EARTHQUAKES

Earthquakes

The crust of the earth is not a rigid and immobile structure. Early civilization were aware of this and constructed buildings that would withstand earthquakes, such as the Royal Palace in Crete. 

How earthquakes occur 

Earthquakes are the result of a slow build up of pressure within the crustal rocks. This pressure will build and then suddenly release which causes parts of the surfaces to experience jerking or vibrations. The point where the pressure is released is the focus, and the point on the surface which receives the worst of the seismic waves is known as the epicentre. The earthquake itself may cause a substantial amount of damage and loss of life but the secondary effects can be just as devastating but may last much longer than the primary damage such as lack of water, spread of disease and loss of homes and economy. 

Continental Drift

In 1620 Francis Bacon noted the jigsaw like link between the coasts of South America and the west coast of Africa. Later in 1912 a German meteorologist Alfred Wegener published his theory that at some point a long time ago the continents joined together in a super continent called Pangaea. This landmass later split and various continents started to from. 

Plate Tectonics

The crust of the earth is divided in to seven layers with a number of smaller sections. These float on a semi molten mantle which move the plates by convection currents. Convection currents are a result of heat generated by the centre of the earth, the hotter semi molten lava from the core rises to the crust and then cools and returns to the core this creates the currents. There are two different types of plates, oceanic and continental. The continental crust is made up of older, lighter rock which is dominated by minerals rich in silicon and aluminium. Oceanic crust is much younger and has a denser rock type. Its dominant minerals are silicon and magnesium.  

Case Studies

MEDC: San Francisco October 1989 

At 5:04pm on October 17th 1989 an earthquake occured in San Francisco measuring 6.9 on the Richter scale. The quake only lasted 9 seconds but the quake was devastating for San Francisco. The city lies on the San Andreas fault line where two continental plates are moving past each other in opposite directions (a consrvative plate boundary). 

The effects of the earthquake;

- 67 Deaths
- 6,000 Homes damaged / destroyed
- Damage to infrastructure - electricity / gas and water mains cut
- 2000 people made homeless
- Upper deck of the Nemitz highway collapsing onto the lower deck crushing people in their cars
- A section of the San Francisco-Oakland Bay Bridge collapsing
- Fire resulting from gas explosions
- Massive economic costs ($4.4 billion)

LEDC: Kashmir 8th October 2005 

On 8 October 2005, an earthquake measuring 7.6 on the Richter scale hit the Kashmir region of Pakistan. The earthquake was the result of collision between the Indian and Eurasian plates.

Effects of the earthquake;

• Approx. 80,000 people died - 79,000 from Pakistan, 1,400 in Kashmir, 4 in Afghanistan
• 3.5 million left homeless
• 380,000 were in need of emergency housing
• 4,000 households were inaccessible by road due to landslides
• 2.3 million people were without food for the winter
• Disease spread, sourced from people drinking the dirty, contaminated water (this was all they had at the time by means of water)
• homeless people died from hypothermia in the mountains (there was little to keep them warm as aid was slow to arrive)