Earthquakes are a shaking or trembling of the Earth's crust caused by the release of huge stresses due to underground volcanic forces, the breaking of rock between the surface, or by a sudden movement along an existing fault line.
Earthquakes are unpredictable and strike without warning. They range in strength from slight tremors to great shocks lasting from a few seconds to a few minutes.
The magnitude of (or energy released by) an earthquake is recorded by a siesmograph using the Richter Scale. There is no upper limit to this scale as there is no upper limit to the amount of energy an earthquake might release. The most severe earthquakes recorded so far have not exceeded 9.5 on the Richter Scale.
Australia's worst earthquakes
In the last 80 years there have been 17 earthquakes in Australia registering 6 or more on the Richter Scale.
Australia's rate of earthquakes is about 1 every 5 five years, compared to a world average of about 140 per year.
Most earthquake casualties result from falling objects or debris because shocks can damage or demolish buildings and other structures.
Electricity and telephone lines, gas, sewer and water mains can be damaged; landslides, faults, subsidence and even tsunamis (huge seismic waves) can be caused leaving many people dead, injured or homeless.
The first recorded (indirect) deaths caused by an earthquake occurred in 1902 at Warooka in South Australia when two people died of shock, and in 1917 one miner died and 5 were injured in an underground rockfall triggered by an earthquake at Kalgoorlie, WA.
Newcastle, NSW (1989) - An Australian Case Study
At 10:27am on 28 December 1989, Newcastle (Australia's 6th largest city) was partially devastated by a moderate earthquake measuring 5.6 on the Richter Scale.
Newcastle was the first 'lethal' earthquake in Australia claiming 13 lives and injuring 150 others. It caused extensive damage to about 35,000 homes and 3,000 buildings with 70,000 buildings in the regions suffering some form of damage.
Insured losses reached $1,124 million while the estimated total damage to Newcastle was $4,480 million.
Newcastle showed that a lethal earthquake can occur in parts of Australia considered to be of low seismic risk. It has resulted in improved building codes and practices, and closer monitoring of seismic activity.
Since 1994 all buildings in Australia (including homes) are now required to be constructed to resist earthquakes.
Know your local earthquake risk
What you should do
- Ask your local Council if whether tremors or earthquakes have ever occurred in your area and what damage resulted.
- Study that information and ask your local Council about ways to make your house safer in the event of an earthquake.
- Find out how and where to turn off power, gas and water supplies.
- Plan together where your family will meet if separated.
- Know your safe areas during an earthquake.
- Check that you have adequate household and contents insurance and which hazards are not covered by the policy.
Watch for possible warning signs
- Erratic animal behaviour - scared or confused pets or birdcalls not usually heard at night may indicate that an earthquake is imminent.
- Ground water levels - Watch for sudden water level changes in wells or artesian bores.
- If you are indoors - stay there (clear of falling debris outside). Keep clear of windows, chimneys and overhead fittings. Shelter under and hold onto a door frame, strong table or bench.
- In high rise buildings, stay clear of windows and outer walls. Shelter under a desk near a pillar or internal wall.
- DO NOT use elevators.
- In crowded areas or stores, do not rush for doors, but move clear of overhead fittings and shelves.
- If outside, keep well clear of buildings, overhead structures, walls, bridges, powerlines, trees etc.
- In a city street, shelter from falling debris under strong archways or doorways of buildings. Don't go under awnings as they may collapse.
- In a vehicle, stop in an open area until shaking stops.
- Beware of downed powerlines and road damage, including overpasses and bridges. Listen to your car radio for warnings before moving.
After an earthquake
- Turn off electricity, gas, water and DO NOT light matches until after you have checked for gas or fuel leaks.
- Check for injuries and apply first aid. DO NOT move seriously injured people unless they are in immediate danger.
- Check for broken water, sewerage or electrical mains.
- DO NOT use the telephone immediately (to avoid congestion) unless there is a life threatening situation.
- Check for cracks and damage to the roof, chimney etc.
- Evacuate the building if it is badly damaged and be prepared for aftershocks.
- Do not waste food and water as supplies may be interrupted. Collect emergency water from heaters, ice cubes, toilet tanks and canned foods.
- Listen to your local radio station and heed warnings and advice on damage and service disruptions.
- Try to avoid driving unless for an emergency (to keep the streets free for emergency services).
- Do not go sightseeing or enter damaged buildings.
- Try to stay calm and help others if possible.
Further information about earthquakes
Last updated 18 December 2011