Definition of Hazard
Types of Hazard
Natural Hazards as Earthquakes
What Are Earthquake Hazards?
2. A hazard is a situation that poses a level of threat
to life, health, property, or environment. Most hazards
are dormant or potential, with only a theoretical risk of
harm; however, once a hazard becomes "active", it can
create an emergency situation. A hazardous situation
that has come to pass is called an incident. Hazard
and possibility interact together to create risk.
Identification of hazard risks is the first step in
performing a risk assessment.
Definition of Hazard
3. Hazards are generally labeled as one of five types:
Physical hazards are conditions or situations that can cause the body
physical harm or intense stress. Physical hazards can be both natural
and human made elements.
Chemical hazards are substances that can cause harm or damage to
the body, property or the environment. Chemical hazards can be both
natural or human made origin.
Biological hazards are biological agents that can cause harm to the
human body. These some biological agents can be viruses, parasites,
bacteria, food, fungi, and foreign toxins.
Psychological hazards are created during work related stress or a
Radiation hazards are those that harm or damage the human body by
directly affecting cells.
Types of Hazard
4. One of the most destructive natural
phenomena is a terrible earthquake and its
after effects. Eartquakes are the cause of
thousands of deaths and colossal loss and
damage of properties and the natural
landscape. Such a devastation and loss
could be significantly mitigated through
advance assessment of seismic hazard and
risk and through the implementation of
approprite land use, construction codes, and
emergency plans. If major earthquakes
could be predicted, it would be possible to
evacuate population centres and take other
measures that could minimize the loss of life
and perhaps reduce damage to property as
well. For this reason earthquake prediction
has become a major concern of
seismologists in the United States, Russia,
Japan, and China. A primary goal of
earthquake research is to increase the
reliability of earthquake probability
Natural Hazards: Earthquakes
- Earthquake and tsunami damage at
Fukushima Dai Ichi Power Plant, Japan, 2011
Geoscientists, ultimately, would like to be able to specify a high probability for
a specific earthquake on a particular fault within a articular year.
5. What Are Earthquake Hazards?
• The first main earthquake hazard (danger) is the effect of
ground shaking. Buildings can be damaged by the shaking
itself or by the ground beneath them settling to a different level
than it was before the earthquake (subsidence).
6. Devastation caused by the recent earthquake in Colombia. As in many recent
earthquakes, the r e s u l t i n g d a m a g e w a s s t r o n g l y a ff e c t e d b y l o c a l
s i t e c o n d i t i o n s (amplification of ground vibrations and by local design criteria
dynamic response of buildings and foundations).
• Buildings can even sink into the ground if soil liquefaction
occurs. Liquefaction is the mixing of sand or soil and
groundwater (water underground) during the shaking of a
moderate or strong earthquake. When the water and soil are
mixed, the ground becomes very soft and acts similar to
quicksand. If liquefaction occurs under a building, it may start to
lean, tip over, or sink several feet. The ground firms up again
after the earthquake has past and the water has settled back
down to its usual place deeper in the ground. Liquefaction is a
hazard in areas that have groundwater near the surface and
8. Why does liquefaction occur?
To understand liquefaction, it is important to recognize
the conditions that exist in a soil deposit before an
earthquake. A soil deposit consists of an assemblage
of individual soil particles. If we look closely at these
particles, we can see that each particle is in contact
with a number of neighboring particles. The weight of
the overlying soil particles produce contact forces
between the particles - these forces hold individual
particles in place and give the soil its strength.
10. STRONG SURFACE WAVES
• Buildings can also be damaged by strong surface
waves making the ground heave and lurch. Any
buildings in the path of these surface waves can
lean or tip over from all the movement. The ground
shaking may also cause landslides, mudslides, and
avalanches on steeper hills or mountains, all of
which can damage buildings and hurt people.
11. GROUND DISPLACEMENT
• The second main earthquake hazard is
ground displacement (ground movement)
along a fault. If a structure (a building, road,
etc.) is built across a fault, the ground
displacement during an earthquake could
seriously damage or rip apart that structure.
• The third main hazard is flooding. An
earthquake can rupture (break) dams or
levees along a river. The water from the
river or the reservoir would then flood the
area, damaging buildings and maybe
sweeping away or drowning people.
• Tsunamis and seiches can also cause a great deal
of damage. A tsunami is what most people call a
tidal wave, but it has nothing to do with the tides on
the ocean. It is a huge wave caused by an
earthquake under the ocean. Tsunamis can be tens
of feet high when they hit the shore and can do
enormous damage to the coastline. Seiches are
like small tsunamis. They occur on lakes that are
shaken by the earthquake and are usually only a
few feet high, but they can still flood or knock down
houses, and tip over trees.
