Earthquakes and Volcanoes

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Earthquakes and Volcanoes Powered By Docstoc
					GEOG 3251: Mountain Geog, summer 2007
Adina Racoviteanu
     What is an earthquake?
• Earthquake = Vibration of the Earth
  produced by the rapid release of energy

• Seismic waves = Energy moving outward
  from the focus of an earthquake
       Why do earthquakes occur?
                                         • Fractures, faults
                                         • Energy released
                                           and propagates
                                           in all directions
                                           as seismic
                                           waves causing
Epicenter = spot on
Earth’s surface directly Focus = location of initial slip on the fault;
                         where the earthquake originates
above the focus
 Where do earthquakes occur?
1) Most earthquakes (90%) occur along the
  edge of oceanic and continental plates

2) Some along faults:
         normal, reverse, transform
            Seismic waves: forms
• P-waves:
   – compressional, or push-pull waves
   – Propagate parralel to the direction in which the wave is moving
   – Move through solids, liquids

• S-waves:
   – Called shear waves
   – Propagate the movement perpendicular
   to the direction in which the wave is

• Surface waves (L-waves or long waves).
   –   Complex motion
   –   Up-and-down and side-to-side
   –   Slowest
   –   Most damage to structures, buildings
   Earthquake size: two ways to

1) Magnitude: Richter Scale

2) Intensity: Mercalli Scale
            1) Richter Scale                  992 times
•   Measures the energy
    released by fault
•   related to the maximum                7
    amplitude of the S           31.5
    wave measured from           times
    the seismogram
•   Logarithmic-scale             6
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
   Descriptor    Magnitude     Average Annually
     Great      8 and higher             1¹
     Major         7 - 7.9               17 ²
     Strong        6 - 6.9              134 ²
   Moderate        5 - 5.9              1319 ²
     Light         4 - 4.9
     Minor         3 - 3.9
   Very Minor      2 - 2.9
  ¹ Based on observations since 1900.
  ² Based on observations since 1990.
Recent Earthquake Activity around the World
Largest earthquake in the world
                       •More than 2,000 killed, 3,000 injured,
                       2,000,000 homeless, and $550 million
                       damage in southern Chile
Chile : May 22, 1960   • tsunami caused 61 deaths
Magnitude 9.5          •$75 million damage in Hawaii;
                       • 138 deaths and $50 million damage in
                       •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

Date            Location    Deaths       Magnitude   Comments

May 31, 1970    Peru        66,000          7.9      $530,000,000
                                                     damage, great rock
                                                     slide, floods.
July 27, 1976   China,      255,000         7.5      Estimated death toll as
                Tangshan    (official)               high as 655,000.
Sept 19, 1985   Mexico      9500           8.0       Estimated death toll as
                Michoacan   (official)               high as 30,000
                                                     Old lake bed magnified
                                                     shock waves by 500%
2001 Jan 26     India       20,023          7.7      166,836 injured,
                                                     600,000 homeless
2004 Dec 26     Sumatra     283,106         9.0      Deaths from earthquake
                                                     and tsunami
India, Gujarat earthquake
       Jan 26, 2001
Later that year…   Arequipa. S.Peru
                   June 2001
         Jun 23, 2001
Magnitude 8.1 earthquake strikes
        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
Natural disasters in the Cordillera Blanca,
          Huascaran avalanche
           Favoring conditions
•   Major tectonic faults that are active
•   Marked glacierization
•   Geologically young, steep mountains
•   Pro-glacial lakes
•   Immediate vicinity of human settlements
           Mass wasting: types

•   Creep
•   Landslides: rock slides
•   Flows: avalanches, debris flow, mud flow
•   Falls
Lahars= debris flows associated with
        volcanic eruptions
        Landslide and Debris Flow
• masses of rock, earth, or debris saturated with water and
  moving down a slope
• They are activated by:
           storms,
           earthquakes,
           volcanic eruptions,
           fires,
           alternate freezing or thawing,
           steepening of slopes by erosion or human

– similar in mechanism to landslide
– it involves a large amount of ice, snow and
  rock falling quickly down the side of a
– ice builds in cornices or forms over a weaker
  layer of snow, creating the danger of an

           Nev. Chacraraju
• Large snow year
• 50 degree F increase in temp over a few
• Caused avalanche
• 4,000 fatalities
             1970 Avalanche
•   Triggered by 7.7 magnitude earthquake
•   Rock face failure
•   Incorporated 30 meters of snow and ice!
•   Moraines confined flow initially
•   Accelerated over a distance of 2.4 km
•   Became airborne at change of slope
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.
1970 Earthquake that caused
the Huascaran disaster killed
about 40,000 people in

Streets of Huaraz after the
1970 Earthquake.

Adobe houses collapsed,
killing people inside.
The town of Huaraz flattened
Huaraz today: a growing tourist town
Church before 1970 avalanche. Note palm trees in foreground.
Many years after the avalanche. Note palm trees survived.
Yungay is now completely abandoned. Cemetery has
a monument to the dead.

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