Rit (Vísindafélag Íslendinga) - 01.06.1971, Side 86

86
GUÐMUNDUR PÁLMASON
sliow some structural irregularities that might affect the amplitudes
in a systematic way. The geometrical spreading factor has been
taken as r-2.
Skardsströnd (1). Both P3- and S3-amplitudes were measured.
The reduced amplitudes (Fig. Cl) are of similar strength. The P3-
amplitude increases somewhat with distance, ahout 0.25 dB/km.
Hengill-Thorlákshöfn (42). Only P3-amplitudes were measured
on this profile. The apparent P3-wave velocity is fairly low, about
6.2 km/sec. The reduced amplitude increases somewhat with distance,
about 0.2 dB/km (Fig. C2). The profile crosses the Hengill high-
temperature thermal area at a distance of about 8-15 km without any
signs of increased attenuation.
Akranes-Hvalfjördur (50). The reduced P3-amphtude appears to
be 5-10 dB stronger than the P2-amplitude. At the minimum delay
time distance of about 26 km the P3-amplitude appears to have a
minimum, ahout 10 dB below that on either side, which may be
caused by the upward bulge in the 2-3 interface (Fig. C3).
Borgarnes-Nordurárdalur (53). The P3- and S3-amphtudes are
about 10 dB stronger than the P2-amplitude. The P3-amplitude is
increasing by on the average 0.4 dB/km over a distance of 25 km
(Fig. C4).
Borgarnes—Mýrar (54). The P3-amplitude is 5—10 dB stronger
than the P2-amplitude. The P3- and S3-amphtudes are similar and
appear to be increasing with distance (Fig. C5).
Arnarffördur (63). The P3-amplitude is about 10 dB stronger
than the P2-amplitude. The same difference is observed hetween the
S3-wave and the S2-wave (Fig. C6).
Kaldalón-Langidalur (64a) and Isafjördur-Kaldalón (64b). This
pair of reversed profiles presents some interesting amphtude data.
The profiles are about 30 km long and the structure appears to con-
sist of 2 layers with P-wave velocities of about 4.9 and 5.5 km over-
lain by a relatively thin lower-velocity layer with a variable thick-
ness. Waves from a deeper layer (layer 3) were not recorded as first
arrivals. Both P- and S-waves were ohserved from both layers. They
will here he denoted by P2a and P2b, S2a and S2b. It tumed out that
the P2b- and S2b-waves had much stronger reduced amphtudes than