Earthquakes

Question 1

what causes earthquakes?

Answer 1

all sorts of causes, fault slip is most common cause

Question 2

hypocenter vs epicenter

Answer 2

hypo: focus
place where fault slip first occurs. earthquake waves expand outward from hypocenter
epicenter: land surface right above the hypo

Question 3

active vs inactive faults

Answer 3

active: ongoing stresses produce motion
inactive: motion occurred in geologic past
not all faults reach surface

Question 4

where does energy creating earthquakes originate from?

Answer 4

rocks break to form new fault
preexisting fault is reactivated
fault remains zone of weakness

Question 5

friction

Answer 5

fault motion stopped by friction
due to bumps along the fault

Question 6

stick slip

Answer 6

faults weaker than surrounding crust
stick: STATIC friction prevents motion
slip: friction briefly overwhelmed by motion

Question 7

foreschocks

Answer 7

precede major earthquakes
smaller tremors indicate crack development in rocks
may warn

Question 8

displacement

Answer 8

greatest near hypocenter
diminishes with distance
faults can offset rocks by 100s of kms over time

Question 9

p-waves

Answer 9

body wave
waves travel by compressing and expanding material
material moves parallel to wave direction
FASTEST
travel through everything

Question 10

S-waves

Answer 10

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

Question 11

Love waves

Answer 11

surface wave
s-wave that intersects land surface
move ground like writhing snake

Question 12

Rayleigh waves (r-wave)

Answer 12

surface wave
p-wave that intersects land surface
cause ground to ripple up and down like water

Question 13

seismometer

Answer 13

measure wave arrivals and magnitude of motion
magnet and electric coil
record data digitally

Question 14

seismogram

Answer 14

data recording earthquake wave behavior
arrival times determine distance to epicenter

Question 15

what is the order at which earthquake waves arrive at station?

Answer 15

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

Question 16

mercalli intensity scale

Answer 16

amount of shaking damage
1 = low
12 = high

Question 17

SEE SCREENSHOT FOR HOW MOMENT MAGNITUDE SCALE WORKS

Question 18

Plate tectonic boundaries

Answer 18

shallow: divergent and transform boundaries
intermediate and deep: convergent boundaries

Question 19

wadati Benioff zone

Answer 19

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)

Question 20

earthquakes at divergent plate boundary

Answer 20

normal faults and strike-slip faults are developed

Question 21

transform plate boundary

Answer 21

plates slide past each other
occur at shallow crustal levels
transforms link segments of the MOR
on continents = MAJOR DISASTERS

Question 22

san andreas is very active strike-slip fault

Question 23

continental rifts

Answer 23

stretching creates normal faults
generate shallow earthquakes similar to MOR

Question 24

collision zones

Answer 24

continental crust
orogenic crustal compression
continental lithosphere compresses along thrust faults
orogenic uplift creates landslide hazards

Question 25

which waves cause the most damage?

Answer 25

s waves (stronger motion than p-waves)
p-waves: up and down motion
s-waves: back and forth motion
l-waves: cause ground to writhe like a snake
r-waves: ripples, also cause a lot of damage

Question 26

severity of earthquake depends on:

Answer 26

magnitude
distance from focus
nature of subsurface material
TRANSMITTAL OF WAVES QUICKLY = LESS DAMAGE

Question 27

extra damage

Answer 27

landslides and avalanches (steep slopes fail due to shaking)
fire
disease outbreaks

Question 28

liquefaction

Answer 28

waves liquefy H2O filled sediments
groundwater forces grains apart, reducing friction
flow as a slurry
sand becomes quicksand, and clay, quicklay
causes soil to lose strength and land slumps

Question 29

tsunami

Answer 29

result from vertical displacement of sea floor
faulting displaces entire volume of overlying water

Question 30

tsunami detection

Answer 30

detectors placed on deep sea floor
sense pressure increases from changes in sea thickness

Question 31

earthquake prediction

Answer 31

can be predicted in long term, not in short term (hours or weeks)
requires examining evidence of past earthquakes
earthquakes do have precursors
can’t stop them but can be prepared for them