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Geography- Hazards > Earthquakes > Flashcards

Earthquakes Flashcards

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1
Q

Give a description of earthquakes

A

Earthquakes have a spatial distribution in linear belts/clusters. They occur anywhere along plate boundaries and dd boundaries, 90% occur along plate boundaries

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2
Q

What are earthquakes?

A

A sudden movement of the earths crust

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3
Q

What is the depth of shallow, intermediate earthquakes and deep earthquakes?

A

Shallow (<70km depth)

Intermediate (70-300km)

Deep (>300)

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4
Q

Why do some earthquakes occur away from boundaries?

A

Reactivation of old fault lines

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5
Q

Longer pressure builds up…

A

…stronger the earthquake

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6
Q

Where do rocks obtain the strength?

A

Interlocking and cementation of grains or crystals of which they are built

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7
Q

What are earthquakes meander using?

A

A seismograph

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8
Q

What do high peaks and troughs show on a seismograph?

A

Worse or more violent earthquake

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9
Q

How many violent earthquakes does the world experience on average each year?

A

20-50

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10
Q

What is the magnitude of a earthquake measured on?

A

A Richter scale

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11
Q

What is the scale of the Richter scale?

A

0-9

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12
Q

On a Richter scale, and earthquake measured at 6 is how many times greater than a quake measured at 5?

A

Ten times more powerful

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13
Q

What instrument is used to measure the effects of the quake on people?

A

A Mercalli scale

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14
Q

How many degrees of severity are present on a Mercalli scale?

A

12 degrees of severity

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15
Q

What scale, abbreviated as Mw, is preferred for measuring earthquakes?

A

The moment magnitude scale

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16
Q

What does the Mw use to base the severity of the earthquake?

A

Total moment release of the earthquake

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17
Q

What is moment?

A

Moment is the product of the distance a fault moved and the force required to move it

18
Q

What is a logarithmic scale?

A

It means for every whole number you go up on the magnitude scale, the amplitude of the ground motion recorded by the seismograph goes up in tens

19
Q

What are the magnitudes 1 and 8 power equivalent to?

A

1- 6 ounces of TNT exploding

8- 6 million tonnes of TNT exploding

20
Q

What are shock waves?

A

Energy released by and earthquake

21
Q

What is the focus?

A

Where shockwaves are released from

22
Q

What is the epicentre?

A

The point on the surface directly above the focus where the waves are felt the strongest

23
Q

What are P waves?

A

P waves or primary waves are compression waves
They move the fastest
Compress the rock in front of them and elongate behind it (to and fro)
That can move through solids liquids and gas

24
Q

What are S waves?

A

Secondary S waves or shear waves, undulate causing an up and down and side to side motion as they roll through the earth
They can only move through a solid
Do more damage than P waves

25
Q

P and S waves travel through the interior of the earth so therefore they are…

A

Body waves

26
Q

What are L waves?

A

The surface L waves are the surface waves whose motion is restricted to near ground surface
Travel more slowly than S waves

27
Q

There are two types of L waves, what are they called and there properties?

A

Love waves- vibrate at Rift angles to the direction of transmission but have no vertical displacement

Rayleigh waves- have both vertical and horizontal movement in a vertical plane pointing in the direction of the transmitted wave

28
Q

Where is the point of maximum displacement of shock waves?

A

The focus

29
Q

In what year were 4 kinds of seismic waves detected?

A

1909

30
Q

Seismographs close to the epicentre picked up waves doing what?

A

P and S waves close to the epicentre moving slowly and further away P waves and S waves were moving faster

31
Q

When these shock waves meet different rock densities, what happens to the waves?

A

They are reflected and refracted

32
Q

If shock waves pass through denser rocks they?

A

Speed up

33
Q

When shock waves pass through less dense rocks they?

A

Slow down

34
Q

From the MOHO, was was detected?

A

Slower waves had travelled from the focus of the earthquake through the upper layer of the crust but, by contrast foster waves have passed through denser material in the earths core, this denser material speeded up the waves and deflected them

35
Q

So what was suggested about the earths crust due to the MOHO?

A

The change in density from 2.9g/cm3 to 3.3g/cm3 marked the boundary between the earths crust and the mantle below

36
Q

What does MOHO stand for?

A

The Mohorovicic discontinuity

37
Q

Later a shadow was found in a area between 105o and 142o, why could they not detect shock waves from within?

A

Shock waves had passed from a liquid to a solid, this S waves would stop and P waves would be refracted, this was effectively the boundary between the mantle and the core

38
Q

What are the primary earthquake effects?

A
  • collapsing buildings
  • falling debris
  • roads, bridges collapsing
  • shock and panic
  • broken gas pipes
  • loss of water supply
  • loss of medical supplies
  • damaged communications
  • Broken water mains
  • power lines destroyed
  • ports destroyed
  • poor quality housing flattered
  • shock waves and ground shaking
39
Q

What are the secondary effects of a earthquake?

A
  • fires
  • landslides and avalanches
  • tsunamis
  • diseases
  • economic losses
  • soil liquefaction
  • fear of future tectonic events
  • homelessness
40
Q

The scale of a earthquake disaster depends on…

A
  • strength of the earthquake
  • depth of focus
  • nature of bedrock
  • building design
  • population distribution
  • wealth of country
41
Q

How do humans cause earthquakes?

A
  • Rocky Mountain in Denver Colorado, injected into underlying rocks during 60’s. Minor earthquakes occurred in a previously earthquake free zone, 1962-1965 700 minor quakes
  • underground nuclear testing, 1968, 120,000 tone bombs in Nevada triggered 30 minor earthquakes
  • Hoover dam, as lake filled underlying rocks were adjusted and increased over 40 km3 of water and 6000 minor earthquakes in 10 years

Geography- Hazards (7 decks)

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