lecture 2 seismology and earths layers

Question 1

what are the 2 types of seismic wave

Answer 1

p and s

Question 2

what are seismic waves

Answer 2

generated by large disturbances at crust

Question 3

difference between p and s

Answer 3

p are pressure, compressing to change size and shape of material its going through |||| | | | | | | | ||||

s change shape but not size ~~~~~~~~~~~~~

Question 4

what can seismic waves be used for

Answer 4

finding out the composition of inside the earth

Question 5

what is a seisimic discontinuity

Answer 5

boundry between two layers within the earth

Question 6

how can seismic waves act within the earth when they hit a discontinouity

Answer 6

refract
reflect
transform eg p wave to s wave

Question 7

how many kilometers to the centre of the earth

Answer 7

6370km

Question 8

what is the moho short for

Answer 8

Mohorovičić

Question 9

what is the moho between

Answer 9

it is the crust mantle boundary within the lithosphere

Question 10

how was the moho discovered

Answer 10

shallow refraction surveying

Question 11

plate techtonics involves moving what?

Answer 11

the lithosphere

Question 12

where can earthquakes happen

Answer 12

only in the lithosphere

Question 13

what is the lithosphere

Answer 13

the rigid outer part of the earth, consisting of the crust and upper mantle

Question 14

what is the asthenosphere

Answer 14

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.

Question 15

why does seismic velocity decrease when it reachers the asthenosphere

Answer 15

it contains a nearly molten peridotite layer that absorbs the waves energy (s waves can still pass)

Question 16

what kind of boundry is the lithosphere asthenosphere boundary

Answer 16

thermal boundary layer

Question 17

what rock type is abover AND below

Answer 17

peridotite

Question 18

what are the four main minerals in peridotite

Answer 18

(olivine, clinopyroxene, orthopyroxene and an Al-rich mineral which varies with depth)

Question 19

what is the mantle transition zone

Answer 19

located between the lower mantle and the upper mantle,

Question 20

what happens to the seismic velocity in the mantle transition zone

Answer 20

rapid increase, anomalously high velocity zone

Question 21

what is the eason for the change in seismic velocity in the mantle transition zone

Answer 21

change in crystal structure of peridotite due to increasing pressure

Question 22

how does olivines shape change

Answer 22

400-450km olivine becomes like the shape of spinel

at 670-700km it changes to the structure of perovskite

Question 23

how much does density increase over the mtz

Answer 23

11%

Question 24

what must also increase in the mtz for velocity to increase

Answer 24

elasticity

Question 25

what happens to sesimic velocity in the lower mantle

Answer 25

steadily increases down to the core mantle boundary

Question 26

how do we know what the mantle is made of

Answer 26

ophiolite suites
xenoliths
meteorites
seismology

Question 27

what are ophiolite suites

Answer 27

A sequence of rocks consisting of deep-sea marine sediments overlying (from top to bottom) pillow basalts, sheeted dikes, gabbro, dunite, and peridotite.

Question 28

what are xenoliths

Answer 28

fragments of mantle peridotite

incorporated into explosive volcanic rocks.

Question 29

what are meteorites

Answer 29

fragments of rock fromm the asteriod belt (many composed of peridotite

Question 30

how can seismology be used

Answer 30

measuring wave velocities