Rit (Vísindafélag Íslendinga) - 01.06.1971, Blaðsíða 88
88
GUÐMUNDUR PÁLMASON
than the P3-wave, and does not either indicate any marked attenua-
tion (Fig. Cll).
Thorlákshöfn-south (L4). Both P3- and P4-amplitudes were oh-
served. The P3-wave appears to be relatively strongly attenuated,
about 0.6 dB/km, but the P4-wave shows no signs of a regular attenua-
tion (Fig. C12).
Thorlákshöfn—Vestmannaeyjar (L5). Both P3- and P4-amplitudes
were measured. The P3-wave appears to be slightly attenuated, about
0.15 dB/km, which is less than on the previous profile. The P4-wave
is considerably stronger and may also be slightly attenuated, although
this is by no means clear (Fig. C13).
Thjórsárós-Eldey (L6). The P3- and P4-amplitudes were mea-
sured. The P3-wave may be attenuated considerably, perhaps about 1
dB/km, but the P4-wave appears to be very little attenuated (Fig.
C14).
Kerid-Hvítárvatn (L7). Both P3- and P4-amplitudes were mea-
sured (Fig. C15). The P3-amplitude appears to be attenuated about
0.5 dB/km, and the P4-amplitude much less, about 0.13 dB/km.
Vík-Lómagnúpur (L8). The P2-, P3- and P4-amplitudes were
measured (Fig. C16). They are all of a similar strength. The P3-wave
appears to be attenuated about 0.4 dB/km, and possibly the P4-wave
somewhat also.
Alvidruhamrar—Breidamerkurdjúp (L9). The P4-amplitude is 5—
10 dB stronger than the P2-amplitude (Fig. C17 and C18). Reliable
measurements of P3-amplitude are not available. Attenuation of the
P4-wave appears to be about 0.13 dB/km on the average, but an ano-
malous attenuation appears also to be associated with the Breida-
merkurdjúp structure (see section 6.10).
VesturhópSkagafjördur (L10). The P3-amplitude was measured
between 15 and 60 km. The reduced amplitude was found to be slight-
ly increasing with distance (Fig. C19). Beyond 60 km no reliable
arrivals were observed, which indicates that the structural change
across the Skagafjördur valley may have an attenuative effect on the
amplitudes. The P4-wave would have been expected to show on the
seismograms, if the structure were similar to that of SW-Iceland,
but it did not.