Earthquakes

1. Magnitude of Earthquake

2. Distance from Epicenter

3. Population Density4. Level of

Preparedness5. Time of

Occurrence6. Type of Soil

Not all Earthquakes cause destruction. There are some factors that will influence the extent in which an earthquake becomes hazardous. What are they?

• Explanation: Magnitude is the amount of strength released during an earthquake, the higher the magnitude the stronger the earthquake with more energy released, leading to more damage.

1) Magnitude of Earthquake

Magnitude of an Earthquake.

• Focus: Point of release of energy within the Earth’s crust

• Epicentre: Point on the Earth’s surface that lies directly above the focus

• The nearer the distance from Epic centre, the greater the intensity of shockwave experienced on the earth surface.

2) Distance from Epic centre

Population Density: The number of people per unit area

Explanation• The higher the population density of an

Earthquake-prone area, the chances of many people being killed or injured during an Earthquake will be higher.

3) Population Density

• People living in Earthquake-prone areas usually adopt a variety of measures to prepare themselves in the event of an Earthquake.

• Damage is reduced when people are prepared for an Earthquake.

4) Level of preparedness

• The time of the day which an earthquake occurs determines how ready people are to evacuate.– If an earthquake happens at night when

many are sleeping, there is a higher chance that most people will be trapped in their houses

5) Time of occurrence

• During an Earthquake, people who live in areas with soft soil tend to be affected more greatly

• The softer the soil is, it reduces the resilience of the soil when the ground is shaken, making it more likely for infrastructure to collapse.

6) Type of soil

Hazards• Tsunamis: Series of huge waves produced as a result

of undersea Earthquakes .

• These huge waves travel long distances (up to thousands of kilometres) before crashing onto the shores

• Example: 2004 Boxing Day Earthquake off the coast of Sumatra brought about tsunami that affected countries like Indonesia, India, Thailand and Sri Lanka– Led to the death of more than 250,000

people

Threat of Tsunamis

Hazards• Vibrations in the ground can snap pipes and

break cables which may cause the outbreak of fires

• Communication services may also be affected• Example: 2004 Earthquake in Kobe, Japan

– Damaged pipes and transmission lines– Disrupted electricity, gas and water supplies

to about a million of Kobe city’s 1.4 million residents.

Disruption of Services

Hazards• Usually not a direct result of Earthquakes• Caused by damaged electrical appliances, overturned

stoves or broken gas pipes when the ground shakes• Results in the collapse of infrastructure, injuries,

death and homelessness• Example: 1995 Earthquake in Kobe, Japan, caused

extensive fires that carried on for 2 days– Hundreds of fires ignited by toppled gas cookers

and kerosene stoves as households were preparing their breakfasts

– Strong winds encouraged fires to spread rapidly.– Firemen unable to control fires as ruptured water

pipes meant that there was no water supply

Fires

Hazards• Landslide: Sliding down of large amounts of rocks

and/or soil from a hill slope• Soil on the hill slopes loosens when the ground

shakes• Loosened soil slides down the hill slopes, burying

people and infrastructure beneath it

• Example: 1970, Earthquake off the coast of Peru destabilised the slopes of Mount Huascaran, triggering a massive landslide.– Landslide travelled more than 160km/hr– Death toll was more than 18,000 and only 200

survived the disaster

Landslides

http://video.nationalgeographic.com/video/101-videos/landslides

Hazards• Common occurrence during an earthquake in

an urban area as infrastructure may not be designed to withstand earthquakes

• Sometimes, despite the lack of visible damages foundations of buildings may be weakened– Repair works need to be carried out to prevent the

infrastructure from collapsing in the future

• Example: 2011 Earthquake in Tohoku, Japan, caused a Tsunami which travelled 10km inland– Extensive structural damage resulted in hundreds of

thousands of people being forced from their homes.

Destruction of Properties

Hazards• Common occurrence during an

earthquake in an urban area as infrastructure may not be designed to withstand earthquakes

• Transportation can be disrupted as it is unsafe to use damaged roads.

• Example: After the 1995 Earthquake in Kobe, Japan, many places in the city become inaccessible or difficult to reach.

Destruction of Infrastructure

Hazards• Loss of lives could result both directly

and indirectly from Earthquakes• Much of it depends on whether

emergency relief is available and if it is delivered in time

Loss of Lives

Direct Indirect

Collapse of buildings Starvation

Explosion/ FireExposure to inclement weather

Landslides Suffocation from being buried

Hazards• Aftershocks (Tremors that occur after the

main Earthquake) can also lead to the loss of lives– May be as strong as the tremors of the main

Earthquake– Can cause more buildings to collapse– May delay rescue efforts– Can endanger more lives

Loss of Lives

Hazards

Remember, HAZARDS are only hazards when lives are at stake.

1. Threat of Tsunamis2. Disruption of Services3. Fires4. Landslides5. Destruction of Properties6. Destruction of

Infrastructure7. Loss of Lives

Types of Volcanoes

Characteristics between Shield and Strato-volcanoes

Shield Volcanoes StratovolcanoesSlope profile Gentle slope Steep slopeBase Wide base NarrowViscosity of lava Low HighType of lava Basic lava AcidExplosiveness Gentle ViolentPresence of Vent Nil Yes