D - The Relevance of Hazard Magnitude and Frequency/Recurrence for Risk Management Flashcards
What is the recurrence interval (return period)?
The expected frequency (in years) for an event of a given magnitude; smaller events happen more often, larger events less frequently.
How do frequency and magnitude typically relate to hazard events?
Small events occur frequently (high frequency/short return period) with low magnitude; large events occur rarely (low frequency/long return period) with high magnitude.
Which events usually require the greatest management?
Low-frequency, high-magnitude events, because they cause the most destruction.
Describe the general annual frequency of ‘Great’ earthquakes (magnitude > 8).
On average, there is about 1 per year, causing total destruction and high loss of life.
Why is the Richter scale considered logarithmic?
Each whole-number increase represents a tenfold increase in amplitude and roughly 31.6 times more energy released.
What scale are scientists increasingly using instead of the Richter scale?
The Moment Magnitude Scale (M), which measures the total energy released by an earthquake.
How does an increase of 1.0 on the Moment Magnitude Scale affect energy release?
It increases the energy released by over 30 times.
What does an increase of 0.2 on the M scale represent?
A doubling of the energy released.
What is the Volcanic Explosivity Index (VEI)?
A scale that measures the explosiveness of volcanic eruptions based on volume of material ejected, eruption column height, and damage caused.
What is considered a ‘very large and violent’ volcanic eruption on the VEI scale?
Any eruption above VEI 5.
How much material does a VEI 8 eruption eject?
More than 1,000 km³ of material, which is 10 times more than a VEI 7.
When did the last known VEI 8 (supervolcano) eruption occur?
About 74,000 years ago.
Give an example of how magnitude and frequency apply to earthquakes.
There are fewer highly destructive (high-magnitude) quakes, but many minor (low-magnitude) ones.
How does the hazard potential of major earthquakes (7.0–7.9) compare to great earthquakes (>8)?
Major quakes (7–7.9) cause serious building damage and potentially large loss of life, while great quakes (>8) often result in total destruction and very high loss of life.
