rock deformation/earthquakes/earth’s internal structure

stress

force applied to a rock per unit area

uniform stress

aka confining pressure. compacts rock. no shape change

differential stress

aka directed pressure. stress is applied unequally to different sizes resulting in distorted rock

yield stress

amount of stress needed to deform a rock. depends on rock strength.

strain

change in shape of rock by deformation

brittle deformation (results? cause?)

results in faults and joints and breaks/fractures. caused by cooling or pressure unloading

ductile deformation (results? cause?)

results in bends/flows/folds (eg chocolate bar in the sun) caused by slow compressional stress

rock strength vs temperature

rocks are weaker at higher temps

rock strength vs confining pressure

rocks are stronger at higher pressure (greater depths)

tensional stress (where? results?)

happens at divergent boundaries. results in extensional stress and stretching/thinning of the crust and normal dip-slip faulting

compressional stress (where? results?)

happens at convergent plate boundaries. results in shortening/thickening of the crust and reverse dip-slip faulting

shear stress (where? results?)

happens at transform plate boundaries. results in strike-slip faults

joints

fractures with no movement. caused from cooling over time and pressure unloading

faults

fractures where the rocks move relative to one another. offset can accumulate over time

strike-slip faults

move horizontally either right-lateral or left-lateral

dip-slip faults

movement is vertical

normal faults. (caused by?)

type of dip-slip fault where hanging wall moves down below footwall. caused by extensional stress

reverse fault (caused by?)

type of dip-slip fault where hanging wall moves up in relation to footwall. caused by compressional stress

folds

rocks warp (ductile behaviour) over long periods of time from compressional stress

anticlines

arch like fold caused by compressional stress

synclines

downward curve of a fold caused by compressional stress

focus/hypocenter

the exact place in the earth’s crust where a rupture happens

epicenter

the spot on the earth’s surface exactly above where the fault ruptured

elastic rebound

when a fault is stuck stress builds up gradually over time and when elastic limit of the material is reached energy is released all at once (rupture) in seismic waves

how often does the locked cascades subduction zone rupture

every 400-500 years

magnitude (measured by? best scale?)

measured by seismometers in the ground. reflect energy release due to rupture and slip. moment scale= best

p(rimary) waves

fastest. compressional (push/pull). (less damaging) propagate parallel to medium.

s(econdary) waves

second fastest. sheer waves. propagate perpendicular to medium. (damage!)

surface waves

3rd waves. released by other waves (biggest). move like water and ripple the earth’s surface. can cause BIG damage

amplification

some materials amplify waves as they pass through (eg unconsolidated sediment)

tsunamis (caused by?)

a series of massive waves that can be devastating. caused when a slip displaces the ocean. most commonly caused by earthquakes but can also be caused by landslides, volcanoes and asteroids.)

crust

1.4% of earth’s volume. rigid, thin and brittle. 6-35 km deep. tectonic plates. made of felsic and mafic rocks

mantle

82.5% of earth’s volume. sits below the MOHO. made of dense ultramafic rocks. part rigid, part molten. ~2900 km thick

outer core

sits below the CMB. liquid. very dense. made of iron and nickel.

inner core

very inner part of the earth. solid iron. super dense.

lithosphere

includes the crust and top part of the mantle. rigid and brittle.

asthenosphere

partially molten part of the mantle. weak and ductile. sits between lithosphere and mesosphere

mesosphere

bottom portion of the mantle. rigid. sits below the asthenosphere.

how do we know about the layers of the earth?

seismic waves change velocity, refract an bend arriving at some depths sooner than we expected due to the nature of rocks there.