Tectonic Processes & Hazards - EQ2 - 1.5 Flashcards
What are the two scales used to measure the impacts of earthquakes
The Richter Scale & The Moment Magnitude Scale
Which earthquake impact scale is more accurate
- Moment Magnitude Scale is more accurate,
- as it uses the energy released by all shockwaves as well as the area of rupture and movement.
What scale measures the intensity earthquakes
Mercalli
What is the Mercalli Scale
- Measures the experienced impacts of an earthquake
- It is a relative scale, because people experience different amounts of shaking in different places
- It is based on a series of key responses, such as people awakening, the movement of furniture and damage to structures
What is the scale of the Richter scale
0-10
What is the Richter Scale
- a measurement of the height (amplitude) of the waves produced by an earthquake
- it is an absolute scale; wherever an earthquake is recorded, it will measure the same on the Richter Scale
How does the richter scale measure the magnitude of an earthquake
uses the arrival times of the P and 5 waves, the amplitude of the 5 wave, and distance from the epicentre
Both the Richter Scale & The Moment Magnitude Scale are ……, meaning
- logarithmic
- each level being 10 times greater than the level below
When are the two different earthquake magnitude scales used
- Richter Scale (most often used in the news)
- Moment Magnitude Scale (the more accurate magnitude reading)
What is the moment magnitude scale
- A modern measure used by seismologists to describe earthquakes in terms of energy released.
- The USGS uses MMS to estimate magnitudes for all large earthquakes.
How is the Moment Magnitude Scale calculated
The magnitude is based on the ‘seismic moment’ of the earthquake, which is calculated from: the amount of slip on the fault, the area affected and an Earth-rigidity factor.
What does the modified mercalli scale range from
I-XII
Describ eho the mercalli scale is relative
- Usually the stronger the magnitude of an earthquake the higher the intensity,
- but local conditions may modify this correlation through secondary hazards or where the epicentre coincides exactly with human settlements
Give 2 disadvantages of the scales used to measure tectonic hazards
- These scales are imperfect in that they typically measure just one or two physical processes that might cause damage.
- The nature of the impact depends on both the event itself (size, duration…) but also on the nature of the environment in which it is happening (remember the risk equation!)
What are tectonic hazard profiles used for
- to try and understand the physical characteristics of different types of hazard
- to analyse and assess the same hazards which take place in contrasting locations or at different times
Hazard profiles are developed for ….
each natural hazard
What is the Volcanic Explosivity Index
- A relative measure of the magnitude (explosiveness) of a volcanic eruption
How is the volcanic explosivity index calculated
- calculated from the volume of products (ejecta), height of the eruption cloud and qualitative observations
Like the Richter Scale and MMS, the VEl is ……….
logarithmic: an increase of one index indicates an eruption that is ten times as powerful
describe the scale of the Volcanic Explosivity Index
- It ranges from 0-8
- It is a composite index combining eruption height, volume of material (ash, gas, tephra) erupted and duration of eruption.
What occurs at a VEI 0-3 erruption
- associated with shield volcanoes and basaltic eruptions at constructive plate boundaries and mid-plate hotspots
What occurs at a VEI 4-7 erruption
- destructive plate margins, erupting high viscosity, high gas, high silica andestic magma
No modern human has ever experienced a VEI…
8 supervolcano
What would the impact be of VEI 8
- These are ones whose impacts would be felt globally, because of the worldwide cooling of the Earth’s climate, perhaps for up to 5 years
Volcanoes have specific locations and usually ……………………., but earthquakes are found in …………………..&……………… Also, not all undersea earthquakes produce ………………
Volcanoes have specific locations and usually give signs that they are about to erupt, but earthquakes are found in broad zones and are unpredictable. Also, not all undersea earthquakes produce tsunamis.
Describe the different characteristics of different tectonic hazards
-spatial predictability
- An area that has never had an event will experience greater impacts as people and places will be unprepared
Describe the different characteristics of different tectonic hazards
-area extent
- The larger the area affected by an event, the greater the impacts will be, as more people and places are affected
Describe the different characteristics of different tectonic hazards
-frequency
- An event that occurs often is more likely to create cumulative impacts (although rare have more energy)
Describe the different characteristics of different tectonic hazards
-magnitude
- The greater the amount of energy released by an event, the greater the impacts are likely to be
Describe the different characteristics of different tectonic hazards
-speed of onset
- The faster the event occurs, the shorter the warning time and the greater the impacts as places are unprepared
Describe the different characteristics of different tectonic hazards
-duration
- The longer an event lasts, the more likely that there will be greater impacts
On the moment magnitude scale, what do the impacts of a magnitude 3 earthquake look like
- Many a year, all around the world
- rarely cause damage
On the moment magnitude scale, what do the impacts of a magnitude 5 earthquake look like
- Moderate: Between 1000 and 1500 a year
- Damage caused over a small region
On the moment magnitude scale, what do the impacts of a magnitude 7 earthquake look like
- Major: Between 10 and 20 a year
- Serious damage over a large area
On the moment magnitude scale, what do the impacts of a magnitude 9 earthquake look like
- Great: One every decade (or longer)
- Serious damage over a large region
What do earthquakes of IV look like on the Mercalli Scale
- Shock waves felt indoors
- Windows rattle
- People woken at night
What do earthquakes of VII look like on the Mercalli Scale
- Slight to moderate damage of well-constructed buildings
- Aseismic designs may be slightly damaged
- Walls crack
- People are alarmed
What do earthquakes of X look like on the Mercalli Scale
- Wooden structures and masonry and frame buildings destroyed
- Train rails bent
- Ground may crack. Landslides caused on steep slopes
What do earthquakes of XII look like on the Mercalli Scale
- Total destruction. Lines of sight and level distorted
- Objects thrown into the air
- Topography and river courses changed
What do eruptions on the VEI scale of 1 look like
- Small, gentle eruption
- Less than 10^6 metres of ejected material
- Often small fissure eruptions
- Hawaiian type
What do eruptions on the VEI scale of 3 look like
- Moderate to large eruption
- Can be severe
- Up to 10^8 metres of ejected material
- Eruption column of ash up to 10.5 km high
- Eruption phases last up to half a day
- Strombolian type
What do eruptions on the VEI scale of 5 look like
- Very large eruption
- 10^10 metres of ejected material
- Eruption column up to 28km high
- Can be cataclysmic
- Composite volcano type (Plinian or Peléean)
What do eruptions on the VEI scale of 7 look like
- Very large, colossal eruption
- 1012 metres of ejected material
- Eruption column height over 47 km
- Eruption phases last over half a day
- Composite cone type (ultra-Plinian)
