Geology Reference
In-Depth Information
0
X
S-wave velocity
(surface model)
X
X
S-wave interval
velocity (downhole,
Borehole 1)
S -wave velocity (BH1
to BH3 crosshole)
X
X
X
X
V
X
X
S -wave velocity (BH3
to BH1 crosshole)
V
X
10
X
(S is the vertically
polarised S-wave)
X
V
X
X
X
X
X
X
X
X
20
X
X
X
X
X
X
X
X
X
X
30
X
500
1000
1500
2000
Velocity (m/s)
Figure 14.7 Comparison of 1D shear-wave velocity model derived from
a ReMi surface survey with downhole and crosshole measurements. The
agreement is reasonable from surface to 20 m below ground level. Thereafter
discrepancies become significant. Data collected at Zetica's test site.
adversely affects the signal-to-noise ratio in active methods. Smoothing may
be required, reducing resolution.
Layer-thickness resolution decreases with depth. As a general rule of
thumb, the minimum thickness that can be resolved is of the order of one-
fifth of the layer depth.
A comparison of borehole (crosshole and downhole) measurements of
shear-wave velocity with surface wave (ReMi) estimates is shown in Figure
14.7. There is a reasonable match down to about 15-20 m below ground
level, beyond which, at this site, the resolution of the surface wave method
falls off quickly.
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