2. HAZARD - A hazard is a situation which 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.
DISASTER - A disaster is the impact of a natural or human-made
hazard that negatively affects society or environment. The root of the
word disaster comes from an astrological idea that when the stars are in
a bad position a bad event will happen.
3.
Earthquakes, also called temblors, can be so tremendously destructive, it’s hard to
imagine they occur by the thousands every day around the world, usually in the form of
small tremors.
Some 80 percent of all the planet's earthquakes occur along the rim of the Pacific Ocean,
called the "Ring of Fire" because of the preponderance of volcanic activity there as well.
Most earthquakes occur at fault zones, where tectonic plates—giant rock slabs that make
up the Earth's upper layer—collide or slide against each other. These impacts are usually
gradual and unnoticeable on the surface; however, immense stress can build up between
plates. When this stress is released quickly, it sends massive vibrations, called seismic
waves, often hundreds of miles through the rock and up to the surface. Other quakes can
occur far from faults zones when plates are stretched or squeezed.
Scientists assign a magnitude rating to earthquakes based on the strength and duration
of their seismic waves. A quake measuring 3 to 5 is considered minor or light; 5 to 7 is
moderate to strong; 7 to 8 is major; and 8 or more is great.
On average, a magnitude 8 quake strikes somewhere every year and some 10,000 people
die in earthquakes annually. Collapsing buildings claim by far the majority of lives, but
the destruction is often compounded by mud slides, fires, floods, or tsunamis. Smaller
temblors that usually occur in the days following a large earthquake can complicate
rescue efforts and cause further death and destruction.
Loss of life can be avoided through emergency planning, education, and the construction
of buildings that sway rather than break under the stress of an earthquake.
5. An earthquake (also known as
a quake, tremor or temblor) is the result of a sudden
release of energy in the Earth's crust that creates seismic
waves. The seismicity, seismism or seismic activity of
an area refers to the frequency, type and size of earthquakes
experienced over a period of time. At the Earth's surface,
earthquakes manifest themselves by shaking and
sometimes displacement of the ground. When
the epicenter of a large earthquake is located offshore, the
seabed may be displaced sufficiently to cause a tsunami.
Earthquakes can also trigger landslides, and occasionally
volcanic activity.
6.
Zone 5
Zone 5 covers the areas with the highest risks zone that suffers earthquakes of intensity MSK IX or
greater. The IS code assigns zone factor of 0.36 for Zone 5. Structural designers use this factor for
earthquake resistant design of structures in Zone 5. The zone factor of 0.36 is indicative of effective
(zero period) peak horizontal ground accelerations of 0.36 g (36% of gravity) that may be generated
during MCE level earthquake in this zone. It is referred to as the Very High Damage Risk Zone. The
state of Kashmir, Punjab,the western and central Himalayas, the North-East Indian region and
the Rann of Kutch fall in this zone.
Generally, the areas having trap or basaltic rock are prone to earthquakes.
Zone 4
This zone is called the High Damage Risk Zone and covers areas liable to MSK VIII. The IS code
assigns zone factor of 0.24 for Zone 4. The Indo-Gangetic basin and the capital of the country (Delhi),
Jammu and Kashmir fall in Zone 4. In Maharashtra Patan area(Koyananager) also in zone 4. but East
Delhi is an earthquake prone area.
Zone 3
The Andaman and Nicobar Islands, parts of Kashmir, Western Himalayas fall under this zone. This
zone is classified as Moderate Damage Risk Zone which is liable to MSK VII. and also 7.8 The IS code
assigns zone factor of 0.16 for Zone 3.
Zone 2
This region is liable to MSK VI or less and is classified as the Low Damage Risk Zone. The IS code
assigns zone factor of 0.10 (maximum horizontal acceleration that can be experienced by a structure
in this zone is 10% of gravitational acceleration) for Zone 2.
8. Examples of earthquakes include:
Descriptor
Richter magnitudes
Micro
Less than 2.0
Very minor
2.0-2.9
Minor
3.0-3.9
Earthquake Effects
Frequency of Occurrence
Microearthquakes, not felt. About 8,000 per day
Generally not felt, but
About 1,000 per day
recorded.
Often felt, but rarely causes
49,000 per year (est.)
damage.
4.0-4.9
Noticeable shaking of indoor
items, rattling noises.
6,200 per year (est.)
Significant damage unlikely.
5.0-5.9
Can cause major damage to
poorly constructed buildings
over small regions. At most 800 per year
slight damage to welldesigned buildings.
Strong
6.0-6.9
Can be destructive in areas
up to about 100 miles across 120 per year
in populated areas.
Major
7.0-7.9
Can cause serious damage
over larger areas.
Great
8.0-8.9
Can cause serious damage in
areas several hundred miles 1 per year
across.
Rare great
9.0 or greater
Devastating in areas several
1 per 20 years
thousand miles across.
Light
Moderate
18 per year
