Earthquakes-In The Eye of Civil Engineer


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Earthquakes-In The Eye of Civil Engineer

  1. 1. Earthquake
  2. 2. Outline What is an Earthquake? Cause of Earthquake Measuring Earthquake Earthquake’s Epicenter Located? Size and Strength of an Earthquake Measured? Destruction from Earthquake Earthquake Prediction Remedial Measures Case Studies
  3. 3. Earthquakes What Is an Earthquake? • Focus or hypocenter is the point within Earth where the earthquake starts. • Epicenter is the location on the surface directly above the focus.  An earthquake is the vibration of Earth produced by the rapid release of energy  Focus and Epicenter
  4. 4. Focus, Epicenter, and Fault
  5. 5. •At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacement of the ground. When a large earthquake epicenter is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides, and occasionally volcanic activity. •Earthquakes are caused mostly by rupture of geological faults, but also by other events such as volcanic activity, landslides, mine blasts, Meteorite strike and nuclear tests.
  6. 6. Types Of Earth Quakes Shallow Focus EQ Earthquakes occurring at a depth of less than 10 km are classified as 'shallow-focus' earthquakes. Intermediate Focus EQ Those with a focal-depth between 70 and 300 km are commonly termed 'mid-focus' or 'intermediate-depth' earthquakes. Deep Focus EQ •In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, deep-focus earthquakes may occur at much greater depths (ranging from 300 up to 700 kilometers). •These seismically active areas of subduction are known as Wadati-Benioff zones. •Deep-focus earthquakes occur at a depth where the subducted lithosphere should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep-focus earthquakes is faulting caused by olivine undergoing a phase transition into a spinel structure.
  7. 7. Cause of Earthquakes  Elastic Rebound Theory Most earthquakes are produced by the rapid release of elastic energy stored in rock that has been subjected to great forces. When the strength of the rock is exceeded, it suddenly breaks, causing the vibrations of an earthquake. Rupture occurs and the rocks quickly rebound to an un deformed shape Energy is released in waves that radiate outward from the fault
  8. 8. Three Types of Faults Strike-Slip Thrust Normal
  9. 9. Slippage along a Fault
  10. 10. Elastic Rebound Theory
  11. 11. Strike-slip Fault Example
  12. 12. Normal Fault Example Dixie Valley-Fairview Peaks, Nevada earthquake December 16, 1954
  13. 13. Thrust Fault Example
  14. 14. Thrust Fault Example
  15. 15. Earthquake Effects - Ground Shaking Northridge, CA 1994
  16. 16. Earthquake Effects - Ground Shaking Northridge, CA 1994
  17. 17. Earthquake Effects - Ground Shaking KGO-TV News ABC-7 Loma Prieta, CA 1989
  18. 18. Earthquake Effects - Ground Shaking Kobe, Japan 1995
  19. 19. Earthquake Effects - Ground Shaking Kobe, Japan 1995
  20. 20. Earthquake Effects - Surface Faulting Landers, CA 1992
  21. 21. Earthquake Effects - Liquefaction Source: National Geophysical Data Center Niigata, Japan 1964
  22. 22. Earthquake Effects - Landslides Turnagain Heights, Alaska,1964 (upper left inset); Santa Cruz Mtns, California , 1989 Source: National Geophysical Data Center
  23. 23. Earthquake Effects - Fires KGO-TV News ABC-7 Loma Prieta, CA 1989
  24. 24. Earthquake Effects - Tsunamis Photograph Credit: Henry Helbush. Source: National Geophysical Data Center 1957 Aleutian Tsunami
  25. 25. Margalla Tower,Islamabad
  26. 26. Total Slip in the M7.3 Landers Earthquake Rupture on a Fault
  27. 27.  Depth Into the earth Surface of the earth Distance along the fault plane 100 km (60 miles) Slip on an earthquake fault START
  28. 28. Slip on an earthquake fault Second 2.0
  29. 29. Slip on an earthquake fault Second 4.0
  30. 30. Slip on an earthquake fault Second 6.0
  31. 31. Slip on an earthquake fault Second 8.0
  32. 32. Slip on an earthquake fault Second 10.0
  33. 33. Slip on an earthquake fault Second 12.0
  34. 34. Slip on an earthquake fault Second 14.0
  35. 35. Slip on an earthquake fault Second 16.0
  36. 36. Slip on an earthquake fault Second 18.0
  37. 37. Slip on an earthquake fault Second 20.0
  38. 38. Slip on an earthquake fault Second 22.0
  39. 39. Slip on an earthquake fault Second 24.0
  40. 40. Causes • While most earthquakes are caused by movement of the Earth's tectonic plates. • Earthquakes are caused mostly by rupture of geological faults, but also by other events such as volcanic activity, landslides. • Violent Volcanic eruptions may cause E.Q. • If ,Meteorite strikes the earth.
