Transcript No Slide Title

Environmental and Exploration Geophysics II
Extracting coincident source-receiver or
normal incidence records
from shot records
tom.h.wilson
[email protected]
Department of Geology and Geography
West Virginia University
Morgantown, WV
The effective source
receiver geometry for the
records shown at right
and in the data you are
interpreting over Granny
Creek consists of source
and receiver sharing the
same surface location.
But - this is not the way
seismic data is usually
collected.
t
t is the normal moveout correction
NMO correction of the reflection events appearing in the shot
records across relatively horizontal strata yields a more accurate
image of subsurface geology.
These data sets are referred to as being single fold data.
Single fold implies only one trace per mid-point. Single
fold data are also sometimes referred to as 100% data
How do you find depth h, velocity V and dip ?
tapex
t0

tapex
t0
2h cos 
2h
V
V
 cos 
1 tapex 
  
cos 
 t0 
xapex  2h sin
h
xapex
2 sin 
If you could not see the direct arrival
then you could then solve for V using
either expressions for t0 or tapex.
This is referred to as a stacking chart. The significance
of the name will become apparent later on.
For next week at this time construct a
stacking chart for a symmetrical split spread
consisting of 12 geophones arranged 6 on
each side of the source.
Bring questions to class on Tuesday
The effect of the moveout correction on the traces in the common midpoint
(CMP) gather is to create a composite normal incidence trace that effectively
shares a coincident source and receiver at the midpoint shared by all the traces
in the gather. We’ll discuss CMP data in more detail in a couple lectures.
• For next week at this time construct a stacking chart for a symmetrical
split spread consisting of 12 geophones arranged 6 on each side of the
source.
Bring questions to class on Thursday. Chart is due next Thursday.
•Complete your reading of Chapter 4. Some of this material has not been
covered in class, but will be covered in coming lectures. In the short term
we will be talking about shot gathers (4.3.2), CMP gathers (4.3.3), we’ve
talked tangentially about resolution, so read through that section, common
midpoint surveying, velocity analysis, etc. The section on migration is
important to understand. Other topics range from specialized (3C & VSP)
to basic interpretation (structural and stratigraphic).
•Prepare a topic outline of your term report by the 13th of October.
• The first three paper summaries will be due on Oct 20th