The Earth's Interior

Question 1

What is the Richter Scale?

Answer 1

Developed to quantify and compare earthquake magnitudes. Logarithmic

Question 2

What is the P-S time interval, and what can it be used for?

Answer 2

The difference in arrival time between P and S waves. Used to ascertain distance between seismometer and epicenter

Question 3

How much faster are P-waves to S-waves?

Answer 3

About twice as fast

Question 4

What two things on the printout of a seismometer are used to determine the magnitude of the earthquake?

Answer 4

1. the maximum amplitude

2. The P-S interval (used to determine distance from epicenter).

Question 5

What is needed to determine the geographical location of the epicenter?

Answer 5

Multiple seismometer stations to triangulate.

Question 6

Why do seismic waves increase in velocity as they travel through the earth?

Answer 6

Velocity of seismic waves increases with the rigidity of a solid, and the middle of the earth is more dense.

Question 7

What is rigidity

Answer 7

A measure of how difficult a solid is to shear

Question 8

How can S-waves travel faster through solids?

Answer 8

The solids must have higher shear moduli

Question 9

What kind of solids can S-waves move through faster?

Answer 9

Solids with higher bulk moduli and shear moduli

Question 10

What is the line of travel of an earthquake wave called?

Answer 10

ray path

Question 11

What causes curved ray paths?

Answer 11

Refraction

Question 12

What is refraction?

Answer 12

The tendency for seismic waves to bend as they change in velocity and/or encounter varying densities of matter

Question 13

Where are the S-wave shadow zones?

Answer 13

The opposite 3/8 of the earths surface?

Question 14

Where are the R-wave shadow zones, if the earthquake is at 12 o’clock?

Answer 14

8 and 4

Question 15

How can we know that the outer core is liquid?

Answer 15

P-waves traveling through the slower liquid core are refracted inwards, causing two shadow zones.

Question 16

How can we know that the inner core is solid?

Answer 16

weak, late P-waves were detected in the shadow zones, meaning they were refracted off something solid

Question 17

What is the Gutenberg discontinuity?

Answer 17

significant change in seismic waves at the core-mantle boundary

Question 18

What is the Lehman discontinuity?

Answer 18

significant velocity increase at the inner core boundary

Question 19

Define the moho discontinuity?

Answer 19

The boundary between the crust and the mantle

Question 20

How was the Moho discovered?

Answer 20

Two different versions of the same seismic wave would arrive at different times. This is caused by some waves moving faster through the mantle than waves movign through the less-dense crust

Question 21

What generates Earths magnetic field?

Answer 21

movement of the rotating, convecting, electrically conducting outer core

Question 22

Explain how a seismometer works

Answer 22

A heavy weight is hung from a support, and the weight bears a pen that writes on paper. As seismic waves move past the mechanism, the earth moves, while the ball and pen stay put, creating lines indicative of the different waves.

Question 23

What information from a seismogram printout does one need to calculate the
distance from that seismogram to an earthquake epicentre?

Answer 23

The P-S interval.

Question 24

Can the location of an earthquake be determined from a single seismogram
printout?

Answer 24

only if two or more seismogram printouts are available from other locations.

Question 25

What does one require from a seismogram printout to plot the magnitude of an
earthquake on the Richter scale?

Answer 25

The maximum amplitude of the seismic waves and the P-S interval

Question 26

What evidence exists for the Gutenberg Discontinuity?

Answer 26

The S-wave shadow zone.

Question 27

What evidence exists for the Lehmann Discontinuity

Answer 27

Weak, indirect P-waves are observed in the P-wave shadow zone

Question 28

What evidence exists for the Moho Discontinuity?

Answer 28

P- and S-waves speed up at depths where the mantle reaches the crust.

Question 29

How deep is the earths crust on average?

Answer 29

15-20km on continental, 5-7 on oceanic