Development and habitation of lands susceptible to hazards , For example, building on floodplains subject to floods, seacliffs subject to landslides, coastlines subject to hurricanes and floods, or volcanic slopes subject to volcanic eruptions. Increasing the severity or frequency of a natural hazard . For example: overgrazing or deforestation leading to more severe erosion (floods, landslides), mining groundwater leading to subsidence, construction of roads on unstable slopes leading to landslides, or even contributing to global warming, leading to more severe storms. Affluence can also play a role, since affluence often controls where habitation takes place, for example along coastlines, on volcanic slopes. Affluence also likely contributes to global warming, since it is the affluent societies that burn the most fossil fuels adding CO2 to the atmosphere.
Catastrophic hazards , which have devastating consequences to huge numbers of people, or have a worldwide effect, such as impacts with large space objects, huge volcanic eruptions, world-wide disease epidemics, and world-wide droughts. Such catastrophic hazards only have a small chance of occurring, but can have devastating results if they do occur. Rapid onset hazards , such as Volcanic Eruptions, Earthquakes, Floods, Landslides, Severe Thunderstorms, Lightening, and wildfires, which develop with little warning and strike rapidly. Slow onset hazards, like drought, insect infestations, and disease epidemics take years to develop.
Primary Effects occur as a result of the process itself. For example water damage due to a flood, and collapse of buildings due to an earthquake, landslide, hurricane, or tornado. Secondary Effects occur only because a primary effect has caused them. For example, fires ignited by earthquakes or volcanic eruptions, disruption of electrical power and water service as a result of an earthquake or flood, and flooding caused by a landslide moving into a lake or river. Tertiary Effects are long-term effects that are set off as a result of a primary event. These include things like loss of habitat caused by a flood, permanent changes in the position of river channel caused by flood, crop failure caused by a volcanic eruption etc.
The Earth has a radius of about 6371 km, although it is about 22 km larger at equator than at poles. Density , (mass/volume), Temperature, and Pressure increase with depth in the Earth. The Earth has a layered structure . This layering can be viewed in two different ways (1) Layers of different chemical composition and (2) Layers of differing physical properties . Compositional Layering Crust - variable thickness and composition. Continental 10 - 70 km thick. Oceanic 8 - 10 km thick. Mantle - 3488 km thick, made up of a rock called peridotite. Core - 2883 km radius, made up of Iron (Fe) and small amount of Nickel (Ni). Layers of Differing Physical Properties , Lithosphere - about 100 km thick (up to 200 km thick beneath continents), very brittle, easily fractures at low temperature. Asthenosphere - about 250 km thick - solid rock, but soft and flows easily (ductile). Mesosphere - about 2500 km thick, solid rock, but still capable of flowing. Outer Core - 2250 km thick, Fe and Ni, liquid Inner core - 1230 km radius, Fe and Ni, solid. Reff. Abbott, Patrick L., 1996, Natural Disasters . Wm. C. Brown Publishing Co.,
Worst earthquake in recorded history occurred in 1556 in Shaaxi, China. Killed 830,000 people, most living in caves excavated in poorly consolidated loess (wind deposited silt and clay). Worst earthquake in this century also occurred in 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.
tectonic activity that causes deformation. Shaking of the ground caused by the passage of seismic waves, especially surface waves, near the epicenter of the earthquake are responsible for the most damage during an earthquake. The intensity of ground shaking depends on:Local geologic conditions in the area. In general, loose unconsolidated sediment issubject to more intense shaking than solid bedrock. Size of the Earthquake. In general, the larger the earthquake, the more intense is the shaking and the duration of the shaking. Distance from the Epicenter. Shaking is most severe near the epicenter and drops off away from the epicenter. The distance factor depends on the type of material underlying the area. There are, however, strange exceptions. For example, the 1985 Mexico City Earthquake (magnitude 8.1) had an epicenter on the coast of Mexico, more than 350 km to the south, yet damage in Mexico City was substantial because Mexico City is built on soft unconsolidated sediments that fill a former lake (see Liquefaction, below). Damage to structures from shaking depends on the type of construction. Concrete and masonry structures are brittle and thus more susceptible to damage wood and steel structures are more flexible and thus less susceptible to damage.
Natural Hazards - Earthquake
Lecture 2MSc. Environmental Science II Amit 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
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 dont 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 (Tang 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
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.