZONES IN INDIA There are five seismic zones named as I to V based on Modified Mercalli Scale (MM Scale) as details given below: Zone V: Covers the areas liable to seismic intensity IX and above on MM Scale. This is the most severe seismic zone and is referred here as Very High Damage Risk Zone. Zone IV: Gives the area liable to MM VIII. This, zone is second in severity to zone V. This is referred here as High Damage Risk Zone. Zone III: The associated intensity is MM VII. This is termed here as Moderate Damage Risk Zone. Zone II: The probable intensity is MM VI. This zone is referred to as Low Damage Risk Zone. Zone I: Here the maximum intensity is estimated as MM V or less. This zone is termed here as Very Low Damage Risk Zone.
- 101. EARTHQUAKE ZONES IN INDIA Zone V: Kashmir, Punjab, the western and Central Himalayas, the North- East Indian region and the Rann of Kutch fall in this zone. Zone IV: Indo-Gangetic basin and the capital of the country(Delhi, Jammu) and Bihar fall in Zone 4. Zone III: The Andaman and Nicobar Islands, parts of Kashmir, Western Himalayas, Western Ghats fall under this zone Zone II: Other parts of India namely Hyderabad, Lakshadweep, Orissa etc. Zone I : No
- 102. EARTHQUAKE ZONES IN INDIA Cities and Zones • Zone III :- Ahemdabad, Vadodara, Rajkot, Bhavnagar, Surat,Mumbai, Agra, Bhiwandi, Nashik, Kanpur Pune, Bhubneshwar, Cuttack, Asansol, Kochi, Kolkata, Varanasi, Bareilly, Lucknow, Indore, Jabalpur, Vijaywada, Dhanwad, Chennai, Coimbatore, Manglore, Kozhikode ,Trivandrum. • Zone IV :- Dehradun, New Delhi, Jamunanagar, Patna, Meerut, Jammu, Amristar,Jalandhar. • Zone V:- Guwahati and Srinagar.
- 104. Overview Meaning of the word Tsunami Definition of Tsunami Characteristics of Tsunami Tsunami Effects Tsunami Vs Tsunami 2004 Formation of Tsunami Tsunami Counter Measures
- 105. Tsunami- Name Meaning IN JAPANESE TSU – HARBOUR NAMI – WAVES TSUNAMI means HARBOUR WAVES
- 106. Tsunami- Definition TSUNAMI IS DEFINED AS SERIES OF GIGANTIC WAVES TRIGGERED IN A LARGE BODY OF WATER BY A DISTURBANCE (LIKE EARTHQUAKE, VOLCANO, LANDSLI DE, METEORITE ETC) THAT DISPLACES WATER VERTICALLY. TSUNAMI HAS SERIOUS EFFECTS IN LOW LYING COASTAL AREAS. IT IS MOSTLY CAUSED BY SUBMARINE EARTHQUAKES
- 107. Tsunami- Characteristics A TSUNAMI IS CAUSED BY AN EARTHQUAKE WHICH HAS ITS FOCUS LESS THAN 50 km A TSUNAMI IS CAUSED BY AN EARTHQUAKE WHOSE MAGNITUDE IS NORMALLY MORE THAN 9.5 THE WAVELENGTH OF A TSUNAMI CAN BE IN THE ORDER OF 100 – 200 KM THE AMPLITUDE OF TSUNAMI WILL BE BETWEEN 0.3m and 0.6m TSUNAMI CAN OCCUR FOR A PERIOD AS LOW AS 5 MINUTES TO AS LONG AS ONE HOUR THE VELOCTITY OF TSUNAMI IS ABOUT 200 m/s or 720 km/hr.
