Natural hazards earthquakes

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  • 1. Earthquakes
    Prof. David Alexander
    Global Risk Forum Davos
  • 2. Physical
    aspects
  • 3. The causes of seismicity:-
    • tectonic activity caused by
    stresses in the earth's crust
    • volcanic activity resulting in stress
    caused by the injection of magma
    into the crust (volcanosiesmicity).
  • 4. A typical year of earthquakes (1996)
    Magnitude
  • 5. Seismology: the study of
    elastic (seismic) waves
    The properties of waves:
    • wavelength and frequency
    (number per unit of time)
    • amplitude (vertical distance
    from crest to trough)
    • phase difference.
  • crest
    AMPLITUDE
    trough
    WAVELENGTH
    (per unit time = frequency)
    PHASE DIFFERENCE
  • 6. Strong motion of the ground:-
    • duration(seconds)
    • 7. frequencies present in the waves
    • 8. maximum amplitude of the waves
    • 9. dispersion if wave energy with
    distance from the point of generation
    • maximum velocity
    • 10. maximum acceleration.
  • Bracketed duration: the period of
    time in which seismic shaking
    exceeds a predefined level.
    Background seismicity: small
    tremors that occur constantly
    during periods of quiescence
    between major earthquakes.
  • 11. Seismogenic zones:-
    • the margins of tectonic plates
    (e.g. subduction zones)
    • zones of geological faults under stress
    • 12. areas of volcanic activity
    and geothermal fluxes.
  • 13. Geological faults (extensive
    planes that divide rock units):-
    • normal faults (extensional movement)
    • 14. inverse (compressional movement)
    • 15. transcurrent(lateral, strike-slip)
    • 16. oblique(diagonal).
  • Types of geological fault
    Overthrust fault
    Reverse fault
    Right-lateral normal fault
    (oblique slip)
    Normal fault
    Fault line
    Hanging wall
    Footwall
    Dip
    Right-lateral fault
    (strike-slip)
  • 17. The elastic rebound theory
    of H.F. Reid:
    • hypocentre (focus): small area in the
    crust where the earthquake begins
    • epicentre: the point on the surface
    directly above the hypocentre
    • deep focus earthquakes:
    hypocentre buried at least 80 km
    • shallow focus earthquakes:
    hypocentre <50 km, often <20 km.
  • 18. The elastic rebound theory of H.F. Reid
  • 19. Types of seismic wave:-
    Body waves:
    P, primus, compression or pressure
    waves - longitudinal
    S, secundus, shear waves - transverse
    Surface waves:
    L, Love S, Stoneley
    R, Rayleigh C, channel
    R waves travel at 92%of the speed of
    S waves, which travel at 58%of the
    speed of P waves, etc.....
  • 20. The main kinds of seismic wave
    Primus
    (pressure)
    'P' waves
    Body waves
    Secundus
    (shear)
    'S' waves
    Love
    'L' waves
    Surface waves
    Rayleigh
    'R' waves
  • 21. LOVE WAVES
    EPICENTRE
    RAYLEIGH
    WAVES
    FAGLIA
    SHEAR
    WAVES
    PRESSURE WAVES
    HYPOCENTRE
    FRONT OF
    THE WAVES
  • 22. Instruments for measuring
    seismic waves:-
    • seismometers produce
    a continuous trace
    • accelerometers only function
    when there is strong motion
    (which triggers them to record)
    Seismic monitoring instruments,
    synchronised to different wavelengths,
    must have an optimum combination of
    robustness and sensitivity.
  • 23. Seismometers
  • 24. Accelerometers
  • 25. Magnitude was originally defined as the
    amplitude of the largest seismic wave
    at a nominal 100 km from the epicentre
    • Richter scale: local magnitude, ML,
    no longer used because it is
    inaccurate at high magnitudes
    • various scales for S-waves
    • 26. Moment Magnitude scale, MW,
    the world standard.
  • 27. In earthquakes energy expenditure
    is proportional to magnitude:
    the points on the magnitude scale have
    a logarithmic relationship in terms
    of energy release - thus:
    M8= 31.6 x M7
  • 28. Relationship between magnitude
    and other variables
  • 29. World seismic activity over
    a typical eight-year period
    Number of earthquakes
    Magnitude
  • 30. Location of epicentres and
    reconstruction of the macroseismic field:-
    • three seismic stations can
    locate an epicentre on the basis
    of the radial distance computed
    from the travel times of
    different kinds of wave
    • the isoseismsof the macroseismic
    field are based on the relationship
    between the tremors and damage.
