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EQ2: Why do some tectonic hazards develop into disasters? (How are…
EQ2: Why do some tectonic hazards develop into disasters?
What are the impacts of tectonic hazards?
Pressure and Release Model (1984)
How are tectonic hazards measured?
Moment Magnitude Scale
The magnitude scale measures the energy released during an earthquake.
It is an updated version of the Richter magnitude scale.
It uses a logarithmic scale - a magnitude 6 earthquake has ten times more ground shaking than a magnitude 5.
A seismograph is used.
Mercalli Scale
The Mercalli scale measures earthquakes intensity on a scale of I to XII.
It measures the intensity of the shaking effects - what you actually feel.
It can’t be easily used to compare earthquakes as the shaking experienced depends on building type, quality, ground conditions and infrastructure.
The relationship between magnitude and death toll is a weak one because:
Some earthquakes cause serious secondary impacts, such as landslides and tsunamis.
Earthquakes hitting urban areas have greater impacts than those in rural areas.
Level of development, and level of preparedness, affect death toll.
Isolated, hard to reach places could have a higher death toll as rescue and relief takes longer.
The Volcanic Explosivity Index scale
VEI eruptions from 0 to 3 are associated with shield volcanoes and basaltic eruptions at constructive plate margins and mid-plate hotspots.
VEI eruptions from 4 to 7 occur at destructive plate margins, erupting high viscosity, high gas, high silica andesitic magma.
VEI eruptions at 8 are very rare caldera eruptions such as Yellostones and Toba. No modern human as experienced this.
How can tectonic events be compared?
Strengths:
Used to analyze and assess the nature of a specific hazard and so help planning.
Compare the physical processes that all hazards share.
Able to identify and rank the hazards that should be given the most attention and funding.
Weaknesses:
Less reliable when comparing different event types.
They only measure physical attributes, not the impacts.
More difficult to compare across hazards, e.g. earthquakes to volcanic eruptions as they have different impacts.
What factors affect hazard risk?
How can contrasting events be statistically analysed?
Correlation
a mutual relationship or connection between two or more things. It does not always mean causation.