Tectonic Hazard Profiles (Edexcel A Level Geography)

Revision Note

Written by: Bridgette Barrett

Reviewed by: Jenna Quinn

Tectonic Hazard Magnitude

Earthquake magnitude

Magnitude is the most common way to measure an earthquake
It measures the energy released at the source (focus)
- The magnitude can be measured on different scales but the one which is reported on the news when a earthquake occurs is the Moment Magnitude Scale (MMS)
- It is measured using seismographs
The MMS goes from 1 which are not felt by humans to 10
The MMS is a logarithmic scale which means that a 6 on the scale is a ten times increase in amplitude from a 5
- The energy release is 32 times greater

Earthquake intensity

The intensity of an earthquake is its impact on people, as well as the built and natural environments
The Modified Mercalli Intensity Scale is used to measure the intensity
The scale goes from I to XII

mercalli-scale — **Modified Mercalli Intensity Scale**

Examiner Tips and Tricks

Remember not to confuse magnitude and intensity.

Magnitude is the amount of energy released. Whereas intensity is severity of ground shaking at a particular place based on the effects on humans, buildings and the environment.

Measuring volcanic eruptions

Every eruption is unique some are gentle, others are hugely explosive
The Volcanic Explosivity Index (VEI) is used to measure the size of an eruption
This can not be measured on a scientific instrument so is calculated based on a series of measurements and observations
- These include:
  - Height of material ejected into the atmosphere
  - Volume of material
  - Duration of the eruption
This is a logarithmic scale from 0-8

887f2077-ef55-4c6d-8f85-361721f6d574 — **Volcanic Explosivity Index**

Examiner Tips and Tricks

Magnitude is one of the key factors in the impact a hazard event has. However, it is important to remember that it is not the only factor - a magnitude 6.1 earthquake can have severe impacts in one area but the same magnitude in another area may have few impacts

Tectonic Hazard Characteristics

Hazard profiles can be used to compare tectonic hazard events
Hazard profiles usually include information about:
- Magnitude
- Speed of onset
- Areal extent
- Duration
- Frequency
- Spatial predictability

Hazard profiles of tectonic hazards

Advantages

Hazard profiles can be used to compare:
- Different hazards
- Same hazards with different processes - a volcano on a destructive boundary compared to one on a constructive boundary
- Same hazards with different human vulnerabilities - an earthquake in a developed country compared to one in a developing country
They can also be used to plan for future events
They are useful when looking at one hazard such as an earthquake

Disadvantages

Hazard profiles do have disadvantages:
- Other factors may have a greater influence on the impact
- They focus on physical factors when human factors may be the most important
- Multi-hazard events are not easily represented on a hazard profile
- They are subjective

Examiner Tips and Tricks

It is important to understand the advantages and disadvantages of using hazard profiles to compare hazards. You should be able to outline the advantages and disadvantages using real life examples.

For example, you can compare magnitude of earthquakes on a hazard profile but the correlation between magnitude and impacts is not always straightforward due to other factors such as level of development. This can be seen in the comparison of Nepal (2015) and New Zealand (2016). They both experienced 7.8 magnitude earthquakes. However the number of deaths in Nepal was almost 9,000 whereas in New Zealand it was 2. Other factors such as population density had more impact on the number of deaths.