SEC3NA Earthquakes & Tsunami
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SEC3NA Earthquakes & Tsunami






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  • Tsunami waves can propagate in all directions. In the deep ocean, tsunami waves can propagate with the speed of 500-1000 km per hour. Wave height in the deep ocean is only about 1 meter. When approaching the coast, the tsunami wave speed decreases to about 30 miles per hour, but its height was increased to tens of meters. Tsunami waves hit can go up to tens of kilometers from the shoreline

SEC3NA Earthquakes & Tsunami SEC3NA Earthquakes & Tsunami Presentation Transcript

  • EarthquakesEarthquakes: What are they? • A natural disaster in which the earth begins to shake violently due to natural movement of the earth’s crust • Causes mass destruction to human infrastructure and lives, depending on the magnitude
  • WHAT ARE EARTHQUAKES? • The shaking or trembling caused by the sudden release of energy • Usually associated with faulting or breaking of rocks • Continuing adjustment of position results in aftershocks
  • EarthquakesEarthquakes: How do they form? • The earth’s crust is divided into plates that slide over the athenosphere, constantly moving • Interaction between plates involves a great amount of pressure, and alterations of the land, especially on the edge of plates • Earthquakes are a result of the pressure-the grinding of the plates causes the land to shake
  • WHAT IS THE ELASTIC REBOUND THEORY? • Explains how energy is stored in rocks • Rocks bend until the strength of the rock is exceeded • Rupture occurs and the rocks quickly rebound to an undeformed shape • Energy is released in waves that radiate outward from the fault
  • The Focus and Epicenter of an Earthquake • The point within Earth where faulting begins is the focus, or hypocenter • The point directly above the focus on the surface is the epicenter
  • Types of Earthquake Deep-focus earthquake Shallow focus earthquake Location of focus Occurs between 70 & 700km below the earth’s surface Occurs in the upper 70km of the earth’s crust Impact on land Smaller impact on the land as vibrations or seismic wave take a long time to reach the surface and would have lost most of the energy by then Greater impact on the land as vibrations or seismic waves reach the land surface more quickly
  • How do you measure Earthquake?
  • Seismographs record earthquake events At convergent boundaries, focal depth increases along a dipping seismic zone called a Benioff zone
  • 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 • Amplitude of the largest wave produced by an event is corrected for distance and assigned a value on an open-ended logarithmic scale
  • HOW ARE THE SIZE AND STRENGTH OF AN EARTHQUAKE MEASURED? • Intensity • subjective measure of the kind of damage done and people’s reactions to it • isoseismal lines identify areas of equal intensity • Modified Mercalli Intensity Map – 1994 Northridge, CA earthquake, magnitude 6.7
  • Richter scale
  • WHERE DO EARTHQUAKES OCCUR AND HOW OFTEN? ~80% of all earthquakes occur in the circum-Pacific belt • most of these result from convergent margin activity • ~15% occur in the Mediterranean-Asiatic belt • remaining 5% occur in the interiors of plates and on spreading ridge centers • more than 150,000 quakes strong enough to be felt are recorded each year
  • LOCATION OF EARTHQUAKE • Occurs at convergent, divergent and transform plate boundaries but occur most frequently at convergent boundaries • This is due to stress build up where a plate subduct
  • ACTIVITY • In pair, do a mind map of the impact of earthquake Impact of earthquake Clue: Refer to your textbook
  • WHAT ARE THE DESTRUCTIVE EFFECTS OF EARTHQUAKES? • Ground Shaking • amplitude, duration, and damage increases in poorly consolidated rocks
  • THE ECONOMICS AND SOCIETAL IMPACTS OF EQS Damage in Oakland, CA, 1989 • Building collapse • Fire • Tsunami • Ground failure
  • EarthquakesEarthquakes: Environmental Effects • Several occur every day, some are not even felt by people • People are displaced, injured, and killed by earthquakes with a magnitude of 6.0 or larger • Costs can range from nothing to billions of dollars to repair entire regions • Many people are left without homes, jobs, communities, and family members • Buildings that are resistant to earthquakes exist, but even those are not a guarantee for safety
  • CAN EARTHQUAKES BE PREDICTED? Earthquake Precursors • changes in elevation or tilting of land surface, fluctuations in groundwater levels, magnetic field, electrical resistance of the ground • seismic dilatancy model • seismic gaps
  • 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
  • CAN EARTHQUAKES BE CONTROLLED? • Graph showing the relationship between the amount of waste injected into wells per month and the average number of Denver earthquakes per month • Some have suggested that pumping fluids into seismic gaps will cause small earthquakes while preventing large ones
  • TOPICS: • Definition of tsunami • The causes of Tsunami • Characteristic of tsunami • The effect • Countermeasures of Tsunami
  • DEFINITION OF TSUNAMI Tsunami(harbor wave): The displacement of water caused by changes in sea surface vertically with a sudden.
  • THE CAUSES OF TSUNAMI 4 causes of sea level changes:  an earthquake centered under the sea  underwater volcanic eruptions  underwater landslides  meteor or lacing at sea Ba
  • CHARACTERISTIC OF TSUNAMI Tsunami cause damage by two mechanisms: • the smashing force of a wall of water travelling at high speed • and the destructive power because of large volume of water.
  • CHARACTERISTIC OF TSUNAMI • While everyday wind waves have a wavelength of about 100 meters and a height of roughly 2 meters, a tsunami in the deep ocean has a wavelength of about 200 kilometers. • Such a wave travels at well over800 kilometers perhour, but owing to the enormous wavelength the wave oscillation at any given point takes 20 or30 minutes to complete a cycle. This makes tsunamis difficult to detect overdeep water. • This is the reason forthe name "harborwave".
  • CHARACTERISTIC OF TSUNAMI •About 80% of tsunamis occurin the Pacific Ocean, but they are possible whereverthere are large bodies of water, including lakes. They are caused by earthquakes, landslides, volcanic explosions
  • THE EFFECT S • To People: -Loss of lives & family. -Loss of jobs & living. -Loss of livestock. -Negative impact on the affected region's economy. -Negative impact of the affected region's tourism.
  • THE EFFECTS • To the Environment: -Alteration of seaside terrain. -Wildlife casualties. -The sea will be temporarily littered with debris after the tsunami. -Coral or Marine Reef damage (In tropical regions).
  • COUNTERMEASURES OF TSUNAMI EFFECT • The detector equipment should be well maintained. • Train the people how to overcome the tsunami. • Make seawall around the shoreline. • Preparation of evacuation • More alert when there is an earthquake above 6 on the Richter scale