Earthquakes Flashcards
What causes earthquakes?
Earthquakes are the sudden violent shaking of the ground. This happens because the Earth’s plates are constantly moving. Sometimes, because of friction, plates try to move and become stuck. Pressure builds up because the plates are still trying to move. When the pressure is released, it sends out huge amounts of energy causing the Earth’s surface to shake violently.
What are features of an earthquake?
The point inside the Earth’s crust where the earthquake originates from is known as the focus. The earthquake’s energy is released in seismic waves and they spread out from the focus. The seismic waves are most powerful at the epicentre. The epicentre is the point on the Earth’s surface directly above the focus.
Where are earthquakes found?
Earthquakes are found at all three plate boundaries: constructive, destructive and conservative plate boundaries.
How are earthquakes measured?
Earthquakes, until recently, have been measured on the Richter scale. The Richter scale measures the magnitude of an earthquake (how powerful it is). It is measured using a machine called a seismometer which produces a seismograph. A Richter scale is normally numbered 1-10, though there is no upper limit. It is logarithmic which means, for example, that an earthquake measuring magnitude 5 is ten times more powerful than an earthquake measuring 4. Earthquakes measuring 1-2 on the scale happen regularly, and they are so small that people cannot feel them. Earthquakes measuring upwards of 7 are less frequent but very powerful, and can cause a lot of destruction.
What do scientists use now to measure earthquakes?
The Richter scale is not very accurate in measuring these larger earthquakes and today scientists use the Moment Magnitude Scale which uses the same logarithmic scale but which more accurately measures the strength of larger earthquakes.
What are conservative plate margins?
Areas between two crustal plates that are moving past each other in opposite directions or at different speeds.
What are destructive plate margins?
When two tectonic plates move towards one another. The oceanic crust is forced to sink back into the mantle, whilst the continental crust rises above. Volcanoes and earthquakes are found here.
What is the Moment magnitude scale (MMS)?
Used to measure the magnitude of earthquakes, in terms of the amount of energy released.
Whats the Richter scale?
The measure by which the strength of earthquakes is determined.
What is a seismometer?
A machine that detects seismic waves caused by earthquakes.
What is meant by the effect of an earthquake?
The effect of an earthquake is the damage which happens as a result of the earthquake.
The effects of an earthquake can vary depending on?
The size of the earthquake on the Richter scale - the higher it is on the scale, the more destruction it can cause.
Level of development - whether it occurs in a rich or a poor country. Richer countries will be more likely to be able to predict, protect and prepare themselves from the effects of an earthquake.
The depth of the focus - if it’s shallow, it can be more destructive.
Distance from epicentre - the effects of an earthquake are more severe at its centre.
Population density - the more people living in an area, the more likely that more deaths and casualties may arise.
The time of day - whether people are in their homes, work or travelling.
We can classify the effects of an earthquake into two categories, what are they?
primary effects - things that happen immediately as a result of an earthquake
secondary effects - things that happen in the hours, days and weeks after the initial earthquake
What are meant by responses?
Responses are how countries react to an earthquake.
How are responses categorised?
Short-term or immediate - a response in the days and weeks immediately after a disaster has happened. Short-term responses mainly involve search and rescue and helping the injured.
Long-term - responses that go on for months and years after a disaster. It involves rebuilding destroyed houses, schools, hospitals, etc. It also involves kick-starting the local economy.
What happened in the Christchurch earthquake?
The earthquake struck on 22 February 2011. It was a 6.3 magnitude earthquake and the focus was very shallow at 4.99 km deep. The earthquake happened on a conservative plate margin between the Pacific Plate and the Australian Plate.
What were the primary effects of the Christchurch earthquake?
181 people were killed. 2,000 injured. Over 50 per cent of the city's buildings were damaged. The city's cathedral spire collapsed. Water and sewage pipes were damaged.
What were the secondary effects of the Christchurch earthquake?
Businesses were closed for a long time.
Christchurch couldn’t hold the five Rugby World Cup matches.
Schools were closed for two weeks due to the damage.
What were the short term responses of the Christchurch earthquake?
International aid was provided (around $6-7 million).
Aid workers from charities such as the Red Cross came to help.
Areas were zoned to assess damage.
300 Australian police officers were flown in.
What were the long term responses of the Christchurch earthquake?
$898 million in building insurance claims.
Water and sewerage were restored to the city by August 2011.
Temporary housing was provided.
What are the 3 P’s?
Protection, Preparation and Prediction
What is prediction / how is it done?
Prediction involves using seismometers to monitor earth tremors. Experts know where earthquakes are likely to happen. However, it is very difficult to predict when they will happen. Even looking at the timescale between earthquakes doesn’t seem to work.
What is protection / how is it done?
Protection involves constructing buildings so that they are safe to live in and will not collapse. Some examples of building improvements are:
rubber shock absorbers in the foundations to absorb the Earth tremors
steel frames that can sway during Earth movements
open areas outside of the buildings where people can assemble during an evacuation
What is preparation / how is it done?
In earthquake-prone countries, hospitals, emergency services and residents practise for an earthquake. They have drills in all public buildings so that people know what to do in the event of an earthquake. This helps to reduce the impact and increases their chance of survival.
What is a fault?
A fracture along which the blocks of crust on either side have moved relative to one another parallel to the fracture?
Whats the mantle?
Is part of the earths interior between the metallic outer core and the crust
What are tremors?
Shaking / vibrating movements
Whats a temblor?
An earthquake
Whats aftershock?
A quake of lesser magnitude following a large earthquake in the same area
Whats the focus?
The point inside the crust where the pressure is released?
Whats the stress?
The force per unit area acting on a plane within a body?
Whats the epicentre?
The point on the earths surface vertically above the focus. Where a seismic rupture begins
What is magnitude?
A number in which characterises the relative size of an earthquake
