Document Sample
					                                                                               Tectonic earthquakes
                                                                                           due to movement along plate boundaries
                       GEOG 1010
                   Introduction to Geography

               EARTHQUAKES &
                 VOLCANOES                                                                                                      epicentre

                    Dr. Hester Jiskoot

                     Seismic waves                                                     8 Oct 2005 Pakistan Earthquake M7.6
                                                                                      Predicted P-wave travel times in minutes
                                                         Think coiled spring          Between the heavy black lines is the P-wave shadow zone

                                                          Think rope

P waves (Compressional           or Primary waves)
   • shake the ground in the direction they are propagating
   • travel at speeds of 1.5 to 8 km/s in the Earth's crust
S waves (Shear or Secondary waves)
   • shake perpendicularly or transverse to the direction of propagation
   • travel at 60% to 70% of the speed of P waves

 Earthquake measurement scales                                                                        Seismograph

 1902 Mercalli: intensity           I to XII
      Damage indicator

 1935     Richter: amplitude-magnitude  1.0 to >8.0 logarithmic
          Measure of seismograph amplitude                                                                           Need ≥ 3 for epicentre location

 1993 moment-magnitude       1.0 to >8.0 logarithmic
      Measure of fault's length, depth and its slip

                                                                               Modern Digital Seismometer

                                                                RICHTER         EARTHQUAKE EFFECTS
                                                    Richter   MAGNITUDE

                                                    scale       < 3.5       Generally not felt, but recorded.

                                                    diagram     3.5-5.4     Often felt, but rarely causes damage.

                                                                < 6.0       At most slight damage to well-designed buildings,
                                                                            but major damage to poorly constructed buildings
                                                                            over small regions.

                                                                6.1-6.9     Can be destructive in areas < 100 km

                                                                7.0-7.9     Major earthquake. Can cause serious damage over
                                                                            larger areas.

                                                                > 8.0       Great earthquake. Can cause serious damage in
                                                                            areas >100 km across.

   EFFECTS OF EARTHQUAKES                                     COMPARISON OF TWO EARTHQUAKES IN 1989
                                                               Magnitude 7.1 Loma Prieta earthquake in least-
                 Dependent on factors:                         populated area of the San Francisco peninsula.
                                                               - population well prepared and well-engineered buildings
1) Intrinsic to the earthquake                                 - rush hour, but few cars on the roads: large opening game on TV
  - magnitude, type, location (epicenter), or focal depth
                                                               - ~ 67 deaths.
2) Local geological conditions                                 Magnitude 6.7 earthquake in war-torn Armenia
  - distance from the event, path of the seismic waves
                                                               (between Russia & Turkey)
  - bedrock type and degree of water saturation
                                                               - epicenter much closer to major cities
3) Societal conditions reacting to the earthquake              - poorly-engineered houses of un-reinforced concrete collapsed
  - quality of construction, preparedness, time of day
                                                               - night-time: everyone in the house in bed: unprepare
                                                               - > 25 000 deaths.

                                                               EARTHQUAKES OCCUR ALONG MAJOR FAULT ZONES IN THE CRUST
   Damage after the 1989 earthquake in Armenia
                                                                 Average number of earthquakes per year
                                                                       at shallow depth (0 - 70 km) and magnitude ≥ 5


       In 1993 UNESCO and the USGS launched the research program

   Earthquake hazard

Seismogram of 3 Jan 2008 earthquake 43 km S of Lethbridge
                                                           Depth ~25km
                                                           Magnitude 3.5ML
                                                     Earthquakes <100km radius
                                                             since 1985

                                                                                         Vancouver         Okanagan
                                                                                           Island            Lake


Ten largest                                                                                                                         EARTHQUAKE THAT
earthquakes                                                                                                                        CAUSED THE 26 DEC 05
since 1900                                                                                                                              TSUNAMI