14. TSUNAMI CHARACTERISTICS
• While everyday wind waves have a wavelength (from crest to crest) of about
100 metres (330 ft) and a height of roughly 2 metres (6.6 ft), a tsunami in the
deep ocean has a wavelength of about 200 kilometres (120 mi). Such a
wave travels at well over 800 kilometres per hour (500 mph), but due to the
enormous wavelength the wave oscillation at any given point takes 20 or 30
minutes to complete a cycle and has an amplitude of only about 1 metre (3.3
ft).This makes tsunamis difficult to detect over deep water. Ships rarely
notice their passage.
• As the tsunami approaches the coast and the waters become shallow, wave
shoaling compresses the wave and its velocity slows below 80 kilometres
per hour (50 mph). Its wavelength diminishes to less than 20 kilometres (12
mi) and its amplitude grows enormously, producing a distinctly visible wave.
Since the wave still has such a long wavelength, the tsunami may take
minutes to reach full height.
15. This is simply a series of massive
ocean waves, triggered by an
earthquake that has occurred in
the sea (or ocean). The
displaced water then runs
ashore and into the land. This
happens when the plates
underneath the Earth's surface
move (focus) so that one slips
Tsunamis may also be caused by
underwater landslides or
Tidal waves differ from
tsunamis. Tidal waves are
usually in circular motion.
Tsunamis are a lot different. The
water moves with a flat surface
and has a lot of speed and
16. When the wave enters shallow water, it slows
down and its amplitude (height) increases.
• The fourth main earthquake hazard is fire. These fires can be
started by broken gas lines and power lines, or tipped over
wood or coal stoves. They can be a serious problem, especially
if the water lines that feed the fire hydrants are broken, too. For
example, after the Great San Francisco Earthquake in 1906,
the city burned for three days. Most of the city was destroyed
and 250,000 people were left homeless.
• Most of the hazards to people come from man-made structures
themselves and the shaking they receive from the earthquake.
The real dangers to people are being crushed in a collapsing
building, drowning in a flood caused by a broken dam or levee,
getting buried under a landslide, or being burned in a fire.
22. Earthquake Prediction
• Earthquake prediction is a popular pastime for psychics and pseudo-scientists, and
extravagant claims of past success are common. Predictions claimed as "successes"
may rely on a restatement of well-understood long-term geologic earthquake
hazards, or be so broad and vague that they are fulfilled by typical background
seismic activity. Neither tidal forces nor unusual animal behavior have been useful for
predicting earthquakes. If an unscientific prediction is made, scientists can not state
that the predicted earthquake will not occur, because an event could possibly occur
by chance on the predicted date, though there is no reason to think that the predicted
date is more likely than any other day.
• Scientific earthquake predictions should state where, when, how big, and how
probable the predicted event is, and why the prediction is made. The National
Earthquake Prediction Evaluation Council reviews such predictions, but no generally
useful method of predicting earthquakes has yet been found.
• Because of their devastating potential, there is great interest in predicting the location
and time of large earthquakes. Although a great deal is known about where
earthquakes are likely, there is currently no reliable way to predict the days or
months when an event will occur in any specific location.
23. • Although we are not able to predict individual earthquakes, the world's largest
earthquakes do have a clear spatial pattern, and "forecasts" of the locations and
magnitudes of some future large earthquakes can be made. Most large earthquakes
occur on long fault zones around the margin of the Pacific Ocean.
• It may never be possible to predict the exact time when a damaging earthquake will occur,
because when enough strain has built up, a fault may become inherently unstable, and
any small background earthquake may or may not continue rupturing and turn into a large
earthquake. While it may eventually be possible to accurately diagnose the strain state of
faults, the precise timing of large events may continue to elude us. In the Pacific
Northwest, earthquake hazards are well known and future earthquake damage can be
greatly reduced by identifying and improving or removing our most vulnerable and
• This is because the Atlantic Ocean is growing a few inches wider each year, and the
Pacific is shrinking as ocean floor is pushed beneath Pacific Rim continents. Geologically,
earthquakes around the Pacific Rim are normal and expected. The long fault zones that
ring the Pacific are subdivided by geologic irregularities into smaller fault segments which
24. • Earthquake magnitude and timing are controlled by the size of a fault segment, the
stiffness of the rocks, and the amount of accumulated stress. Where faults and plate
motions are well known, the fault segments most likely to break can be identified. If a
fault segment is known to have broken in a past large earthquake, recurrence time
and probable magnitude can be estimated based on fault segment size, rupture
history, and strain accumulation. This forecasting technique can only be used for
well-understood faults, such as the San Andreas. No such forecasts can be made for
poorly-understood faults, such as those that caused the 1994 Northridge, CA and
1995 Kobe, Japan quakes.
• One well-known successful earthquake prediction was for the Haicheng, China
earthquake of 1975, when an evacuation warning was issued the day before a M
7.3 earthquake. In the preceding months changes in land elevation and in ground
water levels, widespread reports of peculiar animal behavior, and many foreshocks
had led to a lower-level warning. An increase in foreshock activity triggered the
evacuation warning. Unfortunately, most earthquakes do not have such obvious
precursors. In spite of their success in 1975, there was no warning of the 1976
Tangshan earthquake, magnitude 7.6, which caused an estimated 250,000 fatalities.