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Environmental Risks and Hazards > L5&6 - Earthquates > Flashcards

L5&6 - Earthquates Flashcards

1
Q

Define an Earthquake

A

Vibration in the Earth produced by rapid release of energy

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2
Q

How common are Earthquakes

A
  • 12-14,000/yr

- 35/day

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3
Q

Name 3 categories of Earthquake by depth

A
  • Shallow (0-70km)
  • Intermediate (70-300km)
  • Deep (>300km)
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4
Q

Name 4 natural mechanisms behind earthquakes

A
  • Tectonic Plate Movements
  • Volcanic eruptions
  • Rockfalls and slides
  • Spontaneous rock bursts
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5
Q

Name 2 artificial mechanisms behind earthquakes

A
  • Explosions

- Rock bursts due to minind releasing pressure

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6
Q

What 2 scales are used for Earthquakes

A
  • Richter Scale

- Modified Mercalli Scale

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7
Q

What is the Richter Scale?

A
  • Amplitude of largest waves 100km from source on seismograph
  • Logarithmic
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8
Q

What was the largest ever Earthquake on the Richter scale?

A

9.5 in S. Chile

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9
Q

Below what point on the Richter scale are EQ undetectable by humans

A

> 2,5

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10
Q

What is the Mercalli Scale?

A
  • Describes earthquake-induced damage

- Somewhat subjective, based on observation

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11
Q

How many grades are there on the Mercalli Scale?

A
  • 12(I-XII)
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12
Q

What are the weakest, strongest and middle categories called on the Mercalli Scale?

A 
I = Instrumental
VI = Strong
XII = Cataclysmic
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13
Q

What is the primary hazard associated with EQ?

A
  • Ground Shaking
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14
Q

List 5 Secondary hazards associated with EQ

A
  • Tsunami
  • Soil Liquefaction
  • Landslides
  • Fire
  • Seismic Seiches
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15
Q

What were the 3 main hazards associated with the 1995 Kobe EQ?

A
  • Building collapse
  • Fire
  • Liquefaction
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16
Q

Where do Tsunamis occur?

A
  • Coastlines adjacent to oceanic fault lines
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17
Q

Why and where does soil liquefaction tend to occur?

A
  • Shaking causes soil particles to move apart
  • Occurs in porous, water-saturated sediments
    • E.g. Deltas, drained lake beds
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18
Q

Describe the life-cycle of a tsunami

A
  • EQ with epicentre in Abyssal Plain
  • Very fast in deep ocean 800-900 /hour
  • Slower as they approach shallow water due to friction
    • > Causes water to pile up
  • ‘Draw back’ before tsunami hits land
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19
Q

Where do landslides tend to occur?

A
  • Mountainous regions

- Where soil liquefaction has stabilised slopes

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20
Q

How big was the EQ that induced the 1962 and 1970 Peruvian landslides?

A
  • 7.7
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21
Q

What major hazard caused the majority of damage in the 1906 San Francisco EQ?

A
  • Fire
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22
Q

Where and when were the two deadliest EQ on record?

A
  • China, 1976 - 242,000

- Haiti, 2010 - 222,570

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23
Q

Where and when were the two EQ that affected the most people?

A
  • China (Sichuan), 2008 - 46,000,000

- India, 1988 - 20,000,000

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24
Q

Where and when were the two EQ that were the most costly?

A
  • Japan, 2011 - $210 billion

- Japan, 1995 - $100 billion

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25
Q

What are the two main ways of forecasting EQ

A
  • Probabilistic

- Deterministic

26
Q

How are Probabilistic EQ forecasts made?

A
  • Using long-term stats

- Mapping ‘seismic gaps’

27
Q

What 2 main problems are there with Probabilistic EQ forecasting?

A
  • Assumes no change in EQ distribution or return periods

- Requires long-term record

28
Q

How are Deterministic EQ forecasts made?

A

Attempts to detect early seismic activity

  • Monitoring P-waves for ‘cracks’
  • Measuring Radon Gas
  • Ground movement near faults
29
Q

How common are Earthquakes

A
  • 12-14,000/yr

- 35/day

30
Q

Name 3 categories of Earthquake by depth

A
  • Shallow (0-70km)
  • Intermediate (70-300km)
  • Deep (>300km)
31
Q

What causes the Cascadia Earthquakes?

