Folds, faults, earthquakes

EES 2510

what is compression

squeeze and shorten a body

tension

stretch a body and tend to pull it apart

shearing

push two sides in opposite DRNs

what is brittle rock?

breaks easily, ex) shale- changes a little then breaks suddenly 

what is ductile rock

undergoes smooth and continuous plastic deformation and do not spring back to their original shape when the deforming force is released.

what happens with an elastic formation?

it bounces back like a rubber band

what happens with plastic rock?

permanent change occurs

what is a fold in rock?

a bend in a rock mass

what is a fault in a formation?

break in a rock mass

Anticline fold

upward folded rock (looks like an inch worm)

Syncline fold

downward folded rock (looks like an upside down inchworm)

Dome fold

circular anticline structure (upside down bowl)

oldest rock is in the center 

Basin Fold

bowl-shaped syncline structure

youngest rock in the center 

normal fault

-due to tensional forces

-hanging wall moves down relative to the footwall

reverse fault

-due to compressional forces

-hanging wall moves up to relative to the footwall

strike-slip fault

-due to shear forces

-transform fault

oblique-slip fault

-due to shear and tensional forces

-normal and strike-slip together

hanging wall

all material above the fault line

footwall

everything below the fault line

Horst

upwardly faulted rock

Graben

downwardly faulted rock

where do 80% of earthquakes come from?

the circum-pacific belt

Earthquake

Vibration in the earth from a release of energy, generated from fault activity

foreshock

smaller earthquake that follows main quake

focus

origin of quake within the earth 

epicenter

origin of quake at the surface, directly above focus

what are the two body waves?

p and s waves

what are the two surface waves?

Rayleigh and Love waves

primary waves (p-wave)

-first to arrive on the seismograph

• 1-14km/s (slower moving through liquid 

• compress and expand in the DRN they travel 

-p wave shadow zone: caused by refraction of p-waves through earths core

secondary waves (s-wave)

-second to arrive on seismograph

-1-8 kms/s (does not pass through liquids)

shear motion vibrates the ground perpendicular to the DRN traveling 

-cant go through outer core

Rayleigh waves (R-wave)

-rolling waves

-1-5km/s

-similar to water waves 

Love (L-wave)

-similar to s-wave motion

-2-6 km/s 

-vibrates the ground in horz DRN 

-perpendicular to the way the wave travels 

magnitude

measure of the strength of a quake or strain released (energy released).

-determined by amp of largest seismic wave

-magnitudes go up in scale 10 fold (energy is increased by 30 fold)

what is the most dangerous location of focus?

shallow (less than 50 km deep)

what are things seismologists look for?

-seismic gaps (portions where pressure is building)

-surface elevation changes 

-ground water tables fluctuation 

-local changes in magnetic field

what is the boundary and plates of the san andreas fault?

-transform boundary

-pacific plate and north american plate 

why did ohio used to fault?

faulted from past tectonic activity “rifting” 100 of millions of years ago