  • 31. 5 minutes
    Time
    S waves
    with
    different
    frequences
    Distance
    1000 km
    Epicentre
    Slowing down of P and S waves
    with distance from epicentre
  • 32. stn. 1
    stn. 2
    epicentre
    stn. 3
    Localisation of epicentre on the basis
    of the arrival times of seismic waves
  • 33. Epicentres
    and faults
    located
    for the
    Bam, Iran,
    earthquake
    of 26 Dec.
    2003.
  • 34. Effect of different geological materials
    in amplifying seismic waves
  • 35. Extract from a seismic microzonation map
    showing different shaking potentials
  • 36. A typical sequence of aftershocks
    after a major seismic event
    (Northridge, California, 1994)
    Number of earthquake per day
    all others m<5
    Days after the earthquake
  • 37. Colfiorito earthquake swarm, central Italy
    September - December 1997
    Days after earthquake
    Days after earthquake
    Associated seismic intensities
    Days after earthquake
  • 38. MCS intensities
    for 23-11.1980
    southern Italian
    earthquake M6.8
  • 39. NEW ZEALAND
    Intensities with a probability of
    50% of returning within 50 years
    Return periods of earthquakes
    with intensities of at least MM=VI
  • 40. Comparative data on four earthquakes
  • 41. Consequences of
    Earthquakes
    - and significant issues -
  • 42. Construction failure poses the
    greatest threat to life in
    earthquakes
  • 43. Structural integrity:
    a building's physical adequacy
    for its intended purpose
    Failure: total or partial
    collapse, or the destruction or
    non-functionality of a building.
  • 44. Seismic damage to buildings
    is a function of:-
    • seismic energy expenditure:
    magnitude
    duration of strong motion
    maximum acceleration
    • distance from epicentre
    • 45. surface geology
    (soft sediments amplify waves)
    • effect of construction type
    • 46. regularity of building form
    • 47. state of maintenance of building.
  • 48.
  • 49.
  • 50. In the Tangshan (China) earthquake
    of July 1976 (magnitude 7.6),
    of 352 multi-storey buildings:
    • 4 (1%) maintained their
    structural integrity
    • 177(50%) collapsed completely
    • 51. 85(24%) collapsed partially
    • 52. 86(25%) were severely damaged.
  • Knowledge must be gained of how to:-
    • buttress buildings temporarily
    • 53. repair buildings permanently
    • 54. design and construct
    buildings antiseismically.
  • 55.
  • 56. Antiseismic design utilizes:-
    • experience of a building's
    seismic performance
    • hypotheses about a building's
    seismic response
    • design techniques to combat
    weaknesses in buildings
    induced by earthquakes.
  • 57. The largest urban seismic risk
    is in Istanbul and Tehran
    Major earthquakes represent an enormous
    urban search-and-rescue (USAR) challenge
  • 58. The international relief system is
    hugely expensive and inefficient
    $1,000,000 per life saved!
  • 59. In Italy...
    • in the 20th century 46 lethal
    earthquakes caused 128,000 deaths
    • a damaging quake once in 24-56 months
    • 60. greatest risk is in the
    22,000 historical town centres
    • 70% of the population lives in
    municipalities classified seismic;
    40% in 2,965 highly seismic ones
    • 35.3% of homes in earthquake zones
    are anti-seismically constructed.
  • 61.
  • 62.
  • 63. DISASTER
    VICTIM
    Search and rescue
    UNINJURED
    INJURED
    Medical assistance
    Public health measures
    IMPROVEMENT
    OF CONDITION
    WORSENING
    OF CONDITION
    HEALTHY
    INFECTED
    Medical aid
    HEALTHY
    IMPROVEMENT
    OF CONDITION
    WORSENING
    OF CONDITION
    Mortuarial
    and funeral
    services
    DEATH
    DISEASES
    INJURIES
  • 64. Injuries
    Emergency room
    injuries
    Hospital
    admissions
    No damage
    to buildings
    Damage
    to buildings
    Source: Linda Bourque, UCLA
  • 65. In the Italian Irpinia-Basilicata
    earthquake of 1980 hospitals collapsed.
    In the El Salvador earthquake
    of 1986 hospitals collapsed.
    In the El Salvador earthquake
    of 2001 hospitals collapsed.
