Fróðskaparrit - 01.01.1971, Side 106

114
Seismic Measurements on The Faeroe Islands, 1970
could be observed. For the other seismograms the correlation
of a second event is uncertain.
The travekimes of a seismic event were read from the
original seismograms and were used together with the distances
to calculate the velocities under use of the least-square-met'nod.
Table 2 gives the results.
Table 2
Vt V2
Profile 1: (km/s) (km/s)
shotpoint 9—22 6.1 3.4
shotpoint 35—41 5.6 —
shotpoint I, II, III 5.7 —
The velocities are apparent velocities, because they are ob-
served in only one direction.
The second event of Profile 1 (shotpoint 9 to 17) seems to
be the shearwave (S) belonging to the first arrival of a
compressional wave (P), hereby assuming the ratio of
velocities Vp to V8 is equal to j/3. Remarkable is the lower
velocity of the first event in the second part of Profile 1 (5.6
km/s) when comparing it with the first part (6.1 km/s). The
first arrivals represent a seismic horizon, which has a steeper
downdip in the distance about 60 km than in 23 to 42 km.
The velocity of 5.7 km/s, found for the shotpoints I, II, III,
therefore represents a horizon also with the same downdip.
When comparing these results with the velociities given by
Pálmason (1965) the 6.1 and 5.6 (5.7) km/s seem to be
apparent velocities of the substratum with a real velocity of
6.4 krn/s. The velocities 3.9 and 4.9 km/s of the basalt series
of the islands could not be correlated. Also missing are
velocities belonging to crustal horizons under the investigated
one.