Fragile Systems and Quakes

Question 1

What is sensible vs latent heat?

Answer 1

Sensible: no phase change, heat we can sense/feel
Latent: during phase change, stored potential energy that’s hidden in bonds. Sensible is stored as latent during melting/boiling/sublimating

Question 2

What is return period?

Answer 2

time span of data/number of cases.

Question 3

What are the four frameworks of the course?

Answer 3

Processes: causes
Predictions/Forecasts: how can any aspect be anticipated
Consequences: how were things impacted by the event?
Mitigation: how can we minimize the effects or recover asap?

Question 4

What is hazard/vulnerabililty vs risk?

What is our perception of risk? Risk of a big earthquake here?

Answer 4

Hazard: any situation that could cause harm (human or economic)

Vulnerability: weakness that could be effected by a disaster

Risk:Probability that any hazardous event might occur and the change of a potential loss. Hazard x vul = risk.
Chance of x happening.

Human perception of risk is really skewed.
Walking near cars/ motor cycles/ car accidents/ plane crash/ lottery tickets.
Helmets reduce risk of death in motorcycles.
<1%

Question 5

Are disasters increasing?

Answer 5

No! just our perception of them/ our population is increasing!

Question 6

How is population growing? How is this related to disasters?

Answer 6

Historically exponential (doubling time 63 years) currently its linear (1billion every 13 years) but we will reach a carrying capacity at which we can’t sustainably support wtihin a given domain.

At present, people can be saved, but inftrastructure is destroyed, with more people, infrastructures becomes more important and vulnerable and people are less likely to be evacuated.

Question 7

Describe earth layering.

Answer 7

Crust (thin, cold, low density), Mantle (really warm, higher density 3300), and Core (high pressure, hotter, nickel iron alloy, more dense 9700) (outer core: metallic and liquid, inner core, solid and higher pressure/temp)

Question 8

Describe difference between crust and mantle/lithosphere and asthenosphere.

Answer 8

Crust is top 70km (oceanic basaltic and continental granitic, less dense)
Mantle: upper (ridic) and lower is melting.
Lithosphere: crust and upper rigid mantle. Brittle Rides on..
Asthenosphere: mantle near its melting point, ductile.
Mesosphere: lower mantle, stiff but ductile.

Question 9

Describe plate tectonics. Quantify plate spreading rates and convergence/subduction rates

Answer 9

Wegner thought plates rode around on the asthenosphere. Accounts for a lot of theories. Controlled by composition, density, temperature and gravity.
Density: air 1.2kg/m3, water is 1000kg/m3

2-3 cm year but it deons’t really move that much its more like 2m every hundred years.

Question 10

Explain rock can be brittlel/elastic and plastic

Answer 10

Elastic: springs back, reversible
Ductile: plastic flow, permenant
Brittle: breaks, permenant.
COntrolled by temp, speed and duration of deformation.

Question 11

Describe global distribution of earthquakes?

Answer 11

• THey happen at plate boundaries. Mostly around the ring of fire!

Question 12

What is plasma?

Answer 12

dissociated electrons and nucleir, conductive.

Question 13

What is convection?

Answer 13

Plate tectonics is a huge ductile convection cycle. Continents float due to convection. Heat rising and cool sinking. Mars is too small/cold for this.

Question 14

What forces are acting on plates?

Answer 14

Basal drag: friction between lithosphere and asthenosphere
Slab pull: gravity pulling dense plate down.
Ridge push: heating raising rift raises the edge of crest. Gravity pulls plates down and apart.

Question 15

What are the 3 types of plate boundaries? Fault types Forces?

Answer 15

1. Convergent: thrust/reverse, compression. Strongest, most time before brittle failure, can be pretty deep, but that influences strength.
2. Divergence: normal, tension forces
   (hanging wall going Down D) Weakest frequent quakes, very shallow.
3. Transform, strike slip, shear forces. Medium strength.

Question 16

What determines how big a brittle fracture is gonna be

Answer 16

Temperature Strength and Geometry.

Question 17

Earthquake locations within subduction zones?

Answer 17

On plate interface (megathrust, offshore)
In overriding plate (broadly dispersed. closer to populations, same with downgoing)
In downgoing plate

0-650km keep

Question 18

What is elastic rebound?

Answer 18

Elastic deformation, followed by brittle failure. Faults store and release energy.

At convergent boundaries, you have stored energy (plates lock = stress and deformation, plates release = quake and tusnami)

In an earthquake, we feel the waves produced by the elastic rebound.
Waves propegate along a fault and away from a rupture point.

