1.5 - Measuring Hazards And Hazard Profiles Flashcards
Moment magnitude scale
- 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 an earthquake occurs is the Moment Magnitude Scale (MMS)
- Goes from 1 which is not felt by humans to 10
- Strengths: provides accurate measurements of large earthquakes
- Limitations: requires complex calculations so less immediate, not good for smaller earthquakes
Modified mercalli scale
- The Modified Mercalli Intensity Scale is used to measure the intensity
- Based on its impacts
- The scale goes from I (not felt except by a few) to XII (some well built wooden structures destroyed, most masonry and structures are destroyed)
- Strengths: helps with damage estimation, can work in locations without seismometers, works for smaller and larger earthquakes, easy to understand impacts
- Limitations: relies on subjective data, doesn’t take into account local variations, difficult to apply in real time
Volcanic explosivity index
- 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:
o Height of material ejected into the atmosphere
o Volume of material
o Duration of the eruption - Strengths: can help predict relative impacts, help scientists communicate potential hazards to public and first responders
- Limitations: not useful for effusive eruptions, doesn’t take into account power output, difficult to measure the volume of pyroclastic flow
What is a tectonic hazard profile
A technique used to try to understand the physical characteristics of different types of hazards.
Hazard profiles can be used to analyse and assess the same hazard taking place in different locations at different times
Advantages: can be used to compare different hazards and events, they can also be used to plan for future events
Disadvantages: subjective, focus on physical factors not human factors, other factors may have a greater influence
What information is usually included on a tectonic hazard profile
- Magnitude
- Speed of onset
- Areal extent
- Duration
- Frequency
- Spatial predictability
Basaltic shield volcano hazard profile
Magnitude: small
Speed of onset: fairly slow
Areal extent: local
Duration: fairly long
Frequency: quite high
Spatial predictability: fairly precise
Andesitic cone volcano hazard profile
Magnitude: almost middling
Speed: middling
Areal extent: closer to local than regional
Duration: medium
Frequency: fairly low
Spacial predictability: fairly precise (but less so than basaltic shield)
Tsunami hazard profile
Magnitude: largest
Speed of onset: rapid
Areal extent: largest
Duration: quite short
Frequency: high
Spatial predictability: highest
Subduction zone earthquake hazard profile
Magnitude: more than medium
Speed: very rapid
Size: closer to regional than local
Duration: shortest
Frequency: closer to low than high
Spatial predictability: fairly random
