lecture 2 seismology and earths layers Flashcards
what are the 2 types of seismic wave
p and s
what are seismic waves
generated by large disturbances at crust
difference between p and s
p are pressure, compressing to change size and shape of material its going through |||| | | | | | | | ||||
s change shape but not size ~~~~~~~~~~~~~
what can seismic waves be used for
finding out the composition of inside the earth
what is a seisimic discontinuity
boundry between two layers within the earth
how can seismic waves act within the earth when they hit a discontinouity
refract
reflect
transform eg p wave to s wave
how many kilometers to the centre of the earth
6370km
what is the moho short for
Mohorovičić
what is the moho between
it is the crust mantle boundary within the lithosphere
how was the moho discovered
shallow refraction surveying
plate techtonics involves moving what?
the lithosphere
where can earthquakes happen
only in the lithosphere
what is the lithosphere
the rigid outer part of the earth, consisting of the crust and upper mantle
what is the asthenosphere
he upper layer of the earth’s mantle, below the lithosphere, in which there is relatively low resistance to plastic flow and convection is thought to occur.
why does seismic velocity decrease when it reachers the asthenosphere
it contains a nearly molten peridotite layer that absorbs the waves energy (s waves can still pass)
what kind of boundry is the lithosphere asthenosphere boundary
thermal boundary layer
what rock type is abover AND below
peridotite
what are the four main minerals in peridotite
(olivine, clinopyroxene, orthopyroxene and an Al-rich mineral which varies with depth)
what is the mantle transition zone
located between the lower mantle and the upper mantle,
what happens to the seismic velocity in the mantle transition zone
rapid increase, anomalously high velocity zone
what is the eason for the change in seismic velocity in the mantle transition zone
change in crystal structure of peridotite due to increasing pressure
how does olivines shape change
400-450km olivine becomes like the shape of spinel
at 670-700km it changes to the structure of perovskite
how much does density increase over the mtz
11%
what must also increase in the mtz for velocity to increase
elasticity
what happens to sesimic velocity in the lower mantle
steadily increases down to the core mantle boundary
how do we know what the mantle is made of
ophiolite suites
xenoliths
meteorites
seismology
what are ophiolite suites
A sequence of rocks consisting of deep-sea marine sediments overlying (from top to bottom) pillow basalts, sheeted dikes, gabbro, dunite, and peridotite.
what are xenoliths
fragments of mantle peridotite
incorporated into explosive volcanic rocks.
what are meteorites
fragments of rock fromm the asteriod belt (many composed of peridotite
how can seismology be used
measuring wave velocities
