Seismic hazards

Question 1

Define epicentre

Answer 1

The point directly above the focus on earths surface

Question 2

Define focus

Answer 2

Location in earths crust where earthquake occurs

Question 3

Define seismicity

Answer 3

a measure encompassing earthquake occurrences, mechanisms, and magnitude at a given geographical location

Question 4

What is the Richter scale

Answer 4

A logarithmic scale from 1-10, where 7 on the scale is x10 more more powerful that 6 and x100 more powerful than 5, and is used to measure the magnitude of earthquakes.
However accuracy decreases for larger earthquakes

Question 5

What is the moment magnitude scale ?

Answer 5

A measure of the total distance the fault has moved and the force needed to generate that.

Question 6

What is the modified mercalli scale ?

Answer 6

A measure of the effect on people and infrastructure. A 12 point scale which classifies the impact of the earthquake and indicates severity on humans.

Question 7

Predictability of seismic hazards

Answer 7

-Earthquakes can’t be accurately predicted
-Gap theory maps placed on a margin where earthquakes occur and suggests the “gaps” will have a higher strain build up in the rocks so a higher probability of an earthquake

Question 8

What are body waves ?

Answer 8

-P + S waves (move through rock)
-P waves are the fastest and can also travel through liquids. Cause ground to rock back and forth.
-S waves are slower and can’t travel through liquids. Cause the ground to shake up and down.

Question 9

What are surface waves ?

Answer 9

-Rayleigh and love waves (travel along earths surface)
-Love waves cause ground to move from side to side
-Rayleigh waves cause a rolling motion

Question 10

Explain soil liquefaction

Answer 10

When seismic waves travel through soft sediments, they behave as liquids, due to an increase in pore pressure. Effects unconsolidated sediments less than 10m which are saturated with water. Causes the foundations of building to be unsupportive so topple/sink.

Question 11

Explain a tsunami

Answer 11

When an underwater earthquake occurs the seabed can uplift a column of water as the crust is thrust upwards. The effects of tsunami depend on height of waves and distance travelled, length of event, extent to warnings given, coastal geography, land use, pop

Question 12

Explain landslides

Answer 12

Ground shaking can cause slope failure. In particularly mountainous zones, landslides can be more dangerous than earthquake. Avalanches can be triggered in colder environments.