Impacts of Tectonic Hazards

Question 1

What measures severity of an earthquake?

Answer 1

Logarithmic moment magnitude (MM) scale. It is based on many factors, including area of fault rupture, and amount of fault movement, determining amount of energy released.

Question 2

What is the mercalli scale?

Answer 2

Descriptive measures which depict amount of damage caused by surface shaking of an earthquake.

Question 3

What is a 1-2 mercalli?

Answer 3

Felt by only a few people at rest.

Question 4

What is a 45-55 mercalli?

Answer 4

Considerable damage in normal buildings, partial collapse and cracked ground.

Question 5

What is a >60 mercalli?

Answer 5

Few structures left, bridges destroyed. Broad fissures and underground pipes exposed. Lines of site distorted.

Question 6

How is the magnitude of volcanic eruptions measured?

Answer 6

All form magma and other products, VEI is an 0-8 scale combining:
Total volume of ejected product
Height of eruption cloud
Duration fo eruption
Eruption rate

Question 7

What type of scale is the VEI?

Answer 7

Logarithmic - each interval is a 10x increase in magnitude.

Question 8

What is frequency?

Answer 8

Also called recurrence level, it has an inverse relationship with magnitude.

Question 9

What measures protect against frequency of earthquakes?

Answer 9

Adaptation and mitigation including monitoring, education and community awareness.

Question 10

How can familiarity be an obstacle?

Answer 10

Unfamiliarity can be devastating, but familiarity can lead to resentment or complacency.

Question 11

What is duration of an earthquake?

Answer 11

The length of time for which the hazard exists. Often an initial earthquake can be only 30 seconds but followed by massive aftershocks.

Question 12

Which hazards were involved in the Tohoku multi-disaster?

Answer 12

Earthquake, tsunami and nuclear meltdown.

Question 13

Why are lahars and jokulhalaups so damaging?

Answer 13

They have total spatial and temporal unpredictability.
In 1985 the Nevada Ruiz eruption caused melting of ice, which caused mudflows that killed 23,000.

Question 14

What is the areal extent?

Answer 14

The size of an area covered by the tectonic hazard.

Question 15

What is areal distribution over geographical space?

Answer 15

It is controlled by plate boundaries. The Mt Merapi slopes attract farmers due to the fertile soils. Active volcanoes encourage tourism, leading to 48 dead in the Ontaki, Japan explosion after an unexpected explosion. This is increase vulnerability due to spatial dangers.

Question 16

What is speed of onset and how is it a danger?

Answer 16

How quickly a hazard arrived. Earthquakes usually have little warning, and less time to issue a warning so greater impact, such as the 1995 Kobe Earthquake where only 4 minutes warning was given. Quality of forewarning is useless if theres no time to give warning.

Question 17

What is predictability of occurrence and how is that an issue??

Answer 17

Prediction systems can predict where but not when, but an accurate prediction can reduce impact. Seismic theory dictates that all parts of a fault attain the same average level of movement over time, helping to predict the ‘Big One’. Volcanic eruptions are har to predict precisely even in close monitoring. An example of this is the Vesuvius long-awaited eruption in the Bay of Naples.

Question 18

Where do most earthquakes result from?

Answer 18

faults in rocks - often called a fault zone. Stresses build up until rocks suddenly shift along a fault. As fault moves, shockwaves move as a result of elastic rebound. Faults can be from 1-700km deep.
In Christchurch, NZ they had no knowledge of buried faults.

Question 19

What is a seismic P wave?

Answer 19

Vibrations from compression that spread from the fault in the direction of travel at 8km/s and can cross oceans.

Question 20

What is a seismic S wave?

Answer 20

Moving at 4km/s, they vibrate perpendicular to direction of travel. They’re responsible for a lot of earthquake damage.

Question 21

What are Rayleigh waves?

Answer 21

Surface waves - an elliptical path like ocean waves.

Question 22

What are Love waves?

Answer 22

Similar to R waves but only operate on a horizontal plain and are faster.

Question 23

What are the two most damaging types of wave?

Answer 23

Secondary and Love.