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Question 1

What’s an earthquake?

Answer 1

95% of earthquakes occur along plate boundaries.
* When the plates move against each other they sometimes stick – causing huge amounts of pressure to build up.
* When the pressure becomes too much, the rock fractures along cracks called faults.
* Energy is released as seismic waves, which cause the ground to shake.
Seismic waves are released from inside of the Earth’s crust, along the fault.

Question 2

focus or hypocentre.

Answer 2

The point inside the crust from which the pressure is released

Question 3

epicentre.

Answer 3

The point on the surface directly above that

Question 4

Seismic waves radiate out from the focus. There are three main types:

Answer 4

• Primary ‘P’ waves
• Secondary ‘S’ waves
• Love ‘L’ waves

Question 5

Primary ‘P’ Waves

Answer 5

P waves are body waves – they travel through the Earth’s body.
They are the fastest and the first to reach the surface (8km/sec). They travel through both solids and liquids.
They move in a backwards and forwards motion.
They are only damaging in the most powerful earthquakes.

Question 6

Secondary ‘S’ Waves

Answer 6

S waves are also body waves – they travel through the Earth’s body.
They are slower than P waves (4km/sec). They travel through solids only.
They move in an up and down motion, perpendicular to the direction of travel.
They do more damage than P waves.

Question 7

Love ‘L’ Waves

Answer 7

L waves are surface waves – they travel only on the Earth’s surface.
They are the slowest of the three waves (last to arrive).
They move in a side to side motion, perpendicular to the direction of travel.
They are larger and cause the most damage.

Question 8

Seismic Waves

Answer 8

The overall severity of an earthquake is linked to the amplitude and frequency of these wave types.
The ground surface may be displaced horizontally, vertically or obliquely (slanted) during an earthquake depending on the strength of individual waves.

Question 9

Predicting Earthquakes

Answer 9

Currently there is no method at accurately predicting when or where an earthquake will strike.
* However we can use our knowledge of plate boundaries to forecast where an earthquake is likely to happen. E.g. areas that have had one big earthquake are likely to have another.
* Today, research focuses on precursors, which may suggest a major earthquake is likely to happen:
* E.g. Foreshocks (small earthquake that happen before a larger one)

Question 10

Effects of Earthquakes
The are a number of factors which determine an earthquakes impact:
Physical

Answer 10

Magnitude (the size of the seismic waves)

Depth (the deeper the hypocentre, the more energy the waves lose along the way)

Distance from the epicentre (the closer you are the stronger it is)

Geology – soft rocks can amplify shaking

Question 11

Effects of Earthquakes
The are a number of factors which determine an earthquakes impact:Human

Answer 11

Level of development

Population

Level of preparation

The effectiveness of the emergency response

The impact of secondary hazards

Question 12

Effects of Earthquakes

Answer 12

Primary effects: Those that happen as a direct result of the earthquake

Secondary effects: Side effects of an earthquake (happen as a result of the primary effects) often causing much more
damage.

Question 13

Secondary Effects of earthquakes

Answer 13

Landslides or avalanches

Tsunami

Liquefaction

Question 14

Landslides or avalanches

Answer 14

– Slopes fail as the shaking places stress on them resulting in landslides, rock slides, mudslides and avalanches.

Question 15

Tsunami

Answer 15

Underwater earthquakes generate a series of big waves.

Question 16

Liquefaction

Answer 16

When surface rock lose strength and become more liquid than solid. The subsoil loses its ability to support building/infrastructure foundations, so they sink or tilt.

Question 17

Primary Effects

Answer 17

Ground shaking

Crustal fracturing

Question 18

Ground shaking

Answer 18

causes buildings, bridges, roads and infrastructure to collapse

Question 19

Crustal fracturing

Answer 19

when Earth’s crust cracks due to the energy that is released.

Question 20

Aftershocks

Answer 20

• Aftershocks occur in the general area of the original earthquake, and are a result of the Earth ‘settling down’ or readjusting along the part of the fault that slipped originally.
• They can occur weeks, months or even years after an earthquake and in general the larger the earthquake, the larger and more numerous the aftershocks.
• They are capable of causing additional damage as well as hampering recovery efforts.

Question 21

Aftershocks example

Answer 21

E.g In 2011 a 6.3 magnitude aftershock struck Christchurch in 2010, which caused more damage and loss of life than the original.

Question 22

The 1989 Loma Prieta earthquake

Answer 22

• The geology of an area can have an enormous impact on the effect of an earthquake.
• At 5:04 on 17 October 1989, a magnitude 6.9 earthquake struck near San Francisco.
• The city’s Marina District suffered some of the worst of the damage.
• Built on man-made landfill, the area’s soft, sandy soil amplified the ground shaking, which increased the damage experienced by buildings and other structures.
• The sandy soil also liquefied, which caused buildings to collapse.
• A few miles away, part of the two- level Cyprus freeway also collapsed- causing 42 of the 67 earthquake-related deaths (many drivers on the lower level were crushed by the collapsing upper level)
• As the map and seismogram in Figure 9 show, the part of the freeway that collapsed was built on soft mud; whereas adjoining parts of the freeway, built on firmer ground, remained standing.