- 108. Tsunami- Characteristics THE WAVELENGTH, PERIOD ,AMPLITUDE AND VELOCITY OF A TSUNAMI ARE DEPENDENT ON THE DIMENSIONS OF THE EARTHQUAKE AND THE DEPTH OF WATER. A TSUNAMI OFTEN COMES IN A SERIES OF WAVES , MAY THREE TO FIVE MAJOR OSCILLATIONS SEPERATED BY SMALL INTERVALS OF HALF AN HOUR OR SO. THE TSUNAMI WAVES CAN STRIKE AS HIGH AS 20 – 40 m (60 ft – 140 ft)
- 109. Tsunami- Characteristics THE TSUNAMI WAVES ARE CHARACTERISED BY APPROACH(COMING IN) AND RETREAT(RECEDING OUT). APPROACH AND RETREAT CAN BE EQUALLY DANGEROUS. THE VELOCITY OF TSUNAMI CAN BE CALCULATED BY FORMULA V2 = (gD) where V = velcity of waves in m/s g = acceleration due to gravity in m/s2 D = depth of water in m
- 110. Tsunami- Effects EXTENSIVE INUNDATION OF COASTAL AREAS EXTENSIVE RUN UP OF COASTAL AREAS DAMAGE TO COASTAL STRUCTURES LOSS OF BUILT ENVIRONMENT LOSS OF HUMAN LIFE LOSS OF FLORA AND FAUNA CHANGES IN WATER QUALITY AND QUANTITY
- 111. Tsunami 2004 - Comparison of Stats TSUNAMI TSUNAMI 2004 Earthquake Depth < 50 30 m Earthquake Magnitude > 7.5 9.1 Wavelength 100 – 200 km 180 km Velocity 600 – 800 km/hr 750 km/hr Amplitude 0.3m to 0.6m 0.5m Period 5 min to 1 hour 45 minutes Height of Waves 20m to 40m 35m
- 112. Tsunami Formation Tsunamis can be generated when the sea floor suddenly displaces the overlying water vertically. When they occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. Waves are formed as the displaced water mass, acting under the force of gravity, tries to regain equilibrium. When large areas of the sea floor elevate or subside, a tsunami can be created.
- 113. Tsunami Formation As a tsunami leaves the deep ocean and travels toward the shallow coast, it transforms. A tsunami moves at a speed related to the water depth, therefore the tsunami slows as the water depth decreases. The tsunami's energy flux, being dependent on both its wave speed and wave height, remains nearly constant. As a result, the tsunami's speed decreases as it travels into shallower water, and its height increases. When it reaches the coast, it may appear as a rapidly rising or a series of breaking waves.
- 114. Tsunami Formation As a tsunami reaches the shore, it begins to lose energy . It slows down and height increases when approaching shallow coast Tsunamis reach the coast with tremendous amounts of energy. Destructive power is due to speed and force with which they strike the coastal area. Tsunamis are stronger and retain height longer than waves generated by wind.
- 115. Tsunami – Counter Measures Coastal Protection Structures (Structural) (Sea Walls, Bulk Heads , Revetments , Dikes and Leeves, Breakwaters, Groynes , Jetties and Piers) Coastal Protection Structures (Non Structural) (Vegetation Planting, Groundwater Drainage, Beach Nourishment, Sand Bypassing and Flood Proofing) Tsunami Early Warning Systems (Sensor Networks and Communication Infrastructure) (International and Regional Warning Systems) Coastal Regulations (Avoiding Low Lying Coastal Areas for developmental works) Evacuation Plan
- 116. GROUND DAMAGE AND FAILURE Surface Distortions Liquefaction Fissures Earthquake Fountain Sand Boils & Mud Flows Mud Volcano Landslides & Avalanches Changes in Surface & Ground Water
- 117. GROUND DAMAGE Due to an earthquake, as a result of passing of seismic waves, the ground or the surface may be damaged in several ways. Fault can cause earthquakes. In turn earthquakes will also lead to faults. Apart from these faults, earthquakes are associated with eight distinct damages to the ground
- 118. GROUND DAMAGES Surface Distortions Liquefaction Fissures Earthquake Fountain Sand Boils & Mud Flows Mud Volcano Landslides & Avalanches Changes in Surface & Ground Water
- 119. SURFACE DISTORTIONS (1) After occurrence of some earthquakes, large scale changes in topography take place and the ground surfaces are distorted. (2) This is most dangerous when it occurs along the coastlines. When surface distortions happen at coastlines, there are two possible ways of damage. 1. Submergence/Subsidence of Coastline 2. Uplift of Coastline
- 120. SURFACE DISTORTIONS (3) When coastlines subside or submerge, it is accompanied by transgression of the sea. In case they uplift, it is accompanied by regression of the sea. (4) Eg. - Due to the Great Indian Ocean Tsunami of 2004, the Andaman and Nicobar Islands showed a large amount of subsidence in the southern islands and equal amount of uplift in the northern islands. Car Nicobar and Indira Point subsided by an amount of 3m leading to water inundating for 3 km while Austen Bridge was uplifted by 1.5 m and new shallow coral beaches emerged.
