drrr chapter 4

1. CHAPTER 4 DRRR

2. An earthquake (also known as a quake,
tremor or temblor) is the perceptible
shaking of the surface of the Earth,
resulting from the sudden release of
energy in the Earth’s crust that creates
seismic waves.

5. Geologist explains that an earthquake
is a type of hazard that 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
that normally aggravates its effect on human
and material elements like buildings and
infrastructure.

6. 1. Ground Shaking or Ground Motion
 The earth shakes with the passage of earthquake
waves, which radiate energy that had been “stored” in
stressed rocks, and were released when a fault broke
and the rocks slipped to relieve the pent – up stress
 If an earthquake generates a large enough shaking
intensity, structures like buildings, bridges, and dams
can be severely damaged, and cliffs and sloping
ground destabilized. Perched or stacked object may
fall and injure or bury anyone close by.
 Ground shaking will vary over an area due to such
factors as topography, bedrock type, and the location
and orientation of the fault rupture.

10. 2. Ground or Surface Rupture
 Surface rupture is an offset of the ground surface
when fault rupture extends to the Earth’s surface.
Any structure built across the fault is at risk of
being torn apart as the two sides of the fault slip
past each other.
 Normal – and reverse – (collectively called dip –
slip) faulting surface ruptures feature vertical
offsets while strike – slip faulting produces lateral
offsets. Many earthquake surface ruptures are
combinations of both. Structures that span a
surface fault are likely to suffer great damage
surface ruptures

11. 3. Liquefaction
 Soil liquefaction is a phenomenon in which the strength
and stiffness of a soil is reduced by earthquake
shaking or other rapid loading. It normally occur in
saturated soils, that is, soils in which the space
between the individual particles is completely filled with
water.
 Prior to an earthquake, the water pressure is relatively
low – the weight of the buried soil rests on the
framework of grain contacts that comprise it.
 However, earthquake shaking can disrupt the
structure, the soil particles no longer support and all
the weight, and the groundwater pressure begins to
rise.

12. The soil particles can move farther, and
become entrained in the water – the soil
flows. Liquefied soil will force open ground
cracks in order to escape to the surface.
The ejected material often results in
flooding and may leave cavities in the soil

17. 4. Earthquake – induced ground 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 or to slump down sloping grounds.
 Lateral spreading occurs where sloping ground starts
to move downhill, causing cracks to open up, that are
often seen along hill crest and river banks.

20. 5. Tsunami
 A tsunami also known as a seismic sea wave,
is a series of waves in a water body caused
by the displacement of a large volume of
water, generally in an ocean or a large lake.
Earthquakes, volcanic eruptions and other
underwater explosions, landslides, glacier
cavings, meteorite impacts and other
disturbances above or below water all have
the potential to generate a tsunami.

22. 6. Earthquake – induced landslides
 Landslides are frequently triggered by strong ground
motions. They are important secondary earthquake
hazards.
 The term landslide includes a wide range of ground
movement, such as rock falls, deep failure of slopes, and
shallow debris flows. However, gravity acting on a steep
slope is the primary reason for all landslides.
 Strong earthquake- induced ground shaking greatly
increases the likelihood of landslides where landscape is
susceptible to these types of ground failure.
 If the ground is saturated with water, particularly following
heavy rainfall, the shaking will result in more landslides
than normal

26. What are the four types of fault?
What are the fault lines in the Philippines?
Bring cookies in class (individual activity)