A SEISMIC EXPERIMENT
This coming month on Saturday and Sunday (October 11 and 12) you will be conducting
a high resolution land seismic survey over flat terrain in
Livingston Parish in order
to image sub-surface geology at a depth of no more than 500 m. It is imperative
that you be able to resolve layers 1m thick amongst shales and sandstones whose average
shear-wave velocities are about 500 m/s.
Your equipment is as follows:
* 24-channel seismograph
* 24 sets of 30 Hz shear (horizontal) geophones at 3-m spacing (plus cables and whatever else you need
for proper recording). N.B. 30-Hz phones can pick up frequencies from
30 Hz to as
high as 200 Hz.
(a) Will these geophones serve the purpose or will you need geophones that can
pick up higher frequencies or will you have to decrease your resolution (Please
[ Don't do (b) or (c) for
this homework exercise. Leave (b) and (c) for following
(b) What sampling interval do you need? ( Justify)
(c) What will you Nyquist frequency be? ( Justify)
(d) What will be the shotpoint spacing in order to produce a maximum
fold of (i) twelve CMP/CDP every 3 m or (ii) six CMP/CDP every 3 m.
Derive the equation for this relation. It may be helpful to look at
the answers on the syllabus from 2000.
(For graduate students only) (e) As in real life I want you to determine a "What
If" situation, which happened to me: What if you had to decrease your receiver
spacing to 1.5m but kept your shotpoint spacing at 3m? What will this do to the
fold, and your vertical and horizontal resolution. Please explain and justify with
calculation results if necessary. Please show your work.
(Due 10/2/2003 at 2.00 p.m.)