Geophysics Review Flashcards

1
Q

geoid.

A

equipotential surface

sum of gravity and centrifugal forces

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2
Q

circ of earth is?

A

40,000km

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3
Q

difference between the equator and the poles is approx?

A

21km

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4
Q

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

A

Gravity measurement

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5
Q

gravity measurements must always compensate for the direction of travel

A

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

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6
Q

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

A

True

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7
Q

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

A

true

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8
Q

list the order for arrival times for earthquake seismology

A

p-wave, s-wave, surface wave

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9
Q

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

A

Longest, radio waves

Shortest, Gamma

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10
Q

what are the two modes of mechanical waves?

A

P and S – Longitudinal and Transverse

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11
Q

what are the six processing basics?

A
Velocity
Statics
Noise Removal
----random and coherent
Deconvolution
Moveout correction
Migration (imaging)
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12
Q

what processing basic stops the summing of data?

A

moveout

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13
Q

With RMS Velocities

what is the actual shape of reflection?

A

Bell shape

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14
Q

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

A

VIA a hyperbola

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15
Q

in RMS velocities What do complex rays in depth =?

A

Straight rays in time

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16
Q

In Velocity Analysis, what are you trying to obtain?

A

A velocity profile

17
Q

what does migration do?

A

Spreads energy along a semi-circle

moves dipping reflectors to correct location

18
Q

true or false

impulse is a response

A

true

19
Q

modelling vs migration.

A
Modelling:
forward process
sum energy on a semi circle
spread energy on a diffraction
Both are an impulse response
20
Q

Stress: how many components?

A

9.

3 normal. 6 shear

21
Q

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

A

the stiffness tensor

22
Q

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

A

21

23
Q

VIA symmetrical reduction, reduce the 9 components to ?

A

6 unique components.

6x6 gives a stiffness tensor of 36…

24
Q

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

A

two.

lamda and mew

25
Q

how can wavelets become part of a seismic trace?

A

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

26
Q

what are the two wavelet assumptions

A

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

addition - the amplitudes add.

27
Q

what are the two ways a wavelet can be defined?

A

Space - photograph

time seismic trace

28
Q

five types of wavelets are?

A
casual
min
max
mixed
zero
29
Q

true of false

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

A

False.

its highest freq with Fmax

30
Q

relationships to know

A

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

31
Q

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

A

discrete

continuous

32
Q

if Fsamp = 500Hz then t=??

A

0.002sec

33
Q

data with higher frequencies have a ____ res

A

higher res

34
Q

a periodic waveform is composed of ?

A

sinusoids

35
Q

in convolution integral, a wavelet is moved across what?

A

reflectivity

36
Q

deconvolution formula

A

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

37
Q

true or false

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

A

False.

you Convolve a wavelet with reflectivity then approximate the seismic data