A
  • Juan de Fuca plate subducting underneath NA plate
    • > Creates volcanoes and EQ
  • 13 in last 6000 yrs
32
Q

Name 2 artificial mechanisms behind earthquakes

A
  • Explosions

- Rock bursts due to minind releasing pressure

33
Q

What 2 scales are used for Earthquakes

A
  • Richter Scale

- Modified Mercalli Scale

34
Q

What is the Richter Scale?

A
  • Amplitude of largest waves 100km from source on seismograph
  • Logarithmic
35
Q

What was the largest ever Earthquake on the Richter scale?

A

9.5 in S. Chile

36
Q

Below what point on the Richter scale are EQ undetectable by humans

37
Q

What is the Mercalli Scale?

A
  • Describes earthquake-induced damage

- Somewhat subjective, based on observation

38
Q

How many grades are there on the Mercalli Scale?

39
Q

What are the weakest, strongest and middle categories called on the Mercalli Scale?

A 
I = Instrumental
VI = Strong
XII = Cataclysmic
40
Q

What is the primary hazard associated with EQ?

A
  • Ground Shaking
41
Q

List 5 Secondary hazards associated with EQ

A
  • Tsunami
  • Soil Liquefaction
  • Landslides
  • Fire
  • Seismic Seiches
42
Q

What were the 3 main hazards associated with the 1995 Kobe EQ?

A
  • Building collapse
  • Fire
  • Liquefaction
43
Q

Where do Tsunamis occur?

A
  • Coastlines adjacent to oceanic fault lines
44
Q

Why and where does soil liquefaction tend to occur?

A
  • Shaking causes soil particles to move apart
  • Occurs in porous, water-saturated sediments
    • E.g. Deltas, drained lake beds
45
Q

Describe the life-cycle of a tsunami

A
  • EQ with epicentre in Abyssal Plain
  • Very fast in deep ocean 800-900 /hour
  • Slower as they approach shallow water due to friction
    • > Causes water to pile up
  • ‘Draw back’ before tsunami hits land
46
Q

Where do landslides tend to occur?

A
  • Mountainous regions

- Where soil liquefaction has stabilised slopes

47
Q

How big was the EQ that induced the 1962 and 1970 Peruvian landslides?

48
Q

What major hazard caused the majority of damage in the 1906 San Francisco EQ?

49
Q

Where and when were the two deadliest EQ on record?

A
  • China, 1976 - 242,000

- Haiti, 2010 - 222,570

50
Q

Where and when were the two EQ that affected the most people?

A
  • China (Sichuan), 2008 - 46,000,000

- India, 1988 - 20,000,000

51
Q

Where and when were the two EQ that were the most costly?

A
  • Japan, 2011 - $210 billion

- Japan, 1995 - $100 billion

52
Q

What are the two main ways of forecasting EQ

A
  • Probabilistic

- Deterministic

53
Q

How are Probabilistic EQ forecasts made?

A
  • Using long-term stats

- Mapping ‘seismic gaps’

54
Q

What 2 main problems are there with Probabilistic EQ forecasting?

A
  • Assumes no change in EQ distribution or return periods

- Requires long-term record

55
Q

How are Deterministic EQ forecasts made?

A

Attempts to detect early seismic activity

  • Monitoring P-waves for ‘cracks’
  • Measuring Radon Gas
  • Ground movement near faults
56
Q

How many EQ affect the UK a year?

A
  • 100 /yr
  • 20% effect people
  • Return period of mag. 5 every 10-20yrs
57
Q

What were the largest EQ in the UK?

A

Biggest: 6.1 - Dogger Bank, 1931

Most damaging: Colchester, 1884

58
Q

What area in the UK is most seismically active? Why?

A

North Wales, due to mining

59
Q

What causes the Cascadia Earthquakes?

A
  • Juan de Fuca plate subducting underneath NA plate
    • > Creates volcanos and EQ
  • 13 in last 6000 yrs
60
Q

When was the last Cascadia Megathrust EQ?

A

26 Jan 1700

61
Q

What evidence is there for the Cascadia EQs?

A
  • Sand deposition from tsunamis

- Japanese historical records

Environmental Risks and Hazards (18 decks)

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