Earthquakes-In The Eye of Civil Engineer

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  • Earthquake
  • Outline What is an Earthquake? Cause of Earthquake Measuring Earthquake Earthquakes Epicenter Located? Size and Strength of an Earthquake Measured? Destruction from Earthquake Earthquake Prediction Remedial Measures Case Studies
  • 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
  • Focus, Epicenter, and Fault
  • 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.
  • 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.
  • 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
  • Three Types of Faults Strike-Slip Thrust Normal
  • Slippage along a Fault
  • Elastic Rebound Theory
  • Strike-slip Fault Example
  • Normal Fault Example Dixie Valley-Fairview Peaks, Nevada earthquake December 16, 1954
  • Thrust Fault Example
  • Thrust Fault Example
  • Earthquake Effects - Ground Shaking Northridge, CA 1994
  • Earthquake Effects - Ground Shaking Northridge, CA 1994
  • Earthquake Effects - Ground Shaking KGO-TV News ABC-7 Loma Prieta, CA 1989
  • Earthquake Effects - Ground Shaking Kobe, Japan 1995
  • Earthquake Effects - Ground Shaking Kobe, Japan 1995
  • Earthquake Effects - Surface Faulting Landers, CA 1992
  • Earthquake Effects - Liquefaction Source: National Geophysical Data Center Niigata, Japan 1964
  • Earthquake Effects - Landslides Turnagain Heights, Alaska,1964 (upper left inset); Santa Cruz Mtns, California , 1989 Source: National Geophysical Data Center
  • Earthquake Effects - Fires KGO-TV News ABC-7 Loma Prieta, CA 1989
  • Earthquake Effects - Tsunamis Photograph Credit: Henry Helbush. Source: National Geophysical Data Center 1957 Aleutian Tsunami
  • Margalla Tower,Islamabad
  • Total Slip in the M7.3 Landers Earthquake Rupture on a Fault
  • Depth Into the earth Surface of the earth Distance along the fault plane 100 km (60 miles) Slip on an earthquake fault START
  • Slip on an earthquake fault Second 2.0
  • Slip on an earthquake fault Second 4.0
  • Slip on an earthquake fault Second 6.0
  • Slip on an earthquake fault Second 8.0
  • Slip on an earthquake fault Second 10.0
  • Slip on an earthquake fault Second 12.0
  • Slip on an earthquake fault Second 14.0
  • Slip on an earthquake fault Second 16.0
  • Slip on an earthquake fault Second 18.0
  • Slip on an earthquake fault Second 20.0
  • Slip on an earthquake fault Second 22.0
  • Slip on an earthquake fault Second 24.0
  • 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.
  • 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.
  • Bigger Faults Make Bigger Earthquakes 1 10 100 1000 5.5 6 6.5 7 7.5 Magnitude Kilometers 8
  • Bigger Earthquakes Last a Longer Time 1 10 100 5.5 6 6.5 7 7.5 8 Magnitude Seconds
  • 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
  • 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
  • Earthquake Waves Measuring Earthquakes Seismographs are instruments that record earthquake waves. Seismograms are traces of amplified, electronically recorded ground motion made by seismographs.
  • Seismograph
  • At convergent boundaries, focal depth increases along a dipping seismic zone called a Benioff zone
  • 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 event