Earthquakes

Question 1

What is an Earthquake?

Answer 1

The sudden release of stored energy due to slippage along a fault in Earth’s crust
- energy is released as heat + seismic waves

Question 2

Where and how does seismic waves radiate from?

Answer 2

Radiate outwards from source, the focus

Question 3

What is the epicentre?

Answer 3

the point on Earth’s surface directly above the focus

Question 4

What is the Elastic Rebound Theory?

Answer 4

• rocks on both sides of existing fault is deformed by tectonic forces
• rocks bend + store elastic energy
• once frictional forces along fault are overcome, slip occurs at weakest point (the focus)
• earthquake occurs when deformed rock “springs back” to its original shape (elastic rebound)

Question 5

What are the types of seismic body waves?

Answer 5

• Primary (P) waves
• Secondary (S) waves

Question 6

where do body waves travel through?

Answer 6

Through Earth’s Interior

Question 7

What are primary waves?

Answer 7

• body wave
• compressional
• push-pull (compress + expand) motion, changing volume of intervening material
• travel through solids, liquids, + gases
  (faster in solids than liquids)

Question 8

What are secondary (S) waves?

Answer 8

• body wave
• shear motion at right angles to their direction of travel
• take longer than P waves
• travel only through solids

Question 9

What are the types of seismic surface waves?

Answer 9

• Reyleigh (LR) waves: ground roll (up + down mvmt)
• Love (LQ) waves (side-to-side shaking)

Question 10

Where do surface waves travel?

Answer 10

surface waves travel at Earth’s surface

Question 11

In order, what waves are faster to slow?

Answer 11

body waves (faster) -> surface waves(slower)
P waves , S waves, surface waves

Question 12

how does the difference btwn the arrival times of waves hold importance?

Answer 12

diff of arrival times of waves at diff recording stations helps one determine dist btwn recording station + earthquakes epicentre

Question 13

____ the time difference between arrival of first P waves + arrival of S waves, the _____ the dist btwn the recording station + the earthquake epicentre

Answer 13

Longer, greater

Question 14

What is Magnitude

Answer 14

quantitative measure of amt of energy released during an earthquake (based on characteristics of seismic waves)

Question 15

what is intensity

Answer 15

semi-quantitative measure of observed effects of an earthquake on the natural + human - built environment (based on human eyewitness accounts)

Question 16

What is the Richter Magnitude?

Answer 16

a concept introduced by Charles Richter
- “Ritcher Scale” (aka Local Magnitude Scale)
-based on amplitude (wave height) of largest seismic waves recorded
- accounts for decrease in wave amplitude w/ increase distance
- Ritcher scale is logarithmic

Question 17

What is the Modified Mercalli Index?

Answer 17

MMI scale is used to describe earthquake intensity
- ranked I-XII (in roman numerals)
- lower intensity: felt observations
- higher intensities: damage observation

Question 18

What is the relationship of the magnitude of earthquake to epicentre?

Answer 18

Magnitude of earthquake is constant, the intensity decreases w/ increasing distance from epicentre

Question 19

Can intensity vary?

Answer 19

intensity varies from place to place according to local characteristics of geologic materials
- particles in unlithified (loose) sediment move during shaking

Question 20

Why is the level of destruction from earthquakes high in urban areas?

Answer 20

-poor integrity of human-built structures (buildings, bridges, roads, etc.)
- esp in developing countries where earthquake-proof building design is not high priority in city planning

Question 21

What are tsunamis?

Answer 21

-destructive waves that are often inappropriately called ‘tidal waves’

Question 22

how do tsunami occur

Answer 22

result from vertical displacement along a fault located on ocean floor, a large undersea landslide triggered by an earthquake, or other disturbances

Question 23

How high are tsunamis

Answer 23

-in open ocean, tsunami wave height is less than 1m
- in shallower coastal waters, water piles up to over 30m (due to friction generated on seafloor)
- wave breaks when it can no longer support itself
- can be very destructive

Question 24

When body waves encounter a boundary (change in density), what does the wave energy do?

Answer 24

wave energy is reflected (bounce off) and some is refracted (bends as it transmits through)

Question 25

In solids, the ____ the material, the ____ the wave travels through it

Answer 25

Denser
faster

Question 26

What is the crust-mantle boundary?

Answer 26

• studies of P-waves indicated outer rocky part of Earth (lithosphere) were not uniform
• observations of seismic recording stations, P waves arrived sooner than expected
• led to realization that the crust was underlain by denser material (ultramafic mantle rock (peridotite))

Question 27

What is the Core-Mantle Boundary

Answer 27

-Determined a (slower) outer core based on its P-wave shadow zone
-found that S waves do not pass through outer core (therefore must be liquid)

Question 28

How was the solid inner core discovered

Answer 28

discovered using faint observations of P-waves that bounced off of , or were sped up by, solid inner core + emerged in unexpected locations