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Sun Yudong (1o2 27)
Teo Jun Wei (1o2 30)
What is an earthquake?
 a shaking of the ground caused by the sudden
breaking and movement of large sections (tectonic
plates) of the earth's rocky outermost crust
 Earthquakes shake at different intensities
 They can be measured and presented as data using the
Richter scale.
Shaking intensity of an earthquake
 Measured on Shaking intensity scales
 developed to standardize the measurements and ease
comparison of different earthquakes.
 Shaking intensity varied from barely perceptible to
completely destructive.
 The lower numbers represent imperceptible shaking
levels, XII represents total destruction.
 Below is the table to measure the shaking intensity:
Devices to measure the earthquake
 Earthquakes are measured using seismometers. The
moment magnitude is the most common scale on
which earthquakes larger than approximately 5 are
reported for the entire globe.
 These earthquakes are measured as some number on
the Ricther scale.
Earthquake fault types
 Three main types of fault that may cause an
earthquake:
 Normal
 reverse (thrust)
 strike-slip as shown on the right
Earthquake fault types
 Normal and reverse faulting are examples of dip-slip,
 the displacement along the fault is in the direction of
dip
 movement on them involves a vertical component.
 Normal faults occur mainly in areas where the crust is
being extended such as a divergent boundary.
 Strike-slip faults are steep structures where the two
sides of the fault slip horizontally past each other.
Why do earthquakes happen away
from plate boundaries?
 Plate boundaries  an obvious place for earthquakes
to occur.
 However, the stresses at plate boundaries can manifest
themselves some distance away from the surface
evidence of the boundary.
 Equally, boundaries have fault lines which radiate from
them and are common causes of earthquakes.
Far from plate
boundaries
complex strata
deep fault
zones
earthquakes in
apparently
stable regions
Countries that commonly
experience earthquakes
 Japan
 China
 Chile
 Australia continent
 Countries around the




Ring of fire
Alaska
Philippines
Indonesia
Haiti
What is an aftershock?
 Is an earthquake that occurs after a previous
earthquake, the mainshock.
 Is in the same region of the main shock but always of a
smaller magnitude.
 If an aftershock is larger than the main shock, the
aftershock is redesignated as the main shock and the
original main shock is redesignated as a foreshock.
 Aftershocks are formed as the crust around the
displaced fault plane adjusts to the effects of the main
shock
The possible effects of earthquakes
 Shaking and ground rupture
 Landslides and avalanches
 Soil liquefaction
 Tsunami
The possible effects of earthquakes
 An earthquake may cause
 injury and loss of life
 road and bridge damage
 general property damage
 collapse or destabilization of buildings

potentially leading to future collapse
The possible effects of earthquakes
 The aftermath may bring
 Disease
 lack of basic necessities
 higher insurance premiums
 Earthquakes can also cause
 volcanic eruptions, bringing further problems.
Shaking and ground rupture
 Ground rupture is a visible breaking and displacement
of the Earth's surface along the trace of the fault
 may be of the order of several metres in the case of
major earthquakes.
 Ground rupture is a major risk for large engineering
structures such as dams, bridges and nuclear power
stations
 requires careful mapping of existing faults to identify
any likely to break the ground surface within the life of
the structure.
Shaking and ground rupture
 Shaking and ground rupture are the main effects created by
earthquakes,
 principally resulting in more or less severe damage to buildings
and other rigid structures.
 The severity of the local effects depends on the complex
combination of the
 earthquake’s magnitude
 the distance from the epicenter
 and the local geological and geomorphological conditions,
which may amplify or reduce wave propagation.
 The ground-shaking is measured by ground acceleration.
Shaking and ground rupture
 Specific local geological, geomorphological, and
geostructural features can induce high levels of shaking
on the ground surface even from low-intensity
earthquakes.
 This effect is called site or local amplification.
 It is principally due to the transfer of the seismic
motion from hard deep soils to soft superficial soils and
 to effects of seismic energy focalization owing to typical
geometrical setting of the deposits.
Landslides and avalanches
Earthquakes
severe
storms
volcanic
activity
Landslides
and
avalanches
wildfires
coastal
wave
attack
Landslides and avalanches
 can produce slope instability leading to
landslides or avalanches
 Landslide is a major geological hazard
Landslides
 Landslide danger may persist while emergency
and
personnel are attempting rescue.
avalanches
Soil liquefaction
 Soil liquefaction occurs when, because of the shaking,
water-saturated granular material (such as sand)
temporarily loses its strength and transforms from a solid
to a liquefied solid.
 Soil liquefaction may cause rigid structures, like buildings
and bridges, to tilt or sink into the liquefied deposits.
 This can be a devastating effect of earthquakes.
 For example, in the 1964 Alaska earthquake, soil
liquefaction caused many buildings to sink into the ground,
eventually collapsing upon themselves.
Tsunamis
 Tsunamis are long-wavelength, long-period sea waves
produced by the sudden or abrupt movement of large
volumes of water.
 In the open ocean
 the distance between wave crests can surpass 100
kilometers (62 miles)
 the wave periods can vary from five minutes to one hour.
Tsunamis
 Such tsunamis travel 600-800 kilometers per hour
(373–497 miles per hour), depending on water depth.
 Large waves produced by an earthquake or a
submarine landslide can overrun nearby coastal areas
in a matter of minutes.
 Tsunamis can also travel thousands of kilometers
across open ocean and wreak destruction on far shores
hours after the earthquake that generated them.
Tsunamis
 Ordinarily, subduction earthquakes under magnitude
7.5 on the Richter scale do not cause tsunamis,
although some instances of this have been recorded.
 Most destructive tsunamis are caused by earthquakes
of magnitude 7.5 or more.
References
Special thanks to:
 http://eqseis.geosc.psu.edu/~cammon/HTML/Classes
/IntroQuakes/Notes/intensity.html
 http://en.wikipedia.org/wiki/Earthquake
 http://earthquake.usgs.gov/