- 122. LIQUEFACTION (1) Liquefaction is a phenomenon in which the strength and stiffness of soil is reduced due to the ground shaking done by the earthquake. (2) This takes place when there is water table or water bearing formations (aquifers) at 10m or less from the ground surface (3) Due to liquefaction, the ability of soil to support the foundation may decrease and may lead to collapse of structures built on the soil.
- 123. LIQUEFACTION (4) Liquefaction of soil tends to cause settlement of ground. It can also lead to sand boils and mud flows. (5) Due to the Great Bihar – Nepal earthquake of 1934, a 200 km long and 60 km wide liquefaction belt was formed and was named as Slump Belt. Within the belt, many buildings tilted and many buildings settled leading to damage of floors and foundations.
- 125. FISSURES (1) After many earthquakes, the grounds show a long narrow opening due to the process of splitting or separating of land mass. This is called fissures. (2) The fissures can easily develop in alluvial soils and can tend to be long, wide and deep in such soils. (3) The fissures can disturb the underlying soil and drainage systems. Some fissures have sprouted water and sand like fountains.
- 126. FISSURES (4) If fissures are found in abundance, then it may lead to other effects like liquefaction, sand boils, mud flows etc. (5) Due to the great Indian Ocean Tsunami of 2004, fissures were evident in Andaman Trunk Road (ATR). The fissures ranged for nearly 200 kilometres in this 300 km long road and was observed in areas of Baratang, Port Blair and Mayabunder.
- 128. EARTHQUAKE FOUNTAINS (1) When earthquake occurs in areas with plenty of shallow water, the shaking of ground produces fountains, sprouts or geysers. This phenomenon is termed as earthquake fountains. (2) The earthquake fountains may contain water, sand, clay, silt and even debris. (3) The existence of faults in the area or development of fissures in the area may lead to earthquake fountains.
- 129. EARTHQUAKE FOUNTAINS (4) Due to the Gujarat Earthquake of 2001, earthquake fountains full of water and soils were observed in the areas of Bhachau and Amardi. The fountains rose up to 3m height and emerged mainly from fissures. The fountains were found in adjacent locations in a linear stretch for 4 kms.
- 131. SAND BOILS & MUD FLOWS (1) Due to an earthquake, when Sand is brought up into the land and deposited around the sprouted area, it resembles a crater. This phenomenon is called sand boils. The sand boils may lead to local flooding and silt deposition. When the sand boils are full of mud, they are also referred to as mud flows. (2) Due to the Gujarat Earthquake of 2001, sand boils and mud flows were predominant in the areas adjoining the Rukmavati river.
- 133. MUD VOLCANO (1) The term mud volcano or mud dome is used to refer to volcano like formations created by young sedimentary soils at plate margins. (2)This phenomenon will take place only at destructive plate boundaries. The mud volcanoes may contain hot water mixed with mud and other surface deposits. (3) The Great Indian Ocean Tsunami 2004 caused the eruption of many mud volcanoes in Baratung Island in Andaman Nicobar area. It ejected methane gases and the gas plume created fire and explosions.
