Jökull - 01.12.1989, Page 6

Fig. 2. A contour map of the ice surface in the Grímsvötn area (as mapped in June 1987, based on Björnsson
1988, p. 71, Fig. 5.3.). Contour interval 50 m. Bold lines mark the three seismic survey lines. The dashed
lines mark the cross-sections on Figs. 6a-c.
Mynd 2. Grímsvatnasvœðið. Bil milli hæðarlína 50 m. Sveru strikin eru endurkastsmœlilínurnar. Slitnu lín-
urnar sýna legu þversniðanna á myndum 6a-c.
Hard copies of the data were obtained in the field
using the printer on the Nimbus. The data were also
stored on magnetic tape using a Geometrics G-724S
tape recorder.
A small trailer on skis with a closed compartment
was used on the survey. Inside it there was room for
the seismograph, the tape recorder and the operator.
The hot water drill was stored on a second trailer
and a water barrel supplying the drill, was placed on
the third. These trailers, when moved between
shotholes, were pulled by snowmobiles or a
snowcat. The number of people working on the sur-
vey ranged from 4 to 6, completing 3-5 shots per
hour (360-600 m). The drilling of each shothole
took only about 5 minutes.
DATA REDUCTION
The processing of the data can be divided into
three main steps:
4 JÖKULL, No. 39, 1989