3.1 Earthquakes

Question 1

Describe the formation of an earthquake.

Answer 1

An earthquake occurs where two plates grind past one another, either in the same direction or the opposite direction but at different speeds. As they move past each other, the rough and uneven edges of the plates produce high levels of friction and sometimes if they catch and get stuck, significant pressure Is built up until the pressure overcomes the resistance. This sudden jolt and release of energy is an earthquake. Where the release of pressure occurs is called the focus and where it is felt on earth’s surface is called the epicentre.

Question 2

Describe the differences in deep focus vs shallow focus earthquakes.

Answer 2

Deep focus earthquakes occur when the oceanic plate sinks below the continental plate and a destructive (subduction) plate boundary. They can be very powerful however since they are deep in the crust the seismic waves spread out and dissipate before reaching the surface.

Shallow focus earthquakes occur at conservative plate boundaries, in the upper part of destructive plate boundaries and collision plate boundaries. They are usually less powerful but closer to to the surface so they can inflict damage. Seismic waves also spread horizontally affecting a wider area.

Question 3

Describe the distribution of Earthquakes.

Answer 3

• All earthquakes occur on plate boundaries, specifically destructive (collision and subductive) and conservative ones
• The largest proportion of earthquakes occur on conservative plate boundaries
• The majority of earthquakes are at least intermediate foal depth and most deep earthquakes are around the ring of fire.
• The ring of fire has the highest concentration of earthquakes found globally - Japan and Indonesia are two countries affected along here
• Sometimes, although less frequent, we find earthquakes within major plates, these can be found close to hotspot volcanoes such as Hawaii or along smaller intraplate fault lines

Question 4

How are Earthquakes measured?

Answer 4

Earthquakes are measured using seismometer which detect specifically P waves on the surface. There are two different scales used to measure earthquakes. The Richter scale and the Mercalli scale.

The Richter Scale:
- Measures the energy released with disregard to factors such as depth, terrain
- Uses a logarithmic scale, increases by a factor of 10 each time.

The Mercalli Scale:
- Takes in variables such as depth and terrain into account and tells us the damage that has occurred in relation to people and the environment.

Question 5

How do people prepare for earthquakes?

Answer 5

Preparation techniques for earthquakes:

• Preparing the public. This can include educating the public on the actions they should take in the event of an Earthquake such as getting to safe spaces and what to do in the immediate aftermath. This can be done by making it mandatory for school to do earthquake drills. Examples include world earthquake day in Japan.
• Early warning systems have been implemented in countries such as Japan which can notify people minutes or seconds before an earthquake, not enough time to evacuate, but maybe enough to go to a safe secure place. These systems also can change the direction that a trains take as to avoid the earthquake.

Question 6

What are the short term responses to an earthquake?

Answer 6

Short term responses to an earthquake:

• Search teams are sent out to look for people who are missing and may be trapped underneath rubble from falling buildings since this kills the most people during and earthquake.
• People may be stranded and rescue teams are sent out to retrieve them
• Shelters are constructed as a temporary for those who have been displaced by an earthquake before they find a place to stay. This provides them with warmth, food and water, healthcare and a place to sleep if their house has been destroyed.

Question 7

What are examples of longer term planning after and Earthquake?

Answer 7

Examples of long term planning post Earthquake:

• Rebuilding programmes - When and Earthquakes strikes and urban environments lots of the infrastructure will be destroyed. Therefore it will need to be rebuilt however planners may decide to implement certain Earthquake proofing infrastructure such as shock absorbers to mitigate the impacts in another Earthquake were to strike.
• Earthquake monitoring and hazard mapping - Using seismometers and other detections devices to monitor tectonic activity and extrapolate this data to see trends allowing people to forecast earthquakes early enough to evacuate people before the earthquake occurs.
• Geographical information systems - can provide data on land and infrastructure to mitigate the impacts of an earthquake by assessing areas of high vulnerability and also be able to plan route for evacuees on undamaged roads and bridges. An example of where this was used was in Charleston South Carolina where they used U.S (HAZUS).