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    Earthquake Hazards: Groundshaking

    Uploaded by

    Hannah Andrea Laparan
    Earthquake hazards depend on factors like seismic activity strength, topography, geology and groundwater. Ground shaking from earthquakes can severely damage structures and destabilize sloping ground, potentially causing falling objects that could injure people. Large earthquakes can devastate whole districts. Tsunamis generated by earthquakes or other events can travel long distances at high speed to flood coastal areas. Ground shaking also causes landslides and rockfalls by destabilizing cliffs and slopes. Earthquakes can lead to subsidence or sinking of the ground surface over large areas, and lateral spreading where sloping ground moves downhill. Liquefaction occurs when waterlogged sediments lose strength during shaking, causing buildings to sink or tilt over.

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    Earthquake Hazards: Groundshaking

    Uploaded by

    Hannah Andrea Laparan
    94 views3 pages
    Earthquake hazards depend on factors like seismic activity strength, topography, geology and groundwater. Ground shaking from earthquakes can severely damage structures and destabilize sloping ground, potentially causing falling objects that could injure people. Large earthquakes can devastate whole districts. Tsunamis generated by earthquakes or other events can travel long distances at high speed to flood coastal areas. Ground shaking also causes landslides and rockfalls by destabilizing cliffs and slopes. Earthquakes can lead to subsidence or sinking of the ground surface over large areas, and lateral spreading where sloping ground moves downhill. Liquefaction occurs when waterlogged sediments lose strength during shaking, causing buildings to sink or tilt over.

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    Earthquake hazards depend on factors like seismic activity strength, topography, geology and groundwater. Ground shaking from earthquakes can severely damage structures and destabilize sloping ground, potentially causing falling objects that could injure people. Large earthquakes can devastate whole districts. Tsunamis generated by earthquakes or other events can travel long distances at high speed to flood coastal areas. Ground shaking also causes landslides and rockfalls by destabilizing cliffs and slopes. Earthquakes can lead to subsidence or sinking of the ground surface over large areas, and lateral spreading where sloping ground moves downhill. Liquefaction occurs when waterlogged sediments lose strength during shaking, causing buildings to sink or tilt over.

    Copyright:

    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
    Download as docx, pdf, or txt
    94 views3 pages

    Earthquake Hazards: Groundshaking

    Uploaded by

    Hannah Andrea Laparan
    Earthquake hazards depend on factors like seismic activity strength, topography, geology and groundwater. Ground shaking from earthquakes can severely damage structures and destabilize sloping ground, potentially causing falling objects that could injure people. Large earthquakes can devastate whole districts. Tsunamis generated by earthquakes or other events can travel long distances at high speed to flood coastal areas. Ground shaking also causes landslides and rockfalls by destabilizing cliffs and slopes. Earthquakes can lead to subsidence or sinking of the ground surface over large areas, and lateral spreading where sloping ground moves downhill. Liquefaction occurs when waterlogged sediments lose strength during shaking, causing buildings to sink or tilt over.

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    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
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    Earthquake Hazards

    The type of hazard depends on the strength of seismic activity, along with such factors as local
    topographic and built features, subsurface geology and groundwater. A large earthquake will always be
    followed by a sequence of aftershocks.

    GroundShaking 
    If an earthquake generates a large enough shaking intensity, structures like buildings, bridges and dams
    can be severley damaged, and cliffs and sloping ground destabilised. Perched or stacked objects may fall
    and injure or bury anyone close by. In the largest earthquakes whole districts can be devastated by the
    multiple consequences of ground shaking. 
    Groundshaking will vary over an area due to such factors as topography, bedrock type, and the location
    and orientation of the fault rupture. These all affect the way the seismic waves travel through the ground.
    For an explanation of the exceptional high energy of the Christchurch earthquakes in 2011 have a look
    at this video.
    Tsunami

    Tsunamis are long wavelength oceanic waves generated by the sudden displacement of seawater by a
    shallow earthquake, volcanic eruption or submarine landslide. What is it like to face a tsunami?
    Watch this video!

    A number of waves may be produced and they can travel long distances at high speeds to flood far-off
    shores. The height of a tsunami varies and may be affected by the sea floor depth and shape, and other
    factors. New Zealand is susceptible to tsunamis originating from distance sources around the Pacific Ring
    of Fire as well as from very close to our coastline. Near source tsunamis will allow for very little warning.

    Large earthquakes may generate tsunami waves in enclosed water bodies such as lakes. In New Zealand
    there are large lakes that could be affected, for example Lakes Wakatipu and Wanaka that are near to the
    Alpine Fault.

    Landslides and Rockfalls

    Groundshaking due to earthquakes destabilises cliffs and steep slopes, causing landslides and rockfalls
    as a significant side-effect. Heavy rain and unconsolidated or fractured rock are exacerbating factors.

    Check out this video about the Rockfall Impacts of the Christchurch Quake,

    and this one: Laser Scanning Christchurch Rockfalls

    Subsidence and Lateral Spreading


    Subsidence, or lowering of the ground surface, often occurs during earthquakes.

    This may be due to downward vertical displacement on one side of a fault, and can sometimes affect a
    huge area of land. Coastal areas can become permanently flooded as a result.

    Subsidence can also occur as ground shaking causes loose sediments to “settle’ and to lose their load
    bearing strength (see liquefaction, below) or to slump down sloping ground (see Landslides and
    Rockfalls).

    Lateral spreading occurs where sloping ground starts to move downhill, causing cracks to open up, that
    are often seen along hill crests and river banks.

    Liquefaction

    Liquefaction occurs when waterlogged sediments are agitated by seismic shaking. This separates the
    grains from each other, reducing their load bearing capacity. Buildings and other structures can sink down
    into the ground or tilt over, whilst underground pipes and tanks may rise up to the surface.

    When the vibrations stop the sediments settle down again, squeezing groundwater out of fissures and
    holes in the ground to cause flooding. The aftermath of liquefaction can leave large areas covered in a
    deep layer of mud.

    By learning all of this we are able to know what we are going to do before, during and after an
    earthquake.

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