Rit (Vísindafélag Íslendinga) - 01.06.1971, Blaðsíða 48

48
GUÐMUNDUR PÁLMASON
of 0.3 km in the neighbourhood of the shot point. Layer 1 has an
apparent velocity of 4.4 km/sec and layer 2 5.1 km/sec. Their thick-
nesses, computed on the assumption of horizontal boundaries, are 1.3
and 1.8 km respectively. The travel time diagram does not indicate
any major structural anomalies along this profile.
Comparing the total delay times for the P3-wave on profiles 51
and 53, which run more or less parallel at a distance of 5-10 km from
each other, it is seen (cf. Fig. 12) that the total delay time is con-
siderably higher on profile 51. The difference appears to be mainly
due to the difference in delay time at the shot points. On profile 51
the total delay time for stations near the northeastern end of the pro-
file is about 1.04 sec. Assuming the delay time to be the same at both
ends gives a value of 0.52 sec for each delay time. This is very similar
to the value 0.50 sec given earlier for the northeastern end of profile
53, as is to be expected since the profiles are here only about 5 km
from each other. It is then seen that the difference in total delay time
of about 0.24 sec between profiles 51 and 53 is mainly caused by the
relatively low delay time (about 0.30 sec) at the shot point in Borg-
arnes.
On the Hvítársída profile (52) there appear to be some anomalies
in the travel times at distances of less than 10 km from the shot point,
possibly indicating shallow depth to layer 3. The total delay time of
the P3-wave at larger distances is high, in good agreement with the
general northeasterly increase in depth to layer 3, which is observed
in the Borgarfjördur area.
The last profile to be discussed in this section is the Thingvellir—
Kaldidalur profile (41). It runs to the north from a shot point at
Thingvellir which is common for profiles 39, 40 and 41. The delay
time for the P3-wave at Thingvellir is 0.60 to 0.65 sec as has been
discussed earlier (see section 6.2). The total delay time is about 1.20
sec (cf. Fig. 12), which gives a delay time of 0.55-0.60 sec along the
northem part of the profile. There is some uncertainty in converting
this delay time to depth to layer 3, as the low-velocity surface layer
has an unknown thickness along the northern part of this profile.
A depth of 3.0—3.5 km appears to be the most probable. At Thing-
vellir the depth was earlier found to be about 3.1 km.
6.5. Snaefellsnes Peninsula.
The Snaefellsnes peninsula is discussed separately from the rest
of western Iceland because more detailed work has been done there.