Greinar (Vísindafélag Íslendinga) - 01.01.1976, Page 92

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Ridge constructed from the gravity and seismic data (16, 17).
This section is conspicuously similar to our seismic cross-section
under Iceland. Both the sections display an increase in the thick-
ness of the layer with the velocities of 6.5-7.5 km/sec and forming
an “axis body”. It appears of interest that laterally this body under
Iceland is four-five times smaller than under the ridge, and mat-
ches the sizes of the ridge and rift zones on the surface.
Comparing the structure beneath Iceland and other rift zones
let’s pay attention to the seismic sections of the continental rifts
of the Rhinegraben (18) and Baikal (19, 20). Schematical velocity
Fig. 9: Schematical velocity sections for some rift-zones. 9.1- by Berckemer et al.,
1974; 9.2- by Puzyrev et al., 1973, Puzyrev et al., 1974; 9.3- by Ansorge, Mueller,
1970, Mueller et al., 1974; 9.4- by authors; 9.5- by Talwani et al., 1965; Worzel,
1965.
sections for some rift-zones are shown in fig. 9. In Fig. 3.1 the
reduced travel time graphs include the data for these regions,
which differ from the Icelandic ones in lower (up to 5.5-6.0) velo-
cities over short distances (i.e. at the top of the section).
For Baikal the 7.8 km/sec waves have been traced from dis-
tances of about 200 km and correspond to a depth of 37 km,
(fig. 9.2) and the 8 km/sec waves from 400 km and correspond
to a depth of approx. 70 km (20, Puzyrev, personal communica-