Lecture 2MSc. Environmental

Science IIAmit Gopal Chauhan

What we learn today?

• A bit more about Hazards

• Some details about the earth

• Earthquakes.

• Ritcher scale

• And Modified Mercalli intensity Scale (1956)

Nature of hazard

• Probability of Hazard from human made sources always high as compared to those induced by nature.

• Probability and intensity of nature induced hazard sometimes increases with human interferences and voluntary acceptance ( i.e. benefits overweighed then harm caused. Fig.1.1

Defining a hazard is subject to..

• Location

• Goods at stake

• Peoples perceptions about average conditions

• Variability of a natural event in intensity and duration

• Fig: 1.3

In reality

• Hazards are neither ‘hostile nor ‘benign’ they are neutral.

• Human sensitivity to environmental hazard is a combination of Physical exposure and Vulnerability

• Hazards are Natural, quasi-natural and manmade. Fig. 1.5

Human intervention in natural processes can also increase

vulnerability by• Development and habitation of lands

susceptible to hazards,

• Increasing the severity or frequency of a natural hazard.

• Affluence

Vulnerability to a given hazard depends on:

• Proximity to a possible hazardous event

• Population density in the area proximal to the event

• Scientific understanding of the hazard

• Public education and awareness of the hazard

• Existence or non-existence of early-warning systems and

lines of communication

• Availability and readiness of emergency infrastructure

• Construction styles and building codes

• Cultural factors that influence public response to warnings

Common features of hazards

• Origin is clear and produces characteristic effects.

• Warning time is normally short• Losses suffered very shortly after the

event.• The origin can be endogenous,

exogenous, anthropogenic .

Hazard and Environmental Hazard

• A hazard is a condition (natural or anthropogenic) of the environment which can exert an adverse influence on human life, property or activity.

• Keith Smith (1992) defines environmental hazards as ‘ extreme geophysical events and major technological accidents, characterized by concentrated releases of energy or materials, which pose an unexpected threat to human life and can cause damage to goods and the environment’

Hazards can be grouped according to many characteristics

• Areal extent of damage zone• Intensity of impact at a point• Duration of impact at a point• Rate of onset of the event ( rapid and slow)• Predictability of the event( this grouping has more utility then causally-

based classifications for modelling human response and organizing hazard management. Fig. 1.6)

Effects of Hazards

• Primary i.e. result of the process itself

• Secondary i.e. causes from primary effects

• Tertiary i.e. long-term effects that are set off as a result of primary event. causes from

Layers of Earth

Seismic Hazards, Earthquakes

• Earthquake is a shaking of the ground caused by the sudden breaking and shifting of large sections of the earth’s rocky outer shell.`

• Also, capable of forming waves, some emit lava, some cause shallow to deep divides on the surface, rivers change course, some cause tsunamis.

Are Earthquakes hazardous?

• Depends

• Do not cause direct hazard

• "earthquakes don't kill people, buildings do".

• Thus earthquake hazard risk depends on

• 1. Population density

• 2. Construction standards

• 3.Emergency preparedness

Worst Examples• Kutch 2001• Shaaxi, China 1556, Killed 830,000• China (T'ang Shan Province), killed• 240,000 in 1976. Occurred at 3:42 AM, Magnitude 7.8

Earthquake and magnitude 7.1 aftershock. Deaths were due to collapse of masonry (brick) buildings.

• California 1989(The Loma Prieta, or World Series• Earthquake) with a Richter Magnitude of 7.1 killed about 62

people. • 10 months later, an earthquake with magnitude 6.9 occurred

in Armenia, where no earthquake- proof• building codes existed. The death toll in the latter

earthquake was about 25,000!

Hazards Associated with Earthquakes

• Ground Motion - geologic conditions in the area. Size of the Earthquake. Distance from the Epicenter. Damage to structures from shaking depends on the type of construction.

• Faulting and Ground Rupture• Aftershocks• Fire• Landslides• Liquefaction • Changes in Ground Level• Tsunamis• Flooding

See PDF.2

Richter scale

Modified Mercalli Scale (1956)• I. Only instruments can detect the movement. People

do not feel it.• II. People lying down or on upper floors of tall

buildings might feel• movement.• III. Many people indoors will feel movement.

Hanging objects swing back• and forth.• IV. Most people indoors will feel movement, but

those outside may not.• Dishes, windows and doors rattle. Parked cars rock.

Continued..

• V. Almost everyone feels movement. Sleeping people wake up. Doors

• swing, dishes break, small objects move or are turned over. Trees might

• shake.• VI. Everyone feels movement. It is difficult to walk.

Pictures fall off• walls, objects fall from shelves, furniture moves.

Trees and bushes shake.• There is slight damage to poorly built buildings.

Continued..

• VII. It is difficult for people to remain standing. Cars shake. Furniture

• breaks. Damage is slight to moderate in well-built buildings, heavy in

• poorly built buildings.• VIII. It is difficult to steer cars. Houses may move off

their foundations.• Poorly built buildings may collapse and chimneys

may fall. Well built• buildings suffer slight damage. Tree branches break.

Continued..

• IX. Well built buildings suffer considerable damage. Houses not bolted

• down move off their foundations. Some underground pipes are broken.

• The ground cracks.• X. Most buildings are destroyed. Bridges and dams

are seriously damaged.• Water is thrown out of rivers and lakes. The ground

cracks in large areas.• There are large landslides.

Continued..

• XI. Most buildings collapse. Railroad tracks are bent. Bridges and

• underground pipelines are destroyed. Large cracks appear in the ground.

• XII. Almost every thing is totally destroyed. Large objects may be thrown

• into the air. The ground moves in waves or ripples.