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Earthquakes
 

Earthquakes

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  • Why do rock break? Review three types of stress: tension, compression, shear Three types of deformation resulting: elastic, plastic and brittle We’re concerned with the brittle deformation – causes faults, fractures through which energy, created by the friction, is released Define Focus, epicenter and seismic waves
  • A drop of water – analogy between ripples in the water and seismic waves
  • P-waves: the bell analogy: waves felt by both sound
  • Earliest seismograph was invented in China ~ 2000 years ago (or 136 AD) Easy to make; can make your own at home
  • Write Table 11-1 on the board, to help relate to Richter scale
  • A large mass of ice and rock separated from a vertical face on Nevado Huascaran, the highest peak in Peru The slab fell 1000 m vertically, disintegrated, slid down the lateral slopes of the mountain, and then was launched off a 'ski jump'. Debris reached a velocity as high as 280 km/hr buried the towns of Yungay and Ranrahirca, having traveled 11 km horizontally in about 4 minutes at a mean velocity of 165 km/hr. The death toll in both villages was 20,000.
  • Animals and earthquakes: On February 4, 1975 the Chinese successfully evacuated the city of Haicheng several hours before a 7.3 magnitude earthquake-- based primarily on observations of unusual animal behavior. Conventional science has never been able to adequately explain the phenomenon. Although the majority of accounts pertain to dogs and cats, there are also many stories about other types of animals in the wild, on farms, and in zoos; including horses, cows, deer, goats, possums, rats, chickens, and other birds. The behavior has been reported in many other animal species as well, including fish, reptiles, and even insects. Deep sea fish, for example, have been caught close to the surface of the ocean on numerous occasions around Japan prior to earthquakes (Tributsch, 1982). A number of theories have been proposed to explain this phenomenon, and what the precursory signals that the animals are picking up on might be. Because many animals possess auditory capacities beyond the human range, it has been suggested that some animals may be reacting to ultrasound emitted as microseisms from fracturing rock (Armstrong, 1969). Another candidate is fluctuations in the earth's magnetic field. Because some animals have a sensitivity to variations in the earth's magnetic field (usually as a means of orientation), and since variations in the magnetic field occur near the epicenters of earthquakes (Chapman and Bartels, 1940), it has been suggested that this is what the animals are picking up on.

