Geophysics Review Flashcards
geoid.
equipotential surface
sum of gravity and centrifugal forces
circ of earth is?
40,000km
difference between the equator and the poles is approx?
21km
in exploration geophysics, what is a measurement that is widely used?
Gravity measurement
gravity measurements must always compensate for the direction of travel
whether you are flying / travelling with or against the Earth’s rotation
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
True
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
true
list the order for arrival times for earthquake seismology
p-wave, s-wave, surface wave
under the electromagnetic spectrum, what has the longest and shortest wave length?
Longest, radio waves
Shortest, Gamma
what are the two modes of mechanical waves?
P and S – Longitudinal and Transverse
what are the six processing basics?
Velocity Statics Noise Removal ----random and coherent Deconvolution Moveout correction Migration (imaging)
what processing basic stops the summing of data?
moveout
With RMS Velocities
what is the actual shape of reflection?
Bell shape
In RMS velocities how may the actual shape, bell shape, be approximated?
VIA a hyperbola
in RMS velocities What do complex rays in depth =?
Straight rays in time
In Velocity Analysis, what are you trying to obtain?
A velocity profile
what does migration do?
Spreads energy along a semi-circle
moves dipping reflectors to correct location
true or false
impulse is a response
true
modelling vs migration.
Modelling: forward process sum energy on a semi circle spread energy on a diffraction Both are an impulse response
Stress: how many components?
9.
3 normal. 6 shear
symmetry is in the stress and strain is mapped to the what?
the stiffness tensor
The symmetry of the stiffness tensor reduces from 81 to how many variables?
21
VIA symmetrical reduction, reduce the 9 components to ?
6 unique components.
6x6 gives a stiffness tensor of 36…
how many and what are the parameters in a matrix for isotropic media?
two.
lamda and mew
how can wavelets become part of a seismic trace?
taking different paths:
through the earth
from different reflecting surfaces
from additional exitations
what are the two wavelet assumptions
superposition : the content of one wavelet does not interfere with another wavelet l they pass each other.
addition - the amplitudes add.
what are the two ways a wavelet can be defined?
Space - photograph
time seismic trace
five types of wavelets are?
casual min max mixed zero
true of false
In the sampling theory you must be able to sample the lowest frequency in the data , Fmin
False.
its highest freq with Fmax
relationships to know
sampling frequency - Fsamp = 1 / dt
frequency increment - del f = 1 / Tmax
Max frequency - Fmax Fmax
As t or f tend to zero, _____ FT tends to a ____ FT
discrete
continuous
if Fsamp = 500Hz then t=??
0.002sec
data with higher frequencies have a ____ res
higher res
a periodic waveform is composed of ?
sinusoids
in convolution integral, a wavelet is moved across what?
reflectivity
deconvolution formula
R(f) = S(f) / W(f)
true or false
in synthetic seismogram you deconvolve a wavelet with reflectivity then approximate your seismic data?
False.
you Convolve a wavelet with reflectivity then approximate the seismic data