  41. 41. • While most earthquakes are caused by movement of the Earth's tectonic plates, human activity can also produce earthquakes. Four main activities contribute to this phenomenon: storing large amounts of water behind a dam (and possibly building an extremely heavy building), drilling and injecting liquid into wells, and by coal mining and oil drilling. • Perhaps the best known example is the 2008 Sichuan earthquake in China's Sichuan Province in May; this tremor resulted in 69,227 fatalities and is the 19th deadliest earthquake of all time. The Zipingpu Dam is believed to have fluctuated the pressure of the fault 1,650 feet (503 m) away; this pressure probably increased the power of the earthquake and accelerated the rate of movement for the fault. • The greatest earthquake in Australia's history is also claimed to be induced by humanity, through coal mining. The city of Newcastle was built over a large sector of coal mining areas. The earthquake has been reported to be spawned from a fault that reactivated due to the millions of tonnes of rock removed in the mining process.
  42. 42. Bigger Faults Make Bigger Earthquakes 1 10 100 1000 5.5 6 6.5 7 7.5 Magnitude Kilometers 8
  43. 43. Bigger Earthquakes Last a Longer Time 1 10 100 5.5 6 6.5 7 7.5 8 Magnitude Seconds
  44. 44. What Controls the Level of Shaking? • Magnitude More energy released • Distance Shaking decays with distance • Time Span How long E.Q stays in a locality • Local soils/rock conditions Amplify the shaking M5 M6 M7
  45. 45. Cause of Earthquakes • An aftershock is a small earthquake that follows the main earthquake. Continuing adjustment of position results in aftershocks. • A foreshock is a small earthquake that often precedes a major earthquake.  Aftershocks and Foreshocks
  46. 46. Earthquake Waves Measuring Earthquakes  Seismographs are instruments that record earthquake waves.  Seismograms are traces of amplified, electronically recorded ground motion made by seismographs.
  47. 47. Seismograph
  48. 48. At convergent boundaries, focal depth increases along a dipping seismic zone called a Benioff zone
  49. 49. Seismotectotics Seismotectonics is the study of the relationship between the earthquakes, active tectonics and individual faults of a region. It seeks to understand which faults are responsible for seismic activity in an area by analyzing a combination of regional tectonics, recent instrumentally recorded events, accounts of historical earthquakes and geomorphologic evidence. This information can then be used to quantify the seismic hazard of an area.
  50. 50. Measuring Earthquakes What are Seismic Waves? Response of material to the arrival of energy fronts released by rupture Body Waves: P and S waves Surface Waves: R and L waves
  51. 51. Body Waves: P and S waves • Body waves – P or primary waves • fastest waves • travel through solids, liquids, or gases • compressional wave, material movement is in the same direction as wave movement – S or secondary waves • slower than P waves • travel through solids only • shear waves - moves material perpendicular to wave movement
  52. 52. Surface Waves: R and L waves • Surface Waves – Travel just below or along the ground’s surface – Slower than body waves; rolling and side-to-side movement – Especially damaging to buildings
  53. 53. 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. How is an Earthquake’s Epicenter Located?
  54. 54. How is an Earthquake’s Epicenter Located?  Earthquake Distance • Travel-time graphs from three or more seismographs can be used to find the exact location of an earthquake epicenter. • A circle where the radius equals the distance to the epicenter is drawn. • The intersection of the circles locates the epicenter • The epicenter is located using the difference in the arrival times between P and S wave recordings, which are related to distance. • About 95 percent of the major earthquakes occur in a few narrow zones.  Earthquake Direction  Earthquake Zones
  55. 55. Locating an Earthquake 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
  56. 56. How is an Earthquake’s Epicenter Located?  Earthquake Distance • Travel-time graphs from three or more seismographs can be used to find the exact location of an earthquake epicenter. • A circle where the radius equals the distance to the epicenter is drawn. • The intersection of the circles locates the epicenter • The epicenter is located using the difference in the arrival times between P and S wave recordings, which are related to distance. • About 95 percent of the major earthquakes occur in a few narrow zones.  Earthquake Direction  Earthquake Zones
  57. 57. How is an Earthquake’s Epicenter Located?
