- Earthquakes occur in narrow bands which match the outlines of the earth's tectonic plates.
- They are caused by a sudden movement in the earth's crust.
- Most take place at plate boundaries.
- The place underground where an earthquake originates is called the focus.
- The point onthe surface directly above the focus is called the epicentre.
- A fault line is where a section of crust splits or cracks during an earthquake.
- Seismic waves are waves of energy that travel out from the focus during an earthquake.
- Earthquakes happen when two or more tectonic plates lock together due to friction.
- The forces moving the plates continue to apply pressure on the plates.
- This builds up until eventually the plates move without warning and the crust might split open.
Richter Scale and Mercalli Scale
- The Richter scale runs from 1 to 10 and measures the amont of energy released by an earthquake.
- The Mercalli scale runs from 0 to 12 and measures the amount of damage done by an earthquake.
- The Richter scale is logarithmic, each number being 10 times more powerful than the previous number.
- So an earthquake measuring 7 is 1 times more powerful than one measuring 6.
Primary Effects are the immediate effects of an earthquake. They include:
- Buildings collapsing.
- Liquefaction, where shaking causes water in the soil layers to be brought to the surface and buildings to subside.
- Objects falling from buildings and other structures, e.g. signs, glass and cables.
Secondary effects are the after-effects of an earthquake. They include:
- Fire and landslides.
- Tsunamis, such as the December 2004 tsunami that killed almost 300,000 people.
- Disease from unclean water supplies and lack of hygiene, such as typhoid and cholera.
Short Term Responses
- Emergency aid such as food, water, shelter and medical care.
- Specialist rescue teams with lifting machinery, sniffer dogs and heat-sensing equipment.
Long Term Responses
- Development aid to assist with the rebuilding and reconstruction of the affected area.
- Money to help businesses re-start
- Planning from local and national authorities to prepare for future earthquakes.
Preparing for Earthquakes
People can prepare for earthquakes in a number of ways:
- Predict where they might happen.
- Geologists use seismometers to measure tremors that could indicate afuture earthquake.
- Prepare for when an earthquake happens.
- Earthquake-prone countries run earthquake drills each year and peoplehave earthquake kits containing essential items for survival.
- Prevent damage during an earthquake.
- Strict building regulations stop unstable buildings from being constructed.
- New buildings in earthquake-prone countries have to be designed to be earthquake-proof.
Case Study - LEDC
- Earthquake that hit Haiti in January 2010 was 7 on the richter scale.
- Over 200,000 people were killed and over 300,000 people injured.
- Worst hit was the capital city, Port-au-Prince.
- A third of the buildings collapsed, making 1.5 million people homeless.
- The earthquake destroyed the country's port, airport, parliament, presidential palace and police headquarters.
- This made it hard for emergency help to get to Haiti.
- A poor country, Haiti did not have the resources to be well-prepared for an earthquake.
- It lacked the skilled people or equipment to respond effectively afterwards.
Case Study - MEDC
- An earthquake measuring 7.2 on the Richter scale hit Kobe, Japan, in January 1995.
- Out of 1.5 million, 5000 people died and 300,000 were made homeless.
- It caused over £100 billion of damage.
- 7500 houses collapsed and fires spread rapidly as gas pipes broke.
- Water mains fractured, making it hard to put out fires.
- An elevated road collapsed, as did sections of the bullet train track.
- A rich country, Japan has more than 1000 tremors every year, so people are used to earthquakes and know what to do.
- There are strict building controls and well-trained and equpped emergency response teams.