Earthquakes and Earth's Interior Flashcards
What is an earthquake?
ground shaking caused by sudden movement of rocks slipping past another along faults
What are faults?
fractures in Earth’s crust
What are seismic waves?
energy from eq that radiates outward of hypocenter/focus
epicenter vs hypocenter
epicenter is directly above the hypocenter (abajo)
what are the 3 types of seismic waves?
what do they travel through?
P, S , Surface
P&S waves:interior
Surface waves travel along surface
Which seismic wave has the greatest velocity? Middle? Last?
velocity aka
reach the seismograph stations first? Middle? Last?
P (reach seismograph station first)
S (Second)
Surface (Last)
speed
Seismographs
instruments that detect and record seismic waves
seismograms
what are they used to determine
recordings by seismographs
time and location of EQs
amplitude
wave height
Which waves have the greatest amplitude and therefore are the most dangerous
surface
Which waves leave at the same instant?
pS
What is the relationship btw the arrival times of the first P wave compared to the first surface wave as the distance btw the hypocenter and seismograph increases?
there will be greater difference btw arrival times; the s waves and surface waves might not show up until a while
How do you determine the distance btw a recording station and an epicenter?
what kind of graph are you using
- Determine the P-S wave interval (time elasped from 1st P wave to first S wave)
- On the y-axis, draw a line from 0 to whatever time interval
- Draw ticks on a piece of paper and slide it btw the 2 lines (P at bottom), make sure paper is straight
- once both ticks line up, record the distance from epicenter and time from epicenter to reach station
travel-time graph
using the travel-time graph, how can you find low long it took for the first P wave to reach the station?
knowing the interval btw the 1st P and S wave, use paper with line of that interval, then stop and record distance of P wave curve only! when ticks meet up with lines
how do you locate an epicenter?
- get seismograms from 3 dif stations
- calculate distance from station to epicenter
- use compass to draw 3 circles
- point where all 3 circles connect is the epicenter
how do you use a compass to draw circles?
use the scale at bottom
start from 0 and extend pencil to the number of miles/unit from the epicenter to that station
repeat for other stations’ circles
how can you check to make sure your circle is correct?
radius=P-S interval
how much eq energy originates in narrow zones
95%
what is the zone of greatest seismic activity
what’s another zone
circum Pacific belt
alpine-himilayan belt
do most deep earthquakes occur along: the marigin of the atlantic or pacific basin
pacific
do the eqs that occur along the western margin of the s.america get deeper or shallower inland
deep
at what depth (shallow, intermediate, or deep) do eqs in the middle of the atlntic ocean occur?
shallow
with what geological feature are the eqs in the mid atlantic associated
mid atlantic ridge
What is the thickness of the crust?
5-70 km
What is the layer of the earth that contains the most volume
%
mantle
more thaan 82%
`
what kind of rocks make up the mantle
ultramafic
how thick is the mantle
2900 km
what does rigid mean
stronger/not flexible
mantle layers and its characteristics?
upper and lower
lithosphere: rigid/strong
asthenosphere: weak, hot
^upper
lower: more rigid as depth increases
to what depth does the asthenosphere lie
350 km
core comp and thickness and state of matter
iron-nickel
inner: solid, 1216km
outer: liq 2270km
what indicates greater rigidity
faster p and S waves (higher velocity)
What can’t S waves travel through? why?
liquids (outer core) not rigid
what can’t P waves pass through?
they can pass through ALL layers
Why do S waves magically appear in the inner core?
when P waves are btw inner and outer core, some energy is converted to S waves
does the velocity of p waves and s waves increase or decrease with increased depth in the lithosphere
increase
Does the velocicty of P and S waves increase or decrease immediately below the lithosphere and why
decrease
lithosphere is more rigid than the asthenosphere, so velocity decreasess
when looking at the velocities of the waves, what should you do? ASKKKKKKKK
follow the line, the line that hits it from left to right isn’t the first
Do P waves increase or decrease in veleocity as they enter the outer core and why
decrease upon entering (mantle is rigid to liq outer core) then start to increase inside outer core
How do S and P waves behave when entering the inner core
increase in velocity at border btw outer and inner, then increase slowly
temp increases with
depth
geothermal gradient
rate of temp increase
does earth’s internal temp increase at a constant or changing rate with increasing depth?
changing
is the rate of temp increase from the surface to 100 km greaater than or less than the rate of increase below 100 km
greater
how do you know when a rock has reached its melting temp from a graph
the temp stops increasing
does the melting curve for basalt indicate that the lithosphere above 100 km has or hasn’t reached the melting temp for basalt? is this layer soliid or magma
hasnt
solid
does the graph you constructed support or refute the concept of a weak astehnosphere that can flow
supports bc the lithosphere is solid sisnce basalt and granite haven’t reached melt.point, but at some depth in the asthenosphere (160km) it does, so its magma
