Lecture 1 - intro

Question 1

Active methods

Answer 1

The operator generates the signal and records its propogation/ return

Question 2

2 types of geophysical methods

Answer 2

Active and passive

Question 3

Passive Methods

Answer 3

The operator records signals that have been generated naturally or by other processes

Question 4

Gravity, magnetics, seismic and SP

Answer 4

Types of passive methods

Question 5

Seismic, EM,GPR, IP and resistivity

Answer 5

Types of active methods

Question 6

GPR

Answer 6

Ground Penetrating Radar (method)

Question 7

Velocity of P waves

Answer 7

Can help determine rock type

Question 8

Key measurables in geophysics

Answer 8

Electric, gravity, seismic and magnetic

Question 9

Examples of reasons for different property values

Answer 9

Porosity, weathering, age, fracturing, temperature, pore fluid

Question 10

If void covered/ full of water..

Answer 10

Gravity anomaly much smaller

Question 11

Geophyical surveys

Answer 11

Non-invasive probe of subsurface

Question 12

Contrast between target and surrounding material very
important

Answer 12

Allows identification of anomalies

Question 13

Initial survey considerations

Answer 13

Feasibility, Finances, Logistics, Geology/observations

Question 14

Forward modelling

Answer 14

Have a model and can calculate data at certain points in time/space

Question 15

Inverse modelling

Answer 15

Collect data and from them try to generate a model

Question 16

The only way you can be 100% sure of a model

Answer 16

If you have infinite and perfect data

Question 17

How to choose best method (things to consider)

Answer 17

• Target and subsurface properties
• Time
• Max depth of penetration

Question 18

Method useful for subglacial features

Answer 18

Seismic reflection array

Question 19

Aliasing

Answer 19

The failure of sampling to identify the original signal

Question 20

What is aliasing the result of ?

Answer 20

Insufficiently frequent sampling

Question 21

Noise

Answer 21

Can lead to irregular fluctuations that accompany a
transmitted signal but are not part of it and tend to obscure it

Question 22

Signal- Noise ratio desired in data acquisition

Answer 22

High ratio

Question 23

Coherent noise

Answer 23

Regular/predictable = effect can
be removed from data during processing (e.g.
power line signal)

Question 24

Incoherent noise

Answer 24

Unpredictable/random = may
average out (e.g. waves breaking) or may cause
bigger problems (e.g. a car driving past)