  58. 58. Material P wave Velocity (m/s) S wave Velocity (m/s) Air 332 Water 1400-1500 Petroleum 1300-1400 Steel 6100 3500 Concrete 3600 2000 Granite 5500-5900 2800-3000 Basalt 6400 3200 Sandstone 1400-4300 700-2800 Limestone 5900-6100 2800-3000 Sand (Unsaturated) 200-1000 80-400 Sand (Saturated) 800-2200 320-880 Clay 1000-2500 400-1000 Glacial Till (Saturated) 1500-2500 600-1000
  59. 59. Size and Strength of an Earthquake Measured?  Historically, scientists have used two different types of measurements  intensity  magnitude
  60. 60. How are the Size and Strength of an Earthquake Measured? • Modified Mercalli Intensity Map – 1994 Northridge, CA earthquake, magnitude 6.7 • Intensity – subjective measure of the kind of damage done and people’s reactions to it – Iso-seismal lines identify areas of equal intensity
  61. 61. Modified Mercalli Scale I. Instrumental Not felt except by a very few under especially favorable conditions. II. Feeble Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing. III. Slight Felt quite noticeably by persons indoors, especially on the upper floors of buildings. Many do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibration similar to the passing of a truck. Duration estimated. IV. Moderate Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably. Dishes and windows rattle. V. Rather Strong Felt by nearly everyone; many awakened. Some dishes and windows broken. Unstable objects overturned. Clocks may stop. VI. Strong Felt by all; many frightened and run outdoors, walk unsteadily. Windows, dishes, glassware broken; books off shelves; some heavy furniture moved or overturned; a few instances of fallen plaster. Damage slight. VII. Very Strong Difficult to stand; furniture broken; damage negligible in building of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken. Noticed by persons driving motor cars. VIII. Destructive Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture moved. IX. Ruinous General panic; damage considerable in specially designed structures, well designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations. X. Disastrous Some well built wooden structures destroyed; most masonry and frame structures destroyed with foundation. Rails bent. XI. Very Disastrous Few, if any masonry structures remain standing. Bridges destroyed. Rails bent greatly. XII. Catastrophic Total damage - Almost everything is destroyed. Lines of sight and level distorted. Objects thrown into the air. The ground moves in waves or ripples. Large amounts of rock may move.
  62. 62. How are the Size and Strength of an Earthquake Measured? • Magnitude – Richter scale measures total amount of energy released by an earthquake; independent of intensity – based on Amplitude of the largest wave produced by an event is corrected for distance and assigned a value on an open-ended logarithmic scale Each unit of Richter magnitude equates to roughly a 32-fold energy increase Does not estimate adequately the size of very large earthquakes
  63. 63. Size and Strength of an Earthquake Measured?  Momentum Magnitude • Derived from the amount of displacement that occurs along the fault zone • Moment magnitude is the most widely used measurement for earthquakes because it is the only magnitude scale that estimates the energy released by earthquakes. • Measures very large earthquakes (surface area of fault) x (avg. displacement along fault) x (rigidity of rock)
  64. 64. Earthquake Magnitudes
  65. 65. Some Notable Earthquakes
  66. 66. TSUNAMI A tsunami (plural: tsunamis or tsunami; from Japanese: , lit. "harbor wave" English pronunciation: or also called a tsunami wave train, and at one time incorrectly referred to as a tidal wave, is a series of water waves caused by the displacement of a large volume of a body of water, usually an ocean, though it can occur in large lakes.
  67. 67. Causes Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), landslides and other mass movements, meteorite ocean impacts or similar impact events, and other disturbances above or below water all have the potential to generate a tsunami. Some meteorological conditions, such as deep depressions that cause tropical cyclones, can generate a storm surge, called a meteo-tsunami, which can raise tides several meters above normal levels. The displacement comes from low atmospheric pressure within the centre of the depression. As these storm surges reach shore, they may resemble (though are not) tsunamis, inundating vast areas of land. There have been studies and at least one attempt to create tsunami waves as a weapon. In World War II, the New Zealand Military Forces initiated Project Seal which attempted to create small tsunamis with explosives in the area of today's Shakespear Regional Park; the attempt failed.
