Annual Report 2000 - WIT

196
Altogether, close to 260 shotpoints were covered, recorded by about 220 live channels.
Fig. 6 depicts the location of the threedimensional recording array at the surface
as well as within the gallery.
10 −4
10 −5
Receiver Characteristics
Hydrophone cable on SUMMIT
accelerometers on SEAMEX (1/1000)
100−Hz geophones on SUMMIT (Hilti)
100Hz geophones on SUMMIT (TNT)
Spectral Amplitude
10 −6
10 −7
10 −8
geophones
signal
10 −9
accelerometers
0 1000 2000 3000 4000 5000 6000 7000 8000
Frequency [Hz]
Figure 7: Comparison of different receiver characteristics for the type of receivers used
in the experiment. The full frequency range of the input signal can be estimated from
the accelerometer recordings.
FIRST RESULTS
In this section, we will show some data examples from the triangular test block within
the gallery (see fig. 5). Here, all shots were recorded with three arrays: first, a spread
along the parallel drift, consisting of 74 100-Hz-geophones spaced 0.7 m apart, then
a 48-channel hydrophone cable with 0.5 m spacing which was installed in a 80 m
deep water-filled shaft depicted in fig. 5. Shotpoints were shot several times in order
to cover the whole shaft with the borehole cable. A high-frequency array consisting
of 20 accelerometers was installed in the oblique drift where it crosses the ore dyke.
Fig. 5 also depicts the location of some of the shotpoints that are shown in the example
shotgathers below.