Earthquakes Earthquakes Presentation Transcript

  • Earthquakes
  • Objectives
    • Relate earthquake activity to plate tectonics
    • Define earthquake, and identify the focus and epicenter of an earthquake.
    • Describe the types of waves emitted during an earthquake.
    • Distinguish between earthquake intensity and magnitude.
    • Locate the epicenter of an earthquake
  • Convection currents cause the movement of plates
    • If the plates become “locked”- unable to move
    • Potential Energy (PE) builds up
    • PE may be released as KE and the plates move abruptly apart
    • This sudden release of energy is an earthquake
  • Shifting plates
  •  
  • Why do earthquakes occur?
    • Fractures, faults
    • Energy released
    • and propagates in all directions as seismic waves causing
    • earthquakes
    focus epicenter
  • Where do earthquakes occur:
    • 1) Most earthquakes occur along the edge of the oceanic and continental plate
    • 2) Along faults: normal, reverse, transform
  • definitions
    • Earthquake = Vibration of the Earth produced by the rapid release of energy
    • Seismic waves = Energy moving outward from the focus of an earthquake
    • Focus = location of initial slip on the fault; where the earthquake origins
    • Epicenter = spot on Earth’s surface directly above the focus
  • Seismic waves: forms
    • P-waves: (primary or first)
      • called compressional, or push-pull waves
      • Propagate parallel to the direction in which the wave is moving
      • Move through solids, liquids
      • Fastest moving – reach seismic station first
    • S-waves: (secondary)
      • Called shear waves
      • Propagate the movement perpendicular to the direction in which the wave is moving
      • Reach seismic station second
    • Surface waves (L-waves or long waves).
      • Complex motion
      • Up-and-down and side-to-side
      • Slowest
      • Most damage to structures, buildings
  • Which diagram shows a transverse wave? a longitudinal wave? an s-wave? a p-wave?
    • b
    • a
  • Longitudinal wave P-waves Sound waves Transverse wave S-waves Light waves
  • Measuring earthquakes
    • Seismometers: instruments that detect seismic waves
    • Seismographs
    Record intensity, height and amplitude of seismic waves
  •  
  • Locating the shaking
    • Measure time between P and S waves on a seismogram
    • Need at least 3 seismographs
  •  
  •  
  • Earthquake size: two ways to measure
    • Magnitude : Richter Scale
      • Measures the energy released by fault movement
      • related to the maximum amplitude of the S wave measured from the seismogram
      • Logarithmic-scale; quantitative measure
      • For each whole number there is a 31.5 times increase in energy
        • eg. an increase from 5 to 7 on the Richter scale = an increase in energy of 992 times!!
    • 2) Intensity: Mercalli Scale:
      • What did you feel?
      • Assigns an intensity or rating to measure an earthquake at a particular location ( qualitative)
      • I (not felt) to XII (buildings nearly destroyed)
      • Measures the destructive effect
    • Intensity is a function of:
        • Energy released by fault
        • Geology of the location
        • Surface substrate: can magnify shock waves e.g. Mexico City (1985) and San Francisco (1989)
  • Frequency of Occurrence of Earthquakes ¹ Based on observations since 1900. ² Based on observations since 1990. 1,300,000 (estimated) 2 - 2.9 Very Minor 130,000 (estimated) 3 - 3.9 Minor 13,000 (estimated) 4 - 4.9 Light 1319 ² 5 - 5.9 Moderate 134 ² 6 - 6.9 Strong 17 ² 7 - 7.9 Major 1 ¹ 8 and higher Great Average Annually Magnitude Descriptor
  • Recent Earthquake Activity in the World
  • Largest earthquake in the world Chile : 1960 May 22 19:11:14 UTC Magnitude 9.5
    • More than 2,000 killed, 3,000 injured, 2,000,000 homeless, and $550 million damage in southern Chile
    • tsunami caused 61 deaths
    • $75 million damage in Hawaii;
    • 138 deaths and $50 million damage in Japan;
    • 32 dead and missing in the Philippines;
    • and $500,000 damage to the west coast of
    • the United States.
  •  
  • Most Destructive Known Earthquakes on Record in the World 166,836 injured, 600,000 homeless . 7.7 20,023 India 2001 Jan 26 Estimated death toll as high as 30,000 Old lake bed magnified shock waves by 500% 8.0   9500 (official) Mexico Michoacan Sept 19, 1985 Estimated death toll as high as 655,000. 7.5 255,000 (official) China,  Tangshan July 27, 1976 $530,000,000 damage, great rock slide, floods. 7.9 66,000 Peru May 31, 1970 Deaths from earthquake and tsunami 9.0 283,106 Sumatra 2004 Dec 26 Comments Magnitude Deaths Location Date
  • Earthquake damage
    • Ground Failure - constructions collapse
    • Fires - from broken gas and electrical lines
    • Landslides - EQ's triggered; occur in hilly/mountainous areas.
    • Liquefaction - water-saturated, unconsolidated materials flow
    • Tsunami (seismic sea waves; "tidal" waves) - can grow up to 65 m
  • Earthquakes and the San Andreas Fault 
  •  
  •  
  • Liquefaction
  • Collapse of elevated freeway in Kobe, Japan
  • Generating a tsunami
  • Landslides: May 30, 1970 Peru disaster
    • Magnitude: 7.9
    • A large mass of ice and rock slid from a vertical face on Nevado Huascaran, the highest peak in Peru
    • Debris reached a velocity of 280 km/hr
    • traveled 11 km horizontally in about 4 minutes at a mean velocity of 165 km/hr.
    • Buried the towns of Yungay and Ranrahirca, The death toll in both villages was 20,000.
  • The town of Huaraz flattened
  • India, Gujarat earthquake Jan 26, 2001
  • Jun 23, 2001 S.Peru earthquake Arequipa
    • San Francisco 1906
  • Earthquake risk and prediction
    • Long-term methods
    1) seismic hazard maps 2) probability analysis based on: - historical EQ records - geologic EQ records - slip-rate on active faults - frequency and magnitude of recent EQ's Real-time 24 Hour Forecast
  • Short-term predictions Precursor phenomena (<1 year to days) 1. Foreshocks: usually increase in magnitude 2. Ground deformation 3. Fluctuations in water well levels 4. Changes in local radio wave characteristics 5. Anomalous animal behavior???
  • Impacts of Earthquake Prediction