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

L5&6 - Earthquates Flashcards

(61 cards)

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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
What are the two main ways of forecasting EQ
- Probabilistic | - Deterministic
26
How are Probabilistic EQ forecasts made?
- Using long-term stats | - Mapping 'seismic gaps'
27
What 2 main problems are there with Probabilistic EQ forecasting?
- Assumes no change in EQ distribution or return periods | - Requires long-term record
28
How are Deterministic EQ forecasts made?
Attempts to detect early seismic activity - Monitoring P-waves for 'cracks' - Measuring Radon Gas - Ground movement near faults
29
How common are Earthquakes
- 12-14,000/yr | - 35/day
30
Name 3 categories of Earthquake by depth
- Shallow (0-70km) - Intermediate (70-300km) - Deep (>300km)
31
What causes the Cascadia Earthquakes?
- Juan de Fuca plate subducting underneath NA plate - > Creates volcanoes and EQ - 13 in last 6000 yrs
32
Name 2 artificial mechanisms behind earthquakes
- Explosions | - Rock bursts due to minind releasing pressure
33
What 2 scales are used for Earthquakes
- Richter Scale | - Modified Mercalli Scale
34
What is the Richter Scale?
- Amplitude of largest waves 100km from source on seismograph - Logarithmic
35
What was the largest ever Earthquake on the Richter scale?
9.5 in S. Chile
36
Below what point on the Richter scale are EQ undetectable by humans
2.5
37
What is the Mercalli Scale?
- Describes earthquake-induced damage | - Somewhat subjective, based on observation
38
How many grades are there on the Mercalli Scale?
- 12(I-XII)
39
What are the weakest, strongest and middle categories called on the Mercalli Scale?
``` I = Instrumental VI = Strong XII = Cataclysmic ```
40
What is the primary hazard associated with EQ?
- Ground Shaking
41
List 5 Secondary hazards associated with EQ
- Tsunami - Soil Liquefaction - Landslides - Fire - Seismic Seiches
42
What were the 3 main hazards associated with the 1995 Kobe EQ?
- Building collapse - Fire - Liquefaction
43
Where do Tsunamis occur?
- Coastlines adjacent to oceanic fault lines
44
Why and where does soil liquefaction tend to occur?
- Shaking causes soil particles to move apart - Occurs in porous, water-saturated sediments - E.g. Deltas, drained lake beds
45
Describe the life-cycle of a tsunami
- 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
Where do landslides tend to occur?
- Mountainous regions | - Where soil liquefaction has stabilised slopes
47
How big was the EQ that induced the 1962 and 1970 Peruvian landslides?
- 7.7
48
What major hazard caused the majority of damage in the 1906 San Francisco EQ?
- Fire
49
Where and when were the two deadliest EQ on record?
- China, 1976 - 242,000 | - Haiti, 2010 - 222,570
50
Where and when were the two EQ that affected the most people?
- China (Sichuan), 2008 - 46,000,000 | - India, 1988 - 20,000,000
51
Where and when were the two EQ that were the most costly?
- Japan, 2011 - $210 billion | - Japan, 1995 - $100 billion
52
What are the two main ways of forecasting EQ
- Probabilistic | - Deterministic
53
How are Probabilistic EQ forecasts made?
- Using long-term stats | - Mapping 'seismic gaps'
54
What 2 main problems are there with Probabilistic EQ forecasting?
- Assumes no change in EQ distribution or return periods | - Requires long-term record
55
How are Deterministic EQ forecasts made?
Attempts to detect early seismic activity - Monitoring P-waves for 'cracks' - Measuring Radon Gas - Ground movement near faults
56
How many EQ affect the UK a year?
- 100 /yr - 20% effect people - Return period of mag. 5 every 10-20yrs
57
What were the largest EQ in the UK?
Biggest: 6.1 - Dogger Bank, 1931 | Most damaging: Colchester, 1884
58
What area in the UK is most seismically active? Why?
North Wales, due to mining
59
What causes the Cascadia Earthquakes?
- Juan de Fuca plate subducting underneath NA plate - > Creates volcanos and EQ - 13 in last 6000 yrs
60
When was the last Cascadia Megathrust EQ?
26 Jan 1700
61
What evidence is there for the Cascadia EQs?
- Sand deposition from tsunamis | - Japanese historical records

Environmental Risks and Hazards (18 decks)

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