Earthquakes Flashcards
what causes earthquakes?
all sorts of causes, fault slip is most common cause
hypocenter vs epicenter
hypo: focus
place where fault slip first occurs. earthquake waves expand outward from hypocenter
epicenter: land surface right above the hypo
active vs inactive faults
active: ongoing stresses produce motion
inactive: motion occurred in geologic past
not all faults reach surface
where does energy creating earthquakes originate from?
rocks break to form new fault
preexisting fault is reactivated
fault remains zone of weakness
friction
fault motion stopped by friction
due to bumps along the fault
stick slip
faults weaker than surrounding crust
stick: STATIC friction prevents motion
slip: friction briefly overwhelmed by motion
foreschocks
precede major earthquakes
smaller tremors indicate crack development in rocks
may warn
displacement
greatest near hypocenter
diminishes with distance
faults can offset rocks by 100s of kms over time
p-waves
body wave
waves travel by compressing and expanding material
material moves parallel to wave direction
FASTEST
travel through everything
S-waves
body wave
waves travel by moving material back and forth
material moves perpendicular to wave travel direction
SLOWER THAN P-WAVES
only travel through solids, not liquids or gases
Love waves
surface wave
s-wave that intersects land surface
move ground like writhing snake
Rayleigh waves (r-wave)
surface wave
p-wave that intersects land surface
cause ground to ripple up and down like water
seismometer
measure wave arrivals and magnitude of motion
magnet and electric coil
record data digitally
seismogram
data recording earthquake wave behavior
arrival times determine distance to epicenter
what is the order at which earthquake waves arrive at station?
first p-waves
S-waves
surface waves last
time delay between p and s waves used to establish distance to epicenter
point of intersection of stations is the epicenter
mercalli intensity scale
amount of shaking damage
1 = low
12 = high
SEE SCREENSHOT FOR HOW MOMENT MAGNITUDE SCALE WORKS
Plate tectonic boundaries
shallow: divergent and transform boundaries
intermediate and deep: convergent boundaries
wadati Benioff zone
seismically active area in the Earth’s crust where earthquakes occur when two tectonic plates converge and one is subducted beneath the other
intermediate (downgoing slab is cold and brittle)
deep (mineral phase changes create earthquakes)
earthquakes at divergent plate boundary
normal faults and strike-slip faults are developed
transform plate boundary
plates slide past each other
occur at shallow crustal levels
transforms link segments of the MOR
on continents = MAJOR DISASTERS
san andreas is very active strike-slip fault
continental rifts
stretching creates normal faults
generate shallow earthquakes similar to MOR
collision zones
continental crust
orogenic crustal compression
continental lithosphere compresses along thrust faults
orogenic uplift creates landslide hazards