                                                                 Magnitude                                                       India plate moves NE 6 cm/yr relative
                                                                 (Richter)                                                                 to the Burma plate.
      1       Chile                                       1960    9.5
      2       Prince William Sound, Alaska                1964    9.2                                                                 Megathrust earthquake made
      3       Andreanof Islands, Aleutian Islands         1957    9.1                                                                ~1200km of plate boundary slip
      4       Kamchatka                                   1952    9.0
      5       Off the Coast of Ecuador                    1906    8.8                                                            Average fault plane displacement ~15 m
      6       Rat Islands, Aleutian Islands               1965    8.7
      7       India-China Border                          1950    8.6                                                              Sea floor uplifted by several meters
      8       Kamchatka                                   1923    8.5
      9       Banda Sea, Indonesia                        1938    8.5
      10      Kuril Islands                               1963    8.5
      4       Northeast Indian Ocean (off Sumatra)        2004    9.0             Tsunami animation:

IMPACT OF DEC 26th TSUNAMI ON BANDA ACEH, SUMATRA                                              Earthquakes in the last day - weeks - years
        10 Jan 2003             29 Dec 2004
                                                                                               Red = 24 hours before 12 March 2009 22:12 UTC


   IKONOS satellite images

    LOCATIONS OF ACTIVE VOLCANOES                                                                      Types of volcanic activity

                                                                                                 Effusive eruptions: Sheet volcanoes
                                                                                                    lavaflows    Common in Hawaii and Iceland

   Effusive eruptions
   (gentle flows, lots of lava)
   • cinder cones
   • shield volcanoes
   • plateau basalts

   Explosive eruptions
   (viscous lava, trapped gases)
   • composite volcanoes
   • calderas

 Explosive eruptions: Composite volcanoes                                              Typical composite volcano
   Ashes                or ‘Stratovolcanoes’

                                                      Fujiyama, Japan

                               Crater Peak vent (beneath clouds),
                               Mount Spurr, Alaska

  USGS                         Eruption column up to 18 km asl

Shield/Composite Comparison

                                                                          Obsidian                  Dacite volcanic bomb   Basalt lava
                                                                          (volcanic glass)          and pumice             Hawai’i
                                                                          Portland                  Mt St Helens

 Caldera = a crater lake
                                                 ~6600 yrs ago
                                                 Mt Mazama
                                                 exploded in
                                                 Ash landed as far
                                                 as Calgary

         Is now a caldera:
         Crater Lake, Oregon

                                                                        Grimsvötn, Iceland eruption 1-4 Nov 2004

            Geyser in Iceland                                Volcanic Hazards and Effects
                                                              •   hot ash (pyroclastics)
                                                              •   steam and gas explosions
                       Geysers form when underground          •   lava flows
                       chambers fill with water and are
                       heated geothermally.                   •   poisonous gases (carbon dioxide, sulfuric acid)
                                                              •   landslides
                       When the water reaches its boiling     •   tree blowdowns
                       point, the geyser erupts and the
                       cycle starts again.                    •   lahars (steam-melted ice and snow cause flooding
                                                                  and large mudflows)
                                                              • increase in atmospheric dust

Benefits of Volcanic Eruptions

 • New, fertile soils
   – Hawaii, Philippines, Indonesia, Andes
 • Geothermal energy
   – Iceland, Italy, New Zealand
 • New ‘Real Estate’
   – Iceland, Japan, Hawaii
 • New Rocks & Minerals
   – Diamonds are NOT forever

                Mt. VESUVIUS eruptions                      BIGGEST 20th CENTURY
                e.g. 79 AD: Pompeii                                     ERUPTION              MOUNT PINATUBO
                     1631 AD: Naples                                                             Philippines
                                                                                                15 June 1991

                                                                                                 Earthquakes    warning

                                                                                              Population of 500000 in area

                                                                                               5000 people evacuated from
                                                                                                10 km radius around crater

                                                                                                >800 people died, mostly
                                                                                                  from roof collapses

                                                                                                 Cooled Earth by 0.6º C

Volcanoes & Climate –
    the “haze” and “albedo” effects
                                                           1980 Mt St Helens Eruption
 For volcanic eruptions in past 400 yrs:
 • Few tens of °C winter warming immediately following

 • Few tens of °C summer cooling for up to 2 yrs after a
                                                                Oct 2004 renewed activity
   major eruption

 • Disruption of El Niño & North Atlantic Oscillation

 • Uneven global distribution of effects

 • Climate effect smaller than natural variation