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.
