Fragile Systems and Quakes Flashcards
What is sensible vs latent heat?
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
What is return period?
time span of data/number of cases.
What are the four frameworks of the course?
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?
What is hazard/vulnerabililty vs risk?
What is our perception of risk? Risk of a big earthquake here?
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%
Are disasters increasing?
No! just our perception of them/ our population is increasing!
How is population growing? How is this related to disasters?
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.
Describe earth layering.
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)
Describe difference between crust and mantle/lithosphere and asthenosphere.
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.
Describe plate tectonics. Quantify plate spreading rates and convergence/subduction rates
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.
Explain rock can be brittlel/elastic and plastic
Elastic: springs back, reversible
Ductile: plastic flow, permenant
Brittle: breaks, permenant.
COntrolled by temp, speed and duration of deformation.
Describe global distribution of earthquakes?
- THey happen at plate boundaries. Mostly around the ring of fire!
What is plasma?
dissociated electrons and nucleir, conductive.
What is convection?
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.
What forces are acting on plates?
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.
What are the 3 types of plate boundaries? Fault types Forces?
- Convergent: thrust/reverse, compression. Strongest, most time before brittle failure, can be pretty deep, but that influences strength.
- Divergence: normal, tension forces
(hanging wall going Down D) Weakest frequent quakes, very shallow. - Transform, strike slip, shear forces. Medium strength.
What determines how big a brittle fracture is gonna be
Temperature Strength and Geometry.
Earthquake locations within subduction zones?
On plate interface (megathrust, offshore)
In overriding plate (broadly dispersed. closer to populations, same with downgoing)
In downgoing plate
0-650km keep
What is elastic rebound?
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.
What are the different types of waves ?
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.
How to determine where the epicenter is??
3 seismometers to triangulate location.
Whats magnitude and intensity?
Scales for measuring?
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)
What increases with each step of the momentum magnitude scale?
Ground motion 10x each step
Duration 3.2 x each step
Energy released 32x each time
What influences intensity?
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.
Which waves are the worst?
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.
What building is best to survive earthquakes?
Wooden houses. flexible and lower squat geometry. FLexible and strong is best.
what is resonance?
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!)
what are structural buliding ideas to help defend against disasters?
Using proper materials
Vibration control
1) tuned mass dampers (pendulum)
2)seismic base isolators: decouple builiding from its base.
Where you build matters…why?
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.
What is liquefaction?
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.
Prediction vs forecast?
prediction is specific: when where and how big.
forecast is less specific and is a probability statement.
Precursors to earthquake?
Foreshocks/increased seismic activity, rapid ground deformation, radon/ electromagnetic disturbances.
Many don’t have precursors tho :(
ground signals are monitored but not particularly reliable.
What is recurrence interval of earthquakes?
used past quakes for probabilitic forecasting (vs prediction)
allows us to perform risk assessment. ensure preparedness and folow good construction practice.
what are forcasting approaches for earthquakes?
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)
What is the cascadia subduction zone at risk for?
Megathrust earthquake!
Return period of 500 years.
What are 3 types of quakes? which is worst for vancouver?
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.