- 135. LANDSLIDES & AVALANCHES (1) While landslides and avalanches trigger earthquakes, earthquakes may also induce landslides and avalanches. (2)The term landslide describe to a wide variety of processes that result in downward movement of slope forming materials with a distinct zone of weakness. While landslides are formed from solid rock or soil, Avalanches are formed from snow and ice. (3) Lanslides may either be rotational landslides or translational landslides, based on the movement of the failure surface.
- 136. LANDSLIDES & AVALANCHES (4) The Kashmir earthquake of 2005 had sparked a rotational landslide in Baramulla and Uri regions. The same earthquake had sparked a gigantic translational landslide at Sadhna Pass (5) In September 2010, an earthquake at Christchurch, New Zealand triggered more than 12 avalanches at the famous Mountain Hutt.
- 138. CHANGES IN WATER QUALITY (1) The severe ground shaking associated with any earthquake can disturb the ground water and surface water in a very large area. (2)The changes in water quality can be noticed by changes in colour, odour, turbidity, hardness, oxygen content etc of surface waters. The groundwaters get filled with clay and silt and cannot be used for any purpose. (3) Apart from changing the water quality, earthquakes reduce the quantity of water through diversion of surface waters and water level changes in groundwater,
- 139. CHANGES IN WATER QUALITY (4) Due to the Gujarat Earthquake of 2001, the groundwater wells of Lodai and Tehsil and the surface waters of Rann of Kutch were heavily affected and it took more than 5 years to provide remediation.
- 141. LAST BUT NOT THE LEAST The implication of ground damage to built environment is very huge. If buildings and structures are built on damaged grounds, it poses high vulnerability. In such cases, the structures should be avoided or used only after sufficient ground improvement is done.
- 143. As a part of mitigation measures, it becomes necessary to reduce our vulnerability to the most common natural disaster – earthquakes Experience in past earthquakes has shown that many common buildings and public structures lack basic resistance to earthquake forces. With improved design and construction, it is possible to provide more resistance to seismic/earthquake forces and thereby prevent damage to structures and thereby to human life.
- 144. When a new structure is planned, designed and constructed to withstand earthquakes, the process is called earthquake resistant design or aseismic design of structures. Seismic Retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes
- 145. Ten simple steps for earthquake resistant design and constructions are presented in this lecture. Before that here are the basic things to do during an earthquake 1. STAY CALM 2. INSIDE: STAND IN A DOORWAY, OR CROUCH UNDER A DESK OR TABLE, AWAY FROM WINDOWS OR GLASS DIVIDERS 3. OUTSIDE: STAND AWAY FROM BUILDINGS, TREES TELEPHONE AND ELECTRIC LINES 4. ON THE ROAD: DRIVE AWAY FROM UNDERPASSES/OVERPASSES: STOP IN SAFE AREA AND STAY IN A VEHICLE.
- 146. 1. Symmetry and No Eccentricity While planning and designing a building/structure, great care should be ensured for the symmetry of loads and structures. If there is eccentricity in design (when loads do not coincide with centre of mass), then the earthquake risks are large. 2. As per the Code The design and construction of the building should be as per the BIS (Bureau of Indian Standards) codal provision for earthquake resistant design as given under the code book - IS 1893:1984 Criteria for Earthquake Resistant Design of Structures
- 147. 3. SOLVE THE SOIL The soil on which the proposed building/structure would rest upon should be thoroughly checked for its shear strength, soil liquefaction, presence of water bodies etc. The design for the building should be keeping in with the parameters of the soil 4. GET THE BEST MATERIALS For the structure, select quality materials – be it concrete, stones, brick, steel etc. Especially steel having an elongation of above 14% and yield strength of 415N/mm^2 should be used.