  68. 68. If the first part of a tsunami to reach land is a trough— called a drawback—rather than a wave crest, the water along the shoreline recedes dramatically, exposing normally submerged areas. A drawback occurs because the water propagates outwards with the trough of the wave at its front. Drawback begins before the wave arrives at an interval equal to half of the wave's period. Drawback can exceed hundreds of metres, and people unaware of the danger sometimes remain near the shore to satisfy their curiosity or to collect fish from the exposed seabed.
  69. 69. Intensity scales The first scales used routinely to measure the intensity of tsunami were the Sieberg-Ambraseys scale, used in the Mediterranean Sea and the Imamura-Iida intensity scale, used in the Pacific Ocean. The latter scale was modified by Soloviev, who calculated the Tsunami intensity I according to the formula I= ½ + Log2 H av where H is the average wave height along the nearest coast. This scale, known as the Soloviev-Imamura tsunami intensity scale, is used in the global tsunami catalogues compiled by the NGDC/NOAA and the Novosibirsk Tsunami Laboratory as the main parameter for the size of the tsunami.
  70. 70. Magnitude scales The first scale that genuinely calculated a magnitude for a tsunami, rather than an intensity at a particular location was the ML scale proposed by Murty & Loomis based on the potential energy. Difficulties in calculating the potential energy of the tsunami mean that this scale is rarely used. Abe introduced the tsunami magnitude scale , calculated from, Mt= a log h + b log R = D where h is the maximum tsunami-wave amplitude (in m) measured by a tide gauge at a distance R from the epicenter, a, b & D are constants used to make the Mt scale match as closely as possible with the moment magnitude scale.
  71. 71. The Economics and Societal Impacts of EQs Damage in Oakland, CA, 1989• Building collapse • Ground failure / Liquefaction • Tsunami • Fire
  72. 72. Seismic Vibrations Destruction from Earthquakes The damage to buildings and other structures from earthquake waves depends on several factors.  the intensity  duration of the vibrations  the nature of the material on which the structure is built  the design of the structure.
  73. 73. Significant Causes of Infrastructure Damage Engineered (Institutional Buildings) • Quality of construction and construction materials • Lack of seismic considerations • Lack of monitoring • Building codes • Governance weakness Non-Engineered (Private Buildings/Homes) • Lack of awareness about seismically resistant design • Settling of structures • Aspiration to modernize with insufficient knowledge of safe construction • Cost
  74. 74. Seismic Vibrations Destruction from Earthquakes  Liquefaction • Saturated material turns fluid • Underground objects may float to surface
  75. 75. Tsunamis: the Japanese word for “seismic sea wave” Destruction from Earthquakes  Cause of Tsunamis • A tsunami triggered by an earthquake occurs where a slab of the ocean floor is displaced vertically along a fault. • A tsunami also can occur when the vibration of a quake sets an underwater landslide into motion. Although tsunamis travel quickly, there is sufficient time to evacuate all but the area closest to the epicenter.
  76. 76. Other Dangers Destruction from Earthquakes • With many earthquakes, the greatest damage to structures is from landslides and ground subsidence, or the sinking of the ground triggered by vibrations.  Landslides • In the San Francisco earthquake of 1906, most of the destruction was caused by fires that started when gas and electrical lines were cut.  Fire
  77. 77. A CO2 fire extinguisher rated for flammable liquids and gasses A chemical foam extinguisher with contents. A chemical foam extinguisher with contents. water extinguisher
  78. 78. Can Earthquakes be Predicted? Earthquake Prediction Programs – include laboratory and field studies of rocks before, during, and after earthquakes – monitor activity along major faults – produce risk assessments
  79. 79. Predicting Earthquakes • So far, methods for short-range predictions of earthquakes have not been successful.  Short-Range Predictions • Scientists don’t yet understand enough about how and where earthquakes will occur to make accurate long-term predictions.  Long-Range Forecasts
  80. 80. Remedial Measures Increase public awareness about hazard risk management. Build capacity of professionals and government officials.  Safe building practices and earthquake resistant design. Develop and enforce simple building codes for rural and peri-urban areas.
