DRRR
Earthquake hazard - anything associated with an earthquake that may affect the normal activities of
people
 includes surface faulting, ground shaking, landslide, liquefaction, tectonic , tsunamis, and seiches
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Ground shaking - describes the vibration of the ground during an earthquake
- both a hazard created by earthquakes and the trigger for other hazards such as liquefaction
and landslides
TWO MAIN GROUPS OF SEISMIC WAVES
 Surface waves – travel along the outer layer of the Earth
 Body waves – travel through Earth’s interior
 P Waves (Primary Waves) - push (compress) and pull (expand) rocks in the direction the
wave is traveling
- P waves can travel through solids, liquids, and gases.
 S Waves (Secondary Waves) - shake the particles in rock at right angles to their direction
of travel
- Fluids (gases and liquids) will not transmit S waves.
Epicenter - location on Earth's surface directly above the focus of an earthquake
 There is a close correlation between earthquake epicenters and plate boundaries.
 The principal earthquake epicenter zones are along the outer margin of the Pacific Ocean,
known as the circum-Pacific belt and through the world's oceans along the oceanic ridge
system
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Magnitude and Proximity - most obvious factors that determine the amount of destruction
accompanying an earthquake
Structural damage depends on several factors:
 Intensity
 Duration of the vibrations
 Nature of material
 Design
SECONDARY EFFECTS OF EARTHQUAKE:
 Tsunamis
 Landslides
 Ground subsidence
 Fire
HOW IS GROUND SHAKING MEASURED?
 The strength of ground shaking (or that of the seismic waves) is measured in terms of velocity,
acceleration, frequency content of the shaking, and how long the shaking continues (the
duration).
 Ground acceleration during an earthquake event varies from place to place. How intense the
ground shaking that a site may experience will depend on earthquake magnitude (which to a
large degree is related to fault length) depth of focus, distance from the epicenter, and
duration of shaking. The nature of the ground material or geology also determines the
shaking reaction of the ground.
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Frequency – how often a vibration occurs, unit of measurement is hertz (Hz) or cycles per
second
Natural frequency - frequency at which a system naturally vibrates once it has been set into
motion, depends on the stiffness and mass of the system
Period - the time (in seconds) it takes for one full cycle to occur
Acceleration - rate of change of velocity expressed as a ratio of the acceleration of gravity
EFFECTS OF GROUND SHAKING:
 The horizontal component of seismic wave motion or shaking is the sot destructive to
buildings since it’s easier to shake than to compress rocks. Both shear (S) waves and love waves
are destructive both have horizontal components.
 Shear wave velocity is therefore a good measure of the intensity ground shaking.
 Ground shaking cannot harm you if you are in an open filed. It is the failure of a building due to
inferior design, poor construction, or weak foundation that cause people harm or death.
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Surface rupture - caused by vertical or horizontal displacement on either side of a ruptured
fault, which can affect enormous areas of land
- known to deviate around more substantial structures due to the strength of the foundation and
localized compression of the soil
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Fault - fracture or zone of fractures between two blocks of rock
 Angle of the fault and Direction of slip – used to classify faults
TYPES OF FAULTS:
 Normal Fault - involves mainly downward movement of the ground across the fault called the
hanging wall
 Thrust Fault - involves mainly upward movement of the hanging wall
 Strike-slip Fault - involves a dominantly horizontal shifting of the ground
 Left-lateral
 Right-lateral
 Ground raptures - earthquake faults that have reached the surface
- Liquefaction cracks and fissures are formed on soft ground by the intense shaking during an
earthquake.
Hydrometeorological Hazards - processes which involve the interaction of the atmosphere, bodies of
water, and land and which pose threat to lives and human property
 Tropical Cyclones
 Thunderstorms
 Drought
 Tornadoes
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Heat Waves
Heavy Snowfall
Avalanche
Floods/Flash floods
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Cyclones - intense low pressure system which is characterized by strong spiral winds towards
the center
 Eye – center of a cyclone in a counter-clockwise flow in the northern hemisphere
CLASSIFICATIONS OF CYCLONE:
 Tropical Depression - maximum winds from 35 kph to 63 kph
 Tropical Storm - maximum winds from 64 kph to 118 kph
 Typhoon - maximum winds exceeding 118 kph
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Typhoon - a large, powerful and violent tropical cyclone
- a low pressure area rotating counter-clockwise and containing rising warm air that forms over
warm water in the Western Pacific Ocean
 Hurricane – a typhoon called in Atlantic Ocean
 Wily-wily – a typhoon called in Australia
 Thunderstorm - a weather condition that produces lightning and thunder, heavy rainfall from
cumulonimbus clouds and possibly a tornado
 Tornado - described as a violent rotating column of air extending from thunderstorm to the
ground
 Flash flood - a rapid flooding of geomorphic low-lying areas like washes, rivers, dry lakes and
basins
CAUSES OF FLASH FLOOD:
 heavy rain with a severe thunderstorm
 tropical storm
 melt water from ice
 snow flowing
 Floods are basically HYDROLOGICAL PHENOMENA caused by storm surges, and tsunami
along coastal areas.
 Two key elements are rainfall intensity and duration.
 Intensity - the rate of rainfall
 duration - how long the rain lasts
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Storm Surge - rise of the seawater above normal sea level over the coast
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El Niño and La Niña - complex weather patterns resulting from variations in ocean temperature
in the equatorial pacific
- opposite phases of what is known as the El Niño-Southern Oscillation (ENSO) cycle
 La Niña – cold phase of ENSO, “girl child”
 El Niño – warm phase of ENSO, “boy child”
- El Niño and La Niña episodes typically last nine to 12 months.
- Typically, El Niño occurs more frequently than La Niña.