Rit (Vísindafélag Íslendinga) - 01.06.1971, Blaðsíða 106

GUÐMUNDUR PÁLMASON
106
Fig. 42. Crustál structure of Iceland from surface wave dispersion data
(from Tryggvason, 1962).
duced from surface wave dispersion studies a crustal thickness of
about 10 km on the Reykjanes Ridge and ahout 15 km in the area
north of Iceland. Tryggvason (1962) deduced from surface wave
dispersion the structure shown in Fig. 42, consisting of three layers,
the lowest one with a P-wave velocity of 7.4 km/sec and an unknown
thickness. Tryggvason (1964) observed an arrival time delay of 2-3
seconds for P-waves from distant earthquakes recorded in Reykjavík,
compared to Kiruna and Scoreshysund. He interpreted this as being
due to a thick low-velocity (7.4 km/sec) upper mantle beneath Ice-
land. Francis (1969) used the travel times of body waves from earth-
quakes both to the north and southwest of Iceland to deduce the velo-
city distribution in the upper mantle. He found, neglecting surface
layers, that Vp = 7.0 X (r0/r)3-4 km/sec, where r0 = 6370 km and
Vp is the velocity at radius r. This corresponds to a velocity of 7.06
km/sec at a depth of 15 km.
The above studies thus give a P-wave velocity in the upper mantle
under Iceland between 7.0 and 7.5 km/sec. This is in very good agree-
ment with the value 7.2 km/sec which on the basis of the present re-
fraction data is considered the most likely one for the upper part of
the mantle, and has been used for depth calculations in the present
work. The crustal thickness, i.e. the depth to the 7.2 km/sec layer,
which is indicated by the above work, is in the range of 10-15 km,
which is also in good agreement with the range of 8-16 km found in