Geophysical Techniques - For Final Exam

Question 1

Gravity:

Answer 1

measures the minute variations in Earths gravity field. Bases on these variations, subsurface density and composition can be inferred.

Question 2

Gravity is sensitive to:

Answer 2

density

Question 3

Gravity depth?

Answer 3

Shallow/Deep

Often used for shallow studies, however, gravity anomalies from large scale density changes as deep as the CMB are observed.

Question 4

Resistivity:

Answer 4

Measurement of differences in electric potential at earths surface in response to injection of electrical current

Question 5

Resistivity sensitive to:

Answer 5

electrical resistivity

Question 6

Resistivity depth?

Answer 6

Shallow

depends on length of cable used to inject current

Question 7

Magnetics:

Answer 7

measure disturbances in earth’s natural magnetic field

Question 8

Magnetics sensitive to:

Answer 8

magnetic susceptibility and magnetic remanence

Question 9

Magnetics depth?

Answer 9

shallow/deep

similar to gravity

Question 10

Seismic:

Answer 10

measures travel times and amplitudes of seismic waves at various distances from seismic source

Question 11

Seismic sensitive to:

Answer 11

seismic wave velocity, density, interfaces (k and mu)

Question 12

Active Seismic Depth:

Answer 12

Shallow

some measured up to MOHO, depths approximately less than 100 km

Question 13

Passive Seismic Depth:

Answer 13

Shallow/Deep

we can observe seismic waves that pass through inner core

Question 14

Tradeoff w/ resolution…

Answer 14

Can’t see anything less than wavelength

λ = cT ex. @ core mantle boundary, λ=12km/s * 1s, λ = 12 km, highest possible resolution