earthquakes Flashcards
layers of the earth
lithosphere (crust): brittle, locally ductile
asthenosphere (mantle): very ductile
mesosphere (lower mantle): stiff ductile
what are plate tectonics controlled by?
temperature
density
compression
gravity
which crust is more dense, oceanic or continental?
oceanic
types of deformation
elastic (springs back)
ductile (plastic flow)
brittle (breaks)
what are phase changes controlled by?
temperature & pressure
only ___ plates subduct
oceanic
continental plates are too buoyant
forces acting on the plates
basal drag: friction between rigid lithosphere & more ductile mantle drags plate along
slab pull: cold descending plate pulled beneath hot mantle by gravity
ridge push: heating at rift raises crest, gravity pulls it down
plate boundaries
convergent
divergent
transform
convergent boundary
force: compression
earthquake: thrust or reverse
strongest quake
boundaries: O-O, O-C, C-C
divergent boundary
force: tension
earthquake: normal
weakest quake
boundaries: O-O, C-C
transform boundary
force: shear
earthquake: strike/slip
boundaries: all
fault definition
brittle fracture along the rocks in which movement has occured
the release of stored elastic energy is…
an earthquake
sequence of seismic events
- elastic deformation
- brittle failure
- earthquake
- elastic rebound
body waves
travel inside materials
p waves & s waves
p waves
moves in same direction wave propagates, the fastest, compression driven
s waves
perpendicular to direction wave propagates, slower, shear force driven
surface waves
travel along boundaries between materials
slower than body waves
rayleigh waves & love waves
rayleigh wave
parallel to wave travel direction
love wave
perpendicular to wave travel direction
sequence of waves on a seismograph
p waves -> s waves -> surface waves
magnitude definition
indicates how much energy was released
magnitude scales
richter - based on maximum ground motion
for each increase on magnitude scale, energy released increases by a factor of…
10^1.5 or around 32
intensity definition
how strong ground motion is at felt location
intensity scales
modified mercalli scale
what factors influence our perception of intensity?
- magnitude
- distance from hypocentre
- structural resistance
- duration
why can’t shear waves propagate thru fluids?
you can’t bend a liquid, but you can compress it
how different types of motion affect buildings
horizontal shaking & rolling motions most destructive
vertical shaking relatively undestructive
hazards of earthquakes
- ground shaking -> things falling
- liquefaction
- fire
- tsunami
- landslides
best building design to withstand earthquakes
- flexible and strong
- resonates at high frequencies
building damage mitigation
- tuned mass dampers
- massive pendulum within a building
- decouple building from its base
short term warning signs
- increase in seismic activity
- rapid ground deformation
- electromagnetic disturbances
- animal behaviour
unreliable at best
long term prediction method
evidence of past quakes, imprecise prediction
a forecast is a…
probability statement
earthquake forecasting tools
- land-level change
- seismic gaps
- physical and chemical phenomena
cascadia subduction zone return period, which plates
500 years, juan de fuca plate subducting under north american plate
evidence of 1700 cascadia earthquake
- indigenous stories
- japanese writings
- ghost forest
- sediment deposits
what to do during an earthquake
- anchor objects that might fall
- hide under desk
- avoid doorways and the kitchen
- after help the injured
- evacuate damaged buildings after
