Geology Reference
In-Depth Information
Stage 2 Velocities
Direct wave velocity:
The straight line from the W origin through nearby
SS(W) arrivals extends 60 m to G4.
Velocity
V
1
=
60
/
0.079
=
759ms
−
1
.
The straight line from the E origin through nearby SS(E) arrivals extends
100 m to G7.
Velocity
V
1
=
750 m s
−
1
Intermediate refractor:
Arrivals at G5 from SS(W) and at G5 and G6
from SS(E) do not belong to the 'base refractor' sets (see Stage 1) nor
do they fall on the direct-wave arrival line, suggesting the presence of an
intermediate, '
V
2
', refractor. The
V
2
velocity is poorly controlled but the
arrivals lines should pass above all direct wave (
V
1
) and base refractor
first-arrivals. For the most likely positions, as shown
100
/
0.134
=
746ms
−
1
Average
V
1
value
=
1470 ms
−
1
SS(W):
V
2
=
=
Intercept time
29 ms
SS(E):
V
2
=
1560 ms
−
1
Intercept time
=
77 ms
These velocities suggest that the interface is probably the water table, with
a velocity of about 1500 m s
−
1
.
Base refractor velocity:
Plot LS(W)-LS(E) time differences at each geo-
phone, using a convenient (280-ms) line as time zero.
V
3
=
2420 ms
−
1
/
=
×
/
.
=
.
2
(slope of difference line)
2
220
0
182
Velocity functions:
V
1
,
2
=
V
1
×
V
2
/
√
V
2
−
V
1
=
750
×
1500
/
(1500
2
−
750
2
)
=
870 ms
−
1
−
V
1
=
750
×
2420
/
(2420
2
V
1
,
3
=
V
1
×
V
3
/
√
V
3
−
750
2
)
=
790 ms
−
1
V
2
,
3
=
V
2
×
V
3
/
√
V
2
−
V
1
=
1500
×
2420
/
(2420
2
−
1500
2
)
=
1910 ms
−
1
Stage 3 Depths at shot-points
Depths to intermediate refractor (
d
1
=
/
2
t
i
V
1,2
):
1
Wend:
d
1
=
/
2
×
0
.
029
×
870
=
12
.
6m
1
Eend:
d
1
=
/
2
×
0
.
077
×
870
=
33
.
5m
1
