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Earth And Space > Earthquakes > Flashcards

Earthquakes Flashcards

0
Q

Converge

A

Collide

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1
Q

What are the two types of earthquakes

A

Caused by volcanic activity

Caused by tectonic plate movement

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2
Q

Focus

A

Where the fault initially ruptures under the ground and the origin of seismic waves

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3
Q

Epicentre

A

Where the seismic waves first reach the surface

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4
Q

What are the types of faults

A

Normal fault
Reverse fault
Strike slip fault
Oblique slip fault

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5
Q

A normal fault and eg.

A

Crust is being pulled apart, the land slumps downwards and away from the block on the other side, eg. Taupo volcanic zone and bay of plenty

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6
Q

A reverse fault eg.

A

When two blocks are driven together/compressed so one side climbs up the sloping fault and overlaps the other. Eg. South Island and lower north island

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7
Q

Strike slip fault and eg.

A

Blocks move sideways past each other. Sinistral when far side moves left and dextral when far side moves right eg. many major faults in New Zealand

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8
Q

Oblique slip fault and eg.

A

Different movements are combined. Eg. Wairarapa fault caused 1855 earthquake with reverse and strike slip movement

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9
Q

Deep earthquakes

A

Only occur when a tectonic plate subducts deeply into the mantle

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10
Q

Shallow earthquakes

A

Occur along tectonic plate boundary caused by beginning of subduction of oceanic crust

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11
Q

Two main types of waves

A

Body waves and surface waves

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12
Q

Two types of body waves

A

P wave

S wave

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13
Q

Two types of surface waves

A

Love wave

Rayleigh wave

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14
Q

Primary waves

A

Travel through the earth
Fastest, arriving at seismometer first. Moves rock particles backwards and forwards in the direction the wave is travelling

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15
Q

Secondary waves

A

Move more slowly arriving second Result in a rolling motion
Travel through earth
Move rocks particles perpendicular to the path of the waves

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16
Q

Love and Rayleigh waves

A

Arrive last
Being near surface and MIRV along surface only
Destructive waves because most intense

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17
Q

The two scales for measuring earthquakes

A

Richter scale

Mercalli scale

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18
Q

Richter scale

A

Compares earthquake magnitudes or the amount of energy released of an earthquake

19
Q

Mercalli scale

A

Measures earthquake shaking by its effects on people, buildings and the environment

20
Q

Volcanic earthquakes

A

Magma and volcanic gases moving up towards the surface can break the surrounding rock, producing moderate volcanic earthquakes, tremors and ground swelling

21
Q

Why are earthquakes caused by tectonic plate movement frequent

A

Because nz straddles he AP/PP tectonic plate boundary

22
Q

How are faults formed?

A

When tectonic plates converge or move laterally past each other, the crust slowly distorts and stress builds up over many years. the stress is released by the crust cracking, forming faults and therefore causing earthquakes

23
Q

The strength of an earthquake depends on what?

A

how much of the fault has shifted
the depth of an earthquake
the amount of elastic potential energy that has built up over time

24
Q

Major historical earthquakes

A

Murchison 1929 - white creek fault
Napier 1931
Darfield 2010 -greendale fault
Wairapara 1855 which caused 3 different types of tsunamis

25
Q

What is liquefaction

A

Causes the strength and stiffness of a soil to be reduced by earthquake shaking squeezing out water. The soil flows as a liquid instead.

26
Q

Subduction earthquakes

A

Occur when one plate subducts under another, friction stops the subducting plate sliding smoothly. Pulls the overlying plate causing shallow earthquakes (accretionary wedge)

27
Q

How are earthquakes recorded

A

By a network of seismometers

28
Q

What are seismometers

A

Measure movement of the ground at that particular place

29
Q

What is amplitude

A

Measures the energy of the waves

30
Q

Major faults in nz

A

North Island fault system -cook strait to bay of plenty
Marlborough fault system - marlborough coast to alpine fault
Alpine fault - cook strait to milford sound

31
Q

north island fault system

A 
waiohau
whakatane
waimana
wairarapa
wellington
ruahine
mohaka
32
Q

Marlborough fault system

A

hope
clarence
awatere
wairau

33
Q

example of subduction earthquake

A

Fiordland earthquake 2009

34
Q

When is a fault considered active

A

if it has moved within the last 100,000 years

35
Q

What is the reoccurrence interval for earthquakes on faults

A

The average time between earthquakes on any given fault

36
Q

What is the fault called that caused the murchison earthquake

A

white creek fault

37
Q

What is the fault called that caused the darfield earthquake

A

greendale fault

38
Q

What are faults

A

cracks made in the crust due to stress being built up over time but is then released

39
Q

Example of liquefaction

A

As Christchurch is built on river and swamp sediments the particles of the sediment are often small in size with not much strength. strong shaking from an earthquake cause water pressure to increase and soil particles to move to each other. Therefore causing liquefaction. Soil can no longer support buildings, sewerage or water pipes so they become badly damaged

40
Q

how does the geosphere cause earthquakes

A

there is movement along faults that run through rock

41
Q

how does the hydrosphere cause earthquakes

A

offshore earthquakes cause tsunamis, water between layers of rock increases the chance of landslips after an earthquake. liquefaction occurs only with the right combination of water and water-laden silt

42
Q

how does the biosphere cause earthquakes

A

a hillside well covered in vegetation is les likely to slip after an earthquake thn one that has been stripped of vegetation

43
Q

accretionary wedge and eg.

A

crumpled and uplifter sediments at the subduction zone due to a subducting plate eg. napier

44
Q

how does an accretionary wedge cause an earthquake

A

the wedge contains many faults and movement of one of these with the assistance of the continental subduction pacific plate downwards causes movement along the fault therefore an earthquake

Earth And Space (4 decks)

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