Geophysics Review

Question 1

geoid.

Answer 1

equipotential surface

sum of gravity and centrifugal forces

Question 2

circ of earth is?

Answer 2

40,000km

Question 3

difference between the equator and the poles is approx?

Answer 3

21km

Question 4

in exploration geophysics, what is a measurement that is widely used?

Answer 4

Gravity measurement

Question 5

gravity measurements must always compensate for the direction of travel

Answer 5

whether you are flying / travelling with or against the Earth’s rotation

Question 6

true or false
p waves: travels in solids and liquids, most common in exploration, has a longitudinal displacement, the fastest wave length, is a push-pull / compression-dilatation

Answer 6

True

Question 7

true or false
s - waves: shake, displace perpendicular, do not propagate through a fluid, have half the vel. of a P-wave, have double the amplitude of a p-wave

Answer 7

true

Question 8

list the order for arrival times for earthquake seismology

Answer 8

p-wave, s-wave, surface wave

Question 9

under the electromagnetic spectrum, what has the longest and shortest wave length?

Answer 9

Longest, radio waves

Shortest, Gamma

Question 10

what are the two modes of mechanical waves?

Answer 10

P and S – Longitudinal and Transverse

Question 11

what are the six processing basics?

Answer 11

Velocity
Statics
Noise Removal
----random and coherent
Deconvolution
Moveout correction
Migration (imaging)

Question 12

what processing basic stops the summing of data?

Answer 12

moveout

Question 13

With RMS Velocities

what is the actual shape of reflection?

Answer 13

Bell shape

Question 14

In RMS velocities how may the actual shape, bell shape, be approximated?

Answer 14

VIA a hyperbola

Question 15

in RMS velocities What do complex rays in depth =?

Answer 15

Straight rays in time

Question 16

In Velocity Analysis, what are you trying to obtain?

Answer 16

A velocity profile

Question 17

what does migration do?

Answer 17

Spreads energy along a semi-circle

moves dipping reflectors to correct location

Question 18

true or false

impulse is a response

Answer 18

true

Question 19

modelling vs migration.

Answer 19

Modelling:
forward process
sum energy on a semi circle
spread energy on a diffraction
Both are an impulse response

Question 20

Stress: how many components?

Answer 20

9.

3 normal. 6 shear

Question 21

symmetry is in the stress and strain is mapped to the what?

Answer 21

the stiffness tensor

Question 22

The symmetry of the stiffness tensor reduces from 81 to how many variables?

Answer 22

21

Question 23

VIA symmetrical reduction, reduce the 9 components to ?

Answer 23

6 unique components.

6x6 gives a stiffness tensor of 36…

Question 24

how many and what are the parameters in a matrix for isotropic media?

Answer 24

two.

lamda and mew

Question 25

how can wavelets become part of a seismic trace?

Answer 25

taking different paths:
through the earth
from different reflecting surfaces
from additional exitations

Question 26

what are the two wavelet assumptions

Answer 26

superposition : the content of one wavelet does not interfere with another wavelet l they pass each other.

addition - the amplitudes add.

Question 27

what are the two ways a wavelet can be defined?

Answer 27

Space - photograph

time seismic trace

Question 28

five types of wavelets are?

Answer 28

casual
min
max
mixed
zero

Question 29

true of false

In the sampling theory you must be able to sample the lowest frequency in the data , Fmin

Answer 29

False.

its highest freq with Fmax

Question 30

relationships to know

Answer 30

sampling frequency - Fsamp = 1 / dt
frequency increment - del f = 1 / Tmax
Max frequency - Fmax Fmax

Question 31

As t or f tend to zero, _____ FT tends to a ____ FT

Answer 31

discrete

continuous

Question 32

if Fsamp = 500Hz then t=??

Answer 32

0.002sec

Question 33

data with higher frequencies have a ____ res

Answer 33

higher res

Question 34

a periodic waveform is composed of ?

Answer 34

sinusoids

Question 35

in convolution integral, a wavelet is moved across what?

Answer 35

reflectivity

Question 36

deconvolution formula

Answer 36

R(f) = S(f) / W(f)

Question 37

true or false

in synthetic seismogram you deconvolve a wavelet with reflectivity then approximate your seismic data?

Answer 37

False.

you Convolve a wavelet with reflectivity then approximate the seismic data