Seismic hazards

Question 1

Earthquake

Answer 1

A sudden and violent movement or shaking within the rocks of the earths crust, causing surface vibrations which only last a few seconds

Question 2

Intraplate earthquakes

Answer 2

The small 5% of eqs which occur away from plate boundaries due to build up in crustal stresses in old fault lines overtime which eventually release without warning

Question 3

Alpine collision zone

Answer 3

23% of global eqs
shallow focus eqs
killed more than 10,000 people since 1990 (nepal 2015, turkey - syria 2023)

Question 4

Impact of turkey eqs?

Answer 4

Turkey 1999- 12mit 20,000 deaths identifying how poorly prepared country were
Turkey 2023 - 60,000 deaths tripled!#

Govt introduced disaster tax in turkey to help them prepare for next event raised 3 billion yet tripled deaths

Question 5

Spatial distribution of eqs

Answer 5

• 95% at plate margins
• Ring of fire 75%
• 23% alpine himalyan collision zone
• Some pm more seismaclly active but occur at all
• Most powerful at destructive
• Intensity and depth depends on pm
• Benioff zone = deep focus eqs at destructive and shallow focus at conservative

Question 6

Benioff zone

Answer 6

Found at destructive plate margins where subudcting oceanic plate melts into the mantle 330-700km below the surface

Question 7

Deep focus

Answer 7

Greater spatial impact

Question 8

Shallow focus

Answer 8

Less spatial impact

Question 9

EQS at constructive?

Answer 9

Shallow focus eqs, caused by tensional forces in the crust
Occur at mid-ocean ridges
Little threat to people
Low magnitude

Question 10

EQS at destructive

Answer 10

Deep focus created within the benioff zone
High magnitude and major threat to people

Question 11

EQs at Conservative E

Answer 11

Shallow focus, mid-high magnitude, caused by friction due to sliding can be disastorous e.g. san fransisco 1989

Question 12

What are eqs caused by?

Answer 12

• Stress and friction as plates subduct, diverge or slide within the lithosphere
• When rocks in crust move they fracture along faults sending out shockwaves from focus
• Last few seconds
• Produce aftershocks
• Intraplate eqs caused by human activity e.g. fracking
• eq fault lines reack 10km down cause stresses
• Eq can be caused by human acitivty such as mining, fracking or resivoir construction
  *

Question 13

Focus

Answer 13

The point of origin of the eq

Question 14

Epic centre

Answer 14

The point above the focus where most damage tends to occur

Question 15

Focal depth

Answer 15

The distance between the focus of the eq and the epic centre
The depth can disspate or amplify eq energy

Question 16

Primary pressure waves

Answer 16

• Fastet waves and reach surface first
• like soundwaves, high frequency push through the mantle, core crust
• Faster in dense rocks slower in fluids

Question 17

Secondary shear waves

Answer 17

Half as fast
reach sufrace next
high frequency but shake through crust adn mantle
affect buildings
shadow zone

Question 18

Surface love waves

Answer 18

slowest waves and cause most damage
move side-side
dont penetrate interior or surface

Question 19

Rayleigh waves

Answer 19

Radiate from epic cntre in complicated low frequency rolling motion

Question 20

Amplificattion

Answer 20

seismic waves are amplified as they pass from the focus through basin filled with sedimentary unconsolidated rock
eqs impact will be even greater on the surface

Question 21

Seismometer

Answer 21

The instrument used to detect and monitor earthquakes

Question 22

Seismograph

Answer 22

Produces the reading of the EQ

Question 23

The richter scale

Answer 23

Measures the magnitude of EQS

Question 24

The Mercalli

Answer 24

Measures the earthquakes intensity (impact/effect)

Question 25

Key facts about the RICHTER SCALE:

Answer 25

• Measures the magnitude of the EQ
• Devised in 1935
• Logarithmic scale measuring strength of the seismic waves
• Starts at 0 and each number is 10x the magnitude (slight increase is an enormous effect on the ground
• Destructive reported eqs 67
• 9.5 in chile in 1960 is the largest ever recorded

Question 27

Moment magnitude scale

Answer 27

devised in 1997 considers both magnitude and ground movement used more frequently

Question 28

The modified mercalli intensity

Answer 28

• Measures impact on people, enviroment and structures
• Based on observations of the ground of the actual impact of the EQ
• Devised in 1900
• Not logaraithmic
• A subjective measure of impact
• 12 point scale from I TO XII
• I =
• XII = Catastrophic complete destruction
• Less reliable than richter scale

Question 30

Tsunami

Answer 30

Harbour wave caused by tectonic activity and a series of larger than normal waves
Displaced huge amounts of water

Question 31

Where do tsunamis occur?

Answer 31

• Close to major fault zones
• Countries located around pacific ring of fire 90%

Question 32

What are tsunamis caused by?

Answer 32

• Ocean floor earthquakes
• Megathrust earthquakes
• Submarine volcanic eruptions
• Massive landslides into sea
• Submarine landslides
• Metor
• Asteroid strikes

Question 33

What are the features of a tsunami?

Answer 33

• Low wave height less than 1 metre - reaching shore reach over 25km high

Question 34

Wave length of tsunamis