Question 19

What are the different types of waves ?

Answer 19

Body Waves: inside earth (p and s)
Primary: compression, like a sound wave, propegate in same direction as particle movement. Fastest
Secondary: can’t move through liquid, propegate perpendicular to particle movement. A bit slower.
Surface Waves: move on the surface, slower.
Rayleigh: circular motion like an ocean wave. Less turbulent deeper.
Love: Horizontal movement perpendicular to wave travel. Less turbulent deeper.

P then S then surface.

Question 20

How to determine where the epicenter is??

Answer 20

3 seismometers to triangulate location.

Question 21

Whats magnitude and intensity?

Scales for measuring?

Answer 21

Magnitude: objective, how much energy released.
Intensity: subjective. felt at the location.

Richter (ml) based on grount motion (s wave amplitude) fast but innaccurate
Moment Magnitude (Mw) based on AREA OF RUPTURE and SLIP on fault. Harder to calculate but better accuracy.  Logarithmic. 

Modified mercali scale (1-12 based on subjective feelings)

Question 22

What increases with each step of the momentum magnitude scale?

Answer 22

Ground motion 10x each step
Duration 3.2 x each step
Energy released 32x each time

Question 23

What influences intensity?

Answer 23

Magnitude, distance from hypocenter, structural resistance (buildings meant to take verticle load not shearing, surface are the worst for buildings Brick/concrete BAD wood/reinforced concrete steel GOOD), duration. THe GROUND amplification.
Soft/saturated ground is the most problematic. Wavelength gets shorter, amplitude increases and it gets more dangerous to buildings.

Question 24

Which waves are the worst?

Answer 24

Surface: largest amplitude, for buildings, longest duration
S waves: shear waves, large amp, longer than p waves. main hazard for deep quakes w/o surface boys.
P waves: compressional, smallest amp, near vertical ground motion
Shortest duration.

Question 25

What building is best to survive earthquakes?

Answer 25

Wooden houses. flexible and lower squat geometry. FLexible and strong is best.

Question 26

what is resonance?

Answer 26

objects vibrate at charictaristic frequences based on size/composition and structure.
Tall buildings have lower resonant frequences, so if shaking is same as reonance =bad!)

Question 27

what are structural buliding ideas to help defend against disasters?

Answer 27

Using proper materials
Vibration control
1) tuned mass dampers (pendulum)
2)seismic base isolators: decouple builiding from its base.

Question 28

Where you build matters…why?

Answer 28

Ground can filer frequencies. Bedrock is chill smaller amplitudes and higher frequences, shorter duration.

Soft sediments: larger amplitudes, lower frequencies, longer shaking (jello)
i.e. fraser valley vs. north shore.

Question 29

What is liquefaction?

Answer 29

shaking causes unconsolidated materials to liquefy. soil loses cohesion and flows, things can sink, sand volcanos.
Loses contact forces and vibration wiggles the grains around so water can get through. Increases water pressure in pores spaces, pushes grains apart. WHen shaking stops, water pressure drops, grains stop vibrating, sediments firm again.

Question 30

Prediction vs forecast?

Answer 30

prediction is specific: when where and how big.

forecast is less specific and is a probability statement.

Question 31

Precursors to earthquake?

Answer 31

Foreshocks/increased seismic activity, rapid ground deformation, radon/ electromagnetic disturbances.
Many don’t have precursors tho :(
ground signals are monitored but not particularly reliable.

Question 32

What is recurrence interval of earthquakes?

Answer 32

used past quakes for probabilitic forecasting (vs prediction)
allows us to perform risk assessment. ensure preparedness and folow good construction practice.

Question 33

what are forcasting approaches for earthquakes?

Answer 33

Land level change (GPS, inSAR) satellites or ground based (LIDAR) (volcanos too!)
computer modelling (deformation, how stresses change, how it effects adjacent faults)
CNSN network moniters activity.
Seismic gaps (related to past earthquakes - statistics (period of no quakes = quake coming up?? compression building up in a locked zone??)
Rapid earth warning (new tech)

Question 34

What is the cascadia subduction zone at risk for?

Answer 34

Megathrust earthquake!

Return period of 500 years.

Question 35

What are 3 types of quakes? which is worst for vancouver?

Answer 35

Megathrust (longest), intraplate quake (moderate intensity, older masonry)
crystal quake: violent intensiy, closest to you is the worst!!
Megathrusts would cause the most damage to a bigger area and generate a tsunami.