Jökull - 31.12.2001, Page 57

Seismic soundings on Skeiðarársandur
Figure 2. Skeiðarársandur, its main rivers and location of the seismic profiles. - Skeiðarársandur, helstu ár og
staðsetning endurkastsmœlisniða.
third was located inside the moraine complex. The
second survey was carried out in 1999 when seven
profiles (SKS1-SKS7) were surveyed. Profiles SKS4
and SKS5 were shot inside the terminal moraines near
the snout of Skeiðarárjökull. The other profiles were
at scattered locations on the sandur (Figure 2).
Seismic waves were generated through detonation
of dynamite charges (100--500 g) in 0.3-0.5 m deep
holes in the surface layer and recorded on a linear ar-
ray of geophones. The recording system used was a
24-channel Geometrics seismograph. In 1997 the pro-
files had a spread of 230 m with 24 geophones placed
at 10 m intervals. In 1999 the layout was different
since the spread was 115 m long and had a geophone
spacing of 5 m. At least two shots were fired on each
profile, one at each end of the receiving spread. Be-
fore recording, the returning signal was fed through
a 25-500 Hz bandpass filter in 1997 and 50-500 Hz
bandpass in 1999. The sampling interval was 0.5 ms.
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