Research Collection
Educational Material
Reflection seismic 1 script
Author(s):
Kruk, Jan van der Publication Date:
2001
Permanent Link:
https://doi.org/10.3929/ethz-a-004363847
Rights / License:
In Copyright - Non-Commercial Use Permitted
This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use.
ETH Library
Seismische Mess-Systeme
Land Marine
Source Receiver
Computer
Seismic waves
Important properties:
• Energy
• Waveform
• Repeatability
• Cost and use in the field
Impulsive source/Non impulsive source Explosive source/Non explosive source Advantages/disadvantages
Dynamite (explosive impulsive source):
• 40% of the seismic measurements
• Not really repeatable
• Exact time of detonation is difficult to obtain
• Detonators are sometimes used for shallow applications
• High energy
• For each application the amount of dynamite can be adjusted
dynamite
Trigger cable
Shear wave hammer
Vibroseis truck
Reynolds, 1997
Damping factor h
α
Apparent velocity:
sinα v
app= v
f v
appapp
=
λ
Apparent wavelength:
∞
= v
app∞
=
λ
app= v v
appf
= v
λ
app( )
βsin
) (nβ
= sin
Response function: R
where:
app
x
λ β = π ∆
And n is the number of geophones in a group
apparent
Clustered geophones Geophone arrays
PGS J.W. Schoolmeesters
Chirp
Boomer
(Huntec-systems)
Principle of an Airgun
(Bolt-Systems)
Inside of an airgun
(Bolt-Systems)
One air gun Array of air guns
Principle of piezoelectric effect
Voltage proportional to the variation of the pressure
Acquisition Techniques
Ocean Bottom Cable
Streamer
Vertical Cable Dragged Array Anchored Cable
PGS J.W. Schoolmeesters
PGS J.W. Schoolmeesters
Multi-channel seismic recording system
(Kearey and Brooks, 1991)
sampling
Registration of the measured data at certain time intervals
Sampling interval ∆t sampling rate 1/∆t
Sampling will preserve all frequencies up to the Nyquist frequency:
fN=1/(2 ∆t)
Aliasing
(Kearey and Brooks, 1991)
Nyquist Frequency:
fNy 1 2--- 1
∆t ---
⋅
=
Typical sampling distances:
0.25,0.5 ms:
High resolution seismic 1 ms, 2 ms
Oil exploration 4 ms or larger
Crust seismic
Range which can be measured using different number of bits:
8-bit : 1 mV - 256 mV 24-bit: 1 µV - 16 V
Dynamic range is expressed in dB,
Examples:
÷ø ç ö
è æ
min
log max
20 A
A
dB 1mV 48
256mV log
20 ÷ =
ø ç ö
è æ
dB V 144
1 log 16V
20 =
÷÷øö ççèæ
µ
mV
2 1 8 4
16 32
64 128
Analog Signal 53
Working of an AD-converter
1 0 1 0 1 1 0 0
= 1+..+4+..+16+32+..+..
Saving requirements depend on:
• Number of channels
• Number of values per channel
(Sampling rate,Time window of sampling)
• Number of bytes per sampled value
Example Channels: 96
Sampling rate: 2 ms Time window: 0.8 s
Format: 4 Bytes per value
Þ (800 / 2) Values x 96 channels x 4 Bytes = 0.146 MBytes
Saving requirements