    In the Bam, Iran, earthquake
    of 2003 hospitals collapsed.
    ....haven't we learnt anything at all?
  • 66. "At Olive View Medical Center, two buildings collapsed in 1971, and three people died, including two patients on life-support systems that failed when auxiliary generators did not start. The third was an ambulance driver who was crushed by a falling wall. Olive View was an 888-bed hospital then. It had only been open a month when the quake hit. Because of extensive damage, the hospital was rebuilt, with attention to strengthening it against any future quake. But it was much smaller. Now it has a capacity of 377 patients."
    [Sylmar, California, history file]
  • 67. Of the 58 fatalities caused by building damage, 50 occurred in hospitals. The worst damage to medical facilities occurred at the Veterans Administration Hospital in Sylmar where two large buildings collapsed. Even though the hospital site was right on the edge of the heavily urbanized San Fernando Valley, it took one hour and 22 minutes before a fire department helicopter happened to spot the collapses and send help. The reason for such a delay? The phones didn’t work, the hospital’s radio was in one of the collapsed buildings, and the first message orally delivered by a hospital staff member to a nearby government facility was confused with an already received report of damage to a different nearby hospital.
    [Reitherman 2004]
  • 68.
  • 69.
  • 70.
  • 71.
  • 72. Seismic hazards to hospitals:-
    • loss of structural integrity
    and building functionality
    • seismically-induced flooding,
    landsliding and subsidence
    • loss of trained personnel
    • 73. loss of medical and surgical capacity
    • 74. loss of supplies (including utilities)
    and failure of supply chains
    • inaccessibility.
  • Hospitals
    Seismic design level
    Fully
    operational
    Operational
    Life
    safe
    Near
    collapse
    Collapse
    Unaccaptable
    performance
    Unaccaptable
    performance
    Rare
    60%g
    Unaccaptable
    performance
    Very
    rare
    80%g
  • 75. Capacity:
    • beds (expandable)
    • 76. surgical and curative (fixed or
    diminished in the short term).
  • 77. Resilience
    • ensuring the structural integrity
    of the medical facility
    • ensuring continuity of
    services and medical supplies
    • ability to cope with very
    large surges in demand
    • protecting personnel and
    their immediate families
    • protecting lifelines that enable the
    injured to access medical care.
  • 78. Measures
    • seismic integrity surveys
    (structural and non-structural)
    • emergency planning (...testing,
    revising, diffusing plans...)
    • estimate medical, surgical,
    pharmaceutical and logistical needs
    • earthquake casualty estimation.
  • Internal emergency plan
    Site of the
    disaster
    Other
    hospitals
    and clinics
    in the area
    Health facility network
    emergency plan
    External
    emergency plan
    The three foci of medical emergency planning
  • 79. Disaster
    planning for
    the medical
    centre
    Disaster
    planning
    for the system
    of medical
    centres
    Disaster
    planning for
    the external
    environment
    Disaster
    in the medical
    centre
    Disaster
    in the system
    of medical
    centres
    Co-ordinated
    EMS Disaster
    plans
    Disaster
    in the external
    environment
  • 80. Helicopter links
    Ambulance routes
    Emergency bus transportation
    Telecommunications links
    T1
    T2
    Primary triage point
    Secondary triage points
    Pulmonary
    specialists
    Hospital I
    Hospital II
    T2
    Staging
    area
    T2
    T1
    Burns
    unit
    Disaster
    T2
    Secondary
    treatment
    centre
    Incident
    command
    post
    Incident
    commander
    Mortuary
    Emergency
    operations
    commander
    Emergency
    operations
    centre
    Next-of-kin
    Coroner
  • 81. IMPACT ON THE
    COMMUNITY
    RISK OF EARTHQUAKE
    Characteristics
    of the event:
    magnitude,
    duration,
    location of
    epicentre,
    level ofground
    acceleration
    Buildings,
    drinking water,
    sewerage,
    public transport,
    public buildings,
    hospitals,
    fire stations,
    etc.
    Local geological
    characteristics
    Population
    distribution
    and density
    Aftershocks
    Socio-economic
    characteristics
    RISK OF EARTHQUAKE
    Landslides
    Previous
    experience
    of risk
    Floods
    Casualties,
    economic damage;
    type, costs times
    of reconstruction
    Fires
    Level of
    community
    preparedness
  • 82. Thank
    you
    for
    your
    attention!