  81. 81. Seismic Microzonation • Seismic microzonation is defined as the process of subdividing a potential seismic or earthquake prone area into zones with respect to some geological and geophysical characteristics of the sites such as ground shaking, liquefaction susceptibility, landslide and rock fall hazard, earthquake-related flooding, so that seismic hazards at different locations within the area can correctly be identified.
  82. 82. • Microzonation provides the basis for site-specific risk analysis, which can assist in the mitigation of earthquake damages. • Dynamic characteristics of site such as predominant period, amplification factor, shear wave velocity, standard penetration test values can be used for seismic microzonation purpose. • On the basis of these information, we review our construction design according to seismic hazards, and take preventive measures for stability of structures.
  83. 83. Earthquake Preparedness • Earthquake preparedness refers to a variety of measures designed to help individuals, businesses, and local and state governments in earthquake prone areas to prepare for significant earthquakes. Before Earth Quake • Retrofitting and earthquake resistant designs of new buildings and lifeline structures (e.g. bridges, hospitals, power plants). • We should have response doctrines for state and local government emergency services. • We should train common people by media about Preparedness plans for E.Q.
  84. 84. During Earth Quake • Drop to the ground • Take Cover by getting under a sturdy table or other piece of furniture. • Hold on until the shaking stops. • If You Are Inside • Kneel under a desk, table, or bench. If there aren’t enough sturdy pieces of • furniture to get under, kneel next to an interior walls but away from windows, • overhead light fixtures, and tall pieces of furniture that might fall over. • Stay under cover until the shaking stops (at least one minute). Face away • from windows, and bend your head close to your knees. • Hold on to the table leg or desk (a few inches above the ground to avoid • pinching fingers). Cover your eyes with your other hand. If your “shelter” • moves, move with it. If you don’t have a “shelter” to hang on to, clasp your • hands on the back of your neck to protect your face.
  85. 85. If You Are Outside • Move into the open, away from buildings, fences, trees, tall playground • equipment, utility wires, and street lights. • • Kneel or sit on the ground and cover your head and face with your • hands. • • Once in the open, stay there until the shaking stops.
  86. 86. What You Can Do After an Earthquake • Is it safe to move in ? • Once the shaking has stopped, look around for possible hazards to determine if it is safe for you to move before getting up and helping others. If time permits and there is a small fire that can be put out with the fire extinguisher, do that. • 2. If you are inside, decide whether to evacuate or stay put. • Any of the following require immediate evacuation. • Fire, damage to structure, a gas leak, or hazardous materials spill. • In some situations, you may choose not to evacuate or to delay evacuation. • For example, if there is a slight shaking with no apparent damage and another hazard such as severe weather, it may be more dangerous to move children outside. • If you smell gas or hear a blowing or hissing noise, open a window and then quickly leave with the children, and shut the gas off at the outside main meter.
  87. 87. • you must evacuate immediately (because of fire, severe damage to structure, gas leak, or hazardous materials spill), check all children and adults for injuries and give first aid for injuries. • As time permits, you may need to turn off utilities such as gas, electricity, and water. • If electrical wires are crackling inside, shut off the gas first, then turn off the master electrical switch.
  88. 88. CASE STUDIES Kashmir Earth Quake Chile Earth Quake
  89. 89. Kashmir Earthquake 8th October 2005 7.6-magnitude earthquake took place on Saturday 8th October at 08:25 local time. The epicentre was Muzzaffarabad the capital of the Pakistan administered region of Kashmir, 80km north-east of Islamabad. It was followed by 20 powerful aftershocks
  90. 90. How did the earthquake occur The earthquake in Pakistan is the result of India's long-term, gradual, geological movement north into Asia at a speed of five centimetres a year - a millimetre per week. Plate Boundary ???
  91. 91. Discovering Earth’s Composition Earth’s Layered Structure  Mantle  Crust • Early seismic data and drilling technology indicate that the continental crust is mostly made of lighter, granitic rocks. • Composition is more speculative. • Some of the lava that reaches Earth’s surface comes from asthenosphere within.  Core • Earth’s core is thought to be mainly dense iron and nickel, similar to metallic meteorites. The surrounding mantle is believed to be composed of rocks similar to stony meteorites.
  92. 92. Thanks ??......