- 148. 1. Symmetry and No Eccentricity While planning and designing a building/structure, great care should be ensured for the symmetry of loads and structures. If there is eccentricity in design (when loads do not coincide with centre of mass), then the earthquake risks are large. 2. As per the Code The design and construction of the building should be as per the BIS (Bureau of Indian Standards) codal provision for earthquake resistant design as given under the code book - IS 1893:1984 Criteria for Earthquake Resistant Design of Structures
- 149. 5. STOREY IS THE STORY While planning and designing a building/structure, do avoid weak storeys. Avoid soft storeys in ground floor, especially at car parks. In a frame, care should be taken to avoid weak column and strong beam design 6. ENFORCE REINFORCE The reinforcement design of columns and beams should be done with clear intention to resist lateral forces. A strong reinforcement design would go a long way in ensuring stability against seismic forces
- 150. 7. JUNCTION AND BRACINGS In the junction of columns and beams, the placement of shear walls symmetrically in both directions of the buildings must be done. Alternatively, the provision of cross bracings would also make the structure stable against earthquakes. 8. POST TENSIONING This refers to the provision of unbonded post-tensioning high strength steel tendons to achieve a moment-resisting system that has self- centering capacity against lateral loads like earthquakes.
- 151. 9. BASE ISOLATION Base isolation is a collection of structural elements of a building that should substantially decouple the building's structure from the shaking ground thus protecting the building's integrity and enhancing its seismic performance 10. DAMPING During earthquake, certain amount of energy is transferred to the building and the building will dissipate energy either by undergoing large scale movement or sustaining increased internal strains in elements such as the building's columns and beams. Both of these eventually result in varying degrees of damage. So, by equipping a building with additional devices which have high damping capacity, we can greatly decrease the seismic energy entering the building, and thus decrease building damage
- 152. GUJARAT EARTHQUAKE 2001 1. It is called the 2001 Gujarat earthquake or Kutch Earthquake and it occurred on January 26, 2001, at 08:46 AM local time and lasted for over two minutes. 2. The epicentre was about 9 km south-southwest of the Bhachau Taluka of Kutch District of Gujarat, India. 3. The earthquake reached a magnitude of between 7.6 and 7.7 on the Richter magnitude scale and had a maximum felt intensity of X (Intense) on the Mercalli intensity scale. 4. The quake killed around 20,000 people, injured another 165,000 and destroyed nearly 400,000 homes. . 21 districts were affected and 600,000 people left homeless. The total property damage was estimated at 5.5 billion US dollars 5. This was an intraplate earthquake, one that occurred at a distance from an active plate boundary, so the area was not well prepared. The 2001 Gujurat earthquake was caused by movement on a previously unknown south-dipping fault, trending parallel to the inferred rift structures.
- 153. THE GREAT INDIAN OCEAN TSUNAMI 2004 The 2004 Indian Ocean Tsunami also known as Indonesian tsunami, Sumatra Tsunami or Boxing Day tsunami. was a tsunami triggered by undersea earthquake that occurred at 04:10 AM(IST) on Sunday, 26 December 2004. The epicentre of the earthquake was the west coast of Sumatra, Indonesia. The earthquake was caused by subduction of tectonic plates. With a magnitude of 9.1–9.3, it is the third largest earthquake ever recorded on a seismograph. The earthquake had the longest duration ever observed, between 8.3 and 10 minutes The Tsunami accounted for a killing of over 230,000 people in fourteen countries, and is one of the deadliest natural disasters in recorded history. Indonesia was the hardest-hit country, followed by Sri Lanka, India, and Thailand. The total economic damages were evaluated at more than 20 billion US dollars The risk of famine and epidemic diseases was extremely high immediately following the tsunami and it posed the biggest ever disaster management challenge. The entire world came together to offer rehabilitation for the victims affected by the Tsunami. They were involved in rebuilding homes, children protection, setting up community centres, providing infrastructure, and establishing means of education and livelihood.