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Leaving Cert Geography - > Earthquakes > Flashcards

Earthquakes Flashcards

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1
Q

What is an earthquake

A

Vibrations or shaking in the earths crust caused by movements at plate boundaries or at fault lines (cracks in the earths surface)

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2
Q

Most common boundaries earthquakes occur

A

Transform

Convergent

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3
Q

What is energy released by an earthquake in the form of

A

Seismic waves that give a series of shocks called tremors

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4
Q

Small earthquakes before big earthquake

A

Foreshock

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5
Q

Small earthquakes after big earthquake

A

After shocks

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6
Q

Define focus/ hypocentre

A

Origin of the earthquake deep within the crust, point where seismic waves radiate outwards from

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7
Q

Define epicentre

A

Point on the earths surface directly above the focus where the most damage occurs

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8
Q

Define fault

A

A break in the rocks that make the earths crust along which rocks on either side move

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9
Q

Define Fault scarp

A

A feature on the surface of the earths that looks like a step caused by a slip in the fault

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10
Q

Causes of earthquakes

A

Slipping plates
Sinking plates
Ice age
Ancient faults

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11
Q

Types of earthquakes

A

Shallow focus
Intermediate focus
Deep focus

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12
Q

Where do shallow focus earthquakes occur

A

All types of plate boundaries
Less than 80km below the surface
Most destructive as closer to surface

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13
Q

Where do intermediate focus earthquakes occur?

A

At oceanic and continental subduction zones

Up to 300km below surface

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14
Q

Where do deep focus earthquakes occur

A

At oceanic and oceanic subduction zones
More than 300km below the surface
Don’t do too much damage to surface as they occur so deep

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15
Q

What’s a Wadati-Benioff zone?

A

Dipping, roughly flat zones of increased earthquake activity as an oceanic plate sinks beneath another plate. (Subduction zones)

Deep focus earthquakes occur here

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16
Q

Way of predicting earthquakes

A 
Measuring rock stress
Measuring randon gas emissions 
Observing unusual animal behaviour
Identifying seismic gaps
Early warning systems
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17
Q

How can rock stress be measured

A

Strainmeters (measure build up of stress along fault lines)
Tiltmeters (changes in slope and bulging)
Seismographs (minor movements in earths crust (foreshocks and aftershocks)

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18
Q

Examples of unusual animal behaviour before earthquakes

A

Snakes come out of hibernation
Animals refuse to enter buildings
Restless pets

19
Q

What are seismic gaps

A

An area on a fault where little to no seismic activity has occurred for a long period eg Guerro Gap Mexico

20
Q

% of earthquakes at Pacific ring of fire

A

80%

21
Q

Speak about Earthquakes at convergent plate boundaries

A

Most common
Most intense
Japan 2011- tsunami under ocean (where Pacific and Eurasian collide)
China and India (indo Australian and Eurasian plate collide) recieve Kanu earthquakes

22
Q

Discuss earthquakes at transform plate boundaries

A

SAN Andreas fault 1300km long
Pacific and North American plate
1906 8.3 earthquake san franc

23
Q

Two scales used to measure earthquakes

A

Mercalli scale

Richter scale

24
Q

What does the Richter scale measure

A

Intensity of an earthquake by energy released from the earthquake

25
Q

How is the Richter scale measurements taken

A

Seismometers

One to record primary waves (horizontal shaking)
Another to record secondary waves (vertical shaking)

26
Q

How can the epicentre of an earthquake be found by a seismologist

A

At least three readings are needed from different seismic locations
By measuring the time between each recording at the seismic station, seismologists can estimate how far the waves have travelled.
They then draw circles representing distance from the station the wave travelled and where their circles intersect is the epicentre

27
Q

Explain the increasing measurements on the Richter scale

A

Each unit is 10 times more energy than the previous

28
Q

What is the mercalli scale measured with

A

No instruments

Based on human observation and experience of the effects to people, the natural world and man made structures

29
Q

Measurements on the mercalli scale

A

Ranges from 1-12

1 being a weak earthquake not felt by humans
5 being a moderate earthquake, a noticeable shake in the ground and
12 being almost complete destruction

30
Q

Factors effecting earthquake damage

A

Economic development of country - less developed have poor buildings and infrastructure more likely to collapse

Population density - urban v rural

Time of day - people aren’t on roads at night

Rock type - igneous withstand tremors better than sedimentary

Depth of focus - shallow v deep focus

Energy and duration

31
Q

Ways of reducing the effects of earthquakes

A

Earthquake drills
Efficient urban planning
Early warning system
Earthquake proof infrastructure

32
Q

What is cross bracing

A

When frames of buildings are reinforced with steel which joins the building together allowing it to moves as a single unit and not splitting apart

33
Q

Ways of earthquake proofing infrastructure

A

Cross bracing
Deep foundations into solid rock
Weights on roof counterbalance shakings
Several emergency staircases and exits
Shock absorbers in foundations
Roof covering area immediately outside building to prevent pedestrian being showered with broken glass
Base isolation - bottom section absorbs seismic waves
Foundations with flexible springs as shock absorber

34
Q

When was observing animal behaviour used for earthquake prediction

A

Tianj, China

35
Q

When was japan earthquake/tsunami we study
Richter scale
How many dead
Mention an effect

A

2011
9
25,000
Fukushima power plant, loss of jobs and slowdown in production , towns shifted

36
Q

When was Nepal earthquake we study
Richter scale (magnitude)
How many made homeless
Mention an effect

A 
2015
7.8
3 million homeless 
Avalanche - transport systems damaged (providing aid was therefore difficult)
Disease in camps
37
Q

When was Haiti earthquake we study
Richter scale
How many dead
Mention an effect

A

2010
7
300,000 dead under rubble
€6 billion in aid

38
Q

Japan disaster prevention day

A

Sept 1

39
Q

Earthquake at transform plate example

A

1906

SAN Francisco

40
Q

Big earthquake for San Andreas fault predicted when

A

2032

41
Q

Example of an earthquake at divergent

A

Mozambique 2006

42
Q

Example of poor urban planning

A

2008
Sichuan, China
9000 schoolchildren died whilst buildings around remained intact

43
Q

Example of a building which is earthquake proof

A

Burj khalifa (worlds tallest building)

44
Q

Example of economic slowdown post earthquake

A

2004
Christmas tsunami Thailand
Fear to travel

Leaving Cert Geography - (23 decks)

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