Y12 MB - Earthquakes

Question 1

How do seismic hazards occur?

Answer 1

The movement of tectonic plates cause pressure to build up in the lithosphere. When the pressure is released, a series of tremors called earthquakes occur

Question 2

What percentage of earthquakes occur on plate margins?

Answer 2

90%
The rest are intraplate

Question 3

What is the focus?

Answer 3

The point in the ground at which the breaking point of the earthquake is

Question 4

What is the epicentre?

Answer 4

The point on the ground surface directly above the focus
Here, the most intense ground shaking is experienced and it dissipates the further away from the epicentre you go

Question 5

What are faults?

Answer 5

Fractures in the rock when the pressure that builds up in the lithosphere is suddenly released

Question 6

What focus depth of earthquakes causes the most damage? (Shallow, intermediate, deep)

Answer 6

Shallow faults (0-70km deep) account for 75% of all earthquake energy released

Question 7

Give the common focus depth of earthquakes at each of the plate boundaries

Answer 7

Constructive - shallow
Conservative - shallow
Collision - shallow / intermediate
Destructive subduction - shallow / intermediate / deep

Question 8

What are the different types of shock (seismic) waves?

Answer 8

Body waves (primary and secondary)
Surface waves (love and Rayleigh)

Question 9

What are primary waves?

Answer 9

The fastest waves, reaching the surface first
They travel through both liquids and solids so can travel through both the crust, mantel and core to the opposite side of the earth
Compressional waves (cause expansions and compressions of the ground)

Question 10

What are secondary waves?

Answer 10

Half as fast as primary waves
Cannot travel through liquids such as the outer core
Transverse waves (they shake the ground up and down)

Question 11

Why are surface waves slower than body waves?

Answer 11

They cannot travel through the mantel and the core

Question 12

What are love waves?

Answer 12

The slowest waves but the most destructive
Shake the ground from side to side (causing damage to infrastructure and buildings)

Question 13

What are rayleigh waves?

Answer 13

Travel out from the epicentre near the surface
Move in a rolling motion so can break up the ground surface

Question 14

Are seismic shock a waves primary or secondary hazard of an earthquake?

Answer 14

Primary

Question 15

What are potential secondary hazards of an earthquake?

Answer 15

Tsunamis
Landslides
Liquefaction

Question 16

What is a tsunami?

Answer 16

Giant sea waves generated by shallow focus underwater earthquakes which cause the movement of the seabed

Question 17

What are the features of a tsunami?

Answer 17

Have along wavelength and low wave height in the open ocean
Series of waves that travel extremely quickly
On approaching the cost they slow down and pile up as a massive wall of water before breaking (around 30m high)
Results in a dramatic reduction in sea level (known as a drawdown) when the sea appears to drain away

Question 18

What percentage of tsunamis are associated with the ‘Pacific Ring of Fire’?

Answer 18

Up to 90%

Question 19

Give an example of a recent destructive tsunami

Answer 19

December 2004 ‘Boxing Day’ tsunami

Question 20

What is liquefaction?

Answer 20

Occurs in unconsolidated sediments that are saturated with water. The sediments are made of loosely arranged particles so when shaken by seismic waves, act like a liquid (buildings can sink into the sediments)

Question 21

How can the impacts of liquefaction be reduced?

Answer 21

Using vibrating rods to shake the soils beforehand

Question 22

What is a landslide?

Answer 22

A rapid movement of earth materials down a slope (in this case as a result of ground shaking)

Question 23

Why may intraplate earthquake occur?

Answer 23

Reactivation of an old fault line
Mining
Fracking
Building large reservoirs

Question 24

What are the ways in which the magnitude of an earthquake can be measured?

Answer 24

The Richter Scale (logarithmic - starts at 0 and each interval is 10x the magnitude of the one before it)
The Moment Magnitude Scale (adaptation of the Richter Scale which looks at the total energy released by the earthquake)
Metcalli scale (12 point scale that measures the intensity of the event and its impact instead of the magnitude)

Question 25

How can earthquakes be predicted?

Answer 25

Impossible to predict when or where

Question 26

What is ground rupture?

Answer 26

Primary impact of earthquakes, where there is visible breaking and displacement of the Earth’s surface
Has the potential to damage large buildings and infrastructure such as dams, bridges and power stations

Question 27

What percentage of deaths during an earthquake are caused by collapsing buildings?

Answer 27

75%

Question 28

What are life-safe buildings?

Answer 28

Sophisticated engineered buildings which have features such as cross-bracing and springs which act as shock absorbers to strengthen them so they are less likely to collapse during an earthquake