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EOSC 114 > Earthquakes 3 > Flashcards

Earthquakes 3 Flashcards

1
Q

Elastic Rebound Theory

A

&laquo_space;refer to slides for diagram&raquo_space;

  1. pate tectonic forces stress rocks -> deform
  2. Elastic deformation of lithosphere
  3. Brittle failure / deformation so litho eventually breaks
  4. stored elastic energy is released and deformed rocks go back to original state

(energy stored on either side of failure)

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2
Q

What theory describes how earthquakes occur?

A

elastic rebound theory

-> we feel the waves/vibration produced by elastic rebound

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3
Q

Describe the processes of plates at the boundary

A
  1. Plates lock = stress & deformation
  2. Plates release = earthquake & tsunami
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4
Q

does a rupture propagate far?

A

only along a portion of the fault
-> some areas are still locked

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5
Q

Describe how earthquakes occur in terms of the brittle and elastically deformed crust

A
  • brittle crust ruptures at hypocentre
  • elastically deformed crust rebounds and vibrates
  • waves + energy propagate away in all directions
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6
Q

where is the epicentre in relation to the hypocentre?

A

directly above it

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7
Q

Which type of seismic wave hurt us?

A

surface waves

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8
Q

what are the two types of body waves?

A
  1. Pressure or primary
  2. Shear or secondary
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9
Q

P - waves

A
  • fastest
  • particle motion parallel to propagation (like slingy)
  • can move through solids or fluids
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10
Q

S - waves

A
  • slower than p waves
  • particle motion is perpendicular to propagation (like waves)
  • can ONLY move through solids
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11
Q

Can S waves move through fluids?

A

no

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12
Q

Can P waves move through fluids?

A

yes

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13
Q

Surface waves

A
  • the damaging waves
  • require a surface, cannot travel thru water (?)
  • slower than body waves
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14
Q

What are the types of surface waves?

A
  1. Rayleigh wave
  2. Love wave
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15
Q

Rayleigh wave

A
  • vertical and horizontal motion parallel to wave direction
  • like an ocean wave
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16
Q

Love wave

A
  • horizontal movement perpendicular to wave travel direction and parallel to ground surface
  • like when u wave a rope on the ground
17
Q

rank the seismic waves based on speed

A
  1. P (6 km/s)
  2. S (3.5 km/s)
  3. Surface (2-3 km/s)
18
Q

From a seismograph, how can we tell if we are far or close to the epicentre?

A

far: bigger gap between the P, S, and Surface waves

close: smaller gap ^^

19
Q

On a seismograph, which type of wave appears the largest + longest

A

surface

20
Q

How do we determine where the hypocentre is?

A

We use time delay between the P and S wave arrivals

-> need at least 3 seismometers

21
Q

How many seismometers do we need to pinpoint the hypocenter?

A

at least 3

1 = know how far
2 = gives two points
3 = tada! TRIANGULATION

22
Q

we use scales that measure earthquakes based on _____ & _____

A

Magnitude and Intensity

23
Q

What scale do we use to calculate earthquake magnitude?

A

Moment Magnitude (M_w)
- logarithmic
- quantitative measure of size
- proportional to energy release

24
Q

EQ Magnitude: earthquake hazard is proportional to

A

energy release

25
Q

As EQ Magnitude increases, what grows?

A

both rupture area and duration of shaking grow

-> and risk!

26
Q

EQ Magnitude is based on what wave property?

A

wave amplitudes recorded by seismometer (slip area)

27
Q

For each increase on the Magnitude scale, what factor do ground motion and energy released increase by?

A

ground motion: by a factor of 10
energy released: by a factor of 32!

28
Q

How much bigger is the energy released in a M8 EQ compared to M6?

A

32 x 32
~ 1000

29
Q

What is the ground motion difference between a M6 and M8 EQ?

A

10 x 10
~ 100

30
Q

What is the Moment Magnitude (M_w) based on?

A
  • based on the area of rupture and slip on fault
31
Q

What scale do we use to calculate EQ intensity?

A

Modified Mercali Scale
- ranges from 1 to 12

32
Q

What does the Modified Mercali Scale measure?

A

Qualitative estimate of how ground motion affects population and structures

  • perception of ground shaking intensity
  • observed damage

&laquo_space;slides for scale descriptions&raquo_space;

33
Q

The factors that influence our perception of EQ intensity

A
  1. Magnitude
  2. Distance from hypocentre
  3. Structural resistance
  4. duration
  5. ground material
34
Q

Seismic waves ____ as they travel

A

weaken

35
Q

Shaking from a Mw 9 EQ will last about

A

4-5 minutes

36
Q

what ground materials are worse in an EQ?

A

wet sediments = more intense

rock and compact sands = less intense

37
Q

Building design in an EQ

A

Good: flexible, wood, concrete WITH steel

Bad: brick, stone, concrete without steel

EOSC 114 (30 decks)

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