Chap 17

Question 1

Geophysics

Answer 1

The study of seismic waves and earths magentic field gravity and heat

Question 2

Oceanic crust

Answer 2

-7m thick
Layer one: marine sediment
Layer 2: pillow basalt overlying basaltic dikes
Layer 3: Sill like gabbro intrusions

Question 3

Seismic reflection

Answer 3

The return of some waves to the surface after bouncing off a rock layer boundry

Question 4

Seismic refraction

Answer 4

Bending of seismic waves as they pass from one material to another having different seismic waves velocities

Question 5

Seismic waves

Answer 5

indiciate crust is thinner and denser beneath the oceans than on the continents

Question 6

Lithosphere

Answer 6

Crust and uppermost mantle 70 km thick beneath oceans, 125 km thick beneath continents

Question 7

Moho

Answer 7

boundary between crust and mantle

Question 8

Asthenosphere

Answer 8

beneath lithosphere partially molten rock low velocity zone

Question 9

Isostasy

Answer 9

Equilibrium of adjacent blocks of brittle “floating on upper mantle

Question 10

Isostatic adjustment

Answer 10

Rising or sinking of crustal blocks to achieve isostatic balance

Question 11

Crustal rebound

Answer 11

Rising of crust after large mass of ice was rapidly remoced from the surface at the end of ice ages

Question 12

Gravitational force

Answer 12

Determined by the mass and the distance between objects

Question 13

Positive gravity anomaly

Answer 13

gravity reading higher than normal indicate that tectonic forces hold up a region out of isostatic equilibrium

Question 14

Negative gravity anomoaly

Answer 14

gravity reading lower than normal

Question 15

Magnetic field

Answer 15

region of magnetic force

North and south magnetic poles

Question 16

Magnetic reversals

Answer 16

times when the poles of earths magnetic field switch

Question 17

Paleomagnetism

Answer 17

the study of ancient magnetic fields in rocks allows reconstruction of plate motions over time

Question 18

geothermal gradient

Answer 18

temperature increase with depth into the earth

Question 19

heatflow

Answer 19

the gradual loss of heat through earths surface, major heat sources include original heat and radioactive decay